Dependence of the glass transition temperature of polyacrylonitrile on molecular weight

The glass transition temperature of polyacrylonitrile has been determined for polymer varying in molecular weight from 8 × 10 3 to 3 × 10 6 . Results could be represented by T g = (96.5 ± 1.0) − (2.8 ± 0.1) × 10 5 /M̄ n , giving for the glass temperature of a polymer of infinite chain length, 96.5 ± 1.0°C. Specimens showing coloration gave enhanced glass temperatures attributable to the stiffening effect of conjugated ring structures, and were excluded from consideration of the effect of molecular weight. Determination of T g were made on films prepared from solutions of polymer in dimethylacetamide, butyrolactone, and dimethyl sulfoxide in addition to dimethylformamide. Dependence on weight percentage of polymer, w 2 , for the range 90 < w 2 < 100 was given by T g = (3.19 ± 0.03) w 2 − (232 ± 4), no specific solvent effect being observed.