摘要:

AbstractMeasurements of crosslinking,trans‐vinylene formation, and hydrogen evolution have been made on high‐ and low‐density polyethylenes irradiated at temperatures from about −170 to +240°C. Crosslinking produced during irradiation is mainly in the amorphous areas of the polymer; whereastrans‐vinylene unsaturation is produced as readily in the crystalline areas as in the amorphous areas. Radicals are trapped in the crystalline regions. These can react with oxygen to form carbonyl groups, rather than crosslinks. Thus, in Marlex‐50 irradiation in the crystalline state at 25°C. followed by a 7 day storage in air prior to the crosslinking measurements, was only about one‐sixth as effective in producing crosslinks as irradiation in the amorphous state at 150°C. In the low‐density polyethylene where less trapping occurs the factor is about one‐half for the same conditions of irradiation and storage. The lifetime of radicals trapped in Marlex‐50 when stored in oxygen can be thousands of hours compared with a few hours in low density polyethylene. Both the low‐density polyethylene and Marlex‐50 irradiated in the crystalline state at 25°C. (in nitrogen) could be further crosslinked by quickheating them to the amorphous state at 150°C.—delayed carbonyl formation does not occur in this case. Delayed crosslinking resulting from the quick‐heating of irradiated Marlex‐50 gave only about one‐half of the crosslinks for the same irradiation as when irradiated in the amorphous state. Hydrogen evolution as a function of irradiation temperature for Marlex‐50 is discussed; a satisfactory material balance was obtained in which the radiation yield (Gvalue) for total hydrogen produced nearly equaled the sum ofGfor crosslinking andGfortrans‐vinylene formation. Hydrogen yield was found to be nearly constant in the temperature range −170 to +34°C. where crystallinity is also nearly constant, indicating hydrogen production to be nearly independent of temperature. Therefore, the main change in crosslinking yield in the +34 to +150°C. range is considered to be due almost entirely to change in crystallinity. A comparison method for determining relative values of the degree of crossl

ISSN:0022-3832    

DOI:10.1002/pol.1958.1203212501

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe previous paper discusses the effect of physical state during the irradiation on the fate of the polymer radicals produced. Additional experiments relating to trapped radicals in hydrocarbon polymers are discussed. Three different methods of detection were used; namely, infrared absorption at 5.8 μ, electron paramagnetic resonance, and gasuptake by the irradiated polymer. Conditions for producing trapped radicals at room temperature are that the polymer exist in the crystalline, glassy, or highly crosslinked form during irradiation. Radicals trapped in the crystalline or glassy areas can dissipate either as the result of heating the polymer aboveTmorTgor else by exposure to a radical scavenger, e.g., oxygen or ethylene. The lifetime of radicals trapped in Marlex‐50 can be many thousands of hours at room temperature. Radical decay will take place even with storage in vacuum if given enough time. The decay is arrested by holding the sample at liquid nitrogen temperature. Loss in radical activity in Marlex‐50 when stored in vacuum is due mainly to delayed crosslinking.Trans‐vinylene and vinyl do not appear to enter into the reaction responsible for the decay. A comparison of the decay of radicals trapped in unbranched Marlex‐50 with that in a branched low‐density polyethylene when stored in ethylene, oxygen, and vacuum was made. The results suggest that although radicals are trapped in the crystalline regions of both polymers, there are differences between the two crystals—the crystals in the low‐density polymer do not appear to be as tight as those in the Marlex‐50. Delayed oxidation reactions occurring in the crystalline regions of irradiated Marlex‐50 when stored in oxygen at room temperature require a number of intermediate steps before appearing as carbonyl. An average of 5 molecules of oxygen per polymer radical was used in forming carbonyl. Delayed main chain scissions occur during this process which cause severe embrittlement and loss in physical properties. Significant improvements in physical properties of Marlex‐50 can be achieved through irradiation, but radicals must not be left tr

ISSN:0022-3832    

DOI:10.1002/pol.1958.1203212502

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractAmylopectin samples were obtained from mature and immature sweet, dent, and waxy varieties of corn starch samples by dispersing the starch samples with either 6MLiBr or bufered amyl alcohol solutions. The degree of branching, molecular weights, and radii of gyration were obtained on these amylopectins. The results were explained assuming that Erlander's proposed mechanism for the synthesis of starch from glycogen is valid. The corn amylopectins and an immature sweet corn glycogen sample obtained from Schoch were hydrolyzed at a pH of 4.2 at the refluxing temperature. Samples were taken at various time intervals. The values ofMwobtained from these samples showed that glycogen and amylopectin behave as randomly formed polymers. The rates of hydrolysis obtained in these studies indicate that the large molecules in all corn endosperm amylopectins and glycogens exist in chemical aggregates of four. These chemical aggregates do not appreciably influence the statistical size distribution of the amylopectin and glycogen molecules. A comparison of the properties of a sweet corn glycogen sample and an immature sweet corn amylopectin sample indicates strongly that glycogen is a precursor to starch.

ISSN:0022-3832    

DOI:10.1002/pol.1958.1203212503

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractPolymers of methyl methacrylate, methyl acrylate, vinyl acetate, and acrylonitrile labeled with carbon‐14 in the functional groups have been prepared. The labeled polymers have been subjected to hydrolysis, and the specific activities before and after treatment have been compared. Almost complete hydrolysis of polymethyl acrylate and polyvinyl alcohol is readily achieved. It has been confirmed that polymethyl methacrylate is rather resistant to hydrolysis, but ester endgroups in this polymer are easily detached. During treatment of polyacrylonitrile with acid or alkali, no carbon atoms are lost from the polyme

ISSN:0022-3832    

DOI:10.1002/pol.1958.1203212504

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThere is a surprising lack of agreement between the values which have been reported for both the number‐average and weight‐average molecular weights of polyacrylonitrile. We have undertaken an investigation of both whole polymers and polymer fractions to discover and eliminate the sources of systematic error which would lead to these differences, and thereby to develop procedures yielding reliable molecular weight values for this polymer. Our experience indicates that the procedure which must be followed to obtain reliable osmotic data depends upon the conditions under which the polymer was prepared, whether the sample is a whole polymer or a fraction, and the purity of the solvent. Designating solution polymers by S and those prepared in an aqueous system with a persulfate‐bisulfite initiator by A, we conclude that reliable M̄nvalues can be obtained for S polymers by using dimethylformaide (DMF) which has been purified by deionization or distillation, for fractions of A polymers by using deionized DMF, and for whole A polymers by performing the measurements upon DMF solutions which have been deionized by passage through a column of Amberlite MB‐3 resin. Fictitiously low M̄nvalues are observed for A polymers dissolved in distilled DMF. The value of the secon virial coefficient is very ensitive to the presence of traces of water. Turning to weight‐average molecular weights, a 60% discrepancy exists between the values obtained from light scattering by Stockmayer and Casassa and by Bisschops from sedimentationdiffusion. We believe the correct M̄wvalues lie midway between these. A part of the 60% difference is due to the omission of a correction to the sedimentation data for the effect of hydrostatic pressure. This correction was evaluated from sedimentation data by the procedure of Oth and Desreux and increases the molecular weight values deduced from sedimentation by 30%. The remainder of the difference appears to be due to the effects of depolarization and fluorescence upon the light scattering data. Thus, our data for two fractions which exhibited a limiting depolarization ρu= 0.09 yielded high M̄wvalues standing in agreement with the relation of Stockmayer and Casassa, while the result obtained for a whole polymer having a negligible limiting depolarization agrees with those obtained from the corrected sedimentation data. The latter polymer also exhibited a more normal scattering behavior. A comparison of the weight and number‐average values indicates that the M̄w/M̄nratio is 2.1 ± 0.1 for the whole S polymers and 2.8 ± 0.3 for the whole A polymers. The broader distribution in the latter case suggests that termination occurs by both coupling and disproportionation in the aq

ISSN:0022-3832    

DOI:10.1002/pol.1958.1203212505

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe correctness of the application of the fraction method into summative fractions for polymer fractionation has been proved. The method of interpretation of the results of fractionation into summative fractions is explained. The basis of this method is the consideration of the function φ(β) which determines the relation between the average degree of polymerization and the weight fraction β of the summative fraction. The whole problem has been limited to the consideration of infinitely small calculated individual fractions. The paper describes the relation between the fractionation results and the selectivity of the polymer separation between the phases of the polymer‐liquid system. A scheme of analysis for systematic errors as well as for determining the exactness of the fractionation method is also g

ISSN:0022-3832    

DOI:10.1002/pol.1958.1203212506

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe bands due to stretching of OH groups in celluloses I, II and IIIIhave been studied with plane polarized infrared radiation. The spectra show that all three crystalline modifications contain OH groups which make an angle much smaller than 55° with the chain direction, while other OH groups make angles greater than 55° with this direction. The former OH groups are attributed to intramolecular hydrogen bonds which join successive glucose residues in the cellulose chain. It is shown that ether oxygen atoms must participate in the hydrogen‐bonding systems in all three modifications. The symmetries of the cellulose chains and the relationship between the two chains in the unit cell are discussed in relation to the number of distinguishable OH groups. Structures are described which are in agreement with the infrared results and with the stereochemical considerations presented in Part III of this series. The frequencies of the bands due to intramolecular hydrogen bonds suggest that the chains in cellulose I have a different molecular form from those in celluloses II and IIII. This difference may not be very large, however, in relation to the accuracy with which polymer structures are normally determi

ISSN:0022-3832    

DOI:10.1002/pol.1958.1203212507

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractScale models are described for a stereochemical study of the cellulose chain assuming standard armchair β‐glucose residues crystallizing in space‐groupP21. Infrared evidence about the hydrogen bonding and intensity data for the strongest equatorial and meridional x‐ray reflections are utilized in assessing the validity of many models. The structures published by Meyer and Misch and by other workers do not comply with the criteria thus set up. Some fully hydrogen bonded structures, which are likely to form the basis of the most highly ordered regions in cellulose I and II, are dis

ISSN:0022-3832    

DOI:10.1002/pol.1958.1203212508

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe emulsion polymerization of vinyl acetate was investigated with the use of block copolymers of ethylene and propylene oxides (commercially known as Pluronic surfactants) as emulsifying agents. By electron microscopy, the average polymer particle size was determined as a function of conversion of monomer to polymer and as a function of the surfactant concentration. It was found that the number of polymer particles remained constant during the reaction. The polymer surface area per unit volume of completely polymerized emulsion was proportional to the surfactant concentration. In contrast with styrene polymerization, the number of particles varied with the cube of the emulsifier concentration, and the number of particles per unit of surfactant was much less than the number that would have been expected with styrene. It was concluded that the results were consistent with polymerization theory. An expression giving the number of polymer particles produced in the reactions proved to be much simpler than the accepted equation used in the case of water insoluble monomers such as styrene. This simplicity arises from the partial water solubility of vinyl acetate, which enables the monomer to diffuse completely into the polymer particles very early in the reaction. The variation of latex viscosity with polymer particle size was also investigated. At constant solids concentration, the logarithm of the viscosity was proportional to the polymer surface area per unit of latex.

ISSN:0022-3832    

DOI:10.1002/pol.1958.1203212509

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe effect of a number of iron complexing agents on the persulfate‐bisulfite catalysis of acrylonitrile polymerization was studied. Several complexing agents were found to be effective in retarding suspension polymerization of acrylonitrile with this redox system. A relationship was found betweeen the redox potential of the iron complex and polymerization rate. Evidence was shown that the persulfate‐bisulfite polymerization of acrylonitrile requires the presence of iron or other metal i

ISSN:0022-3832    

DOI:10.1002/pol.1958.1203212510

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY