Synthesis, characterization, and gamma radiation effects over well-defined poly(vinylsiloxanes) copolymers

摘要

Anionic ring-opening polymerization (AROP) was employed for the controlled synthesis of linear model block copolymers of 1,3,5,7-tetrametil-1,3,5,7- tetravinyl(cyclotetrasiloxane) (V _4) and 1,3,5- dimethyl(cyclotrisiloxane) (D _3) monomers by using sec-butyl lithium (sec-Bu ~-Li ~+) as initiator, and high-vacuum anionic polymerization techniques. V _4 copolymerization was promoted by employing D _3 and sec-Bu ~-Li ~+ producing living silanolates that open the stable V 4 ring. For this purpose, two strategies were applied: (a) sequential addition of monomers, and (b) one-step copolymerization at different reaction temperatures. According to the experimental results, higher levels of V _4 incorporation (a 18.14 mol %) were obtained by mixing both co-monomers and performing the reaction at high temperature (80°C). This strategy allowed the control of the V _4 incorporation into the copolymer structure, giving the opportunity of synthesizing model vinyl-siloxane polymers. The gamma radiation of these materials showed that lower doses are needed to achieve the same gel content as in a model poly(dimethylsiloxane) (PDMS). In such a sense, these results constitute one of the first reports regarding the effect of gamma radiation on vinyl-containing silicon polymers, and may be of fundamental importance if a biomedical cross-linked rubber-type PDMS is needed at earlier doses of sterilization.