Miscibility, crystallization, and morphology of poly(epsilon-caprolactone), a semicrystalline polymer with poly(styrene-co-4-hydroxystyrene) amorphous copolymers

The miscibility of poly({dollar}varepsilon{dollar}-caprolactone) (PCL) with poly(styrene-co-4-hydroxystyrene) (PHS) copolymers was investigated as a function of comonomer composition. PCL was found to be completely miscible with PHS copolymers containing 5 or more mole percent of 4-hydroxystyrene (HS) comonomer units for the entire range of blend compositions. Segmental interaction densities Bij's were determined by the analysis of the equilibrium melting point depression and by the application of the binary interaction model. By correlating the segmental interaction energy densities with binary interaction model thermodynamic miscibility is achieved for {dollar}rm ysb1>0.05,{dollar} which is in agreement with the experimental phase behavior. Application of association model for specific interactions to blends also correctly predicts the miscibility boundary and theoretical phase behavior for all the PHS copolymers/PCL blends, which also seems to be in agreement with the experimental phase behavior. Kinetic data analysis according to Hoffman-Lauritzen theory indicates that crystallization of PCL in some blends show a regime II-III transition, while crystallization of PCL takes place in regime II. Secondary nucleation analysis indicates that with increasing PHS copolymer in the blend the crystal lateral surface free energy {dollar}sigma{dollar} of the PCL crystal decreases. Thus in the miscible blends with {dollar}chisb{lcub}rm blend{rcub} < 0,{dollar} the competition between lower mobility due to interaction between polymer chains and lower surface free energy {dollar}sigma{dollar} controls the crystallization growth (spherulitic growth rates). In the case of miscible PHS/PCL blends, the formation of ring-banded spherulites of PCL displaying high regularity were observed in regimes I, II and III. A theoretical expression for periodicity of banding (L) was obtained by a combination of expressions from theory of elasticity and thermodynamics of polymer blends.