Synthesis and phase behavior of a polynorbornene-based molecular brush with dual "jacketing" effects

Abstract

J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2116-2123 A series of molecular brushes with dual "jacketing" effects were synthesized by ATRP and ROMP using the "grafting through" method. All the PNb-g-PMPCS molecular brushes form a Φ N phase. The confinement effect and the increased MW effect of the brush architecture play important roles in the phase behaviors of these molecular brushes. In this study, a series of well-defined liquid crystalline molecular brushes with dual "jacketing" effects, polynorbornene-g-poly{2,5-bis[(4-methoxyhenyl)oxycarbonyl] styrene} (PNb-g-PMPCS), were synthesized by the "grafting through" method from ring opening metathesis polymerization of α-norbornenyl-terminated PMPCS. The rigid PMPCS side chain was synthesized by Cu(I)-catalyzed atom transfer radical polymerization initiated by N-[(2-bromo-2-methylpropanoyl)ethyl]-cis-5-norbornene-exo-2,3-dicarboximide. The chemical structures of the molecular brushes were confirmed by 1 H NMR and gel permeation chromatography (GPC), and the thermal properties were studied by thermogravimetric analysis (TGA). GPC results reveal that the molecular brushes have relatively narrow polydispersities. TGA results show that the molecular brushes have excellent thermal stabilities. The PMPCS side chains in all the molecular brushes form the columnar nematic liquid crystalline phase, which is a little different from the behavior of linear PMPCS possibly due to the confinement or other effects of the brush architecture which leads to decreased order.