Two DSC Glass Transitions in Miscible Blends of Polyisoprene/Poly(4-<i>tert</i>-butylstyrene)

Abstract

Conventional and temperature-modulated differential scanning calorimetry (DSC) experiments have been carried out on miscible blends of polyisoprene (PI) and poly(4-tert-butylstyrene) (P4tBS) over a broad composition range. This system is characterized by an extraordinarily large Tg difference (∼215 K) between the two homopolymers. Two distinct calorimetric glass transitions were observed in blends of intermediate compositions (25%−50% PI) by both conventional and temperature-modulated DSC. Good agreement was found between the component Tg values measured by the two methods. Fitting of the component Tg values to the Lodge−McLeish model gives a ϕself of around 0.63 for PI in this blend and 0.03 for P4tBS. The extracted ϕself for PI is comparable to reported values for PEO in blends with PMMA and is significantly larger than values reported for PI in other blends with smaller homopolymer Tg differences. This observation is consistent with the presence of a nonequilibrium or confinement effect in PI/P4tBS blends, which results in enhanced dynamics of the fast component below the Tg of the slow component