1992 рік

2-Isopropenylnaphthalene (2-IPN) and 2-vinylnaphthalene (2-VN) were polymerized in toluene with sec-butyllithium initiator. For 2-IPN, equilibrium monomer concentrations were determined, as well as the enthalpy, entropy and 'absolute' ceiling temperature, for its polymerization. Densities of both polymers were measured and their solubility parameters were calculated. They are, respectively, for 2-IPN, 1.105 g cm - 3 and 9.2 cal 1/2 cm - 3/2, and for 2-VN, 1.108 g cm - 3 and 9.4 cal 1/2 cm- 3/2.

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Single crystals were prepared from poly (phenyl ethyl ketone) (PEK) oligomers and compared with those of the corresponding polymer with respect to morphology, electron and X-ray diffraction patterns. The present comparison shows a drastic change in morphology when going from the extended chain oligomer to the folded chain polymer, the regular, lozenge-shaped crystals of the oligomer degenerating into irregular, knobbly laths for the polymer. At the same time the diffraction patterns are becoming more poorly defined, the reflections broadening and shifting to smaller angles (these effects being largest along the a direction) all indicating reduced lattice perfection. All these effects, the degeneration in the morphology and lattice order, must clearly be associated with chain folding in the polymer. The above is in sharp contrast with the behaviour of the paraffin-polyethylene system where the onset of chain folding with increasing chain length has no qualitatively noticeable effect on morphology and lattice order. We envisage the effects in PEK arising due to the more bulky and stiffer character of the chains which, while folding for kinetic reasons, cannot do so over a similarly short distance as in the paraffin-polyethylene system or other flexible polymers. The larger fold-spans then require larger volume along the fold surface exerting stresses on the underlying crystals. These stresses, being cumulative, will expand and distort the lattice and eventually set a limit to the size of the coherent structure entity in the growing crystal leading to the observed irregular, knobbly morphology. We venture to generalize this scheme to other members of main chain aromatic polymers, and beyond, to all regular polymers which crystallize slowly and with poorly defined morphologies with the difficulty in folding being the common factor.As a further step, we also invoke the degenerate morphologies of copolymers of otherwise fully flexible chains where exclusion of crystallographically incompatible comonomer units (e.g. branches)

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The preparation of poly(p-phenylene vinylene) specifically labelled at the vinylene positions is herein described. The extent of deuteration is estimated by i.r. spectroscopy, and the mechanism of hydrogen/deuterium exchange during the polymerization process is discussed

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The pressure-volume-temperature (PVT) properties of a number of polymer liquid samples as a function of molecular weight have been investigated. The polymers studied included polyethylene (PE), poly(dimethyl siloxane) (PDMS), poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG). The properties of the end-groups and their effect on the density, compressibility, thermal pressure coefficient and expansivity as a function of their concentration are discussed. The specific volume exhibits a clear 1/M, dependence for those molecules with weakly interacting end-groups, i.e. PE and PDMS. The specific volume is found to be independent of M, for PEG and PPG, which can hydrogen-bond to each other. The data sets have been compared using equation-of-state theories

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The synthesis of epoxy-terminated polystyrene was studied by high performance gel permeation chromatography and titration of sodium hydroxide in the presence of hydrochloric acid. The effect of the terminated reaction was also studied. The introduction of an end-capping reagent, cyclosulphide propane, had a retarding effect on the side reaction, whereas ring opening substances had an end-capping effect linking with carbanionic living polystyrene. The properties of the products would be expected to differ from those of the oligomers without capping, because carbanionic living polystyrene promotes thermal stability rather than an end-capping reagent character; this was deduced by acid-base titration and gel permeation chromatographic analysis in tetrahydrofuran.

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The morphology of crystallites in a low molecular weight copolymer of 1,4-oxybenzoate and 2,6-oxynaphthoate units is investigated with transmission electron microscopy (TEM), scanning electron microscopy (SEM) and small-angle X-ray scattering. Selected-area electron diffraction patterns exhibit aperiodic meridional maxima, indicating random sequencing of units along the chains, while sharp equatorial reflections suggest some level of crystallinity. Strongly diffracting crystalline entities, whose number and dimensions depend on thermal history, can be imaged in dark-field TEM. They orient with their thin axis parallel to the molecular director. Similar crystallites are also observed in SEM micrographs of chemically etched bulk samples, and give rise to a small-angle reflection on the meridian of an X-ray fibre pattern. The reflection corresponds to the mean distance between crystallite centres. Crystal thicknesses determined from mean crystallite spacings and percentage crystallinities (measured from wide-angle X-ray scattering) are compared with predictions for various models. The data clearly indicate lateral register between aperiodic sequences, which is the basis of non-periodic layer crystallites.

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Isothermal crystallization of a pure n-paraffin at temperatures near its melting point results in extended chain crystals whose growth rate-crystallization temperature curve exhibits a maximum and whose melting point appears to be lower than that expected. This behaviour can be explained in terms of polymer crystal nucleation theory with a model in which registration of chain ends is not perfect resulting in a transient layer of cilia on the crystal and to an end surface free energy a' for that ciliated surface. The presence of the maximum, however, requires a decreasing nucleation rate with decreasing temperature--contrary to customary expectations. This can be shown to be a consequence of the crystallization of (essentially) fixed length stems : the combination of the relevant nucleation and backward reaction terms thus giving rise to the maximum. The temperature at which the maximum occurs is a function of the degree of imperfection at the end surface.

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Copolymers of N,N-dimethylacrylamide (DMA) with C 1-C4 alkyl and alkoxyethyl acrylates form aqueous solutions with lower critical solution temperatures (LCST) between 0 and 100°C. As weakly crosslinked gels they exhibit strong cloud points and volume shrinkage with rising temperature. Copolymers of DMA with higher alkyl acrylates are insoluble down to 0°C, but form hydroplastics and hydrogels with strong cloud points. The LCST is determined by the hydrophobicity and amount of comonomers. The ability of these copolymers to form aqueous solutions with LCSTs can be attributed to a random copolymer structure, which allows an abrupt phase transition from a fully hydrated to a predominantly hydrophobically interacting polymer

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The density of an amorphous polymer near its interface with a flat solid surface was investigated using neutron reflectometry. Bulk poly(methyl methacrylate) with a monodisperse molecular weight in contact with a silicon single crystal wafer was the first system studied, and the emphasis was placed on the temperature dependence of the interface density profile. The temperature range studied encompassed the glass transition temperature of the polymer and a reversible change in the density profile was discovered.

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Toughened epoxy networks based on diglycidyl ether of bisphenol A (DGEBA) prepolymer, 4,4'-diamino diphenyl sulphone (DDS) curing agent and epoxy-terminated butadiene-acrylonitrile copolymer-2,2'-bis(4- aminophenoxy)phenyl propane (ETBN-BAPP) adduct were prepared using a two-step process and compared to DGEBA-DDS-ETBN networks prepared using a one-step process. The kinetics of the reaction was followed by size exclusion chromatography and differential scanning calorimetry: the extent of reaction was found to be higher at the cloud point and lower at gelation in the two-step process. The morphology was studied by transmission and scanning electron microscopy. For the same initial rubber content, large differences were observed: when a two-step process was used, the dispersed particles showed irregular contours with a broad diameter distribution, but the volume fraction of dissolved rubber in the rigid matrix was independent of the process. The effect of the cure cycle on the morphology, mechanical and viscoelastic properties was examined. All of the samples had the same impact strength (= 30 kJ m-2) with an identical modulus and glass transition temperature. These results confirm that the most

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