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Abstract  

The relaxation of electric field-induced polar orientation in a side-chain-bearing liquid-crystalline polysiloxane was measured by means of thermally stimulated depolarization currents. Different relaxation mechanisms were identified and characterized: the glass transition cooperative relaxation exhibits compensation behaviour. On the other hand, lowerT g and upperT g discharges were observed and their molecular nature is discussed.

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Journal of Thermal Analysis and Calorimetry
Authors: S. Radhakrishnan, N. Somanathan, T. Narashimhaswamy, M. Thelakkat, and H. Schmidt

Abstract  

Series of thiophenes containing mesogenic side chains at the 3rd position are synthesized. The thermal transitions and thermal stability of the synthesized monomers and polymers are studied. The polarizing microscopic studies of synthesized monomers showed nematic liquid crystalline phase and these mesophases further confirmed by differential scanning calorimetric study. The obtained melting and the isotropic temperatures decrease linearly with the increase of aliphatic chain length. The transition temperatures determined from DSC analysis, overlap well with the temperatures obtained from optical microscopy studies. Thermal stability of the compounds is analysed using thermogravimetric studies. Thermal stability of monomers and polymers has been determined by calculating IPDT values. Structural influence on thermal degradation patterns of monomers and polymers are also discussed.

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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.

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DSC and X-ray studies on side-chain crystallization of comb-like polymers

Fluorinatedn-alkyl acrylate and methacrylate polymers

Journal of Thermal Analysis and Calorimetry
Authors: Y. Shibasaki, H. Saitoh, and K. Chiba

Abstract  

Thermal properties of acrylate and methacrylate monomers containing long-fluorocarbon chains (H(CF2)nCH2OCOCH=CH2, (FnA) and H(CF2)nCH2OCOC(CH3)=CH2, (FnMA), wheren=6, 8, 10) and their comb-like polymers have been investigated by differential scanning calorimeter (DSC) and X-ray diffraction. The comb-like polymers (PF10A and PF10MA) with sufficiently long-fluorocarbon chains showed a simple melting and crystallizing behavior. For the fusion of PF10A in 1st heating, enthalpy change δH f was 18 kJ mol−1 and entropy change δS f was 45 J K−1 mol−1, while for PF10MA the values δH f and δSf were 5.3 kJ mol−1 and 14 J K−1 mol−1, respectively. Melted PF8A crystallized slowly, whereas PF8MA with same fluorocarbon chain and also both of PF6A and PF6MA with shorter fluorocarbon chains can hardly crystallize by the aggregation of side-chains. Effects of the length of side-chain and the flexibility of main chain on the side-chain crystallization of comb-like polymers are clear. Crystallization process of the methacrylate monomers was sensitively affected by the scanning rate of DSC measurement and the length of fluorocarbon chains.

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Abstract  

It is shown that insertion in methacrylic polymers of bulky electron donor/acceptor side-groups with taper-shaped flourinated tails promotes a self-organization of the respective side-chain polymers due to the space demands of the bulky D/A side-groups, leading to a columnar hexagonal mesophase. The presence of an Lc-phase is evidenced by DSC and identified by X-ray analysis. The orientation in the respective copolymers and polymer blends is additionally improved by the CT-interaction between the D/A side-groups. An increased packing effect due to this CT-orientation effect is evidenced in DSC by an increase of the respective transition temperatures. CT-interaction is responsible as well for a preferential polymerization of monomeric D/A-complexes leading to copolymers of alternating structures and for a zip-like arrangement along the main chain of the A/D-complexes between the interacting side-groups in polymer blends. Formation of mesophases is even observed in CT-interacting blends between the Lc-D/A side-chain polymethacrylates and the respective amorphous D/A side-chain polysiloxanes.

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Abstract  

To understand better the antagonistic behaviour of the backbone in comparison with the mesogenisity of the pendant side groups in side-chain liquid crystal polymers series of measurements using mechanical spectroscopy as well as DSC were carried out on two disubstituted polynorbornene derivatives. In order to clarify the specific arrangement of chains, the influence of thermal history on the smectic phase stabilisation were studied. By quenching samples from different temperatures, it was possible to obtain the systems which were either in the glassy liquid-crystalline (LC) state or in the glassy isotropic amorphous state. The samples prepared in such ways were used to study the influence of the LC structure on the mobility of chains in amorphous regions. The quality model of the supermolecular structure of the LC polymers is proposed.

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Abstract  

The effects of nitrogen (N2) pressure on amphiphilic di-block copolymer, PEO114-b-PMA(Az)40, were investigated by scanning transitiometry. The isotropic transition temperature increased with the increase of pressure above 20 MPa. The hydrostatic pressure effects evaluated with the Clapeyron equation were smaller than the value obtained by mercury as a pressurizing medium because the amount of absorbed gas decreases the volume change at the isotropic transition.

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Abstract  

High temperature pyrolysis studies of poly(phenylene vinylene)s PPVs with lateral substituents poly(ε-caprolactone) (PPV–PCL) or poly(ε-caprolactone) and alternating Br (PPV–PCL–Br) or polystyrene (PPV–PSt) clearly showed that thermal stability of both the substituent and PPV were affected by the thermal stability of the other. In all the polymers under investigation, decomposition started by the degradation of the substituent. The thermal stability of the PPV backbone increased in the order PPV–PCL–Br < PPV–PCL < PPV–PSt. When the thermal stability of the substituent was significantly lower than that of the PPV backbone, as in the case of PPV–PCL and PPV–PCL–Br, then the radicals generated at early stages of pyrolysis coupled before the temperature reached to the values necessary for complete decomposition. This inturn yielded a thermally more stable crosslinked structure. The increase in thermal stability was greater upon coupling of the radicals generated on the PPV backbone.

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Abstract  

The enzymatic synthesis of three isotopomers of l-DOPA labeled with deuterium and tritium at α carbon atom was elaborated. These compounds were converted into [(1S)-2H]–, [(1S)- 3H]–, and doubly labeled [(1S)-2H/3H]-dopamines using enzyme tyrosine decarboxylase. Doubly labeled (1R) isotopologue, i.e., [(1R)-2H/3H]-dopamine, was afforded by enzymatic decarboxylation of authentic l-DOPA carried out in deuteriated and tritiated incubation medium.

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Abstract  

Vinylated polyhedral oligomeric silsesquioxane (POSS-M) was prepared by the reaction of POSS containing amine groups with acrylic acid. Azobenzene liquid crystalline copolymer (LCP-POSS) was then synthesized with 6.0 mol% POSS-M and 94.0 mol% acrylate monomer containing azobenzene liquid crystalline moiety (Azo-M) by free-radical copolymerization. Homopolymer of Azo-M (LCP) was also synthesized under the same conditions. Their thermal properties and liquid crystallinity were characterized by Thermal gravimetric analysis (TG), differential scanning calorimetry (DSC), Wide-angle X-ray diffraction experiments (XRD) and polarized optical micrographs (POM). The results showed that LCP-POSS has higher thermal stability and glass transition temperature than pure LCP due to the incorporation of the rigid cage-like POSS. Especially, LCP-POSS exhibits enantiotropic smectic and nematic liquid crystalline behaviors, its smectic-nematic transition temperature (T SN) and nematic-isotropic transition temperature (T NI) are higher than those of pure LCP, which may promote and extend its applications on stimuli-responsive materials and devices.

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