bluuebunny/crossref_metadata_2025 huggingface dataset:
Hyperfine structure observed in EPR spectra of polyphenylacetylene solutions
Authors: Whitte W. M. , Kang E. T. , Ehrlich P. , Carroll J. B. , Allendoerfer R. D.
Published: April 2003

The high‐temperature (>120C) electron paramagnetic resonance (EPR) spectrum of solutions of polyphenylacetylene have been deconvoluted into the spectra of two separate radicals, a delocalized π radical, whose EPR spectrum consists of a single 15‐G wide Gaussian line comprising about 90% of the total signal and a second, more localized π radical exhibiting complex hyperfine structure in its EPR spectrum. Some possible structures for the minor component radical are suggested and their hyperfine splitting constants calculated using molecular orbital theory.
Thermal rearrangements of polybutadienes with different vinyl contents
Authors: Golub Morton A.
Published: April 2003

A study was made of the loss of double bonds in equibinary (1,4‐1,2) polybutadiene (EB) and in polybutadienes with 30% 1,2, 70% 1,4 (FI), and 10% 1,2, 90% 1,4 (DI) double‐bond content, when heated in vacuum under nonpyrolytic conditions (temperature range 220–280°C). These polymers were found to undergo second‐order loss of 1,2 unsaturation with similar activation energies (Ea = 34.0 ± 3 kcal/mole), by analogy to the previously reported thermally induced loss of double bonds in 1,2‐polybutadiene (VB) (Ea = 33.6 ± 3 kcal/mole). Moreover, EB and FI exhibited also second‐order loss of 1,4 unsaturation, with Ea ca. 36 and 40 kcal/mole, respectively, while DI showed negligible loss of 1,4 unsaturation below 260°C, in common with cis‐1,4‐polybutadiene (CB) (with 2% 1,2 double bonds) examined earlier. The loss of 1,2 double bonds in the various polybutadienes with different vinyl contents is accompanied by substantial methyl production, ranging from about one methyl group formed for every 4–5 vinyl units lost in VB, to one methyl for every two vinyls lost in EB, and to almost one methyl for each vinyl lost in DI or CB. Mechanisms are proposed for the thermally induced loss of 1,2 and 1,4 unsaturation in various polybutadienes and for the accompanying methyl production.
Irradiation of aromatic polymers: The effect of irradiation temperature on crosslinking and scission in polystyrene
Authors: Bowmer Trevor N. , O'Donnell James H. , Winzor Donald J.
Published: April 2003

Polystyrene of narrow molecular weight distribution, Mw/Mn ≈ 1.03, was subjected to γ irradiation at 100 and 150°C. The yields of scission and crosslinking, G(S) and G(X), where determined from the changes in molecular weight distribution using gel permeation chromatography, (GPC) with supporting evidence from osmometry and viscometry. The ratio G(S)/G(X) increased from 0.02 at 30°C, obtained previously, to 2.8 at 150°C. This was mainly due to a tenfold increase in G(S), whereas G(X) apparently decreased slightly. These results are compatible with increased disproportion of chain scission radicals relative to their combination, analogous to the temperature dependence of mutual termination in the free radical polymerization of styrene. There was no obvious discontinuity through the glass transition temperature, although there may be a change in sign of the temperature coefficient of G(X). This system provides an excellent example of the applicability of measurements of molecular weight distributions and averages to determinations of G(S) and G(X) under conditions when gel measurements are inappropriate, either because of the failure of the system to form gel, or, as in the present case, because of the very large radiation doses required for gel formation.
Studies of redox polymerization. I. Aqueous polymerization of acrylamide by an ascorbic acid–peroxydisulfate system
Authors: Narain H. , Jagadale S. M. , Ghatge N. D.
Published: April 2003

The polymerization of acrylamide initiated by an ascorbic acid–peroxydisulfate redox system was studied in aqueous solution at 35 ± 0.2°C in the presence of air. The concentrations studied were [monomer] = (2.0–15.0) × 10−2 mole/liter; [peroxydisulfate] = (1.5–10.0) × 10−3 mole/liter; and [ascorbic acid] = (2.84–28.4) × 10−4 mole/liter; temperatures were between 25–50°C. Within these ranges the initial rate showed a half‐order dependence on peroxydisulfate, a first‐order dependence on an initial monomer concentration, and a first‐order dependence on a low concentration of ascorbic acid [(2.84–8.54) × 10−4 mole/liter]. At higher concentrations of ascorbic acid the rate remained constant in the concentration range (8.54–22.72) × 10−4 mole/liter, then varied as an inverse halfpower at still higher concentrations of ascorbic acid [(22.72–28.4) × 10−4 mole/liter]. The initial rate increased with an increase in polymerization temperature. The overall energy of activation was 12.203 kcal/mole in a temperature range of 25–50°C. Water‐miscible organic solvents depressed the initial rate and the limiting conversion. The viscometric average molecular weight increased with an increase in temperature and initial monomer concentration but decreased with increasing concentration of peroxydisulfate and an additive, dimethyl formamide (DMF).
Preparation and thermal behavior of poly‐p‐phenylene diacrylic acid dimethyl ester
Authors: Hasegawa Masaki , Yurugi Tadashi , Namiki Satoru , Shiobara Takatoshi , Nakanishi Hachiro , Nakanishi Fusae
Published: April 2003

The photopolymerization behavior of p‐phenylene diacrylic acid dimethyl ester (p‐PDA Me) crystal and the thermal behavior of the resultant poly‐p‐PDA Me were investigated. From the kinetic study of polymerization at various temperatures a topochemical process via a stepwise mechanism was observed. Continuous change from monomer to polymer crystals was demonstrated by x‐ray diffraction pattern and DSC analysis. Crystallinity of the reacting phase was maintained at an extremely high degree during the polymerization process in support of monomer crystal lattice control. Thermal study on as‐polymerized poly‐p‐PDA Me crystal confirmed that the thermal reaction was a polymer crystal lattice‐controlled depolymerization, which was followed by miscellaneous processes that involved vaporization, sublimation, and deterioration of the oligomeric or monomeric units of p‐PDA Me. Thermal stability was dependent on the molecular weight. All the results are compared with those of four‐center‐type photopolymerization in the crystalline state.
Redox polymerization‐kinetics of the reaction inititated by the system CH2(CH)2MN(III) in aqueous H2SO4 and the system CH2(CN)2MN(OAC)3 in DMF and acetic acid
Authors: Jayakrishnan Athipettah , Haragopal Mahadevan , Mahadevan Venkatanarayana
Published: April 2003

Polymerization of acrylonitrile and methyl methacrylate by the redox systems propanedinitrile‐Mn(III) in aqueous sulfuric acid and propanedinitrile‐Mn(OAc)3 in DMF and glacial acetic acid was investigated in the temperature range 20–40°C. The kinetics are consistent with the formation of an intermediate complex whose irreversible decomposition yields the initiating radical. With both monomers mutual termination predominates. The main difference between aqueous H2SO4 and acetic acid compared with DMF lies in the ease of oxidation of the primary radicals by the oxidant. Rate and equilibrium parameters were estimated and their significance discussed.
The preparation and reactions of polymeric azides. I. The reaction of poly(vinylbenzyl azide) with acetylenic and olefinic derivatives
Authors: Cohen H. L.
Published: April 2003

The preparation and reactions of polymers and copolymers of vinylbenzyl azide with olefinic and acetylenic derivatives are described. With acetylenes, a 1,3‐dipolar addition gave almost complete conversion to polymeric 1,2,3‐triazoles. Yields were excellent and light‐colored derivatives were obtained.
Charge transfer polycondensation of diethyl chelidonate with diamines in the presence of polyvinylcarbazole
Authors: Ogata Naoya , Sanui Kohei , Abe Masahiko
Published: April 2003

Polycondensation of diethyl chelidonate (DEC), which contains an electron‐accepting γ‐pyrone nucleus, with hexamethylenediamine (HMD) takes place easily even at room temperature to form a corresponding polyamide. Since DEC was expected to form a charge transfer complex with an electron‐donating compound such as polyvinylcarbazole (PVK), the polycondensation of DEC with diamines was carried out in the presence of PVK as a matrix. It was found that the rate of the polycondensation of DEC with diamines in dioxane was enhanced either by the presence of PVK or by the irradiation with ultraviolet (UV) light. Moreover, the polycondensation of DEC with HMD in the presence of PVK was accelerated by the UV irradiation, probably owing to the transfer of light energy.
Gamma radiation‐initiated polymerization of styrene at high pressure. II. Chain termination
Authors: Moore P. W. , Clouston J. G. , Chaplin R. P.
Published: April 2003

The pressure dependence of the termination rate constant kt for the free radical polymerization of monomers such as styrene is a function of polymer chain length, chain stiffness, and monomer viscosity, all of which influence the rate of segmental diffusion of an active radical chain end out of the coiled polymer chain to a position in which it can react with a proximate radical. Although kt is not sensitive to changes in chain length, the large increase in molecular weight is responsible for a significant reduction in kt at high pressures. For most of the common vinyl polymers, which exhibit some degree of chain stiffness, kt is inversely proportional to a fractional power of the monomer viscosity because it depends in part on the resistance of chain segments to movement and in part on the influence of viscosity in controlling diffusion of the chain ends. The fractional exponent appears to increase with pressure and this is interpreted as evidence that the polymer chains become more flexible in a more viscous solvent. Because the fractional exponent is higher for more flexible chains, the value of the activation volume for chain termination is an indication of the degree of flexibility of the polymer chains, provided that the monomer is a good solvent for the polymer and that chain transfer is negligible.
Mechanisms of thermal decomposition in totally aromatic polyurethanes
Authors: Foti S. , Maravigna P. , Montaudo G.
Published: April 2003

The primary fragmentation mechanisms in the thermal decomposition of polyurethanes were studied in detail by direct pyrolysis into the mass spectrometer. The remarkable difference in the thermal stability of the two totally aromatic polyurethanes I and II (Fig. 1) reflects their different decomposition pathways. In fact, polymer I undergoes a depolycondensation process that yields diiscyanate and dialcohol as primary thermal fragments. The thermal decomposition of polymer II proceeds instead via the formation of a cyclic compound that has been isolated and characterized. In contrast, open‐chain fragments are generated in the thermal decomposition of the partially aliphatic polymer III.
Kinetic approach to radiation‐induced grafting in the polyethylene‐styrene system. IV. Comparison between high density polyethylene and low density polyethylene
Authors: Imai Masahiko
Published: April 2003

The investigation method reported in earlier articles was applied to preirradiation methods of the reaction of low‐density polyethylene (LDPE) in liquid and vapor and compared with high‐density polyethylene (HDPE). Monomer concentrations during reactions and monomer feed rates were determined gravimetrically. Increasing patterns of the degree of grafting were obtained and compared. Monomer concentration during the reactions was lower in LDPE than HDPE and radical decay was more rapid in LDPE. A model calculation was applied to this experiment and a schematic explanation was attempted. The differences between the reaction mechanisms of HDPE and LDPE are explained.
Effects of water, methanol, and ethanol on the production of starch‐g‐polystyrene copolymers by cobalt‐60 irradiation
Authors: Henderson Alex M. , Rudin Alfred
Published: April 2003

Starch‐g‐polystyrene copolymers were made by simultaneous 60Co irradiation of mixtures of wheat starch and styrene at room temperature. The extent of conversion of monomer to polymer is increased drastically with increasing water content up to a level of about 26 wt % on starch. Methanol had approximately the same effect as water at equivalent concentrations but ethanol was clearly less effective as a promoter of homo‐ and graft copolymerizations. Drying the starch reduced the conversion to polymer with all promoters but caused the greatest deterioration in the ability of ethanol to promote polymerization. The effects of physically swelling the starch by freeze drying the gelatinized material were also studied, as were preirradiation graft copolymerizations. The effects of promoters on graft polymerization parallel their abilities to scavenge stable radicals in irradiated starch. Water and methanol are better radical scavengers and polymerization promoters because they are better able to disrupt hydrogen bonds and permeate the starch structure. Radiolysis of the promoter is important in the grafting reaction.
Effect of carbon on sulfuration under a binary accelerator system
Authors: Das C. K. , Fegade N. B. , Millns W.
Published: April 2003

The continuous measurements of cure characteristics were monitored with a Monsanto rheometer and compared with the volume swell measurement of cross‐link density in benzene. Both methods of measurement indicated the formation of a complex of MBT and DPG in equimolar proportions, confirmed by the chemical probe technique and activation energy data. Presence of HAF did not alter vulcanization; that is, HAF has almost no qualitative effect on the kinetics of sulfuration but some on the state of the cure, optimum cure time, and onset and rate of vulcanization. Activation energy remained unchanged by the addition of HAF black.
Interaction between dyes and polyelectrolytes. XII. Excitation energy transfer between bound dyes
Authors: Shirai Masamitsu , Ohyabu Motoshi , Tanaka Makoto
Published: April 2003

Methylene blue‐photosensitized isomerization of cis‐p‐(phenylazo) phenyltrimethylammonium iodide to the transisomer was used advantageously to investigate the effect of polyanions on the triplet excitation energy trasfer between cationic dyes in aqueous media. The efficiency of the excitation energy transfer was improved by the addition of potassium poly(vinyl sulfate) (PVS), potassium poly(styrene‐sulfonate) (PSS), sodium poly(acrylate) (PAA), and sodium poly(methacrylate) (PMA) and was dependent on the polyanion concentration in the system. PVS and PSS were much more effective than PAA and PMA. The efficiency of the excitation energy transfer under the most appropriate conditions was about 67 times higher than in the absence of polyanions. Correlation with dye binding to polyanions and the efficiency of the excitation energy transfer between dyes was discussed.
Preparation of copoly(vinyl alcohol‐styrenesulfonic acid) resin and its catalytic activity on hydrolysis of carbohydrates. III. Kinetic analysis of the catalysis
Authors: Arai Kenichiro , Ogiwara Yoshitaka , Kuwabara Chiharu
Published: April 2003

Hydrolysis of dextrin in the presence of copoly(vinyl alcohol‐styrenesulfonic acid) resin was investigated kinetically. The hydrolysis rate increased nearly proportionally with increases in the concentrations of the substrate and the catalyst copolymer. This is in contrast to the results found in a similar homogeneous reaction in the presence of soluble copoly(vinyl alcohol–styrenesulfonic acid) in which the reaction rate clearly followed Michaelis–Menten type kinetics. However, the hydrolysis was inhibited by the addition of copoly(vinyl alcohol–styrene) resin or poly(vinyl alcohol). Activation parameters of the hydrolysis in the presence of the copolymer resin as catalyst were also investigated, and it was found that the enthalpy and entropy of the activation in the presence of the copolymer resin were lower than those in Amberlite 120B and slightly decreased when vinyl alcohol unit was introduced. From these results it was concluded that the poly(vinyl alcohol) sequence introduced into the insoluble catalyst copolymer resin also played an important part in the acceleration of dextrin hydrolysis in a manner similar to the case of a soluble catalyst, although the interaction with the substrate was weaker.
ESCA applied to polymers. XXXI. A theoretical investigation of molecular core binding and relaxation energies in a series of prototype systems for nitrogen and oxygen functionalities in polymers
Authors: Clark D. T. , Harrison A.
Published: April 2003

Nonempirical LCAO MO SCF computations (in the ΔSCF formalism) were performed on the ground and core‐hole states of a range of nitrogen‐containing model systems which encompass most of the common functionalities of interest in the study of polymers. The data complement those previously presented on oxygen functionalities and show that for specific functionalities (e.g. nitrate esters and nitriles) substituent effects can be substantially different than normally anticipated on the basis of a simple additivity model. A comparison was drawn in appropriate cases with experimental data on simple model systems and polymers.
Fracturing silica‐based catalysts during ethylene polymerization
Authors: McDaniel M. P.
Published: April 2003

The rate and extent to which silica‐based catalysts fracture during the polymerization of ethylene in a slurry process were examined. Reactions were stopped at various times to yield as little as 20 g of polymer per gram of catalyst to more than 20,000 g/g. The catalyst residue was then collected and analyzed. Fragmentation of the catalyst was complete within the first minute or two of polymerization, whereas the rate of reaction continued to increase for more than an hour. Therefore fragmentation cannot be the rate‐controlling step. A comparision of the kinetics of Cr/silica and Ti‐Mg/silica led to the same conclusion. The most active silica gels also tended to be the most porous, which suggests fragility as a necessary requisite. Although 98% of their surface was internal, their activity was comparable to that of nonporous silicas, in which all the surface was external. This suggests that long polymer chains can diffuse out of the pores.
Radiation‐induced polymerization at high dose rate. VI. Butadiene in n‐hexane solution
Authors: Hayashi Kanae , Kagawa Kazunori , Okamura Seizo
Published: April 2003

Polymerization of butadiene by electron‐beam irradiation was studied in n‐hexane solution. Kinetic features of the polymerization and microstructure of the product were similar to those in bulk polymerization, which indicated a cationic mechanism. Both the rate of polymerization and average molecular weight of the product decreased by about 20% in the solution system. Soluble polymer was obtained up to ca. 40% conversion at the monomer concentration of 50 mol%, whereas in the bulk system the gel formed in polymer conversion exceeded 10%. A kinetic equation was proposed to explain the change in rate of polymerization with the monomer concentration.
Reactions of cationic living poly(tert‐butyl aziridine)
Authors: Munir Arshad , Goethals Eric J.
Published: April 2003

The cationic polymerization of N‐tert‐butyl aziridine (TBA) can be conducted in such a way that the rate of termination is much slower than the rate of propagation, thus permitting preparation of a corresponding polymer which is “temporarily living”. Reactions of N‐methyl‐N‐tert‐butyl aziridinium triflate (which is the model for the active species of the living polymer) with different nucleophiles show that, at room temperature, the aziridinium ring reacts almost instantaneously with nucleophiles to form the corresponding ring‐opened product. Analogous reactions with the aziridinium end group of living poly‐TBA lead to polymers with varying end groups such as hydroxy, ester, primary, secondary or tertiary amino, halogen, and others. End group analysis by means of 360‐MHz 1H‐NMR nuclear magnetic resonance spectroscopy showed that the concentration of the end groups was in all cases equal to the concentration of the methyl head group, originating form the initiation reaction, if the terminating nucleophile was added five minutes after initiation (at 15°C). Under these conditions the polymerization is quantitative for initiator concentrations down to 0.01 mol L−1.
Anionic polymerization of styrene sulfonic acid derivatives
Authors: Whicher S. J. , Brash J. L.
Published: April 2003

As a preliminary to the preparation of block copolymers of p‐styrene sulfonic acid and isoprene, anionic polymerization of several derivatives of the former was investigated. Radical anions of naphthalene were used as the initiator for this study, in which the effects of polymerization variables including counterion, temperature, monomer and initiator concentrations, and solvent were investigated. Synthesis techniques were modified to obtain monomers of sufficient purity for anionic polymerization of n‐propyl, isopropyl, and methyl styrene sulfonates were successfully initiated, but only a limited degree of polymerization could be achieved under a wide variety of polymerization conditions. It is tentatively suggested that the living polymeric anions become dormant owing to a complexation between the anion and nearby sulfonate groups on the polymer coil.
Degradation of low‐density polyethylene in the presence of water and deuterium oxide
Authors: Sedgwick R. D. , Al‐Sultan Y. Y. , Abushihada A. M.
Published: April 2003

The degradation of low‐density polyethylene in the presence of water as the degradative agent was studied at a temperature of 450°C and a pressure greater than 160 atm. The experimental work was conducted in an autoclave of 333‐mL capacity. The products (gases, liquids, and solids) were analyzed by microanalytical methods and GC‐spectroscopic techniques. The results indicate the presence of paraffins, olefines, dienes, and aromatics in the degradation products. The occurrence of aromatics in the products demonstrates the importance of this degradation procedure for obtaining these valuable materials. The present work (Part 1) is believed to be the first publication to discuss the production of aromatics from polyethylenes degradation.
Studies of carbazole‐based polyarylates
Authors: Biswas Mukul , Das Sukhendu K.
Published: April 2003

A low temperature solution condensation method with pyridine as acceptor‐catalytic reagent was applied to the synthesis of polyarylates from carbazole and bisphenol A/phenolphthalein. The polyarylates were classified with respect to their structure, thermal stability, and dielectric behavior.
Degradation of lignin by ozone. I. The kinetics of lignin degradation of ozone
Authors: Mbachu R. A. D. , Manley R. St. John
Published: April 2003

The ozonolysis of spruce periodate and cuoxam lignins and protolignin in spruce wood has been studied in 45% aqueous acetic acid at room temperature. Stirring affected the rate of reaction and a tentative explanation is given. Degradation followed first‐order kinetics characterized by a rate constant K with values of 6.96 × 10−4s−1 for periodate lignin, 5.10 × 10−4s−1 for cuoxam lignin, and 5.09 × 10−4s−1 for protolignin in spruce wood. The similarity of the rate constants shows (1) that periodate and cuoxam lignins are good models for wood lignin and (2) that the carbohydrate matrix has an insignificant effect on the rate of delignification of the protolignin by ozone. The average rate of ozone consumption per C9 unit for periodate lignin was determined as 0.12 mol/min and 0.08 mol/min for cuoxam lignin. The implications of the various results are discussed.
Degradation of lignin by ozone. III. The fate of the carbohydrate matrix during the degradation of spruce protolignin by ozone
Authors: Mbachu R. A. D. , Manley R. St. John
Published: April 2003

Solvent‐extracted spruce wood meal was ozonized in 45% aqueous acetic acid at room temperature. The ozone‐treated wood meal was then extracted with dilute alkali at 65°C for 1 h. Lignin, α‐cellulose, and hemicellulose content and the viscosities of the pulped wood‐meal samples were measured as a function of the time of ozonization. Results indicate that although the attack on the wood components by ozone is not selective in this medium cellulose and hemicelluloses are degraded slowly compared with lignin. Lignin degraded approximately four times faster than the carbohydrates. At the fiber liberation point the pulp retained 78% of the original hemicelluloses and about 90% of the α‐cellulose compared with 25% of the lignin. The pulp samples obtained during ozonization of the wood meal showed a slow decrease in the average degree of polymerization (DP); the limit reached near 350 was attributed to the inaccessibility of the ordered regions in native cellulose to ozone.
Synthesis of polyamides from active O,O′‐diacyl derivatives of N‐hydroxy compounds and diamines under mild conditions
Authors: Lu Chengxun , Liu Peigang , Hu Chang
Published: April 2003

Two new routes to polyamides were established, based on the polycondensation of two new typical active diesters: the active diester of N‐hydroxy‐5‐norbornene‐2,3‐dicarboximide, such as N,N′‐(terephthaloyldioxy)bis(5‐norbornene‐2,3‐dicarboximide), and the active diester of 3‐hydroxy‐4‐oxo‐3,4‐dihydro‐1,2,3‐benzotriazine, such as 3,3′‐(isophthaloyldioxy)bis(4‐oxo‐3,4‐dihydro‐1,2,3‐benzotriazine) with diamines. The polycondensation occurred at room temperature in solution without added catalyst. Dipolar aprotic solvents which included dimethyl sulfoxide and N‐methyl‐2‐pyrrolidone were used as solvents for polymerization. Before polymer synthesis the aminolysis of two active monoesters was carried out as a model compound study.
Polymerization of cyclohexene oxide with Al(acac)3‐ silanol catalyst
Authors: Hayase S. , Ito T. , Suzuki S. , Wada M.
Published: April 2003

The polymerization of cyclohexene oxide was investigated with a new catalyst system of Al(acac)3‐ silanol compounds. Catalyst activity varied with the ratio of silanol/Al(acac)3 and the structure of silanol compounds. Catalyst deactivation appeared to be caused by self‐condensation of silanol and the addition of silanol to the epoxy ring. Polymer structure was investigated by 13C‐NMR spectroscopy and x‐ray diffraction. The mechanism of the polymerization appears to be cationic.
Water‐soluble copolymers. III. Dextran‐g‐poly(acrylamides) control of grafting sites and molecular weight by Ce(IV)‐induced initiation in homogeneous solutions
Authors: McCormick Charles L. , Park Lee Soon
Published: April 2003

Model graft copolymers were synthesized by grafting acrylamide onto dextran (Mw = 500,000) utilizing an initiation method in which a Ce(IV)/HNO3 solution was added to the dextran solution in order to allow coplexation prior to monomer addition. Three synthetic reaction parameters were optimized on the basis of conversion and solution viscosity: monomer concentration, dextran concentration, and nitric acid concentration. Molar ratios of [Ce(IV)]/[dextran] were changed systematically to affect the number and length of the acrylamide grafts. The number of grafting sites and graft chain lengths, determined by selective hydrolysis of the carbohydrate backbone, were in good agreement with those theortically predicted from knowledge of initiation efficiency and monomer conversion. Rheological studies of the model graft copolymers were conducted in aqueous solutions as a function of temperature, added salt, and copolymer concentration.
Autocatalysis and equilibrium in polyimide synthesis
Authors: Kaas Roger L.
Published: April 2003

Model compounds have been used to determine the mechanism of the reaction of aromatic diamines with aromatic cyclic dianhydrides to form poly(amic acids). Phthalic anhydride was used to model the anhydride functionality, while either 4,4′‐diaminodiphenyl ether or aniline was used for the amine functionality. The reaction between these materials was shown to follow second‐order, autocatalytic, and reversible kinetics. The rate constants for the mechanism were determined using a Runge–Kutta numerical integration of the rate equation and a Fibonacci technique to determine the reverse rate constant which minimzed the sum of squared deviations of the experimental data from the predicted line. Autocatalytic reversible kinetics are also followed by the formation of the poly(amic acid) precursor to a thermoplastic polyimide. In this polymerizing system, pyridine shifts the equilibrium to higher degrees of conversion to give higher molecular weights, while the opposite effect is obtained with acetic acid. Similarly, low temperatures favor higher equilibrium conversion and higher molecular weights. Thus the molecular weight of polyimides can be systematically controlled by manipulating factors which control the equilibrium conversion during the original formation of the poly(amic acid) precursor.
Post‐irradiation grafting of tetrafluoroethylene at low temperatures
Authors: Barkalov I. M. , Kiryukhin D. P. , Muydinov M. R.
Published: April 2003

Low‐temperature postirradiation grafting of tetrafluoroethylene (TFE) to polyolefines and silicone elastomers was the subject of study. After preliminary dissolution of TFE in the polymer at 273°K the system was slowly cooled to 77°K. In this process a certain part of TFE in polyolefines (ethylene‐propylene copolymer and polypropylene) is retained by the vitreous polymer matrix. When slowly heated after radiolysis at 77°K this system shows graft polymerization of dissolved TFE after Tg. The graft copolymer is soluble and its IR spectra contain absorption bands characteristic of polytetrafluoroethylene. In polydimethylsiloxane rubber (SKT) the dissolved TFE when frozen to 77°K remains sorbed between the SKT crystallites rather than in a separate phase. When these radiolyzed samples are heated the graft‐polymerization occurs primarily over the temperature range between the TFE and SKT melting points. The technique provedes for 100–150% grafting of TFE. This method also permits grafting to silicone rubbers and to several other polymers and elastomers.
Functional monomers and polymers. XCV. Photochemical reactions on synthetic polymers having pendant thymine bases in polymethyl methacrylate film
Authors: Kita Yasuo , Uno Taizo , Inaki Yoshiaki , Takemoto Kiichi
Published: April 2003

The photodimerization reaction of synthetic polymers which contain thymine bases was studied in polymethyl methacrylate film. The quantum efficiency for the photodimerization of the thymine bases of polyacrylate and polymethacrylate, fixed in the polymethyl methacrylate film was measured. The value of the film was higher than those measured in solution.
Head‐to‐head vinyl polymers. III. Preparation and characterization of head‐to‐head poly(acrylic acid) and its esters
Authors: Otsu Takayuki , Quach Loc
Published: April 2003

Head‐to‐head (h‐h) poly(acrylic acid) (PAA) and some h‐h poly(alkyl acrylates) (PRA) with methyl, ethyl, n‐propyl, n‐butyl, isobutyl and 2‐ethylhexyl substituents were prepared by hydrolysis or esterifications of the alternating copolymer of ethylene with maleic anhydride. In general, these esterification reactions became increasingly difficult as the carbon chain in the alcohols lengthened or branched. The softening, glass transition, and degradation temperatures of the h‐h polymers obtained were somewhat higher than those of the corresponding head‐to‐tail (h‐t) polymers. The main degradation products of both h‐h and h‐t PRA were identified by pyrolytic gas chromatography as the alcohol and monomer. In addition, the relative ratios of the amounts of alcohol to monomer were larger for h‐h than for the corresponding h‐t polymers.
Head‐to‐head vinyl polymers. V. Preparation and characterization of alternating head‐to‐head copolymers of alkyl acrylates with alkyl methacrylates
Authors: Quach Loc , Otsu Takayuki
Published: April 2003

Alternating head‐to‐head (h‐h) copolymers of methyl or n‐butyl acrylates with the corresponding methacrylates were synthesized by alternating copolymerization of ethylene with citraconic anhydride, followed by esterification and Characterization. The respective equimolar (1:) head‐to‐tail (h‐t) copolymers were also prepared by conventional radical copolymerization as comparison. The alternating, relatively low molecular weight h‐h copolymers obtained showed softening, glass transition, and degradation temperatures somewhat higher than those displayed by the 1:1 h‐t copolymers. After pyrolysis the main decomposition products from both h‐h and h‐t copolymers were alcohols, acrylates, and methacrylates. Furthermore, the ratios of alcohols to acrylates were larger for the h‐h than for the h‐t copolymers and smaller for the methyl than for the n‐butyl esters.
Calculation of molecular weight distribution of thermally polymerized polystyrene
Authors: Tung L. H.
Published: April 2003

The molecular weight distribution of thermally polymerized polystyrene prepared under steady‐state conditions is expected to obey the simple exponential distribution function. By integrating this simple distribution function with conversion the overall distribution of polystyrene prepared under more complex conditions can be predicted without invoking other kinetic constants. Good agreement between prediction and experiments has been obtained when a mercaptan compound was used to broaden the molecular weight distribution.
Effects of curing on the glass transition temperature and moisture absorption of a neat epoxy resin
Authors: Danieley Ned D. , Long Edward R.
Published: April 2003

Apparent glass transition temperature (Tg) measurements were made on smaples of a neat epoxy resin that had been cured at four different temperature and for four different times at each temperature. The apparent Tg data increase with cure time toward an asymptote that was dependent on cure temperature. The asymptotic dependence of Tg on cure temperature may be explained by the effect of cure temperature on the reaction rates and available reaction sites. The asymptotic increase with cure time may be understood in terms of the resin's extent of cure. Moisture‐conditioning studies were also made and the amount of moisture absorbed was correlated with the extent of cure. The absorbed moisture's interaction with the resin's molecular structure was deduced to by primarily at hydroxyl sites.
Functional monomers and polymers. XCVI. Photochemical reactions on oligo‐ and polyethyleneimines which contain pendant thymine bases
Authors: Inaki Yoshiaki , Suda Yasuo , Kita Yasuo , Takemoto Kiichi
Published: April 2003

The photodimerization reaction of oligo‐ and polyethyleneimine derivatives which contain pendant thymine bases in various amounts was studied in aqueous solution in a wide pH range and in N, N‐dimethylformamide solution. The photodimerization reaction of these derivatives in poly(methyl methacrylate) was also studied. It was found that its quantum efficiency tended to increase as thymine units were added to the oligomers and copolymers. This result is discussed in terms of the effect of the nearest neighboring thymine units and singlet energy migration, particularly in the polymers.
Further discussion of the cyclopolymerization of acrylic anhydride in terms of ring size control
Authors: Matsumoto Akira , Kitamura Takao , Oiwa Masayoshi , Butler George B.
Published: April 2003

Radical cyclopolymerization of acrylic anhydride (AA) was conducted under various polymerization conditions to yield highly cyclized polymer, and the content of the five‐membered ring of cyclic poly‐AA obtained was examined in detail. Five‐membered ring formation was favored with increased solvent polarity, raised polymerization temperature, and decreased monomer concentration; the ring size of the cyclic structure could be controlled freely by choosing appropriate polymerization conditions. In addition to these results, the rate of polymerization and the molecular weight of the polymer were reduced under polymerization conditions where the five‐membered ring formation was favored. Finally, a mechanistic discussion is given in order to interpret these results; a reaction scheme for propagation based on polymerization equilibrium is proposed.
Solution properties of poly(4,4′‐oxydiphenylene)‐4‐amidophthalamic acid
Authors: Alvino William M. , Ray John R.
Published: April 2003

A series of polymers based on 4‐chloroformyl phthalic anhydride (TMAC) and 4,4′‐diaminodi‐phenylether (DAPE) was prepared and shown to be soluble in N, N‐dimethylacetamide which contained 0.1N LiBr. These solutions were characterized by light scattering, membrane osmometry, and viscosity. A relationship between the viscosity and molecular weight was formulated and the nature of the polymer chain in solution was postulated.
Synthesis of vinyl polymers with pendant phenoxazinyl group
Authors: Kamogawa Hiroyoshi , Todo Yasuto , Nanasawa Masato
Published: April 2003

Vinyl monomers bearing phenoxazine units, were synthesized: 2‐vinyl‐phenoxazine starting with phenoxazine in a five‐step synthesis; 3‐acrylamido‐ or 3‐methacrylamido‐phenoxazines with or without 10‐PhCH2 or 10‐Me‐substituent starting with o‐benzylideneaminophenol or o‐anisidine via 3‐aminophenoxazines; and 3‐(p‐styrenesulfonamido)phenoxazines with or without 10‐PhCH2‐ or 10‐Me‐substituent, also via 3‐aminophenoxazines. Polymerizations of these noval monomers proceeded smoothly, except those having no 10‐substituent. Changes of the visible absorption spectrum of iodine in THF with addition of the polymers and oligomers thus prepared were considerable, with the appearance of new absorption peaks for polymers with 10‐Me‐substituent.
Polymerization of coordinated monomers. XVII. Alternating copolymerization of methyl methacrylate with styrene by boron compounds
Authors: Hirai Hidefumi , Takeuchi Kazuhiko , Komiyama Makoto
Published: April 2003

By the use of various boron compounds methyl methacrylate and styrene were copolymerized under photoirradiations at −20°C. The alternately regulating activities of the boron compounds in the copolymerizations were in the following order: boron trichloride > ethylboron dichloride > boron trifluoride > diethylboron chloride ≫ triethylboron (≃0). Boron trichloride and ethylboron dichloride exhibited such high regulating activities that their presence in 1 mol% in the charged methyl methacrylate was sufficient to complete equimolar alternating copolymerization. The alternating copolymerization proceeded in the steady state. The copolymerization rates decreased in the following order: boron trichloride ≫ ethylboron dichloride > diethylboron chloride ≫ triethylboron (≃0). The cotacticities of methyl methacrylate‐centered triads in the resulting copolymers were identical to those prepared with boron trichloride, ethylboron dichloride, and diethylboron chloride. The mechanism of the alternating copolymerization is discussed.
Polymers with improved flammability characteristics. I. Phenolphthalein‐related homopolymers
Authors: Lin M. S. , Pearce E. M.
Published: April 2003

Improved fire resistance occurs for phenolphthalein‐related polycarbonates and polyesters compared to bisphenol‐A polymers and emphasizes the importance of polymer composition and polymer structure in affecting the flammability of a polymer. Phenolphthalein‐related polymers are able to produce a higher degree of crosslinking during pyrolysis which subsequently leads to higher char yields. The correlations between oxygen index and char yield for various polymers are obtained and discussed. Polycarbonates and polyamides usually show higher oxygen indices than the corresponding polyesters of related structures. This indicates that the nature of the pyrolysis products has a measurable effect on the flammability of a specific polymer. Among many factors, polycarbonates should release more CO2 from the breakdown of the carbonate group, and polyamides should produce relatively nonflammable nitrogen‐containing products during pyrolysis, thus accounting in part for these results.
Acidic peroxo salts. A new class of initiators for vinyl polymerization. I. Kinetics of polymerization of acrylonitrile initiated by potassium monopersulfate catalyzed by Ag(I)
Authors: Samal Rajani K. , Das R. R. , Nayak M. C. , Suryanarayana G. V. , Panda G. , Das D. P.
Published: April 2003

The kinetics of polymerization of acrylonitrile initiated by KHSO5 and catalyzed by Ag(I) have been investigated in an aqueous medium over the temperature range of 35–50°C. The rates of polymerization Rp have been calculated and studied with respect to monomer and initiator. The catalytic activity of various metal ions on the initiator has been determined from a comparison of Rp values. The effects of monomer, catalyst, neutral salts, various amines, and inhibitor (hydroquinone) on the initial rate as well as maximum conversion have been studied. From the kinetics results a suitable reaction scheme has been proposed.
Energy transfer in connection with the photo‐oxidation of polystyrene and its blends with poly(2,6‐dimethyl‐1,4‐phenylene oxide)
Authors: Jensen J. P. Tovborg , Kops J.
Published: April 2003

By fluorescence spectroscopy it is possible to investigate some of the photophysical processes, particularly the energy transfer, that occur during the photo‐oxidative degradation of polystyrene (PS), poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO), and homogeneous blends of these. In connection with the irradiation, a part of the absorbed energy is transferred from excited phenyl groups in PS to PPO. The decrease in PS excimer fluorescence at 319 nm by admixture of PPO is greater than expected from the absorption of PPO at the excitation wavelength. A radiative energy transfer is suggested from PS to PPO which absorbs at 319 nm. Energy transfer also occurs to groups formed during photo‐oxidation. The quenching of PS excimer fluorescence during the process has been studied for both the homopolymer and the blends, and in all cases the reactions occurring during photo‐oxidation result in marked quenching at 319 nm.
Thermal degradation study of phenolphthalein polycarbonate
Authors: Lin M. S. , Bulkin B. J. , Pearce E. M.
Published: April 2003

Phenolphthalein polycarbonate underwent complicated thermal degradation which included random scission, rearrangement, hydrolysis, Friedel‐Crafts acylation, and cross‐linking. The carbonate group and lactone ring were both susceptible to thermal deterioration. Kinetic parameters were determined from the dynamic TGA thermograms. During early stages of degradation the measured reaction order was nearly 1, which suggested a random chain scission mechanism. The measured activation energy was 42.6 kcal/mol, compared with 41.2 kcal/mol calculated from isothermal aging. The Arrhenius preexponential constant was 3.09 × 1011 min−1. Below 80% weight residue the plot of fractional weight against 1/T revealed that complicated reactions with different activation energies occurred simultaneously and resulted in a final overlap of TGA curves for different heating rates indicative of cross‐linking and a lower preexponential constant. The reaction order changed and kept increasing in the last stages of degradation. Pyrolysis of this polymer was performed at 350°C under vacuum, followed by GC‐mass spectroscopic identification of products. The volatile products (17.5%) contained CO2, CO, O2, H2O, phenol, fluorenone, diphenyl carbonate, xanthone, anthraquinone, 2‐hydroxylanthraquinone, 2‐benzoxyanthraquinone, phenolphthalein, and trace amounts of benzoxyphenol and hydroquinone; the other 82.5% of products was insoluble gel. Functional group changes were examined by Fourier transform infrared spectroscopy (FT‐IR). Lactone, carbonate, and aromatic absorptions decreased during degradation. Increasing absorptions at 1739, 1728, 1280–1200, and 1138–1075 cm−1 were believed to result from aromatic ester (1728 cm−1) and phenyl aromatic ester (1739 cm−1) cross‐linkages ortho to the aromatic ether group (increases at 1155 cm−1 and 1280–1200 cm−1). Existence of 2‐hydroxyanthraquinone and xanthone contained in the crosslinked polymer matrix were also detected. Mechanisms for random scission, rearrangement, Friedel‐Crafts acylation, hydrolysis, and cross‐linking were suggested.
Aromatic polyamides. III. Mechanistic studies on the role of substituent chlorine in flame retarding aromatic polyamides
Authors: Khanna Y. P. , Pearce E. M.
Published: April 2003

The flammability of poly(1,3‐phenylene isophthalamide) and poly(chloro‐2,4‐phenylene isophthalamide) was measured by the oxygen index method. The chloro polyamide had reduced flammability shown by a 10–15 higher oxygen index. Analysis of the chars of the two polymers at 700°C by thermogravimetry (TGA) and elemental analysis showed that the chlorine caused a significant increase in the retention of C, H, N, and O in the pyrolysis residue. Most of the chlorine in the chloro polyamide, however, was lost by 700°C. Based on these results, we have suggested that the chlorine imparts flame retardancy by a combination of vapor‐ and condensed‐phase mechanisms. The origin of condensed‐phase activity is discussed.
Elementary radical formation and conversion processes in γ‐irradiated polyvinylchloride
Authors: Torikai Ayako , Adachi Tetsumi , Fueki Kenji
Published: April 2003

Elementary processes of γ‐irradiated polyvinylchloride (PVC) have been investigated by both electron spin resonance (ESR) and optical absorption measurements. On irradiating PVC film with γ rays at −196°C, alkyl‐type radicals are produced. When the PVC film is warmed to room temperature, the radicals convert to polyenyl type. γ Irradiation of PVC film containing biphenyl (Ph2) or pyrene (Py) at −196°C yields the corresponding radical cation. The relative ESR peak heights of the radicals decrease and the G values for the formation of cation radicals increase with increasing additive concentrations. These facts indicate that energy is transferred from the precursor of the radicals to the additive. In the case of PVC film containing Py, the Py cation radical decreases and the cyclohexadienyl‐type radical from Py is produced by thermal annealing. A possible mechanism for radical formation and conversion is proposed.
Synthesis of carbon‐carbon chain polymers by phase‐transfer‐catalyzed polycondensation of phenylacetonitrile with activated dichlorides
Authors: Imai Yoshio , Kameyama Atsushi , Nguyen Tien‐Quang , Ueda Mitsuru
Published: April 2003

Two‐phase polycondensation of phenylacetonitrile with α,α′‐dichloro‐p‐xylene and other activated dichlorides in an aromatic solvent‐aqueous sodium hydroxide system with various phase‐transfer catalysts produced carbon‐carbon chain polymers with inherent viscosities up to 0.6 dL/g. Reaction variables of the polycondensation are discussed in some detail. These polymers had melting temperatures below 220°C and were soluble in tetrahydrofuran and polar aprotic solvents that included dimethylformamide and dimethyl sulfoxide.
A carbazole‐based polymeric azodye
Authors: Biswas Mukul , Das Sukhendu K.
Published: April 2003

A new polymeric azodye has been synthesized from carbazole by diazotization of its derivative N‐methylcarbazole‐3,6‐diamine and subsequent coupling reaction with 2,2‐bis(4‐hydroxyphenyl‐3‐sulfonate‐Na)‐propane prepared from bisphenol‐A. Its physico‐chemical, electrical, and thermal properties have been characterized; finally, its application to the preparation of colored semiconductive films from polyvinyl alcohol has been studied.
Radical capture efficiencies in emulsion polymerization
Authors: Hawkett Brian S. , Napper D. H. , Gilbert R. G.
Published: April 2003

A theoretical procedure is developed that allows the importance of bimolecular termination in the aqueous phase of an emulsion polymerization to be determined. This shows that with sparinglysoluble and slowly propagating monomers like styrene, significant termination occurs in the aqueous phase at high initiator concentrations, as found experimentally. With more water soluble monomers, aqueous phase termination is likely to be small.