Atactic poly heating

When the atactic poly(a,a-dimethylbenzyl methacrylate) was heated at 170°C for 30 min under vacuum, it decomposed into volatile and nonvolatile components. The former was found to be a-methylstyrene and the latter was to be very similar to polyfmethacrylic acid) as determined by H NMR spectroscopy. Figure 3 shows the infrared spectra of atactic and isotactic poly(a,a-dimethylbenzyl methacrylate)s heated at 174°C under vacuum for various times. In the spectra of the atactic polymer, the absorption of the ester carbonyl at 1729 cm-1 decreased and that of the acid carbonyl at 1700 cm-1 increased as the heating time increased. After heating for a period of 30 min... 

Figure 3. Infrared spectra of isotactic and atactic poly(a,a-dimethylbenzyl methacrylate)s heated at 174° C under vacuum for various times.

Figure 4. Infrared spectra of (A) isobutyric anhydride, (B) glutaric anyhdride, and (C) isotactic and (D) atactic poly(a,a-dimethylbenzyl methacrylate)s heated at 174° C under vacuum for 2 and 3 hr, respectively.

KA2 Kagemoto, A., Murakami, S., and Fujishiro, R., The heats of dilution in atactic poly(methyl methacrylate) solutions. Bull. Chem. Soc. Japan, 40, 11, 1967. 

LEW Lewis, G. and Johnson, A.F., Heat of dilution of polymer solutions. Part II. Atactic poly(methyl methacrylate) solutions, J. Chem. Soc. (A), 3524, 1971. 

Poly(ethylene oxide) decomposes upon heating at lower temperatures than does polyethylene. Among the volatile products are found formaldehyde, ethanol, ethylene oxide, carbon dioxide, and water. Polyipropylene oxide) is also less heat stable than polypropylene. Isotactic poly(propylene oxide) is somewhat more stable than the atactic one. 

If the thermoformed sheet is still amorphous, its chemical resistance will be similar to that of atactic polystyrene sheet. Therefore, after thermoforming one has to apply an additional heating step to obtain crystallinity (and thus chemical resistance) or use heated molds (180 °C). The food packaging industry utilizes similar technology with crystalline poly(ethylene terephthalate) (CPET) to make oven-capable food trays, which can also be prepared from SPS. 

Figure 2. Heat capacity vs. temperature curves for amorphous, atactic, and isotactic poly(styrenes).

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