Synthesis of Vinylic Macromolecular Rotaxane Cross-Linkers
Endowing Network Polymers with Toughness
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Abstract
Macromolecular rotaxane cross-linkers
having two radically polymerizable
vinyl groups (RCs) were first synthesized and used to prepare network
polymers. A crown ether/<i>sec-</i>ammonium-type pseudorotaxane
initiator having an OH terminal-containing axle and a crown ether
wheel with a vinyl group was subjected to the living ring-opening
polymerization of δ-valerolactone followed by end-capping with
a bulky isocyanate to yield a polyester axle-tethering macromolecular
[2]rotaxane cross-linker (RC). Rotaxane cross-linked polymers (RCPs)
were prepared by the radical polymerization of <i>n</i>-butyl
acrylate in the presence of RCs (0.25, 0.50 mol %). The properties
of the RCPs and covalently cross-linked polymers (CCPs) were characterized
mainly by mechanical properties. Both fracture stress and strain values
of RCPs were much higher than those of CCPs, probably owing to the
increased network homogeneity by the rotaxane cross-link. The hybrid-type
RCPs obtained from a mixture of RC and covalently connected cross-linker
(CC) showed poorer mechanical properties similar to that of CCPs,
indicating the importance of RCs in increasing the toughness of the
network polymers