bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polyimide solution properties
Authors: Wallach M. L. 
Published: April 2003

AbstractSolution characterization measurements indicate that cylization of the polyamic acid from 2,4‐diaminoisopropylbenzene and pyromellitic dianhydride (PMDA) to the polyimide can be effected with small change in number‐average degree of polymerization. An increase in weight‐average molecular weight on conversion to polyimide is attributed to branching side reactions. Inherent viscosities of polyimides from 4,4′‐diaminodiphenyl ether and PMDA decreased slowly with time in concentrated (97%) sulfuric acid, probably as a result of hydrolytic cleavage. The zero‐time viscosity intercepts were related to both the precursor and the estimated polyimide molecular weight. The latter gave ηinh (c = 0.5% solids) = 2.76 × 10−3M̄0.53w for 60,000 < Mw < 300,000. The exponent is near the lower limit of 0.5 found in theta solvents. The characteristic ratio of the root‐mean‐square end‐to‐end distance of a chain to the square root of its molecular weight is 1.1 Å and the steric factor is 1.1; these results suggest that the unperturbed polyimide chain is almost as extended as an equivalent freely rotating chain, a general feature of long‐bonded polymers with p‐phenylene rings in the chain backbone.
General dynamic theory of macromolecular networks. I. Definitions and classification
Authors: Ziabicki Andrzej , Takserman‐Krozer R. 
Published: April 2003

AbstractThe problem of the structural theory of macromolecular networks is formulated and discussed in general terms. The conditions required for a system to become a homogeneous macromolecular network are defined and discussed. Networks are divided according to the nature of their junctions into three classes: energetic (with chemical or quasi‐chemical crosslinks), topological (with entangled chains), and contact (with frictional interactions). The main features of these three classes are discussed. A distribution density function ψ describing the configurations of macromolecules in network systems is introduced. The phase space of variables is 4(N + 1)‐dimensional and includes the coordinates of (N + 1) vectors hi joining the adjacent network junctions and (N + 1) contour lengths li of the network chains. The system of simultaneous equations required for the determination of the function ψ includes the equation of continuity, kinematic equations for the deformation velocity of the individual junctions, the force balance equation needed for the determination of sliding rates li, kinetic equations for the processes of junction breakage and reformation, and the equilibrium distribution of network junctions defining the initial conditions for the distribution function ψ.
Diffusion in glassy polymers. III
Authors: Wang T. T. , Kwei T. K. , Frisch H. L. 
Published: April 2003

AbstractThe diffusion studies of several solvents in epoxy polymer reported by Kewi and Zupko in Part I of this series are explained with the solution obtained from the generalized diffusion equation which includes the internal stress contribution. The rate of permeation of a penetrant through a polymer film and the time lag needed to reach steady state are also given for the generalized diffusion equation.
Gel‐permeation chromatography and cellulose. I. Effect of degree of nitration of cellulose on molecular weight distribution data
Authors: Segal Leon , Timpa J. D. , Wadsworth J. I. 
Published: April 2003

AbstractConsideration is given to the effect on gel‐permeation chromatographic (GPC) data of the extent of substitution in nitrated cellulose. GPC parameters for samples containing 13.55–13.81% nitrogen (14.14% corresponds to complete substitution, DS = 3) were hardly affected by this variation in substitution. Variations that were observed are considered to arise within the samples themselves. Experiments with low molecular weight organic iodides, nitrates, and hydroxyl compounds indicate longer chain lengths than actual; this is attributed to extensive solvation of the substituent groups. The very long chain lengths obtained for cellulose nitrate by the present GPC procedure may arise from such an affect.
Molecular weight distributions in radiation‐induced polymerization. III. γ‐Ray‐induced polymerization of styrene at low temperatures
Authors: Huang Robert Y. M. , Westlake John F. 
Published: April 2003

AbstractThe kinetics of the γ‐radiation‐induced polymerization of styrene was studied at radiation intensities of 8 × 104, 2.4 × 105, 3.1 × 105, and 8.3 × 105 rad/hr over a temperature range of −10°C to 30°C. The water content of the irradiated samples varied from 1.0 × 10−3 to 7.5 × 10−3 mole/l. The power dependence of the rate of polymerization on the dose rate at −10°C varied from 0.53 to 0.71 as the water content of the sample varied from 7.5 × 10−3 to 1.0 × 10−3 mole/l. A value of 3.1 kcal/mole was determined for the overall activation energy. Molecular weight distribution studies by gel‐permeation chromatography indicated the presence of two distinct peaks. The contribution of each peak was dependent on specific experimental parameters. Kinetic data and molecular weight distribution data indicate the coexistence of two propagating species. Analysis of the data strongly suggests that a free‐radical mechanism and a cationic mechanism are involved.
Synthesis of a spirobenzothiazoline polymer and its thermal rearrangement to a polydihydrobenzothiazine
Authors: Augl J. M. , Wrasidlo W. J. 
Published: April 2003

AbstractThe reaction of 3,3′‐dimercaptobenzidine with 1,4‐cyclohexanedione leads to a soluble, high molecular weight, spirobenzothiazoline polymer. Above 200°C the spirolinks of this polymer rearrange into a ladder structure leading to a polydihydrobenzothiazine.
Reformulation of the general theory of ionic polymerization. II. Rate of change of degree of polymerization with time
Authors: Deleanu Th. , Dimonie M. 
Published: April 2003

AbstractBy means of the kinetic equations of polymerization some approximate relations were deduced by using the concomitant rate of change of intrinsic viscosity in many concrete cases. These relations were easy to handle and were sufficiently precise for direct calculation of the rate constants of polymerization.A detailed mathematical study was carried out to improve the suggested approximations as well as the extension of these considerations.
Polymerization of vinyl monomers by alkali metal–thiobenzophenone complexes
Authors: Minoura Yuji , Tsubio Sadao 
Published: April 2003

AbstractThe polymerization of vinyl monomers by use of alkali metal (Li, Na, K)–thiobenzophenone complexes was studied. Monoalkali metal complexes of thiobenzophenone (thioketyls) induced the polymerization of vinyl monomers such as acrylonitrile (AN) and methyl methacrylate (MMA), and dialkali metal complexes of thiobenzophenone (dianion) induced the polymerization of styrene (St), butadiene (Bd), and isoprene (Ip) as well as AN and MMA. The polymerization of MMA with the dianion was initiated by both the mercaptide and the carbanion of the dianion, but that of styrene was initiated by the carbanion alone. In the case of polymerization of MMA by the thioketyl, the initial rate of polymerization depended on the catalyst concentration and the square of the monomer concentration. Similar results were obtained in the case of the dianion. The polymer yield increased with increasng polarity of sovents. In the copolymerization of AN with MMA, the copolymer obtained consisted almost of AN units. From these results, it was concluded that the polymerization proceeded by anionic mechanisms.
Kinetics of high‐intensity electron‐beam copolymerization of a divinyl urethane and 2‐hydroxyethyl methacrylate
Authors: Labana S. S. 
Published: April 2003

AbstractThe kinetics of the electron‐beam‐induced copolymerization of di(2′‐methacryloxyethyl)‐4‐methyl‐m‐phenylenediurethane (DVU) with 2‐hydroxyethyl methacrylate (HEMA) were studied. Monomer mixtures containing 1.96–82.8% DVU have been described at dose rates of 1.7–17 Mrad/sec with the use of 270‐kV electrons. Based on rates of conversion, gel formation, and intensity‐rate data, a kinetic scheme is proposed in accord with a model which undergoes unimolecular termination and for which the copolymerization and gel formation take place in a crosslinked network swollen with monomers. The rate of gel formation is: In[(1 + g)/(1 − M2g)] = A (1 + M2)t, where g is the gel fraction, M2 is the mole fraction of DVU in the monomer charge, and A is kpki/kt. Up to 55% conversion, the rate of disappearance of unsaturation for concentrated DVU solutions (M2 > 0.03) is: In[Mo/M(1 − M2g)] = A (1 + M2t), where M is the total unsaturation. For dilute solutions of DVU, the rate expression for pregel copolymerization simplifies to: In(Mo/M) = A (1 + M2)t. These results show that at a certain optimum concentration of monovinyl monomer—70% in the present system—both rapid reaction rates and complete copolymerization occur. Because of the inability of gel bonds to undergo polymerization, a limiting conversion is reached for copolymerizing mixtures containing insufficient monovinyl monomer.
Radiolysis of poly(vinyl chloride)
Authors: Salovey R. , Luongo J. P. 
Published: April 2003

AbstractAllyl free‐radical intermediates are detected by ultraviolet absorption at 255 mu in poly(vinyl chloride) irradiated at −196°C and stored at 25°C. In vacuum at 25°C, allyl radicals are converted into polyenyl free radicals and polyenes. From the nature of allyl radical decay in vacuum, radical chain transfer between polyenyl radicals and poly(vinyl chloride) is inferred. Allyl and polyenyl free radicals are scavenged by oxygen on post‐irradiation storage in air.
Radiation chemistry of aqueous poly(ethylene oxide) solutions. I
Authors: King P. A. , Ward J. A. 
Published: April 2003

AbstractThe γ radiolysis of aqueous high molecular weight poly(ethylene oxide) solutions has been studied. The crosslinking and eventual gelation of these solutions appears to occur via an indirect effect. Solubility measurements on the gelled solutions showed that the ratio of crosslinking to degradation is about four. G(H2) increased from 1.3 in neutral solutions to 3.5 in 0.1N HCl solutions. In heavy water solutions, HD is the major gaseous product. Solvated electrons are not important precursors to hydrogen at neutral pH. Intramolecular crosslinking appears to be an important phenomenon in solutions of high molecular weight polymers.
Chain twisting in long‐chain aliphatic compounds and polyethylene
Authors: Welsh H. K. 
Published: April 2003

AbstractRate parameters for dielectric relaxation and the thermal properties of long‐chain molecular systems are shown to provide evidence for chain twisting at chain lengths shorter than previously suggested. Comparison of the temperatures of maximum absorption at 1 Hz for mechanical and dielectric relaxation suggests that the underlying motion is not the same for the two observed quanties. The evidence for relaxation in polyethylene is shown to be compatible with this suggestion.
Mechanism of cerium (IV) oxidation of glucose and cellulose
Authors: Pottenger Charles R. , Johnson Donald C. 
Published: April 2003

AbstractCerium (IV) oxidations of model compounds for the hydroxylic functional groups of cellulose were conducted in 1.0M perchloric acid. Glucose, the model selected for the reducing end group, was oxidized 360 times faster than Schardinger β‐dextrin, the model for anhydro‐D‐glucose repeating units. In the presence of a fourfold excess of glucose, stoichiometry indicated specific conversion to arabinose; the competitive oxidation of arabinose produced is insignificant. Specific C1–C2 bond cleavage was also indicated for 2‐O‐methyl‐D‐glucose, galactose, 2‐O‐methyl‐D‐galactose, and cellobiose. Anhydro‐D‐glucose units were oxidized predominantly by C2–C3 bond cleavage as shown by the identification of erythrose and glyoxal in hydrolyzates of cerium (IV) oxidized Schardinger β‐dextrin and cellulose. Kinetic studies showed that chelate complexes were involved in oxidations of glucose, methyl β‐D‐glucopyranoside, 1,5‐anhydro‐D‐glucitol, and Sahardinger β‐dextrin. The oxidations of glucose derivatives which differed with respect to substituents on C1 and C2 demonstrated the importance of the hemiacetal group and the presence of oxygen on C2. For example, the relative rates of oxidation at 15°C for methyl β‐D‐glucopyranoside, 1,5‐anhydro‐D‐glucitol, 2‐deoxy‐D‐glucose, glucose, and 2‐O‐methyl‐D‐glucose are 1:1:12:360:1860, respectively. The mechanism of glucose oxidation is thought to involve formation of a chelate complex, disproportionation of the complex to form a free radical at either C1 or C2 and further rapid oxidation to 4‐O‐formyl‐D‐arabinose which is hydrolyzed in the reaction medium. General implications of the experimental results pertaining to initiation of vinyl graft polymerization on cellulose are discussed.
Stereospecific polymerization of methacrylonitrile. IV. Polymerization by ate complex‐type catalysts
Authors: Joh Yasushi , Kurihara Seiki , Sakurai Toshio , Imai Yoshikatsu , Yoshihara Toshio , Tomita Tatsunori 
Published: April 2003

AbstractMethacrylonitrile was polymerized by a number of ate‐complex catalysts. The catalysts used were NaAlR4, LiAlR4, LiZnR3, Li2ZnR4, RMg[AlR4], and Mg[AlR4]2. It was found that the ate‐complex catalysts in which one of the alkyls is replaced by a diphenylamino group are capable of producing polymers with higher degrees of crystallinity than those of polymers obtained by unmodified catalysts. It was shown that the diphenylamide linkage in these catalytic systems must play an important role in the steric control in the propagation steps of this type of polymerization, although the mechanism is not clear at present. The crystallinity index used in this research gave a linear relation against I measured by NMR, and can be used as a measure of the stereo‐regularity of the polymer.
Radiation‐induced postpolymerization of nitroethylene
Authors: Yamaoka Hitoshi , Obama Isamu , Hayashi Koichiro , Okamura Seizo 
Published: April 2003

AbstractRadiation‐induced postpolymerization of nitroethylene in 2‐methyltetrahydrofuran glass has been studied and discussed in reference to the results obtained from ESR measurements. No postpolymerization occurred at the temperature below −150°C. In the temperature range between −135°C and −78°C, the polymer yield decreased with increasing postpolymerization temperature. The polymer yield increased linearly with the increase of the preirradiation dose in the range below 0.9 × 106 r. The mean value for chain initiation was estimated to be about 1.3. The following correlations were observed between the results of the postpolymerization and ESR measurements. The postpolymerization started in the temperature range between −140°C and −135°C, where the ESR spectrum due to the anion radicals of nitroethylene disappeared. The polymer yield of the postpolymerization decreased with the photoirradiation at −196°C before warming the samples in parallel with the photobleachability of the anion radicals observed in the glassy mixture by the ESR method. It was concluded from these results that the radiation‐induced postpolymerization was initiated by the anion radicals of nitroethylene formed by the capture of electons.
Studies in cyclocopolymerization. V. Further evidence for charge‐transfer complexes in cyclocopolymerization
Authors: Butler George B. , Campus Alfred F. 
Published: April 2003

AbstractPrevious work from this laboratory has shown that certain 1,4‐dienes which readily undergo cyclocopolymerization with certain alkenes also form charge‐transfer complexes with the same alkenes. The results observed and the proposed cyclocopolymerization mechanism are consistent with participation of the charge‐transfer complex as a distinct species in the copolymerization. It was the purpose of this investigation to determine whether there was a dilution effect on the relative reactivities of the monomers in support of the charge‐transfer participation concept, and whether the results of a suitable terpolymerization study would also support this postulate. In the divinyl ether–fumaronitrile system, the maximum rate of copolymerization occurred at a monomer feed ratio of 1:2 and the composition of the copolymer was also 1:2 at a total monomer concentration of 3 mole/l. However, when the concentration was progressively lowered to 0.5 mole/l. at the same monomer feed ratio, the fumaronitrile content of the copolymer decreased in a linear manner. In a series of terpolymerization experiments with the divinyl ether–maleic anhydride–acrylonitrile system, it was shown that the divinyl ether–maleic anhydride ratio in the terpolymer was always less than 1:1 and had an upper limit of 1:2, regardless of the feed ratio of the termonomers. These results are consistent with the participation of the charge‐transfer complex of divinyl ether and maleic anhydride in a copolymerization process with either maleic anhydride or acrylonitrile as the comonomer.
Electron spin resonance study of poly‐3,3‐bis(chloromethyl) oxetane irradiated with electron beams and ultraviolet light
Authors: Tsuji Kozo , Hayashi Koichiro , Okamura Seizo 
Published: April 2003

AbstractPoly‐3,3‐bis(chloromethyl)oxetane (poly‐BCMO) was irradiated at −196°C with electron beams and ultraviolet light, and observed ESR spectra were compared. A three‐line spectrum (coupling constant of about 21 gauss) and a two‐line spectrum (coupling constant of about 18 gauss) were observed after irradiation with electron beams in vacuo. They were attributed to free radicals and respectively. On the other hand, a three‐line spectrum (coupling constant of about 20 gauss) and an asymmetric singlet spectrum were observed after ultraviolet irradiation in vacuum. They were assigned to free radicals and CH2O·, respectively. Mechanisms of radical formation were discussed in each case. When poly‐BCMO was irradiated with electron beams at −196°C in the presence of air, peroxy radicals were produced after subsequent treatment at −78°C. The reaction between alkyl radicals and oxygen molecules was found to be diffusion‐controlled.
Polymerization of vinylcyclopropanes. IV. Radical copolymerization of 1,1‐dichloro‐2‐vinylcyclopropane with maleic anhydride
Authors: Takahashi Takako 
Published: April 2003

AbstractRadical copolymerization between 1,1‐dichloro‐2‐vinylcyclopropane (M1) and maleic anhydride (M2) was studied. Rearrangement of the radical caused from monomer M1 and cyclization of growing chain, which was suggested from a consideration of composition and structure of the obtained copolymer, complicate the propagation step in this system. A peculiar copolymer composition equation containing four reactivity ratio parameters was developed, and these parameters were determined.
Electron spin resonance studies of polycarbonate irradiated by γ‐rays and ultraviolet light
Authors: Hama Yoshimasa , Shinohara Kenichi 
Published: April 2003

AbstractParamagnetic species produced in polycarbonate (PC) by γ‐ or ultraviolet irradiation were investigated by ESR. In γ‐irradiation, scissions of carbonate groups in the main chain occur. ESR spectra (g = 2.0034) composed of a sharp singlet, some broad singlets, and a small signal with hyperfine structure are obtained, and they are assigned to trapped electrons, positive radical ions, phenoxy‐type free radicals, phenyl radicals, and OC6H4C(CH3)2 radicals. The G value for total yields of paramagnetic species at 77°K is 1.8. The percentage of CO and CO2, the dominant gases evolved, is 65.4 and 33.8%, respectively. In ultraviolet irradiation, energy is absorbed selectively at the surface region. The surface region becomes insoluble in methylene chloride because of crosslinking of phenyl groups. The ESR spectrum obtained at 77°K is a broad singlet and assigned to phenoxy‐type free radicals, phenyl radicals, and polyenyl‐type free radicals. Some differences in effects of γ‐ and ultraviolet irradiation of PC are discussed.
NMR study of poly(vinyl chloride)‐β,β‐d2
Authors: Cavalli L. , Borsini G. C. , Carraro G. , Confalonieri G. 
Published: April 2003

AbstractThe high‐resolution NMR spectra at 60 and 100 Mcps of poly(vinyl chloride)‐β,β‐d2 in o‐dichlorobenzene, pyridine, and C2HCl5 solutions are reported. The use of low molecular weight samples and of {D} spin‐decoupling experiments, which yield higher resolution spectra, results in the observation of a number of additional resonances for the α‐proton. These can be interpreted in terms of pentad configurational sequences of monomer units. It is found that, whereas the S syndiotactic pentads cannot be resolved, two components of the H heterotactic and all of the possible I isotactic pentads are clearly discernible. From the tacticity values of polymers prepared at +40, 0, and −40°C, enthalpy and entropy of activation for isotactic and syndiotactic monomer placement are found to be 630 cal/mole and 1.5 eu, respectively.
Crosslinking, filler, or transition constraint of polymer networks. II
Authors: Blanchard A. F. 
Published: April 2003

AbstractThe theory of Part I is developed by application to filler reinforcement of NR and SBR. For unswollen but prestretched networks it quantifies entire stress–strain curves and applies new concepts of extensibility and strain hardening. Constraint of swelling is expressed by a constant φ, termed linkage reinforcement, and by an effective hard fraction Ch per cubic centimeter of compound. For rubber–filler swelling vc the modified Flory functions F(vc) in part 1 need 3% correction. Then, relative to gum fix points 1/F0(vr):

where Ch ≤ 1.15C for filler concentrations C per cubic centimeter of compound. The effective Ch comprises the volume fraction C* of bonded particles and 5–10 Å of surface–bound rubber that has been stretched hard by swelling. When needed, the actual crosslink density and intrinsic linkage reinforcement φ0 can be obtained by dividing by (1 + 2.5Cφ) where Cφ = (C ln φ)/(1 + 2.5C). The case Ch ≤ 1.15C with Graphon or inert fillers is identified and assessed by equations:

Results Ch > 1.15C are invalid, but then Ch ≈ 1.15C* ≈ 1.15C, e.g., for carbon blacks. Even Graphon is distinguished from inert fillers at low concentrations C by substantial constraint reinforcement F0(vr)/F(vc) > 1. For prestressed dry rubber a modulus G, network extensibility αb − 1, and upturn coefficient μh express the whole curve; G and μh show identical constraint strength distributions. Network extensibility αb − 1 is the microbreaking strain (prestretch); for pure elastomer it is elongation at break. The relation of stress F to extension ratio α is:

where C2* = 0.7 and j = 0.4 from NR/MPC data. Strain‐hardening coefficients h are obtained from μh by the theory given in Part I. Hard modulus components Gh = 0.7 ln (h/h0) vanish as h → h0 (gum) = 110. After high prestresses the residual ln‐(h*/h0) due to strong carbon‐rubber linkages implies Gh* = 0.42 kg/cm2, i.e., ca. 10% of the normal cure crosslinks.
Studies on monomer reactivity ratios. I. An electronegativity model
Authors: Hoyland James R. 
Published: April 2003

AbstractA model based on an electronegativity scheme is proposed for treatment of monomer reactivity ratios in free‐radical bulk copolymerization. Values for each monomer are assigned to three parameters: a relative localization (or resonance stabilization) energy, a radical electronegativity, and a monomer electronegativity. Parameters for 17 monomers are given and calculated reactivity ratios are tabulated for a large number of copolymerizations. Agreement with experiment is usually obtained to within experimental error except for systems involving acrylonitrile. Computed parameters are rationalized on the basis of molecular orbital theory.