Effect of Glycerol in Soft and Hard Segments on Properties of Shape Memory Polyurethane

Hypothesis: 

Chemical cross-linked shape memory polyurethanes (CSMPUs) can have various applications in different fields such as medicine, where mechanical behavior and shape memory are improved in these samples compared to linear shape memory polyurethanes. Shape memory polyurethanes consist of at least two different phases. The first phase, which is in the form of a net point, is responsible for maintaining the permanent shape of the shape memory polyurethane. In contrast, the second phase, also known as shape memory switches, temporarily fixes the temporary shape of the polyurethane by crystallinity. The aim of this research is the synthesis of linear and star polycaprolactones (PCLs) in the first step and the synthesis of CSMPUs using linear and star PCLs in the second step, as well as the investigation and comparison of hydrogen-bonding indices through -C=O groups and -NH CSMPU samples that were synthesized using glycerol as the initiator of the soft segment or the chain extender of the hard segment.

Linear and star polycaprolactones (PCLs) were synthesized using ring-opening polymerization (ROP) of caprolactone, and shape memory polyurethanes with chemical cross-linking (CSMPU) were synthesized using a two-step pre-polymerization method. By changing the molar ratios of the functional groups, the weight percentage of the hard segment in polyurethane samples was kept constant at 10%.

The hydrogen-bond index is decreased with the introduction of glycerol as a chain extender. Also, the degree of crystallinity in CSMPU samples is decreased compared to those of pure PCLs. With the increase of chemical cross-linking the crystallinity of CSMPU samples is decreased. In addition, in the studies of mechanical behavior no significant difference was observed in the presence of glycerol in the soft segment or the hard segment.