摘要:

AbstractA series of polymers have been prepared that contain ethyl,n‐propyl,n‐butyl,n‐pentyl, andn‐hexyl branches. We have determined the rocking vibrations of the branches and have shown that branches in solid polymers have their rocking vibrations at frequencies comparable with those shown by liquid hydrocarbons. The ethyl branches in seven different polymers have infrared absorption bands in the 785–760 cm.−1(12.74–13.18 μ) region. The terminaln‐propyl group absorbs at 740 cm.−1(13.51 μ) and then‐propyl branch at 735 cm.−1(13.61 μ). Then‐butyl,n‐pentyl, andn‐hexyl branches in polymers have their infrared absorption at 724 cm.−1(13.81 μ), 723 cm.−1(13.83 μ) and 722 cm.−1(13.85 μ), respectively. The above data have been used to identify ethyl,n‐propyl, andn‐butyl branches in polymers produced by the cation

ISSN:0021-8995    

DOI:10.1002/app.1961.070051501

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

年代:1961

数据来源: WILEY

摘要:

AbstractThe heterogeneous anionic polymerization of acrylonitrile in petroleum ether by potassium alcoholic alkoxide solutions at low temperature was studied. Alkoxides of the more electropositive metal were more active catalysts, ROK>RONa. Increasing amount of alcohol in the polymerization mixture up to a limit, had an activating effect. Yield of polymer increased with catalyst concentration. The mechanism of the polymerization consists of initiation by direct interaction of alkoxide anion with monomer, with no cocatalyst; this is substantiated by the presence of alkoxyl groups in the polymers and by the existence of steric effects of bulkyl alkoxide groups. Termination is by proton abstraction from alcohol. In accordance with this, the degree of polymerization was found to be independent of catalyst concentration, directly proportional to monomer, and inversely to alcohol concentrations, according to the equation, DP =kp[M]/kt[ROH]. Plot of DP versus monomer and the reciprocal of the alcohol concentrations gave values forkp/ktof about 35. All polymerizations showed an induction period with the following regularities. It increased with increasing concentration of alcohol and with lowering of temperature, and decreased with increasing catalyst and monomer concentrations and was smaller with the more active potassium catalysts. Induction periods seem to originate from the competing side‐reaction of cyanoethylation, the initiation step of the polymerization being identical with the first step (RO−addition) in the cyanoethylation reaction. Cyanoethylation products were isolated from polymerization mixtu

ISSN:0021-8995    

DOI:10.1002/app.1961.070051502

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

年代:1961

数据来源: WILEY

摘要:

AbstractPrevious investigations on the solution properties of sodium carboxymethylcellulose (CMC) have led to the conclusion that crystalline cellulose regions, remaining after processing act as binding or crosslinking sites for the establishment of a fraction comprised of swollen gels or aggregates in solution. The present paper deals with recent work which has led to a broader characterization of the degree of aggregation of CMC and its control in solution. Stages of disaggregation are defined for CMC when added to a solvent, ranging from a polymer particle unaffected by solvent through various degrees of swelling to a state of complete dispersion. Examples are given of these various disaggregation stages which were attained and controlled by varying the solvation power and/or ionic strength of the solvent. Degrees of disaggregation were characterized by broad variations in rheological behavior. Viscosity differences of several hundredfold as well as other physical changes in the solutions were found. The results are interpreted to mean that the numerous binding centers which cause CMC aggregation have a wide distribution of strengths. The addition of CMC to a good solvent causes the weaker binding forces to be destroyed and the stronger to remain intact, imparting rheological properties commensurate with the resulting degree of aggregation. The use of a poorer solvent or the addition of a simple electrolyte causes fewer binding centers to be destroyed, and a corresponding change in dispersion properties. Little, if any, re‐formation of broken binding centers has been detected. Known and proposed forces involved in the dispersion of macromolecules into solvent are discussed and applied to observations from the present wor

ISSN:0021-8995    

DOI:10.1002/app.1961.070051503

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

年代:1961

数据来源: WILEY

摘要:

AbstractA previously reported theory for the Mullins softening effect has been used to interpret various new data for the behavior of filled SBR rubber under tensile load. The strength of the filler–rubber bond, the filler surface area per polymer molecule attachment, and the average filler surface separation have been determined for two fillers, HAF black and Hi Sil‐233 (a silica). A styrene–butadiene type filler (Pliolite S‐6) has also been investigated. The temperature dependence of the filler–rubber bond has been measured; results lead to the conclusion that the bonds to carbon black and silica are high energy bonds, probably chemical in nature. It is shown that the recovery of hardness in prestretched, filled SBR is a rate process having an activation energy of about 22 kcal./mole. It is inferred from this and from permanent set data that the recovery is the result of the chemical breaking and reforming of the rubber chain network at the higher temperatures where recovery occurs. Silica‐filled rubbers are shown to possess a pseudoyield stress which gives rise to an anomalous shape for the stress–strain curve of this material when it is stretched for the first time. A prestretched, silica‐filled rubber recovers its hardness when left at 115°C. for 20 hr., but the anomalous portion of the curve is replaced by more normal behavior. Possible interpretations of the observed r

ISSN:0021-8995    

DOI:10.1002/app.1961.070051504

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

年代:1961

数据来源: WILEY

摘要:

AbstractA method is described by means of which reliable intrinsic viscosities, [η], can be obtained for a polymer–solvent system from viscosities determined at only one concentration. The method involves, first, the preparation for one sample of the polymer of an ηsp/Cand ln ηr/Cvs.Cplot. The ratio of the slopes of these two curves yields then a parameter γ which is independent of molecular weight, and which allows single point [η] determinations on samples of the polymer at any other molecular weight, whether homogeneous or not. Results are presented to show that the method described yields [η]'s in good agreement with those obtained in the usual manner from multipoint viscosity measu

ISSN:0021-8995    

DOI:10.1002/app.1961.070051505

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

年代:1961

数据来源: WILEY

摘要:

AbstractThermogravimetric data are generally more extensive than are comparable isothermal aging data, and therefore afford preliminary kinetic information in greater abundance. The kinetic analysis of the thermogram, by use of either its exact equation or a more convenient approximation formula, is straightforward in cases of volatilization via simple kinetics. Application of the analytical procedure to the thermogram for the zero‐order volatilization of octamethylcyclotetrasiloxane yielded an estimate of 11.65 kcal./mole as the average heat of vaporization in the temperature range of 80 to 145°C. The apparent activation energy for the first‐order pyrolytic volatilization of 200‐mg. samples of pulverized polytetrafluoroethylene was estimated to be 66 to 68 kcal./mole in the temperature range of 520 to

ISSN:0021-8995    

DOI:10.1002/app.1961.070051506

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

年代:1961

数据来源: WILEY

摘要:

AbstractThe sulfur contentsScand degrees of chemical crosslinking 1/2M*c,chemhave been determined for a series of vulcanizate networks obtained by curing unaccelerated natural rubber–sulfur mixes for various times at 140°C. The independent estimates of 1/2M*c,chemwere obtained for each vulcanizate from stress–strain measurements (C1and λ*) on the unswollen vulcanizate and use of the methods described by Mullins. The disparity in the values of 1/2M*c,chemobtained by the two methods reflects the scission of natural rubber main chains during the vulcanization process, the extent of such scission being found to increase with increasing cure time. When allowance is made for chain scission theScand 1/2M*c,chemdata yield values of the efficiency of sulfur as a crosslinking agent. It is found that between about 40 and 55 sulfur atoms must be combined in the network to produce one chemical crosslink, values which reflect the marked structural complexity of the network as is also inferred from the structures of the products derived from sulfur–olefin interaction a

ISSN:0021-8995    

DOI:10.1002/app.1961.070051507

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

年代:1961

数据来源: WILEY

摘要:

AbstractTreatment of unaccelerated natural rubber–sulfur vulcanizate networks with triphenylphosphine in benzene at 80°C. effects the removal of part of the combined sulfur, the proportion removed decreasing with increasing cure time. This partial desulfurization of the network is attributed, on the basis of the mode of interaction of simple organic di‐ and polysulfides with triphenylphosphine, to the conversion of polysulfide linkages in the network into either mono‐ or disulfide groups. Knowledge of the amount of sulfur removed by the reagent, and of the chemical degree of crosslinking and combined sulfur content of the untreated networks permits the following semiquantitative conclusions to be reached concerning the structures of the sulfur linkages in the networks: (1) long polysulfidic crosslinks (S11 to S12) are initially formed, which on continued cure progressively decrease in length to a limiting value of S2 to S4; and (2) a very high proportion to the combined sulfur (ca. 77% for short cure times, increasing to ca. 95% on extended cure) is present in cyclic monosulfide groups situated along t

ISSN:0021-8995    

DOI:10.1002/app.1961.070051508

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

年代:1961

数据来源: WILEY

摘要:

AbstractThe glass‐transition temperaturesTgof various copolymers of acrylonitrile and vinyl acetate were measured by observing the linear expansion of molded discs. For vinyl acetate contents of 0 to 27 wt‐.% the glass temperature is constant at 87°C. This value agrees with the results of Kolb and Izard for pure polyacrylonitrile. Fitting of the glass temperature–composition data above 27% vinyl acetate to the equation of Fox and Loshaek leads to an extrapolated value of 110°C. for completely amorphous polyacrylonitrile, which agrees with similar data of Krigbaum and Tokita. The difference between the two values can be explained in terms of the effects of crystallinity analogous to those discussed by Nielsen for ethylene–vinyl acetate copolymers. Moreover, experimental values of 92 and 103°C. were found for specially prepared samples of polyacrylonitrile. These samples were found to be less crystalline or to have a different ordering of the polymer chains as evidenced by x‐ray data. It is concluded that the glass temperature of completely amorphous polyacrylonitrile can be no greater than 110°C. and that experimental values for semicrystalline polyacrylonitrile may range

ISSN:0021-8995    

DOI:10.1002/app.1961.070051509

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

年代:1961

数据来源: WILEY

摘要:

AbstractButadiene, and butadiene and styrene, can be emulsion polymerized and copolymerized smoothly and rapidly in the presence of carbon black when the initiator is hydroperoxide rather than persulfate. With 15 parts of black per 100 parts monomer the recipe developed yields 100% conversion in 5–6 hr. and it insensitive to either molecular oxygen or appreciable quantities of ferrous iron. However, it is strongly dependent on the method employed for dispersion of the carbon black prior to polymerization. The latices obtained are very fluid and stable, showing no tendency either to cream or to settle. Nevertheless, they coagulate readily and cleanly with salt–acid to yield nonbleeding polymers containing all the black charged. The Mooney viscosities of the polymers are very high, ranging from 120 to 170. In spite of this, the rubbers mill easily and smoothly, and they rapidly absorb on a mill any additional carbon black to be incorporated. Butadiene–styrene copolymers, prepared at 50°C. by reaction to 70% conversion in the presence of 15 parts of black and compounded to 40 parts carbon black per 100 parts polymer, have been found to yield ultimate tensile strengths of about 4100 psi at 660% elongation. These tensile strengths are superior to those shown by comparable rubbers prepared at 50°C. in the absence of carbo

ISSN:0021-8995    

DOI:10.1002/app.1961.070051510

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

年代:1961

数据来源: WILEY