HIGH TEMPERATURE STABLE ELASTOMERS: THE SYNTHESIS OF NOVEL N-METHYLATED COPOLYAMIDES AND THE EFFECT OF SILICA SURFACE MODIFICATION ON THE THERMAL STABILITY OF POLY(DIMETHYL SILOXANE)

Part I. The Synthesis of Novel N-Methylated Copolyamides: N-methylated polyamides and copolyamides derived from sebacic acid, N,N\u27-dimethylethylenediamine, and ethylenediamine were synthesized. Both interfacial and melt polycondensation were examined, with chloroform, hexane, and benzene being employed as the organic solvent interfacially.^ Random and block copolyamides were synthesized from interfacial polycondensation. The diamine sequencing in the copolyamide backbone was controlled by the relative abilities of the diamines to partition from the water into the organic phase. Diamines with substantially unequal partition coefficients reacted at different rates, with the diamine possessing the larger coefficient reacting initially. This resulted in block copolyamides. Diamines with similar partition coefficients reacted equally with the diacid chloride yielding random copolyamides.^ Melt polycondensation resulted in block copolyamides owing to the greater condensation rate of primary diamines with dicarboxylic acids. The melting points and viscosities of the block copolyamides prepared by melt polycondensation were very similar to those prepared by interfacial polycondensation.^ Part II. The Effect of Silica Surface Modification on the Thermal Stability of Poly(dimethyl siloxane): Fumed silica samples with varying concentrations of surface silanol groups were prepared by annealing at 200(DEGREES)C, 400(DEGREES)C, and 480(DEGREES)C. The silica samples were then incorporated into an -OSi(CH(,3))(,3) terminated poly(dimethyl siloxane) and a 0.6 per cent vinyl containing poly(dimethyl siloxane). The effect of the silica on the thermal stability of the polymers in inert atmospheres was studied. The effect of the silica on the thermal stability of the -OSi(CH(,3))(,3) terminated poly(dimethyl siloxane) in air was also examined.^ At temperatures approaching the depolymerization temperature of poly(dimethyl siloxane), fumed silica reduced the rate of weight loss in inert atmospheres. The smaller the concentration of hydrogen-bonded silanol groups and the greater the concentration of isolated silanol groups on the silica surface, the slower the rate of weight loss from poly(dimethyl siloxane). At lower temperatures in inert atmospheres, the depolymerization of poly(dimethyl siloxane) was catalyzed by silica. The rate of weight loss, however, was independent of the concentration of silica silanol groups.^ The rate of weight loss from silica filled samples in air was less than that of the unfilled samples. The rate of weight loss was independent of the silica surface silanol concentration.