bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation and properties of polyamides and polyimides containing phenoxathiin units
Authors: Ueda Mitsuru , Aizawa Tatsuo , Imai Yoshio 
Published: April 2003

AbstractNovel polyimides and polyimides having phenoxathiin units have been prepared. Polyamides with inherent viscosities in the range of 0.5–2.9 were readily prepared by the polycondensations of phenoxathiin diamines with aromatic diacyl chlorides and of aromatic diamines with new phenoxathiin diacyl chlorides. The polyimides were synthesized from phenoxathiin diamines and pyromellitic dianhydride by using a two‐step procedure. The polyamic acids which formed in the first step had inherent viscosities ranging from 1.0 to 1.6, and they were converted to the polyimides by thermal cyclodehydration. Some of the phenoxanthiin‐containing polyamides were highly soluble in polar amide solvents and dimethyl sulfoxide. A series of novel polymers containing phenoxathiin units were much more thermostable than the corresponding polymers having open‐chain diphenyl ether linkages.
Application of ESCA to polymer chemistry. XVI. Electron mean free paths as a function of kinetic energy in polymeric films determined by means of ESCA
Authors: Clark D. T. , Thomas H. R. 
Published: April 2003

AbstractElectron mean free paths as a function of kinetic energy have been measured by the substrate overlayer technique for in situ‐polymerized films of poly(p‐xylylene) and the monochloro‐ and monobromo‐substituted derivatives. The results are compared with previous estimates of mean free paths available in the literature for organic materials. Comparison is also drawn with corresponding experimental data for typical metals and semiconductors, and it is shown that organic polymers fit into a consistent picture which may be rationalized on the basis of existing theory. For electrons of kinetic energy ∼969 eV, ∼1170 eV, 1202 eV, and 1403 eV, mean free paths of ∼14 Å, ∼22 Å, ∼23 Å, and ∼29 Å, respectively, are obtained for the poly(p‐xylylene) polymer films studied in this work.
Radical polymerization of methyl methacrylate in the presence of isotactic poly(methyl metacrylate). VII. Determination of the rate constants for template polymerization
Authors: Gons J. , Vorenkamp E. J. , Challa G. 
Published: April 2003

AbstractThe separate rate constants kp and kt for propagation and termination of radical template polymerization of methyl methacrylate along isotactic poly(methyl methacrylate) as a polymer template have been determined. The polymerizations were carried out in the strongly complexing solvent dimethylformamide at 5°C. For the evaluation of k/kt from stationary kinetic experiments, the rates of initiation were determined by employing a scavenger method. The nonstationary experiments yielding kp/kt were performed by means of the rotating sector technique. As the template rate effects increased with decreasing initiator concentration, the rotating sector curves were corrected for variation in light intensity. It appeared that the radical lifetime increases from 8.4 sec for normal or blank polymerization to 64 sec for template polymerization. The calculated values of kp are 26.6 and 5.9 l./mole‐sec and of kt 140 × 104 and 1.7 × 104 l./mole‐sec for blank and template polymerization, respectively. The changes in kp and kt, due to the presence of template polymer, are explained in terms of an extra loss of activation entropy in the stereoselective propagation step and a strong hindrance of segmental diffusion for the termination reaction of the chains growing along the polymer template.
Dielectric studies of photodegradation and photooxidation of polystyrene
Authors: Weir N. A. 
Published: April 2003

AbstractThe effects of vacuum photolysis at 254 nm and the short‐(λ = 254 nm) and long‐wave (λ > 300 nm) photooxidations on the dielectric constants (ϵ′) and dielectric losses (ϵ″) of polystyrene have been investigated at 25 ± 1°C. Dielectric constants generally increase on photodegradation, but more pronounced increases occur in the low‐frequency region on vacuum photolysis. It is suggested that such increases are associated with Maxwell‐Wagner‐Sillars polarization. Increases in dielectric losses are observed in three main frequency regions: around 102 Hz, 104 Hz, and at 3 × 106 Hz. The lowest frequency loss which occurs in both the vacuum‐irradiated and in the photooxidized samples is attributed to a combination of the effects of interfacial polarization and of the increased direct‐current conductivity of the polymer which occurs as a result of these reactions. The 104 Hz dispersion associated only with photooxidation is related to the presence of small, volatile, polar oxidation products, like ketones. The loss peak overlaps the intrinsic γ‐relaxation of polystyrene, and it appears that the motions of small molecules, or of relaxing dipoles in these, are coupled to the phenyl group rotational vibrations. The high‐frequency losses (3 × 106 Hz) are ascribed to orientation polarization of carbonyl dipoles attached to chain ends, these compounds being produced as a result of hydroperoxide decompositions. A good correlation between the carbonyl dipole relaxation strength and carbonyl concentration is observed. It would appear that relaxation strength measurements could provide quantitative kinetic information for polystyrene oxidation.
Peroxide‐Initiated crosslinking of styrene‐grafted polymers and copolymers of butadiene
Authors: Gasperowicz Aleksandra , Łaskawski Włodzimierz 
Published: April 2003

AbstractLow molecular weight polymers and copolymers of butadiene were grafted with styrene. The graft products were then crosslinked by using dicumyl peroxide as initiator. The optimum peroxide concentration was established (5 phr). Infrared analysis showed that the reactivity of 1,2‐vinyl and that of 1,4‐trans double bonds in styrene‐grafted polybutadiene is similar. Crosslinking of the graft product seems to involve a radical‐chain polymerization of double bonds in the polymer. The reaction rate is proportional to the square root of peroxide concentration and to the concentration of polymer double bonds. Activation energy, reaction heat, reaction order, and crosslinking efficiency were also determined from DSC measurements. No relation was found between the activation energy of crosslinking and the molecular weight of backbone polymer or density of grafting. Crosslinking efficiency was to 25–50 crosslinks per molecule of decomposed peroxide. The crosslinking efficiency for grafted butadiene–styrene copolymers is somewhat lower than that for grafted polybutadienes. From thermogravimetric measurements it was found that the crosslinked grafted polymers show lower resistance to thermal degradation than ungrafted polymers.
Dielectric properties of moist cellulose
Authors: Boutros S. , Hanna A. A. 
Published: April 2003

AbstractThe dielectric constant ϵ′ and the dielectric loss ϵ″ for cellulose fiber were measured over a frequency band 0.2 to 10 Mc/sec and a temperature range from −20 to 80°C. Also, the variation of the dielectric behavior with relative humidity was measured at 25°C. From these data, both the specific resistivity Rs and the dissociation energy U0 were calculated. The results showed that the dielectric constant increased with frequency and temperature. This may be due to the increase in the rotation and the polarization of the flexible part in the fiber. The variation of the dielectric loss with temperature showed a maximum absorption corresponding to the β‐relaxation. For the moist fiber, it is found that as the relative humidity increases, the dielectric constant and the dielectric loss increase. This increase may be due to the presence of polar water molecules, to the freeing of the polar groups, and to the freeing of the ions in the fiber molecule as well as to the increase in the number of OH− and H+ ions resulting from the ionization of water. A relation between the dielectric constant and resistivity at different humidities is represented graphically. From this relation, it is found that the dissociation energy is equal to 0.318 × 10−12 and 5.46 × 10−12 erg below and above 52% RH, respectively.
Asymmetric induction copolymerization of optically active l‐menthyl vinyl ether with styrene and N‐phenylmaleimide
Authors: Kurokawa Masahiro , Doiuchi Tohru , Yamaguchi Hidemasa , Minoura Yuji 
Published: April 2003

AbstractThe copolymerizations of l‐menthyl vinyl ether (l‐MVE) with styrene (St) and N‐phenylmaleimide (N‐PMI) as comonomers were carried out in benzene with azobisisobutyronitrile (AIBN) as an initiator to give optically active copolymers. After the removal of the optically active menthyl group by use of hydrogen bromide gas, the ether‐cloven l‐MVE‐N‐PMI copolymer (VA‐N‐PMI) was still optically active. On the other hand, the optical activity of l‐MVE‐St copolymer disappeared after ether cleavage. It is thought that asymmetric induction took place in the polymer main chains. The optical rotatory dispersion and circular dichroism of the original and ether‐cloven copolymers were measured in order to confirm the asymmetric induction.
Cationic polymerization with boron halides. V. Synthesis of poly(isobutylene‐b‐styrene) and poly(styrene‐b‐isobutylene)
Authors: Kennedy J. P. , Feinberg S. C. , Huang S. Y. 
Published: April 2003

AbstractBlock copolymers of isobutylene and styrene, PIB‐b‐PSt and PSt‐b‐PIB, have been prepared by a two‐step synthesis involving (1) preparation of terminally chlorinated (telechelic) polyisobutylene or polystyrene “prepolymers” by using the H2O/BCl3 initiator system and (2) blocking from these telechelic prepolymers a second polymer segment by using an alkyaluminum, e.g., Et2AlCl coinitiator. The telechelic polyisobutylene and polystyrene contain tertiary and benzylic chlorine termini, respectively. Block copolymer characterization included detailed selective solvent extraction procedures, coupled with GPC determinations, PMR, solubility, and intrinsic viscosity studies. The synthesis of PIB‐b‐PSt and PSt‐b‐PIB provides direct chemical evidence for the presence and position of active chlorine termini in BCl3‐coinitiated olefin polymerizations.
Distribution of polymer deposition in plasma polymerization. II. Effect of reactor design
Authors: Yasuda H. , Hirotsu Toshihiro 
Published: April 2003

AbstractThe effects of relative positions of the monomer inlet and the r.f. coil, and of the inlet and outlet, on the distribution of polymer deposition in plasma polymerization of ethylene were investigated using an electrodeless glow discharge by a 13.5‐MHz radiofrequency source. The diffusional transport of active species created under the r.f. coil, diffusional transport of polymer forming species, and flow of gas in the system are important factors that determine the distributions of polymer deposition observed in plasma polymerization of ethylene. The mechanisms of polymer deposition are discussed in conjunction with postulated plasma polymerization mechanisms.
Reactivity of halophenol and formation of phenoxo–copper(II) complex in basic copper‐catalyzed halogen displacement polymerization
Authors: Tsuruya Shigeru , Okumoto Kazutomo , Yoshimatsu Atkashi 
Published: April 2003

AbstractThe halogen displacement polymerization of 2,4,6‐trihalophenol with heterogeneous basic copper(II) complex is described. The corresponding poly(dihalophenylene oxides) have been obtained from 2,4,6‐trichloro‐, 2,4,6‐tribromo‐, and 2,4,6‐triiodophenol with the present catalytic system. In the halophenols used, the order of reactivity was as follows; 2,4,6‐trichloro‐ < 2,4,6‐tribromo‐ < 2,4,6‐triiodophenol. With 2,4,6‐trichlorophenol as a monomer, the 2,4,6‐trichlorophenoxo–copper(II) complex, which had the composition Cu(OCH3)(C6H2Cl3O) and was considered to be a reaction intermediate, was isolated. The ESR spectrum of this complex at room temperature showed a sharp peak considered to be free organic radical, in addition to the broad one based on copper(II) ion. Poly(dichlorophenylene oxide) was obtained by thermal decomposition of the phenoxo–copper(II) complex. It was concluded that the formation and decomposition of the phenoxo–copper(II) complex were intermediate steps of halogen displacement polymerization of 2,4,6‐trihalogenophenol with heterogeneous basic copper(II) catalyst.
Vinyl polymerization by metal complexes. XXV. Photopolymerization of vinyl monomers by porphyrin–iron(III) complex
Authors: Inaki Y. , Takahashi M. , Kameo Y. , Takemoto K. 
Published: April 2003

AbstractPhotopolymerization of methyl methacrylate was studied in the presence of the system of the tetraphenylporphine–iron(III) complex, free amine, and carbon tetrachloride at 0°C in methanol solution. It was found that the activity of the complex for polymerization does not depend upon the structure of the free amines added. The effect of the polymeric amines on the polymerization was also examined. The photochemical reaction process among the iron(III) complex, amine, and carbon tetrachloride was followed also under similar conditions by ultraviolet and visible spectroscopy. The scheme for the initiation species presented is supported by the results on the posteffect of the photopolymerization.
Preparation of polymers containing the 1,3,4‐oxadiazoline‐5‐thione structure and their application to the activation of N‐protected α‐amino acids
Authors: Fukuda Hiroyuki , Endo Takeshi , Suyama Masayoshi , Okawara Makoto 
Published: April 2003

AbstractTwo new monomers with pendent 1,3,4‐oxadiazoline‐5‐thione structures were prepared. Homopolymerization of 2‐isopropenyl‐1,3,4‐oxadiazoline‐5‐thione (V) and copolymerization with styrene (M1)(r1 = 0.02, r2 = 1.56, Q = 4.12, e = 1.06) were examined. Further, 2‐(4‐methacryloylaminophenyl)‐1,3,4‐oxadiazoline‐5‐thione (VIII) having a phenylcarbamoyl group between the isopropenyl and 1,3,4‐oxadiazoline‐5‐thione ring as a spacer was also synthesized and polymerized. The resultant polymers were allowed to react with N‐protected α‐amino acids such as Z‐AlaOH, Z‐LeuOH and Z‐PheOH by the DCC method. The polymers containing amino acids thus obtained were reacted with ethyl glycinate to give the corresponding dipeptides in excellent yields without racemization.
Synthesis of vinyl graft copolymers of poly(hexamethylene adipamide) and poly(m‐phenylene isophthalamide)
Authors: Kashani H. Akhavan , Barrie J. A. , George M. H. 
Published: April 2003

AbstractNylon 66 [poly(hexamethylene adipamide)] and Nomex [poly(m‐phenylene isophthalamide)] were metalated by using solutions of sodium in liquid ammonia. Metalation of the Nomex polymer was also carried out by using sodium naphthalene in tetrahydrofuran. The metalated polymers were then reacted with acrylonitrile monomer to yield the corresponding anionic graft copolymers. The heterogeneous nature of these reactions is discussed in relation to the structure of the graft copolymers.
15N‐NMR spectroscopy. III. Neighboring residue effects in sequence polymers containing glycylglycine units
Authors: Kricheldorf Hans. R. , Hull William E. 
Published: April 2003

AbstractThe tripeptides Phe‐Gly‐Gly, β‐Ala‐Gly‐Gly, and ϵ‐Aca‐Gly‐Gly as well as the peptide derivatives δ‐isothiocyanatovaleroyl‐Gly‐Gly and ϵ‐isothiocyanatocaproyl‐Gly‐Gly were synthesized by using known methods so that the peptide nitrogen between the two glycyl residues was isotopically enriched in 15N to a level of 0.8–0.9%. These monomer units were then used to produce the sequence polymers (Phe‐Gly‐Gly)n, (β‐Ala‐Gly‐Gly)n, (δ‐Ava‐Gly‐Gly)n, and (ϵ‐Aca‐Gly‐Gly)n. The 18.24 MHz 15N‐NMR spectra of the oligo‐ and polypeptides were obtained by using trifluoroacetic acid as solvent, since the solutions have relatively low viscosity and exhibit a strong negative nuclear Overhauser enhancement of the 15N signals. For comparison, 15N‐NMR spectra of the homopolymers (Gly)n, (β‐Ala)n, (γ‐Abu)n, (δ‐Ava)n, and (ϵ‐Aca)n were also recorded. The 15N signals from the ω‐aminoacyl residues in the sequence polymers appear up to 11 ppm upfield of the signals observed for the homopolyamides. The 15N signals from the two glycyl residues are separated by 3–7 ppm. Comparison with the 13C‐NMR spectra of the same polymers indicates that 15N‐NMR is better suited for the characterization and sequence analysis of these types of polymers.
Microheterogeneity in crosslinked polysiloxanes
Authors: Katz D. , Zewi I. G. 
Published: April 2003

AbstractPreviously reported studies on crosslinked castable poly(dimethylsiloxanes) have been extended. A series of dimethylsiloxane difumarates were copolymerized with styrene, and some of their rheological properties were determined. Investigation of these and previously prepared polymers has shown that segregation on a microscale can take place in two‐component crosslinked systems with relatively short network chains. This may occur even if one of the components is a nonpolymeric species involved in crosslinking. Microheterogeneity was observed in systems made up of prepolymer chains of a single type, when these were short enough to expose a specific structure of the crosslinking site. It seems that microheterogeneity can be expected in crosslinked polymers when the size of the crosslinking site is significant in comparison with the network chain length and when its cohesive energy density differs considerably from that of the main network chains. Additional factors affecting microphase separation include the existence of physical interactions between chemical groups, steric positioning of interacting groups during the process of crosslinking, and physical effects of the degree of crosslinking leading to local differences in the density of the system.
Photopolymerization of methyl methacrylate with the use of iodine monobromide as photoinitiator
Authors: Ghosh Premamoy , Banerjee Harihar 
Published: April 2003

AbstractIodine monobromide easily induces photopolymerization of methyl methacrylate (MMA) at 40°C under visible light. Initiator exponent and monomer exponent values were found to be 0.5 and 2, respectively, at low initiator concentrations, while the corresponding values at high initiator concentration conditions were zero and 3. The chain transfer constant of IBr at 40°C was found to be 13.0. Kinetic and other data indicate a radical polymerization mechanism involving complexation of monomer molecules with iodine monobromide prior to radical generation, and termination is believed to take place biomolecularly at low IBr concentrations and unimolecularly, involving reaction with the initiator, at high IBr concentrations (initiator termination).
Polymerization of vinyl chloride at reduced monomer accessibility. II. Polymerization at subsaturation pressure with emulsion PVC as seed
Authors: Hjertberg Thomas , Sörvik Erling M. 
Published: April 2003

AbstractVinyl chloride was polymerized at 59–92% of saturation pressure in a water‐suspended system at 45–65°C with an emulsion poly(vinyl chloride) (PVC) latex as a seed. A water‐soluble initiator was used in various concentrations. The monomer was continuously charged as vapor from a storage vessel kept at lower temperature. Characterization included determination of molecular‐weight distribution and degree of long‐chain branching by gel permeation chromatography (GPC) and viscometry, thermal dehydrochlorination, and microscopy. The polymerization rate decreases with decreasing pressure but is reasonable even at the lowest pressure. The molecular weight decreases with decreasing pressure and increasing initiator concentration and also with increasing polymerization temperature, if the initiator concentrations are chosen to give a constant initiator radical concentration. The degree of long‐chain branching increases with increasing initiator concentration and decreasing monomer pressure but is unaffected by the polymerization temperature, if the initiator radical concentration is kept constant. The thermal stability decreases with decreasing Mn, while the degree of long‐chain branching has only a minor influence. The most important factor in the system influencing the molecular parameter is the monomer accessibility.
Supported bis(indenyl)– and bis(fluorenyl)–chromium catalysts for ethylene polymerization
Authors: Karol Frederick J. , Munn William L. , Goeke George L. , Wagner Burkhard E. , Maraschin Norma J. 
Published: April 2003

AbstractSilica‐supported bis(indenyl)– and bis(fluorenyl)–chromium catalysts show good activity in ethylene polymerization. For maximum productivity with the indenyl chromium catalyst, the silica must be dried, with higher dehydration temperatures giving a significant increase in polymerization activity. Less deactivation on thermal aging of the supported bis(indenyl)–chromium catalyst allows ethylene polymerization to proceed for many hours, which provides polyethylenes of low residual chromium content. In contrast to the behavior of supported chromocene catalysts, the indenyl–and fluorenyl–chromium catalysts require a higher hydrogen/ethylene ratio to achieve a specific polymer melt index. Nevertheless, highly saturated polyethylenes are produced with these new catalysts. This result indicates that chain transfer to hydrogen remains the major chain transfer reaction. Addition of cyclopentadiene to a supported indenyl–chromium catalyst provided a catalyst with a much higher transfer response to hydrogen. This result suggests that ligand exchange occurred, producing a supported chromocene catalyst. These overall results are consistent with an active‐site model which comprises a supported divalent chromium center attached to an indenyl or fluorenyl ligand during the polymerization process. Polymerization is believed to occur by a coordinated anionic mechanism of the type previously discussed for a supported chromocene catalyst.
Copolymerization and homopolymerization reactions in systems containing electron‐donor monomer, electron‐acceptor monomer, and lewis acid
Authors: Kuran Witold , Pasynkiewicz Stanisław , Florjańczyk Zbigniew , Łyszkowska Danuta 
Published: April 2003

AbstractInvestigations of the copolymerization of acrylonitrile, methacrylonitrile, methyl acrylate, methyl methacrylate, acrylic acid, acryloyl chloride, methyl vinyl ketone, and acrolein with styrene, and of acrylonitrile with acenaphthylene and 1,3‐cyclopentadiene in the presence of Lewis acids as catalysts have been carried out. It was found that the free‐radical alternating copolymerization and ionic copolymerization or homopolymerization reactions can proceed in these systems. The yield of the competitive free‐radical and ionic reactions was related to the type of monomers and strength of the Lewis acid. The mechanism of the catalytic effect of Lewis acids in the reactions studied is discussed.