Phenylethynyl-endcapped oligomides with low melt viscosities and high T g s: effects of the molecular weights

Abstract

Phenylethynyl-endcapped imideoligomers (oligomides) with low melt viscosities and high glass transition temperatures (T _g) were prepared by the high temperature polycondensation of 2,3,3′,4′-biphenyltetracarboxcylic anhydride (a-BPDA), 4,4′-methylenebis(2,6-dimethylaniline) (MBDA) and 4-phenylethynyl-phthalic anhydride (4-PEPA). Experimental results indicated that the oligomides were mixtures of biphenylethynyl-endcapped imide oligomers with different degrees of polymerization (DP = 0, 1, 2, 3, 4), corresponding to the molecular weights (M _n) of 737 to 2787 determined by MALDI-TOF. The melt viscosities of the oligomide were reduced by lowering the calculated molecular weight (Calc’d M _n). The thermally cured polyimide neat resins showed glass transition temperatures (T _g) of > 400 °C and 5% weight loss temperature (T ₅) of > 499 °C. It was also found that the mechanical properties of the thermally cured polyimide neat resins were dependent on the Calc’d M _n values of the oligomide, and improved gradually with increasing Calc’d Mn.