摘要:

AbstractIntroduction of primary covalent crosslinks into linear, segmented elastomers was followed by observing their modulus–temperature behavior. The behavior of the linear segmented polymers is explained by association of glassy segments into regions which act as filler and quasi‐crosslink. In several cases crosslinkage disrupts these regions and thereby lowers the “plateau”

ISSN:0021-8995    

DOI:10.1002/app.1967.070110801

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe viscoelastic properties of amylose films plasticized with dimethyl sulfoxide were studied. The modulus–temperature curves of dimethyl sulfoxide‐plasticized amylose are typical for semicrystalline polymers at the higher concentrations of amylose and pass to those of amorphous polymers with the decrease of amylose content. The glassy modulus is not affected by the incorporation of dimethyl sulfoxide, but the rubbery modulus andTgare depressed with increased dimethyl sulfoxide. The change ofTgwith plasticization can be represented by two approximately straight lines, one representing the lower concentration region of amylose and the other the higher one. The critical concentration is about 60% amylose. When the results of modulus–time measurements and x‐ray diffraction are considered together, in a system of amylose–dimethyl sulfoxide, amylose exists as a semicrystalline polymer at high concentrations of amylose, and it acts intermediate between semicrystalline and amorphous polymers at lower concentrations below about 60%. From an extrapolation of the data ofTgof plasticized amylose,Tgof pure amylose appears to be approximately 330°C. The viscoelastic properties of amylose films plasticized with dimethyl sulfoxide–sorbitol mixtures were

ISSN:0021-8995    

DOI:10.1002/app.1967.070110802

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

年代:1967

数据来源: WILEY

摘要:

AbstractA heterogeneous cellulose reaction was studied by reacting cotton fiber in pyridine medium with propionyl chloride at different initial molar concentrations and at different temperatures. It has been observed that the kinetics of reaction does not follow Sakurada's diffusion equation closely, and the deviation is more noticeable at lower initial concentrations of the reagent and at lower temperatures. A non‐uniform reaction rate is also evident from the time–substitution curve. The rate of substitution changes twice during the reaction, the latter change being associated with the loss of cellulose I crystal structure. In an attempt to treat the data according to simple chemical kinetics, the order has been found to decrease continuously from the beginning, suggesting thereby an autocatalytic type of behavior. However, at the finàl stages of the reaction, when the cellulose I structure was completely lost, the reaction behaved as a pseudo first‐order type. The x‐ray diffractograms of the reacted samples indicate that cellulose I crystallinity decreases from the beginning of the reaction and that a new crystalline lattice develops gradually. The formation of this new crystal lattice is hindered in the cellulose crystalline region due to the lack of freedom of the chains. The diffusion equation has been modified by substituting a crystallinity index for the rate of diffusion of solvent in a solvent–gel system and thus extending Sakurada's equation. A new mechanism has been proposed considering the simultaneous reactions in the amorphous and crystalline regions. This mechanism can explain the deviation of Sakurada's equation. The kinetics expressions are derived, based on the proposed mechanism. The kinetics of decrystallization of cellulose I is also presented. A satisfactory theoretical explanation is given for the fact that the fall of reaction rate occurs at the conclusion of decrystallization of the cellulose I

ISSN:0021-8995    

DOI:10.1002/app.1967.070110803

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

年代:1967

数据来源: WILEY

摘要:

AbstractA method is proposed for the prediction of the intrinsic viscosity of θ solutions, based upon the constitution of the dissolved polymer. The method makes use of additive values for constitutional groups to calculate a quantity that represents the specific chain stiffness per main chain atom

ISSN:0021-8995    

DOI:10.1002/app.1967.070110804

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

年代:1967

数据来源: WILEY

摘要:

AbstractPolymer degradation has been studied by using gel‐permeation chromatography (GPC) to measure the product distribution. The method is rapid and has a good accuracy that permits one to see most of the degradation products, as they elute at a point different from the starting material. In the cases studied, polystyrene cleavage has the result of random cleavage, as judged by the product distribution. A GPC curve to be expected from random cleavage has been put together to aid in the evaluation. Both wide and narrow molecular weight distribution polystyrenes have been studied after degradation. The narrow distribution products were degraded by peroxides, irradiation, and weathering. With the latter, the combination of simple fragments to form the starting portions of cromslinking were measured in small amounts. In none of the cases studied did degradation in solution produce crosslinked products. Kinetic rate studies were made that concerned the action of peroxides and inhibitor

ISSN:0021-8995    

DOI:10.1002/app.1967.070110805

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

年代:1967

数据来源: WILEY

摘要:

AbstractSeveral phosphorus derivatives of methyl 2‐(chloromethyl)acrylate, including three phosphonium salts and one phosphonate ester have been prepared. A brief study was made of their polymerization characteristics under free‐radical conditions. Several factors were noted which prevented the synthesis of methyl 2‐[(diethoxyphosphinyl)‐methyl]acrylate in high yields in initial experiments. Homopolymerization of these phosphorus derivatives does not take place readily in the presence of free‐radical i

ISSN:0021-8995    

DOI:10.1002/app.1967.070110806

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

年代:1967

数据来源: WILEY

摘要:

AbstractIt is shown that the glass temperature (Tg) for homopolymers of the type CH2CXYcan be expressed by a simple additive equation involving two terms: (1) a parameterEwhich is directly related to the molar cohesion energy and (2) a parameterEs*which is a measure of restricted rotation about valence bonds.Es*, at least for a large number of polymers, is related to the Mark‐HouwinkKθvalue (as measured in θ solvents atTθ) via anti‐logEs*∝ 1/Kθ2/3. It is also shown that for homologous series [e.g., poly(n‐alkyl methacrylates)], there is a constant relationship betweenEand antilogEs*. TheTgvalues for copolymers may be estimated by a simple weighted (via mole fraction) summation of theEandEs*values of the components. When used in this form, a linear variation betweenTgand composition is assumed, which may not be strictly correct but still yields usef

ISSN:0021-8995    

DOI:10.1002/app.1967.070110807

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

年代:1967

数据来源: WILEY

摘要:

AbstractDifferential thermal analyses of many 66 nylon samples have shown two endotherms in the melting range. This effect occurs with drawn nylon yarn, as previously observed by White, and also with annealed and precipitated nylon samples. Methods for the preparation of these samples are reported. At 242°C. the development from the melt of crystalline material which gives two melting peaks is associated with annealing rather than with the primary crystallization process. Previous observations of multiple melting peaks with other polymers are discussed

ISSN:0021-8995    

DOI:10.1002/app.1967.070110808

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

年代:1967

数据来源: WILEY

摘要:

AbstractFurther studies of a new and highly effective method for the surface treatment of low surface energy polymers for adhesive bonding are reported. Mechanisms are suggested for the increase in the cohesive strength in the surface region of polyethylene when it is exposed to activated species of inert gases. The technique is unique because, in contrast with results obtained with other methods, bulk properties of the polymer such as color or tensile strength and elongation are unaffected and surface properties such as wettability and dielectric properties such as surface conductivity are essentially unchanged.

ISSN:0021-8995    

DOI:10.1002/app.1967.070110809

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

年代:1967

数据来源: WILEY

摘要:

AbstractDynamic mechanical measurements were made with a torsional pendulum of a TiO 2 −filled epoxy polymer (crosslinked with hexamethylene diamine) over a temperature range from 20–90°C., at filler concentrations of 0–40 wt.‐%. The second‐order transition temperature (Tg) was raised as the filler content increased. The behavior of TiO2filler results in a long‐range immobilization of the highly crosslinked system with resultant increases in shear modulus (higherG′) as well as decreased capacity for energy dissipation (lower damping factor). The out‐of‐phase modulus (G″) increased with filler content as well. The magnitudes of the slope parametersHr(representingG′ data aboveTg) andHg(representingG′ data belowTg) decreased with greater filler content. The possibility is set forth that the TiO2filler causes a different distribution of mobility around the nitrogen junction as well as a change in the effective number of

ISSN:0021-8995    

DOI:10.1002/app.1967.070110810

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

年代:1967

数据来源: WILEY