Tomasz Ganicz

Side-chain Liquid Crystal Polymers (SCLCP): Methods and Materials. An Overview

This review focuses on recent developments in the chemistry of side chain liquid crystal polymers. It concentrates on current trends in synthetic methods and novel, well defined structures, supramolecular arrangements, properties, and applications. The review covers literature published in this century, apart from some areas, such as dendritic and elastomeric systems, which have been recently reviewed.

Organosilicon mesomorphic polymer systems

Abstract This review is devoted to unusual organosilicon polymers exhibiting birefringence due to the formation of mesophase (μ) of the ‘condis’ (conformationally disordered) type. The polymers (cyclolinear and linear polysiloxanes, polysilanes, poly(oxymultisilanes), polycarbosilanes, their copolymers having organic monomeric units and their networks) are able to form thermotropic mesophases, basically of columnar architecture, although the macromolecules do not incorporate any typical ‘rod’- or ‘disc’-like mesogenic moieties. Their structure and morphology (if studied), as well as methods of synthesising them are reviewed with particular stress on the effect of polymer composition, molecular weight, and types of side chain substituents on the stability of mesophases and phase transfer temperatures. Most of these polymers show mesomorphic behaviour over a wide temperature range, even at rather elevated temperatures and the isotropisation occurs often only at the decomposition point. It is believed that they may be of importance as relatively simple structures with potential practical applications.

Synthesis and characterization of liquid crystal polycarbosilanes: poly(1-methyl-1-silaethylene), poly(1-methyl-1-silabutane) and poly(1-silabutane) with pendant mesogenic groups

Abstract The synthetic routes for preparation of side chain liquid crystal polycarbosilanes, with rod type mesogens, pending from every second and every fourth atom in the main chain, forming ‘comb-like’ and ‘double comb-like’ polymers, are described. Structure—property relationships were investigated. X-ray measurements of the smectic materials, oriented in a magnetic field, proved the S A1 phase to be a dominant one for these new mesomorphic polymers; however, generation of S Ad and more ordered S B phases was also detected. Polycarbosilanes present useful, highly thermally and chemically resistant materials, which provide useful models for studies of the influence of the main chain architecture on the properties of polymers with various pendant groups.

Liquid crystal dimers with organosilicon spacers as models for side chain LC polymers

Abstract A series of six mesogenic dimers were prepared containing terminal 4’-methoxyphenyl-4-octenyloxybenzoate groups, of the general formula [MeOC 6 H 4 O(O)CC 6 H 4 O(CH 2 ) 8 SiMe 2 ] 2 R, where R=–CH 2 –, –(CH 2 ) 2 –, –(CH 2 ) 3 –, –SiMe 2 –, –O– and –NH–. Their liquid crystal properties were compared with those of the structurally relevant side chain polymers with the same mesogenic moiety: polycarbosilanes, polyethylene, and polysiloxane. It is shown that the low molecular dimers can be used as models for evaluating and predicting mesogenic characteristics of macromolecular systems with backbones structurally equivalent to spacers of the dimers.

Comb-like polycarbosilanes-routes to a new group of liquid crystal polymers

Abstract Routes to two novel types of liquid crystal polycarbosilanes are described and preliminary studies of their properties are reported.

A novel organometallic route to phenylethenyl-modified polysiloxanes

We have synthesized a series of cyclic and linear siloxane materials with phenylethenyl substituents via transition metal complex-catalyzed coupling of the respective vinylsiloxane systems with styrene and α-methylstyrene. It has been shown that the non-carbene metal catalysts [RuCl(H)(CO)(PPh3)3] and [RuCl(SiMe3)(CO)(PPh3)2] are the most effective ones, pointing to a silylative coupling pathway as the most plausible mechanistic route. The process was studied in the presence of a series of catalysts and styrene polymerization inhibitors under different reaction conditions, leading to useful silicone materials characterized by high refractive index values ranging from 1.51 to 1.59 due to strong π-conjugation in side chain substituents.

Organosilicon Fragrance Carriers

Five different organosilicon carriers, with various molecular architectures - [(poly-(dimethylsiloxane-co- methylsiloxane) (containing 61 % of [–SiMeHO-] monomeric units) (P), silicone resin (Q), tetramethyldisiloxane (M) tetramethylcyclotetrasiloxane (D) and tris (dimethylsilyl)methane [HC(SiMe2H)3, (T)] were covalently bonded with model fragrant systems, including 1- and 2-phenylethyl alcohol, acetophenone, 2-phenylpropionic aldehyde, geraniol, 2-phenyl-1-propyl alcohol, 2-octanone and octyl aldehyde in order to obtain novel controlled fragrance release systems. Hydrolytic release of the fragrances was studied under base (NaOH) and acid (HCl) catalysis. It has been shown that polymer carriers allow for a controlled slow release of the relevant fragrant ingredients from the conjugates, whereas the low molecular weight systems (M, D and T) more easily cleave off fragrant moieties.

Synthetic approach to condis-type mesophase networks

This paper presents a synthetic pathway leading to a new class of materials--crosslinked acrylic-polydiethylsiloxane copolymers. They combine the mesomorphic properties of long alkyl-substituted siloxanes with well defined acrylic/siloxane networks. In order to obtain telechelic bis(3-aminopropyl)-oligodietythylsiloxanes, the equilibration reaction of nexaethylcylotrisiloxane with bis(3-aminopropyl)-tetramethyldisiloxane has been studied. The next synthetic step of the synthesis involved the addition of amino terminated oligosiloxanes to vinyl isocyannates leading to UV-crosslinkable vinyl macromonomers. Several crosslinking reactions of the vinyl terminated oligosiloxanes in acrylic matrix have been carried out. Variable proportions of siloxane and acrylate components led to the mesomorphic elastomers with different mechanical properties.

Mesomorphic organosilicon polymers

Two broad groups of organosilicon polymers are reviewed, presenting different structural features. Some polysiloxanes and polysiloxanes, referred often to as condis crystals, do not contain any architectural elements of rigid rod- or disc-like type moieties, despite the fact, that these flexible chain polymers show an interesting mesomorphic behavior and generate columnar mesophase. The second group involves macromolecules with mesogens incorporated into main or side polymer chains. The advantage of using inorganic flexible backbones lies in lowering phase transition temperatures compared to many organic polymer systems.

Analysis of mesophase formation in side-chain liquid crystalline polycarbosilanes

This paper is concerned with an analysis of the thermodynamics and kinetics of mesophase formation by cooling from the isotropic state of side-chain liquid crystalline polycarbosilanes containing spacers in the range from 3 to 11 CH2-groups. The polymers are characterized by their thermotropic behaviour as far as temperature, enthalpy and entropy of the transitions are concerned. The kinetics was followed by optical and calorimetric methods. Longer spacer length leads to more perfect ordering in the mesophase, higher isotropization temperatures, and lower glass transition temperatures. The Avrami and Ozawa formalism to describe the transition kinetics to the mesophase from the isotropic state cannot be interpreted as the nucleation and growth mechanism known from crystallization.