The effect of soft segment content and linker length on shape recovery and mechanical properties of laterally linked polyurethane copolymer

Abstract

AbstractLateral flexible linking of shape memory polyurethane (SMPU) by a polyethyleneglycol (PEG) linker through the allophanate linking method was studied, while adjusting the soft segment content and PEG length. The SMPU was composed of 4,4′‐methylenebis(phenylisocyanate) (MDI), poly(tetramethyleneglycol) (PTMG), 1,4‐butanediol (BD), and PEG‐200 as a linker. A second MDI was used to connect the carbamate group of the SMPU chain and PEG. The impact of soft segment content and PEG length on the mechanical properties and shape recovery of two series of SMPU were compared. In the best case, a 545% increase in maximum stress compared to a linear polymer was attained. The flexibly crosslinked SMPUs behave similarly to natural rubber in their stress–strain curve, but their tensile mechanical properties surpassed those of natural rubber. Shape recovery went up to 96%, which is among the best SMPUs tested so far, and shape recovery remained above 90% after four cyclic tests. The extraordinary shape memory results are analyzed and discussed together with DSC and IR data. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011