The equilibrium melting temperature and isothermal crystallisation kinetics of cyclic poly(butylene terephthalate) and styrene maleimide (c-PBT/SMI) blends

The equilibrium melting point ($$ T-{\text{m}}^{0} $$ T m 0) and isothermal crystallisation kinetics of cyclic poly(butylene terephthalate) (c-PBT) and styrene maleimide (SMI) blends prepared by solid dispersion and in situ polymerisation of cyclic butylene terephthalate oligomers (CBT) within SMI were investigated. This c-PBT/SMI blend is a miscible semicrystalline-amorphous blend system. The $$ T-{\text{m}}^{0} $$ T m 0 of c-PBT/SMI blends was determined using the Hoffman and Weeks method, while Avrami crystallisation kinetic model have been applied to study their isothermal crystallisation kinetics. It was found that $$ T-{\text{m}}^{0} $$ T m 0 decreased with increasing SMI content in the blend compositions. All the crystallisation exotherms were obtained from differential scanning calorimetry under isothermal experimental conditions. The average value of Avrami exponent, n, is in the range of 2.4-2.8 for the primary crystallisation process for c-PBT and its blends, which suggest that heterogeneous nucleation of spherulites occurred and growth of spherulites was between two-dimensional and three-dimensional.