Dynamic Mechanical Relaxation Behavior of Low Molecular Weight Side-Chain Cyclic Liquid Crystalline Compounds near the Glass Transition Temperature

1996 ◽  
Vol 29 (17) ◽  
pp. 5650-5657 ◽  
Author(s):  
Michael E. De Rosa ◽  
W. Wade Adams ◽  
Timothy J. Bunning ◽  
Hongqin Shi ◽  
Shaw H. Chen
Keyword(s):  
Molecular Weight ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Liquid Crystalline ◽  
Relaxation Behavior ◽  
Side Chain ◽  
Mechanical Relaxation ◽  
Low Molecular Weight ◽  
Dynamic Mechanical

Properties and Structure of Elastomers

1966 ◽  
Vol 39 (4) ◽  
pp. 881-896 ◽  
Author(s):  
Joginder Lal ◽  
Kenneth W. Scott
Keyword(s):  
Tensile Strength ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Alkyl Group ◽  
Side Chain ◽  
Transition Temperatures ◽  
Glass Transition Temperatures ◽  
Dynamic Mechanical ◽  
Alkyl Ethers

Abstract The glass transition temperatures of high molecular weight poly (vinyl n-alkyl ethers) decrease with increasing length of the n-alkyl group. On lengthening the n-alkyl group, 14 per cent of the specific volume increase is free volume. Branching or substitution in the alkyl group of the polymer increases the Tg value. A comparison of poly (vinyl n-alkyl ethers) and polymers of normal α-olefins shows that an ether group and a methylene group in the side chain are equivalent in influencing the glass transition temperature. We have varied systematically the side chain alkyl group in poly (vinyl alkyl ethers) and evaluated at 3 different temperatures the influence of these variations on the dynamic properties of the vulcanizates of these polymers. The relative position of the curves, relating dynamic resilience to dynamic modulus of these polymers, is generally in the order of their glass transition temperatures. The dynamic mechanical property data on poly (vinyl n-pentyl ether) and poly (vinyl 2-ethylhexyl ether), which have the same glass transition temperature, fall on a common curve characteristic of the temperature of measurement. Apparently, the Tg is a major factor in correlating the dynamic mechanical behavior of these elastomers. The size and shape of the alkyl group appear to be reflected primarily in their effect on the Tg. Polysulfidic crosslinks are not essential for the attainment of high tensile strength in natural rubber vulcanizates cured with a sulfur-diphenylguanidine system. Data for the samples which had lost significant amounts of polysulfidic crosslinks by reaction with triphenylphosphine fitted a curve of tensile strength as a function of 300 per cent modulus for the control samples.

Preparation and characterization of post-derivatives from functional polystyrene (ATRP) with p-nitroanilineazomethine phenol and their thermal and optical study

e-Polymers ◽  
2006 ◽  
Vol 6 (1) ◽  
Author(s):  
Xifei Yu ◽  
Guo Zhang ◽  
Tongfei Shi ◽  
P.K. Dutta ◽  
Lijia An
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Liquid Crystalline ◽  
Gel Permeation Chromatography ◽  
Side Chain ◽  
Scanning Calorimetry ◽  
Xrd Study ◽  
Covalently Linked

AbstractThe functional polystyrene, (Cl-PS)2-CHCOOCH2CH2OH (designated as XPSt and coded P2) was prepared by ATRP at 1300C using CuCl and bipyridine as catalysts, 2,2-dichloro acetate-ethylene glycol (DCAG) as multifunctional initiator and THF as solvent. 4-Nitoroaniline azomethine-4’ phenol (P1) as chromophores were covalently linked to the functional end groups of the polymer by using simple displacement reaction. The functional polystyrenes, namely XPSt (P2) and (PS)2-CHCOOCH2CH2OH, designated as X-PSt and coded P3 and their post-derivatives, namely, DXPSt (P4) and DX-PSt (P5) respectively were characterized by IR, NMR and UV spectroscopies, gel permeation chromatography (GPC) and thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), polarising optical microscopy (POM) and XRD studies. DSC showed that incorporation of chromophores in the side chains of polymers towards the polystyrene moiety increases the rigidity of the polymer and subsequently, its glass transition temperature; however the incorporation of side chain towards the alcoholic functional group decreases the glass transition temperature. The post derivatives do not play any significant role to increase the thermal stability (TGA). There was evidence for liquid crystalline properties in the resulting polymer derivative DXPSt (P4) as observed from POM study, which defines the alignment of chromophores into the polymers. The XRD study shows crystalline behaviour of the polymer derivative, P4. The polymer derivative, DXPSt (P5) does not show such behaviour and this may be due to the bonding of azomethine towards the short chain alcoholic telechelic alcoholic sides of the copolymer.

Investigation of thermochromism in a series of side-chain, liquid-crystalline, azobenzene-containing polymers

2004 ◽  
Vol 82 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Stephan Freiberg ◽  
François Lagugné-Labarthet ◽  
Paul Rochon ◽  
Almeria Natansohn
Keyword(s):  
Thin Films ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Liquid Crystalline ◽  
Electronic Absorption Spectra ◽  
Side Chain ◽  
Hypsochromic Shift ◽  
Vis Spectroscopy ◽  
Thermochromic Properties

The thermochromic properties of a series of liquid crystalline polymethacrylates, containing azobenzene side-chains with variable spacer lengths, were investigated. Annealing the amorphous polymer thin films above the glass transition temperature results in a rearrangement of the azobenzene moieties, causing a hypsochromic shift in the electronic absorption spectra. A detailed investigation of the spectral shift was performed by in situ UV–vis spectroscopy and indicated the formation of H-type aggregates by the side-chain chromophores above the glass transition temperature. The rate at which the hypsochromic shift occurs is faster for polymers with shorter spacers since their high glass transition temperature results in a higher thermal energy during the thermochromic effect. Experimentally determined activation energies show that the aggregation occurs primarily due to side-chain relaxation (β-relaxation) and main-chain relaxation (α-relaxation). Further annealing above the isotropization temperature resulted in the onset of deaggregation and in most cases showed that the chromophores were freed from the ordered state.Key words: liquid-crystalline polymer, thermochromic properties, chain relaxation, aggregation, thin films, azobenzene mesogens.

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