Incorporation of polydimethylsiloxane into polyurethanes and characterization of copolymers

Novel copolymers of polyurethane (PU) were prepared by direct transurethanetion reaction of a commercial PU with polydimethylsiloxanes (PDMS, MW 1000, 5000, and 10,000) containing hydroxyl end-groups. Transurethanetions with different mass ratios of hydrophobic PDMS to hydrophilic PU chains (PDMS1000–PU: 43:57, 67:33, 71:29, and 80:20; PDMS5000–PU: 37:63, and 51:49; PDMS10000–PU: 51:49) were carried out in solution at 65 and 100 °C. In catalyzed reactions, dibutyltin dilaurate (SnC₃₂H₆₄O₄) was used to promote bond breaking in the PU chain and accelerate the reaction between hydroxyl end-groups of PDMS and regenerated isocyanates of PU. The chemical structures of the prepared copolymers were comprehensively characterized by ¹H, ¹³C, and ²⁹Si NMR spectroscopies. According to elemental analysis, the content of PDMS varied between 3 wt.% and 16 wt.%, and results obtained from the ¹H NMR spectroscopy were in good agreement with the results of elemental analysis. Increased length of the hydrophobic chain increased the content of PDMS in the copolymer. The GPC results showed that molar masses of the PUPDMS copolymers were lower than the molar mass of the starting PU. The glass transitions (T_g) of the copolymers were shifted to lower temperature as compared with T_g of the starting polyurethane. ATR FTIR spectroscopy showed the surface of the copolymer films to be enriched with siloxane groups and, according to electron microscopy, it was textured with microspheres. The static contact angles for copolymer films measured with deionized water ranged from 94° to 117°. The different structural, thermal and surface properties of the PUPDMS copolymers as compared with PU indicated that transurethanetion had taken place.