JOURNAL OF POLYMER SCIENCE: PART A VOL. 1, PP. 321-329 (1963)

Effect of Crystallization on the Thermal Stability of Polyvinylphthalic Acid and Its Methyl Ester

EUGENE C. WINSLOW and JEAN A. MARRIOTT,* Department of Chemistry, University of Rhode Island, Kingston, Rhode Island

-INTRODUCTION In an earlier paper in this Journal' the preparation of polyvinylphthalic

acid and the thermal stability of its salts was reported. The effect of crys- tallization on the thermal stability of the polyacid and its ester is a logical supplementary question.

DISCUSSION Because many of the catalysts necessary for the preparation of crys-

talline polymers react with acid functional groups, the stereospecific acid cannot be synthesized directly. It was decided, therefore, to produce first a crystalline ester of poly(4-vinylphthalic acid) and then hydrolyze the ester to the free acid.

The synthesis of dimethyl 4-vinylphthalate was effected by the direct esterification of 4-vinylphthalic acid with diazomethane. This acid was polymerized stereospecifically with boron trifluoride etherate as a catalyst. Crystallization of poly(dimethy1 4-vinylphthalate) was realized by treat- ment with boiling n-octane. The hydrolysis of this ester gave crystalline poly(4-vinylphthalic acid). The presence of crystallinity was verified by x-ray diffraction and the polarizing microscope.

Thermogravimetry and differential thermal analysis was employed in the investigation of the thermal stability of the polymers. Analyses were carried out in air as well as in a nitrogen atmosphere, so that oxidative effects could be evaluated.

When boron trifluoride etherate was added to a solution of dimethyl 4-vinylphthalate1 polymerization proceeded slowly. The polymer was isolated by destroying the catalyst with water and precipitating the mix- ture in petroleum ether. The material separated as an elastomer. Drying in air gave a brittle solid.

Polymerizations were carried out in the temperature range from - 10 to -25OC. with toluene as solvent. ' The monomer: solvent ratio could be varied from 1 : 3 to 1 : 5. When this solvent was used, all polymers formed were found to be easily crystallized. In this temperature range, therefore,

* Present address: Electric Boat Compitny, New London, Connecticut. 331

322 E. C. WINSLOW AND J. A. MARHIOTT

temperature had no apparent effect on the crystallizability of the product. When dioxane was used as solvent, however, the polymers formed were diffcult to crystallize. Perhaps the increased basicity of this solvent allowed s&cient separation of the propagating ion pair so that steric con- trol is diminished. The conversion to the polymer over a period of three days was only 10%. The unreacted monomer, however, could be re- covered and the yield therefore, was nearly 100%.

Williams et a1.2 found that polystyrene could be crystallized by refluxing in various organic solvents for periods of 16-18 hr. The methods of Wil- liams were adopted and the polymers of dimethyl 4-vinylphthalate were crystallized by refluxing in n-octane for periods ranging from 16 to 32 hr.

100

5 0

0 2 4 6 8 10 12 14 16

MICRONS

100

50

2 4 6 a 10 12 14 16

MICRONS

Fig. 1. Infrared spectra of: ( a ) dimethyl 4vinylphthalate; (a) 4vinylphthalic acid.

Dimethyl 4vinylphthalate is a colorless, viscous liquid which rapidly becomes yellow in contact with air. It is very easily polymerized and solidifies on standing if left in an air atmosphere. A small amount of impurity such as water, however, will slow down the polymerization of the ester and, therefore, the liquid can be kept for longer periods of time in solution.

Polymeric dimethyl 4-vinylphthalic acid is a hard, brittle polymer which is insoluble in nearly all organic solvents with the exception of chloroform and methyl cellosolve. It is unusually clear and exhibits a remarkable adhesion to glass.

The infrared spectra of dimethyl 4-vinylphthalate and 4-vinylphthalic acid are given in Figure 1.

EFFECT OF CRYSTALLIZATION 323

Viscosity measurements indicated a molecular weight range of crys- talline methyl polyvinylphthalate in the vicinity of 60,000 if constants which have been determined for poly(methy1 methacrylate) in chloroform were used.a The vitreous benzoyl peroxide-initiated polymer from the same monomer gave a molecular weight in the vicinity of 30,000. Viscosity data for boron trifluoride etherate-catalyzed poly(dimethyl4-vinylphthal- ate) with chloroform as a solvent are listed in Table I. The plot of these

TABLE I Viscosity Data for Boron Trifluoride Etherate-Catalyzed Poly( dimethyl

4Vinylphthalate) (Chloroform aa Solvent)

Concentration, Flow time, g./100 cc. sec. ?red VSP ? S P / C

0.494 31.4 1.171 0.171 0.346 0.247 29.0 1.081 0.081 0.328 0.097 27.6 1.030 0.030 0.311 0.049 27.2 1.015 0.015 0.304 0.000 26.8 - - -

viscosity data is given in Figure 2. The viscosity data for benzoyl per- oxide-catalyzed poly(dimethy1 4-vinylphthalate) with chloroform as a solvent are given in Table 11. The plot of these data is presented in Figure 3.

. 2 lim = 0.307 C 4 J

I I 1 I I

.1 . 2 3 .4 .5

Fig. 2. Plot of viscosity data.

Concentration g/lOOcc.

All thermogravimetric curves presented in this paper were determined at a heating rate of 2'C./min. in an air atmosphere. The thermogravi- metric curve (Fig. 4) for crystalline poly(dimethy1 4-vinylphthalate) shows less weight loss initially than that of the noncrystalline polymer (Fig. 5). A larger amount of char as indicated by the inflection at the end

324 E. C. WINSLOW AND J. A. MARRIOTT

. 3 -

. 2 -

.1.

TABLE I1 Viscosity Data for Benzoyl Peroxide-Catalyzed Poly( dimethyl 4Vinylphthalate)

(Chloroform aa Solvent)

" . . - 1 - - -

lim. i&$) = 0.18 c+o

I I 8 I I 3 6 9 1.2 1. 5

Concentration, Flow time, g./lOo cc. sec. Wed ' I J P rls*/c

100'

mg.

80

60

%! ...

40- 5

2c

1.340 33.6 1.252 0.252 0.185 0.536 29.4 1.097 0.097 0.181 0.214 27.8 1.039 0.039 0.182 0.084 27.2 1.015 0.015 0.176 0.000 26.8 - - -

-

-

-

I I 1 I 100 200 300 400 500 600 7(

EFFECT OF CRYSTALLIZATION 325

loo: 80

600 700 Temperature

Fig. 5. TGA thermogram for noncrystalline poly( dimethyl 4vinylphthalate).

of the curve is observed for the crystalline polymer. Apparently crys- tallization retards thermal breakdown to some extent. The major weight loss in both crystalline and noncrystalline material, however, occurs at about 300OC.

Figure 6 is the thermogravimetric curve for noncrystalline poly-(4- vinylphthalic acid). An inflection in the curve showing weight loss at about 200OC. can possibly be attributed to anhydride formation. After the major volatilization begins at 3OO0C., a second inflection occurs show- ing a retardation of the thermal breakdown at 400OC. No appreciable char remains at 500OC. The thermogravimetric curve for the crystalline

Temperature

Fig. 6. TGA thermogram for noncrystalline poly(4vinylphthalic acid).

326 E. C. WINSLOW AND J. A. MARRIOTT

100 r

80 - mg.

60 - P M .*

$ 40 -

20 -

100 2 00 300 400 5 00 600 70 Temperature

Fig. 7. TGA thermogram for crystalline poly(4vinylphthalic acid).

EXOTHERMIC

ENDOTHERMIC

100 200 300 400 5 0 0 600 700 Temperature

Fig. 8. DTA thermogram for noncrystalline poly(4vinylphthalic acid), nitrogen atmosphere.

EFFECT OF CRYSTALLIZATION 327

polymer (Fig. 7) shows no pronounced inflection at 200OC. corresponding to that of the noncrystalline polymer. The inflection in the curve during major thermal breakdown is less pronounced and occurs at a lower tem- perature than does that in the curve for the noncrystalline polymer. A marked difference in the two curves is the occurrence of an appreciable char residue, as evidence by the inflection at 450OC. in the crystalline polymer curve. The noncrystalline polymer does not show this char residue.

I I 1 1 I I I

100 200 300 400 500 600 700 Temperature

Fig. 9. DTA thermogram for noncrystalline poly(4vinylphthalic acid), steam atmosphere.

As evidence for the possibility of anhydride formation in the non- crystalline polymeric acid, differential thermal analysis curves were run for the noncrystalline polymeric acid in nitrogen atmosphere (Fig. 8) and in steam atmosphere (Fig. 9). An endothermic trough can be observed in both curves in the vicinity of 200OC. A steam atmosphere displaces the trough to a higher temperature, indicating the probability of water evolu- tion from the sample at that temperature. Anhydride formation is a reasonable explanation of this shift in the endothermic trough.

EXPERIMENTAL Preparation of Dimethyl 4-Vinylphthalate

A suspension of 10 g. of 4-vinylphthalic acid' in 200 ml. of anhydrous ether was cooled to OOC. in an ice bath. A calculated amount of stand-

328 E. C. WINSLOW AND J . A. MARRIOTT

ardized diazomethane was allowed to run in. The solution was dried over night with anhydrous magnesium sulfate and was filtered. Evap- oration of ether gave 10.8 g. (95% of theoretical) of the pale yellow liquid, b.p. 176OC./1-2 mm.

ANAL. Calc.: C, 65.15%; H, 5.45%. Found: C, 65.09%; H, 5.400/,.

Polymerization

Dimethyl 4-vinylphthalate (10 g.) and 30 ml. of toluene were placed in a gas pressure bottle and degassed by passing nitrogen through the solution. Boron trifluoride etherate (0.3 ml.) was added and the bottle was sealed. Precipitation occurred almost immediately upon addition of the catalyst. The mixture was stirred with a magnetic stirrer for two days. At the end of this time the catalyst was destroyed by the addition of 5 ml. of water. The organic layer was separated and poured into petroleum ether (b.p. 30-6OOC.) . A viscous liquid settled out. The petroleum ether was separated by decantation. To the viscous oil was added 25-50 ml. of dry toluene. The polymer separated as an elastomer and was removed. The remaining toluene was added to fresh petroleum ether and a second fraction of the polymer was precipitated. The conversion of monomer to polymer was low (approx. 10%). The unreacted monomer, however, could be recovered from the petroleum ether and the yield, therefore, was nearly 100%.

Polyvinylphthalic Acid (Crystalline)

A l-g. portion of crystalline poly(dimethy1 4-vinylphthalate) was dis- solved in concentrated sulfuric acid. The solution was poured on to chipped ice and poly(4-vinylphthalic acid) was separated. The solid was removed by suction filtration, washed with water, and dried in a vac- uum desiccator.

A portion of this research waa supported by a contract with the Quartermaster Corps of the United States Army.

References 1. Winslow, E. C., and A. L. Laferriere, J. Polymer Sci., 60,65 (1962). 2. Williams, J. L. R., J. Van Den Berghe, K. R. Dunham, and W. J. Dulmage, J . Am.

3. Walling, C., and K. B. Wolfstern, J. Am. Chem. SOC., 69,852 (1947). Chem. Soc., 79,1719 (1957).

Synopsis The synthesis of dimethyl 4-vinylphthalate waa accomplished by direct esterification of

Pvinylphthalic acid with diazomethane. This monomer waa polymerized stereospe- cifically by the use of boron trifluoride etherate. The polymer waa crystallized by refluxing in n-octane. The preparation of crystalline poly(4vinylphthalic acid) was realized by hydrolyzing crystalline poly(dimethy1 4vinylphthalate) with concentrated sulfuric acid. The thermal behavior of the prepared polymers waa studied by the tech- niques of differential thermal analysis and thermogravimetry. Crystallization ap- parently retards thermal breakdown somewhat but the temperature of major weight

EFFECT OF CRYSTALLIZATION 329

loss by volatilization is essentially the same for the crystalline and the noncrystalline polymer. Differential thermal analysis indicates that anhydride formation occurs in the noncrystalline polymeric acid at 200OC. This transition is less pronounced in the case of the crystalline polymer.

R6sum6 La synthhse du 4vinylphtalate de dimethyle a 6t6 r6alis6e par esterification directe

de l’acide 4-vinylphtalique par le diazom6thane. Le monomhre a 6t6 polym6rise ster6osp6cifiquement par l’emploi de trifluorure de bore 6th6r6. Le polymhre Btait cristallise dans l’octane-n. La preparation du polyacide 4 vinyl-phtalique cristallin a Bt6 r6alis6e en hydrolysant par l’acide sulfurique concentr6 le polydim6thyl-Pvinyl phtalate cristallis6. Le comportement thermique de ces polymhres a 6t6 6tudi6 en utilisant les techniques d’analyse thermique differentielle e t par thermogravimetrie. La cristallisation retarde quelque peu la degradation due B l’effet thermique mais la temp6rature B laquelle s’effectue la perte principale en poids par volatilisation est essen- tiellement le m6me pour un polymhre cristallin e t non-cristallin. L’analyse thermique differentielle montre que la formation d’anhydride apparait A 20OoC. pour le polyacide non-cristallin. Cette transition est moins prononc6e pour le caa du polymhre cristallin.

Zusammenfassung Dimethyl-4vinylphthalat wurde durch eine direkte Veresterung von 4-Vinylphthal-

saure mit Diazomethen dargestellt. Dieses Monomere wurde mit Bortrifluoridatherat stereospezihch polymerisiert. Das Polymere wurde durch Behandlung mit n-Oktan unter Ruckflup zur Kristallisation gebracht. Kristalline Poly-4vinylphthalsaure wurde durch Hydrolyse von kristallinem Poly-dimethyl-4vinylphthalat mit konzentrierter Schwefelsaure hergestellt. Das thermische Verhalten der hergeetellten Polymeren wurde mit Differentialthermoanalyse und Thermogravimetrie untersucht. Kristallisa- tion vereogert scheinbar die thermische Spaltung ein wenig, die Temperatur des Haupt- gewichtsverlustes durch Verfluchtigung ist jedoch fur kristalline und nichtkristalline Polymere gleich. Die Differentialthermoanalyse weist auf eine Anhydridbildung der nichtkristallinen polymeren Saure bei 200” hin. Diese Umwandlung tritt beim kristal- linen Polymeren weniger hervor.

Received August 15, 1961 Revised October 23, 1961