Effect of residual water and free volume on the glass‐transition temperature and heat capacity in polystyrene/poly(vinyl acetate‐co‐butyl acrylate) structured latex films

Abstract

The dynamic heat capacity and glass-transition temperature of polystyrene (PS)/poly(vinyl acetate-co-butyl acrylate) (VAc-BA) (50:50 w/w) structured latex films as a function of annealing time at 70, 77, and 85°C were examined with modulatedtemperature differential scanning calorimetry. The PS and poly(vinyl acetate-co-nbutyl acrylate) components were considered to be the cores and shells, respectively, in the structured latex. The dynamic heat capacity decreased with time. The glasstransition temperatures of the PS and VAc-BA phases shifted to higher values after annealing. The results of thermogravimetry showed that there existed about 1.8% residual water in the films. The mean free volume and relative concentration of holes at room temperature (before and after annealing) and 85°C, as a function of time, were obtained with positron annihilation lifetime spectroscopy (PALS). The PALS results indicated no significant change in free volume during annealing. It is believed that the loss, by diffusion, of residual water mainly caused a decrease in heat capacity and an increase in the glass-transition temperatures. As little as 1.8% residual water in the structured latex films had a significant influence on the thermal properties.