Study of certain relationships of styrene grafting on polypropylene films

STUDY OF CERTAIN RELATIONSHIPS OF STYRENE GRAFTING ON POLYPROPYLENE FILMS* A S TEVLINA, H. S KOLESN1KOV. S N SIVIDOVA and V V I~YL'TSEV D. I. Mcndelcycv Chemmotcchnologlcal In~Ututc, Moscow (Recewed 24 December 1966)

A DESCRIPTIO:N was given m a previous paper [1] of the production of styrenepolypropylene graft copolymers, in order to carry out further chemical conversions. In this paper we attempt to study in more detail the relationship of grafting styrene to polypropylene and evaluate the effect of the properties of polypropylene itself on grafting and on the properties of graft copolymers and the properties of ion-exchange resin films obtained from them A non-stabihzed polypropylene film prepared in the Scientific Research Institute for Addition Polymers (film i) and a stabilized oriented film (film 2) prepared in the M. V Lomonosov Inst:tute of Fine Chemical Technology in Moscow (see Table 1) were used. TABLE

Film

I. P R O P E R T I E S

Stabilizer

Ionol t

O F INITIAL P O L Y F R O P Y L E N E

Ormntatlon

Umax--all stretchmg

Tenbde strength, kg/cm 2 127 1020

FILMS

[t/] (decalm, 135°) Atactm:ty*, O/ ,O dl/g 3 0

25

11-7 124

* Atacttctty was e v a l u a t e d b ) extraction w i t h boiling n-heptanc aSSlllnlllg t h a t tile fraction d l s s o h e d conststcd e h t l r e b of a t a c t m p o l y m e r [2] -~ 2,6-Dl-(tert b u t ) l)-4-methylphenol

When investigating graft copolymerization of styrene on a polypropylene film we studied the effect of various factors--amount of Initiator, temperature, polymer, monomer ratio, reaction time, on the yield of graft polystyrene We tried to find a combination of the above conditions under which graft copolymerization would occur most sat:sfactorily, using a mathematical statistical method of planning the experiment, as previously applied by the authors to a similar system [3] The ymld of graft polystyrene was chosen as the optimum criterion, determined gravimetrically as weight percent of the initial film * Vysokomol. soyed. A9: No. 11, 2473-2477, 1967. 2797

2798

A. S. TEVLINA et

al.

Optimum grafting condltmns were established: imtiator--azobisisobutyronitrfle 0.7 tool.% , polypropylene styrene ratio 0.00344, reaction temperature 66 ° To compare the properties of graft copolymers from films 1 and 2, we obtained graft films with the same grafting efficmncy of 30%. The efficiency of grafting (%) was determined as the ratio of the weight of graft polystyrene to the overall weight of the graft copolymer. Grafting times required for achieving this efficiency. 1 hr 45 min for film 1 and 2 hr l0 min for film 2. Optimum conditions for obtaining graft copolymers for these films were the same, except for grafting time In film 2 the stabilizer apparently retards the swelling process in styrene, and consequently also retards the grafting process, which is in agreement with the authors' w e w [4]. 1

3O

2

~2o 3

~z

1

r

~

o

60

120

180

2

#

TLme J r n l n

FIG. 1

6 8 [P] xtn2 ~it, i

FzG. 2

FxG. 1. Dependence of grafting efficiency on reaction time: /--for unstablhzed polypropylene film l; 2--for stabdlzed, ormnted polypropylene film 2. Fro. 2. Dependence of 1//5 of polystyrene on the polypropylene: styrene ratio, (P/[M]). /--for unstabfllzed polypropylene film 1; 2--for stabilized, oriented polypropylene film2. We investigated the dependence of grafting efficiency (GE) on time [5], it is linear at the beginning of the reaction and non-hnear in the subsequent period. The cause of this dependence, in addition to the delay of the breakage reaction (Trommsdorf-Nuffit effect, gel effect) is the special nature of heat exchange in bulk polymerization With increase of the degree of polymerization, the viscosity of the polymer-monomer system increases and temperature begins to rise as a consequence of poorer heat exchange between the reaction mass and stuTounchng atmosphere. Under these conditions, first of all it is difficult to obtain a graft copolymer with a given degree of grafting, secondly at high degrees of grafting the film obtained is brittle. To avoid these shortcomings, we used a method of gradual grafting. With this method grafting was interrupted at the moment which, according to the

Certain relatmnshlps of styrene grafting on polypropylene films

2799

graph, corresponded to the beginning of transition from linear to non-linear time dependence of grafting efficiency Vmually, this moment corresponds to the beginning of block formatmn The graft film was seperated from the homopolymer by prolonged extraction wxth ethyl acetate until the extractmn of the soluble part was complete, when it was dried and placed m a fresh initiator solutmn in monomer (similar to the oraginal one) to continue grafting The linear dependence on time of grafting efficiency was not dmturbed Thus, a graft eopolymer wxth a predetermined graftmg efficmney could be obtained with an accuracy of up to 0.5% The results of determining optamum grafting condxtions are ahown an Fig 1 From the tangent of the gradient of straight hnes and sections cut off by them on the abscmsa axis the coefficients of functional dependence on time of grafting efficiency were determined For film 1 these were: y--(0.35x--7.0)× 100, for film 2: y : ( 0 . 2 8 x - - 5 . 6 ) × 1 0 0 , where y is the grafting efficiency, x--grafting time. During graft copolymerization a macroradical initiating the reaction is formed as a result of chain transfer through the polymer during polymerization of styrene. To evaluate the possxbility of chain transfer, we attempted to determine the transfer constant, Cp, through the polymer We determined the chain transfer constant, in order to evaluate the reactivity of films 1 and 2 in the reaction of chain transfer The chain transfer reaction mainly affects the average coefficient of polymerization of the polymer. For thermal polymerizatmn of styrene m the presence of chain transfer agents the Mayo equation can be used to determine the transfer constant [6] 1 1 +Cp Iv] g Po [M] where P0 is the mean coefficient of polymerizatxon of the polymer without a chain transfer agent; P is the mean polymerization coefficient of the polymer in the presence of a chain transfer agent, I-P] is the concentration of the cham transfer agent; [M] -- monomer concentration. Results of determining the chain transfer constant are shown in Table 2 and in Fig. 2 To determine the chain transfer constant the reaction was carried out in sealed ampoules without imtiator. The ampoules were previously degassed and evacuated. The polypropylene film was dissolved m styrene and kept at 66 ° until the monomer polymerization was 10-20% 20 to 30 hr were needed for this. The molecular weights of the po]ymers obtained were determined viscometrically. The chain transfer constant was determined from the tangent of the gradient of the straight line showing the dependence o£ 1/P on [P]/[M] (see Fig 2). The value of 1/P detrmined b y extrapolation of straight lines to zero polypro-

2800

A. S TEVLINAet al. TABLE 2. D E T E R M I N I N G

T H E C H A I N T R A N S F E R CONSTANT

[t/] of polystyMolecular PolymerlzaF,hn -[P] - × 102 rene (benzene, weight of poly- tmn coeffi[M] 25°), dl/g styrene cmnt P 1

1.24 2 48 5.59 7.70

30 2 42 1 73 1 50

2

1.24 2.48 5.59 7.70

22 1.9 1.8 12

1/P × 104

Chain transfer constant Cp × 103

1,120,000 813,000 512,000 427,000

10,800 7800 4940 4100

0.93 1.28 2.03 2.74

26

708,000 589,000 575,000 316,000

6800 5650 5500 3040

1.47

30

1.78 1.84 3.29

pylene concentration is m agreement with the value found experimentally in styrene polymerization under the same conditions without polypropylene (1//5o= 0.9 × 10 -4 for film 1 and 1.2 × 10 -4 for film 2; the value of 1/P 0 found experimentally is 1.3 × 10-4). A comparison of chain transfer constants shows t h a t for unstabilized (film 1) and stabilized polypropylene film (film 2) the chain transfer constants are practically the same, i.e. the stabihzer retards the rate of graft copolymerization. but does not influence the mechanism of graft copolymerization. I f we compare the chain transfer constant of polypropylene with t h a t of polyethylene [5], the higher chain transfer constant of polypropylene indicates higher reactivity during graft copolymerization. This is, apparently, explained by the presence in the polypropylene macromolecule of CH groups, which readily take part in chain transfer reactions. I t was of interest to compare some properties of graft copolymers from films 1 and 2. An important problem was to determine the number and length of graft branches of polystyrene From literature data [7] on the identity of composition and molecular weight of graft branches and the simultaneously formed homopolymer, we calculated the density of grafting (Q), which is characterized by the number of elementary polypropylene units between the graft branches of polystyrene This made it possible to determine the average number of polystyrene branches grafted to the polypropylene macromoleeule (of course, mean statistical values were found in both cases) The results obtained are shown in Table 3. Grafting density was calculated by means of the formula: Q = g e e , M~ gPS

MZB '

where gPe is the weight of the imtial film; gPS is the weight of the graft polysty-

Certain relationships of styrene grafting on polvpropylene films

2801

rene; MB -- molecular weight of graft side branches of polystyrene; MzB--moleeu]ar weight of the elementary polypropylene umt Figure 3 shows curves of the molecular weight dastribution of homopolvstyrene formed by grafting polystyrene on po]ypropylene films 1 and 2. Poly~D2 4 12

A?s 12

08

8

O0

4

056

08g

06# ~s

Fie. 3 Molecular weight dlstmbutlon of polystyrene. 1, 2--unstabfllzed polypropylone film 1, 3, 4 stablhTed, oriented polypropylene film 2, l, 3--(hfferentlal curves, 2, 4--integral curves. dispersion was studied by turbldimetrie) titration using a FEK-M photocolorimeter at 20±0-I o. Benzene was used as solvent and methanol as precipitant TABLE 3.

Film

1 2

DENSITY

OF GRAFTING

POLYSTYRENE

Molecular weight Molecular welght of the m,txal of the graft polypropylene polystyrene 513,000 316,000

71,000 71,000

ON POLYPROPYLENE

Gra~mg denmty, Q

Number of polystyrene branches per polypropylene macromolecule

4200 4200

3 2

I f we assume t h a t the homopolystyrene formed during grafting has not only the same molecular weight as the graft branches, but also the same molecular weight distribution, it can be seen in Fig. 3 that, in grafting on both polypropylene films, the side branches of polystyrene are characterized by a marked polydispersion. A study was made of the variation of mechanical properties of graft copolymers (tensile strength) according to the degree of grafting for films 1 and 2. the data obtained are shown in Table 4.

2802

A. S. TEVLINA et al. TABLE 4.

MECHANICAL

ACCORDIHG

Degree of g~aftmg, oo

T

PROPERTIES

TO THE

OF GRAFT

DEGREE

. . . . . . . . . . . .

Tensile strength, kg/cm -~

Degree of grafting, °o

I)

i

I

Tensile strength, kg/cm 2

Film 2

Fdml 14 30 46

COPOLYMERS

OF GR~FTING

130 155 190 280

0 14 30 46

1600 1000 930 690

Tensile s t r e n g t h was d e t e r m i n e d in a SZ-50-1 t e s t i n g machine. T a b l e 4 shows t h a t t h e tensile s t r e n g t h of film 1 increases a n d t h a t of film 2 decreases w i t h increased degree of grafting. A r e d u c t i o n in t h e s t r e n g t h of film 2 is a p p a r e n t l y due to r e l a x a t i o n processes t a k i n g place a t increased t e m p e r a t u r e during g r a f t c o p o l y m e r i z a t i o n , as a result of which the film becomes less o r i e n t a t e d T h e orient a t i o n of film 2 r e m a i n s fairly high so t h a t t h e tensile s t r e n g t h of film 2 is twice as high for a degree of g r a f t i n g of 4 6 % as t h a t of film l for t h e s a m e degree of grafting. CONCLUSIONS

(1) A study was m a d e of the characteristics of g r a f t i n g s t y r e n e on p o l y p r o p y l e n e films o f different s t r u c t u r e s (2) I t was f o u n d t h a t t h e o p t i m u m 'conditions for o b t a i n i n g g r a f t c o p o l y m e r s for an unstabilized, oriented p o l y p r o p y l e n e film are the same, e x c e p t for grafting t i m e (3) S o m e p r o p e r t i e s of p o l y p r o p y l e n e - p o l y s t y r e n e g r a f t c o p o l y m e r s were investigated. Translated by E. SEMERE REFERENCES

1. A. S. TEVLINA, S. V. KOTLYAROVA and E. P. AGAPOVA, Vysokomol. soyed. 6" 1327, 1964. (Translated m Polymer ScL U.S.S.R. 6" 7, 1467, 1964) 2. T. KRESSER, Polypropylene, Izd-vo mostr, h t , p. 82, 1963 3. S. P. NOVIKOVA, H. S. KOLESNIKOV, A. S. TEVELINA and V. V. BIRYUKOV, Vysokomol. soyed. A9 605, 1967 (Translated m Polymer Sel. U.S S.R. 9 3, 679, 1967). 4. ZHUN ZHUI, Kh. A. STASYUK, L A. K O C H E R G I N S K A Y A , N. D. ROZENBLYUM, A. A. KONKIN and Z. A. ROGOVIN, Khlmmh volokna No 5, 12, 1963 5. S. V. KOTLYAROVA, Dissertation, 1965 6. K. BAMFORD, U. BARB, A. JENKINS and P. ONION, Kmetlka rad~kal'nm pohmemzatsn vmalovykh soyedmenu (Kmetms of Radical Polymemzatlon of Vinyl Compounds). Izd-vo mostr, h~., p.37. 1961 7 Y. OGATA, N. JASUMOTO, T. FUJINE, J. MINOURA and M. IMOTO, J Chem. Soc. Japan, Industr. Chem. See. 65: 1136, 1962