摘要:

AbstractA nonionic, high water content, high‐strength hydrogel based onN‐(2‐hydroxyethyl)methacrylamide (HMA), 2‐hydroxyethyl methacrylate (HEMA), and a strengthening agent, 4‐t‐butyl‐2‐hydroxycyclohexyl methacrylate (TBCM). The HMA was prepared by the reaction of methacryloyl chloride with ethanol amine. The copolymerization of HMA with varying concentrations of HEMA and TBCM resulted in transparent hydrogel films possessing a wide range of mechanical and physical properties. A copolymer composition of 79 parts HMA, 20.7 parts TBCM, and 0.3 parts ethylene glycol dimethacrylate (EGDMA) gave a transparent, flexible film possessing a water content of 72.6%, a Young's modulus of 0.45 MPa, oxygen permeability of 28 barrers, and a tear strength of 28 N/m. In contrast, a copolymer composition of 40 parts HMA, 59.7 parts TBCM, and 0.3 parts EGDMA gave a hard, transparent film possessing a water content of 33% and a modulus of 504 MPa. © 1993 John

ISSN:0021-8995    

DOI:10.1002/app.1993.070491101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractNonaqueous dispersion (NAD) of poly(vinyl acetate) (PVAc) particles sterically stabilized by poly(2‐ethylhexyl methacrylate) were examined by ESR spectroscopy after introduction of a trace quantity of a spin probe, 3‐carbomoyl‐2,2,5,5‐tetramethyl 3‐pyrolin‐1‐yloxy. ESR spectra were monitored as a function of temperature from ‐160 to 100°C. In spite of the complex morphology of the particle, it is found that the behavior of the probe in the NAD was essentially identical to that in a pure PVAcmatrix. Solvent penetration into (NAD) particles were studied. These colloidal particles were exposed to a dilute solution of the spin probe, and the bimodal distribution of the ESR spectra of this probe molecule were carefully monitored as a function of time. Fickian‐type diffusion of spin probes into the particles was observed and a spherical model was employed to obtain the diffusion coefficients (D) in various solvents.Dvalues were found around 10–15cm2/s and were interpreted as the parameter, inversely proportional to the apparent viscosity of the environment inside the PVAcparticle. The maximum amount of diffused solvent molecules (M∞) into the PVAcparticle was found inversely proportional to polymer‐solvent interaction through the solubility parameters. ©

ISSN:0021-8995    

DOI:10.1002/app.1993.070491102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractIt has been ascertained that chemiluminescence‐time curves for samples of poly(2,6‐dimethyl‐p‐phenylene ether) blended with high‐impact polystyrene containing polybutadiene yield a very reproducible pattern even at a temperature of 190°C. The chemiluminescence light emission has been associated with consumption of double bonds in polybutadiene, and a corresponding rate constant and activation energies of chemiluminescence decay from both the isothermal and nonisothermal parts of chemiluminescence‐time curves have been determined. As demonstrated by these curves, an attempt, to stabilize the blends toward thermooxidation by the peroxide decomposer and stabilizer led to retardation of the oxidation process only and further investigation searching for an optimum stabilizing system is required. © 1993 John Wi

ISSN:0021-8995    

DOI:10.1002/app.1993.070491103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe factors that influence the morphology and the interfacial parameters during dynamic vulcanization of hydrogenated nitrile rubber/nylon blends are examined. The particle size of the dispersed phase (R̄) and the correlation distance (ξ) of a 50 : 50 blend decreased with increasing mixing time at 250°C, attained a minimum value, and then increased. The increase in the number of particles with time (dn/dt) may be expressed as (dn/dt) =k'nm, wherenis the number of dispersed particles at timet, andmandk'are constants.R̄and ξ gradually increased as the mixing temperature was increased from 250 to 300°C at a constant mixing time of 10 min. The particle size increased also with the increasing gel fraction of the rubber. At a constant mixing time of 10 min at 250°C, the particles were larger when the addition of the cross‐linker was delayed. These observations can be explained with the help of a hypothetical model, similar to that proposed by Wu, considering the breaking down of rubber particles, coagulation and coalescence of droplets, and droplet rupture in a matrix of nylon. On vulcanization, the thickness of the interface (λ) reduced from 62 to 48 nm. The interaction parameter and interfacial tension, as estimated from λ, for a bilayer specimen vulcanized insitu, at 250°C were 2.8 × 10–3and 0.24 mN/m, respectively. The high value of λ for the dissimilar polymer pair may be due to polymer‐polymer graft formation at high temperature. © 1993 Jo

ISSN:0021-8995    

DOI:10.1002/app.1993.070491104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractEffective thermal conductivities of powder‐filled epoxy composites were experimentally obtained using a transient method. Fillers used were aluminum and cupric oxide. Comparisons of these data with published correlations indicate that Agari's model can give better fits. Nielsen's model may also give a good prediction of the shape of particles can be determined and values of parametersAandϕmare available. An alternative method of dealing with parameterC2in Agari's model is suggested. © 1993 John Wiley&Sons,

ISSN:0021-8995    

DOI:10.1002/app.1993.070491105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe mechanisms of fatigue crack initiation for various stress levels and thicknesses have been determined for single‐edge notched specimens of polycarbonate and used to assemble a map. Three basic fatigue crack initiation mechanisms were identified and named as cooperative ductile (the damage zone formed ahead of crack consisting of yielded material), solo‐crack brittle (very little damage zone development), and cooperative brittle (identified as a cloud of microcracks or crazes that developed at the notch tip). With a given applied stress and within the same failure mechanism, the values of the number of cycles to crack initiation decrease with increase in thickness. The transition from cooperative ductile to solo‐crack brittle initiation mechanisms is sudden with increasing thickness. Transition from cooperative ductile to cooperative brittle with decreasing stress was less well defined. Regions where combinations of mechanisms were observed are also identified in the map. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070491106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractFour kinds of epoxy resins: cresol novolac, tris‐hydroxyphenylmethane, tetramethylbiphenol, and bisphenol A, were cured with phenol novolac epoxy resins. Characteristics of these epoxy compounds were studied by the positron annihilation lifetime (PAL) technique. Glass transition temperatures, thermal expansion coefficients, and volume of intermolecularspace holes among polymer chains were obtained from the lifetime, τ3, of the long‐lived component ofortho‐positronium. It was revealed that, at the glass transition temperature,Tg, the volume of the hole created among polymer chains expanded 1.4 times the volume at room temperature. The smaller flexural modulus of tris‐hydroxyphenylmethane than that of the other samples was explained by the volume of intermolecular‐space holes obtained from τ3. Aging effects were seen in the data of the intensities,I3, ofortho‐positronium, which became smaller after heating the samples aboveTg.I3and τ3were strongly affected by the density of cross‐linkings, and their chemical structures. The larger the density of cross‐linkings, the smallerI3and higherTgwere obtained. Epoxy compounds with the higher water‐absorption rates had larger intermolecular‐space holes. © 19

ISSN:0021-8995    

DOI:10.1002/app.1993.070491107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractPressure‐volume‐temperature measurements were performed on five amorphous thermoplastics. From these data, first derivatives of internal energy with respect to volume were calculated. These derivatives were cast into the Lennard‐Jones form and the two defining parameters were evaluated for each polymer. It was found that, when the polymer is in the glassy state, these parameters correspond to the volume and internal energy of the polymer at absolute zero. For melts, the first derivatives are constant within the accuracy of these experiments regardless of temperature, pressure, or volume. As a result, the Lennard‐Jones potential was found to be a good model for the amorphous glassy state and inappropriate aboveTg. © 1993 John Wiley&S

ISSN:0021-8995    

DOI:10.1002/app.1993.070491108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe creation of oxidized structures and double bonds in polyethylene (PE) and polypropylene (PP) samples implanted with P+ions was studied. The surface polarity and the electrical conductivity of the ion‐implanted polymers were also examined. As a result of the ion implantation, the polymer macromolecules are broken up and the material is degraded. An oxygen penetration into the radiation‐damaged polymers is also observed, with PE being more vulnerable to the oxidation. The ion‐implanted PP exhibits higher surface polarity and sheet conductivity compared to that of PE. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070491109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractSoft‐segment molecular weight, soft‐segment crystallization, hard‐segment‐type, and reactive diluent level were examined in urea and urethane acrylates. Increasing soft‐segment molecular weight led to a decreased tensile modulus, increased strength, and increased elongation at break. Soft‐segment crystallization increased the modulus below the melting temperature, but decreased the modulus above the melting temperature because crystallization interfered with cross‐linking. Materials with hard segments that allowed for greater phase separation showed a higher modulus, higher ultimate stress, and higher ultimate elongation. Materials with reactive diluents 2‐hydroxyethyl methacrylate (HEMA) andN‐vinyl pyrrolidinone (NVP) showed qualitatively different behavior. HEMA caused the modulus and strength to increase with little effect on elongation up to concentrations of 50 wt %; at higher concentrations, the elongation decreased. NVP also increased the modulus and strength; however, at 40 wt % NVP, ultimate elongation increased in a well‐phaseseparated system and decreased in a poorly phase‐separated system. In tensile tests, samples with 40% NVP also showed substantial sample necking and drawing. © 199

ISSN:0021-8995    

DOI:10.1002/app.1993.070491110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY