摘要:

AbstractYoung's modulus distributions in the depth direction within injection moldings made from polystyrene have been investigated by empolying two independent techniques. Both methods show that the material close to the surface exhibits relatively high stiffness, whereas at all other depths a lower uniform stiffness exists. The depth dependency of other material characteristics, such as tan δ peaks in the dynamic mechanical thermal analysis spectra and molecular orientation, have been investigated in an attempt to correlate them with the stiffness distributions. It appears that the thermomechanical history of the different regions within the moldings, particularly the stresses acting during flow and the temperature gradients set up during cooling, are primarily responsible for the Young's modulus distributions presented here. © 1993 John Wiley&Sons, In

ISSN:0021-8995    

DOI:10.1002/app.1993.070470201

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

年代:1993

数据来源: WILEY

摘要:

AbstractA series of novel polyetherurethaneurea elastomers based onm‐TMXDI, polyether macrodiols containing 4, 6, 8, or 10 methylene groups between the ether linkages, and aliphatic and aromatic diamines was prepared by two‐step solution polymerization. All the materials were thermally processable at 120–160°C except one that was solvent‐castable. Mechanical properties and hydrolytic stability (at neutral pH) were found to depend on the macrodiol and chain extender. Poly(tetramethylene oxide)‐based polyetherurethaneureas that were chain‐extended with primary aliphatic diamines, other than 1,3‐propanediamine, exhibited significantly better mechanical properties than those chain‐extended with secondary aliphatic or aromatic diamines. The mechanical properties and hydrolytic stability of polyetherurethaneureas containing poly(hexa‐, octa‐, or decamethylene oxide) and 1,6‐hexamethylenediamine were considerably better than those containing 1,2‐ethylenediamine. The hydrolytic stability increased with the increasing C/O ratio of the macrodiol. With poly(hexamethylene oxide)‐based materials, the phase separation between soft and hard domains was higher than that of the other materials as determined by DSC.

ISSN:0021-8995    

DOI:10.1002/app.1993.070470202

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe photoaging of different linear low‐density polyethylenes (LLDPEs), namely, ethylene–butene (EB) and ethylene–hexene (EH), has been studied. Experiments have been carried out under natural and accelerated UV exposure. We focused our investigation on the changes of elongation at break and the modifications in the chemical structure (measured by the IR technique) occurring over the photoaging process. Our results showed that the changes of elongation at break were different under the two modes of irradiation from the very beginning of UV exposure; in contrast, the comparison of stoichiometry displayed a small difference in the later stage of UV irradiation. That pointed out the difficulty of establishing a relationship between the buildup of carbonyl groups and the mechanical changes due to UV irradiation, which has been usually attempted. In addition, it appeared that the density, oxygen permeability, and the type of α‐olefin of the polymer might have an effect upon the elongation‐at‐break changes. From our data, it can be suggested that the prediction of weathering resistance of polymers can be based on both mechanical changes and modifications in chemical structure to minimize erroneous prediction. © 1993 John Wi

ISSN:0021-8995    

DOI:10.1002/app.1993.070470203

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe kinetics of the swelling of sodium polyacrylate (NaPA), a hydrophilic polymer, was studied gravimetrically, by microscopic observation, and calorimetrically. The swelling process followed first‐order kinetics and the rate constant was of the order of 10−2s−1. The gravimetric method, however, was not useful for kinetic studies. The rate constant was depressed by the addition of sodium chloride. The activation energy of the swelling was 46.0 ± 6.2 (kJ mol−1) and decreased with the increase in sodium chloride concentration. In acid solution, the activation energy was almost the same as that in water. The heat of the swelling was 196 ± 17 J g−1and did not vary with the addition of sodium chloride. © 1993 John Wil

ISSN:0021-8995    

DOI:10.1002/app.1993.070470204

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

年代:1993

数据来源: WILEY

摘要:

AbstractA novel family of fluoroterpolymers was prepared, containing perfluoroalkylethyl methacrylate (PFAEM), methacrylic acid (MAA), and 2‐hydroxyethyl methacrylate (2‐HEM) residues. The refractive index of the fluoroterpolymers is in the range of 1.3675 ≤n≤ 1.4275. The surface tension of cured thin films falls in the interval from 15 mN/m to as low as 8 mN/m. Upon heating, these polymers undergo thermally initiated self‐crosslinking and develop tenacious bonding to substrates. The associated chemical reactions and products were identified by IR spectroscopy and some thermogravimetric scans. The spectra indicate that the reaction products are ester and anhydride groups. In general, the formation of esters occurs more rapidly and requires lower temperatures (≥ 110°C) than does the formation of anhydrides. Prolonged heating, especially at higher temperatures (≤ 150°C), favors the formation of anhydrides. When the molar ratio of MAA to 2‐HEM is substantially larger than 1.0, the formation of anhydride is favored; when the ratio is 1 : 1, the formation of ester is favored; and when the molar ratio is much smaller than 1.0, the rate of formation of both esters and anhydrides is greatly reduced. In the case of the fluoroterpolymers, the formed esters and anhydrides essentially originate exclusively from the MAA and 2‐HEM and seem not to involve any attack on the PFAEM residues. Only after very long heating at the higher temperatures employed, some loss of CF band intensity was noted. In acopolymer of PFAEM and MAA, a substantial and rapid attack by the acid on the ester group in the PFAEM residues takes place under relatively mild conditions. Such and more drastic conditions appear not to affect at all a homopolymer of PFAEM alone. This suggests that in the fluoroterpolymers the more polar MAA and 2‐HEM tend to aggregate close together, so that, when heated, they preferentially react with each other, forming both esters and anhydrides. In the absence of 2‐HEM, the MAA may react with itself or with PFAEM, producing only anhydride groups. Both esters and anhydrides may be intermolecular and/or intramolecular, resulting in a cross‐linked system in which the cross‐link concentration is directly related to the combined amount of ester and anhydride groups

ISSN:0021-8995    

DOI:10.1002/app.1993.070470205

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe irreversible deformation behavior of coextruded microlayer composites, consisting of 49 alternating layers of polycarbonate (PC) and styrene—acrylonitrile polymer (SAN), was examined in the triaxial stress state achieved at a semicircular notch during slow tensile loading. Variations in the proportions of PC and SAN were manifest as changes in the relative thicknesses of PC and SAN layers. When the SAN layers were thicker than the PC layers (PC/SAN 25/75 v/v) or the layer thicknesses were about the same (53/47 v/v) the composites were only slightly more ductile than SAN and the deformation behavior of the layers mimicked that of the components. Examination of optical micrographs showed that the damage zone closely resembled that of SAN and consisted of internal notch crazes in the SAN layers that grew out from the notch surface in conformity with a mean stress condition. Shear processes became more evident when the PC layers were thicker than the SAN layers (PC/SAN 65/35 and 74/26 v/v). An unusual transition was observed in the SAN layers from internal notch crazing to interactive crazing and shear banding. The internal notch crazes ceased to grow when they terminated in a pair of microshear bands in the SAN layer. Subsequently a macroscopic shear‐yielding mode was observed as two sets of intersecting slip lines that grew out from the notch surface in both PC and SAN layers. Stress intensification caused by the plastic zone was responsible for the appearance of a second family of internal crazes in the SAN layers that originated in front of the notch tip. © 1993 John Wiley&Sons,

ISSN:0021-8995    

DOI:10.1002/app.1993.070470206

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe brittle‐to‐ductile transition in continuous microlayer composites of polycarbonate (PC) and styrene–acrylonitrile copolymer (SAN) was investigated under the triaxial tensile stress state achieved at a semicircular notch. The availability of microlayer compositions with variations in the proportion of the components and also variations in the total number of alternating layers made it possible to examine the transition from SAN‐like, relatively brittle behavior, to PC‐like properties where the ductile component dominated yield and failure. Examination of the damage zone that formed at the notch root revealed that cavitational mechanisms dominated in the brittle composites that were those with the highest proportion of SAN and fewest number of layers. Shear‐yielding modes characteristic of PC dominated the damage zone of the ductile composites. Cavitational mechanisms were almost totally absent in these compositions that included those with the highest proportion of PC and the largest number of layers. A broad range of transitional behavior was observed with intermediate compositions where elements of both cavitational mechanisms and shear modes were superimposed. These compositions provided an opportunity to examine the interaction of cavitational and shear processes at the macro‐ and microscales. © 1993 John W

ISSN:0021-8995    

DOI:10.1002/app.1993.070470207

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper describes the polymerization and the copolymerization of dicyclopentadiene and norbornene nitrile by metathesis polymerization. It is found that the metathesis polymerization of dicyclopentadiene, which is very fast and exothermic, can be controlled by the addition of norbornene nitrile. Though the norbornene nitrile delays the polymerization at room temperature, at high temperatures, because of the presence of nitrile group, polymerization is accomplished in reaction injection molding time. Physical and mechanical properties of the polymers and copolymers are described. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070470208

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

年代:1993

数据来源: WILEY

摘要:

AbstractMelt blends of ABS and PMMA were prepared using three types of ABS having different acrylonitrile (AN) content, and PMMAs with different MW. From TEM micrographs, it was found that ABSs containing 24 and 27 wt % AN were miscible, and the one containing 35 wt % AN was immiscible with PMMA. Morphologically miscible blends showed welldefined semicircles in Cole—Cole plots, whereas immiscible ones showed immiscible drifts from the semicircle. In addition, as the compounding temperature increases, the dispersed PMMA phase became stratified, and more rubber particles, especially larger ones, migrated toward the PMMA phase. Miscible blends gave viscosities lower than additivity would predict, whereas immiscible ones gave positive (ABS‐rich phase) and negative (PMMA‐rich phase) deviations from the additivity. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070470209

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe dynamic mechanical properties of polymeric composites composed of crosslinked poly(n‐butyl methacrylate) continuous‐phase and crosslinked polystyrene dispersed phase with poly(n‐butyl methacrylate) occlusion have been examined. The composite samples were prepared by mixing and swelling of the crosslinked polystyrene particles obtained by emulsifier‐free emulsion polymerization, withn‐butyl methacrylate and crosslinker, then photopolymerizing at the desired temperature. The composite microstructure was varied by either changing the crosslink density of polystyrene, and temperature of swelling and polymerization, or using different sizes and contents of polystyrene particles. The tan δ peak positions of composite samples are found to be dependent on morphological characteristics as well as the properties of the dispersed phase while the peak height seems to be dependent on the effective volume of dispersed phase composed of polystyrene and poly(n‐butyl methacrylate) occlusions. Special attention has been paid to the comparison among composite, homonetworks, and bulk IPN samples that are expected to have the identical structure with the complex dispersed phase of the composite samples. © 1993 John Wi

ISSN:0021-8995    

DOI:10.1002/app.1993.070470210

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

年代:1993

数据来源: WILEY