1999 рік

Holographic interferometry is applied to precursor films to determine their biaxial stresses. The theory of membrane deformation and vibrations is briefly reviewed to establish the relationship between stress and measured frequencies. Membranes for vibrational analysis are prepared using a circular precursor polymer. The biaxial stresses of the PHA, PAA, and 50/50 PHA/PAA are fairly constant with increasing frequencies: 6.85–7.61 MPa, 27.01–27.70 MPa, and 11.13–12.08 MPa, respectively. Regardless of the vibration modes, the biaxial stresses remain constant.

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The polymerization of new sulfur containing spiro orthocarbonates with the ability to undergo double ring-opening is reported. Various initiators were used in the cationic polymerization study, and the polymer structure determined. The polymerization is proposed to occur via a controlled tandem double ring-opening mechanism.

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The kinetics of ethylene polymerization catalyzed by Cp 2ZrCl 2 – different aluminoxanes was studied. More than one type of active site was presented in the polymerization reaction based on an analysis of the GPC curves. A multiple active sites kinetic model (MSmodel) was proposed. Good agreements in polymerization rate and variation of polydispersity were achieved for fitting the kinetic profiles with the MSmodel.

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The controlled radical polymerization of methyl methacrylate (MMA) and 2-hydroxy ethyl methacrylate (HEMA) were successfully performed at ambient temperature. MMA was polymerized in acetonitrile with ethyl-2-bromopropionate (EPN-Br)/CuCl/2, 2 0 -bipyridyl (bpy) at 40°C. The final polymer was with a narrow molecular weight distribution (Mw/Mn < 1.5) and controllable molecular weight. The controllable nature might have been contributed mainly by the high value of dielectric constant of acetonitrile. The bulk polymerization of HEMA, a monomer with a high value of dielectronic constant, can be well controlled with EPN-Br/CuCl/ bpy at 20°C. The halogen terminated PMMA and PSt were then used as macroinitiators to copolymerize with some other monomers. As a result, some block copolymers, such as PMMA-b-PSt, PMMA-b-PHEMA and PSt-b-PHEMA, were synthesized.

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The relaxation times of the conformational rearrangements of the main-chain segments of a liquid crystalline side-chain polymer was determined from differential scanning calorimetry experiments in the temperature interval around and below its glass transition. Phenomenological models with fitting parameters were used to evaluate the temperature dependence of the relaxation times and the form parameter of the relaxation times distribution. These parameters were compared with its counterparts in the dielectric a relaxation process which appear in the temperature interval immediately above the calorimetric glass transition. For the temperature interval below the calorimetric glass transition the differential scanning calorimetry (DSC) results were compared with the dielectric results obtained by the thermally stimulated depolarisation technique.

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Cyclic oligoamides and alternating oligo(amide±ester)s have been prepared by a novel polymer supported method in yields ranging from 28±48%. In the case of the synthesis of cyclic oligo(undecanamide±undecanoate)s the cyclics obtained ranged in size up to ones having at least 288 ring atoms. The polymer beads recovered at the end of the syntheses contained material accounting for 25±48% of the bound starting monomers. The nature of this material is unclear but a significant fraction may be large cyclics wrapped round the network. Experiments to clarify this last point are in hand.

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It is shown that for diolic perfluoropolyethers having short chain lengths the ''anomalous’’ (non monotonic) relationship between isothermal melt viscosity and molecular weight, reported in recent papers, is not anomalous at all but fully explainable when one takes into account the fact that the glass transition of the samples Tg is itself a function of the molecular weight. For low molecular weight polymers the viscosities have to be compared not at the same T but at the ''normalised’’ temperature T ⫺ Tg.

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Reactive polyimide containing hydroxyl functionalities was prepared from the reaction of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride and 3,3 0 -diamino-4,4 0 -dihydroxybiphenyl. Commercial epoxy resin was cured in the presence of different ratios of the reactive polyimide, giving a series of polyimide modified epoxy films. The transparent films had excellent solvent resistance. The tensile measurements of the films showed that, with the increase of the polyimide content, tensile modulus of the film increased but there was almost no change in the elongation at break. Viscoelastic measurements showed that glass transition temperature shifted with the increase of the polyimide content; 1278C for 13.5%, 2208C for 29.4%, 2608C for 45.4% and 2908C for 62.5%. Thermogravimetric analysis showed the increase of the thermal stability with the increase of the polyimide content.

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Local intramolecular mobility in regular linear polyesters with exible siloxane and more rigid ester aromatic fragments providing in some cases LC state was studied by dielectric spectroscopy. The dielectric transitions related to the local mobility in the ester aromatic fragment were observed. It was shown that two local relaxation processes (b 0 and b 00 ) with different mechanisms of mobility took place in these systems. One of them, the b 00 process, having the shortest relaxation times (t , 10 27 s) is connected with the motion of ester groups and phenyl rings. It is determined only by intramolecular interactions. The second local process, b 0 , re¯ects the motion of the polar ester group including the central part of the ester aromatic fragment (t , 10 21±10 24 s). This motion can be realized at the beginning of ¯ipping of the aromatic ring. Parameters of the b 0 process depend on intra- and intermolecular interactions.

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A lyotropic solution of hydroxypropylcellulose in m-cresol has been studied in channel flows containing inhomogeneous shearing kinematics (planar Poiseuille), or mixed shearing and extensional kinematics (slit-contractions and expansions). We have used X-ray scattering as a probe of orientation, to test and extend previous birefringence measurements in the same system [Bedford BD, Burghardt WR. J Rheol 1996;40:235]. Orientation changes dramatically in contraction and expansion regions, which cannot be explained by changes in superficial velocity alone. Calculations using Ericksen’s Transversely Isotropic Fluid model show that the addition of a modest amount of extension to otherwise shearing kinematics can influence alignment by perturbing tumbling orbits either into or out of the shear plane, in addition to inducing a transition from tumbling to flow aligning behavior. Away from the centerline, orientation is rotated away from the downstream direction, presumably due to streamline bending near the contraction and expansion. However, the degree of rotation is different in contraction and expansion flows.

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