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, lowerTg and upperTg discharges were observed and their molecular nature is discussed.
Authors:S. Radhakrishnan, N. Somanathan, T. Narashimhaswamy, M. Thelakkat, and H. Schmidt
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.
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.
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 δHf was 18 kJ mol−1 and entropy change δSf was 45 J K−1 mol−1, while for PF10MA the values δHf 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
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.
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.
Authors:T. Yamada, S. Boyer, T. Iyoda, H. Yoshida, and J. Grolier
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.
Authors:Yusuf Nur, Demet Colak, Ioan Cianga, Yusuf Yagci, and Jale Hacaloglu
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.
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.
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 (TSN) and nematic-isotropic transition temperature (TNI) are higher than those of pure LCP, which may promote and extend its applications on stimuli-responsive materials and devices.