摘要:

AbstractGraft interpenetrating polymer networks (graft‐IPNs) of polyurethane (PU) and the diglycidyl ether of bisphenol A (epoxy) were prepared by first grafting excess PU prepolymer to the epoxy and then simultaneously polymerizing the PU prepolymer and epoxy. The fracture properties, at high shear rate (e.g., impact) and low shear rate (e.g., pseudostatic tensile fracture energy measurement) of these graft‐IPNs exhibit opposite behavior. Although dispersed rubber particles can enhance the Izod impact strength, toughening of the matrix of graft‐IPNs was found to be the main contribution. In contrast, it was found that a heterogeneous morphology with suitably dispersed rubber domains of appropriate size as well as the toughness of the matrix are requirements for effectively increasing the fracture energy at low shear rate. A reinitiating crack in the plastic matrix is proposed as the main toughening mechanism and can be invoked to interpret the fracture behavior at high and low shear rates of the graft

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280601

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe transport properties of silicone rubber are reported at 35°C for a series of pure gases (He, N2, CH4, CO2, and C2H4) and gas mixtures (CO2/CH4and N2/CO2) for pressures up to 60 atm. The effects of pressure and concentration on the permeability of various gases have been analyzed to consider plasticization and hydrostatic compression effects. Over an extended pressure and concentration range, both compression of free volume and eventual plasticization phenomena were observed for the various penetrants. In pure component studies, plasticization effects tended to dominate hydrostatic compression effects for the more condensible penetrants (C2H4and CO2) while the reverse was true for the low sorbing N2and He. These issues are discussed in terms of penetrant diffusion coefficients versus pressure to clarify the interplay between the opposing effects for the penetrants of markedly different solubilities. Additional insight into the somewhat complex interplay of the plasticization and hydrostatic compression effects are given by mixed gas permeation results. It was found that the permeability of nitrogen in a 10/90 CO2/N2and a 50/50 CO2/N2mixture was increased by the presence of CO2because the plasticizing nature of CO2is able to overcome nitrogen's compression effect

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280602

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractStatic and dynamic molecular properties are obtained from simultaneous elastic and quasielastic light scattering experiments for nine narrowly distributed polystyrene fractions in nine solvents covering the cross‐over region from theta to good‐solvent conditions. This set of consistent experimental data is compared with theoretical predictions of two renormalization group theories: the first‐order ϵ‐expansion calculations of Oono et al. and second‐order calculations within the “renormalized two‐parameter” theory of Douglas and Freed. Static properties (the penetration function) are found to be exactly described by the ϵ2‐order model, while dynamic behavior seems to be in better accord with Oono's ϵ1‐order calculations. No evidence of draining effects is detected. Solutions with benzene (and partially with toluene) exhibited atypical, nonuniversal behavior. Some features of static and dynamic exponents behavior in the crossover region are also discussed and compared with previously published t

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280603

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractRaman spectroscopy has been used to study PVC gels made in cyclohexanone in the wet state at concentrations from 21 to 93% by weight of PVC. Parallel and perpendicular spectra were obtained in the C‐Cl stretching region, and after subtraction of the solvent spectrum they were analyzed into a set of overlapping peaks due to various structural components. The positions of the peaks found were in good agreement with those found earlier for PVC samples in the solid state. The fractional contribution of the areas of peaks assigned to crystalline material to the total area under the C‐Cl stretching region was used to estimate the crystallinity of the gels, and changes in their depolarization ratios and relative intensities were interpretated as providing further evidence for the presence of two types of crystallites in PVC gels. From a determination of the crystallinity at the gel transition point and reasonable assumptions, the contributions of the two types of crystallites to the total crystallinity were estima

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280604

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe crystallization behavior of two ethylene/octene copolymers, which differ in hexyl branch concentration, and their fractions were assessed. Fractionation of the crystalline linear low density polyethylenes (LLDPEs) was achieved by temperature rising elution fractionation. As the column temperature was raised, the eluted fractions exhibited a reduction in branch concentration and an increase in molecular weight. This was attributed to the difference in reactivity between ethylene and octene and the subsequent depletion of the ethylene monomer in the solution process. Spherulites formed during the crystallization of the whole polymers were well developed, banded, and displayed a wide distribution of sizes. However, spherulites of the LLDPE fractions were less well developed, more uniform in size, and tended to progressively deteriorate and become smaller as the concentration of branches increased. The ethylene and octene blocks of the copolymer crystallized independently, and it was proposed that the octene portion formed short, curved lamellae in the interfacial region of the lamellae formed from the linear ethylene portion of the molecule. Decreases indspacing for fractions with increased short chain branching corresponded with similar drops in molecular weight.

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280605

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe miscibility of a series of styrene/acrylic acid copolymers with various polyacrylate and polymethacrylate homopolymers, as well as a series of styrene/methyl methacrylate copolymers, has been investigated. According to the binary interaction model, the miscibility diagram for styrene/acrylic acid copolymers with styrene/methyl methacrylate copolymers indicates that acid and ester groups interact endothermically. The phase behavior of the homopolymers also implies this. The analysis ignores the association and self‐association observed for the polymer blends and the low‐molecular‐weight analogs used to model them. The heat of mixing of low‐molecular‐weight analogs depended greatly on both composition and acid

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280606

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractA new method to measure the extremely slow chain diffusion in polymer systems at and below the glass transition temperature is proposed. It requires polymers that can be fragmented in a well‐defined manner in the glassy state. The idea is first to split all chains, while their conformations are frozen in, and then to measure at some higher temperature the diffusion of the chain fragments by small‐angle neutron scattering. The structure factor changes in the course of the fragment diffusion from that of the initial long chains to that of the uncorrelated fragments. Preliminary results from experiments on blends of thermosensitive copolycarbonates and tetramethylpolycarbonate are presented. They demonstrate the viability of the techni

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280607

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractPoly( 1,3‐dioxocane) was synthesized by cationic ring‐opening polymerization with triphenyl‐methane hexafluoroantimoniate as the initiator and was studied with regard to its solubility, unperturbed chain dimensions, and thermal transitions. The intrinsic viscosity and Flory‐Huggins interaction parameter were used to determine the solubility parameter, δp= 9.6 cal1/2cm−3/2, a value that agrees with that calculated empirically. Fractions were obtained from the solvent/non‐solvent system benzene/methanol at 25°C. The number‐average molecular weightMnand intrinsic viscosity [η] were measured in toluene at 25°C. The relation [η]= 1.459. 10−4Mn0.79was found. A value of 5.3 was obtained for the characteristic ratio 〈r2〉0/nl2. Results are correlated with the main thermal transi

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280608

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe swelling of crosslinked poiy(N,N′‐alkyl substituted acrylamides) in water was studied in relation to temperature changes. Conventional swelling theory and separation of the polymer solvent interaction parameter into enthalpic and entropic contributions were used to characterize the temperature dependence of swelling in water. The thermosensitivity of swelling can be attributed to the delicate hydrophilic/hydrophobic balance of polymer chains and is affected by the size, configuration, and mobility of alkyl side groups. A sharp swelling transition may occur at an optimum hydrophilic/hydrophobic balance but was found only in theN‐isopropylacrylamide network among the networks tested. This swelling transition pattern was also reflected by the endothermic peak of the DSC thermogram of the swollen s

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280609

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractStructure and properties of presumed polypropylene(PP)‐b‐polyethylene(PE) block copolymers (PPPE) and the corresponding blends (PP/PE) have been investigated by wide‐angle x‐ray scattering (WAXS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), torsional pendulum apparatus, and other techniques measuring mechanical properties. Crystallinity, morphological structure, and mechanical properties of the block copolymers and blends vary with the PP and PE compositions. Compared with PP homopolymers and PP/PE blends, PP and PE segments in PP‐PE block copolymers have a reduced crystallinity, especially PE segments. An additional peak at about −40°C is observed in dynamic relaxation spectra; substantially different morphology is revealed; and mechanical properties are greatly improved for the sequentially copolymerized PP‐PE block copolymers, indicating the existence of PP‐PE

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280610

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY