Relationship between conformation and molecular motion of soft segment in polyurethane elastomers under elongation

In this study, the molecular aggregation state and molecular motion of the poly(oxypropylene) glycol (PPG), 1,4-butane diol and 4,4'-diphenylmethane diisocyanate (MDI) based polyurethane elastomers were investigated using dynamic viscoelastic measurement under elongation. Two PPGs with different molecular weight (M_n=2000 and 4000) were employed for the preparation of the PUEs. The peaks assigned to a relaxation of the PPG were clearly observed in the loss tangent (tan δ) curves at various strains. The onset temperature of these peaks decreased with an increasing strain. This result indicates that the size of corporate motion of glass transition decreased due to the orientation of the soft segment chains with an increasing strain. Also, the amount of temperature shift of 2000 molecular weight PPG-based PUEs were larger than that for 4000 one. This is correlated to the phase separation state of the PUEs.