Structure correlated properties of metallocene catalysed polyethylenes by modulated temperature differential scanning calorimetry

Conventional and modulated temperature differential scanning calorimetry (MT-DSC) have been used to evaluate quantitatively the thermal properties of a set of advanced polyethylenes synthesised from metallocene catalysts. This study is sought to establish correlations between polymer chain molecular characteristics and crystallisation behaviour in a set of tailor-made polyethylenes. Melting is described by at least two different structure forming processes that behave independently of each other with Avrami analysis showing singular exponents and low rate constants from melting kinetic data. Avrami exponents from crystallisation kinetic data are broadly in line with typical values for polyethylene. Non-isothermal crystallisation kinetic studies revealed the presence of dual crystallisation peaks on linear cooling from the melt. The first crystallisation peak was found to shift moderately with cooling rate to lower temperatures of crystallisation whereas the second crystallisation peak remained invariant. Application of MT-DSC following discrete step-wise crystallisation has been successful at identifying initial crystallinities and the presence of reorganisational crystallisation during polymer melting. Melting is seen primarily in the reversing signal of the modulated heat flow, and reorganisational crystallisation during melting in the non-reversing heat flow signal. (C) 1999 Elsevier Science B.V. All rights reserved.