摘要:

AbstractThe radiation‐induced graft copolymerization of styrene and various kraft softwood lignins was studied. Expression of the results as the usual “per cent graft” was impossible, because grafting caused the lignin to become extractable in solvents for the styrene homopolymer. However, evaluation of the effects of various solvents on the degree of reaction was made through an indirect, and possibly more characteristic, measure. Grafting was least pronounced under conditions of low lignin accessibility (e.g., when less than 10% methanol was present), but increased with the addition of better lignin solvents or with higher methanol concentrations. The precipitating nature of the latter conditions was also found to contribute to an accelerated rate of grafting. Surprisingly, the graft copolymer was found to degrade at higher doses. Proof of grafting is offered in a fractionation scheme. Measurement of the molecular weight of the polystyrene separated from the lignin backbone allows the estimation of approximately one polystyrene graft per lignin molecule in benzene‐extractable copolymers. Two glass transition temperatures could be detected in several fractionated cop

ISSN:0021-8995    

DOI:10.1002/app.1972.070160101

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

年代:1972

数据来源: WILEY

摘要:

AbstractMethacrylic acid (MAA) and methyl methacrylate (MMA) were grafted onto nylon 6, cellulose triacetate, cotton, viscose rayon, and polyester fibers, and the stereoregularities of the grafted polymers were determined. The graft polymerization was carried out with preirradiation techniques using γ‐rays from a Co 60 source. The grafted copolymers were then separated from the homopolymers by Soxhlet extraction. The grafted (branch) polymers were isolated from the trunk polymers by acid hydrolysis and their stereoregularity was determined with a 100 MHz NMR spectrometer. The stereo‐regularity of PMAA or PMMA grafted onto viscose rayon or cotton fiber was different from that of the polymers formed in ordinary radical polymeriza

ISSN:0021-8995    

DOI:10.1002/app.1972.070160102

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

年代:1972

数据来源: WILEY

摘要:

AbstractAtactic polystyrene glasses were molded at high pressures by cooling the polymer melt at pressures up to 5000 atm. Changes found in the properties of the samples included: a lower mechanical damping factor at temperatures from 50°K to 300°K; a higher compressive elastic modulus; a maximum in compressive yield stress at a molding pressure around 1000 atm; faster relaxation at yield; appearance of an exothermic dilational relaxation belowTgwhen the samples were heated; and faster relaxation in methyl ethyl ketone vapor. The observed behavior is interpreted in terms of a model based on pressure‐induced heterogeneities in local order. The initial effect of increased molding pressure is to produce a more compact polymer which has less segmental mobility and more extensive interchain forces. Above molding pressures of about 1000 atm, a second effect develops due to the apparent formation of localized conformations which are stable under the high‐pressure vitrification conditions, but not at room conditions. The spontaneous decay of these high‐energy regions leads to subsequent formation of microvoid defects and more rapid structural relaxation effects. The existence of an optimum molding pressure somewhat below 1000 atm is indicated for poly

ISSN:0021-8995    

DOI:10.1002/app.1972.070160103

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

年代:1972

数据来源: WILEY

摘要:

AbstractIn a polyacid consisting of polyacrylic acid attached to a polyamide matrix, marked effects in equilibrium acid–base characteristics are observed, attributable to a hindered polyelectrolyte structure. In the presence of neutral electrolyte, the very high values found for pKadrop sharply. A break in the Henderson‐Hasselbalch curve indicates a conformational transition at α = 0.55 which is deferred to 0.95 by the presence of neutral electro

ISSN:0021-8995    

DOI:10.1002/app.1972.070160104

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe thermal degradation of methyl α‐D‐glucopyranoside, a cellulose model of intermediate complexity, was investigated in an attempt to gain insight into the pyrolytic reactions of analogous cellulose systems. The pure glucoside pyrolysis proceeds through formation of an intermediate of higher thermal stability. Nitrogenous bases bring about decomposition of the glucoside at lower temperatures and without formation of a detectable intermediate. Phenyl phosphates and phosphoramides induce thermal degradation of methyl α‐D‐glucopyranoside at lower temperatures than observed for the pure glucoside. The postulated degradation mechanism involves esterification of the glucoside followed by dehydration and skeletal rearrangements. Nitrogenous bases assist the dehydration process but reduce the yield of residue and bound phosphorus. Levoglucosan, the cellulose degradation product responsible for flaming combustion, was pyrolyzed in the presence of model flame retardants. Nitrogenous bases were found to inhibit thermal polymerization of levoglucosan and to induce its decomposition at lower temperatures. Zinc chloride exerted its effects in two stages: acid‐catalyzed polymerization at lower temperatures and dehydration at higher temperatures. Phenyl phosphates and phosphoramides alter levoglucosan pyrolysis by action as Lewis acids in a manner similar to zi

ISSN:0021-8995    

DOI:10.1002/app.1972.070160105

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

年代:1972

数据来源: WILEY

摘要:

AbstractColor stability in irradiated PVC may be achieved by (1) structural modification to block dehydrochlorination, (2) addition of radiation protectors, or (3) addition of radical scavengers. This study explores the latter approaches. Twenty‐six compounds representing a variety of structural types were screened for their effectiveness as measured by subsequent color development. Fifteen of the compounds imparted partial or complete postirradiation stability. Possible stabilizer mechanisms are discusse

ISSN:0021-8995    

DOI:10.1002/app.1972.070160106

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe importance of selecting the most suitable form of agitation for the prepolymerization step in the production of rubber‐modified polystyrene by a bulk polymerization procedure is related to the non‐Newtonian behavior of the polymerizing system and to the existence of a minimum shear rate requirement. The procedure for the design and calibration of a small‐scale reactor system is described which is shown to produce an adequate phase inversion of the prepolymer and from which data can be evaluated for any change in scale of the operation. Structural patterns in the final polymer are linked with average shear levels in the re

ISSN:0021-8995    

DOI:10.1002/app.1972.070160107

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe ultraviolet degradation of poly(vinyl chloride) films was studied in a photoreactor which supplied energy near 3000 Å. It was noted that the rate of degradation and color development was increased when the level of residual solvent in the cast films was increased. Two solvents were employed in the study: tetrahydrofuran and dichloroethane. The amount of residual solvent was correlated with the height of a characteristic peak at 2800 Å for tetrahydrofuran and 1900 Å for dichloroethane. Films which had very small traces of solvent showed excellent resistance to ultraviolet degradation, even in the absence of ultraviolet stabilizers. The analysis of solubility data showed that chain scission was controlling in the early stages of exposure, while crosslinking was controlling at later stages. As a result, it was not possible to apply Charlesby's treatment of radiation‐induced degradation. Comparison with the results obtained by other workers for degradation at 2537 Å showed that degradation at this wavelength was much faster than degradation at 3000 Å. Furthermore, degradation at 2537 Å appeared to be controlled by crosslinking at all stages of e

ISSN:0021-8995    

DOI:10.1002/app.1972.070160108

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

年代:1972

数据来源: WILEY

摘要:

AbstractMonofilament fibers were spun continuously from the free surface of a pool of molten poly(ethylene terephthalate) without the aid of a spinneret. For take‐up velocities in the range of 12 to 400 ft/min, the denier of the filaments produced was an inverse power function of take‐up velocity, and the birefringence was an inverse power function of the filament diameter. Production rate and product uniformity were strongly dependent on take‐up velocity and surface temperature of the melt

ISSN:0021-8995    

DOI:10.1002/app.1972.070160109

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

年代:1972

数据来源: WILEY

摘要:

AbstractABA‐type “tapered” block polymers were prepared from styrene (monomer A) and butadiene or isoprene, using an initiator ofsec‐butyllithium complexed with two molecules of ethyl ether. The stress–strain curves of polymers containing about 20–50% styrene show the usual resemblance to curves of crosslinked elastomers. The SBS polymers had higher tensile strengths than the SIS polymers. They also had slightly higher tensile strengths than comparable SBS polymers made withsec‐butyllithium. The SIS polymers, however, had generally lower tensile strengths than those made withsec‐butyllithium. This is probably caused by higher styrene content of the isoprene block, brought about by increased randomization of the styrene–isoprene copolymerization due to the presence of the ether. The A and B blocks become more compatible, producing loss of strength in the polymer. Infrared analyses of polydienes made with thesec‐C4H9Li·2(C2H5)2O initiator showed a 6% to 8% increase in 1,2‐content (for polybutadiene) or 3,4‐content (for polyisoprene), compared to polymers made withsec‐butyllithium. The polymer microstructures still have high (>80%) total 1,4‐content, however. Thus, this amount of ether can be tolerated in the polymerization system without great loss of rubbery properties or block structu

ISSN:0021-8995    

DOI:10.1002/app.1972.070160110

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

年代:1972

数据来源: WILEY