Macroscopic kinetics of fast polymerization processes. Review

Polymer Science U.S.S.R. Vol. 31, No. 9, 10p. 1953-1976, 1989 Printed in Poland

0032-3950fll9 $10.004-.00 © 1990 Pergamon Pt'ees pie

MACROSCOPIC KINETICS OF FAST POLYMERIZATION PROCESSES. REVIEW* AL. AL. BYERLIN, K. S. MINSKER, YU. A. PROCHUKItAN and N. S. YENIKOLOPYAN Bashkir Fortieth October AnniversaryState University Aspects of the macrokinetics of fast polymerization processes in turbulent flows are considered. The dependences of the yield and molecular characteristics (MM and MMD) of the polymer formed on the geometryof the reaction volume and the parameters of mixing and heat transfer processes (rates of flows, turbulization, boiling, etc.) have been established. It is shown that such reactions call for special methods of investigationand control. A fundamentallynew material-, resource- and energy-savingtechnologyhas been devisedfor obtaining isobutylene polymers based on she developedmodel of fast flow polymerization. INTRODUCTION

IN polymer chemistry and technology very fast processes of polymerization lasting 10-1_10-3 see are quite widespread but have been little studied. In carrying out these processes, as a rule, it is not possible to ensure effective mass and heat exchange and they occur at variable temperatures and concentrations of the reactants in the reaction zone. Allowance for the influence of spontaneous warming of the reaction mass on the rate and direction of the chemical process and also the molecular characteristics of the polymer formed are of great importance both for the control of the chemical reaction and calculation of industrial reactors. The very fast processes of polymerization in their current form both in the laboratory and at industrial levels are poorly controllable. Therefore, they are characterized by a low yield and poor quality of the end product and the uncontrolled temperature regime of tlae reaction may produce such phenomena as heat explosion and powerful hydro- and pneumo-shocks, etc. Among the polymerization processes occurring at very fast rates we would note some solid phase reactions on photo- or radiation-initiation [1], explosive polymerization of monomers on compression with shear [2], certain processes of cationic polymerization in presence of quite strong electrophilic catalysts, for example, polymerization of styrene, vinylalkyl ethers, isobutylene, etc. in presence of BF3, A1CI3 and SnCI4 [3], some reactions of anionic polymerization of vinyl monomers [4], ionic polymerization of formaldehyde [5] and acetaldehyde, radical polymerization of ethylene at high pressures [6], a number of processes of non-equilibrium polycondensation [7], and so forth. Among the very fast processes of polymerization of the utmost interest by virtue of general theoretical clarity and at the same time great practical importance is the cationic liquid phase polymerization of isobutylene (IB) [3, 8] which may be regarded as a model of the classical fast polymerization reaction. * Vysokomol. soyed. A31: No. 9, 1779-1798, 1989. 1953

AL. AL. BYEItLIN et al.

t9~4

Anticipating, in part, the results presented below, we would note that some traditional concepts, fot example, on the kinetics of polymerization of 1B and also the shaping of the teclmological- process Of producing 1B oligomers and polymers, etc. require fundamental revision or, at least, elaboration of certain new theoretical and practical approaches. Therefore, deep interest in fundamental and promising investigations in the field of IBandJts polymers has been maintained for many years and is constantly stimulated by new experimental data. At least in the last few years it has been clearly shown that the problems of the chemistry and technology of oligo- and polyisobutylene are far from as simple as appeared at first sight. The extremely high polymerization rates pose instead of the traditional tasks (removal of heat and intensification of the process) other more complex tasks-modelling and control of ultrafast polymerization reactions with the establishment of energy-, resource- and material-saving technological processes. The new methodological and experimental approachesand the original results obtained are of genera! importance and applicable to other very fast polymerization processes cationic, anionic and free radical. PROBLEMS OF THE KINETICS OF FAST POLYMERIZATION PROCESSES

Isobu~ylene is a classical monomer polymerizing at very fast rates exclusively by. the cationic mechanism. From the experimental data available the polymerization process.of IB in presence of metal halides (Lewis acids) combined with Br6nsted acids occurs (as ".Illustrated by the use of MeX~ and H20 [10]) by the following scheme. Formation'ofa catalytic complex MeX~+H20 ~ MeX," H20 ~ H *+,

MeX,OH 6-

Initiation a 8+,

MeX.OH 6- + CH2 = C(CH3)2 ~ (CH3)3C~+,

MeX.OH 8 -

(I)

Chain giowth kp

(CH3)3C~+,

MeX~OH~- + CH2 = C(CH3)2 -~ -~ (CH3)3C- CH 2 - (CH3)2 C6+,

MeXnOH6-

etc.

(II)

C~ain transfer (preferably to the monomer) CIt2 ktr

, .~CfI.:_.C ~

- j - (CH~),~C6~ ,

\

CHa MeX 01t 8"' C!I,,!;~+(CIt3)2, M P X O H 8+ !- (:11.: -( (t:ll:d.., ....

CHa ktr

//

\ CHz MeX, OH 6 -

Macroscopic kinetics of fast polymerization processes

1955

Transfer of a proton to a counter-ion (probable reaction)in some: cases may be disregarded CH,: ktr

~1111,- C ¢

)

I- I t ~ "

MeX,, O H 6

,_ 1t 6-.

MeX ()I18

\\

(',1I:) ~(;II.:(;~'((:[l:~)~, M(,X Oft 6 - - Cll)

k+r (:II~

Chain termination with capture of a fragment of the counter-ion kt

~('.tI..C((',Ha)~.X _L MeX~._IOtt

~(,It,C6÷((;H.~).,~. IeX, <)It ~ __1--

(Va)

>"

J__k_ t . . . . (:IL,C,(Ct~,~),,<)H :- MeX,,,

IV[,)

regenelation of the catalyst on fast re-initiation (reaction (Vb)) being transformed to a chain transfer reaction to the counter-ion. Thus, to model the chemical process it is necessary to use the kinetic scheme ki

C + M --, A*

(VI)

A~+M~A* .

.

.

.

.

.

.

.

.

(VII) .

.

, kp .a.. A.-1 + M -*

ktr

A* + M -* A* + H

(VIII) (IX)

The rate of initiation in line with the experiment is quite high (ki/> kp) and, therefore, for kinetic analysis the concentration of the active centres is equated with that of the catalyst. In general, the degree ot polymerization in accord with the scheme (1)-O/) depends on the monomer concentration [9] 1

= (kt + kt,) [M]/kp[M]

(1)

Since the main reaction determining the magnitude of the MM and MMD over a wide temperature region is chain transfer to the monomer (III) then P. and MMD of the polymer formed in each sufficiently small element of the reaction volume are determined in the given case only by temperature and do not depend on the concentrations of catalyst and monomer kp k v (2)

P.-ktr- ~rtrexp(Etr-Ep)/RT 1 p.(j)--~-exp(-j/P.)

P~

(3)

1956

AL. AL. BYERLIN et aL

Here Pn(J) is a numerical distribution function over the degrees of polymerization; j is the degIee of polymerization. ' A distinguishing feature of 1B is its very high reactivity in relation to cationic agents which accounts for the very high polymerization rate accompanied by the release of a considerable quantity of heat which as a rule, cannot be removed from the reaction zone. Therefore, quite precise measurement of the rate of cationic polymerization of IB on the basis of investigations in the kinetic field because of difficulties in the staging of correct quantitative experiments (non-isothermicity of the process, impurities) and the absence of strict experimental results on the nature and concentration of the active centres has been undertaken by hardly anyone. Without committing an error one may note with sufficient justification that the information available in the literature on the kinetics of polymerization of IB at best is of a special nature and is appioximate to the highest degree even where the experimental investigation had to do with processes occurring at a moderate rate and formation of polymeric products of low MM. The literature provides some evaluations of the rate constant of chain propagation k, on cationic polymerization of IB. In [10] the probable rate constant of the polymerization of 1B was calculated on free ions in presence of solid ZnO: kp = 1.5 x 10s l./mole.sec at 273 K. A kp value close to this was obtained in [11] on polymerization of pure IB on exposure to ?-radiation. In the interval 300-335 K the temperature dependence of the polymerization rate is very weak [or values kp = 3 x 106 l./mole.sec and k t = 3 x 102 see-! (the system A1Cla-CHaC1 in CH3C1). To this may also be added that the values of + the absolute rate constants of interaction of IB with relatively stable cations (C6Hs)2CH +

and C6HsCH2 which may be regarded as the lower limit of kp are put at 106 l./mole.sec (Pulse radiolysis; 297 K) [12]. Thus, the high order of the numerical values of the constant kp is beyond doubt. This fact also determines the possibility in principle of assigning the reactions of cationic polymerization of IB to very fast polymerization processes. The kp values, as may be seen, lie below the diffusion limit. In particular, ka for most monomers with viscosity 0.5 kPa.sec at 300 K is ~ 101° l,/mole.sec. However, on formation of a viscous product, especially on low temperature polymerization of IB, the kD values diminish appreciably, for example, for the system isobutane-PIB kD,~ 106 L/mole.see [13] and the kinetic constants kp in many cases may be even above kD. It may be noted that the very high polymerization rates coupled with exothermicity of the process (Q = 54.0 kJ/mole) create a situation in which even very slow introduction of initiator and rapid agitation are insufficient to remove the heat released in the reaction. Only the use of extremely dilute monomer solutions (,-~0.01--0.02 mole]l.) which naturally are of no interest for real polymerization processes of 1B, possibly may still ensure a regime close to isothermal [3, p. 144]. In general, with the entry of drops of initiator into a liquid monomer the reaction begins even before the initiating particles have had time to diffuse very far. The reaction proceeeds so fast that IB may be polymerized 10ng before the two drops-monomer and initiator-mix. Even with the aid of highspeed cinematography (-,~3000 frames]see) it has not been possible to establish what

Macroscopic kinetics of fast polymerization processes

1957

is the time interval between the impact of the drop of a solution of AICla onto the surface of isobutylene (at 195 K) and the appearance of the polymer [3]. F r o m this it follows that in these and indeed in many other ionic and non-ionic Systems uniformity of the distribution of reactants and temperature in volume is not ensmed and tl~is means that in practice the MMs of the polymeric products formed are appreciably lower and the MMDs wider, i.e. the real processes of cationic polymerization Of IB and other like fast reactions are difficult to contiol. This calls for a search for and elaboration of new approaches to the kinetic study of fast polymerization processes and exploration of new ways of evaluating the kinetic and other characteristics of the corresponding reactions and also methods of control of the processes using without fail the equations of chemical kinetics, heat transfer, diffusion and convection. MODELUNG OF THE FAST POLYMERIZATION PROCESSES (CATIONIC POLYMERIZATION OF ISOBUTYLENE)

The specific methodological features o f the study of fast polymerization processes have been identified in analysis o f change in the real M M and M M D values of the polymeric products formed with the conditions of conducting the reaction. In [14] a laboratory model system was used to obtain PIB in flow (Fig. 1) helping to regulate the linear rates of introducing the reactants, measure at specified points of the reaction volume the temperature and monitor change in it.

1

F.___

4'

log 1

E

0

-1

A I

1

~

L

3

~

I

~

]

5 j , lO -~

FIG. 1 FIG. 2 FIQ. 1. Layout of polymerization unit: 1 - reactor; 2, 2' - pumps; 3 - tank for mixing monomer and solvent; 4-6-tanks of monomer, solvent and catalyst; 7-EP-09RDMZ recording device; A - F sampling points. FIG. 2. Semilogarithmie anamorphoses of the MMD function of polyisobutylene against the length of the reaction zone 0.02 (1), 0.10 (2), 0.30 (3) and 0.48 (4) m at [M] 12~o by weight and concentrb.tions of monomer 5 (5), 10 (6), 12 (7) and 15yo by weight (8) for l=0.3 m;

1958

As... At.. BYEgt.~ e t aL

The solutions of 1B (12 ~o b~ weight) and catalyst (C2HsA1Clz, 1"4 x 10 -2 mole.1.-~) in heptane were introduced at an identical constant rate (I x 10 -2 re.see-i and higher). The M M and M M D of the polymer formed were measured on a gel chromatograph fitted with two detectors: refractometer and a specific detector for double bonds (ADS) |151. Measurement of temperature at different points of the reaction zone showed that the process occurs at the highest rate at the point 0fentry of the catalyst (Fig. 1, point B). The lowest reaction rate is observed close to the walls of the leactor (point C). It is significantthat the polymerization process of IB also proceeds at an appreciable rate at point A (before the point of entry of the catalyst), evidence of the important role of back longitudinal diffusion, the reaction occurring in the main (by 50-70 ~o) in the zone of entry of the reactants in I-2 sec (point B). The temperature of the reaction mass is variable arid depends on the concentration of the reactants, in particular, IB. Fall in the M M of the polymer is simultaneously noted with increase in the 1B concentration in the initial mixture. The experimental findings are due to increase in the amount of heat released during ~polymerization and enhancement of the role of the termination reactions of the matetial chain through transfer to the monomer. The reaction also continues on distancing the reaction mass fIom the point of entry of the catalyst (conversion increases from point B to point F) with rise in temperature. This accounts for the dependence of the M M and M M D values on the length of the reactor. The M M D functions in the coordinates log p,(j) against j are presented in Fig. 2. Widening of the M M D through the appearance in PIB of considerable amounts of the low molecular mass fraction with distancing of the site of sampling from the point of entry of the catalyst and also with increase in the monomer concentration in the reaction mixture is obvious. Mathematical modelling of the process of fast polymerization of IB in flow (jet) is based on the kinetic scheme of the reactions (VI-IX) and relations (2) and (3) [16, 17]. Account was taken of the fact that usually on polymerization in ideal mixing apparatus high linear speeds of motion of the reaction mass are ensured (up to 10 m/sec). The use of the flow (jet) polymerization method is desirable from several angles already noted in reference [18]: this is the most convenient way of experimentally studying very fast chemical reactions; it is the best way of conducting the reaction with maximum intensity, in minimal time and in minimal volume; investigation of the kinetics of the reaction in a steady jet with intense agitation is, in principle, simpler than investigations of chemical reactions when conducted in a closed volume; the conduct of chemical reactions in flow (in a jet) including very polymerization reactions presupposes an easier and more convenient practical check on the theoretical modelling by sampling at different points along the length of the reaction volume and determinafion-0f the characteristic parameters o f the polymer f0rmed. . . . . - The high flow rates in the reaction zone (1-10 m/see) ensure turbulent mixing o f .the catalyst solution ([C]o= 10-4--10 - t mole/1.), the polymer formed and the solvent used (isobutane, methylene chloride, etc.). The value of the Reynold's criterion Re calculated for a given linear speed of flow, its density (0"5-1.0) × 103 kg/m a, the dynamic

Macroscopic kinetics of fast polymerization processes

"I'959

viscosity coefficient (5 x 10 -4 kg/m.sec) and the diameter of the reaction apparatus (0.1 m) amounts to 104 and higher. The turbulence of tlae system is evidently even greater because of the increased density as a result of the reaction (concentraction on polymerization reaches 30-40 %). Boiling of the reaction mass thanks to the release of a considerable quantity of heat is also possible. Therefore, as mass and heat transfer coefficients one may as a first approximation use the turbulent diffusion coefficient equal to the temperature conductivity coefficient DT --~T pc

(4)

Usually tneoretical calculations of tlae hydrodynamics of such systems: are extremely difficult and require the introduction of many empirical parameters. Yet for some model systems cl03e to real this appears possible. Strictly speaking, such systems must be described by the effective co~fficient of tulbulent diffusion variable in space Dr. However, as shown by special evaluations, the changes in D T over the whole reaction volume in open systems are slight (less than 2 times) and are even less~in the:zone of the effective chemical reaction. True, it must be borne in mind that the effectiveness of mixing depends largely on the configuration of the reaction volume, the system of entry of the catalyst relative to the direction of the flows, the energy of flow turbulization, etc. Calculations showed that the value Dr (disregarding contraction through polymerization and boiling of the components of the reactionmixture} depending on the geometry of the reaction zone for reasonable values of turbulization energies are within the limits 10-2-10 -a m2/sec {.respectively for laminar flow 10 -9 ~m2/sec) and with reference to boiling and contraction the Da- value is even higher. Therefore, in calculating and modelling the fast polymerization reaction of 1B constancy of Dr Over tlae reaction volume and accordingly the temperature conductivity coefficient was assumed with variation in the Dr values from 10 -3 to 10-1 m2/sec. Kinetic equations describing the changes in the concentration of monomer and active centres and also temperature on fast polymerization of IB in flow with axial symmetry have the form a[M](x,r)

Ot

_ a2[M], -- DT ~ - t

DT~[M] _ ~92[M] r Or + I')T ~X 2

-

~[A*](x , r) D (~2[A*]+Dza[A*] t~t

--

T

~

r

¢~r

.,

v ~: rILMj _ kO [ M ] [ A * ] exp ( - Ep/RT)

ax

a 2[A •]

"

~ [A*]

q-DT ~ x 2 - V

0---~-

::~T,

7".

- kt° [A*] exp ( - E,/R T)

~ T ( x , r)

pc "" ~[ "

- t~2T Ar c~T

~2T

c~T

o

= ~.T ~F2 "~ -~ ~ r "~ "~T ~ , ~ - V pc ~ x + Q kp [ M'l

(5)

[A*]exp(-Ep/RT)

(6)

(7)

1960

AL. AL. BYI3RLIN e t a L

with boundary conditions on central entry of the catalyst into the flow of the monomer solution

T ( - d , r ) f To [M] ( - d , r ) = ~ [M]°

(o

for

[A*] ( - d, r) = ~ 0 ([A*]o O[ M ] ( x , R)

for

for for

R>r>r o

R > r > ro

Or(x, R) Or

(9)

r
O[A*](x, R)_O[A*](x, 0)_O I'M] (x, O)_OT(x, 0)__0 Or 01" Or Or

Or

(8)

r
=~ {T0(x, R)- r~}

(10)

(11)

Here x and r are coordinates over the length and radius of the reaction zone; T is the temperature in the reaction zone; To and /'1 are the temperatures of the reactants introduced and of thermostatting; d the elngth of the return zone (varied until independence from d was reached). If it is assumed that the process occurs steadily then 0 [ M ] ( x , r, t) OA*(x, r, t)=OT(x, r, t)= 0

Ot

Ot

Ot

(12)

As a result calculation of the mathematical model boils down to solution of a marginal problem for the set of equations (5)-(7) using an implicit difference scheme. As well as calculating the concentration fields M(x, r) and A*(x, r) and also the fields of the reaction rates (kp [M] [A*]) we calculated the MMD and the mean MMs of the polymeric products formed. The mass distribution function Pw(J) over the degrees of polymerization at the outlet of the reactor of length I and the moments of the distribution function Io-13 were calculated from the formulae 1 R

;.(,)= ff-~exp(-j/Ps)k.[A*][M]exp(-E.,RT)2nrdxdr. (13)

-dO

where

P~ffikp/ktr-- k°p/k° exp [ - ( E , - Et,)/RT] ~o

R

1

Io--[:'@')dj-ff 0

0 -.d R

=f f

Z

lk°[A*][M]exp(-Ep/RT)2~rdrdx (14)

J dP. 0 -d

1961

Macroscopic kinetics of fast polymerization processes oo

R

!

It = I Pw(j)dj = I I k°[ A*'] [ M ] e x p ( - E f l R T ) 2 n r d r d x 0 co

(15)

0 -d

R

I

I2 = I JPw(J)dj = ~ 1 2P. k ° [A*] [ M ] exp ( - Ep/RT) 2rcrdrdx 0 -4

0

R

!

= I I [(k°v)2/k°r] [A*] r M ] exp [-(2Ep-Et,I/RT] 4nrdrdx

(16)

0 -d oo

R

1

13= j'j2pw(j) dj= I I 0

2rcrdrdx

6 P .2 kp0 FA • ] FM] e x p ( - E f l R T )

0 -d R

[

= I 1 6 [(k°)a/(kt°r) 2"] [A*] [ M l exp [-(3Et,-Et,)/RT ] 2rcrdrdx

(17)

0 -4

P,=Iz/Io, .Pw=I2/Ix, a n d P:=I3Iz at the outlet of the reactor. R

The

integrals

l

I I f ( x, r)drdx were calculated f r o m an existing network. T h e numerical values of 0 --d

Ep a n d Nt for the fast processes o f cationic polymerization of IB are low [11]. Therefore calculations were m a d e disregarding the t e m p e r a t u r e dependences o f kp, kt a n d D r . Figure 3 gives the t e m p e r a t u r e and concentration fields* of the m o n o m e r a n d catalyst. It is clear that the process of cationic polymerization o f 1B occurs, as in the experi-

(Et.- Ep)R,K ~.&

3000

5000

I

L

1

0 l',~rn

123

14

0"8

2,

O.tt x~m

0.4 ¸

0"8

"2's'\#' \ 5'\\7' I*8' S' b"tG. 3

r

1

i

2 [ M]o, rnole/l.

FiG. 4

FIG. 3. Temperature and concentration fields of monomer and catalyst: kp=105 1./mole.sec; kt = 1 see-t; [M]o=l mole]L; [A*]o= 10 -2 mole/l.; D r = 1 m2/sec; ct=0; T°=310 (1), 313 (2), 320 (3) and 330 (4); [M]o=0'9 (1'), 0-7 (2'), 0.5 (Y), 0.2 (Y), 0.15 (6'), 0.085 (7'), 0"035 (8') and 0.016 (9) mole/l.; [A*]o=l x 10 -4 (D), 5 × 10 -4 (C), 1 × 10 -3 (B) and 2 × 10 -3 (A) mole/1. Fro. 4. Dependences of Pw/P, (I, 1') and P=/P~,(2, 2") on (Err- Ep)/R (1, 2) and concentrations of monomer (1', 2'): k,-- l0 s L/mole. sec; kt = 1 see- 1; [A*]o = 10- 2 mole/l.; Dr = 1 m2/sec; ct= 0; 1= 1 m.

1, 2-(Et,--Ep)/R= 5000 K. * By field is meant change in the parameter studied in arbitrary units over the coordinates of the reaction zone.

1962

A.L.

AL.

BYERLIN

et aL

mental conditions, i.n the main, at the. entry o f the cata!yst to the reaction zone on its mixing with the monomer Solufiom AS is characteristic of fast chemical processes, the temperature and rate of the reaction in the zone of polymerization of 1B turn out to be variable and dependent on: the initial: concentrations of the reactants, the:magnitude Dr and the heat transfer coefficient through the wall ~. Although the maximum of'the polymerization rate is: observed close t o the-zone of entry of the catalyst the reaction continues quite far along axis x leading to change in the yield and properties of the polymer on moving away from the site of entry of the catalyst, ~ ~. :?~ • . . ' ~. ' . ~ ~ , f. ~:,~'~ The formation of a polymer at &fferent pomts of the reactlon volume (acordmgly at different temperatures) leads to widening of the M M D as compared with the most probable [t).(j)]=ilP. exp(j/l~,,)], characteristiC0f iS0t~rmal conditions. Since the mean MM and the M M D are determined by the reaction of chain transfer to the mon0mer the main factor influencing these characteristics is the difference in the activational energies of the chain transfer and l~ropagation reactions Et,-E,.,Figure 4 shows dependences of/~w//~, and /~J/~w on Et,--E,. For appreciable deviation of the M M D from the most probable (Pw/P,=2) the values of Et, and E, must differ at least by several units which, in general, corresponds to the experimental data for the polymerization of IB [19]. Increase in the coefficient • with the other parameters of the process constant: causes some narrowing of the M M D corresponding to smoothing of the temperature field. However, heat transfer through the impermeable side wall may have an appreciable influence only in the case of small dimensions of the reaction vessel and high values of the coefficient Dr and 2r. The temperature field in the reaction zone is determined by the rate of the process and the quantity of heat released and, consequently, by the concentrations of monomer and catalyst. The influence of the concentration of the monomer on the M M D parameters is also shown in Fig. 4. The M M D widens appreciably with rise in the monomer cotlcentration chiefly through the appearance of a large amount of the low molar mass fraction. Similar patterns are observed with variation in the catalyst concentration. Increase in it as well as the expected increase in polymer yield raises the temperature and temperature gradient in the reaction zone and consequently also leads to a drop in the mean MM and widening of the M M D (increase in the ratio/~w//~,). Analysis of the fast polymerization reactions showed that the effects detected on mathematical modelling are identical to those observed experimentally on cationic polymerization of IB. An important consequence of the non-isothermicity of the process is deterioration of the qual!ty of the polymer, external_ thermostatting, in general, not :being sufficiently effective and, therefore, limiting the use of dilatometry and many Other classical and special experimental techniques of studying the .kinetics of the process. -: ' :-Thus, the preparation of polymeric ploducts.with MMD-_clo~e to that characteristic of isothermal processes in one apparatus, in general; requires confinement Of the reaction zone to a region of comparatively low monomer conversions. This, in turn, also sets a limitation on t h e s i z e Of the reaction zone .proper (size of the apparatus),

Macroscopic kinetics of fast polymerization processes

1963

MACROKINETIC FEATURES OF FAST POLYMERIZATION PROCESSES (CATIONIC POLYMERIZATION OF iSOBUTYLENE)

I n fast polymerization process thermostatting of the reaction zone presents insurmountabledifficulties [20]. Nearly always the diagrams of change in temperature during local measurement in real processes using voluminous ideal mixing reactors present periodically repeating variations of varied amplitude which is a consequence, in particular, of the kinetic features of cationic polymerization of IB. The process occurs, in the main, at a distance less than 1-10 cm from the point of entry of the catalyst and is limited by the mixing of catalyst and monomer. Accumulation of heat in the reacting system with high turbulence and instability of the movement of the reaction mixture in a real apparatus also leads to swings in temperature in the reaction zone in time. In view of the non-isothermicity of the process change in M M and M M D of the polymer is observed in the course of the process along the length of the reaction zone.

50

-

_

o

q,%

'

20 .

30K~,210"

"

,

10 "---'---"-'2"5

[A*]

x, ro

5"0

~H]o,mole/L

FIG. 5

~l" I0-~

0.5 FIG. 6

F[6. 5. Dependence of lJw/P, (1) and P, (2, 3) on the concentration of monomer (1, 2) and catalyst AICI3 (3) (solvent C2H5C1). 1, 2-[C]o = 3.71 x 10-3 mole/l.: 3-[M]o = 1.9 mole/l. FIG. 6. Temperature and concentration fields of monomer and active centres on polymerization: Dr=0"025 m2/sec; [A*lo=4"5 × 10-3 mole/l.; [M]o=l mole/1.; R/r=O.1; kt=20 sec -x. The macrokinetic consequence of the rapid local course of the polymerization reaction of ]B is the dependence of the mean M M on the concentration of catalyst and monomer and also the considerable widening of the M M D with increase in the initial concentration o f monomer (Fig. 5) while the kinetic scheme (the M M of the polymer formed is determined by chain transfer to the monomer) predicts in the isothermal regime independence of the M M and M M D from the concentrations of catalyst and monomer. Moreover, as a rule, the monomer and catalyst solutions are introduced into the reactor irregularly and in view of the very fast polymerization rates do: not have time to mix well with the reaction mass. T hisfeature causes additional instability of the course o f the very fast chemical plocess.

1964

AL. AL. BYERLIN et aL

Calculations (see below) as an approximation of the real work of the reactor actually show the formation on contact o f catalyst and monomer of fields o f change in temperatures and also concentrations of monomer and catalyst (Fig. 6). In standard industrial ideal mixing reactors conversion in one run is 25-30~o by weight which is in quite good agreement with calculation and the front of propagation of the reaction is characterized by the formation o f a local zone ("torch"). The propagation front o f the reaction of polymerization of IB is smaller than the volume o f the reaction zone which may lead to the appearance o f zones of breaktllrough of the monomer. Thus, the existence of a torch regime with the temperature and concentration gradient of monomer and catalyst and breakthrough of the monomer along the outer walls o f the reactor may lead to fall in the yield of polymer per run, overstating of the required reaction time and, as a consequence, fall in the efficiency and productivity o f existing reactors. It is important to note that the rapid and local course o f the reaction and the presence of a torch regime when the reaction zone does not extend to the inner and outer heat exchange surfaces of the reactor account for a new macrokinetic feature o f the polymerization o f IB when all heat removal is practically ineffective. PATTERNS OF THE FAST PROCESSES OF LIQUID PHASE POLYMERIZATION IN FLOWS

Existence of several macrokinetic regimes. Analysis o f the experimental results and theoretical calculations Of the fast polymerization processes as illustrated by polymerization of IB revealed the appreciable influence of the geometric parameters of the reaction zone-- the radius R and length I on the kinetic parameters o f the process and molecular characteristics of the polymeric product formed a consequence of the formation in the reaction zone of fields of concentrations of monomer and catalyst and of temperatures in volume over the coordinates along x and across R of flow [21]. Conversion o f the monomer and the molecular-mass characteristics of the polymeric product were found to depend on the radius R of the reaction zone (it is considered DEPENDENCEOF THE DEPTHOF CONVERSIONOF THE MONOMER,DEGREBOF POLYMERIZATIONen and the polydispersity index Pw/P. on the radius of the reaction zono R (kv = 105 L/mole-see; kt= 20 sec- 1; [M]0 = 1 mole/L; [A*] = 0.0045 mole/T; DT= 0.025 m2/scc) Type of reaction A

B C

R, m 0"01 0"03 0"05 0"08 0"I 0"25 0"50

Conversion, ~o b y weight 10o 100 100(97.7)* 99.3 90.0(90.0)

65.0 32.0(29.7)

P") 13 13 12(30) 10 8(21) 6 6(17)

P~P" 2.0 2.0 2.1(3;1) 2-1 2.2(3.7) 2-4 2"4(4"0)

* In parentheses experimental results obtained on polymerization ofIB (AICIs in ethyl chloride; 243 K; same condition@. t The dllfea~nce between the calculated and experimental values of Pa and Pw/Pnis explained by the ratio kp[kt, chosen and whero necessary may be readily removed,

Macroscopic kinetics of fast polymerization processes

1965

that the reaction zone along the flow is quite large and the reaction proceeds to completion to the~xtent possible). A distinct tendency for the conversion of the monomer to fall with inbr~ase in R is seen (Table) a n d in topochemical terms three macroscopic types o f the process m a y be singled o u t - A , B and C. T

1-o

~

/~R~m

P R,m

!l, m

C

A

I

d

e.o

I"0

.25 r~?, m

e

~ R, m

I lTm 2"0

[~m 2"0

C

0"5 R~m FIG. 7. Fields of temperatures (a, c, e) and concentrations of monomer and active centres (b, d, f ) o n polymerization for R=0.08 (a, b), 0-25 (c, d), 0.5 (e,f) for maximum conversion 99.3 (a, b) 65.0 (¢, d) and 327. (e,f) and AT=20 (a, b), 22 (c, ar) and 9 (e,f); 74o=300 K; [M]o=l mole/L; [A*lo =0.0045 mole/l.; Dr=0.025 ma/see; kt=20 see-l; R/r=2.5.

1966

AL. A L . BYERLIN et al.

•

For small radii R (type=A) the mixing of the reactants is sufficient; !he active eentres A* are distributed comparatively uniformly (Fig. 7b) and, as a consequence, the temperature of the reaction is distributed regularly over the radius of the reaction zone (Fig. 7a). The surfaces of equal concentrations of the monomers, the active centres and temperatures constitute planes perpendicular to the axis of the reaction zone. All this accounts for the high (up to 100~o) conversion of the monomer and the regime of quasi-ideal extrusion in the highly turbulent flows. Another limiting case (local torch regime) is realized for relatively high values of R (type C). The active centres A* perish and do not have time to diffuse to the peripheral regions of the reaction volume which are thus zones of breakthrough of the non-reacting monomer (Fig. 7f). Specific fields of complex configuration of the monomers, active centres and temperatures form (Fig. 7e) determining the onset of the reaction turbulent torch, the size of which is determined by the ratio of two competing processes - mixing (diffusion) of the accompanying flows and decay of the active centres. The reaction does not reach the reactor walls and conversion because of breakthrough of the monomer between the boundary of the torch and the reactor wall appreciably diminishes. Type B (third macroscopic type) determines the intermediate regime of the process due to the formation of a torch without zones of breakthrough of the monomer. The regimes C and B are characterized by the presence of temperature gradients, active centres and monomers both along the axis x and over R (Fig. 7c, d) which appreciably influences the homogeneity of the polymeric product formed (the M M D widens). One of the most important results obtained in modelling the process is evidence of the influence of the geometry of the reaction volume, i.e. passage from one macrokinetic regime to another (zones A, B and C) on the molecular characteristics of the products formed (Table). With increase in the radius R the width of the M M D (/~1/~,) grows with simultaneous fall in the number average MM of the polymeric product. This is connected with the fact that for the reaction zone with a low R value the temperature in volume is distributed relatively uniformly while the appearance of the temperature gradient in the form of a torch along the coordinates of the reaction volume for radii above Rcr (by Rcr is meant a certain value of R governing passage from regime A to regime B) leads to widening of the M M D through accumulation of the share of the low molar mass fraction. At the same time it should be borne in mind that the MMD of a polymeric product widens on moving away from the point of entry of the catalyst along the axis x as a result of rise in temperature. As the Table shows the calculations correctly reflect the tendency of the influence of the radius and agree with the experiment. Thus, increase in the volume of the reaction zone and supply of a large quantity of the reaction mixture with the same linear speed unlike classical chemical processes may lead in the case of fast polymerization reactions to appreciable fall in conversion and a large drop in the productivity of the reactors. .... . . . . .

• Relationship between the kinetic and hydrodynamic consiants andthe geomeiric para= meters of the reaction zone, Passage from the regime of quasi-ideal extrusion to the ~t0rch regime is accompanied by fall in the conversion of the monomer and worsening of the

Macroscopic kinetics of. f~st_ poly.~erjzation processes

1967

molecular-mass characteristics:of the polymer (fall in/~,, and widening of the MMD). Let us denote the critical radius determining the passage from one regime of work of the reactor to another by Rc~ [! 4, 22]. The critical radius is determined by the ratio of the processes of diffusion and decay of the active centres. From the dimensionality ratio Re, is presented in the form R~,= m X/~.r,

(18)

where as Rer we take the value of the radius of the zone of :the ~eaction in which the polymer yield falls by 1 0 ~ as compared witla that for R-o0. As shown by the results of mathematical modelling such a ratio actually holds (Fig. 8) for a proportionality coellicient m = 2 + 0 . 2 . It should be noted that with change in the radius (for a constant linear s p e e d o f flow) three different regions of the flow of fluid may be isolated: laminar (small R), transitional and turbulent (larg e R) regimes. Characteristic of each regime is its own values of the mean characteristic mixing times ( r ~ , g

R2/D).

._ T~icx~iiii / 1

04

0"05

0.05 ~r,/~o.m ....

I

fO

30 R,cm

Fie. 8 FIG. 9 FIG. 8. Dependence of R e r o n FIG. 9. Mixing time "¢mix=R2/D'ra s a function of the flow radius R for the laminar (1), transitional (2) and turbulent (3, 4) regimes. V= 2.5 (3) and 5 (4) m/see. Broken line corresponds to ~= 1/kt.

Dr/kt.

In the laminar regime the diffusion coefficient is very small: D = 10-9 m2/sec. As a consequence the mixing times are long and rise with R as R 2. In the transitional regime the effectiveness of mixing D rises sharply and Vm~, falls. In the turbulent regime the values Dr = 10-3-1 m2/see are very large and increase approximately by the law D r ~ R. Comparing ~ml. with the characteristic time of the chemical reaction ~oh,m we see that the conditio n of quasi,ideal extrusion (rmix < rchcm) is respected in the intervals 0 < R < RI and R2 < R
AL. AL. BX~RLINet aL

1968

Thus, the interval of turbulent flow R2 < R < Ra with very high productivities remains fairly narrow (depending on Zch©mand lO (Fig. 9). For example, for V= 1 m/see productivity is -~20 ma/hr and in the range of iadii fiom R2 =3 cm to R 3 = 15 cm the productivity of the tube reactor varies from 20 to 500 ma/hr. Increase in the flow speed widens the possible region of exploitation of the reactor (R 2 falls but Ra rises) although the hydrodynamic resistance of the reactor grows. Consequently, it is necessary to raise the pressure which may produce undesirable effects (rise in the boiling point of the reaction mass, stiffening of the requirements for the design of the apparatus; rise in the load on the pumps, etc.). An important aspect of the problem (associated with the course of very fast polymerization processes) is the establishment of the length I of spread of the reaction front along the axis x. Since the extent of the reaction zone is linked with the rate of polymerization by the linear speed of movement of the accompanying V, the effective time of stay of the reaction mass in the reaction zone 1IV is correlated with the effective time of the chemical reaction which represents a certain combination of values 1/kt and ]/kp [A*]0. For a reactor with ideal extrusion the polymer yield in analytical form is determined by the relation

fl= l-¢xp{

kP[~t*]°[I-exp(-kt~)] }

(19)

If we take the parameter (l/V)©f~,the effective time of stay determining the length of the reaction zone at which the polymer yield reaches 90~o of the limiting value at 1--,oo, then 1 ( kt (I/V)'tf=--~tln~l+~ln

[0"1 +0"9 exp ( k P [ t * ] ° ~ ] ~ kt ]J]

(20)

In this case the dependence of (l/V)eff on 1/kp[A*]o has the form presented in Fig. 10.

(//V)eff,seo

o-q,%/ 8O

04 I l l

0.01

I

i__

0-8

o.~,Z/
20

0.02 //kp[A*]o,sec

I

ZS

_L

J

75 V~m ~ec

FIG. 11 Fro. 10 FIG. 10. Calculated dependence of (I/V)ou on 1/kplA*]o for an ideal (continuous line) and quasi-ideal (points) expulsion reactor; R=0.08 m, V=2.5 m/see. Fie. 11. Dependence of polymer yield on the duration of the reaction (1) for l = 2 m and flow speed (2). Here and in Fig. 12 zffi0.2 sec; To--300 K; R=0"25 m; [A*]offi0.045

mole/L; [M]o=2 mole/l.

Macroscopic kinetics of fast polymerization processes

1969

Two extreme cases are important. At high concentrations of catalyst kt/kp[A*])o> and (l/V),ff-2"3/kt. Calculation of very fast polymerization processes taking into account longitudinal diffusion but with the condition R<~I-DT/kt showed that the curves of the dependence of (I/V)eff on 1/kp[A*]o for different (in a wide interval) values of [A*] are close to those calculated from equation (20) (Fig. 10). As is known determination of the elementary constants of fast polymerization processes is extremely difficult. The above data open the way to the experimental determination of the main elementary constants. Studying change in the polymer yield with the length of the reaction zone and/or the flow speed at different concentrations of catalyst with the condition that R is less than Rcr, one may evaluate the rate constants kp and kt if one uses both regions of the ratios kt/kp[A*]o or at least one of them when both regions of the ratios cannot be encompassed. The method of calculating the kinetic constants proposed enabled us to evaluate kp and kt for the process of cationic liquid phase polymerization of IB (A1Cla-3"7 x 10-3 mole/l., IB=3.5 mole/1.) which at 243 K were kp= 1.0 × 106 l./mole.sec which corresponds to the published data [11, 13, 19] and kt=17.5+5 sec -1 evaluated for the first time.

AT 6O 3

5

2

-3

y_:t +

q

z~O

2

5

v, re~see

10

20 0.125

R~rn

0.25

FIo. 12 FIG. 13 FIG. 12. Dependenceof P, (1) and/5[p, (2) on flow speed. Fic. 13. Radial temperature profiles for Dr=0.0045 (for V= 10 m/see) (1, 2) and 0-01 m2/sec (for V=2.5 m/see) (3, 4) and depth of conversion q=90 (1, 3) and 60% (2, 4). Thus the kinetic parameters of the fast polymerization processes determine the geometric dimensions of the reaction zone. A mutual link exists between the elementary constants of the process kp and kt and the geometric dimensions of the reaction zone R, l and also V. Essentially new (unlike the standard- only kinetic and thermodynamic) methods of controlling the process appear determining the extent of conversion of the monomer and the molecular-mass characteristics of the polymeric products formed, in particular, forced change in the radius R of the reaction zone.

Influence of the linear speed of movement offlow on the coefficient of turbulent diffusion and molecular-mass characteristics of the product. The turbulent diffusion coefficient

1970

AL. AL. BYERLINet aL

DV may be varied within quite wide limits by preliminary turbulization changing the method of mixing and the direction and the speed of movement of the flows of reactants. For the process of polymerization occurring in reactors with a radius larger than Rcr conversion of the monomel in the course of the reaction usually does not reach 100 %. Increase in the turbulent diffusion coefficient several times, for example, through increase in the speed of movement of the flows, leads to appreciable increase in the depth of conversion of the monomer (for R>Rcr) despite the shortening of the stay time of the raw material in the reaction zone (Fig. 11). If the region of the reactions for all values of the flow speed is limited to one stay time, for example z=0.2 sec (Fig. 11, curve 2) then with rise in DT other things being equal, conversion of the monomer in the fast polymerization processes may rise more than three times with increase in the flow speed from 2.5 to 10 m/see. Simultaneous, and this is important, with increase in the extent of monomer conversion (with rise in DT) the molecular-mass characteristics of the product al~o change. Increase in the speed of movement of the flow raises the number average MM ~n with simultaneous narrowing of the M M D of the product (Fig. 12). Figure 13 indicates the changes in temperature according to R for different values of the linear speeds of movement of the flow of the reactants (turbulent diffusion coefficient DT) and the reaction times vp = l/E It will be seen that with increase in V and accordingly rise in DT, the temperature maxima in the reaction volume are smoothed despite rise in the total polymer yield. Levelling of temperature leads to rise in the mean MMs and narrowing of the MD of the product. The condition for the low sensitivity of the M M and M M D to temperature in the reaction zone (to be more precise to the temperature gradient) which determines the quasi-isothermal regime of the process is the relation RT 2 AT<<~.tr_E p,

(21)

where Tis the mean temperature and d T is the difference in temperatures in the reaction zone. The temperature gradient AT in the reaction zone is determined by the equality of the rates of release of heat on polymerization wp and its distribution through turbulent transfer .wT WT--2TdTt~-- CppDTktdT~wp=pVqzIMv ' '

(22)

where J = V/k t is the length of the reaction zone for kp[A*]o<
kt,~T RT2 P V~qAM (Err- Ep) >>1

(23)

Thus, to observe the conditions for the formation of the quasi-isothermal regime in extrusion reactors in turbulent flows two criteria must be respected - t h e relations (18) and (23).

Macroscopic kinetics of fast polymerization processes

1971

The characteristic size of the levelling (averaging) of the temperature of the reaction is proportional to x/2x~x/DT~x/~" since in the turbulent regime DT~2T~ V and the temperature drop along the axis of the reactor and accordingly lengthening of the reaction zone are proportional to V (linear dependence). Therefore, increase in the speed of flow violates condition (23) and at V--*~ the regime becomes close to the ideal extrusion regime (in the classical variant) with a very wide M M D of the product characteristic of it. Fall in the flow speed leads to passage from the turbulent to the laminar regime and because of the shalp fall in ~ the criterion (23) ceases to apply whicn also means deviation from the quasi-isothermal regime. In other words, a limited range of flow speeds exists for iealizing the quasi-isothermal regime. Thus, by changing the flow speed one may significantly increase the yield of the polymeric product with simultaneous rise in the MM and improvement of its quality (narrowing of the MMD), i.e. effectively influence the course of the polymerization process.

Influence of the mode of supply of catalyst on the turbulent diffusion coe~cient and monomer conversion. The way in which the catalyst is supplied influences the nature of the fast polymerization processes occurring in the liquid phase in conditions of turbulent flow of the reacting non-isothermal fluxes in the axis-symmetrical reactor. Within a single mathematical model we studied the influence of the radial and accompanying introduction of the catalyst into the reaction zone on polymerization of 1B to oligoisobutylene (M---1000). The fnitial level of the turbulent pulsations chosen was 50~o. Two models are compared: model I assuming constancy over the volume of the reaction zone Dr but the change in the mode of supply of catalyst may be modelled by change in tile coefficient Dr; model II based on the numerical solution Navet-Stoke~ equations within the q-~ model of turbulent flow [17]. The results of the calculations show that other things being equal with the radial mode of supply of catalyst to the flow of monomer as compared with on line entry, turbulization of the flow increases and mixing improves. Increase in Dr is observed, the reaction zone "compacts" and monomer conversion increases. The molecular characteristics of the polymeric products also improve. Thus, the processes of entry of the reacting flows and their mixing significantly influence the macrokinetics of fast polymerization processes and the molecular-mass characteristics of the polymeric products formed. E.ff~ciency of internal heat removaL An effective way of thermostatting chemical processes is internal heat removal by boiling the components of the reaction mixture. Such a procedure is, in particular, used on polymerization of IB in an ethylene solution where thermostatting of the process is ensured by boiling the ethylene. Limitation of the temperature of the reaction mixture by boiling differently influences the MW of the polymer depending on the radius of the reaction zone R. In the region of small R, i.e. when a flat reaction front forms, and the temperature of the flow is distributed relatively uniformly over the radius of the reaction zone, P', of the polymer in a certain temperature interval ceases to depend on the initial

A.L. AL. BYERLINet aL

1972

temperature of the raw material (Fig. 14a). Polymerization of the monomer comes about in conditions close to isothermal, the polydispexsity index Pw/P, of the product approaching that characteristic of isothermal regimes, but depends on the difference in the initial temperature of the raw material Tinit and the boiling point of the reaction mass Tin,. With increase in the radius of the reaction zone above Rc, when breakthrough of the monomer in the parietal regions of the reaction zone is observed, the characteristic break in the curve of the dependence of log _P, on 1/Zinit smooths (Fig. 14a, log 5n

M~.lg-e

71

1"5 lOO

•

11

0.7 I

1

3

14

I

3G

tl'f

0.6 [/7~nit,'fO 3

FIG. 14. Calculatedlog P, (a) and experimental M (b) dependenceson llTl,tt a: R=0-08 (1) and 0.5 (2) m; [M]o=0-5 mole/L; [A*]o=0.0045 mole/1. ~=0. b: R=0.025 (1) and 0.5 (2) m; [M]o=20% by weight in isobutane; [AIC13]=1 x 10-3 mole/1. curve 2) since zones exist with a wide set of temperatures along the coordinates of the reaction. As a consequence macromolecules differing in size form and the zone of boiling of the reactors is confined to the epicentre of the "torch". Since the zone of the "torch" embraces only a small part of the reaction volume the inefficiency of the internal heat removal for relatively large volumes of the reaction zone through local boiling of the reactants is obvious. Calculation and modelling of the process of fast polymerization of IB with internal heat removal through boiling of the reactants agree well with the experiment (Fig. 14b). Thus, the formation of the volumetric temperature gradient, i.e. conduct of the polymerization reaction in the "torch" regime, complicates control of the process. Thermostatting of the reaction mass by local boiling of the reactants is insufficiently effective. Effect of the linear speed of movement of the flow on the efficiency of external heat removal. Intensification of heat and mass exchange during any chemical process is associated with change in the magnitude DT [23]. Usually increase in the linear speed of movement of the raw material V for a fixed length of the reaction zone l reduces the contact time of the polymerizate with the thermostatted surface which, in turn, entails fall in the efficiency of external thermostatting through the wall.

Macroscopic kinetics of fast polymerization processes

1973

Changes in/~. and the mean temperature of the flow along the length of the reaction zone for different speeds of movement of the raw material and, accordingly, DT are indicated in Fig. 15. Despite the fact that the initial conditions of the polymerization process are identical increase in the speed of flow substantially (2 times) raises P.. This is connected with change in the temperature profile in the reaction zone along its length. Despite the shortening of the contact time of the polymerizate with the AT 60

6

qO

q

20

2

#

6

#

#

1.0

l,m

25

5O

76

o~

FIG. 16 FIG. 15 FIG. 15. Dependence of change in P. (1, 2) and AT (3, 4) along the length of reaction zone l on the speed of movement of the flow V and Dr: 1, 3--DT=0"045 m2/sec; V= 10 m/sec; 2, 4-D,r=O'025 m2/sec; V=5 m/see. FIG. 16. Dependence of change in P. (1, 2) and P~,/P,, (3, 4) on the intensity of external heat removal o~: 1, 3-Dx=0'045 m2/sec; V= 10 m/sec; 2, 4-Dx=0-025 m2/sec; V=5 m/see. thermostatted wall increase in V leads to sharp rise in the efficiency of the external heat removal through rise in Dx and )Ix (Fig. 16). It is important to note that for V=2.5 m/sec (respectively Dr=0.01 m2/sec) with increase in the heat transfer coefficient through the wall from 0 to 100 P. rises only 1.5 times while at V---10 m]sec (DT=0-045 m2/sec) P. rises 3.5 times with the M M D of the polymer tending to the most probable. It is particularly important to note the fact the polymerization of the monomer proceeds to a practically equal extent of conversion (85 7o in the conditions considered). Rise in M M and narrowing of the M M D are connected with change in the temperature AT Ct

b

l,m

d

l

l,m

FIG. 17, Surfaces of temperatures average in section in conditions of external heat remov~,l for

V=5 (a) and 10 (b).

1974

AL. AL. BYl~UN et

aL

profile with increase in the efficiency of mixing in :conditions of external heat removal. Figure 17 presents the surfaces of the temperatures of the polymerization reaction average in section as a function of the efficiencyof external heat removal and the distance from the point of entry of the catalyst. Increase in Dr with increase in V appreciably lowers the temperature in the reaction zone. Another important point is that in conditions of absence of heat removal (~ =0) for high V values at the initial stages of the process (1= 1 m, z=0.5 sec) the temperature in the reaction zone is lower than at low speeds of movement of the flow. Thus, increase in the flow speed greatly intensifies heat and mass exchange through increase in turbulization which, other things being equal, increases the yield of the polymer, raises its MM and narrows the MMD. CONCLUSION

The results of theoretical and experimental study of the macrokinetic features of ultrafast chemical processes of polymerization suggest that they should be assigned to a special class. An analogous example is provided by the processes of combustion which are divided off into a separate class of reactions of oxidation thanks to the macrokinetic features due to positive feedback between the large value of the heat of the reaction and the high sensitivity of the reaction late to temperature (high activational energy). A characteristic feature of ultrafast polymerization processes is the signficant interaction of the processes of mixing, heat transfer and the reaction proper, a consequence of which is the dependence of the rate of the process, the yield and molecular characteristics of the products formed on the volume and geometric parameters of the reaction zone, the characteristics of mixing and heat transfer (flow rate, the parameters of its turbulization, the presence and design of special devices for intensifying turbulization and heat transfer, boiling of the reactants, etc.). The presence of characteristic fundamental features of fast polymerization reactions predetermines both the essentially new modes of controlling the process, for example, forced change in the reaction zone, change in the linear flow rates, methods of mixing catalyst and monomer, the geometric characteristics of the turbulizing devices, inclusion of the boiling process, etc. and the fundamentally new techniques of studying it: determination of the effective rate constants of the different stages of the chemical reaction and simultaneously the parameters of mixing and heat transfer by varying the size and shape of the reaction zone and also the turbulent diffusion coefficient. Thus, it may be noted that fast polymerization processes must be regarded as an independent class of chemical reactions with their own individual specifics and methodology of study. All the distinguishing signs exist for this: test object-polymerization processes proceeding by any known mechanism and modes of synthesis of polymeric products marked by fast and comparable characteristic times of the chemical reaction and transfer; individual specifics of investigating and contlolling the process peculiar only to this class of chemical reactions; and new fundamental laws. As a consequence the new class of chemical reactions-very fast polymerization processes-at plactical level must also be carried out by a specific technology. In particular, a fundamentally

Macroscopic kinetics of fast polymerization processes

1975

new way of obtaining IB h o m o - and copolymers with M = 200-50,000 has been developed in the U.S.S.R. permitting sharp change and optimization of technology and the instrumental design of the process [23, 24]. The new way of obtaining 1B polymers and the apparatus for its execution ensure without additional capital expenditure sharp contraction o f the production a r e a s including separation of polymerization, 3-5 fold and higher increase in the total productivity of the process, 103-10 s fold increase in the specific productivity of the reactor, reduction in metal tanks and the volume of the reactor by 2-3 orders, appreciable reduction in expenditure on water and electrical power, sharp contraction of the stay times of the reaction mixture in the reactor and decrease in the contribution of side and harmful reactions, shortening of the duration of a number of auxiliary operations and universality of the process giving for the ~ame technological scheme and equipment a wide range of polymeric products differing in M W and M W D , which determines the considerable advantages over existing processes of oligo- and polyisobutylene production [8]. Translated by A. Cgoz~ REFERENCES

1. I. M. PAPISOV, V. A. KABANOV and V. A. KARGIN, Vysokomol. soyed. 7: 1779, 1965 (Translated in Polymer Sei. U.S.S.R. 7: 10, 1959, 1965) 2. N. S. YENIKOLOPYAN, A. A. KHZARDZHAN, E. E. GASPARYAN and V. B. VOL'EVA, Dokl. Akad. Nauk SSSR 294: 1151, 1987 3 . J. KENNEDY, Kationnaya polimerizatsiya olefinov. Kriticheskii obzor. (Cationic Polymerization of Olefins. CIitical Review). (Translated from the English) 430 pp., Moscow, 1978 4. M. SWARC, Anionnaya polimerizatsiya. Karbkationy zhivushchiye polimery i protsessy s perenosom elektrona (Anionic Polymerization. Carb Cations, Living Polymers and Processes with Electron Transfer). p. 669, Moscow, 1971 5. N. S. YENIKOLOPOV and S. A. VOL'FSON, Khimiya i tekhnologiya poliformal'degida (Chemistry and Technology of Polyformaldehyde). p. 279, Moscow, 1968 6. S. GOTO, K. YAMAMOTO, S. FURUI and M. SUGIMOTO, J. Appl. Polymer Sci. Applied Polymer Syrup. 36: 21, 1981 7. V. V. KORSHAK, Neiavnovesnaya polikondensatsiya (Non-Equilibrium Polycondensation). p. 696, Moscow, 1968 8. K. S. MINSKER and Yu. A. SANGALOV, Izobutilen i ego polimery (Isobutylene and Its Polymers). 222 pp., Moscow, 2986 9. B. L. YERUSALIMSKII and S. G. LYUBYETSKII, Protsessy ionn0i pblimerizatsfi (Processes of Ionic Polymerization). 256 pp., Leningrad, 1974 .... 10. R. B. TAYLOR and F. WILLIAMS, J. Amer. Chem. Soc. 91: 3728, 1969 11. J. P. KENNEDY, A. SHIKAWA and F, WILLIAMS, J. Polymer Sci. A9: 1551, 1971 12. L. M. DORXMAN and V. M. PALMA, Proc. 30th Intern. Meet. Thiais, 1977, p. 215, Amsterdam, 1978 13. S. A. VEITLINGER, Pronitsayemost' polimernykh materialov (Permeability of Polymeric Materials). 296 pp. Moscow, 1974 14. AI. AI. BYERLIN, K. S. MINSKER, Yu. A. SANGAIX)V, D. D. NOVIKOV, T. L POZDNYAK, Yu. A. PROCHUKHAN, A. P. KIRILLOV and A. G. SVINUKHOV, Vysokomol. soyed. B21: 468, 1979 (Not tanslated in Polymer Sci. U.S.S.R..) 15. T. L POZDNYAK, D. M. LISITSYN, D. D. NOVIKOV and F. F. D'YACHKOVSKII, Ibid. A19: 1168, 1977 (Translated in Polymer Sci. U.S.S.R. A19: 5, 1348, 1977)

1976

Yu. YA. GOTLIB et al.

16, AI. AI. BYERLIN, K. S. MINSKER, Yu. A. SANGALOV, V. G. OSHMYAN, A. G. SVINUKHOV, A. P. KIRILLOV and N. S. YENIKOLOPYAN, Ibid. A22: 566, 1980 (Translated in Polymer Sci U.S.S.R. A22: 3, 625, 1980) 17. Yu. A. PROCHUKHAN, K. S. MINSKER, AI. AI. BYERLIN, M. M. KARPASAS, V. Z. KOMPANIYETS, A. A. KONOPLEV and N. S. YENIKOLOPYAN, DokL Akad. Nauk SSSR 298: 1428, 1988 18. Ya. B. ZEL'DOV1CH, Khimicheskaya fizika i gidrodinamika (Chemical Physics and Hydrodynamics). 374 pp., Moscow, 1984 19. G. A. MIKHAILOVSKII, Dissert. Cand. Tekhn. Sci. (in Russian) Inst. Catalysis Siberian Division, Akad. Nauk SSSR, Novosibirsk, 1976 20. K. S. MINSKER, AI. AI. BYERLIN, A. G. SVINUKHOV, Yu. A. PROCHUKHAN and N. S. YENIKOLOPYAN, Dold. Akad. Nauk SSSR 286: 1171, 1986 21. AI. AI. BYERLIN, K. S. MINSKER, Yu. A. PROCHUKHAN, M. M. KARPASAS and N. S. YENIKOLOPYAN, Ibid. 287: 145, 1986 22. Yu. A. PROCHUKHAN, AI. AI. BYERLIN, K. S. MINSKER and N. S. YENIKOLOPYAN, Ibid. 287: 682, 1986 23. Italy Pat. 1184654 24. France Pat. 2590581

PolymerScienceU.S.S.R.Vol.31, No. 9, pp. 1976-1983,1989 Printedin Poland

0032-3950/89 $I0.00+.00 © 1990PergamonPreu plc

DISTRIBUTION OF THE CORRELATION TIMES AND PATTERNS OF 13C NUCLEAR MAGNETIC RELAXATION AND THE OVERHAUSER EFFECT* V u . YA. GOTLIB, ]. M . NEYELOV, I. A. TORCHINSKII a n d V. A . SI-IEVELEV Institute of High Molecular Weight Compounds, U.S.S.R. Academy of Science.s (Received 21 January 1988) The dependences of the spin lattice relaxation time T~e and the Overhanser effect for different correlation time distributions used to describe the relaxational properties of polymers are examined. The dependence of TIe and the value of the nuclear Overhauser effect has been established (as a function of COcrwhere O~c is the resonance frequency and ~ is the time characteristic of the given spectrum) on the form, width and asymptotic behaviour of the correlation time spectra for short and long times. These values are sensitive to the parameters of the relaxation spectra and may serve for their discrimination.

RECENTLY to t h e t r a d i t i o n a l m e t h o d s o f s t u d y o f t h e local d y n a m i c p r o p e r t i e s o f m a c r o m o l e c u l e s has been a d d e d t h e n u c l e a r O v e r h a u s e r effect [I-5]. T h e spectral m a n i festation o f the O v e r h a u s e r effect consists in the fact t h a t s a t u r a t i o n o f t h e a b s o r p t i o n * Vysokomol. soyed. A3I: No. 9, 1799-1804, 1989.