Bisphenol-A polycarbonate (PC)/poly(methyl methacrylate) (PMMA) blends (PC/PMMA) were prepared by melt mixing with and without a trans-esterification catalyst (tetrabutylammoniun tetraphenylborate), which is able to promote interexchange reactions between PC and PMMA. Evidences of the ester-ester exchange reaction taking place were pointed out via Fourier Transform Infra-Red and size exclusion chromatography analyses. A series of enthalpy relaxation measurements were carried out for the pure polymers and for blends thereof. The data were analyzed on the basis of the Tool-Narayanaswamy-Moynihan/Kohlraush- Williams-Watts model. This model characterizes the structural relaxation in the glass transition region by means of four parameters: the apparent activation energy (Δh*), the nonlinearity (x), the nonexponentiality (β), and the pre-exponential factor (τ0). The apparent activation energy can be determined from the cooling rate dependence of the fictive temperature (Tf) measured using DSC. Δh* values of homogeneous blend and of the starting polymers were determined in this way, while an estimation of x, β and τ0 was proposed. Comparisons were made between a single glass transition temperature PC/PMMA blend and homopolymers data. The experimental values of Δh* suggest that the degree of cooperativity decreases on going from the starting polymers to the blend.
Enthalpy relaxation in bisphenol-A polycarbonate/poly (methyl methacrylate)blends
PENCO, Maurizio;SARTORE, Luciana;
2007-01-01
Abstract
Bisphenol-A polycarbonate (PC)/poly(methyl methacrylate) (PMMA) blends (PC/PMMA) were prepared by melt mixing with and without a trans-esterification catalyst (tetrabutylammoniun tetraphenylborate), which is able to promote interexchange reactions between PC and PMMA. Evidences of the ester-ester exchange reaction taking place were pointed out via Fourier Transform Infra-Red and size exclusion chromatography analyses. A series of enthalpy relaxation measurements were carried out for the pure polymers and for blends thereof. The data were analyzed on the basis of the Tool-Narayanaswamy-Moynihan/Kohlraush- Williams-Watts model. This model characterizes the structural relaxation in the glass transition region by means of four parameters: the apparent activation energy (Δh*), the nonlinearity (x), the nonexponentiality (β), and the pre-exponential factor (τ0). The apparent activation energy can be determined from the cooling rate dependence of the fictive temperature (Tf) measured using DSC. Δh* values of homogeneous blend and of the starting polymers were determined in this way, while an estimation of x, β and τ0 was proposed. Comparisons were made between a single glass transition temperature PC/PMMA blend and homopolymers data. The experimental values of Δh* suggest that the degree of cooperativity decreases on going from the starting polymers to the blend.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
