摘要:

AbstractThe concentration of solvent in the gel phase of a swelling polystyrene–divinylbenzene copolymer bead has been measured as a function of the radius by optical interference techniques. It is found that an appreciable gradient exists even shortly after the core disappears. Results are presented for two cases: a very lightly crosslinked bead that exhibits negligible birefringence while swelling, and a more tightly crosslinked network in which the birefringence must be considered. It is also found that the refractive index of the unswollen bead is considerably less than that found by extrapolation from the swollen state; this effect is reasonable when the “free volume” in the bulk polymer is consi

ISSN:0449-2978    

DOI:10.1002/pol.1967.160050501

出版商:John Wiley&Sons, Inc.    

年代:1967

数据来源: WILEY

摘要:

AbstractThe dispersion of birefringence in oriented amorphous polymers is discussed. It is shown that for polystyrene, the birefringence can be considered as the product of an orientation function and a function of the wavelength of the light. This leads to a method for expressing the birefringence dispersion as a function that is characteristic of the polymer. This function is determined for polystyrene, and from it the birefringence at infinite wavelength is found to be 11% lower than that measured with the mercury green line (5461 A.).

ISSN:0449-2978    

DOI:10.1002/pol.1967.160050502

出版商:John Wiley&Sons, Inc.    

年代:1967

数据来源: WILEY

摘要:

AbstractThe molecular dimensions of polydipropylsiloxamer were studied by intrinsic viscosity measurements in toluene and in 2‐pentanone. The relationships between the molecualr weight and the intrinsic viscosity were found to be: [η]25°C., toluene = 4.35 × 10−4M0.58; [η]θ(10°C.), toluene = 1.09 × 10−3M0.5; [η]θ(76°C.), 2‐pentanone = 8.71 × 10−4M0.5. This held reasonably well for molecular weights from 25,000 to 3000,000. The root‐mean‐square end‐to‐end length ratio, (r02/M)1/2as calculated from the constantK, exceeds the free rotation value by approximately 100%. The disparity is greater than that found with polydimethylsiloxamer, indicating a lower degree of flexibility for the polydipropylsiloxamer. This is largely due to the short range steric interaction between near neighboring units of the chain. Gel permeation chromatography was also employed to demonstrate the lower degree of flexibility for polydipropylsiloxamer as compare

ISSN:0449-2978    

DOI:10.1002/pol.1967.160050503

出版商:John Wiley&Sons, Inc.    

年代:1967

数据来源: WILEY

摘要:

AbstractThe present study is concerned with some network properties of polyurethane elastomers in which stability is acheived via physical crosslinkages such as microcrystallites or secondary bonding. The techniques of isothermal, thermo‐, and photoelasticity have been used to gain better insight into the mechanisms which occur during the deformation of these materials. It was found that stable networks are obtained only after mechanical and thermal conditioning. The well‐known stress lowering which is observed during the second deformation is manifested primarily in the entropy component of the retractive force. This implies that the stress lowering results from a reduction in the number of effective network chains and not from time‐dependent effects or crystallinity changes. Depending upon the chemical structure of the material, both positive and negative energy components of the force have been

ISSN:0449-2978    

DOI:10.1002/pol.1967.160050504

出版商:John Wiley&Sons, Inc.    

年代:1967

数据来源: WILEY

摘要:

AbstractIn earlier work we have indicated a superposition principle for moderately concentrated mixtures (c≲ 2/[η]) in good and poor solvents. By an examination of data on a number of vinyl polymers and cellulose derivatives in good as well as poor solvents, the validity of this principle is extended to concentrated solutions (c≲ 50%). The characteristic concentration factor γ is proportional toM −a 1over the whole concentration range, with 0.47 ≤ a1≤ 1.10 being larger for good than for poor solvents, the result obtained earlier. Significant deviations from this relationship are noted in good solvents for those low molecular weights at which deviations from the usual intrinsic viscosity relationship occur. This may be related to the expansion factor of the polymer coil. On the basis of these results, the concentration and molecular weight dependence of the viscosity in the concentrated solution can be related to each other in terms of the parameter a1and thus to thermodynamic characteristics. In this manner a bridge between the relatively dilute and concentrated regions is established. Currently used semiempirical expressions are analyzed in terms of these results. For the polystyrene–cyclohexane systems and θ − 9 ≦T≦ θ + 3, γ can be identified with the critical concentration for phase separation. Provided an “entanglement” concentrationceexists, in the neighbourhood of which the concentration dependence of the viscosity changes reapidly, γ can alternatively be shown to be proportional toce, orce∝M −a 1. The temperature reduction scheme sugge

ISSN:0449-2978    

DOI:10.1002/pol.1967.160050505

出版商:John Wiley&Sons, Inc.    

年代:1967

数据来源: WILEY

摘要:

AbstractAn extension of the results of a previous to higher molecular weights is made. The viscoelastic parameters ηt,Je, τm, andEmare found experimentally through stress relaxation tests. The predictions of the Rouse‐Bueche (RB) theory and its modified Ferry, Landel, Williams (FLW) form concerning the molecular weight dependencies of these perameters are compared with the data. It is found that the RB and FLW predictions are not rigorously obe

ISSN:0449-2978    

DOI:10.1002/pol.1967.160050506

出版商:John Wiley&Sons, Inc.    

年代:1967

数据来源: WILEY

摘要:

AbstractLiving polystyrene was grafted on fractions of poly(methyl methacrylate) by an anionic grafting reaction. Unreacted polystyrene was separated by fractional precipitation. The composition of copolymer, i.e., the molecular weight of main chains and side chains, was determined. The influence of molecular weight and structure of graft copolymers on the intrinsic viscosity of solutions was examined. This may be expressed in the form [η] =KMagn. The dependence betweenaandnin this equation was established

ISSN:0449-2978    

DOI:10.1002/pol.1967.160050507

出版商:John Wiley&Sons, Inc.    

年代:1967

数据来源: WILEY

摘要:

AbstractMolecular weightMand concentrationcdependencies of the zero‐shear viscosity (η) were measured over wide ranges ofMandcfor concentrated solutions of linear and branched poly(vinyl acetate) as well as of polystyrene under θ conditions. The log η versus logMand log η versus logccurves for a given system can be superposed by the horizontal shift along the abscissa, giving smooth master curves. From the shift factors the ratio of two exponents β and α, which appear in the following equation, can be evaluated: η =K′(cρ)αMβ, where ρ is the density of the solution andK′ is a constant at constant temperature. The evaluated values of β/α for the systems under θ conditions are equal to or very close to 0.50 as was anticipated from the previous work. The above superposition method was also applied to available viscosity data, and it was found that β/α had a good correlation withain [η] =KMa. This indicates that the individual molecules in concentrated solutions maintain the same individuality as in dilute solutions, and might be a positive support to the packed sphere model proposed previously by the authors. The effect of solvent on the molecular weight and the concentration dependencies of viscos

ISSN:0449-2978    

DOI:10.1002/pol.1967.160050508

出版商:John Wiley&Sons, Inc.    

年代:1967

数据来源: WILEY

摘要:

AbstractThe homopolymer and many of the copolymers ofN‐acrylylglycinamide yield thermally reversible gels in water. These systems are uniquely suitable for studying synthetic photographic gelatin substitutes and for understanding the mechanism of the gelation process. Polymerization ofN‐acrylylglycinamide has been studied under a variety of conditions. The homopolymer is aggregated in dilute aqueous solution and probably molecularly dispersed in 2Mthiocyanate solution. At concentrations of several per cent, in water, thermally reversible gels are formed whose melting points rise with increasing concentration and increasing molecular weight. The heat of gelation crosslinking has been calculated to be −8.8 kcal./mole of crosslinks. Introduction of small amounts of carboxyl groups into the polymer raises the melting points of the aqueous gels. The effect of various organic and inorganic reagents on gelation is presented. The ability to prepare copolymers which can be flocculated has been demonstrated as well as the usefulness of the monomer in certain types of photoresist systems. Copolymerization with acrylic acid and β‐aminoethyl vinyl ether has been studied, and ther1andr2values for these systems have been calculated as well asQandevalues forN‐acrylylg

ISSN:0449-2978    

DOI:10.1002/pol.1967.160050509

出版商:John Wiley&Sons, Inc.    

年代:1967

数据来源: WILEY

摘要:

AbstractFree radicals produced in irradiated polypropylene were studied by the electron spin resonance method. Two temperature regions in which the free radicals decay rapidly were found at around 170°K. and 260°K. The first temperature region corresponds to the γ‐dispersion of polypropylene and the second to the β‐dispersion. Steric configurations of the free radicals were investigated, and it was concluded that the free radicals trapped in polymer, conformation of which is appreciably twisted from the stable31‐helical structure, decay with small‐scale motion of the matrix polymer. The decay of free radicals trapped in polymer of less twisted conformation is associated with the large‐scale motion of the matrix polymer. Activation energies of decay were found to be 11 kcal./mole at the lower temperature and 48 kcal./mole at the higher temperature. Time constants of the decay reactions were compared with those for molecular motion of the matrix, with results reflecting the relations of the decay of the polymer radicals to molecular motion

ISSN:0449-2978    

DOI:10.1002/pol.1967.160050510

出版商:John Wiley&Sons, Inc.    

年代:1967

数据来源: WILEY