Comb-shaped liquid crystalline stereoregular cyclolinear methylsiloxane copolymers: synthesis, behaviour in bulk and behaviour in monolayers

Abstract

Stereoregular cyclolinear organosiloxane copolymers containing vinyl groups with diorganosiloxane spacers as well as cyclohexasiloxane fragments were synthesised. Comb-shaped liquid crystalline (LC) cyclolinear polymethylsiloxanes with mesogenic side groups were prepared by hydrosilylation of stereoregular cyclolinear organosiloxane copolymers with (4′-cyanobiphenyl-4-yl)-11-(1,1,3,3-tetramethyldisiloxyl)undecanoate in the presence of the Karstedt catalyst. The chemical structure of the copolymers synthesised was confirmed by proton and silicon nuclear magnetic resonance spectroscopies and infrared spectroscopy. Their phase behaviour was characterised by differential scanning calorimetry, X-ray analysis and optical polarising microscopy. It was shown that the appearance of the LC state, the temperature range of its existence and polymesomorphism are determined by the molecular mass of the copolymer and by the content of the mesogenic groups. The introduction of three mesogenic groups per monomer unit results in polymesomorphic transitions. The tacticity of the backbone influences the interchain distances in the comb-shaped LC cyclolinear methylsiloxane copolymers. Studying the Langmuir films of the stereoregular LC methylsiloxane copolymers revealed that different types of molecular arrangements could be observed depending on the number of mesogenic groups attached. LC copolymers having three mesogens per monomer unit demonstrate a two-stage monolayer collapse.