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

The kinetics of spherulitic growth of alpha-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 micros copy and analyzed by the Lauritzen-Hoffman (LH) secondary nucleation t heory. The composition dependence of the equilibrium melting temperatu re of alpha-phase PPVL was determined directly from the analysis of sp herulitic growth rate data evaluated at various crystallization temper atures between 169.4 and 217.4 degrees C. The estimated equilibrium me lting temperatures were analyzed by the Nishi-Wang method to yield a n egative Flory-Huggins interaction parameter (chi(F-H) = -0.06 +/- 0.03 ) Analysis of the composition dependence of the nucleation constants, K-g, in crystal growth regimes II and III suggests that the PPVL cryst al/melt lateral interfacial free energy, sigma, decreases markedly wit h increasing P(VF2-TFE) concentration in the blends. The present resul ts were examined in light of conclusions drawn from previous studies o f PPVL/PVF2 blends and allowed us to state that the composition depend ence of K-g and sigma for alpha-phase PPVL is unequivocally a function of the strength of the specific interactions between the blend compon ents. These observations are rationalized through arguments based on t he minimization of the free energy of demixing and an increase in the conformational entropy of chains adsorbed at the melt/crystal interpha se (i.e. an increase in crystal/melt lateral interfacial thickness) wi th an increase in the strength of the specific interactions.