New High-Tg, Heat-Resistant, Cross-Linked Polymers. 2. Synthesis and Characterization of Polymers from Di-p-ethynyl-Substituted Benzyl Phenyl Ether Monomers

Abstract

Six different neat di-p-ethynylbenzyl phenyl ether (EBEs) monomers were thermally polymerized. The progress and nature of the polymerization reaction were studied by FTIR, Raman, and DSC. The monomers had melting points between 94 and 197 °C. FTIR, Raman, and DSC showed that the monomers polymerized to high conversion after heating to 290 °C at 15 °C/min (no remaining acetylenic groups). The monomer DSC thermograms showed two intense exotherms. The first was correlated with the thermal polymerization of the acetylenic groups to form a polyene structure with unusually high enthalpies of polymerization, between 106 and 178 kJ/mol. The second DSC exotherm enthalpies varied between 31 and 64 kJ/mol and are due to further coupling of the polyene chains. The cross-linked resins exhibited an initial decomposition temperature in nitrogen between 389 and 410 °C; they had a very high anaerobic char yield (61-71% at 800 °C). The benzyl phenyl ether link was found to be thermally and thermooxidatively stable in the cured polymers. This was attributed to their high cross-link density. Well-consolidated, voidfree films were obtained when the EBEs melt-polymerized. 4-Ethynyl-1-[ (4-ethynylphenyl)methoxy] benzene(1) and 2,5-bis[(4-ethynylphenyl)methoxy]toluene (4) had wide "processing windows" of 55 and 40 °C, respectively, at a heating rate of 15 °C/min (DSC). The polymers of 4 and l,4-bis[(4-ethynylphenyl)methoxy]-2-chlorobenzene (5) had Tg's of 364 and 330 °C, and their linear thermal expansions were 1.2 and 1% from room temperature to their Tg's. The cross-linked resins were amorphous. Their densities varied from 1.18 to 1.32 g/cm3.