摘要:

AbstractTo clarify the stereospecificity of Natta‐type catalysts, the temperature dependence of the isotacticity of a polypropylene has been investigated by using H‐type or A‐type TiCl3with Al(C2H5)3or Al(C2H5)2Cl in a study of the kinetic behavior of the polymerization under the conditionsT= 30–75°C.,P≈︁ 1 atm., and [Al]/[Ti]= 1. With the use of Al(C2H5)3the isotacticity increases with a rise in polymerization temperature, and it approaches that of Al(C2H5)2Cl, which is almost independent of the polymerization temperature. On the other hand, with the use of Al(C2H5)3the number of the polymerization centers decreases with a rise in temperature, while that with Al(C2H5)2Cl remains unchanged. To explain these results, two kinds of polymerization center have been proposed; one is stable at any temperature and produces a higher‐isotacticity polymer, and the other is stable at the higher temperatures and produces a lowerisotacticity polymer. Some solvent effect of the isotacticity has been observed with the use of A‐TiCl3. The isotacticity with A‐TiCl3decreases by several per cent whenn‐heptane is used instead of toluene. This solvent effect has been explained on the basis of the existence of a considerable amoun

ISSN:0449-2994    

DOI:10.1002/polc.5070230203

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

年代:1968

数据来源: WILEY

摘要:

AbstractGraft copolymerization of methyl methacrylate onto bovine serum albumin (BSA), trypsin, and α‐amylase was carried out by the ceric ion method. The grafted polymer chains were separated by selective hydrolysis of the backbone proteins with hydrochloric acid. The number of grafting sites were 0.02 to 0.3 moles/mole. Graftings were greatly affected by denaturation of the protein molecule. It is concluded that the grafting onto BSA is likely to occur at cysteine and cystine residu

ISSN:0449-2994    

DOI:10.1002/polc.5070230204

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

年代:1968

数据来源: WILEY

摘要:

AbstractTypical Ziegler‐type catalysts derived from AIR3and TiCl4were found to be effective in the syndiotactic polymerization of methyl methacrylate at low temperatures. The influences of polymerization variables on the polymer yield, the molecular weight of the polymer produced, and the syndiotactic regulating capacity of the catalysts were investigated. In general AlEt3/TiCl4molar ratios of 3:10 mixing of both the catalyst components and aging of the catalyst system in the temperature range of −30 to 30°C. using aromatic hydrocarbon solvents such as toluene as a polymerization medium, and low polymerization temperature, such as −78°C. are the preferred conditions for the formation of syndiotactic, high molecular weight poly(methyl methacrylate) in high yield. From the results of testing catalyst activities of the separated catalyst systems it was concluded that some cooperation between AIR3and the insoluble Ti halide compound obtained by the reduction of TiCl4with AIR3is essential for the formation of syndiotactic poly(methyl methac

ISSN:0449-2994    

DOI:10.1002/polc.5070230205

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

年代:1968

数据来源: WILEY

摘要:

AbstractCommercial samples ofcis‐1,4‐polybutadiene andtrans‐1,4‐polybutadiene have been chlorinated with chlorine gas in a chloroform solution and precipitated with methanol. The precipitates were thoroughly washed with a large amount of methanol and dried in vacuum at 40°C. The samples were fractionated with the tetrahydrofuran‐water system at 40°C. The viscosity measurements were made at 30°C. in various solvents. The light‐scattering measurements were made with a modified Brice‐type light‐scattering photometer with unpolarized blue light and with a cylindrical cell, over the angular range from 35° to 145°, at room temperature. The relation between the intrinsic viscosity and the molecular weight was obtained for each sample. The unperturbed mean‐square end‐to‐end distance was estimated by the Stockmayer‐Fixman equation, and was used for calculating the conformational parameter\documentclass{article}\pagestyle{empty}\begin{document}$ \sigma = \;(\overline {r_0 ^2 } /\overline {r_{0f} ^2 })^{1/2} $\end{document}for each chlorinated sample. The relation between the chemical configuration and the chain conformation for each chlorinated sample was discussed in terms of the unperturbed molecular dimension and rotational isomers of model compounds for a rotation around the

ISSN:0449-2994    

DOI:10.1002/polc.5070230206

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

年代:1968

数据来源: WILEY

摘要:

AbstractPrecision measurements of dielectric properties of polytetrafluoroethylene and copolymers of tetrafluoroethylene and hexafluoropropylene were made over a temperature range of –40 to +180°C. at frequencies of 10 Hz to 300 kHz. Polytetrafluoroethylene exhibited the typical dielectric behavior of a nonpolar substance: no dielectric loss peak was found over the experimental range of temperature and frequency. The dissipation factor remained constant, being about 2 × 10−5. Copolymers of tetrafluoroethylene and hexafluoropropylene showed two dielectric loss peaks: one occurred at about 100°C. and the other at about −20°C. There was a break point, or an abrupt bend, near 60°C. in the curve of dielectric constant versus temperature, indicating the existence of a transition point. The high‐ and low‐temperature loss peaks correspond to the α and γ relaxations, respectively, which have been found for the mechanical behavior of this copolymer. The dielectric relaxation in the copolymer was attributed to the slightly polar nature of the perfluoromethyl side groups. The activation enthalpy and entropy are 80 kcal./mole and 180 eu for the α relaxation and 12 kcal./mole and 15 eu for the γ relaxation, respectively. The σ and γ relaxations are discussed in connection with the molecular motion of

ISSN:0449-2994    

DOI:10.1002/polc.5070230207

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe piezoelectric modulus of Wood has been measured in the temperature range of −170°C. to +150°C. The kind of wood investigated is hinoki (Chamaecyparis obtusaEndl.). When a sinusoidal stress is longitudinally given to the thin plate specimen, the polarization is produced in the direction perpendicular to the surface of the plate. It has been found that the piezoelectric modulus generally increases with the rise of temperature. However, the modulus‐temperature curve shows discontinuous changes in slope at about −80, 30, and 130°C. These temperatures seem to be associated with transitions in amorphous regions of cellulose and other macromolecules in wood. Gamma‐ray irradiation up to 1.7 × 108rad causes little variation in the magnitude and the temperature dependence of the piezoelectric modulus. Treatments with liquid ammonia, sodium hydroxide, and ethylenediamine result in a large increase in the magnitude and the temperature dependence of the piezoelectric modulus. The crystal lattices of cellulose II and III are more favorable than that of cellulose I for producing the piezoelec

ISSN:0449-2994    

DOI:10.1002/polc.5070230208

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe mechanism of enzymic film formation of Japanese lacquer viao‐quinone derived from urushiol is revealed by the spectral and molecular‐weight changes of the substrate under mild enzymic oxidation as well as by the laccase‐catalyzed aqueous reaction of urushiol homol

ISSN:0449-2994    

DOI:10.1002/polc.5070230209

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe flow behavior of a solution of poly(vinyl pyrrolidone) (Mv, 1.0 × 104−9.0 × 105) has been studied at 35°C. in pure water, in 0.25MMgCl2aqueous solution, inn‐propanol, and in water‐n‐propanol at various concentrations (0.5‐1.5 g. per 100 ml.). The measurements were carried out with a Maron‐Belner low‐shear capillary viscometer with various capillary bore sizes (radiusR, 0.0190–0.0761 cm.) within the range of shear stress, 0.2–20 dynes/cm.2at the capillary wall. The viscosity is 10–30% lower in the smallest capillary bore than in the largest one at the same shear stress. This phenomenon may be attributed to a steric hindrance of the capillary wall to the thermal motion of the polymer molecules near the wall. The results are represented by the modified Ree‐Eyring generalized flow formula, for a flow system containing one Newtonian flow unit and one non‐Newtonian unit, which includes the new additional terms dependent on the capillary bore size. Furthermore, by assuming the existence of wall layer (of thicknessd) in the liquid flowing in the capillary tube an equation of the viscosity was derived, and by combining this equation with the aforementioned equation a calculation of the thicknessd, where the rate of shear tends

ISSN:0449-2994    

DOI:10.1002/polc.5070230210

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

年代:1968

数据来源: WILEY

摘要:

AbstractOsmotic pressures of polydimethylsiloxane in chlorobenzene, toluene, and cyclohexane were measured over a wide range of concentration (0

ISSN:0449-2994    

DOI:10.1002/polc.5070230211

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

年代:1968

数据来源: WILEY

摘要:

AbstractVolume‐temperature relations of six kinds of epoxy resin‐acid anhydride composite and different curing times are discussed on the basis of free‐volume and occupied‐volume concepts. The specific volumeVaat a fixed temperature aboveTgdecreases linearly with increasingTg, but the specific volumeVbbelowTgincreases linearly. The specific volumeVgatTgincreases linearly with increasingTg. The relation betweenTgand log crosslinkage is linear except in the final stage of the curing process. The slopeBof theVg‐Tgrelation is obtained from the iso‐free‐volume theory of glass‐transition phenomena asB=Voαb(1 – ΔVo/Vf·Vf/Vo· αa– αb/αb), whereVois the occupied volume,Vfthe free volume, αa– αbthe thermal expansion coefficient of free volume, αbthe thermal expansion coefficient of occupied volume;Vois the sum of the two componentsVoandVo, whereVois the occupied volume in the strict sense andveis the empty volume into which polymer chains cannot flow. The equation predicts quali

ISSN:0449-2994    

DOI:10.1002/polc.5070230212

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

年代:1968

数据来源: WILEY