bluuebunny/crossref_metadata_2025_split huggingface dataset:
Poly‐α‐ester degradation studies. II. Thermal degradation of poly(isopropylidene carboxylate)
Authors: Sutton G. J. , Tighe B. J. , Roberts M. 
Published: April 2003

AbstractThe thermal degradation of poly(isopropylidene carboxylate) has been studied over the temperature range 200–800°C by using the kinetic and analytical techniques described in Part I of this series. Over a wide range of temperature, tetramethyl glycollide, acetone, carbon monoxide, and, to a lesser extent, methacrylic acid are observed when the products are rapidly swept away from the reaction zone. As decomposition temperature is increased, tetramethyl glycollide takes on the role of an intermediate, the more stable products carbon monoxide and acetone being formed from it. At the highest temperature examined, carbon monoxide begins to predominate, and its formation is accompanied by formation of small amounts of a carbonaceous residue. When the reaction products are allowed to remain in the reaction zone, which is possible at the lower end of the temperature range, methacrylic acid becomes the major product. This is interpreted as a dual decomposition route, involving the tetramethyl glycollide intermediate. Kinetic studies have shown that the decomposition is a first‐order process and that the first‐order rate constant k is related to temperature (T) by the expression:

The results are interpreted in terms of an intramolecular ester interchange process involving tetramethyl glycollide as the primary decomposition product.
Synthetic thermally reversible gel systems. VIII. Poly(vinyl chloride)–dioxane
Authors: Haas Howard C. , MacDonald Ruby L. 
Published: April 2003

AbstractWhen interpreted by network theory, equilibrium swelling measurements on poly‐(vinyl chloride) (PVC) film in dioxane and moduli measurements on the equilibrium swelled films yield values for the approximate molecular weight between thermally reversible crosslinks and for the number of these crosslinks per polymer chain. These values are in reasonable agreement with the thermodynamic analysis of PVC–dioxane gels by Takahashi, Nakamura, and Kagawa and with the premise that three‐dimensional network formation in these gels occurs by crystallization of a very limited number of syndiotactic sequences per chain having a sequence length of between 8 and 10. Failure to observe fusion endotherms by DTA on PVC–dibutyl phthalate gels supports the view that PVC gels have a low crystalline crosslink density and a low heat of crosslinking. The heat of crosslinking obtained by the method of Eldridge and Ferry shows only moderate agreement with expectations based on the heat of fusion of PVC and the number of repeating units per PVC chain passing through a crystalline crosslink in a PVC–dioxane gel.
Synthesis of poly‐α,α‐diphenylglycine. I. Thermal polymerization of 4,4‐diphenyl‐Δ2‐1,2,3‐triazolin‐5‐one
Authors: Ikeda K. , L'abbé G. , Smets G. , Delvaux M. C. 
Published: April 2003

AbstractThe thermal decomposition of 4,4‐diphenyl‐Δ2‐1,2,3‐triazolin‐5‐one (I) was reinvestigated and shown to yield poly‐α,α‐diphenylglycine (III) instead of the previously reported 3,3,6,6‐tetraphenylpiperazine‐2,5‐dione (II). Differentiation between the two structures was made by molecular weight determinations and spectroscopic analyses. The infrared spectra were studied in detail and compared with model compounds. They showed that the absorption peak at 1470 cm−1 must be attributed to the trans‐amide II absorption of the polymer. Furthermore, the polymers were found to contain terminal CONH2 as well as triazolinone or ether functions (from alcohol). Fractionation was performed in three solvents based on solubility differences: dichloroethane (or chloroform), methanol, and n‐hexane. All the fractions were characterized by physical methods. A mechanistic investigation revealed that the polymerization process cannot be rationalized by a radical or cationic mechanism, but is compatible with a molecular mechanism involving triazolinone functions at the growing chain ends.
Organometallic polymers. XXV. Preparation of polyvinylferrocene
Authors: Sasaki Y. , Walker L. L. , Hurst E. L. , Pittman C. U. 
Published: April 2003

AbstractThe synthetic details of solution polymerization in benzene and bulk polymerization of vinylferrocene are reported. In benzene solutions, with azobisisobutyronitrile (AIBN) as the initiator, small yields of low‐polydispersity low molecular weight (M̄n ≃ 5000) polyvinylferrocene is obtained. However, high yields can be obtained by continuous or multiple AIBN addition. Higher molecular weight polymers and binodal polymers can be obtained as the monomer concentration is increased. In bulk polymerizations, yields of 80% can be obtained. The molecular weight increases as temperature decreases from 80 to 60°C in bulk polymerizations, and an increasing amount of insoluble polymer results. The soluble portion is often binodal, the higher molecular weight node consisting of an increasingly branched structure. Lower molecular weight polymer was readily fractionated into narrow fractions from benzene–methanol systems, but higher molecular weight polymer proved impossible to fractionate into narrow fractions due to branching.
Semiconducting polymers based on charge‐transfer complexes. III. Complexing and chemical stability of charge‐transfer complexes in solution
Authors: Litt Morton H. , Summers James W. 
Published: April 2003

Abstract10‐Methylphenothiazine and p‐(methylthio)anisole were compared to polymers which contained these donor molecules on the side chains of N‐acyl‐substituted polyethylenimines. Charge‐transfer absorption spectra were compared for these donors with the acceptors: dichlorodicyanobenzoquinone, tetracyanoquinodimethane, tetracyanoethylene, and 2,4,5,7‐tetranitrofluorenone. Benesi‐Hildebrand plots show that the formation of the polymer complexes have 3 to 50 times higher equilibrium constants than those of the corresponding model complexes. This can be explained by complexing parallel to the polymer backbone. The polymer has the proper geometry for complexing (6.4 Å, repeat distance in the polymer backbone), and an acceptor molecule can therefore be inserted between two adjacent donor molecules for increased stability. Shifts of the absorption maxima to longer wavelength for some of the polymer complexes can be rationalized by the probability that in the polymer, an acceptor is sandwiched between two donors and thus forms 2:1 complexes; the extra resonance energy may shift the absorption maximum to longer wavelength. A second possible explanation is based on solvation of the complex which reduces the energy of the excited state. Polymers absorb mainly in the complex form. Model compounds absorb mainly by contact charge transfer, which is nonsolvated and thus occurs at higher energy or shorter wavelength. Extinction coefficients are higher for the model complexes than for the polymer complexes. Contact charge transfer, which can contribute in greater proportion to the model than to the polymer complexes, explains this. The amount of contact charge transfer can be calculated simply from the probability of a donor being in the solvent shell of an acceptor. Complex decomposition rates were determined based on measuring changes in the intensities of the charge‐transfer absorption spectra. Dichlorodicyanoquinone complexes were unstable, while the other complexes were stable.
Semiconducting polymers based on charge‐transfer complexes. IV. Electrical properties and structure of polymeric charge‐transfer complexes
Authors: Summers James W. , Litt Morton H. 
Published: April 2003

AbstractModel electron donor molecules, 10‐methylphenothiazine and 4‐(methylthio)anisole, and polymeric electron donors which contained these molecules on the side chains of N‐acyl‐substituted polyethylenimines, were complexed with the electron acceptors, dichlorodicyanoquinone (DDQ), tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), and tetranitrofluorenone (TNF). The model donors formed 1:1 complexes with all the acceptors except TCNE. The polymeric donors formed amorphous complexes with DDQ, TCNQ, and TCNE. Crystalline complexes were formed with TNF which had low melting points (lower than the model complexes and the pure polymer). This is apparently due to poor lateral packing of the polymer chains. Electrical resistivities were lower for all the polymer complexes than for the corresponding model complexes. Electrical resistivity also decreased with increase in complex crystallinity. In the best case the polymer complex was two hundred times as conducting as the model. The concentration of unpaired electrons measured by EPR was nearly independent of temperature. Most of the electrons seen are trapped and do not participate in conduction. Thermal activation energies for conduction were in the range of 0.5–1.8 eV and were nearly equal for the model and corresponding polymeric complexes. Elongation of polymer complex with TCNQ by rolling produces a decrease in resistivity in the roll direction, although the complex is amorphous. This reinforces the hypothesis that conduction is parallel to the polymer backbone. A polymer–tetranitrofluorenone complex was photoconducting, though the photoconductivity was smaller than the dark conductivity at the level of illumination used. Dember and Seebeck effects indicated that the major carrier in the complex was holes.
Oxidative thermal degradation of polytetrafluoroethylene
Authors: Paciorek K. L. , Kratzer R. H. , Kaufman J. 
Published: April 2003

AbstractOxidative thermal degradation studies were performed on polytetrafluoroethylene in air and oxygen by using a stagnation burner arrangement. The autoignition behavior as a function of temperature and oxidizing medium and the nature and relative proportion of the volatiles produced prior to ignition, on ignition, and during combustion were determined. In oxygen only COF2, CO2, and CF4 were formed; in air C2F4 was observed, together with a spectrum of rearrangement derived fluorocarbons in addition to the expected oxidation products. The autoignition temperature in air was found to be considerably higher than in oxygen (575°C compared to 512°C).
Polymerizability and related problems in the anionic polymerization of lactams
Authors: Sekiguchi Hikaru , Coutin Bernard 
Published: April 2003

AbstractThe anionic polymerization of lactams at low temperatures is not governed by thermodynamic equilibrium between the cyclic monomer and the linear polymer. On the basis of our reaction mechanism we propose therefore a new criterion (in contrast to the thermodynamic one) for estimating the chemical polymerizability of lactam: kendo/klactam, where klactam is the rate constant of alkaline hydrolysis of the lactam and kendo that of the endocyclic imide bond in the corresponding N‐acyl lactam. The value thus found for α‐piperidone and giving the theoretical polymerizability of this lactam accounts, however, only partially for its low polymerizability. Finally, the behavior of α‐piperidone derivatives in α‐pyrrolidone polymerization, as well as that of α‐pyrrolidone and α‐piperidone in polymerization in the presence of inorganic salts such as LiCl and LiSCN, shows that the unusually low ability of this lactam to polymerize could be explained in terms of the hydrogen‐bond‐rich structure of the resulting polymer appearing at a lower stage of conversion than that of other lactams and which might encage the active site situated at the end of the growing chain and thus hinder the access of lactam anion.
Effect of chemical structure in photochromic polymers of the mercury thiocarbazonate series
Authors: Kamogawa Hiroyoshi , Watanabe Hideo 
Published: April 2003

AbstractThe effects of the chemical structure of the functional portion as well as the comonomer composition on the photochromic behavior of vinyl polymers containing mercury thiocarbazonate functional groups in the side chains were investigated. It was found that, for p‐acrylamidophenyl mercuric thiocarbazonate polymers, the uses of β‐naphthyl and strongly electron‐releasing p‐methoxyphenyl groups for the thiocarbazone residue provide absorption maxima shifted somewhat to longer wavelengths as compared with the use of unsubstituted phenyl groups, whereas the electron‐withdrawing o‐trifluoromethylphenyl group brings about much larger shifts towards shorter wavelengths, the o‐trifluoromethylphenyl group and those groups capable of exerting steric hindrances such as β‐naphthyl and o‐methylphenyl groups causing slower light and dark reactions too. The increase of free volumes in the polymers by regulating the comonomer composition, i.e., the lowering of Tg, was found to improve photochromic responses strikingly.
Hydrolysis of linear polyurethanes and model monocarbamates
Authors: Matuszak Michael L. , Frisch K. C. , Reegen S. L. 
Published: April 2003

AbstractAlkaline hydrolysis of model carbamates, polyurethanes, and poly(urethane‐ureas) has been investigated. The model carbamates were based upon phenyl, benzyl, and cyclohexyl isocyanates. The polyurethanes and poly(urethane‐ureas) were prepared from tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), and 4,4′‐dicyclohexylmethane diisocyanate (H12MDI) and a poly(oxyethylene)glycol of 6000 molecular weight. Pseudo‐first‐order rate constants of hydrolysis were obtained in aqueous pyridine solution at 110°C, and second‐order rate constants were obtained in aqueous KOH solution for the model biscarbamates. Pseudo‐first‐order rate constants of hydrolysis were obtained in alcoholic KOH solution for the polyurethanes and poly(urethane‐ureas). The hydrolysis of the model carbamates showed that the stability increased in the following manner: phenyl < benzyl < cyclohexyl. The pseudo‐first‐order rate constants were dependent upon the pKb of the corresponding amines. The hydrolysis of the polyurethanes and poly(urethane‐ureas) showed that the stability increased in the following manner: aromatic < aralkyl < cycloaliphatic. It was shown that polyurethanes are more susceptible to alkaline hydrolysis than to acidic hydrolysis.
Properties of isocyanurate‐type crosslinked polyurethanes
Authors: Sasaki Nobuyoshi , Yokoyama Tetsuo , Tanaka Takehide 
Published: April 2003

AbstractPolyurethane elastomers containing isocyanurate rings as crosslinking structure were prepared by crosslinking the prepolymers in N,N‐dimethylformamide solution with sodium cyanide catalyst. Physical properties such as gel fraction, swelling ratio, density, glass transition temperature, Young's modulus, tensile strength, and elongation at break were measured. The effects of diisocyanate structure, the degree of crosslinking, and the crosslinking structure on the properties of polyurethanes were studied. The stress–strain curves of isocyanurate‐type crosslinked polyurethanes prepared from poly(oxytetramethylene)glycol rose at lower extensions and gave higher tensile properties than those of triol‐cured and diamine‐cured polyurethanes. The observed high tensile properties were attributed to the rigid crosslinking structure of isocyanurate ring.
Radiation‐induced polymerization of glass forming systems. VI. Polymerization rate at higher conversion in binary systems
Authors: Kaetsu Isao , Ito Akihiko , Hayashi Koichiro 
Published: April 2003

AbstractThe effect of temperature and composition on the inflection point in the time–conversion curve and the saturated conversion was investigated in the radiation‐induced radical polymerization of binary systems consisting of a glass‐forming monomer and a solvent. In the polymerization of completely homogeneous systems such as glycidyl methacrylate (GMA)–triacetin and hydroxyethyl methacrylate (HEMA)–propylene glycol systems, the time–conversion curve has an inflection point at polymerization temperatures between Tvm (Tv of monomer system) and Tvp (Tv of polymer system). Such conversions at the inflection point changed monotonically between 0 and 100% in this temperature range. Tv was found to be 30–50°C higher than Tg (glass transition temperature) and a monotonic function of composition (monomer–polymer–solvent). The acceleration effect continued to 100% conversion above Tvp, and no acceleration effect was observed below Tvm. The saturated conversion in homogeneous systems changed monotonically between 0 and 100% for polymerization temperatures between Tgm (Tg of monomer system) and Tgp (Tg of polymer system). Tg was also a monotonic function of composition. No saturation in conversion was observed above Tgp, and no polymerization occurred below Tgm. In the polymerization of completely heterogeneous systems such as HEMA–dioctyl phthalate, no acceleration effect was observed at any temperature and composition. The saturated conversion was 100% above Tg of pure HEMA, and no polymerization occurred below this temperature in this system.
Photoinduced ionic polymerization. V. Coexistence of cationic and anionic polymerizations
Authors: Irie Masahiro , Tomimoto Setsuko , Hayashi Koichiro 
Published: April 2003

AbstractPhotopolymerization of a mixture of cyclohexene oxide and nitroethylene was carried out with the purpose of carrying out cationic and anionic polymerizations simultaneously in the same system. The excitation of the charge transfer band by light of wavelength longer than 390 nm gives rise to the polymerization of both monomers. No polymer was obtained in the dark. Additives affect the composition of the polymer, the rates of polymerization, and the molecular weight distributions. These data show that cationic polymerization of cyclohexene oxide and anionic polymerization of nitroethylene occurs simultaneously in this system.
ESR studies of methallyl monomers with redox systems
Authors: Izumi Zenzi , Rånby Bengt 
Published: April 2003

AbstractThe effects of three types of free radical initiators (HO·, H2N·, and H3C·) from redox systems, have been studied for four types of methallyl monomers, by use of ESR with a flow system. The structure, the relative concentrations, and the steric conformations of the monomer radical intermediates have been derived from the ESR spectra. In the case of H2N · and HO · addition to methallyl alcohol (MAA), methallyl amine (MAAm), and sodium methallyl sulfonate (SMAS), the ESR spectra of the reacting species are interpreted as monomer head radicals only (H2N · and HO · are added to the monomer tail). Methallyl acetate (MAAc) with HO ·, is an exception, giving hydrogen abstraction to form an allyl type radical. This reaction may influence the polymerization behavior of MAAc. The methallyl monomers behave differently from the allyl monomers, where appreciable amounts of monomer tail radicals were found in addition to the head radicals which were the main species. For methallyl monomers, this may be due to steric hindrance caused by the two substituents on the α carbon. The CH3 radicals add only to positively polarized reactive double bonds, i.e., in SMAS in this study, and allyl alcohol in a previous study. The coupling constants of β CH2 protons vary considerably with the substituents. For β1 protons, the coupling constants decrease in the order OH > CH3 > NH2. For β2 protons (allyl hydrogen), the coupling constants decrease in the order CH2OH > CH2NH2 > CH2OCOCH3Na, i.e., the constants decrease in the order of increased bulkiness of the groups. Some exceptions are interpreted as due to complex formation with Ti4+. The effects of pH of the reaction medium are largely those expected.
Effect of solvent on the reactivity of functional groups in polycondensation reactions
Authors: Ogata Naoya , Ikari Tokuo 
Published: April 2003

AbstractThe effect of solvent on solution or interfacial polycondensations was investigated in terms of selectivity and control of functional groups such as amine or hydroxyl groups toward polycondensation reactions. Solution polycondensation of a mixture of resorcinol (RL) and m‐xylyenediamine (m‐XD) with isophthaloyl chloride was affected by solvents to such extent as to change the course of the polycondensation reaction, and hexamethylenephosphoramide (HMPA) caused the formation of amide‐rich polymer, while tetrahydrofuran (THF) was a solvent favoring formation of a polyamide ester with a regular structure. Polycondensation of 3,3′‐dihydroxybenzidine (DHB) with isophthaloyl chloride yielded exclusively a linear polyamide in HMPA solution, while with aldehyde as a solvent polyester was obtained owing to the preservation of the amine group. Thus, it was found that the course of polycondensation reactions of monomers having different functional groups could be controlled by selection of a suitable solvent.
Formation and homolytic cleavage of the Ni(II)–styryl σ‐bond
Authors: Henrichi‐Olivé G. , Olivé S. 
Published: April 2003

AbstractA Ni–carbon σ‐bond is formed from biscyclooctadienenickel(0) and styrene in the presence of organic acids. Homolytic cleavage of this bond gives free radicals. The mechanism of formation and disappearance of the radical‐supplying species is deduced from kinetic and other data. A competing coordinated ligand insertion reaction is discussed.
Radiation‐induced polymerization at high pressure of cis‐ and trans‐1,3,3,3‐tetrafluoropropene in bulk and with tetrafluoroethylene
Authors: Brown Daniel W. , Lowry Robert E. , Wall Leo A. 
Published: April 2003

AbstractThe radiation‐induced polymerization of cis‐ and trans‐1,3,3,3‐tetrafluoropropene in bulk and with tetrafluoroethylene was studied at pressures between 5000 and 15000 atm and temperatures between 21 and 100°C. At 103 rad/hr the homopolymerization rates range from about 10−4 to 1%/hr. The activation enthalpy and volume are about 8 kcal/mole (33 kJ/mole) and −10 cm3/mole, respectively, for both isomers. The cis isomer polymerizes about twice as rapidly as the trans isomer. The latter freezes in the experimental range of temperature and pressure; the polymerization rate is very low in solid phase. Polymer intrinsic viscosities increase with polymerization pressure and decrease with polymerization temperature; the largest value obtained was 0.23 dl/g. In the copolymerizations all reactivity ratios favor incorporation of tetrafluoroethylene by factors of 6–16. The preference is stronger when the trans isomer is used.
Fracture process and molecular kinetics of PMMA
Authors: Johnson F. A. , Radon J. C. 
Published: April 2003

AbstractThe critical value of the stress intensity factor,K1c, (fracture toughness) has been measured for poly(methyl methacrylate) (PMMA) over a wide range of testing speed (K≃ 4 toK̇≃ 50 × 106lb/in3/2‐sec) and temperature (from −197°C to +21°C) in air and inert gas, by use of single‐edge notch, double cantilever beam (normal and compact types) and instrumented impact tests. Some features of the toughness curves were found to be subject to time–temperature shifts and were explained in terms of relaxation motions of parts of the polymer molecule, (second‐order thermodynamic transitions). Correlation with published data on mechanical energy losses in vibration experiments, dielectric losses and NMR results provided an identification of the operative relaxations. The coincidence of the fracture mode transition in the glassy state with the peak of the β relaxation was observed and the trend ofK1cvalues in a transition region was attributed to the close relationship ofK1cto the complex modulus for the hard glassy state. Impact and propagating crack values ofK1chave been discussed in general terms, and the limitations of fracture mechanics in studying a time‐dependent material property have been considered in the light of recent rheological studies on the fracture of polymers.
Polymerization of styrene with chromium acetylacetonate–triisobutylaluminum catalyst system
Authors: Deshpande A. B. , Kale S. M. , Kapur S. L. 
Published: April 2003

AbstractStyrene is polymerized with chromium acetylacetonate–triisobutylaluminum catalyst at 40°C in a benzene medium. At the stoichiometric ratio of Al/Cr of 4, the activity for polymerization was found to be maximum. Further, the kinetic studies were carried out at this ratio of Al/Cr of maximum activity. The kinetics of polymerization and the total activation energy around 10.00 kcal/mole suggest a coordinate anionic mechanism.