A series of comblike semiflexible polymers, in which the alkyl side chains were located nonsymmetrically on the ring, were synthesized by reacting hydroxypropylcellulose (HPC) with hexyl, octyl, dodecyl, and octadecyl isocyanates. Side-chain melting was observed in DSC experiments for polymers with 12 and 18 carbons in the pendant groups (C12HPC and C18HPC). Wide-angle X-ray (WAXS) studies indicated that the alkyl groups in C12HPC crystallized in a form similar to the βT crystal of hydrocarbons but multiple crystalline forms coexisted in C18HPC. However, reorganization of the alkyl side chains was observed as the polymers underwent thermal transitions. A better packing of the alkyl side chains could be induced by shearing the samples in the molten state followed immediately by slow cooling. Quenching and annealing studies suggested that side-chain crystallization and reorganization could influence the packing of the semiflexible backbone. The interplay between the main chain and the side chain in order development is described.

SynopsisThe progress of photo-and photooxidative degradation of nylon films were studied by FT-IR spectroscopy. The gases evolved from the photolysis of various nylons and their model amides were also analyzed. The formation of double bonds, changes of crystallinity, and the effect of amino and carboxyl end groups has been studied and discussed. The band shapes of the IR spectra pertaining to the carbonyl groups formed by thermal oxidation or photooxidation were found to be very similar, suggesting that the two oxidation mechanisms might be similar. The broadness of these bands indicates that the carbonyl groups may belong to more than one species. The photodegradation of nylons containing purposely inserted carbonyl groups formed -CH=CH, groups. Carbonyl groups formed during oxidation, and present either as keto groups or part of N-acylamide units make nylons susceptible to degradation reactions entailing mainly a Nonish type I1 mechanism.From ESR s t~d i e s ,~,~ kinetic studies,6 and chemical analyses,' the photolysis mechanisms were suggested to occur by degradation involving direct cleavage of the amide bond according to a Nonish Type I mechanism. Moore suggested that both Type I and Type I1 mechanisms occurred in the degradation of nylons.8Recently, Mazzocchi and Bowen studied the photolysis of N-alkylamides in solution by analyzing the products and concluded that the Type I process was predominant and the Type I1 process was quite ineffi~ient.~ They rationalized

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SynopsisThe effects of heat and oxygen on nylon films were studied by FT-IR spectroscopy. Nylons 6, 66 and nylons containing carbonyl groups in either the diamine or the diacid moiety were prepared. Nylon f i l m s cast on aluminum were studied in an environmental chamber under controlled conditions. The progress of chemical and physical changes was monitored by FT-IR spectroscopy. Thermal energy caused largely an increase in crystallinity due to annealing and also an increase of nonhydrogen-bonded amide groups, which seemed to entail mainly amide groups from the amorphous region. The intensities of IR absorption bands related to the folded structure reduced as soon as heating began. The IR spectra of the carbonyl groups formed by thermal oxidation showed band shapes that indicated that the formed carbonyl groups were of many different origins. The presence of keto groups purposely inserted into the backbone chains increased the rate of oxidation. Pyrolysis of the nylons was also studied to supplement data obtained a t lower temperatures.

SynopsisThe investigation of the thermal degradation of the char-forming phenol-formaldehyde resins is conducted to provide information for the systematic design of high temperature flame-resistant phenolics. Three different processes of curing are used (1) Formaldehyde or s-trioxane is reacted with m-substituted phenol-formaldehyde oligomers under acidic conditions to give the methylene bridged-novolac resins. (2) Phenol and rn-substituted phenols are reacted with CH20 under basic conditions and then heated to give the methylene bridged resol resins. (3) p-Terephthaloyl chloride and m-and p-substituted novolac oligomers are reacted to give cured resins with ester linkages. The evaluation of the effect of various substituents indicates that the oxygen index (01) increases from about 33 for unsubstituted phenolics to about 75 for meta-halogen substituted phenolics. The evaluation of the effect of various crosslinking agents shows that the 01 for CHzO-cured phenolics is 75 as compared to 50 for the trioxane cured phenolics and to 40 for the terephthaloyl chloride cured phenolics. A set of phenolic copolymers with different weight percentage content of halogen substituted phenols are synthesized as novolacs and resols. The results surprisingly indicate no increase of 01 for the cured novolac copolymers, whereas the increase is observed for the cured resol copolymers. The activation energy for the thermooxidative degradation of the cured novolacs is about 12-15 kJ/mol lower as compared to tpt of the cured resols.