摘要:

AbstractThe intrinsic viscosity of four poly(N‐vinylpyrrolidone) fractions in the molecular weight range from 2.75 × 104to 3.5 × 105was measured in a cosolvent mixture of water/sodium decyl sulphate with different sodium decyl sulphate concentrations below its critical micellar concentration. Measurements were made in the temperature range 25−40°C.The value of theaandKparameters of the Mark‐Houwink‐Sakurada equation were determined. The values obtained forawere in general high, as expected for good solvents. Using the Stockmayer‐Fixman equation with the data,KθandB, i.e. the short and long range interaction parameters respectively, were calculated, which showed the existence of a conformational change at 12.3 mM sodium decyl sulphate concentration, at all temperatures.The polymer‐solvent interaction parameterXfor the fraction of molar mass 3.5 × 105was

ISSN:0007-1641    

DOI:10.1002/pi.4980200602

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractDifferent techniques were used to analyse the reaction mechanisms and kinetics of the system 2,2‐[4‐(2,3‐epoxypropyl)phenyl]propane polycondensed with 4,4′‐sulphonyl‐dianiline in the temperature range 100−185°C. The results show the role of catalysts, of stoichiometry and of curing cycles in the reaction mechanisms and paths.Based on chemical balances of residual epoxy groups, and of hydroxy and ether groups formed, we have shown the effect of these functions on the thermal properties o

ISSN:0007-1641    

DOI:10.1002/pi.4980200603

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThe present work was undertaken to determine the influence of immobilization of acid phosphatase by entrapment in poly(2‐hydroxyethyl methacrylate) (poly‐HEMA) gels on the rate and duration ofp‐nitrophenyl phosphate hydrolysis. This enzyme was selected as model system for the sake of comparison with other immobilization techniques studied previously making use of natural polymers. Under certain conditions, catalyst inactivation induced by chemical agents employed during polymerization was very low. Activity recovery in the enzymatically filled hydrogels depends on acid phosphatase loading and attains a maximum at 2 mg per gram of support. The use of low molecular weight linear polymers as matrix fillers is advisable. The best results were achieved with poly(ethylene oxide) PEG 1500, but PEG 6000 and poly(N‐vinylpyrrolidone) PVP 10 000 are also effective. Bovine serum albumin (BSA) is useless. The highest value of activity recovery obtained was 24% that of free enzyme. Roughly 30% of enzyme is retained in active form in the hydrogel and works with an efficiency ranging from 97% to 90% depending on average particle size. The kinetic parametersKmandEasuggest the presence of a combined diffusive and enzymatic reaction‐controlling mechanism. Only a minor shift of optimum pH was observed. Both operational and storage stability are largely improved upon entrapping in

ISSN:0007-1641    

DOI:10.1002/pi.4980200604

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractIt is estimated that only between 30‐70% of the fertiliser applied in agriculture is used for plant nutrition, the rest is carried away by ground water or lost through nitrification‐denitrification. Apart from the economic loss due to wastage, severe environmental problems arise due to increasing nitrate concentrations in public drinking water. The research reports a method of binding the fertiliser urea into natural rubber thus forming a matrix of rubber encapsulated fertiliser. A special ‘split‐feeding’ mixing technique is necessary for a good product; also found important were mixing and vulcanisation temperatures with the optimum being in the 70−82°C range and 95°C

ISSN:0007-1641    

DOI:10.1002/pi.4980200605

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractAdsorption of polycarbonate (I) from dilute chloroform solution on to ‘clean’ platinum flags was investigated through the use of Iodide‐125 radio tracer. Coverage versus concentration plots produced a logarithmic dependence of coverage on polymer concentration. A new method for clinging solvent removal was employed which increased the reproducibility of the coating. Both the effect of molecular weight and thermal stability of the polymer were investi

ISSN:0007-1641    

DOI:10.1002/pi.4980200606

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractKinetic models for describing the time dependence of the polymerization rate and active centre concentration for high activity Ziegler‐Natta catalyst systems are discussed. It is demonstrated that the decay in the rate of polymerization and in the concentration of active centres with time for the polymerization of propylene with the heterogeneous catalyst system MgCl2/EB/TiCl4Al(i‐Bu)3/EB can be represented better by a modified multi‐centre first order decay model than by the other models which are con

ISSN:0007-1641    

DOI:10.1002/pi.4980200607

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractSBS/PS semi‐interpenetrating polymer networks (semi‐IPNS) were synthesized by swelling a linear styrene‐butadiene‐styrene (SBS) triblock copolymer (SBS, Kraton 1102) with styrene monomer plus benzoin as photoinitiator and divinylbenzene as cross‐linking agent. Polyblends were prepared by solution casting of SBS and polystyrene (PS) in their ideal solvents. Measurements were made for viscoelastic properties and mechanical properties of phase‐separated polymer alloy (including SBS copolymers Kraton 4122), semi‐IPNs and polyblends of several SBS and PS, with the same total PS content (48% PS). The dynamic mechanical behaviour shows distinct transitions for each polymer, in agreement with electron microscopy results that SBS/PS polymer alloy forms two phases; however, the phase domains were finer in the semi‐IPNs than in SBS triblock copolymer and in polyblends of the corresponding polymers. Stress‐strain data show that semi‐IPNs exhibit higher tensile strength and modulus than the other two corresponding polymer alloys. A master curve was plotted to illustrate the stress relaxation behaviour of samples at higher temperatures. Our results also reveal that semi‐IPNs have much better high‐temperat

ISSN:0007-1641    

DOI:10.1002/pi.4980200608

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractPolymers incorporating conventional mesogens and diazo‐18‐crown‐6‐ether were prepared. The crown ether unit seems to be too flexible and only weak liquid crystal character can be observed by optical microscopy except when the mesogen is terphenyl. These liquid crystalline characteristics disappeared when the polymers were complexed with potassi

ISSN:0007-1641    

DOI:10.1002/pi.4980200609

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractContrary to an earlier report, monomers (e.g.p‐tert‐butylstyrene and octadecyl methacrylate) which are less soluble in water than styrene have been found to polymerise in emulsion using persulphate initiation. At 60°C, the order of the Interval II polymerisation rate of octadecyl methacrylate is 0.48 in persulphate concentration and 0.68 in sodium dodecyl sulphate concentration. The rate is increased by addition of methanol to the aqueous phase. Unlike styrene,p‐tert‐butylstyrene could not be polymerised in aqueous suspension by persulphate in the absence of emulsifier. High emulsifier‐monomer ratios were used in these experiments so that it is possible that mini‐emulsion droplets were a significant re

ISSN:0007-1641    

DOI:10.1002/pi.4980200610

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractPolyurethanes were obtained by the reaction of hydroxyl groups of castor oil with hexamethylene diisocyanate, isophorone diisocyanate or diphenylmethane diisocyanate using an NCO/OH ratio of 1.6. These polyurethanes were swollen in ethyl acrylate monomer and subsequently polymerized by radical polymerization initiated with benzoyl peroxide in the presence of the crosslinking agent ethylene glycol dimethacrylate. A series of interpenetrating polymer networks (PU/PEA IPNs) were obtained as tough films by casting in glass moulds. The characteristics of these films were determined: resistance to chemical reagents, thermal behaviour (DSC, TGA), tensile strength, Young's modulus, elongation at break (%) and Shore A hardness. The morphology was determined by scanning electron microscopy, and the dielectric properties such as electrical conductivity, dielectric constant (ε′), dielectric loss (ε″) and loss tangent (tan δ) were s

ISSN:0007-1641    

DOI:10.1002/pi.4980200611

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY