摘要:

AbstractThe dilute solution properties of poly(2,6‐diisopropylphenyl methacrylate) (PDPP) in various solvents were studied by viscosity, exclusion chromatography and osmotic pressure measurements. The Mark‐Houwink‐Kuhn‐Sakurada relationships were established. The unperturbed dimensions, the rigidity factor σ, the characteristic ratioC∞ and the thermodynamic parameters were determined using the Stockmayer‐Fixman equation and from data in theta solvent (binary mixture). The rigidity factor of PDPP is abnormally high. The conformational behaviour of this polymer is analysed in terms of the effect of the side chain structure. The results are compared with other polymers of the

ISSN:0959-8103    

DOI:10.1002/pi.4990240102

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractPolyetherurethaneureas (PEUUs) were synthesised from polyethylene‐glycols (PEGs) of molecular weight 400, 600 and 1000, 4,4′‐diphenylmethanediisocyanate (MDI) and aliphatic diamine chain extenders, 1,3‐propanediamine (PDA) and 1,6‐hexanediamine (HDA). Polymer films were irradiated with 365 nm light at 293 K and the effects of polyether soft segment length and urea hard segment on photo‐oxidative stability were studied by following the variation in weight‐average molecular weight (Mw), gel formation and stress‐strain properties. Changes in ultraviolet and infrared spectroscopy were monitored on photo‐oxidation and hydroperoxide content determined. The soft segment length was increased by increasing the molecular weight of PEG from 400 to 1000 and hard segment structure was changed by variation of diamine. It was noted that the structure of urea and polyether soft segment length plays an important role in photostability of PEUUs. PDA chain extended PEUUs were more stable than HDA cha

ISSN:0959-8103    

DOI:10.1002/pi.4990240103

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe intrinsic viscosity of a polymer is traditionally measured with a capillary tube viscometer where the shear rate range is moderately high. Such method is valid when the polymers are non‐ionic and have low to moderate molecular weight. The viscosity‐shear rate curves obtained for dilute aqueous solutions of two high molecular weight polyacrylamides using two rotational viscometers indicate a strong shear‐dependent viscosity in the medium to high shear rate regions. The zero shear intrinsic viscosity of the polymers determined by extrapolation from the high shear rate region to the zero shear condition may result in large errors. Its implication in predicting the molecular weight of polymers using the Mark‐Houwink‐Sakurada equation is discussed. A rheological equation for intrinsic viscosity as a function of shear rate is

ISSN:0959-8103    

DOI:10.1002/pi.4990240104

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractDSC, TMA, hot‐stage microscopy and WAXS have been used to examine the effect of concentration of angular units and molecular weight on the thermal transitions of poly(p‐oxybenzoate‐co‐m‐phenylene terephthalate)s. Copolymers containing molar fractions ofm‐phenylenedioxy units between 0·20 and 0·30 are melt processable nematogenic materials. In contrast, poly(p‐oxybenzoate‐co‐p‐phenylene isophthalate)s remain nematogenic over a wider concentration range (0·20–0·40) of angular isophthaloyl units. Comparison of fibres produced from copolymers with the same fraction of angular units (0·25) indicates that those with isophthaloyl units have a higher modulus than those withm‐phenylenedioxy units. These differences are ascribed to differences in planarity of chains containing isophthaloyl andm‐phen

ISSN:0959-8103    

DOI:10.1002/pi.4990240105

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractPoly(ethyl methacrylate) (PEMA) containing small amounts of cholesteryl additives was studied by dielectric and dynamic mechanical spectroscopy. Dielectric data from pure PEMA and PEMA + additive systems were fitted to the WLF equation. Using the WLF constants obtained from the data for pure PEMA, theTo values for PEMA + additive systems were determined in order to get the best fit of the experimental points to the WLF curve. Values of tan δmax (dielectric and mechanical) for all the PEMA + additive systems shift to higher temperatures compared with that for pure PEMA. In the glassy region, the moduli of PEMA + additive systems are higher than that of pure PEMA. Viscometric studies of PEMA + additive systems indicate the presence of some interaction. FTIR spectra of the polymer + additive systems show no shift in carbonyl bond frequency. The shift ofTg to higher temperatures indicates that chain motion in this region is hindered greatly by these additives and the reason for this may be the fitting or aligning of the additive molecules in the polymer matrix

ISSN:0959-8103    

DOI:10.1002/pi.4990240106

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractVinyl chloride (M) was polymerized in the presence of a low molecular weight polybutadiene (S) at 60°C in the presence of x,x′‐azobisdiisobutyronitrile as initiator, which does not affect the transfer reaction.The raw material was fractionated for the purpose of separating the pure PVC homopolymer.The number‐average molecular weight of PVC homopolymer, determined by size exclusion chromatography (SEC), was used in Mayo's equation to obtain the value of the transfer constantCs, which was found to be 11. A simplified reaction scheme is given according to which it is possible to explain why the reaction yield decreases and the crosslinking density increases by increasing the [S]/[M

ISSN:0959-8103    

DOI:10.1002/pi.4990240107

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe appropriateness of pH‐stat methodology in the dynamic monitoring of the kinetics of hydrolysis of phosphate esters catalysed by alkaline phosphatase (from human placenta) has been studied. This methodology involves autotitration of the H+released or consumed during a given reaction time. The lack of specificity of the method, titrating the total H+, together with the known effect of the dissolution of environmental CO2on the reacting system, giving rise to carbonic acid, implies an overtitration of the H+released in the hydrolysis reaction. Because of this, parallel to each series of reaction kinetics, the dissolution kinetics of environmental CO2under working conditions are quantified with suitable blanks, thus enabling one to subtract them from the global kinetics of the release of H+. Although no background buffers are added to the reacting system in order to maintain a constant pH, the buffering capacity of the system itself obliges one to quantify it by calibrations in order to calculate the true release rate of H+in the reaction. These two principal limitations of the pH‐stat methodology, the dissolution of environmental CO2and the inherent buffering capacity of the system, can be partially mitigated by working within an inert atmosphere of N2and having a good knowledge of the acid/base characteristics of the reagents and reaction products, which together will permit the choice of a working pH range in which the second limitation will be negligible. Having studied theoretically the acid/base balances of the system in reaction, it is concluded that optimum working conditions for the pH‐stat methodology are between pH 8·5 and 11·0, since over this pH range the buffering capacity is null (thus eliminating the need for calibrations) and the stoichiometry of H+(nH+) is close to unity. These theoretical predictions have been confirmed experimentally with calibrations and measurements ofnH+at different pH

ISSN:0959-8103    

DOI:10.1002/pi.4990240108

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0959-8103    

DOI:10.1002/pi.4990240111

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0959-8103    

DOI:10.1002/pi.4990240114

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0959-8103    

DOI:10.1002/pi.4990240116

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY