摘要:

AbstractGraft polymerizations of vinyl acetate onto granular corn starch were initiated by cobalt‐60 irradiation of starch‐monomer‐water mixtures, and ungrafted poly(vinylacetate) was separated from the graft copolymer by benzene extraction. Conversions of monomer to polymer were quantitative at a radiation dose of 1.0 Mrad. However, over half of the polymer was present as ungrafted poly‐(vinyl acetate) (grafting efficiency less than 50%), and the graft copolymer contained only 34% grafted synthetic polymer (34% add‐on). Lower irradiation doses produced lower conversions of monomer to polymer and gave graft copolymers with lower % add‐on. Addition of minor amounts of acrylamide, methyl acrylate, and methacrylic acid as comonomers produced only small increases in % add‐on and grafting efficiency. However, grafting efficiency was increased to 70% when a monomer mixture containing about 10% methyl methacrylate was used. Grafting efficiency could be increased to over 90% if the graft polymerization of vinyl acetate‐methyl methacrylate was carried out near 0°C, although conversion of monomers to polymer was low and grafted polymer contained 40‐50% poly(methyl methacrylate). Selected graft copolymers were treated with methanolic sodium hydroxide to convert starch–g–poly(vinyl acetate) to starch–g–poly(vinyl alcohol). The molecular weight of the poly(vinyl alcohol) moiety was about 30,000. The solubility of starch–g–poly(vinyl alcohol) in hot water was less than 50%; however, solubility could be increased by substituting either acid‐modified or hypochlorite‐oxidized starch for unmodified starch in the graft polymerization reaction. Vinyl acetate was also graft polymerized onto acid‐modified starch which had been dispersed and partially solubilized by heating in water. A total irradiation dose of either 1.0 or 0.5 Mrad gave starch–g–poly(vinyl acetate) with about 35% add‐on, and a grafting efficiency of about 40% was obtained. A film cast from a starch–g–poly(vinyl alcohol) copolymer in which homopolymer was not removed exhibited a higher ultimate tensile strength than a comparable phys

ISSN:0021-8995    

DOI:10.1002/app.1979.070230121

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

年代:1979

数据来源: WILEY

摘要:

AbstractThe decomposition of the peroxide group on fibrous carboxymethyl cellulose (CMC) and its ability to initiate graft copolymerization were investigated. The peroxide on CMC liberated hydrogen peroxide when the sample was heated in an aqueous medium. The decomposition of the peroxide was markedly increased by the use of ferrous salt and the irradiation with light of λ>300 nm. The grafting of methyl methacrylate on CMC peroxide was initiated by heating or irradiating with light, where the rate of grafting and the reciprocal of the average molecular weight of grafts in general were proportional to the square root of the peroxide content of the sample. The peroxide content of the sample was related closely to the number of grafts in initiation. The number was estimated as 17 times for thermal initiation and 6 times for photoinitiation at the maximum values. The CMC peroxide showed a marked activity toward photografting of acrylamide, acrylic acid, acrylonitrile, and vinyl acetate on the substrate

ISSN:0021-8995    

DOI:10.1002/app.1979.070230122

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

年代:1979

数据来源: WILEY

摘要:

AbstractA reduced unit cell derived from the presently accepted unit cell and a new parallel chain arrangement is proposed for cellulose II (regenerated cellulose). In the present structure, all the cellulose chains are identical and there is only one chain passing through each unit cell. The intensity data for all reflections withdspacings greater than 1.747 Å have been calculated and were found to be in good agreement with the corresponding observed x‐ray intensities. The calculated agreement factor is R = 0.50. Two intrachain hydrogen bonds parallel to the fiber axis and one interchain hydrogen bond perpendicular to the fiber axis stabilize the structure. The hydrogen bonding network is in fair agreement with infrared dichroic data, and the chain arrangement conforms to stereo‐chemical criteria. No short contacts are observed. The parallel chain is also compatible with the structure of cellotetraose and the accepted hypothesis of cellulose biosynthesis, as well as the latest parallel structure for Val

ISSN:0021-8995    

DOI:10.1002/app.1979.070230123

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

年代:1979

数据来源: WILEY

摘要:

AbstractA method has been devised whereby the S8permeability and solubility in silicon resin are determined by observing the reaction between sulfur vapors and silver particles within the polymer. The particles (∼10 μm diameter), which may vary between 0.1 and 100 μm in diameter, are dispersed in the polymer at a concentration up to 20% within a glass cylinder (also an aluminum container). The polymer is cured according to procedure and exposed to S8saturated vapors at various temperatures (55°–125°C), leaving one end of the cylinder open. The Ag particles are a perfectsinkfor sulfur, which is consumed as soon as it reaches the reaction boundary that separates the reacted and unreacted Ag particles. Consequently, a distinct black region containing Ag2S product is left behind as the boundary advances. The line displacement, measured at time intervals for the several temperatures, is used to calculate the gas permeability in the polymer as a function of temperature on the basis of a mass transport model developed from diffusion theory. The S8solubility in the polymer is calculated from the permeability and diffusivity. The latter is determined independently by measuring the time that the Ag2S reaction is delayed when a layer of plain polymer separates a silver surface and the sulfur envi

ISSN:0021-8995    

DOI:10.1002/app.1979.070230124

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

年代:1979

数据来源: WILEY

摘要:

AbstractChemical reactions on polymers in homogeneous medium were used to characterize the structure of the macromolecules. The polymer was in the form of polyamide fibers dissolved inm‐cresol to give a fairly highly concentrated solution (approximately 6%). Kinetic studies of hydrolysis, acetylation, and deamination reactions on the polyamide fibers were carried out in homogeneous medium at different temperatures. All the three reactions studied followed first‐order kinetics. Rate constants and apparent activation energies were determined for these reactions, which show two rates—an initial fast rate followed by a slow one. A new microfibrillar model of the polymer dissolved inm‐cresol is proposed, and the existence of two rates is explained on the basis of the two‐phase structure of the proposed microfibril. The fast rate is attributed to the free chain segments, and the slow rate is shown to correspond to the regions which are strongly hydrogen bonded and which hold the various chains together to give the microfibrillar structure of the polymer in the homogeneous phase. The apparent activation energy for hydrolysis was 3.20 and 0.18 kcal/mole for the fast and slow rates, respectively. The apparent activation energy values for acetylation were 1.50 and 0.80 kcal/mole, while those for the apparent deamination reaction were 6.90 and 4.60 kcal/mole, respectively. Lower values of apparent activation energies are attributed to the ease of reaction in the difficult‐to‐penetrate regions of the microfibril due to the role played by the solvent of the homogeneous phase in carrying the reacting species inside these regions while simultaneously breaking the hydrogen bonds between the polypeptide chains. The apparent deamination reaction is shown to be a resultant reaction of simultaneous deamination and “amination” through hydrolytic breakdown of the

ISSN:0021-8995    

DOI:10.1002/app.1979.070230125

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

年代:1979

数据来源: WILEY

ISSN:0021-8995    

DOI:10.1002/app.1979.070230126

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

年代:1979

数据来源: WILEY

ISSN:0021-8995    

DOI:10.1002/app.1979.070230127

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

年代:1979

数据来源: WILEY

ISSN:0021-8995    

DOI:10.1002/app.1979.070230128

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

年代:1979

数据来源: WILEY

ISSN:0021-8995    

DOI:10.1002/app.1979.070230129

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

年代:1979

数据来源: WILEY