Endgroup substituent effects on the rate/extent of network formation and adhesion for phenylethynyl-terminated poly(arylene ether sulfone) oligomers

A series of poly(arylene ether sulfone) thermosets were synthesized from oligomers (M-n = 4-8000 g/mol) endcapped with various phenylethynyl moieties which differ in their electron-withdrawing abilities of their attached substituent. C-13 NMR showed that the nature of the substituent (e.g. ether, ketone, sulfone, imide) influences the electron density around the ethynyl bond, as well as the terminal phenyl-ring carbon atoms. Kinetic studies on the rate of cure at 320 and 350 degrees C were conducted using FTIR, and in both cases the rate laws approximated second-order reactions at low to moderate conversions of the ethynyl bond. The rate of the curing reaction was observed to increase with the electron-withdrawing ability of the substituent on the phenylethynyl endcapper Grass transition temperatures (T-g) and the elastic modulus above the T-g of the networks increased with increasing electron-withdrawing ability of the substituent. Cured materials were solvent resistant and all formed tough creasable films, even when the oligomer M-n was as low as 4000 g/mol. The adhesive strengths of the cured materials were studied by Ti-Ti lap shear tests, and excellent values comparable to those of control polyimides, 5329 psi (37 MPa), were recorded. Interestingly, under constant curing conditions, the values obtained increased with the electron-withdrawing ability of the reactive endgroup. (C) 2000 Elsevier Science Ltd. All rights reserved.