Well defined columnar liquid crystalline polydiethylsiloxane

The kinetics of the anionic ring opening polymerization of hexaethylcyclotrisiloxane (D₃^Et) with the cryptate Li⁺/211] as counterion have been studied by means of ¹³C NMR spectroscopy. The propagation reaction was found to be of first order in monomer as well as living end concentration. It proceeds by two decades slower than the corresponding reaction with hexamethylcyclotrisiloxane (D₃^Me) as monomer. The Li⁺/211] system could be used to synthesize well defined polydiethylsiloxane (PDES) samples (M?_w/M?_n <1.2). However, when the polymerization was aimed at high molecular weights (≥ 600 000 g/mol), the obtained molecular weights were lower than expected, and the molecular weight distributions became broader. All PDES samples were capable of forming a columnar mesophase. The temperature range in which this phase exists was found to be strongly molecular weight dependent. Initiation of the D₃^Et polymerization with polybutadienyllithium and coupling of the living chain ends yielded a PB-PDES-PB triblock copolymer, which could be crosslinked, resulting in a mesomorphic network.