1994 рік

Novel copolymers of poly(ether sulfone) (PES) containing ring trifluoromethyl groups have been synthesized by starting from trifluoromethyl aryl sulfone monomers. Materials incorporating CF 3 groups ortho to the ether bond have low molecular weights due to the instability of the CF 3 group in the polymerization process. Higher-molecular-weight materials, involving CF 3 groups ortho to the sulfone group, can be prepared: these materials show a number of modified properties when compared to PES, such as crystallinity and a lower uptake of water, although they are also somewhat less thermally stable

Детальніше...  

Copolymers of methyl methacrylate with acrylophenone, tert-butyl acrylophenone and p-chloroacrylophenone have been photolysed in benzene solution and the structures of the unsaturated end groups in the oligomeric products determined by n.m.r. It is shown that photodegradation takes place mainly by a Norrish Type I process, similar to that which occurs with methyl methacrylate-methyl vinyl ketone copolymers, but that there is a minor, non-classical Type II component which is most apparent in methyl methacrylate-pbutylacrylophenone.

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A strong positive correlation exists between the flammability of acrylonitrile-butadiene-styrene (ABS)/poly- (vinyl chloride) (PVC) blends and the amount of PVC present.

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New oligomeric polyurethanes have been prepared from polyether diols, chain extender and 4,4': dicyclohexylmethane diisocyanate or 4,4'-diphenylmethane diisocyanate, which are terminated with a mixture of 2-hydroxyethyl methacrylate (2-HEMA) and non-functional terminators such as n-propanol or technical hydroabietyl alcohol. The oligomers may be cured by electron beam or u.v. radiation to give pressure-sensitive adhesives.

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Block copolymers containing polyamide-3 as one constituent have been synthesized by anionic polymerization. The reaction conditions for the two blocks have to be quite different. Chemical heterogeneity of the products has been studied using thin-layer chromatography. The cyclohexane-insoluble parts of poly(styrene-b-acrylamide) and poly(ct-methylstyrene-b-acrylamide) with high incorporation rate of polyamide as well as the acetonitrile-insoluble part of poly(methyl methacrylate-b-acrylamide) are mainly block copolymers. Infra-red measurements confirm these results.

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Two samples of isotactic polypropylene (PP), with different treatment histories, were studied by carrying out a number of proton n.m.r, measurements, namely free induction decay (FID) and spin-lattice relaxation in both the laboratory and rotating frames. The results were subjected to detailed mathematical analysis, and are shown to yield information about the domain structure and intrinsic relaxation parameters. Inversion-nulled FID analysis shows that the samples contain a spatially resolved distribution of crystallinities, which is responsible for bi-exponential spin-lattice relaxation.

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Polyvinylphenol forms strong hydrogen bonds with fluoride to an extent dependent on the solvent environment. Remarkable changes in the Fourier transform i.r. spectra and the thermal behaviour of the polymer are observed on formation of strongly hydrogen bonded complexes which can be used as highly nucleophilic forms of the polymer suitable for derivatization

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Aggregation of poly(allylammonium) chloride (PAAH+C1 -) and sodium 1-octanesulfonate (Na+OcS -) has been examined by the energy transfer from 2-naphthalenesulfonate ion (2-NpS-) to 1-pyrenesulfonate ion (1-PyS-) using steady-state fluorescence spectroscopy. In aqueous PAAH+C1 - solution without Na+OcS -, both 2-NpS- and 1-PyS- are in an isolated state around the polyion under the conditions studied, indicating no energy transfer between them. In the presence of Na+OcS -, on the other hand, efficient energy transfer takes place between 2-NpS- and 1-PyS-. In such a system, the aggregate of PAAH + and OcS- is formed owing to the electrostatic interaction between PAAH* and OcS- and the hydrophobic interaction among OcS - ions bound to the polyion. Both 2-NpS - and 1-PyS - are incorporated in close proximity in the hydrophobic domain of the aggregate, which leads to energy transfer between them. The concentration at which the aggregation of PAAH + and OcS- occurs was about three orders of magnitude lower than the critical micelle concentration of OcS- alone. The fluorescence probe technique using pyrene has also been employed to monitor the aggregation.

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This paper describes the synthesis of poly[NS-(2-hydroxyethyl)-L-glutamine]( PHEG) by the aminolysis of poly(7-benzyi-L-glutamate) (PBG) with 2-aminoethanol. The effects of the temperature and addition of the bifunctional catalyst, 2-hydroxypyridine (2-HP), on the kinetics of aminolysis were studied. The results suggest that the aminolysis reaction takes place much faster with increasing temperature and an increasing amount of added catalyst. Moreover, chain scission, due to aminolysis of the amide bonds of the polymer backbone, can be minimized by the addition of the appropriate amount of 2-hydroxypyridine. These data demonstrate the feasibility of the described method to prepare PHEG derivatives with well controlled molecular weights

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A new technique to process ceramic/polymer grain boundary capacitors has been developed and demonstrated using BaTiO3 as the ceramic conducting phase and LaRC-TPI polymer as the insulating phase. The particles were characterized by transmission electron microscopy and the dielectric properties of the capacitors were measured at room temperature and 100kHz. The overall best composite grain boundary capacitor was made with 40vo1% polymer after milling the powder for I h. It had a dielectric constant of 58 and a dielectric loss of 0.01. The dielectric properties of the grain boundary capacitors could be manipulated by changing processing variables such as milling time and volume fraction of polymer.

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