Miscibility of Poly(<i>n</i>-butyl acrylate)/Poly(propylene glycol) Blends. 1. Phase Behavior and Dielectric Relaxation

Abstract

We report the cloud point, glass transition temperature Tg, and dielectric relaxation for blends composed of poly(n-butyl acrylate)s (PBA) and a linear poly(propylene glycol) (PPGD) and for blends of PBA and a star-shaped PPG having three arms (PPGT). The phase diagram is of the upper critical solution type (UCST), and the critical temperature varies from 340 to 220 K depending on the molecular weight of the PBA. The interaction parameter χ for PBA/PPGD is higher than that for PBA/PPGT. For blends of high molecular weight PBA and PPGD, a sharp glass transition and a subsequent broad glass transition were observed by differential scanning calorimetry, but for mixed blends a relatively sharp single Tg was observed. The temperature dependence of the dielectric loss factor ε‘ ‘ of phase-separated blends exhibited two loss maxima. The low-temperature peak can be assigned to the segmental mode relaxation (α-process) of PPG and the high-temperature peak to the normal mode of PPG and the segmental mode of PBA. Mixed blends exhibited a single loss maximum having an asymmetrical shape, indicating that there is local heterogeneity.