Effects of copolymer composition and free volume change on the miscibilityof poly(styrene-co-vinylphenol) with poly(epsilon-caprolactone)

A series of poly(styrene-co-vinylphenol) (PSOH) copolymers were prepared an d characterized. The miscibility and hydrogen bonding between the partially hydroxylated polystyrene with poly(is an element of -caprolactone) (PCL) b lend were investigated by differential scanning calorimetry and Fourier tra nsform infrared spectroscopy. The copolymers containing higher than 13 mol % vinylphenol were found to be fully miscible with PCL according to differe ntial scanning calorimetry studies. Quantitative analyses on the fraction o f hydrogen-bonded carbonyl groups in the solid state were made by FTIR spec troscopy, and good correlations between thermal behaviors and infrared resu lts were observed. The critical vinylphenol content of 0.1 mol % in PSOH co polymer for the blend to be miscible was predicted from the Painter-Coleman association model and binary interaction model. The discrepancy between th e experimental result and theoretical prediction is probably caused by sign ificant free volume increase in this blend system, which is analyzed by the Kovacs' free volume theory. The free volume of the PSOH/PCL is increased w hich give a positive contribution in the Gibbs free energy. As a result, th e polystyrene needs to incorporate more poly(vinylphenol) in PSOH copolymer in order to overcome the free energy increased caused by the free volume i ncrease predicted by the Painter-Coleman association model and the binary i nteraction model.