1994 рік

Poly(glycidyl methacrylate) and water-soluble copolymers of glycidyl methacrylate with N-vinylpyrrolidinone were prepared by free-radical-initiated solution polymerization in chloroform. Polymer microstructure was investigated by high-field 1H and 13C nuclear magnetic resonance (n.m.r.), IH decoupled 13C n.m.r., 1H-13C correlation n.m.r, and 135 DEPT (distortionless enhancement by polarization transfer) n.m.r. The combined use of these techniques allowed unequivocal ~3C and 1H n.m.r, assignments of carbons and protons to be established. Copolymer composition was thus determined from IH n.m.r.

Детальніше...  

Several masked disilene monomers, i.e. 1-phenyl-7,8-disilabicyclo[2.2.2]octa-2,5-dienes, were prepared regioselectively by the reaction of unsymmetrically substituted dichlorodisilanes with biphenyl radical anions. These monomers gave polysilylenes with highly ordered structures. Important information on the tacticity of polysilylenes was obtained by detailed analysis of n.m.r, spectra. The mechanism of monomer formation as well as the polymerization mechanism are discussed

Детальніше...  

Wide-angle X-ray diffraction analysis of poly(vinyl alcohol) (PVA) fibres shows that the amorphous scattering at 20 = 20 ° concentrates on the equator, and the degree of concentration becomes stronger with increasing draw ratio. This indicates that the amorphous chains must be highly oriented in the highly drawn fibres. Small-angle X-ray scattering (SAXS) analysis shows that the meridional SAXS intensity of the highly drawn fibres decreases with increasing draw ratio, indicating that the amorphous chains are packed more densely. On the other hand, a new meridional diffraction peak appears at 20 = 35.5 ° (d = 2.52 A) and the intensity becomes stronger with increasing draw ratio. The 20= 35.5 ° diffraction peak is broader than the (020) diffraction (d = 1.26 ~.) peak. The thermal expansion coefficient estimated from the 20 = 35.5 c peak is positive, while that estimated from the (020) peak is negative above ca. 120°C. These results suggest that this meridional peak (20= 35.5 °) is not the (010) diffraction, which never appears in the normal PVA crystal but might appear in some disordered crystals, but is due to the intrachain scattering of a single amorphous chain with an almost planar zigzag conformation.

Детальніше...  

The crystal structure of poly[oxy-l,3-(2-cyanophenylene)-oxy-l,3-phenyleneJ was determined by X-ray diffraction. The structure belongs to the monoclinic system with the space group P21/a, and has unit cell constants of a=8.62A, b=13.07/~, c (chain axis)=9.03 A and fl=99.0 ° (second setting). There are four monomer units (i.e. four chains) in the unit cell. The molecules in the crystal are constricted by 0.5 A per monomeric unit from the fully extended conformation, and the planes of the adjacent benzene rings lie at an angle of ~ 90 ° to each other. The longitudinal elastic modulus of the crystalline component was estimated to be 44 GPa from the X-ray diffraction measurements. Because the polymer is not fully extended, this elastic modulus is not very high.

Детальніше...  

Ammonium salts of pre-gelled epoxy networks, in the form of spherical clusters, were prepared by the addition of hydrogen chloride in methanol solution to partially cured bisphenol A diglycidyl ether/ethylene diamine epoxy resins. The formation of ammonium salts resulted from the interaction of hydrogen chloride with the amine groups of the pre-gelled epoxy networks, as indicated by their infra-red and solid-state 13C n.m.r, spectra and X-ray diffraction patterns. By increasing the time allowed for branching reactions or by increasing the concentration of branched molecular chains, the spherical clusters tended to form as agglomerations of ribbon textures, which were then demonstrated to be associated with the packing of the branched molecular chains. The packed networks could also be detected through X-ray diffraction studies of the post-gelled epoxy resins.

Детальніше...  

Aromatic diisocyanates, such as phenylene-1,4-diisocyanate have proved to be very effective coupling agents of ct-X functional co-hydroxy poly-e-caprolactone (PCL). Very high yields (> 98%) have been observed in the presence of triethylamine, in tetrahydrofuran. Accordingly ct,co-X functional PCL of a two-fold molecular weight have been obtained and characterized by size exclusion chromatography and nuclear magnetic resonance spectroscopy. More interestingly, the same coupling reactions have been successfully carried out when applied to the precursor living polyester (X-CHE-O-PCL-O-AIEt2) rather than to the chains recovered after hydrolysis of the living propagating sites. Terephthalic acid chloride has been the most efficient coupling agent and, in the presence of pyridine, has yielded quantitatively the expected ~,co-functional polyesters

Детальніше...  

The propagation and termination processes in free-radical copolymerization of styrene (1) and ethyl acrylate (2) in the bulk at 40°C were examined by the rotating-sector technique. A marked penultimate-unit effect was observed for the terminal radical 1 (sl =0.27), in conformity with the prediction of the stabilization energy model. The concentration of the terminal radical 2 in this system was too small for the details about this radical to be elucidated. The termination process conforms to the notion of diffusion control, but conclusively not to that of chemical control. The experimental data, however, were not described very accurately by the North diffusion model. An alternative simple, no-parameter model, conceptually analogous to the Ito O'Driscoll model, was proposed and found to describe the experiments better

Детальніше...  

The reaction between carbon monoxide and the Ti-polyethylene bond was investigated using a stopped-flow (short-time) polymerization method which provides quasi-living polymers with very low molecular weights. Ethylene polymerization was conducted with a typical homogeneous Cp2TiC12-methylaluminoxane catalyst. The Ti-terminated polymers were introduced into toluene saturated with carbon monoxide or containing laC-enriched carbon monoxide at -78°C. The mixture was gradually heated up to room temperature, and a small portion of the reaction mixture was taken out at - 78°C, 0°C and room temperature to analyse the structure of each polymer by FTi.r., gel permeation chromatography, 1H n.m.r, and 13C n.m.r. It was found from these analyses that carbon monoxide is incorporated into the polymer mainly as a ketone carbonyl.

Детальніше...  

The preparation of polystyrene macromonomers containing a norbornene unit and their living ring opening metathesis polymerization (ROMP) to produce comb graft copolymers is described. The ROMP was initiated by the well defined Schrock initiators, Mo(~---CHR)(=NAr)(OR')2, where R is (CH3)3C- or C6HsC(CH3)2-, Ar is 2,6-diisopropylphenyl and R' is (CH3)3C-. Well characterized macromonomers and comb graft copolymers with polystyryl grafts with average degrees of polymerization (DPs) of 4, 7, and 9 were successfully produced. The graft copolymers exhibit single mode molecular weight distributions and narrow polydispersities. Attempts to prepare copolymers with longer polystyryl grafts gave products which exhibited bimodal molecular weight distributions in which one component of the distribution had the same retention time as that of the macromonomer, this observation is rationalized in terms of steric inhibition of the ROMP of such macromonomers.

Детальніше...  

A number of phosphoranimines were prepared via the Staudinger coupling of the suitably substituted phosphite with trimethylsilyl azide. These compounds were polymerized under various conditions using fluoride initiators and then characterized by 1H and 31p nuclear magnetic resonance, size exclusion chromatography versus polystyrene standards, and differential scanning calorimetry. The condensation by-products of the polymerization were analysed by gas chromatography-mass spectrometry. Mechanistic details of these polymerizations are also discussed. N-Blocked phosphoranimines were prepared and used as chain terminators to control the molecular weights of these polymers. Several random copolymers were produced by the simultaneous polymerization of two phosphoranimines, and the first reported block copolymers were synthesized by the homopolymerization of one monomer followed by the subsequent addition of a second. The synthesis of the first soluble aryl-substituted polyphosphazenes via the phosphine azide route is also discussed

Детальніше...