Rongben Zhang

Liquid crystal elastomers, networks and gels: advanced smart materials

The principal concepts, preparation methods, important features of liquid crystal elastomers, anisotropic networks and gels, as well as recent exciting progress in this field are reviewed. Discussions are focused on their potential applications as smart materials for converting electrical or optical energy into mechanical energy and vice versa – such applications include artificial muscles, light scattering electro-optical switches and display materials, electro- or photo-controllable micro- or nano-machinery, electrically switchable color-tunable reflectors (mirrors) and full-color reflective display, fine-tunable and low-threshold mirror-less lasing, etc. In addition, some innovative anisotropic networks consisting of ferroelectric liquid crystals, discotic mesogens and mesomorphic ladder-like polysiloxanes are also highlighted.

Synthesis and characterization of reactive ladderlike polyallylsilsesquioxane and polyvinylsilsesquioxane

Abstract Ordered reactive ladderlike polyallylsilsesquioxane (hereafter referred to as Allyl-T) and polyvinylsilsesquioxane (hereafter Vi-T) were synthesized via stepwise coupling polymerization. During this reaction, coupling agent p-phenylenediamine (PDA) is supposed to act as a template which enables silane molecules to self-assemble through strong hydrogen-bonding interaction between Si–OH groups and N–H groups. The structure of the polymers was characterized by IR, X-ray diffraction, DSC, GPC, 1H-NMR, 13C-NMR and 29Si-NMR. The data show that the two polymers have ordered ladderlike molecular structure. Hence, the stepwise coupling polymerization is suitable to synthesize ladderlike polysilsesquioxanes (LPSs) containing grafted reactive vinyl-terminated groups.

Study of the Steric Tacticity of Novel Soluble Ladderlike Poly(phenylsilsesquioxane) Prepared by Stepwise Coupling Polymerization

A novel kind of soluble ladderlike poly(phenylsilsesquioxane) (LPPS) was prepared by stepwise coupling polymerization. Various techniques, such as fluorescence spectroscopy, X-ray diffraction (XRD), molecular simulation and calculation, were combined to indicate that the steric structure in LPPS was predominantly cis-isotactic. It is anticipated that stepwise coupling polymerization is a useful synthetic method for preparing ladder-like poly(silsesquioxane)s with cis-isotactic structure, which have potential applications as functional polymers or as precursors for the further synthesis of novel advanced polymers. Schematic presentation of the steric strocture of LPPS: (a) cis-isotactic (b) cis-syndiotactic.

A triphenylene-containing side chain liquid crystalline ladder-like polysiloxane and its highly ordered superstructure

A liquid crystalline discotic triphenylene-containing side chain ladder-like polysiloxane (LPS) derivative was prepared by hydrosilylation. The superstructure was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and isotherm surface pressure (π)-area (A) diagrams based on LB-film experiments. The XRD results suggest that the discotic triphenylene units in the side chains stack to form a columnar structure and the columns further align with each other to form a board-like superstructure because of the semi-rigidity of the ladder-like backbone. This suggestion has been confirmed by parallel nanowire-like stripes observed in the AFM image. Mixing small amounts of the corresponding low molar mass molecules with the polymer leads to a more ordered and denser columnar stacking, as shown by sharpened XRD patterns and a π-A curve with a steeper slope, higher collapse pressure and lower collapse area than those obtained either for the low molar mass molecules or the polymer individually.

Synthesis and Characterization of Novel Alcohol-Soluble Ladderlike Poly(silsesquioxane)s Containing Side-Chain Hydroxy Groups

Two novel kinds of alcohol-soluble ladder-like poly(silsesquioxane)s containing side-chain hydroxy groups (OH-T 1 and OH-T 2 ) were prepared successfully for the first time by hydrolysis of ladderlike poly(silses-quioxane)s with side-chain ester groups (Ester-T 1 and Ester-T 2 ), which were synthesized by stepwise coupling polymerization. A variety of characterization methods including FT-IR, 1 H NMR, 13 C NMR, 29 Si NMR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), vapor pressure osmometry (VPO), gel permeation chromatography (GPC), and X-ray diffraction (XRD) were combined to demonstrate that the obtained alcohol-soluble polymers have ladderlike structures, although some structural defects still existed.

The synthesis and X-ray diffraction study of the ladder-like polysilsesquioxanes with side-chain ester groups

The highly regular ladder-like polysilsesquioxanes with different length side-chain ester groups were first synthesized via the hydrosilylation reaction. Various vinyl-terminated esters (methyl acrylate, butyl acrylate, octyl acrylate and 2-ethyl hexyl acrylate) were linked to the homopolymeric ladder-like polyhydrosilsesquioxane and copolymethyl-hydrosilsesquioxane in the presence of dicyclopentadienyl platinum dichloride as catalyst respectively. They are soluble in toluene and tetrahydrofuran and insoluble in hexane, acetone and methanol Their structures have been characterized by IR spectroscopy, 1H-NMR (nuclear magnetic spectroscopy), 29Si-NMR and X-ray diffraction. X-ray diffraction patterns indicated that the regularity of ladder-like polysilsesquioxane with longer side-chain ester is higher than that with shorter side-chain ester. The regularity of the homopolymeric ladder-like polyhydrosilsesquioxane with side-chain ester is lower than that of the corresponding copolymethyl hydrosilsesquioxane.

A glance at the relation of stepwise coupling polymerization to supramolecular chemistry

Abstract A relationship between supramolecular chemistry and stepwise coupling polymerization (SCP) found by our group is briefly described. By SCP reaction a series of new kinds of microstructure-controlled polymers and their corresponding supramolecular inclusions such as: (1) reactive ladder-like polysiloxanes (LPS); (2) liquid crystalline ladder-like polysiloxanes and their metal complexes including fishbone-like LCPs (FBLCPs) and their metal complexes (M-FBLCPs) and rowboat-like LCPs (RBLCPs); (3) tubular polymers (TPs) and their supramolecular inclusions (TPIs) and (4) sieve-plate-like network polymers (SNPs) and their supramolecular clathrates (SNPC) have been successfully prepared. It is reasonably stated that SCP is a supramolecular interaction-aided reaction and moreover, SCP is an effective method to generate new supramolecules.

Synthesis and characterization of oligomeric silsesquioxane with pendent carboxylic acid groups

Abstract An oligomeric silsesquioxane with pendent carboxylic acid groups and with supposedly ladder structure was prepared by preaminolysis process followed by the controlled hydrolysis of pendent ester groups. A variety of characterization techniques including 1 H-NMR, 29 Si-NMR, FTIR, vapour pressure osmosis, X-ray diffraction, and DSC demonstrated the structure of the final product. The resulting oligomer exhibits excellent film-formability thanks to the formation of hydrogen-bonded network between the pendent carboxylic acid groups even though its molecular weight is low, which predicts its direct usage as coatings for a variety of purposes.

Synthesis of ring-structured polysiloxane as host materials for blue phosphorescent device

A ringed polysiloxane with a side chain of dibenzothiophene groups (BS-PSQ) is successfully synthesized as confirmed by MALDI-TOF MS and 1H-NMR. DSC, TGA, AFM and spectra reveal its good film-forming ability, high thermal and morphological stability, and good miscibility with the dopant FIrpic. In addition, it also has a high triplet energy and a wide band gap. The BS-PSQ may be used as a host for the blue light emitter iridium complex FIrpic. The electrophosphorescent device based on BS-PSQ as the active layer exhibits typical blue emission, and the performance of the device is superior to that of any other POSS-based host material reported and also to some of the small molecular host materials.

Synthesis and characterization of ladder-like copolymethyl-epoxysilsesquioxane

Abstract A new kind of copolymethyl-epoxysilsesquioxane (CPMES) was synthesized for the first time by hydrosilation reaction of allyl glycidyl ether (AGE) with the ladder-like polymethylhydrosilsesquioxane (Me-H-T) in the presence of dicyclopentadienylplatinum dichloride (Cp2PtCl2) as catalyst. The graft polymer was characterized by infrared spectroscopy (IR), 1H-NMR, 29Si-NMR, X-ray diffraction (XRD), gel-permeation chromatography (GPC), vapour pressure osmometry (VPO), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results indicate that CPMES possesses good solubility in organic solvents, and a greatly improved thermostability compared with polymethyl-epoxysiloxane with a single backbone.