Crystallization of polydimethylsiloxane: effect of silica filler and curing

Previous publications on the low temperature behavior of polydimethylsiloxane (PDMS) described semiquantitatively or in an incomplete way the different features appearing during the heating cycle of previously cooled PDMS. The main deficiency of these descriptions is in the quantitative measurement of the heat of fusion This value was reported per mole of chain atom, which has been misunderstood by other researchers as being per mole of structural units. The object of the present work is to give a systematic view of the low temperature behavior of PDMS with special attention to the melting behavior of the polymer. The effects of the previous cooling rate, molecular weight of the polymer, filler addition and crosslinking on the characteristics of d.s.c. thermograms of PDMS are reported and discussed. A simplified view of the different effects is presented, which allows the calculation of the heat of fusion of the different samples from the corresponding value of a completely crystalline polydimethylsiloxane. (C) 1998 Elsevier Science Ltd. All rights reserved.