Data di Pubblicazione:
2007
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.
(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.
Tipologia CRIS:
1.1 Articolo in rivista
Elenco autori:
Penco, Maurizio; Sartore, Luciana; DELLA SCIUCCA, S.
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