Novel liquid crystalline resins based on MQ siloxanes

doi:10.1016/j.jorganchem.2006.07.043

Journal of Organometallic Chemistry

Volume 691, Issue 23, 15 November 2006, Pages 5052-5055

https://doi.org/10.1016/j.jorganchem.2006.07.043 Get rights and content

Abstract

MQ siloxane resins containing Si–H functions have been made from tetramethyldisiloxane and tetraethoxysilane. Hydrosilylations with mesogenic alkenes give low molecular weight liquid crystal MQ resins with potentially useful properties.

Graphical abstract

Low molecular weight siloxane polymers with liquid crystal properties may be synthesised by hydrosilylation of mesogenic alkenes with readily available MQ resins containing Si–H bonds; they constitute a new group of versatile materials

Introduction

Studies on the synthesis and applications of structurally diverse side chain liquid crystal polymers have grown exponentially over the last 20 years [1]. Their improved mechanical resistance compared to low molecular weight liquid crystal materials is of great practical importance. For many applications, such as displays, optical data storage materials, switches and shutters, etc., linear, high molecular weight materials exhibit a too long response time, when supramolecular orientation is achieved by changes in external electric or magnetic fields. [2] Therefore, much current research concentrates on so called hybrid liquid crystals of intermediate molecular weight, especially oligomers such as cyclic [3], [4], linear [5], [6] siloxanes, and structures of globular shape, having topologies giving decreased viscosity in melt, while preserving the robust mechanical properties of polymers (silsesquioxanes, dendritic and dendrimeric systems [7], [8]).

Current research in this area proved that many structures of intermediate molecular weight (especially cyclic siloxanes) exhibit the fast electro-optical response of low molecular weight liquid crystals and can find therefore a number of applications [9]. Industrial standards for electro-optical devices are becoming ever more demanding and a search for new LC materials of such the type is still a challenge. Cost effectiveness is also an important factor.

Well-defined siloxane monomers can serve as models for studies of structure–property relations, but they are much less important as applied materials [10]. An attempt to attach mesogenic substituents to mixtures of cyclic siloxanes (MeRSiO)_x, where R = mesogen and x = 6–20, led to liquid crystalline materials whose properties were not reproducible. Fractions of cyclic siloxanes were obtained by simple distillation and therefore their composition varied over a wide range [4].

Section snippets

Materials and methods

Dichloromethane, methanol, HCl aq. 35–36%, MgSO₄, butanol, NaOH and Karstedt’s catalyst (Pt₂[(ViMe₂Si)₂O]₃, 3–3.5% of Pt in xylenes) (ABCR) have been used as supplied. Toulene was dried by standard methods and stored over a molecular sieves.

4-(pent-4-enyloxy)-benzoic acid 4-methoxyphenyl ester [CH₂ double bond CH(CH₂)₃OC₆H₄C(O)OC₆H₄OCH₃], (S)-2-chloropentanedioic acid 5-ethyl ester 1-(4′-undec-10-enyloxybiphenyl-4-yl) ester [CH₂=CH(CH₂)₉OC₆H₄C₆H₄O(O)CCH(Cl)CH₂CH₂C(O)OC₂H₅] were made according to literature

Results and discussion

The use of M^HQ resins (R_nSiX_mO_y, where R = CH₃, X = H, n + m + y = 4) as a novel anchoring backbone for mesogens opens up a way to a new group of readily available hybrid liquid crystalline materials. MQ resins themselves, including those bearing reactive groups, have been widely used for pressure release adhesives, silicone rubbers, coatings and additives [14]. Currently vinyl functionalised M^ViQ resin platinum complexes are used as silicone-soluble hydrosilylation catalysts [15].

Some of them are

Acknowledgements

We thank the Ministry of Science and Information Technology for a grant (3 T09B 040 28) (T.G.) that supported this work. W.A.S. wishes to thank warmly DuPont, Wilmington, US, for financial assistance through the European University Support Program.

The authors thank prof. Alan Bassindale for valuable comments.

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^☆: “M” stands for Me₃SiO–, “D” for Me₂SiO₂, “T” for MeSiO3 and “Q” for O₂SiO₂.

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NoteNovel liquid crystalline resins based on MQ siloxanes☆

Abstract

Graphical abstract

Introduction

Section snippets

Materials and methods

Results and discussion

Acknowledgements

Polymer

J. Phys. Chem. B.

Liq. Cryst.

Trends Polym. Sci.

J. Chem. Soc., Chem. Commun.

Mol. Cryst. Liq. Cryst.

Note
Novel liquid crystalline resins based on MQ siloxanes☆