UV cured platinum-free, soft PDMS networks : UV cured platinum-free, soft PDMS networks

In recent years, UV chemistry has gained importance in curing of elastomers as it allows for rapid reactions at ambient temperature and thereby saves energy in processing. Current techniques often apply platinum in the UV-cured systems, which is challenged by the increasing cost of platinum. A novel platinum free photochemical curing method for soft poly (dimethyl siloxane) (PDMS) networks based on commercially available starting materials was developed. Soft PDMS networks were obtained through photochemical thiol-ene crosslinking of α,ω-vinyl terminated PDMS with a hexa-functional thiol PDMS. Investigations showed that direct photochemical crosslinking led to slow curing kinetics and resulted in a soft PDMS with inferior materials properties. The efficiency of the crosslinking chemistry was substantially improved, through development of a two-step curing reaction. Initially, the crosslinker and excess linear α,ω-vinyl-PDMS were reacted below the gel-point under UV irraditation into hyperbranched structures. The hyperbranched structures were found to be fast and efficiently crosslinked into ideal networks with good mechanical properties. Finally the approach also allows for localization of fillers in the polymer matrix. The properties of the prepared networks were investigated by both rheology and dielectric spectroscopy.