INVESTIGATIONS IN THE FIELD OF THE

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INVESTIGATIONS IN THE FIELD OF THE

RADIATION-INDUCED SOLID STATE POLYMERIZATION*

VI. GA:3L\lA-RADIATIO::\" I::\"ITLUED SOLID STATE POL YMERI ZATIOK OF Y!::\"YL LA"CRATE

By

Gy. HARDY, K. ~YITRAI,

J.

^VARGA ^and M. PATKO

Department of Plastics and Rubber Industry. Poly technical Lniversity. Budapest (Received December 2, 1964)

In connection with the gamma radiation-induced solid phase polymerization of cethyl methacrylate we ha...-e deyeloped a hypothesis of the adyaneed effect of long-chain aliphatic suhstituents on the solid phase polymerization of vinyl monomers [1]. The polymerization of methyl methacrylate in solid phase advances very slowly [2). But in a glass-like solid phase, ohtained by addition of paraffin oil, a more significant polymerization rate can he ob- seryed [3). Cethyl methacrylate, howeyer, haying a long-chain aliphatic suhstituent, can he easily polymerized in solid phase. As to the vinyl esters, successful studies on solid phase polymeri7ation of vinyl acetate could only recently he made [2). Its polymerization also takes place slowly, effected only hy very high dose rates. Solid phase polymerization of vinyl stearate, initiated by gamma-radiation and accelerated electrons, was investigated [4, 5

J

and it was stated that the polymerization reaches a maximum near to the mel~ing

l)oiut, and henzoquinone acts as inhihitor on the reaction.

Investigations of the solid phase polymerization of vinyl laurate pro- mised to he interesting in general from the point of view of the influencing

effect of the long-chain aliphatie suhstituent on the solid phase polymerization of vim·l esters.

Experimental

Our applied methods were the .same, as mentioned in our previous paper [1]. According to the method descrihed in the literature [6] vinyllaurate was ohtained hy the transesterification of ...-inyl acetate with lauric acid. The purity of the monomer used was 100⁰₀ which was estimated hy means of a gaschromatographic analysis.

Characteristics of the twice distillated ,-inyl laurate were: hoiling point 89 cC/O.'! torr, melting point 3

cc.

n1⁵= 1.4387. When the polymerization ended the polymeric system was soh-eel in henzoquinone-containing gasoline

• Part Y. :31akromolekulare Chemit": in press.

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138 GY. HARDY et al.

at the temperature of radiation in order to prevent further reactions during treatment. The polymer was precipitated from the solution by the addition of methanol at a temperature of about -15 to-20°C. In this way polymer is precipitated in a suitable form for drying.

The kinetics of the liquid phase polymerization was measured by the dilatometric method.

Results and discussion

The kinetics of the gamma-radiation initiated liquid phase polymerization of vinyllaurate at different temperatures is shown on Fig. 1.

10 20 30 ~o 60 70 80 90 100 110 120 minutes

Fig. 1. Kinetics of liquid phase polymerization of viuyl laurate at a dose rate of 46.000 rjh by 30°C (3), 40°C (2) and 50°C (1)

The activation energy of the liquid phase polymerization based on the measurement of the dependence of polymerization rate from temperature could be determined and was found to be 6.65 kcalfmole, which shows good coincidence v.-ith that found by other vinyl monomers.

Fig. 2 shows the dependence of the rate in liquid phase radiation initiated polymerization of v-inyl laurate in function of the dose rates. The polymerization rate varies ""\v-ith the 0.51 power of the dose rate, the value of which is generally accepted as an ev-idence of radical mechanism and a bimolecular chain termination reaction. The fact that inhibitors (like benzoquinone, di- phenylpicrylhydrazil [DPPH]) inhibit the liquid phase radiation polymerization, gives another proof of the above statement.

Fig. 3 shows the kinetics of solid phase polymerization of v-inyllaurate at different temperatures.

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RADIATWS·I.YDUCED SOLID STATE POL YJfERIZATWS 139

Fig. 4 shows the same at

oce,

with varying dose rates. On the basis of the figures it can be established that the kinetics of the solid phase polymerization of vinyl laurate up to 20% conversion has a linear character, above it a re-

10 20 ItO 50 60 70 80 90 100 minutes

Fig. 2. Kinetics of liquid phase polymerization of vjnyllaurate with varied dose rate: 2. - 46.100 rih., 4. - 28.250 r/h .• 5. - lS.O'tO r/h.

20

~ .~ c:: 15

.,

~

"-

c::

'"

l.J

10

5

1

,/2 ⁱ

ⁱ ^{2-16 CO}^{1 0}^C'

I

3-78 CO

J I

ⁱ_I

ⁱ ^I

ⁱ^I^I

I I

3

I

I I

o

⁸⁰ 120 hours

Fig. 3. Kinetics of solid state polymerization of vinyllaurate with a dose rate of 22.050 r/h at 0, -16 and -78°C.

tarding tendency, 0.65 being the exponent of the dependence of solid phase polymerization rate "with the dose rate referring to radical polymerization mechanism in the solid phase, too.

The Arrheruus diagram for temperature dependence of polymerization rates is shown on Fig. 5. It can be seen that the rate of solid phase polymerization has its maximum near to the melting point, i. e. the dependence has the

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140 GY. HARDY et al.

same character as in case of cethyl methacrylate [1] and vinyl stearate [4, 5].

It should to be mentioned thatin the applied temperature range with the method of differential thermoanalysis no secondary transition point was observable

~o ,---p~'>7-=-_,_-_,_;=---

iJ 20 40

22050 rln 2 16300 rln 3. 10250 rln I; 6150 rln 5. 4700 rln

60 hours

Fig. 4. Ki!l~tici' of the solid ,tate polymerization of yinyl laurate at OC C with yaried dose rates

Vbr·fO~

molellsec

1

,\

^I^I

\~

_\

:

_I

"

- -

I

: \

111

3.0

I I I

I I I I I ,I

\

^,

-,

, i

4,0

! I

!

I I

i

I

i

I

I I

I

I I

"

"-... ^I^I ⁱi ⁱI

:~I_I

!

,

i

5.0 tiT-If?

Fig. 5. Dependence of polymerization rate of yinyllaurate on the temperature in liquid phase at a dOi'e rate of 16.000 r/h (below calculated for ~2.050 r/h) and in solid state at a dose rate

of 22.050 rih.

1Il the solid state, therefore, the dh-ersion of the Arrhenius curye cannot be explained by this fact.

The ,'ariation of the molecular weight of polymers, obtained by solid phase polymerization of vinyl laurate can be seen in Fig. 6. The molecular

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RADIATIO.Y·I.YDl"CED SOLID STATE POL Y.UERIZATIO.Y 141

weights grow with ach'ancing conversion, and finally, after reaching a conversion of about 30-40 ~.~ some insoluble products are formed. Similarly the molecular weight of the polymers increases in function of the growing dose rates, thus they differ from our previous observations with cethyl methacrylate and \'-inyl stearate, where the molecular weight of polymers showed no relation

0.6 [Til

0.5 QIt

0.3

..

0.2 0.1

8 12 16 20 24 28 32 36 40 H 48 52 56 houz

Fig. 6. Yariation of molecular weight of polyvinyl laurate obtained in solid state at 0° C in function of conversion and dose rate: 1. - ~2.050 r/h., 2. - 10.250 r/h., 3. - 6.150 r/h.

""

Qc: 30 f - - - , , c . .!:e

~

:§

u 20 f----f"--I'---r----."-- -.-.-. ___ .

10f-h^L/ - " - - . - - - - . • . - -

o 20 ''0 60 hours

Fig. 7. Kinetics of solid state polymerization of vinyl laurate at 0²C by dose rate of 22.050 r/h. in the presence of 0.1 ⁰~ of diphenylpicrylhydrazile and benzoquinone

to the conversion grade, dose rate or temperature. This difference leads to the conclusion that the molecules of vinyl laurate are more mobile in solid state and at OC C, than those of other monomers having similar character.

Fig. 7 shows the kinetics of solid phase polymerization of vinyl laurate in thc presence of 0,1

%

DPPH and benzoquinone resp., whereas Fig. 8 shows the effect of varying concentration of these inhibitors with the conversion achieved during the same radiation period. The inhibitors have a "well notice-

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142 GY. HARDY el al.

able retarding effect on the solid phase polymerization of vinyl laurate.

The explanation of this effect can be given in this case as by other monomers ha'ving long chain aliphatic substituents with associated position of the molecules, where their polar, resp. apolar parts adjoined. Inhibitors which do not

35

~ 30 c:: c

~

_c::

DPPH

'---

^.

tl 25~----~----~~---~

2f) f---'---

18 1--_ _ -"-_ _ _ '---_ _ -"-_ _ ---1

. 0,03 0,05 0,07 0,09 0,11.

concentration of inhibitors %

Fig. 8. Dependence of conversion of solid state polymerization of vinyllaurate on the concentra- tion of inhibitors at 0° C, at a total dose of 918.600 r., irradiated with dose rate of 22.050 rjh.

15

5

r .

_I • 1 ^"

I ;

{'

²

k _I

^I^• ^v ^i.ⁱ^r ⁰ ³⁴

^I

ÎÎ Î

1-2-3 = -78 'C .O'C 10

~ =-196 'C 0 CC

i ,

20 60 65 hours

o

Fig. 9. Kinetics of post-polymerization of vinyl laurate irradiated at _78⁰C with dose rate of 22.050 r/h. and heated up to 0° C. 1: total dose 695.900 r., 2. 331.825 r., 3. 169.344 r., 4.

irradiated at -196° C and then heated up to 0° C, in case of total dose 169.344. r.

dissolve well in pure hydrocarbons, are placed next to the polar end of one molecule by crystallization of the system, so that they give a higher inhibiting effect (they are concentrated around the v-1nyl groups) compared to those in case of solid phase polymerization of monomers '''-1th shorter aliphatic substituents.

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IlADIATIO.Y-I.YDUCED SOLID STATE POLYl.IEIlIZATIOiV 143

The kinetics of post-polymerization of vinyl laurate is shown in Fig. 9.

In three cases radiations of different durations were carried out at _78⁰C, followed by warming up to 0⁰ C. In another case radiation was effected at -196° C followed by warming up to 0° C. The kinetical curves prove that post- polymerization is very rapid: the greater the total dose of preliminary irradiation, the higheris the degree of conversion that the polymerization can reach.

In the case of the same total dose, lower temperature ofirradiation results a higher rate and a higher conversion. From these measurements we can con- clude that the quenched active centres formed by radiation become rather mobile already at 0° C and that they disappear quickly by spontaneous re- combination or polymerization followed by chain termination reactions. In the same circumstances irradiation at lower temperature results in a higher number of active centres thus giving an accelerated post-polymerization and greater conversion as result.

Summary

Gamma-radiation initiated solid state polymerization of vinyl laurate is characterized by a maximum rate near the melting point. Inhibitors considerably retard the polymerization.

Kinetics of postpolymerization, as well as the variations of molecular weight of polymers formed in solid phase, lead to the conclusion that in the solid state vinyl laurate molecules are more mobile than cethyl methacrylate and .-inyl stearate of similar structure at temperatures near to the melting point.

References

1. HARDY, Gy., ::\"YITRAI, K., Koy_.\.cs, G., FEDOROVA, N.: Magyar Kemiai Folyoirat 69, 437 (1963).

2. BARKALOV, J. 11., GOLDAl'\SKII, V. 1., El'\IKOLOPYAN, 1'1. E., TEREKHOVA, S. F., TROFBIOVA, G. :31.: Journal Polym. Sci. C. 4, 909 (1963).

3. A.:\IAGI, Y-., CHAPIRO, A .. : J. chitn. phys. 59., 537 (1962).

4. RESTAIl'\O, A. J., }IESROBIAl'\, R. B., :3IoRAwETz, H., BALLAl'\TINE, D. S., DIEl'\ES, G. J., METZ, D. J.: Journal Am. Chem. Soc. 78, 2936 (1956).

5. BURLAl'\T, W., ADICOFF, A.: Journal Polym. Sei. 27, 269 (1958).

6. Organic Syntheses. Vo!. 30. John Wiley and Sons Inc.1'Iew York, 1950, p. 106.

Dr. Gyula HARDY

1

Karoly NYITRAI

J

6zscf VARGA

J'

l\l<irton PAT KO

Budapest XI., Sztoczek u. 2-4. Hungary.

INVESTIGATIONS IN THE FIELD OF THE