Design of Polyurethane Composed of only Hard Main Chain with Oligo(ethylene glycol) Units as Side Chain Simultaneously Achieved High Biocompatible and Mechanical Properties

In order to create a novel rigid polymer material for biomedical application, we designed the polymer structure of polyurethane, bearing oligo(ethylene glycol) (OEG) as the side chain, which was synthesized by only hard main chain using diisocyanate and short diol monomers. We investigated the effect of the graft structure of OEG units on polymer properties using pentaethylene glycol (OEG₅) or propanediol (PDO) in the main chain as the other diol monomers. Furthermore, the rigid 4,4′-methylenebis(cyclohexyl isocyanate) (HMDI) and symmetric hexamethylene diisocyanate (HDI) were selected for the isocyanate monomers. As a result, there is a significant difference in various properties, depending on both the existence and the position of OEG units in the polymer structure. For example, differential scanning calorimetry (DSC) showed that the graft structure of OEG caused a decrease in the glass transition temperature from 73 to 35 °C in the case of using HMDI as well as a disappearance of the melting point in the case of using HDI. The Fourier transform infrared (FT-IR) spectra showed that the ordered hydrogen bonding of Cî - O stretching vibration at 1682 cm^-1 was not observed in the polyurethane grafted with OEG. In the mechanical test of polyurethane composed of HMDI, the sample grafted with OEG exhibited excellent values of elastic modulus of 1.7 GPa and elongation at break of 184%, while that with OEG₅ and PDO in the main chain showed 115 MPa with 370% and 739 MPa with 19%, respectively. The polyurethane grafted with OEG showed around 0.6 μg/cm² of protein adsorption, almost the same as that with OEG₅ in the main chain, while that using PDO in the main chain showed more than 3.0 μg/cm². Therefore, the polyurethane design bearing OEG as the side chain provides excellent rigidity, toughness, and biocompatibility simultaneously.