Synthesis and Properties of Polyurethanes Graft Modified by Long Polydimethylsiloxane Side Chain

Long side chain polyurethane oligomers were synthesized from tolylene diisocyanate (TDI), polyether triol (N330) and monohydroxy terminated polydimethylsiloxane (M-PDMS, ), and the structures were characterized by FT-IR spectrum. Subsequently, they were mixed with polyurethane oligomers synthesized from TDI and polyether triol (N220) to obtain M-PDMS graft modified polyurethanes (M-PDMS-PUs). Dihydroxy terminated polydimethylsiloxane modified polyurethanes (D-PDMS-PUs) were also prepared for the study in contrasts with M-PDMS-PUs. The influence of concentration and length of PDMS on the surface, thermal and mechanical properties was investigated by contact angle measurement, thermo-gravimetric analysis (TGA), different scanning calorimeter (DSC) and mechanical testing. Water contact angles showed the M-PDMS-PUs had higher contact angles than that of D-PDMS-PUs. Added with low amount of PDMS (2.6 wt%), the water contact angle of M-PDMS-PU was 95.5°C while that of D-PDMS-PU was 88.0o. TGA data showed that M-PDMS-PU (Tmax = 368.0°C) had better thermal stability than that of D-PDMS-PU (Tmax = 362.2°C) at low PDMS concentration (2.6 wt%). DSC data revealed that the incorporation of PDMS into PU resulted in a decrease in Tg values and the Tg values of D-PDMS-PUs decreased more drastically than those of M-PDMS-PUs. Mechanical testing indicated that the tensile strength, elongation at break and Shore A hardness of the PDMS modified polyurethanes decreased with the increase of the PDMS content. The morphologies of the fracture surfaces of the copolymers showed that microphase separation between PU and PDMS was formed in both types of PDMS modified polyurethanes and the size of the polysilicone phase became larger with increasing the PDMS content.