document: The viscoelastic behavior of elastomers containing small amounts of unattached chains has been investigated to characterize the dynamics of the polymer chains trapped in fixed networks [66–68]. Polymer chains trapped in fixed networks constitute a simpler system for the study of the polymer chain dynamics than the corresponding uncrosslinked polymer melts. This is because the complicated effect of the motion of the surrounding chains on the dynamics of the probe chain – called “constraint release” [69] – is absent in the fixed network systems. Most of the earlier studies employed randomly crosslinked elastomers as host networks. In this case, precise control of the mesh size of the host networks is not possible, and the mesh size has a broad distribution. The end-linking systems give the host networks a more uniform mesh size, and they can control the mesh size by the size of the precursor chains. We investigated the dynamic viscoelasticity of end-linked PDMS elastomers containing unattached linear PDMS as functions of the size of the unattached chains (Mg) and the network mesh (Mx) (Fig. 9a) [70]. We employed two types of host networks with Mx>Me and Mx<Me where Me (≈10,000 for PDMS) is the molecular mass between adjacent entanglements in the molten state. The Mx>Me and Mx<Me networks (designated as NL and NS, respectively) were designed by end-linking the long (Mn=84,000) and short precursor chains (Mn=4,550), respectively. The mesh of the NL networks is dominated by trapped entanglements, while that of the NS network is governed by chemical cross-links.
doc_bio_tags: O B I O B O O O O B I O O O O B I I I I I I O O O O O B I O O O O O O O O O O O O O B I O O O O O B I O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O B I O O O O O O O B I I I I O O O O O O O O O B O O O O O O O O O O O O O O O B O O O O O O B O O O O O O B I O O O O O O O B B O O O B O O O O O O O B I B O O O B B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O B I O O O B O O B O O O O O O O O O O B O O O O O O
extractive_keyphrases: characterize the dynamics of the polymer chains control of the mesh size crosslinked elastomers elastomers mesh mg mx nl ns pdms polymer chain polymer chains polymer melts precursor chains probe chain unattached chains viscoelastic behavior
abstractive_keyphrases: chemical cross-links. constraint release mx<me mx>me network mesh pdms elastomers