bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymerization and reaction rate studies on substituted phenylmethylbis(dimethylamino)silanes
Authors: McManus Samuel P. , Patterson William J. , Pittman Charles U. 
Published: April 2003

AbstractThe synthesis of seven para‐ or meta‐substituted phenylmethylbis(dimethylamino)‐silane monomers has been carried out. These silanes were polymerized with 1,4‐bis(hydroxydimethylsilyl)benzene in tetrahydrofuran at 30°C, and the polymerization kinetics were followed by monitoring dimethylamine evolution for 200 min. The polymers were quenched by precipitation in methanol and molecular weight data were obtained. The polymerizations followed second‐order kinetics in every case as evidenced by the linear plots of 1/(a − x) versus time. The molecular weight data generally correlated with the specific reaction rate constant k2 to show an increasing polymer molecular weight with increasing polymerization rate, although the range of k2 values obtained for the substituted aminosilanes was relatively small (2.50 × 10−5–6.67 × 10−5 l./mole‐sec). The value of k2 increased in the following order: p‐OCH3, p‐F, m‐CH3, H, m‐OCH3, p‐CF3, 3,5‐di(CF3). The logarithms of the rate constants correlated with the σ constants for the substituents, with a reaction constant, ρ of 0.391. The displacement at silicon in these reactions is discussed in terms of bimolecular mechanisms in which a four‐center transition state may participate.
Influence of copolymeric poly(diethylene glycol) terephthalate on the thermal stability of poly(ethylene terephthalate)
Authors: Hergenrother W. L. 
Published: April 2003

AbstractCopolymers of poly(ethylene terephthalate) (PET) containing 1–24% poly(diethylene glycol)terephthalate (PDEGT) were prepared and characterized by infrared spectra. The energy and entropy of activation for the thermal degradation were measured for these copolymers and for the PDEGT. These activation energies and energies and entropies were found to decrease steadily with increasing diethylene glycol content. From these measurements the mechanism of degradation of PDEGT was found to be different from that of PET. Fibers prepared from seven different copolymeric compositions were heat‐aged at 121°C and 204°C for 24 hr. From the changes observed in intrinsic viscosity, per cent ether, hydroxyl and carboxyl endgroups during heat aging it became apparent that the mechanisms for decomposition are operative below melt temperatures and can rapidly destroy such copolymers.
Polyurethane–polyacrylate interpenetrating polymer networks. I
Authors: Frisch K. C. , Klempner D. , Migdal S. , Frisch H. L. 
Published: April 2003

AbstractTwo‐component topologically interpenetrating polymer networks (IPN) of the SIN type (simultaneous interpenetrating networks) composed of a melamine‐cured polyacrylate and five different polyether‐based polyurethanes were made. The linear polymers and prepolymers were combined in solution, together with the necessary crosslinking agents and catalysts; films were cast, chain‐extended, and crosslinked in situ. Infrared spectroscopy indicated that little or no reaction between the different networks occurred. In all cases, except for one IPN which was made from a very highly crosslinked polyurethane, maxima in tensile strength, significantly higher than the tensile strengths of the components, occurred. This was explained by an increase in crosslink density resulting from interpenetration. Some enhancement in other physical properties (impact strength and thermal resistance) was also noted.
Molecular chain conformation and crystallite structure of cellulose. I. Fine structure of rayon fibers
Authors: Watanabe Sadayoshi , Hayashi Jisuke , Akahori Tadayoshi 
Published: April 2003

AbstractA most reasonable folded‐chain model for the fine structure of rayons (cellulose II) has been developed through experimental work on a theoretical basis. All the materials uniformly gave a levelling‐off DP of about 40, equivalent to a length around 200 Å, for cellulose molecule segments at the early stage of heterogeneous acid hydrolysis when the first minor fraction is scarcely dissolved. Measurements by small‐angle and wide‐angle x‐ray scattering put the crystallite length from various rayon fibers at about 200 Å, without exception. A family of GPC chromatograms, furthermore, on the hydrolyzed cellulose exhibited a single peak considered to represent monodispersed materials. These data suggest that clearly divided sections exist within the microfibril along its axis in a regular manner at an interval of about 200 Å. This cannot be explained in terms of the fringed micelle model. On the other hand, the possibility that cellulose II may have a folded‐chain conformation has been demonstrated. A single cellulose molecule is essentially folded back and forth in the (101) plane to form a sheetlike structure. Such a structure is the basic unit that can fit perfectly into the unit cell of cellulose II. The cellulose molecule can achieve a fairly sharp U‐turn in the (101) plane, with only one glucose unit of in the half‐boat conformation. A crystallite consists of a number of sheets held together by secondary forces in the (101) plane. Accordingly, crystallographically, the crystallites are closely packed at the surface of each fold at its longitudinal edges to make up the cellulose microfibril. According to our model, the oxygen atom of the glucosidic link in the fold, where acid hydrolysis would have to take place, protrudes partially from the surface of the crystallite; a pair of atoms at the folds are then facing each other and are therefore, accessible for hydrolysis. This would explain chain scission of cellulose II at these sites in hydrolysis. This folded‐chain model is supported further by other experimental evidence.
Gel‐permeation chromatography: X. Molecular weight detection by low‐angle laser light scattering
Authors: Ouano A. C. , Kaye Wilbur 
Published: April 2003

AbstractEffluent from a gel‐permeation chromatographic column has been simultaneously and continuously monitored with a differential refractometer and a low‐angle laser light‐scattering (LALLS) photometer. This provides a true and direct determination of molecular weight distribution rather than through a calibration method as obtained by conventional GPC techniques. Computer assisted data reduction provides a rapid determination of M̄w, M̄n, M̄z, M̄w/M̄n, as well as a plot of molecular weight distribution. Samples of very narrow molecular weight distribution (MWD) polystyrene from Pressure Chemicals Co. and relatively wide MWD samples of poly(methyl methacrylate) in chloroform have been characterized.
Identification of the principal high molecular weight fragments in the thermal degradation of poly(methyl acrylate)
Authors: Haken J. K. , Ho D. K. M. , Houghton E. 
Published: April 2003

AbstractThe pyrolysis of poly(methyl acrylate) has been studied with identification of the major pyrolysis products. The degradation mechanism of Cameron and Kane involving random homolytic scission of the polymer chain followed by a series of intermolecular and intramolecular transfer reactions is extended and confirmed, and it is apparent that a series of saturated and unsaturated oligomers of methyl acrylate are produced.
Kinetics and mechanism of stereospecific polymerization of methyl methacrylate with VOCl3–AlEt2Cl catalyst system
Authors: Gandhi V. G. , Deshpande A. B. , Kapur S. L. 
Published: April 2003

AbstractMethyl methacrylate was polymerized at 40°C with VOCl3–AlEt2Cl catalyst system in n‐hexane. The rate of polymerization was proportional to catalyst and monomer concentration at Al/V ratio of 2 and overall activation energy of 9.25 kcal/mole support a coordinate anionic mechanism of polymerization. The catalytic activity and stereospecificity of this catalyst system is discussed in comparison with that of VOCl3–AlEt3 catalyst system.
Ethylene–propylene terpolymers based on methylcyclopentadienyl‐5‐norborn‐2‐enylmethane derivatives
Authors: Cesca S. , Duranti P. V. , Roggero A. , Santi G. , Bruzzone M. 
Published: April 2003

AbstractThe terpolymerization of ethylene, propylene, and methylcyclopentadienyl‐5‐endonorborn‐2‐enylmethane (III) by means of different vanadium‐based coordination catalysts was investigated. The structure of III and its isomeric composition was studied by using vapor‐phase chromatography, mass spectrometry, and NMR, infrared, and ultraviolet spectroscopy. The catalyst system V Acac3–Et2AlCl was used under different conditions, and the influence of several variables regulating the terpolymerization process were related to the properties of the resulting terpolymers (EPTM). The insertion of III into EPTM chains takes place randomly and does not influence the random distribution of comonomers. The selective opening of the norbornene double bond of III has been demonstrated by use of 2,3‐dihydro‐III as model compound. Tritiated III gave a radiochemical titer of unsaturation in excellent agreement with the value deduced from ultraviolet measurements. The influence of Lewis bases added to VAcac3–Et2AlCl catalyst is discussed.
Phosphorescence from nylon polymers: Effects of thermal and photochemical oxidation
Authors: Allen N. S. , McKellar J. F. , Phillips G. O. 
Published: April 2003

AbstractThe phosphorescence from the nylon polymers 6, 66, 11, and 12 has been studied from the aspects of excitation and emission wavelength location and of emission lifetime. In contrast to the other nylons, the 66 polymer exhibits two distinct phosphorescence bands, both of which are sensitive to thermal and photochemical oxidation of the polymer. The species responsible for these emissions are concluded to be carbonyl in nature and their role in the complex reactions that occur during thermal and photochemical oxidation of the polymer is discussed.
Effect of primary radical termination on chain length and initiator efficiency
Authors: Ito Katsukiyo 
Published: April 2003

AbstractIn polymerization with primary radical termination, when reaction between primary radicals, which escape from solvent cage, is not negligible, a relation between chain length and polymerization rate is found regardless of tractable approximate procedures. Such a relation is applied to the kinetic data obtained in the polymerizations of methyl methacrylate (MMA) and vinyl acetate (VA) initiated by 2,2′‐azobis(2,4‐valeronitrile) at 50.0°C. Further, when the primary radical termination is high, an initiator efficiency can not be approximated to a ratio of the primary radicals escaping from the cage to the total primary radicals formed in the cage. In the polymerization of MMA, after the primary radicals escapes from the cage, they immediately react with the monomer. Thus, the reaction between the primary radicals is not significant. However, in the polymerization of VA, the rate of reaction between the primary radical and the monomer might be comparable to the rate of reaction between the primary radicals when the initiator concentration is quite high.
Effects of mercaptides on anionic polymerization. III. Polymerization of methyl methacrylate by thiophenoxides in polar aprotic solvents
Authors: Hirahara Takuji , Minoura Yuji 
Published: April 2003

AbstractSodium thiophenoxide initiated the polymerization of methyl methacrylate in polar aprotic solvents (DMF, DMSO, HMPA). The active species that initiated the polymerization of the monomer was found by spectrophotometric measurements and by the sodium fusion method to be sodium thiophenoxide itself. The activation energy for the polymerization of the monomer in DMF solvent obtained was E = 3.4 kcal/mole below 30°C, and E = −3.3 kcal/mole above the temperature. The phenomena were reasoned as the result of the formation of two active species: a solvent‐separated ion pair and a contact ion pair. The effects of counterions on the reactivity of thiophenoxide increased with increasing electropositivity of the metals: Li < Na < K. Sodium phenoxide, the oxygen analog of thiophenoxide, was also found to initiate the polymerization of the monomer in the solvents. The relative reactivity of thiophenoxide to phenoxide for the monomer in HMPA at 30°C was thus determined: phenyl‐SNa > phenyl‐ONa. The relative effect of the polar aprotic solvents on the reactivity of thiophenoxide was also as follows: HMPA > DMF > DMSO. The kinetic studies were made by the graphical evaluation of rate constants. The following results were obtained for the monomer at 20°C in DMF solvent: Kp = 3.5 × 102 1./mole‐hr and Kt = 9.8 × 10−2/hr.
Thermal decomposition of poly(tert‐butyl N‐vinylcarbamate)
Authors: Schulz Gerald O. , Harwood H. James 
Published: April 2003

AbstractPyrolysis of poly(tert‐butyl N‐vinylcarbamate) at 185–200°C in bulk yields a rigid foam containing cyclic urea units, primary amine units, and a small amount of urea crosslinks. The yield of primary amine units (ca. 13%) and the yields of carbon dioxide (ca. 57%), isobutylene (ca. 57%), and tert‐butanol formed in this reaction indicate that it involves pairwise decomposition of adjacent carbamate units to form cyclic urea units, tert‐butanol, carbon dioxide, and isobutylene. The vinyl amine units are formed from carbamate units that become flanked by urea units. The amounts of amine units and residual carbamate units were determined as a function of degree of pyrolysis by an ion‐exchange technique and agreed with values expected for a random cyclization process. The pyrolyzed polymers are useful as ion‐exchange resins and as rigid foams having good thermal stability.
Chromocene‐based catalysts for ethylene polymerization: Thermal removal of the cyclopentadienyl ligand
Authors: Karol Frederick J. , Wu Chisung 
Published: April 2003

AbstractThermal aging of a chromocene catalyst, (C5H5)2Cr/SiO2, in an inert atmosphere leads to a modified catalyst which shows poor response to hydrogen as a transfer agent. Polyethylenes prepared at a polymerization temperature of 90°C with this modified catalyst have a low melt index and high vinyl unsaturation level. By thermogravimetry the weight loss of the catalyst, relative to dehydrated silica, was equivalent to loss of one cyclopentadienyl ligand per chromium site. Pyrolytic gas chromatography showed cyclopentadiene was liberated in the thermal process. These overall studies provide strong evidence that loss of a cyclopentadienyl ligand in supported chromium catalysts has a profound effect on overall polymerization behavior.
A novel scheme of heterogeneous polymerization of ethylene
Authors: Watanabe Terutaka , Wada Takeshi , Takehisa Masaaki , Machi Sueo 
Published: April 2003

AbstractThe heterogeneous polymerization of ethylene initiated by radiation in tert‐butyl alcohol was studied. The polymerization was carried out in a 100‐ml reactor at 25–100°C and pressures of 200–300 kg/cm2 in the presence of 50 ml of tert‐butyl alcohol containing 7 wt‐% water. The amounts of polymerized monomer, the average molecular weight of polymer formed, and the molecular weight distribution of polymer were measured at various stages of reaction and at various temperatures. The molecular weight distribution was found to be very much dependent on the reaction time and temperature. For the polymer formed at 50–60°C in the very early stages of reaction, the molecular weight distribution is unimodal, and in the intermediate stage a shoulder appears at a molecular weight higher than the first peak which increases as the polymerization proceeds; eventually a bimodal curve is formed. The bimodal distribution curves were analyzed to determine the fractions and average molecular weights of the each peak. On the basis of these data for the molecular weight distribution and kinetic behavior, a new scheme for the heterogeneous polymerization is proposed which indicates that the polymerization proceeds via propagating radicals in two different physical states, namely, loose and rigid states.
Polymerization of vinyl chloride by use of modified Ziegler–Natta catalysts. I. Overall kinetic features
Authors: Chesworth A. G. , Haszeldine R. N. , Tait P. J. T. 
Published: April 2003

AbstractVinyl chloride has been polymerized by a modified Ziegler‐Natta type catalyst VOCl2 · 2THF–Al(i‐Bu)3–THF, and the kinetics of the polymerization reaction have been investigated in some detail. The present kinetic analysis has demonstrated that the generation of active centers is directly proportional to the catalyst concentration, and that their depletion is by a second‐order decay process. Triisobutylaluminum has been found to contribute to the effective removal of active centers through complex formation.
Photochemical polymerization of gaseous ethyl acrylate
Authors: Dixon G. Douglass 
Published: April 2003

AbstractExposure of gaseous ethyl acrylate to ultraviolet radiation causes deposition of poly(ethyl acrylate) at a rate depending on a number of parameters, including the wave‐length of the radiation, its intensity, and exposure time. The rate also depends upon the monomer pressure and the presence of contaminants, most notably moisture and oxygen.
Stereoregularity of poly(alkyl α‐chloroacrylates) and mechanism of isotactic polymerization
Authors: Uryu Toshiyuki , Ohaku Ken‐Ichi , Matsuzaki Kei 
Published: April 2003

AbstractThe catalytic activity of the complexes prepared by the reaction of Grignard reagents with ketones, esters, and an epoxide as polymerization catalysts of methyl and ethyl α‐chloroacrylates was investigated. The modifiers which gave isotactic polymers were α,β‐unsaturated ketones such as benzalacetophenone, benzalacetone, dibenzalacetone, mesityl oxide, and methyl vinyl ketone, and α,β‐unsaturated esters such as ethyl cinnamate, ethyl crotonate, and methyl acrylate. Catalysts with butyl ethyl ketone, propiophenone, and propylene oxide as modifiers produced atactic polymers but no isotactic polymers. It was revealed that the complex catalysts having a structure CCOMgX (X is halogen) gave isotactic polymers. The mechanism of isotactic polymerization was discussed. In addition, for radical polymerization of ethyl α‐chloroacrylate, enthalpy and entropy differences between isotactic and syndiotactic additions were calculated to give ΔHi* − ΔHs* = 910 cal/mole and ΔSi* − ΔSs* = 0.82 eu.
Linear polyesters containing isocyanurate rings
Authors: Kauffman W. J. 
Published: April 2003

AbstractTwo series of linear polyesters containing isocyanurate rings have been prepared to determine the effect of structural variations on thermal and solubility properties. The polyesters were prepared by the polycondensation reaction of isocyanurate containing difunctional acid and ester monomers with linear diols. The substituent on the isocyanurate ring and the length of the acid side chain have been shown to have considerable effect on the glass transition temperature Tg. Different solubility properties were observed for the series of polyesters in which the pendant substituent was C6H5 and the acid side‐chain was CH2CO2H. These polymers were insoluble in THF, and the polyester prepared from 1,6‐hexanediol was also insoluble in chloroform. Thermal gravimetric analysis (TGA) indicated that structural differences had no significant effect on the thermal stability of these linear polyesters.
Polymerization of acetylenes catalyzed by arene–group vib tricarbonyls
Authors: Woon Paul S. , Farona Michael F. 
Published: April 2003

AbstractThe polymerization of phenylacetylene and other terminal and internal alkynes has been achieved in homogeneous reactions catalyzed by ArM(CO)3, where Ar is an arene; M is Cr, Mo, or W. The polymerization of phenylacetylene proceeds by way of an intermediate which has been isolated and identified as a ladder compound composed of fused cyclobutane rings. The ladder compound, which is stable in the absence of the catalyst, breaks down in the presence of the catalyst to give the final polyconjugated polymer. Available evidence indicates that the conversion of the ladder compound to polyphenylacetylene proceeds by way of a free‐radical mechanism. A mechanism for the electronic conversion of the ladder compound to the final polymer is proposed, as is a method of chain propagation.
Photosensitized copolymerization of optically active N‐l‐menthylmaleimide with styrene and methyl methacrylate
Authors: Sakota Naokazu , Kishiue Kiyoshi , Shimada Shyozo , Minoura Yuji 
Published: April 2003

AbstractPhotosensitized copolymerization of optically active N‐l‐menthylmaleimide (NMMI) with styrene (Sty) and methyl methacrylate (MMA) was carried out in tetrahydrofuran (THF) at 30°C with benzoyl peroxide (BPO). The monomer reactivity ratios for the copolymerization of NMMI (M2) with Sty (M1) and MMA (M1) were r1 = 0.08 ± 0.10, r2 = 0.20 ± 0.05 and r1 = 2.85 ± 0.06, r2 = 0.07 ± 0.06, respectively. Copoly‐MMA–NMMI and poly‐NMMI showed positive circular dichroism(CD) curves of equal intensity and shape over the wavelength region from 230 to 270 nm; copoly‐Sty–NMMI also showed a positive CD curve which was similar in shape but was different in intensity from that of poly‐NMMI. The correlation between monomer unit ellipticity of the copolymers and their composition would suggest the alternating and stereoregular copolymerization of NMMI with Sty.
Heat‐resistant polymers containing bipyridyl units. III. Polyimides having o‐, m‐, or p‐phenylenedioxy linkage
Authors: Kurita Keisuke , Williams Roy L. 
Published: April 2003

AbstractNew series of diamines having pyridine rings and o‐, m‐, or p‐phenylenedioxy linkages were prepared by condensation of chloronitropyridine with isomeric dihydroxybenzenes followed by chemical reduction. The polymerization of the diamines with benzo‐phenonetetracarboxylic acid dianhydride gave polyamic acids with the inherent viscosities in the range 0.21 to 1.30 dl/g. The conversion of these polyamic acids to polyimides was carried out thermally and the resulting polyimides exhibited very good solubility in organic solvents.
Reaction of poly(vinyl alcohol) with potassium persulfate and graft copolymerization
Authors: Ikada Yoshito , Nishizaki Yasuko , Sakurada Ichiro 
Published: April 2003

AbstractA study of the oxidation of poly(vinyl alcohol) (PVAL) by potassium persulfate (KPS) in aqueous solutions showed that the decomposition of KPS was greatly enhanced by the presence of PVAL, its hydroxyl groups being oxidized to ketones in a yield of about one mole of ketone from one mole of KPS. The decomposition rate of KPS was found to be given by the equation, −d[S2O82−]/dt = k[S2O82−] [PVAL]1/2, which was essentially the same as in the oxidation of alcohols of low molecular weight by persulfate ion. The occurrence of gelation of PVAL solutions and graft copolymerization of methyl methacrylate (MMA) onto PVAL in the presence of KPS was evidence for PVAL radical as an intermediate species in the oxidation of PVAL. A characterization study was also carried out for the reaction products of the graft copolymerization of MMA onto PVAL with KPS in dimethyl sulfoxide solution.
Stationary copolymerization of formaldehyde and 1,3‐dioxolan
Authors: Penchev P. I. , Minin V. A. , Kedrina N. F. , Ivanov V. V. , Enikolopyan N. S. 
Published: April 2003

AbstractA. study on the kinetics of gas‐phase copolymerization of formaldehyde and 1,3‐dioxolan effected by stannic chloride in a flow reactor with ideal mixing is reported. Equations were calculated describing the run of process depending on the composition of the outgoing flow measured with a gas chromatograph. It was established that the reaction takes place under stationary conditions. The change of the degree of conversion of monomers, and composition of the stable portion of the copolymer, and copolymer molecular weight with catalyst concentration was examined. It was shown that a kinetic and diffusion area may be possible. A product of high molecular weight and thermostability was obtained. The molecular size distribution was ascertained to be close to the exponential type. The average number of blocks and units of both monomers was calculated. Different posteffects for the two reacting substances were found.