Effects of polyol types and hard segment contents on the crystallization of thermoplastic polyurethanes

Effects of the polyol type and the hard segment content of thermoplastic polyurethane (TPU) on the crystallization of hard segments in TPUs were studied employing differential scanning calorimetry. Diols used for the preparation of TPUs were poly(tetramethylene ether glycol) (PTMEG), poly(propylene glycol) (PPG). polycaprolactone (PCL), poly(butylene adipate) (PBA) the molecular weights of which were 2000 and the hard segments contents of TPUs were 35 similar to 44 wt%. We found that crystallization of hard segments in TPUs were observed at higher temperatures and became faster with increasing hard segment contents of TPUs. The crystallization rate of TPU was also affected by the types of polyols used for the preparation of TPUs. It is postulated that lower miscibility of soft segments and hard segments results in higher crystallization rate and increase of cooling crystallization temperatures due to better hydrogen bonding between hard segments in melts.