Effect of side groups of polymer glycol on microphase‐separated structure and mechanical properties of polyurethane elastomers

The effect of side methyl and dimethyl groups of the soft segment component on the microphase‐separated structure and mechanical properties of polyurethane elastomers (PUEs) was investigated. Poly(oxytetramethylene) glycol (PTMG), and PTMG incorporating dimethyl groups (PTG‐X) and methyl side groups (PTG‐L) were used as a polymer glycol, which forms a soft segment in the PUEs. The PUEs were synthesized with 4,4′‐dipheylmethane diisocyanate 1,1′‐methylenebis(4‐isocyanatobenzene)], 1,4‐butane diol, and 1,1,1‐trimethylol propane by a prepolymer method. The degree of microphase separation of the PUEs became weaker with increasing side group content in polymer glycols. Dynamic viscoelastic properties measurement showed reorganized‐crystallization and melting of the soft segment for the PUEs based on PTMG, PTG‐L, and PTG‐X with a lower content of the side groups, but not for a PTG‐L and PTG‐X with higher content of the side groups. Tensile testing revealed that increasing methyl group concentration made the PUEs soften and weaken. The PTMG‐based PUEs obviously exhibited strain‐induced crystallization of the soft segment chains during elongation process. In contrast, for the PTG‐L and PTG‐X‐based PUEs, crystallinity decreased with increasing side group content, and the PUEs with PTG‐L and PTG‐X with highest methyl group content did not crystallize even at a large strain. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2054–2063, 2008