Research on preparation, structure and properties of TiO2/polythiourethane hybrid optical films with high refractive index

Hybrid optical films of TiO2-triethoxysilane-capped polythiourethane (TCPTU) with high refractive indices have been prepared via an in situ sol-gel method. The high refractive index triethoxysilane-capped polythiourethane (TCPTU) was synthesized by polyaddition of the triethoxysilane-modified trimercaptothioethylamine (TMTEA) and 2,2'-dimercaptoethylsulfide (MES) with 2,4-tolylene diisocyanate (TDI). The titania content in the hybrid films can be adjusted from 0 to 80 wt.-% by the feed ratio of titania precursor [Ti(OBu)(4)] to polymer (TCPTU). Both FTIR and DSC analyses indicate that there is chemical bonding between the titania domain and the polymer chain. TGA results suggest that the titania of high content was successfully incorporated into polymer matrices and this series of hybrid films have good thermal properties. AFM measurements indicate that in the hybrid films the titania domains are of nanosize scale and the domain size averagely decrease from 60-80 nm to 5-20 nm with increasing content of titania, and the variation of surface roughness for the hybrid films has the same trend. These may be relative to the content of TCPTU and the interaction between titania and polymer (TCPTU). The refractive indices of the hybrid films at 632.8 nm increased from 1 632 to 1 879 as the titania content varied from 0 to 80 wt.%.