Tailored phase transitions via mixed-mesogen liquid crystalline polymers with silicon-based spacers

Ingrid A. Rousseau, Haihu Qin, Patrick T. Mather

Research output: Contribution to journalArticle

34 Scopus citations

Abstract

Control over thermotropic phase behavior in low-T g main-chain liquid crystalline polymers (LCPs) is desired for a variety of applications, including soft actuation when cross-linked. Here, we describe the synthesis of new silicon-based main-chain LCPs, including homopolymers, blends, and copolymers, with tunable clearing temperatures as governed by their chemical composition. Two mesogenic groups, namely, 1,4-bis[4-(4-pentenyloxy)benzoyl] hydroquinone (M 1) and 2-tert-butyl-1,4-bis[4-(4-pentenyloxy)-benzoyl] hydroquinone (M 2), were polymerized with various silicon-based flexible spacers, specifically, 1,4-bis(dimethylsilyl)benzene (S 1), 1,1,3,3,5,5-hexamethyltrisiloxane (S 2), and hydride-terminated poly-(dimethylsiloxane) (DP = 8) (S 3) spacers, following routine hydrosilation reaction techniques. These mesogens and flexible spacers were chosen so that both copolymerization and blending of homopolymers would allow for potential tailoring of phase behavior. Indeed, despite their similar chemical structure, the clearing transition temperatures of M 1 and M 2 differ dramatically (ΔT NI=140°C), while the silicon-based spacers offer accessibility to a large range of molecular flexibility. High-molecular-weight LCPs were successfully prepared using Pt-catalyzed addition polymerization. Interestingly, the polymers exhibited wide liquid crystalline windows with relatively high degree of order (smectic phases) except for the S 1-based blends, which, in addition to a smectic phase, also displayed a narrow nematic phase. As expected, a drastic decrease of the glass transition temperature arose on polymerizing with longer, more flexible spacers, from about 56 to -17°C. Finally, in comparing the two approaches to phase behavior tailoring, namely, blending vs copolymerization, the former led to apparently immiscible systems with constant isotropization temperatures, while the latter yielded homogeneous, single-phased materials with tunable isotropization temperatures dictated by the M 1/M 2 ratio of the copolymers.

Original languageEnglish (US)
Pages (from-to)4103-4113
Number of pages11
JournalMacromolecules
Volume38
Issue number10
DOIs
StatePublished - May 17 2005

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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