Crystallization of PDMS The effect of physical and chemical crosslinks

Calorimetric studies of the crystallization behavior of physically and chemically crosslinked semicrystalline polymer, polydimethylsiloxane ( PDMS) are presented. Physical crosslinks are introduced either via entanglements in high-molecular-weight PDMS, or by anchoring chain ends to rigid polyethylene oxide (PEO) endblocks in a PEO-b-PDMS-b-PEO triblock copolymer. Chemical end-linking of di-vinyl PDMS chains results in the formation of a crosslinked network. Comparison of the thermograms obtained for each of these systems at constant cooling/heating rates with their noncrosslinked analogues indicates that, contrary to conventional wisdom, the different types of crosslinks result in an increased crystallization tendency. We suggest that this effect is a manifestation of the enhancement of local ordering together with reduced dynamics as compared to the non-crosslinked melt.