Glass transitions of styrene/α‐methylstyrene statistical copolymers and of their blends with PPO® resin

The glass transition temperatures ( T g ) and specific heat increments (Δ C p ) at T g of S/AMS statistical copolymers having weight fractions AMS of 0.00, 0.09, 0.17, 0.26, 0.36, and 0.44 are (by DSC) 380.0 (0.280), 384.2 (0.275), 388.8 (0.284), 391.5 (0.275), 398.3 (0.272), and 405.9 (0.27) °K (J·g − ·deg − ), respectively. The T g (Δ C p ) for the PPO resin are 492.2 (0.221). The glass transitions of P(S/AMS) (1) + PPO resin (2) blends having w2 = 0.25, 0.50, and 0.75 were also measured. Examination of the copolymer and blend T g vs. composition data indicates that a relation recently proposed by Couchman gives a somewhat better approximation than the simple Fox relation. However, the nonadjustable k = Δ C p 2/Δ C p 1 constant in the Couchman relation must be replaced by a smaller empirical k to give a true match of calculated to observed T g .