摘要:

AbstractChanges in crystalline structure of high‐tenacity ultra‐high‐molecular‐weight polyethylene fabric brought on by ballistic impact from a small projectile were determined by X‐ray diffractometry. A suitable X‐ray diffraction method that averages out the fiber orientation effects in the diffraction pattern was used. The Spectra 1000™ polyethylene fabrics were successfully characterized in terms of both the predominant orthorhombic and the minor monoclinic crystal content. Crystallinity values for the undamaged fabric are consistent from sample to sample and show an average orthorhombic fraction of 0.61 and an average monoclinic fraction of 0.04. Fabric damage by the projectile impact results in either an increase in monoclinic fraction, attributed to recrystallization at temperatures nearing the normal polyethylene melting point, or disappearance of monoclinic material as that temperature is exceeded. The latter predominates where ballistic penetration is complete. However, actual melting need not be involved: Transformation to the hexagonal (“rotator”) phase and the disappearance of the monoclinic phase could have occurred rather than true melting. © 1993 Jo

ISSN:0021-8995    

DOI:10.1002/app.1993.070470701

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn considering the processing characteristics of typical linear low‐density polyethylenes, it is very likely that the nature and amount of the “high‐density” portion of the short chain branching distribution has a strong effect on rheological behavior. In this study, highdensity resins of varying molecular weight were blended into a linear low‐density polyethylene base resin to determine the effect on viscosity, elasticity, and onset of haze. It was determined that it is not only the high‐molecular‐weight characteristics of the high‐density portion but also the linear nature of the molecules that has a negative effect on processability. © 1993 John

ISSN:0021-8995    

DOI:10.1002/app.1993.070470702

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

年代:1993

数据来源: WILEY

摘要:

AbstractTwo series of copolymers have been prepared from α‐methylstyrene and α‐methylstyrene units modified by the incorporation of the hydrogen‐bond donor units, methyl carbinol and trifluoromethyl carbinol, designated PαMS (I) and PαMS (II), respectively. It has been observed that if the concentration of the donor unit exceeds 4 mol %, one‐phase blends can be prepared with a series of polymers containing hydrogen‐bond acceptor sites such as poly(vinyl acetate), poly(vinyl pyrrolidone), poly(4‐vinyl pyridine), and some poly(alkyl acrylate)s, none of which are miscible with the unmodified PαMS. All the one‐phase blends formed are stable at temperatures above the glass transition temperature,Tg, of the blend, but eventually phase separate when the temperature is increased sufficiently. These lower critical cloud‐point curves have been measured for a wide range of the blends and act as an indicator of the effectiveness of the hydrogen bonds in enhancing one‐phase blend formation. TheTg's of the blends are in many cases higher than those calculated from the simple rule of mixtures and reflect the reduction in chain mobility in the blends caused by extensive hydrogen bonding. The results demonstrate the effect that specific interactions have in enhancing miscibility in binary polymer blends. © 19

ISSN:0021-8995    

DOI:10.1002/app.1993.070470703

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

年代:1993

数据来源: WILEY

摘要:

AbstractComposites of starch‐g‐polyacrylamide, starch, and polyacrylamide have been prepared by gamma radiation‐initiated polymerization of acrylamide in the presence of starch in aqueous medium. The polymerization was studied as a function of the (i) amount of water (ii) monomer concentration, and (iii) total dose. The optimum conditions for maximum conversion of the monomer to homopolymer and graft copolymer have been evaluated. Percentage of grafting of polyacrylamide could not be determined precisely as both the homopolymer and the graft are soluble in common solvents and all attempts to separate the graft from the homopolymer were unsuccessful. However, the formation of the starch‐g‐polyacrylamide copolymer was confirmed by the turbidimetric studies using acetone as a nonsolvent. The products of polymerization of acrylamide in the presence of starch consisted of unreacted starch, starch‐g‐polyacrylamide, and polyacrylamide and is referred to as the composite. Acrylamide was also polymerized in the absence of starch using γ‐rays as means of initiation and the optimum conditions for maximum conversion of acrylamide to polyacrylamide have been evaluated. Viscosity behavior of the composite and polyacrylamide was studied in aqueous medium at 30±0.04°C. The reduced specific viscosity of the aqueous solution of acrylamide and the composite as well was found to increase with increasing dilution, the effect being more pronounced in the composite. This tends to indicate that both the homopolymer and the composite behave as polyelectrolytes. An attempt has been made to explain the polyelectrolytic behavior of the homopolymer and the composite. © 1993 J

ISSN:0021-8995    

DOI:10.1002/app.1993.070470704

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

年代:1993

数据来源: WILEY

摘要:

AbstractA geometric method proposed by Kaelble and Moacanin for analyzing energetic characteristics of solid surfaces is discussed. It is shown that a number of characteristics can be presented in a visual geometric form. The method is applied to the analysis of adhesion in a three‐component system. Results of the analysis, concerned with the problem of creation of biocompatible materials, support the Andrade hypothesis that materials with zero interfacial tension of their water–solid interface show maximum biocompatibility. Data are obtained on wetting of polyethylene by different liquids before and after glow discharge plasma treatment. The analysis of these data in terms of geometric method shows the plasma treatment increased the polar component of the polymer surface energy to change the surface adhesiveness toward probable enhancement of polymer biocompatibility. That is consistent with available data on glow‐discharge‐treatment enhancement of biocompatibility for a number of polymers. © 1993 John Wiley&S

ISSN:0021-8995    

DOI:10.1002/app.1993.070470705

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

年代:1993

数据来源: WILEY

摘要:

AbstractAn investigation is reported on the flammability and thermal behavior of polyamide‐6, obtained by anionic polymerization of ϵ‐caprolactam, carried out in bulk, in the presence of the followingN‐substituted phosphorus‐containing lactam derivatives: diethyl‐(N‐caprolactam)‐phosphonite (PL1), diethyl‐(N‐caprolactam)‐phosphonate (PL2), and 2,5‐dichlorophenyl‐bis(N‐caprolactam)‐phosphinate (PL3). Phosphorus‐containing lactam derivatives PL,1and PL3are used as activators of the anionic polymerization of ϵ‐caprolactam, and PL2, as a modifying additive. The phosphorus‐containing polyamide‐6 possesses improved flame retardancy, as well as improved thermo‐ and thermooxidative resistance. Destruction kinetics were studied in nitrogen and air atmospheres, and the activation energy for thermal and thermooxidative destruction have been determined. The effect of PL1PL2, and PL3on the melting temperature (Tm) and glass‐transition temperature (Tg) of polyamide‐6 w

ISSN:0021-8995    

DOI:10.1002/app.1993.070470706

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

年代:1993

数据来源: WILEY

摘要:

AbstractFor some binary systems, an extended Flory–Huggins equation is applicable to both vaporliquid equilibria (VLE) and liquid–liquid equilibria (LLE) using the same adjustable parameters. New LLE and VLE data are reported for polystyrene (PS) (MW = 100,000)/cyclohexane and for poly(ethylene glycol) (PEG) (MW = 8,000)/water. Experimental results for the PS/cyclohexane system agree well with the semiempirical model, whereas those for PEG/water do not, probably because, for PEG/water, the temperature range of the VLE data is about 55°C lower than that of the LLE data. Excellent fits were obtained for our previously published experimental results for PS/cyclohexane (upper critical solution temperature, UCST), PS/ethyl acetate (lower critical solution temperature, LCST), PS/tert‐butyl acetate and PS/methyl acetate (both UCST and LCST), and PEG/water (closed‐loop). The semiempirical model also fits well with new data obtained for the polymer blend PS/poly(vinyl methyl ether). © 1993 John Wiley&

ISSN:0021-8995    

DOI:10.1002/app.1993.070470707

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

年代:1993

数据来源: WILEY

摘要:

AbstractPoly(glyceryl methacrylate) hydrogels with different degrees of hydration (75–98% H) and cross‐linking densities (X= 0.005–0.05 mol tetraethylene glycol dimethacrylate/mol glyceryl methacrylate) have been prepared by solution polymerization. Cross‐linking densities of the fully swollen hydrogels were analyzed using a modified Flory equation. Poly(glyceryl methacrylate) gels polymerized with no added cross‐linker were found to be highly cross‐linked, the degree of cross‐linking depending upon monomer dilution at polymerization. Modeling studies indicated that entanglement of polymer chains explained the highly cross‐linked nature of these materials. Gels polymerized with tetraethylene glycol dimethacrylate exhibited higher cross‐link densities than did gels polymerized with no added cross‐linker. However, for gels polymerized with cross‐linker, but at different initial dilutions, cross‐linking densities varied depending upon initial concentration, indicating that entanglement contributed appreciably to cross‐linking. These hydrogels may be regarded as highly swollen entangled networks, contrary to previous views. Correlation of these findings with those from earlier studies on the ultrafiltration behavior of the poly(glyceryl methacrylate) hydrogels suggested that the packing density of polymer fibers in the matrix may be more predictive of ultrafiltration behavior than is mesh size. ©

ISSN:0021-8995    

DOI:10.1002/app.1993.070470708

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe polymerization of benzene was studied in bulk and in nitrobenzene using BF3O (C2H5)2as a supporting electrolyte at platinum electrodes to obtain poly(p‐phenylene). The polymers were formed as a black thready mass on the anode and their yields were restricted to the area of the anode in the electrochemical cell. The yields of the polymers formed in the bulk and in nitrobenzene were almost equal, although electrical resistances of the polymers obtained from the bulk were relatively lower. Cyclic voltammetry measurements suggest that the polymerization of benzene took place from the species generated anodicallyin situ. © 1993 John Wiley&Sons, I

ISSN:0021-8995    

DOI:10.1002/app.1993.070470709

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe characteristics of the adhesions of polyimide to silicon and to polyimide and the autohesion of a polyimide blend have been investigated. As found, the peel strength of pyromellitic dianhydride–4,4′‐oxydianiline (PMDA–ODA) on silicon can be greatly improved by blending with 20 or 40% benzophenone tetracarboxylic dianhydride–p‐phenylene diamine (BPDA–PDA). Exposing in air for a 2 day period resulted in a serious deterioration in adhesion for the pure PMDA–ODA system, while in no deterioration for the blend systems. Regardless of adhesion or autohesion, the resulting peel strength decreased markedly with the increase of the curing temperature. It was also found that based on the same curing temperature the diffusion of NMP is much faster in the film of PMDA–ODA than in the blend containing 20% BPDA–PDA. Beside curing temperature, imide‐to‐imide compatibility seems to play an important role in affecting the adhesion characteristics. © 1

ISSN:0021-8995    

DOI:10.1002/app.1993.070470710

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

年代:1993

数据来源: WILEY