Kinetics of Spherulitic Growth of Poly(pivalolactone) in Blends with Poly(vinylidene fluoride-co-tetrafluoroethylene): Effect of Specific Interactions on the Thermodynamic and Kinetic Secondary Nucleation Parameters

Abstract

The kinetics of spherulitic growth of α-phase poly(pivalolactone) (PPVL) in blends with poly(vinylidene fluoride-co-tetrafluoroethylene) (P(VF2-TFE)) has been investigated as a function of blend composition and crystallization temperature by hot-stage polarized optical microscopy and analyzed by the Lauritzen−Hoffman (LH) secondary nucleation theory. The composition dependence of the equilibrium melting temperature of α-phase PPVL was determined directly from the analysis of spherulitic growth rate data evaluated at various crystallization temperatures between 169.4 and 217.4 °C. The estimated equilibrium melting temperatures were analyzed by the Nishi−Wang method to yield a negative Flory−Huggins interaction parameter (χF-H = −0.06 ± 0.03). Analysis of the composition dependence of the nucleation constants, Kg, in crystal growth regimes II and III suggests that the PPVL crystal/melt lateral interfacial free energy, σ, decreases markedly with increasing P(VF2-TFE) concentration in the blends. The present results were examined in light of conclusions drawn from previous studies of PPVL/PVF2 blends and allowed us to state that the composition dependence of Kg and σ for α-phase PPVL is unequivocally a function of the strength of the specific interactions between the blend components. These observations are rationalized through arguments based on the minimization of the free energy of demixing and an increase in the conformational entropy of chains adsorbed at the melt/crystal interphase (i.e. an increase in crystal/melt lateral interfacial thickness) with an increase in the strength of the specific interactions.