摘要:

AbstractThe mechanism of precipitation polymerization of vinyl chloride was studied by gradual transition from homogeneous to heterogeneous polymerization. Diethyl oxalate and 2,4‐dichloropentane were used as solvents. In diethyl oxalate the initial course of polymerization is homogeneous up to 7.5 moles/l. The order with respect to monomer is 1.2. At higher concentration of monomers, the order decreases due to aggregation. From about 10 moles/l, the polymerization is heterogeneous. A break is observed in the kinetic curves with a distinct acceleration accompanied by a decrease of the order with respect to monomer and of the degree of polymerization. In the presence of CBr4the polymerization is heterogeneous in the whole range of monomer concentration studied. In 2,4‐dichloropentane the initial rate is lower than in diethyl oxalate and the order with respect to monomer is 1.6. It was shown that in the initial course of precipitation polymerization the propagation rate decreases to such an extent that a termination reaction besides the transfer to monomer bimolecular termination must be taken into considerat

ISSN:0449-2994    

DOI:10.1002/polc.5070160203

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

年代:1967

数据来源: WILEY

摘要:

AbstractThis paper describes a study of dilute solutions of polycaprolactam in mixed solvents TFP‐H2O‐LiCl with the objective of finding the most convenient solvent for determining the molecular weight of polyamides by the light‐scattering method. Selective adsorption of both TFP and LiCl on the polyamide has been proved and quantitatively determined. The adsorption of TFP decreases the measured value of molecular weight, whereas that of LiCl increases it. A composition has been found (TFP‐10% H2O‐0.1MLiCl) in which the two effects exactly compensate. In this mixed solvent 24 fractions of hydrolytic and alkaline polycaprolactams were measured in a rangeMw= 9 × 1033to 3.5 × 105. The same solvent andm‐cresol have also been selected for measuring the intrinsic viscosities and determining the constants of the Mark‐H

ISSN:0449-2994    

DOI:10.1002/polc.5070160204

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe kinetics of pheriyl glycidyl ether polymerization in dichloroethane using boron trifliioride as a catalyst was studied. The polymerization is very fast in the absence of water and both the conversion obtained and the reaction rate depend only on boron tri‐ fluoride concentration. The initial rate of polymerization decreases and the yield in‐ creases with increasing water concentration. The rate of polymerization depends on boron trifluoride and monomer concentrat

ISSN:0449-2994    

DOI:10.1002/polc.5070160205

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

年代:1967

数据来源: WILEY

摘要:

AbstractDensity, morphology, and melting data on linear polyethylene and high molecular weight polymethylene crystallized from the melt under elevated pressure are presented. For approximately constant supercooling a sharp density increase is noted above 2300 atm. crystallization pressure. Above 4000 atm. densities above 0.99 are achieved. The high molecular weight polymethylene has larger lamellar thickness than polyethylene, but does not reach full chain extension. The melting of polymethylene is extremely sharp with no evidence of premelting up to at least 136°C. Equilibrium maximum melting points of 138.7 and 141.4°C. have been measured for polyethylene of 105weight‐average molecular weight and polymethylene of 107molecular wei

ISSN:0449-2994    

DOI:10.1002/polc.5070160206

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

年代:1967

数据来源: WILEY

摘要:

AbstractParameters of the phase equilibrium of the system atactic polypropylene‐atactic polystyrene‐toluene (volume of phases, molecular weight, and relative and total concentration of polymers in both phases) as a function of concentration of polymers and temperature have been studied. Considerable changes of the parameters were found in the vicinity of the point at which formation of one‐phase systems occurs. Limiting miscible concentrations and temperatures in which the system becomes homogeneous for various molecular weights of both polymers have been determined. On the basis of the Flory‐Huggins theory the polymer‐polymer interaction parameter α23has been calculated from the parameters of the phase equilibria as well as from the critical parameters of the system. The value of the interaction parameter depends on the temperature and the concentrations of polymers in the system. From our results we can obtain a very approximate value of the interaction parameter [α23] for a homogeneous mixture of polypropylene‐polystyrene in the absence of solvent. This value could be a measure of the compatibility of a pai

ISSN:0449-2994    

DOI:10.1002/polc.5070160207

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

年代:1967

数据来源: WILEY

摘要:

AbstractLow molecular weight silanolates of tetramethylammonium hydroxide and tetrabutylphosphonium hydroxide have been prepared. The kinetics of octamethylcyclo‐tetrasiloxane polymerization induced by either of these bases was studied and the activation energies were determined. It was found that the activities of these catalysts were much greater than that of the potassium silanolate (about 50–150 times). Nevertheless the activation energies did not differ from those found for polymerizations catalyzed by alkali metal silanolates (19.5 kcal./mole). The polymerization rate of the octamethylcy‐clotetrasiloxane‐tetramethylammonium silanolate system is thus comparable to the polymerization rate of the potassium silanolate‐tetradecamethylcycloheptasiloxane system, which is the most reactive of the low molecular cyclic poly (dimethyl siloxanes). Also the decomposition of the silanolates of the onium compounds was studied. It was found that tetramethylammonium silanolate is more stable than the phosphonium compound, the half‐time of decomposition at 100°C. of the former being more than five times that of the latter. Activation energies of the decomposition were also different: 42 kcal./mole for the ammonium compound and 28.5 kcal./mole for the phosphonium compound. This corresponds to a different proposed mechanism of the reaction, as described by Ingold. The most striking feature is that the decomposition follows first‐order kinetics. By analogy with experiments performed by Ingold and his co‐workers, we expected the second‐order kinetics in this medium of low dielectric constant. The first‐order kinetics was found even if excess potassium silanolate was added at 120°C. The rate of decomposition remained unaffected, the half‐time of decomposition being 27 min. This agrees quite well with the value of 24 min. found at the same temperature in the absence

ISSN:0449-2994    

DOI:10.1002/polc.5070160208

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

年代:1967

数据来源: WILEY

摘要:

AbstractBinary mixtures of polystyrene, two low molecular weight model compounds, ethyl‐benzene and 1,3‐diphenylbutane, and benzene have been studied. The mixing parameters of these systems have been determined by calorimetry, pyenometry, and osmometry, and by measurement of vapor pressures and degrees of swelling. The results correspond qualitatively to predictions from the cell theory and from theories based on the theorem of corresponding states. The enthalpy, entropy, and volume of mixing are more negative in the homologous series for a greater difference in the molecular sizes of the components; the free enthalpy of mixing, however, becomes less negative and thus thexparameter increases. Several equations, useful in evaluating the mixing parameters according to the new Flory et al.11,12theory have been derived. The values of the interaction parameterx12have been calculated by means of these, and it has been found that the theory represents the measured data semiquantitativ

ISSN:0449-2994    

DOI:10.1002/polc.5070160209

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe decomposition of dicumyl peroxide in polyethylene‐polyisobutylene mixtures initiates, along with the crosslinking of polyethylene and the degradation of polyiso‐butylene, the formation of an interpolymer as a consequence of the interpolymer combination of macroradicals. Analysis of the kinetics of these transformation processes involves obtaining data for the transformation of the individual polymers in toluene solution, verification of the derived quantitative relations for the model system polyethylene‐low molecular weight only polyisobutylene, and finally application of these relations to a mixture of high molecular weight polymers. On the basis of the obtained results, the physical import of the individual kinetic parameters is interpreted, and the values are compared for the two types of mix

ISSN:0449-2994    

DOI:10.1002/polc.5070160210

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

年代:1967

数据来源: WILEY

摘要:

AbstractA new method for the determination of diffusion as well as partition coefficients of low molecular weight substances in membranes of polymers was developed, based on the solution of Fick's equation with appropriate boundary conditions (both concentrations variable). On its basisDandkof dilute (0.05%) KCl solutions in swollen hydrophilic gels of different porosity were determined. From the temperature dependence of diffusion coefficients the activation energy of the process was computed and a simple model describing the structure of the heterogeneous membrane was proposed. The diffusion coefficients strongly depend on the structure of the system investigated.

ISSN:0449-2994    

DOI:10.1002/polc.5070160211

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe preparation of aromatic macromolecular structures by nucleophilic substitution reactions (A), in which polymerization proceeds via the formation of ether linkages, and by the electrophilic substitutions, (B) and (C), where sulfone or ketone linkages are formed is described.

ISSN:0449-2994    

DOI:10.1002/polc.5070160212

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

年代:1967

数据来源: WILEY