Radiation-induced solid state polymerization of N-substituted acrylamides and methacrylamides at reduced temperature

Radial Phys. Chem. Vol. 23, No. 4, pp. 385-392, 1984 Printed in Great Britain.

0146-5724/84 $3.00 + .00 Pergamon Press Ltd.

R A D I A T I O N - I N D U C E D SOLID STATE POLYMERIZATION OF N-SUBSTITUTED ACRYLAMIDES A N D METHACRYLAMIDES AT R E D U C E D TEMPERATURE J. ~URAKOWSKA-ORSZAGH, A. GUMUEKA and J. BARTNIK Department of Chemistry, University of Warsaw, ul. Pasteura l, 02093 Warszawa, Poland (Received 22 M a r c h 1983)

Abstract--Radiation-induced solid state in-source polymerization and post-polymerization at reduced temperature of a series of N-tert-alkylacrylamides and pairs of monomers of the aerylamide and methacrylamide series with identical aliphatic, aromatic and alicyclic substituents has been studied. The effect of the changes in the structure of particular monomers on their reactivity at reduced temperature as compared with their reactivity at room temperature has been considered.

INTRODUCTION MUCH WORK on the kinetics of radiation-induced solid state polymerization has been concerned with N-substituted acrylamides and methacrylamides. °-'4) Usually, the reaction was performed to high conversions at room temperature. 0-g'H-'3) However, in our recent papers the problem of the effct of temperature on the reactivity of these monomers was also studied. Some interesting observations were made on the relations between the chemical structure of particular monomers and their activation energy calculated for in-source polymerization o°) as well as postpolymerization, o4) The present report is a continuation of publications. °°'m4)Its main purpose is the study of the effect of the changes in the chemical structure of particular monomers of these series on their reactivity during solid state polymerization at reduced temperature in comparison with their reactivity during polymerization at equal temperature, if possible, for all monomers. EXPERIMENTAL The list of monomers used in these investigations comprises pairs of acrylamide and methacrylamide derivatives with identical aliphatic, aromatic and alicyclic substituents (Table 1), and a series of N-tert-alkylacrylamides (Table 2). The monomers were obtained by the methods previously described.('-" The purification, preparation of the samples as well as the technique of in-source irradiation and preirradiation are given in detail in papers.O0,t4) The samples were sealed in Thermosil glass tubes filled with pure dry nitrogen. All irradiations were carried out in eCo 7 source Gammacell 220 at a dose rate of 81888 rad/h = 0.227 Gy/s. The samples destined for post-effect polymerisation before irradiation were cooled down in solid carbon dioxide to 195 K and then irradiated at this temperature to a dose of 1.4 Mrad = 14 kGy. Both in-source polymerization and post-

polymerization were performed at reduced temperature determined by the following relation: Tpol/T=, I = 0.9, where Tm,~is the melting point of a given monomer. The reduced temperature of all monomers studied are summarized in Tables 1 and 2. For comparison the polymerizations by simultaneous irradiation and preirradiation were carried out also at equal temperature of 300 and 330 K. Beside the conventional gravimetric method described previouslyO.'0)X-ray diffractometry was also used for deterruination of polymerization rate. For this purpose a wideangle powder diffractometer TuR M61 (GDR) with copper target radiation and Geiger-Miiller counter was employed. The incident beam was monochromatized by means of a bent quartz crystal. The corrections for the nonlinearity losses of the Geiger-Mfiller counter were determined by use of multiple foils.(".) Powder samples for X-my diffraction examination were prepared in a standard way.(lib)The X-ray determination of the conversion was based on the crystallinity of the residual monomer in the polymerized samples estimated from diffractograms by measuring the area of the highest peak of a given monomer. RESULTS AND DISCUSSION The kinetic curves of radiation-induced solid state polymerization of acrylamide, methacrylamide and their derivatives with identical substituents are presented in Figs. I(A-D). The respective figures illustrate the course of the polymerization performed at reduced temperature by in-source irradiation (Fig. 1A) and pre-irradiation (Fig. 1B) as well as by simultaneous irradiation and pre-irradiation at temperature of 330 K (Figs. 1C, D). The examination of the kinematic curves shows that independently on the conditions and technique applied the presence of the substituents usually decreases the reactivity of the monomers in the solid state. Therefore, acrylamide and methacrylamide are more reactive than their derivatives with the exception of N-l,l-dimethylethylacrylamide (Cugve 2 in 385

J. ZURAKOWSKA-ORSZAGHet al.

386

TABLE1. LISTOF MONOMERSOF ACRYLAMIDEAND METHACRYLAMIDESERIES

~tonomor

Chemical formula

Acrylamide

~-II

N-tert-butylacrylmnlde

A-?-CII 3 CII3

Melting point K

Reduced temp. o f polymn. K

Symbol on graphs

357,2

321,5

1

403,1

362,8

2

386t2

347,6

11

380,2

342,2

12

368,2

331,4

ia

327,6

294,9

2g

381,0

342~9

11 j"

359,7

32317

,%

N-oyclohexylacrylamtde

N-phenylacrylamide

cH 2 CH2-CH2

AO

Methacrylamide

I~A-H

N-tert-butylmethacrylamlde

MA'~I-CtI 3 CII3

N-cyclohexT1methacrylamlde

fII2-C~I2 MA-CII CH 2 l CII2-CH2

II

N-phenylmethaorylamtde A- =

CH2=CH-CO-NH-

MA- =

CH2=C.-CO-NII-

?H3

Fig. 1A) of which polymerization rate at reduced temperature by simultaneous irradiation is higher than that of acrylamide (Curve 1 in Fig. 1A). On the other hand, the analysis of the curves presented in Figs. 1A, IB indicates that the polymerization rate of monomers of the acrylic series carried out at reduced temperature by simultaneous irradiation (Fig. 1A) or pre-irradiation (Fig. IB) is always higher than that of corresponding monomers

of the methacrylic series with identical substituents on the nitrogen atom. A similar order of kinetic curves is observed for polymerization performed at equal temperature (Figs. 1C, D). As seen from Fig. I(B) the reactivity of Nsubstituted methacrylamides in the postpolymerization reaction at reduced temperature contrary to the other monomers studied is strikingly

387

Solid state polymerization at reduced temperature TABLE 2. LIST OF MONOMERSOF N-TERToALKYLACRYLAMIDESERIES

Monomer

N - t e r t - b u t y l a c r y 1a m l d e N-1,1-dime thylcthylacrylamlde

Chemical

Melting

Reduced

Symbol

formula

point K

temp.

on

CII3 A-C-CH 3 ! CI! 3

of

polymn. K

graph s

403,1

362,8

2

CII

N-1,1-dlmothyl.~ropylaoryla~tde

A-~-C2H 5 CII3

367t0

330,3

3

N-l,l-dimethylbutylacrylamide

A-~-C3II7 CII3

337,4

303,7

4

N-l-me thy 1-1-e thylpropyl acrylamidc

A~-C2It5 C2II5

345,6

311,0

6

N-l,l,2-trimethylpropylaorylamidc

~II3/CII3 A-C-CII CH3 CH3

373,2

335,9

9

N-1,1-dimethylamylacryle~lde

A-C-C4II9 CII3

334,3

300,9

5

N-l-me thyl-l-e thylbutylacrylamide

A-C-C 3It 7 C2II5

355,2

319,7

7

N-1 t l - d i e t h y ] p r o p y I ac r y I amid e

C2H5 A-C-C2115 C2115

387,0

348,3

8

CII3 CII3 A-C-CH~-CIt CII3 CII3

331,7

298,5

10

,%

3

,%

N-l, I, 3-trlmethy lbutyl-

acrylamlflc

A- =

small. This effect appears in the case of N-tert-butyl, cyclohexyl as well as phenyl substituents and is presumably connected with large steric hindrances formed by two substituents on the ~-carbon which hamper the chain propagation reaction, especially when the radiation energy is supplied only before the RPC Vol.23, No. 4--B

CII2=CH-CO-NHbeginning of the polymerization reaction, as is the case o f post-effect reaction, since in this case for the lack of further energy inflow the hindrances can hardly be surmounted. The solid state polymerization of the homologous series of N-tert-alkylacrylamides, namely: N-l,1-

388

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F]o. 1. Solid state polymerization and postpolymerization of acrylamide, methacrylamide and their derivatives with identical substituents at reduced temperature (A, B) and at 325 K (C, D) (meaning of curve symbols in Table 1). dimethylethylacrylamide, N- 1,1-dimethylpropylacrylamide, N-l,l-dimethylbutylacrylamide and N-I,1dimethylamylacrylamide, is shown in Figs. 2(A-D). As can be seen from the curves in these figures, with increase of the length of the substituent the polymerization rate at reduced temperature decreases clearly. This effect is observed when polymerization is induced both by simultaneous irradiation (Fig. 2A) and by pre-irradiation (Fig. 2B). Additional investigations of the complete conversion of these monomers to polymers at reduced temperature o2) performed by gravimetric method (Fig. 3, Curves 2-5) have shown that the decrease in reaction rate from N-1,1-dimethylethylacrylamide up to N-l,l-dimethylamylacrylamide takes place practically over the whole conversion range. This order in polymerization rate of ithe above homologous series has been confirmed by X-ray diflYactometric studies o2) based on the measurements of the monomer crystallinity although the conversion values obtained for particular monomers are considerably higher (Fig. 3, Curves 2R, 3R, 4 ~ and 5R).

When the polymerization is carried out at the same temperature the reactivities of this homologous series of monomers are, in principle, ranged in the inverse order. This effect is observed both for in-source polymerization (Fig. 2C) and post-polymerization (Fig. 2D). However, this inverted order is disturbed by the position of N-l,l-dimethylamylacrylamide which seems to be responsible for the lower polymermization rate in comparison with that of 1,1-dimethylbutylacrylamide. It may be connected with differences in the crystal symmetry displayed by these monomers. As shown by crystallographic investigations (13,14) the space group of N-I,1dimethylamylacrylamide (P2Jn) differs from that of the other monomers of this series (space group P2=/c) and contains twice as many molecules in the unit cell (8 molecules) as obtained b y theoretical calculations (4 molecules). °5) These differences in crystal structure of N-l,l-dimethylamylacrylamide may have a hampering effect on the polymerization reaction of this monomer at room temperature. The polymerization curves of the N-tert-

Solid state polymerization at reduced temperature A

5

1

389 4

5

3

C

5

10 20 TIME OF POST-POLYMERIZATION (h)

10 20 TIME OF POST-POLYMERIZATION (h)

FIG. 2. Solid state polymerization and postpolymerization of acrylamide (1), N-l,l-dimethylethylacrylamide (2), N-l,l-dimethylpropylacrylamide (3), N-l,l-dimethylbutylacrylamide (4) and N-I,Idimethylamylacrylamide (5) at reduced temperature (A, B) and at 300 K (C, D).

hexylacrylamide isomers and cyclohexylacrylamide are presented in Figs. 4(A-D). For polymerization at reduced temperature performed by simultaneous irradiation (Fig. 4A) as well as by pre-irradiation (Fig. 4B) the highest reactivity, at least for very low conversions, is exhibited by the symmetric cyclohexylacrylamide, whereas in the case of polymerization at 300 K the reactivity of this monomer is the lowest one (Figs. 4 C , D, Curve 11). Similar variation in the reactivity is observed with some of N-tert-heptylacrylamide isomers, as shown in Figs. 5(A-D). At reduced temperature when the reaction is in-

Z 0 60 er

840 20

i

I

i

i

10 20 TIME OF POLYMERIZATION (h)

FIG. 3. SoEd state polymerization (complete conversion) during irradiation of N-l, l-dimethylethylacrylamide (2, 2s), N-l,l-dimethylpropylacrylamide (3,3s), N-l,l-dimethylbutylacrylamide (4, 4R) and N-l,l-dimethylamylacrylamide (5, 5R) at reduced temperature as studied by gravimetry (Curves 2-5) and X-ray diffractometry (Curves 2g, 3~, 44 and 5s). Dose rate 36000rad/hr = 0.1gy/s.

390

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~s U't

a:

10 C

Z

ILl

Z O (J

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10 20 TIME OF POLYMERIZATION (h)

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tO 2O TIME OF POST-POLYMERIZATION (h)

FIG. 4. Solid state polymerization and postpolymerization of N-tert-hexylacrylamide isomers (4, 6, 9) and cyclohexylacrylamide (11) at reduced temperature (A, B) and at 300K (C, D) (meaning of isomers symbols in Table 2). duced by simultaneous (Fig. 5A) as well as by pre-irradiation techniques (Fig. 5B) the monomer of symmetric structure with three ethyl groups, i.e. N-l,l-diethylpropylacrylamide, on the tertiary carbon has the highest polymerization rate. In the case of Polymerization at room temperature the same monomer has the lowest reactivity (Figs. 5C, D, Curve 8). As seen f r o m these results the inverse order of kinetic curves describing the solid state polymerization carried out at reduced temperature in comparison with that obtained for the polymerization performed at 300 K is observed with homologous series of N-tert-alkylacrylamides (Figs. 2A-D) as well as with cyclohexylacrylamide (Figs. 4A-D, Curve 11) and N-tert-heptylacrylamide isomer, i.e, N-l,l-diethylpropylacrylamide (Figs. 5A-D, Curve 8). This phenomenon may be explained by the occurrence of two opposing effects which play a fundamental part in the solid state polymerization, namely: the molecular mobility of monomer and of the grow-

ing polymer chain and on the other hand the steric hindrances caused by large substituents on the ~-carbon of vinyl group. At equal temperature of polymerization (300 K) for all monomers studied the mean molecular mobility is different for particular monomers depending on the distance from their melting points as well as on the number, size and shape of substituents on the ~-carbon. At reduced temperature, however, the average mobifity of monomer molecules resulting from relatively equal distance of polymerization temperature from melting point would be expected to be approximately t h e same for all monomers; consequently the reaction rate appears to depend mainly on the number, size and form of subsfituents which hinder in different measure the propagation of polymerization reaction. In view of this the lower reactivity of methacrylamide in comparison with that of ac~lamide may be explained by presence of the methyl group substituted in acrylamide immediately to ~-carbon. The lower reactivity of N-substituted acrylamides

Solid state polymerization at reduced temperature

391

t/1 1 9

C9

.° '~.

LYM

TIME OF POLYMERIZATION (h)

~,z~,,o! °~I

~

o

11 e

10 20 TIME OF POST-POLYMERIZATION (h)

;

'

:

i

.

-~

,

IO 20 TIME OF POST-POLYMERIZATION (h)

FIG. 5. Solid state polymerization and postpolymcrization of N-tert-heptylacrylamide isomers (5, 7, 8, ]0) at reduced temperature (A, B) and at 300 K (C, D) (meaning of isomers symbols in Table 2).

,o

~

21 3

6 11 8 4 9 7 5

o/

ol ~

10

o

1*~

12

s

0

, I 20 30 TIME OF POLYMERIZATION (h) FIG. 6. Solid state polymerization during radiation at reduced temperature of all monomers studied (symbols in Tables I and 2). This figure is an extension of Figs. 1A, 2A, 4A, 5A. 10

,

392

J. ~.URAKOWSKA-ORSZAGHet al.

compared with that of acrylamide may be accounted for by the presence of a large group of hydrocarbons substituted directly to nitrogen atom. The lower reactivity of N-substituted methacrylamides as against N-substituted acrylamides with identical substituents may be explained by the presence of the other substituent on the ~-carbon, namely: the methyl group. Finally, the reactivity differences between particular N-substituted acrylamides may be accounted for by the size and shape of the substituents on the nitrogen. Thus, the reactivities of monomers of N-tert-alkylacrylamide series with symmetric substituents on the tertiary carbon are higher in their group than those of monomers with different substituents and with increasing length of at least one of these substituents the monomer reactivities decrease. All this can easily be seen in collective Fig. 6 which gives the dependence of conversion of monomers studied on time of polymerization at reduced temperature. These considerations leads to the conclusion, and it needs to be strongly emphasized, that the study of the sofid state polymerization at reduced temperature gives results which seem to be more directly connected with the chemical structure of the monomers due to the fundamentally similar molecular mobility resulting from the relatively equal distance of polymerization temperature from the melting points of particular monomers. Acknowledgement--The authors wish to thank the Institute of Radiation Chemistry of the Technical University in Lodz for financial support.

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