bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of N‐methyl substitution on the thermal decomposition processes in aliphatic–aromatic polyamides
Authors: Ballistreri Alberto , Garozzo Domenico , Montaudo Giorgio , Giuffrida Mario 
Published: April 2003

AbstractThe thermal decomposition processes of two polyamides, derived from succinic acid and two aromatic diamines, were studied by direct pyrolysis mass spectrometry.Fast atom bombardment (FAB) mass spectrometry has been also used in order to provide additional information for the elucidation of the thermal degradation mechanism of the polymers investigated. FAB mass spectra, obtained by introducing in the FAB ion source the solid residues from polymer pyrolysis performed in thermogravimetric experiments, allowed the detection of diagnostic compounds up to about 1600 amu.Our results indicate that the thermal stability of the N‐methyl‐substituted polyamide is higher than that of the unsubstituted polyamide. The difference in the thermal degradation mechanism accounts for the difference in the thermal stability of the two polyamides. In fact, the unsubstituted polyamide decomposes via an intramolecular exchange and a concomitant NH hydrogen transfer process with formation of compounds with amine and/or succinimide end groups. Instead, the N‐methyl‐substituted polyamide decomposes via an α CH hydrogen transfer process from the methyl group to the nitrogen atom with formation of compounds with amine and/or 2,5‐piperidinedione end groups.
FT–IR spectroscopic study on the thermal and thermal oxidative degradation of nylons
Authors: Do C. H. , Pearce E. M. , Bulkin B. J. , Reimschuessel H. K. 
Published: April 2003

AbstractThe effects of heat and oxygen on nylon films were studied by FT–IR spectroscopy. Nylons 6, 66 and nylons containing carbonyl groups in either the diamine or the diacid moiety were prepared. Nylon films cast on aluminum were studied in an environmental chamber under controlled conditions. The progress of chemical and physical changes was monitored by FT–IR spectroscopy. Thermal energy caused largely an increase in crystallinity due to annealing and also an increase of nonhydrogen‐bonded amide groups, which seemed to entail mainly amide groups from the amorphous region. The intensities of IR absorption bands related to the folded structure reduced as soon as heating began. The IR spectra of the carbonyl groups formed by thermal oxidation showed band shapes that indicated that the formed carbonyl groups were of many different origins. The presence of keto groups purposely inserted into the backbone chains increased the rate of oxidation. Pyrolysis of the nylons was also studied to supplement data obtained at lower temperatures.
Liquid crystalline polymers containing heterocycloalkane mesogens. 2. Side‐chain liquid crystalline polysiloxanes containing 2,5‐disubstituted‐1,3‐dioxane mesogens
Authors: Hsu C. S. , Rodriguez‐Parada J. M. , Percec V. 
Published: April 2003

AbstractPolysiloxanes and copolysiloxanes containing 2‐(p‐hydroxyphenyl)‐5‐(p‐methoxyphenyl)‐1,3‐dioxane and 5‐(p‐methoxyphenyl)‐1,3‐dioxan‐2‐yl as mesogenic units and an aliphatic spacer containing 11 and 10 methylene units, respectively, were synthesized. Their phase behavior was studied by differential scanning calorimetry and optical polarization microscopy, and compared with the phase behavior of the polysiloxanes and copolysiloxanes containing 4‐methoxy‐4′‐hydroxybiphenyl and 4‐cyano‐4′‐hydroxybiphenyl mesogens attached to the polymer backbone through an aliphatic spacer containing 11 methylene units. All synthesized polymers present smectic mesomorphism. The polymers containing 4‐methoxy‐4′‐hydroxybiphenyl and 4‐cyano‐4′‐hydroxybiphenyl are also crystalline, while the polymers containing 1,3‐dioxane based mesogens do not crystallize.
Polymer‐supported bases. 7. Nucleophilic acyl rearrangements catalyzed by polymer‐supported aminopyridine or imidazole bases
Authors: Tomoi Masao , Arita Yasushi , Kakiuchi Hiroshi 
Published: April 2003

AbstractPolymer‐supported aminopyridine or imidazole catalysts were effective for acyl rearrangements of O‐acylated substrates to C‐acylated products. Some of the aminopyridine catalysts, which had much higher activity than the imidazole catalyst, exhibited high activity comparable to that of the corresponding soluble catalyst, 4‐N, N‐dimethylaminopyridine. The activity of the immobilized aminopyridines was studied as a function of the percentage of ring substitution, spacer‐chain length, and solvents. The affinity of the substrates for the immobilized catalysts played an important role for the rearrangements. The increased catalytic activity resulted from the increased affinity of the substrates for the catalysts. The activity of the immobilized bases decreased gradually owing to the reaction of the active site with the products as the catalysts were used repeatedly. The treatment of the used catalysts with nucleophiles restored the activity to some extent. The activity decrease can be minimized by shortening a contact time between the catalysts and the products.
Enantioface differentiation by chiral polymers having (+)‐5,6‐exo‐bornanediol moieties. II. Asymmetric reduction of prochiral ketones by chiral polymers containing (+)‐5,6‐exo‐bornanediol derivatives
Authors: Liu Jui‐Hsiang , Lin Shyuh‐Rurng , Kuo Jue‐Cheng 
Published: April 2003

AbstractThe asymmetric reduction of prochiral aromatic ketones with modified reagents prepared from sodium borohydride and carboxylic acids in the presence of both chiral polymers and relating low molecular weight compounds having (+)‐5,6‐exo‐dihydroxybornyl derivatives was carried out. The enantioface differentiation took place effectively by raising the reaction temperature, and the highest enantiomeric excess was achieved at 10°C (24.3%) in the presence of the chiral polymers. A higher optical yield (87.8%) can be obtained in the asymmetric reduction by using the low molecular weight (+)‐5,6‐exo‐diol compounds. The effect of the reaction temperature, solvents, and the advantages of the chiral polymer‐bound reagents were also discussed.
The influence of molecular weight on the reactivity of a vinylbenzyl ether macromonomer of poly(2,6‐dimethyl‐1,4‐phenylene oxide)
Authors: Mühlbach Klaus , Percec Virgil 
Published: April 2003

AbstractThe synthesis of a series of vinylbenzyl ether macromonomers of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO–VBE) with number average molecular weights between 1,000 and 27,000 and narrow molecular weight distribution is presented. The reactivity ratio r1 was determined for the comonomer pairs methyl methacrylate (MMA) and butyl methacrylate (BMA), respectively (M1), and PPO–VBE (M2) over the entire range of molecular weights of the macromonomer. r1 was determined by the single experiment intergrated equation. Since both the monomer and macromonomer present an induction period, it has been shown that the determination of r1 from one single point experiment is not correct. Accurate r1 values can be obtained from one single copolymerization experiment only when the comonomer conversions are determined at several different reaction times. The macromonomer reactivity (1/r1) increases with its molecular weight up to about 5,000–7,000. Above these values its reactivity decreases. An attempt to explain this behavior based on the kinetic excluded free volume effect is presented.
Synthesis and properties of new polybenzimidazoles and N‐phenyl polybenzimidazoles with flexibilizing spacers on the polymer backbone
Authors: Scariah K. J. , Krishnamurthy V. N. , Rao K. V. C. , Srinivasan M. 
Published: April 2003

AbstractSeveral new polybenzimidazoles (PBIs) and N‐phenyl PBIs were synthesized by high temperature solution polycondensation techniques. Three different tetramine hydrochlorides and one N‐phenyl tetramine hydrochloride were condensed independently with p‐phenylenedioxydiacetic acid (PDDA), 2,2′‐[isopropylidene bis(p‐phenyleneoxy)] diacetic acid (bisacid A2) and 2,2′‐[sulfonyl bis(p‐phenyleneoxy)] diacetic acid (bisacid S) in polyphosphoric acid (PPA) at high temperatures. The polymers were obtained in 55–65% yield with inherent viscosities in the range 0.58–0.96 dL/g. Four model benzimidazoles (MBI) were also synthesized to confirm the formation of polybenzimidazoles. The PBIs and MBIs were characterized by infrared spectroscopy and elemental analysis. The properties of the polymers such as solubility, density, crystallinity, and thermal, thermoxidative, and isothermal stabilities were studied.
High performance polymers and composites. IV. Copolymers containing benzoxazole units
Authors: Mathias Lon J. , Livant Peter D. , Ahmed Sharf U. 
Published: April 2003

AbstractSeveral new copolymers have been synthesized. Initial polycondensation of mixtures of aryl and arylalkyl carboxylic acids containing aromatic hydroxyl and amine substituents led to random copolyamides. Thermal cyclization of these prepolymers (inherent viscosities of about 0.2 dL/g) gave copolybenzoxazoles with inherent viscosities of about 1.4 dL/g. Thermal stability as measured by TGA was similar for the 1:1 copolymers and the homopolymers containing hydrocinnamic units; i.e., catastrophic decomposition occurred at 450°C. Copolymers with lower ratios of the hydrocinnamic units displayed greatly improved thermal stability while maintaining good molecular weight.
Synthesis and characterization of liquid crystalline polysiloxanes containing benzyl ether mesogens
Authors: Hsu C. S. , Percec V. 
Published: April 2003

AbstractSide chain liquid crystalline polysiloxanes were synthesized by the hydrosilation of poly(methylhydrosiloxane) with p‐(1‐undecenyl‐11‐oxy) benzyl ethers of 4‐cyanophenol (IM), 4‐methoxyphenol (IIM), 4‐cyano‐4′‐hydroxybiphenyl (IIIM), 4‐methoxy‐4′‐hydroxybiphenyl (IVM), and 2‐cyano‐6‐hydroxynaphthalene (VM). The phase behavior of both monomeric and polymeric liquid crystals was characterized by differential scanning calorimetry and optical polarization microscopy. IM is a monotropic liquid crystal, IIM is crystalline, and IIIM and IVM are enantiotropic liquid crystals, whereas VM presents two virtual liquid crystalline transitions and crystalline polymorphism. All the synthesized polysiloxanes present enantiotropic smectic mesomorphism.
Uniform encapsulation of fine inorganic powder with soapless emulsion polymerization
Authors: Hasegawa Masahiro , Arai Kunio , Saito Shozaburo 
Published: April 2003

AbstractThe encapsulation of inorganic powder of submicron sizes was attempted with soapless emulsion polymerization of methyl methacrylate in water in the presence of the powder. The powders used were barium sulfate and calcium carbonate. The polymerizations were initiated by potassium persulfate and by sodium bisulfite‐oxygen redox reaction. The encapsulation state of the powder with the polymer formed varied considerably with the initiators used. With potassium persulfate initiator the powder surface was partially or totally covered by polymer particles, while with redox initiator under air atmosphere the powder surface was well encapsulated with a film‐like polymer layer. From the differences in the encapsulation states, an encapsulation mechanism is suggested for each initiator system. Based upon this mechanism, a new encapsulation process capable of covering uniformly fine powders with a film polymer is proposed. An important factor in the new process is the addition of an extremely small quantity of a surfactant into the reaction system prior to the polymerization.
Benzocyclobutene in polymer synthesis. II. Solid state diels–alder polymerization utilizing an in situ generated diene and an alkyne
Authors: Tan Loon‐Seng , Arnold Fred E. 
Published: April 2003

AbstractA novel class of aromatic imide AB‐monomers with benzocyclobutene and an alkyne (primarily phenylethynyl group) as the reactive units have been prepared. The monomers have been utilized in thermally induced Diels–Alder polymerizations. The differential scanning calorimetric study of the AB‐monomers provided two observations: (i) primary acetylene began its homopolymerization (202°C max.) before the electrocyclic ring opening of benzocyclobutene (270°C max.); (ii) the phenoxy group connecting between phenylacetylenyl group and the aromatic imide fragment suppressed polymerization in Diels–Alder fashion. Furthermore, thermoxidative stability evaluation on the cured samples (250°C for 8 h and then 350°C for another 8 h under N2 atmosphere), carried out at 650°F (air) for 200 h, indicated the more rigid phenylethynyl phthalimide system was the most heat‐resistant.
Synthesis and characterization of poly([3H]‐thiazole‐2‐thione)s
Authors: Katritzky Alan R. , Tarr Richard D. , Heilmann Steven M. , Rasmussen Jerald K. , Krepski Larry R. 
Published: April 2003

AbstractThe reaction of dithiocarbamate salts with α‐haloketones is extended to (i) dithiocarbamate salts with bis(α‐haloketones), (ii) bis(dithiocarbamate salts) with α‐haloketones, and (iii) bis(dithiocarbamate salts) with bis(α‐haloketones). Both (i) and (ii) give bis([3H]‐thiazole‐2thiazole‐2‐thiones) in high yields, and (iii) gives the corresponding polymers which are described and characterized.
Effect of surfactant adsorbed on encapsulation of fine inorganic powder with soapless emulsion polymerization
Authors: Hasegawa Masahiro , Arai Kunio , Saito Shozaburo 
Published: April 2003

AbstractThe encapsulation of fine inorganic powder was carried out with the soapless emulsion polymerization of methyl methacrylate in water in the presence of the powder, a layer of surfactant being adsorbed. The powder used was titanium dioxide. Surfactants added prior to the polymerization were sodium dodecyl sulfate, dodecyltrimethyl ammonium bromide, and polyoxyethylene sorbitan mono‐oleate. The encapsulation state of the powder with polymer was closely related to the amount of surfactant adsorbed on the powder; and an amount of adsorption above a certain value was necessary for uniform encapsulation. Ionic surfactants were more useful than nonionic in the surfactants used, and could be adsorbed utilizing the electrostatic interaction between powder and the ionic end group. The combination of electric charges between the ionic end groups of surfactant and initiator was found to influence the molecular weight of capsulating polymer.
The initiation of the free radical polymerization of vinyl monomers by hexakis(arylisocyano) derivatives of chromium (o)
Authors: Hargreaves K. 
Published: April 2003

AbstractThe present paper describes studies carried out to determine the effect of structure on the free radical polymerization of vinyl monomers initiated by means of the hexakis(arylisocyano) derivatives of chromium (o) in which chlorine, methoxy, and methyl groups have been substituted into different positions of the benzene ring.The kinetics of the initiation reactions resembles that studied in detail for the parent compound hexakis(phenylisocyano) chromium (o). The observed changes in the initial rates of the polymerization of methyl methacrylate at 80°C in the presence of carbon tetrachloride can be accounted for by the electronic effects associated with these substituents. However, when steric overcrowding occurs, the initial rates of polymerization are reduced considerably.The results obtained confirm the mechanism of initiation proposed earlier in which the rate determining step is the Sn2 displacement of an arylisocyano ligand by a monomer or reactive solvent molecule. An attempt has been made to explain the increased rate of radical formation observed when chlorine is substituted into the benzene ring.
Synthesis and properties of polyamides derived from systematically halogenated terephthalic acids with fluorine, chlorine, or bromine atoms
Authors: Nagata Minoru , Tsutsumi Naoto , Kiyotsukuri Tsuyoshi 
Published: April 2003

AbstractAromatic polyamides were prepared from systematically halogenated terephthalic acids with hexamethylene diamine, piperazine, 4,4′‐diaminodiphenylether and p‐phenylene diamine by interfacial or low temperature solution polycondensation. The halogenated terephthalic acids used have mono‐, di‐, or tetra‐substituted fluorine, chlorine, or bromine atoms on the benzene ring. The nonhalogenated terephthalic acid was also used for the comparison. The effects of halogen substitution on the benzene ring on the synthesis and some properties of polymers were examined. Reduced specific viscosity decreased in the order F > Cl > Br by halogen substitution. The incorporation of halogen substituents on the ring led to a decrease of crystallinity and fluoro‐substituents hindered the crystallization more strongly. The melting point (Tm) decreased in the order F > Cl > Br by mono‐substitution, and Br > Cl > F by di‐and tetra‐substitution. The change of Tm caused by the difference of the number of halogen substituents differed depending on the rigidity of polymer chains. The flame‐retardancy estimated by thermogravimetry, self‐ignition, and flash‐ignition test increased with increasing halogen content of the polymers. Solubility increased remarkably by halogen substitution. The peak temperature of tan δ decreased by halogen substitution. Some discussion was made on these effects of halogen substitution.
Preparation and properties of 1‐ethoxy‐2,2,2‐trifluoroethyl esters of acrylic and methacrylic acids and of their polymers
Authors: Hrabáak F. , Lokaj J. , Bílá J. , Pivcová H. , Tkaczyk M. , Biroš J. 
Published: April 2003

Abstract1‐Ethoxy‐2,2,2‐trifluoroethyl esters of acrylic (I) and methacrylic (II) acids were synthesized from 1‐ethoxy‐2,2,2‐trifluoroethanol and acryloyl‐ and methacryloylchloride, respectively, and their densities, mass, 1H‐ and 13C‐NMR spectra were measured and the rate constants of hydrolysis were determined. Poly(I) and poly(II) were prepared by radical homopolymerization; the rates of polymerization, specific volume contractions in polymerization, limiting viscosity numbers, average number degrees of polymerization, temperature dependences of the heat capacities both in glass and liquid state, glass transition temperatures, and the initial temperature of the spontaneous thermal decomposition of homopolymers were determined. The monomer reactivity ratios of the styrene (S) copolymerizations, SI and SII, and the Alfrey–Price copolymerization constants e and Q for I and II were calculated from the composition of copolymers of I and II with styrene.
Preparation of polysiloxanes from silicic acid. X. Preparation and properties of allyldimethylsilylated silicic acids
Authors: Abe Yoshimoto , Kaijou Akira , Nagao Yukinori , Misono Takahisa 
Published: April 2003

AbstractIn order to obtain polysiloxanes capable of forming a film, the preparation and properties of allyldimethylsilylated silicic acid was investigated. The reaction in variable molar ratios of allyldimethylchlorosilane to silicic acid gave partially silylated silicic acids with different degrees of silylation. They provided not only fibrous polysiloxanes but also films from concentrated polymer solutions. Spinnability and film formation depended on the solvent, degree of silylation, molecular weight, and allyl group.
Highly active supported catalysts for olefin polymerization: Preparation and characterization of the catalyst
Authors: Yano Takefumi , Inoue Tokuji , Ikai Shigeru , Shimizu Michimasa , Kai Yoshiyuki , Tamura Masanori 
Published: April 2003

AbstractWith use of the support prepared by the reaction1 of a Grignard reagent with reaction mixture of AlCl3 and CH3Si(OC2H5)3, an immobilized active stereospecific titanium catalyst was prepared by the three‐step treatment of the support, first with TiCl4, second with ethylbenzoate, and third with TiCl4 again. The catalyst was also prepared by the two‐step treatment of the support, with the mixture of TiCl4 and ethylbenzoate, and with TiCl4. Solids obtained in each step of the catalyst preparation were characterized by elemental and IR analysis, and their activities for propylene polymerization were determined with triethylaluminum as a cocatalyst under an atmospheric propylene pressure for 1 h at 60°C. The experimental data support the idea that both TiCl4 and ethylbenzoate as donors are immobilized on the surface of the active stereospecific catalyst without any interaction between them.
Copolymerization of trioxane with phenylglycidylether
Authors: Mateva R. , Sirashki G. 
Published: April 2003

AbstractThis study deals with the regularities and peculiarities of the copolymerization of trioxane (TO) and phenylglycidylether (PhGE) in nitrobenzene catalyzed by the cationic initiator BF3Et2O. The additions of PhGE were varied in wide bounds from 5 up to 50 mol %. No data were found about the course of copolymerization process, as well as about the influence of the polymerization conditions on the rate of exhaustion of the monomers and the composition of the copolymer. The effect of the polymerization conditions on the rate of exhaustion of comonomers was established. The kinetics of the process has been followed; the following equation is proposed:

The activation energy was determined to be Eα = 15.3 kcal/mol. The course of copolymerization of TO/PhGE was compared with those of TO/DO, TO/EO, TO/St, and TO/ECH. The variation of comonomer concentrations was measured by gas chromatographic methods. The copolymers were characterized by elemental analysis, IR‐, and NMR‐spectroscopy, as well as by their molecular weights (Mv).
Molecular structure and photoreaction of poly(methylpropylsilane)
Authors: Ban Hiroshi , Sukegawa Ken 
Published: April 2003

AbstractThe molecular structure and photoreaction of poly(methylpropylsilane) (PMPrS) are investigated. The 29Si‐NMR spectra reveal that PMPrS is a linear polymer with no blanches. Fine multiple splitting of 29Si‐NMR is observed at room temperature. This multiple splitting is thought to be due to molecular conformation. The photo‐oxidation reaction of the PMPrS film is found to be caused by light irradiation at the UV absorption band, 330 nm. Quantum efficiencies of scission and crosslink related to photodegradation are evaluated. There is little difference in either the molecular structure or photoreactivities between the high and the low molecular weight portions of the bimodal molecular weight distributions of PMPrS.
Organotin polymers.I. Copolymerization on tributyltin methacrylate with (hydroxy) alkyl methacrylates
Authors: Dharia J. R. , Pathak C. P. , Babu G. N. , Gupta S. K. 
Published: April 2003

AbstractCopolymers of tributyltin methacrylate (M1) with cyclohexyl methacrylate, ethoxyethyl methacrylate, ethyl methacrylate, 2‐hydroxyethyl methacrylate, and 2‐hydroxypropyl methacrylate were synthesized in solution at 55°C utilizing azobisisobutyronitrile initiator. Copolymer compositions were determined by tin analysis; monomer reactivity ratios were calculated by Kelen‐Tüdös method. Since the reactivity ratios indicate the distribution of different monomer units in the polymer chain, the measured values are compared and discussed. Preliminary results of the biotoxicity studies on some of the copolymers are also reported.
Copolymerization of trifluoropropene with itaconic acid and ethylvinylether by using gamma rays
Authors: Otsuhata Kazushige , Jin Cao , Tabata Yoneho 
Published: April 2003

AbstractCopolymerization of trifluoropropene (TFP) with itaconic acid (IA) and ethylvinylether (EVE) have been carried out by using gamma rays from a 60Co source. Copolymers of TFP‐IA and TFP‐EVE were white powder and white grease, respectively. The copolymerization rate of TFP‐IA system is proportional to 0.64 power of dose rate and that of TFP‐EVE system is proportional to 1.0 power of dose rate. The apparent activation energy for TFP‐IA system is 4.3 kcal/mol and it is 10 kcal/mol for TFP‐EVE system. The copolymerizations of both TFP‐IA and TFP‐EVE are inhibited remarkably by a radical scavenger, PBQ. The reactivity ratios for those systems were determined roughly to be rTFP = 0.55, rIA = 13 and rTFP = 0.30, rEVE = 0.20.