Hai-Liang Zhang

Effects of molecular weight on liquid-crystalline behavior of a mesogen-jacketed liquid crystal polymer synthesized by atom transfer radical polymerization

Abstract The synthesis of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) with different molecular weight and low polydispersity was achieved by atom transfer radical polymerization in methoxybenzene solution using 1-bromoethylbenzene as an initiator and CuBr/sparteine complex as a catalyst. The concentration of the living centers throughout the polymerization was found to be constant. The liquid-crystalline behavior of the polymers with Mn ranging from 3800 to 17,400xa0g/mol was studied using DSC and POM. Only the polymers with Mn beyond 10,200xa0g/mol formed a liquid-crystalline phase, which was quite stable with a high clearing point (higher than the decomposition temperature of the polymer).

Hierarchical Supramolecular Ordering with Biaxial Orientation of a Combined Main-Chain/Side-Chain Liquid-Crystalline Polymer Obtained from Radical Polymerization of 2-Vinylterephthalate

The liquid-crystalline (LC) phase structures and transitions of a combined main-chain/side-chain LC polymer (MCSCLCP) 1 obtained from radical polymerization of a 2-vinylterephthalate, poly(2,5-bis{[6-(4-butoxy-4-oxybiphenyl) hexyl]oxycarbonyl}styrene), were studied using differential scanning calorimetry, one- and two-dimensional wide-angle X-ray diffraction (1D and 2D WAXD), and polarized light microscopy. We have found that 1 with sufficiently high molecular weight can self-assemble into a hierarchical structure with double orderings on the nanometer and subnanometer scales at low temperatures. The main chains of 1, which are rodlike as a result of the jacketing effect generated by the central rigid portion of the side chains laterally attached to every second carbon atom along the polyethylene backbone, form a 2D centered rectangular scaffold. The biphenyl-containing side chains fill the space between the main chains, forming a smectic E (SmE)-like structure with the side-chain axis perpendicular to that of the main chain. This biaxial orientation of 1 was confirmed by our 2D WAXD experiments through three orthogonal directions. The main-chain scaffold remains when the SmE-like packing is melted at elevated temperatures. Further heating leads to a normal smectic A (SmA) structure followed by the isotropic state. We found that when an external electric field was applied, the main-chain scaffold greatly inhibited the motion of the biphenyls. While the main chains gain a sufficiently high mobility in the SmA phase, macroscopic orientation of 1 can be achieved using a rather weak electric field, implying that the main and side chains with orthogonal directions can move cooperatively. Our work demonstrates that when two separate components, one offering the jacketing effect to the normally flexible backbone and the other with mesogens that form surrounding LC phases, are introduced simultaneously into the side chains, the polymer obtained can be described as an MCSCLCP with a fascinating hierarchically ordered structure.

Crystallization kinetics of new copoly(ethylene terephthalate-imide)s

Crystallization kinetics of copoly(ethyleneterephthalate-imide)s (PETIs) of various imide contents were studied by the DSC technique. The results of isothermal and nonisothermal crystallization kinetics studies showed a consistent trend in that the crystallization of all copolyesterimides comprised a primary stage and secondary stage, and that the crystallization mechanism was a three-dimensional growth with athermal nucleation. The crystallization rate of PETIs first increased and then decreased as the content of imide units in the copolyesterimides increased. This indicates that the imide units in the copolymer decreased the chain-packing regularity of poly(ethylene terephthalate) (PET) and the same units also enhanced the copolymer chain rigidity. The copolyesterimide with 0.2 mol% imide unit content showed a dramatic increase of the crystallization rate, and exhibited the highest crystallization rate of all the studied compositions. Studies of isothermal and nonisothermal crystallization kinetics, showed that small amounts of imide units in the the backbone act as nucleating agents during the crystallization process of copolyesterimides.

Atom-Transfer Radical Polymerization to Synthesize Novel Liquid Crystalline Diblock Copolymers with Polystyrene and Mesogen-jacketed Liquid Crystal Polymer Segments

The synthesis of a series of new rod-coil diblock copolymers with different molecular weights and low polydispersity was achieved by atom transfer radical polymerization. The block architecture (coil-conformation of styrene segment and rigid-rod conformation of 2,5-bis[(4-methoxyphenyl)-oxycarbonyl]styrene segment) of the diblock copolymers was experimentally confirmed by proton nuclear magnetic resonance (1H NMR) and differential scanning calorimetry (DSC). The liquid crystalline behavior of the copolymers was studied using DSC and a polarized optical microscope (POM). It was found that the liquid crystalline behavior was dependent on the molecular-weight of the rigid segment. Only those copolymers with Mn of the rigid block beyond 9,300 g/mol could form liquid crystalline phases above the glass transition temperature of the rigid block.

Mesogen-jacketed liquid crystalline polymer with flexible dicyclopentyl terephthalate as side group

Hui-lin Tu, Dong Zhang, Xin-hua Wan, Xiao-fang Chen, Yu-xiang Liu, Hai-liang Zhang,Qi-Feng Zhou*Department of Polymer Science & Engineering, College of Chemistry, Peking University, Beijing 100871,Chinaqfzhou@pku.edu.cn(Received: April 24, 1999; revised: June 21, 1999)SUMMARY: For the first time the flexible cyclopentyl ring is used to build mesogenic units, and thus anovel mesogen-jacketed liquid crystalline polymer (MJLCP) poly(dicyclopentyl vinylterephthalate) is syn-thesized. The polymer forms a stable mesophase which changes to an isotropic phase at 267

A free radical initiated optically active vinyl polymer with memory of chirality after removal of the inducing stereogenic center

Free radical polymerization of (+)-2,5-bis[4-((S)-2-methylbutyloxy)phenyl]styrene yields a chiral polymer with memory of optical activity after the initial stereogenic center in the side group of the monomer is chemically removed.

Effect of rod-like imide unit on crystallization of copoly(ethylene terephthalate-imide)

The effect of the imide unit on the isothermal and non-isothermal crystallization, kinetics crystallization of a new family of copoly(ethylene terephthalate-imides) (called copolyesterimides or PETIs) was investigated using differential scanning calorimetry. With a combined Avrami and Ozawa equation, one can describe the non-isothermal crystallization process of copolyesterimides, and the results show the same tendency as that in the isothermal crystallization process. These studies show that the processes of crystal nucleation and growth result in mainly three-dimensional growth with a thermal nucleation. In both isothermal and non-isothermal crystallization processes, the crystallization rate of PETIs, with imide content below 0.5%, is higher than that of neat PET, while PETI-3 (0.3 mol% imide) has the highest crystallization rate. This rate is significantly enhanced over PET homopolymer. It is proposed that imide units precipitate from the melt and act as nucleating agents during the crystallization process of these novel copolyesterimides.