1992 рік

The fluorescence has been measured in dilute solution and in glassy poly(methyl methacrylate) for polyesters in which 2,6-naphthalene dicarboxylate is the rigid unit, and (CH2)= (m=2-6) is the flexible spacer. Bichromophoric compounds in which the same flexible spacer connects two molecules of 2-naphthoate were also studied. The anisotropy in the rigid medium demonstrates the existence of intramolecular energy migration, which becomes more important as m decreases from 6 to 2. The F6rster radius is ~ 12 A in the bichromophoric compounds and 14 A in the polyesters.

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Fourier transform infrared spectroscopy (FTi.r.) and electron spin resonance spectroscopy (e.s.r.) have been used to follow the kinetics of the polymerization of methyl methacrylate to high conversion at 60°C. The FTi.r. absorbance at 6152 cm-~ was used to monitor the time dependence of the concentration of double bonds, and the concentration of the polymer-chain propagation radicals was monitored using the e.s.r. absorption spectrum. These data were analysed to obtain instantaneous estimates of the kinetic rate parameters for propagation and termination across the range of conversion, and of the initiator efficiency at high conversion. The kinetic parameters were found to be consistent with values obtained by other methods and with the predictions of recent theories.

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The effects of annealing on the mechanical properties of nylon-6,6 have been studied. Extruded, isotropic samples were annealed at temperatures in the range 60°C to 200°C for times up to 3 h (10800 s). It was found that significant increases in tensile modulus and small increases in strength were induced by annealing. The optimum annealing temperature was around 150°C, but annealing at 60°C appeared to produce more rapid improvements than at 100°C. Annealing at 200°C led to deterioration in mechanical properties. Specimens constrained to constant length during annealing were found to have less pronounced increases in modulus than unconstrained samples. These results are discussed in terms of possible microstructural changes.

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Wide-angle X-ray scattering procedures are utilized to study the local structure of isotropic and anisotropic aqueous solutions of hydroxypropyl cellulose (HPC). The X-ray scattering data for a systematic series of solutions with 0-100% w/v HPC are reported and these curves show distinct and significant variations as the concentration of HPC is increased. In particular, a diffuse scattering peak whose position (s ~ 0.34-0.54 A- 1 ) is composition dependent, develops in parallel with the formation of the anisotropic liquid crystal phase. There is no evidence to support the concept of clusters of HPC molecules in the anisotropic phase. The variations in peak positions and the synergistic nature of the scattering suggests that the water is largely associated with each HPC chain.

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Solid state 13C n.m.r, was used to study the phase heterogeneity of poly(phenylene sulphide), PPS, at room temperature. Relative fractions of crystal, rigid amorphous and liquid-like amorphous phases were determined from X-ray and thermal analyses. Samples containing very different fractions were examined using cross-polarization contact time and spin-lattice relaxation measurements. The optimum carbon/proton contact time for cross-polarization/magic angle spinning studies was found to be ~ 1000 #s. Peak intensity of the protonated carbons was studied as a function of delay time. A pronounced amorphous halo exists in the n.m.r, spectrum of PPS films containing a large fraction of liquid-like amorphous phase, and the halo decreases significantly with increasing delay time. A very insignificant halo exists in the n.m.r. spectrum of PPS containing a large fraction of rigid amorphous phase. We conclude that this halo is from the most mobile, liquid-like amorphous phase. Using spin-lattice relaxation measurements, we studied the dynamic heterogeneous phase behaviour of PPS. Here we find that from the standpoint of spin-lattice relaxation time, T1, 100% amorphous PPS shows phase heterogeneity at room temperature. The longest T1 is ~45s, corresponding to a mass fraction of 0.57. In semicrystalline PPS, spin-lattice relaxation measurements show a much larger amount of the material possesses longer relaxation time. The 7"1 of semicrystalline PPS ranges from 150 to 200 s, corresponding to mass fractions of 0.91-0.94. This indicates that semicrystaUine PPS is more nearly homogeneous: the crystals and most of the amorphous phase are very 'rigid' at temperatures far below the glass transition of PPS.

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The effects of various casting parameters were measured for films of novolacs (cresol-formaldehyde resins) containing pyrene groups either covalently bound to the polymer chain or physically dispersed in the novolac matrix. Aggregation of the dispersed pyrene was observed, as measured by excimer fluorescence and crystallite formation of the pyrene. The phase separation was enhanced in static-cast films over spin-cast films. Pyrene aggregation in films was also affected by the choice of casting solvent even though no significant solvent effects were observed for the tagged polymer or free pyrene in solutions of the casting solvents. A minimum in the plot of the excimer-to-monomer ratio for the films versus the dipole moment of the casting solvent occurred at about the dipole moment expected for the novolac. Pyrene aggregation appears to be more dependent on the interactions of the casting solvent and the host polymer rather than on the interaction of either with the pyrene itself

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The electropolymerization of methyl methacrylate and methyl acrylate was investigated. The reactivity ratios of the monomers in this electrochemically initiated reaction were calculated and found to be equal to 0.33 and 0.89, respectively. The composition of the monomer-electrolyte solution and the parameters of the electrocopolymerization-coating process, which provides formation of thin (submicrometre) even coatings on carbon fibres (CF), were found. Composites from CF coated with the methyl methacrylatemethyl acrylate copolymer showed an improved strain energy release rate (40-200%) and interlaminar shear strength (up to 20%) in comparison with specimens from untreated CF. A pot-life of more than 1 month for the monomer-electrolyte solution was achieved.

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Whilst the [WC16/SnMe4] initiating system leads to crosslinked polymers of dicyclopentadiene (DCP), a quasi-selective metathetic process can be carried out with [W(OAr)2CI4/SnMe4] as initiator to obtain soluble poly(DCP). The control of molar masses is carried out by transfer to acyclic olefins. By using unsaturated diesters as transfer agents, difunctional oligomers are obtained. The quantitative reduction of ester end groups leads to hydroxy-ended oligomers which could be used for chain extension by diisocyanate

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Sequence analysis of soluble copolymers of various compositions of vinylidene fluoride and tetrafluoroethylene is performed based on 19F nuclear magnetic resonance spectral intensities at very high field. A new strategy is proposed for the adjustment of a first-order Markov polymerization scheme to the experimental data. Previous line assignments are then discussed and minor lines arising from impurities can be eliminated

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Concentration-dependent phase separation into two polymer-containing liquid phases has been studied for the polymer pair poly(ethylene glycol) and dextran. Below the point of phase separation, the light scattering of polymer mixtures was considerably greater than for single polymers in solution. Also the viscosity of polymer mixtures was larger than the sum of the viscosity increments of polymer solutions. On the other hand, both heat capacity and density were additive in the one-phase region. The possible solvent structure in mixed polymer solutions is discussed.

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