1994 рік

A thermodynamic simulation of the phase separation process in a modified thermosetting polymer was carried out. The polydispersity of the generated polymeric species was taken into account in the frame of a conventional Flory-Huggins equation. The example considered in the simulation was a diglycidyl ether of bisphenol-A (DGEBA)-ethylenediamine (EDA), epoxy-amine polymer, modified by the addition of 15 wt% castor oil (monodisperse modifier). The size increase of the oligomeric species and the corresponding decrease of the entropic contribution to the free energy of mixing made a modifier-rich phase (B-phase) segregate from the matrix (a-phase) at a particular conversion level. The B-phase is enriched in monomers and low-molecular-weight species of the polymer distribution. This produces a significant decrease of the B-phase conversion with respect to the overall conversion. The monomer with the smaller size and functionality is preferentially segregated into the B-phase, leading to a stoichiometric imbalance. When a semipermeable B-phase is assumed, i.e. no oligomeric species are allowed to transfer to the or-phase, a secondary phase separation inside the B-phase is generated. This leads to a sub-matrix (6-phase) which is rich in modifier, and a sub-segregated phase (),-phase) which is rich in thermosetting polymer. This process may continue well beyond the gelation of the a-phase, due to the low conversion level of the B-phase at the time the or-phase gels. The thermodynamic simulation explains some recent experimental observations in systems of commercial interest.

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Monte Carlo generation of polymer chains allows evaluation of the steric partition coefficient, K, for any pore shape and any chain flexibility. This in turn enables the chromatographic radius of macromolecules, Re, to be defined as the radius of a sphere with the same K value and allows the ratio Rc/R, to be studied. R, is defined as the radius of the sphere with the same product [r/]M, where M is the molar mass and It/] the intrinsic viscosity. Rc is shown to depend on the pore geometry. For a given pore geometry, Rc/R ~ is not strictly independent of the flexibility and the relative thickness of the macromolecule. Experimentally, for flexible polymers, the so-called universal calibration is often found to work well. However, simulations show that the universal calibration is not strictly valid and deviations are expected in particular when the global flexibility of standard and sample are different.

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Using an on-line, continuous, single-capillary viscometer and a refractometer in gel permeation chromatography (g.p.c.), two sets of polymer standards (polystyrene and polyisobutene) of narrow distribution and low/median molecular weight were investigated for their intrinsic viscosities. The experimentally obtained intrinsic viscosity versus molecular weight relations of the polystyrenes conform well to the Mark-Houwink- Sakurada (MHS) equation and the Dondos-Benoit (DB) equation in the molecular-weight ranges considered. The deduced viscometric constants were found to be very close to the values reported in the literature. By using both number-average and weight-average molecular weights, the experimental intrinsic viscosity versus molecular weight relations of the polyisobutenes were found to conform to the MHS equation or the DB equation in the molecular-weight range studied. This characteristic of the polyisobutenes provides easy access to the indirect g.p.c, calibration introduced by Dondos.

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Allyl alcohol and allyl alcohol containing the polyoxyethylene unit were found to react with fluoroalkanoyl peroxides to afford the corresponding fluoroalkylated allyl alcohol oligomers via a radical process under very mild conditions. In particular, fluoroalkylated allyl alcohol oligomers containing the polyoxyethylene unit were shown to be effective in reducing the surface tension of water, and to be applicable for new non-ionic fluorinated amphiphiles.

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An empirical equation is presented to describe the mobility of polymer melts as a function of temperature and pressure. This is accomplished in terms of the order parameter in a hole theory and temperature, combined in a Fulcher-Tammann-Hesse type equation. Experimental data for various amorphous polymers are described successfully

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Mixtures of nylon 6 and lightly sulfonated polystyrene ionomers (M-SPS, where M = Li, Mg, Zn or Mn) exhibit lower critical solution temperature (LCST) phase behaviour. Miscibility was a consequence of specific complex formation between the metal sulfonate and amide groups. The interactions were strongest when the cation was Zn 2+ or a transition metal such as Mn 2+. The LCSTincreased as the sulfonation level increased and as the cation was changed in the order of Mg 2 ? < Li ? < Zn 2 ? < Mn 2 ?. Despite large differences in the molecular weights of the two polymers, the liquid-liquid phase diagrams were symmetric about the 50/50 composition. The glass transition temperature of miscible blends showed a positive synergism due to the physical network resulting from intermolecular complex formation. Although both polymers were hygroscopic, the blends exhibited less water absorption than either of the two components alone, which was a consequence of the complex removing sites for hydrogen bonding of water. The amount of water absorption decreased when the cation was varied in the order of Mg2+> Li+> Zn 2 +.

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The influence of reaction conditions and temperature on the free radical copolymerization of furfuryl methacrylate with N-vinylpyrrolidone, initiated by 2,2'-azobisisobutyronitrile (AIBN) is studied. The initiation step is promoted by the thermal decomposition at 50°C of the AIBN molecules in N,N-dimethylformamide (DMF) solution or photochemically at 0 and 40°C in bulk. The variation of the average composition of copolymer chains with the conversion for two different compositions of the monomer feed, f~=0.02 and 0.50, is analysed from the classical integrated copolymerization equation. Since the reactivity ratios of this pair are very different, rF=3.92 and rp=0.004, a simplified approximation of the integrated Skeist's equation is proposed. The experimental data obtained under different experimental conditions fit adequately the theoretical predictions, suggesting that the reaction medium (solution or bulk) or initiation technique (thermal or photochemical) do not affect the average composition of the copolymer chains at different conversions. However, the variation of the cumulative composition of copolymer chains with the degree of conversion is very sensitive to the initial composition of monomer feed. In addition, the average rate of copolymerization seems to be also dependent on the feed composition

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The normal X-ray fibre pattern of polyacrylonitrile (PAN) consists of just two sharp equatorial peaks (dl ~ 0.53 nm and d2 ~ 0.30 nm), and very diffuse meridional and off-axis scattering. This has been attributed to a hexagonal packing of chains, with no periodicity along the chain axis. In this work, we have investigated the effect of a tensile stress on this fibre pattern. It was found that both dl and d2 decreased with increasing stress, but the ratio d~/d 2 remained constant within experimental error at x/~/1. This indicated that the 'molecular rods' decreased in diameter on application of the stress, but their packing remained essentially hexagonal. The normal meridional scattering from PAN shows a two-component broad peak; when stress was applied, there was no shift in the positions of either component, but there was a transfer of intensity from high to low 20 values. This was also consistent with a slight extension of the rod. By adopting a simple model of extending rods, it was possible to compute an X-ray stress-strain curve and a modulus from the change in the two equatorial peaks

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Room temperature ultrasonic surface modifications of poly(vinylidene fluoride) (PVDF) with germanium phthalocyanine dichloride in the presence of lithium lead to the formation of Ge-C bonds on the PVDF surfaces. Based on the analysis of attenuated total reflection Fourier transform infra-red, X-ray photoelectron spectroscopy (X.p.s.) and ultraviolet-visible (u.v.-vis.) spectra of the PVDF modified surfaces, it is shown that these species are chemically bonded through a central metal atom. This is demonstrated by the appearance of the 613 cm- ~ band due to the Ge-C stretching mode, and a parallel disappearance of the C-F and C-H modes at 764, 1182 and 1209 cm- ~. Although more data are needed to establish mechanistic aspects of these reactions, X.p.s. and u.v.-vis, spectral analyses also indicate a removal of HF groups from the PVDF surface and the formation of C-Ge bonds.

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Miscibility in the crystal phase was investigated for blends between two types of poly(vinyl alcohol)s (PVAs) with different syndiotacticities, 54 and 58 mol% of diad content. They were basically in isomorphic relation with each other, and were designated as atactic (a-) PVA and syndiotacticity-rich (s-) PVA, respectively. The melting temperature measured by differential scanning calorimetry and the crystal dispersion temperature obtained by thermomechanical measurements were used to describe the phase structure of the blends. A cocrystallized phase was found with miscible amorphous phase. Phase separation into a-PVA-rich and s-PVA-rieh crystal phases was found locally at blend compositions with small contents of s-PVA. Analysis of these coexisting crystal phases by using a drawing and relaxing method was shown to be useful for discussion of the two structures in terms of the excess free energy of each crystal phase.

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