bluuebunny/crossref_metadata_2025_split huggingface dataset:
Description of oxygen permeability in various high polymers using a graph theoretical approach
Authors: Surgi Marion R. , Polak A. J. , Sundahl R. C. 
Published: April 2003

AbstractGraph theory methods are shown to complement group additivity methods of predicting oxygen permeability in certain types of polymers. Graph theory is a topological approach that assigns a set of indices to a molecule to describe its structure. Since many physical properties of molecules depend upon their structure, graph theory indices can be used to describe important properties of molecules. In this work a set of graph theory indices are used to describe the property of a polymer based on a modified representation of the monomer unit. More specifically, Randic indices are used to describe the log of the oxygen permeability with 3.2% average relative error. Polymers comprising the basis set contain backbones of sp2, sp3, or aromatic carbons, oxygen, or silicon and have substituents that contain chloride, fluoride, alkyl groups, hydrogen, oxygen, aromatic carbons, or chloro and/or fluoro substituted alkyl groups. The correlation coefficient (R2) (0 ≤ R2 ≤ 1) of a nonlinear model is 0.91. The graph theory method for describing the oxygen permeability of these selected groups of polymers is in good agreement with that predicted by the permachor model. The permachor method makes oxygen permeability predictions based upon group additivity and distinguishes the degree of crystallinity of a polymer by empirically assigning different permachor (π) values to identical groups based upon the polymer crystallinity. The inability of graph theory to explain the remaining 9% of the scatter in the data is probably due to failure to incorporate into the graph theory model terms which quantify crystallinity.
Kinetics of polyesterification: Adipic acid with ethylene glycol, 1,4‐butanediol, and 1,6‐hexanediol
Authors: Kuo Chin‐Tsou , Chen Show‐An 
Published: April 2003

AbstractPolyesterifications of adipic acid with ethylene glycol, 1,4‐butanediol, and 1,6‐hexanediol in the absence and presence of the foreign acid (p‐toluene sulfonic acid) as catalyst were carried out under constant reaction temperatures of 140–180°C (rather than at constant oil‐bath temperatures) and at ratios of diol to diacid of 0.9867–3.5880. The experimental data fit the rate equations proposed by Chen and Wu: d(RCOOR′)/dt = kaeαp(RCOOH)2(R′OH) – kh(H2O)(RCOOR′) and d(RCOOR′)/dt = kac(AH)eαp(RCOOH)(RO′H) – kh(H2O)(RCOOR′) for self‐catalyzed and acid‐catalyzed reactions, respectively; the data did not fit the other equations appearing in the literature. Here p is the conversion of acid, and α is the constant related to dielectric constants. The reaction rate constants and activation energies for self‐catalyzed and acid‐catalyzed reactions are calculated. The activation energy is found to decrease with chain length of the alkyl group of the diol. This result is consistent with that observed by Brauman and Blair using ion cyclotron resonance spectroscopy for the variation of acidity of alcohols with chain length of the alkyl group.
Synthesis and properties of high strength high modulus ABA block copolymers
Authors: Tsai Tsu T. , Arnold Fred E. , Hwang Wen F. 
Published: April 2003

AbstractA series of novel ABA block copolymers were synthesized containing a rigid‐rod (B) block for reinforcement and a flexible coil (A) block as the matrix. Poly[(benzo[1, 2d: 4, 5d′]bisthiazole‐2,6‐diyl)‐1,4‐phenylene] (PBT) was the rigid‐rod (B) block utilized in this study and was polymerized in such a way as to provide carboxylic acid end‐groups. The carboxy‐terminated PBT was copolymerized with the AB monomers, 3,4‐diaminobenzoic acid and 4‐amino‐3‐mercaptobenzoic acid, which generates a benzimidazole or benzthiazole (A) block, as well as grafts the blocks together. Composition of the blocks could be varied by the weight of AB monomer used in the copolymerizations. Solution behavior of the copolymers in methanesulfonic acid was determined, and fibers were obtained by wet spinning techniques. The block copolymers exhibited typical tenacities of 200 ksi, 16 Msi modulus, and an elongation to break of 1.4%. Critical concentration values for fabrication increased approximately 3% over mechanical mixtures of the same heterocyclic components.
Organosilane polymers: Formable polymers containing methylsilylene units
Authors: Qiu Huayu , Du Zuodong 
Published: April 2003

AbstractOrganosilane polymers containing methylsilylene units were prepared by sodium condensation of MeHSiCl2alone or with R1R2SiCl2(R1and R2= alkyl, aryl, or aralkyl) in a blend of toluene and dioxane followed by fast filtration under N2. These polymers are readily soluble in common solvents and can be drawn into fibers or formed into films by molding, casting, or potting. They can be crosslinked by oxidation, irradiation, or hydrosilylation of vinylsilane in the presence of platinum complexes. The effect of the quantity of MeHSiCl2on molecular weights of copolymers was also discussed.
Organosilane polymers: Formable polymers containing reactive side groups
Authors: Qiu Huayu , Du Zuodong 
Published: April 2003

AbstractFormable organosilane polymers containing various reactive side groups were synthesized by hydrosilylation of unsaturated compounds containing reactive groups with poly(methylsilane) in the presence of platinum complexes. These polymers have appreciable solubility in common solvents, can be molded or cast into films or drawn into fibers, and are photoactive.
Functionalization of crosslinked poly(4‐vinylpyridine) and poly(4‐vinylpyridine‐co‐styrene) with permanganate species: Preparation of poly(4‐vinylpyridinium permanganate)s and their use as oxidizing reagents
Authors: John K. J. , Pillai V. N. Rajasekharan 
Published: April 2003

AbstractCrosslinked poly(4‐vinylpyridine) and poly(4‐vinylpyridine‐co‐styrene) were functionalized with permanganate group to afford the corresponding poly[4‐vinyl(pyridinium permanganate)] resin. These resins were found to selectively oxidize alcohols to corresponding carbonyl compounds. These insoluble functionalized polymers possess the desired characteristics of the polymeric reagents, including operational simplicity, filterability, and regenerability. The influence of solvent, duration of reaction, and molar excess of the reagent in these oxidation reactions was investigated to find out the optimum conditions for effective oxidation reactions. The reactions were found to be more facilitated in nonpolar solvents, and a large excess of the polymeric reagent did not have any significant effect on the extent of reactions. The poly[4‐vinyl(pyridinium permanganate)] resin bears a contrast to KMnO4 and other polymer‐supported oxidizing agents like poly[4‐vinyl(pyridinium chlorochromate)] in that it does not bring about the oxidation of the alcohol group directly attached to the ring structure.
Alternating copolymerization of 2,4‐dicyanobut‐1‐ene and isoprene: Structural analysis
Authors: Cowie J. M. G. , Cree S. H. 
Published: April 2003

AbstractThe two monomers 2,4‐dicyanobut‐1‐ene and isoprene undergo spontaneous copolymerization when mixed together. A more controlled set of solution copolymerizations have been carried out in toluene to low conversions (< 4%), and analysis of the data gave monomer reactivity ratios ofr1, (DCB) = 0.016 andr2(IP) = 0.109. Alternating copolymers are formed over a wide feed range, and the copolymer structure has been analyzed using1H,13C‐NMR and IR spectroscopy. This shows that the isoprene units are predominantly in thetrans‐1,4 conformation and are attached to the DCB through the 1 position when adding onto the chain. The presence of a 1:1 donor–acceptor complex has been identified in CCl4, solutions of the monomers with an equilibrium quotient ofK= 0.055 dm3mol−1at 333 K. The frontier orbital approach has been used in an attempt to elucidate the most likely structure of the D‐A complex.
Polyethylene and elastomeric polypropylene using alumina‐supported bis(arene) titanium, zirconium, and hafnium catalysts
Authors: Tullock Charles W. , Tebbe Frederick N. , Mulhaupt Rolf , Ovenall Derick W. , Setterquist Robert A. , Ittel Steven D. 
Published: April 2003

AbstractBis(arene) complexes of zerovalent titanium, zirconium, and hafnium supported on partially dehydroxylated, fumed alumina are effective catalysts for the polymerization of olefins. The zerovalent complexes react with surface hydroxyls with loss of one equivalent of arene to yield the active species. The polyethylenes derived from these catalysts are very high molecular weight. Polymerization of propylene yields elastomeric stereoblock polymers which are composed of isotactic and stereoirregular sequences. The polymers are stiffer than polypropylenes obtained with similar catalysts derived from tetra(neophyl)zirconium. The chain microstructures of the various components of the whole polymers have been characterized by 13C‐NMR and solvent extraction studies. The ether soluble component of these polymers is of a relatively high molecular weight and the microstructure of the backbone is largely stereoirregular. It is the cocrystallization of this fraction of the polymer with the crystalline, isotactic fractions which is critical to the observed elastomeric properties.
Poly(3‐hydroxyoxetane)—an analog of poly(vinyl alcohol): Synthesis, characterization, and properties
Authors: Vandenberg E. J. , Mullis J. C. , Juvet R. S. , Miller T. , Nieman R. A. 
Published: April 2003

AbstractThe spontaneous polymer formed from 3‐hydroxyoxetane (HO), as first reported by Wojtowicz and Polak, is linear, low molecular weight, water‐soluble, atactic, poly(3‐hydroxyoxetane) (PHO) of high crystallinity with OCH2CH(OH)CH2OH end units. The highly crystalline nature of this atactic polymer may be related to the crystalline nature of atactic poly(vinyl alcohol) since PHO can be considered a copolymer of vinyl alcohol and formaldehyde. Spontaneous PHO apparently is formed in a cationic polymerization by the carboxylic acids produced by the air oxidation of HO on standing at room temperature for several months. The polymerization can be duplicated by the addition of 2% hydroxyacetic acid to HO. The rate of this unusual cationic polymerization increases greatly with acid strength, e.g., trifluoromethanesulfonic acid reacts explosively with pure HO. A mechanism is proposed for this cationic polymerization. High molecular weight, water‐soluble, linear atactic, and highly crystalline PHO (mp = 155°C) was made by polymerizing the trimethylsilyl ether of HO with the i‐Bu3Al–0.7 H2O cationic catalyst followed by hydrolysis. Two 1H‐NMR methods for measuring the tacticity of PHO were developed based on finding two different types of methylene units at 400 MHz with the methine protons decoupled. Also, an 1H‐NMR method was developed for measuring branching in HO polymers. High molecular weight, linear PHO with enhanced isotacticity (80%) has been obtained in low yield as a water‐insoluble fraction with Tm = 223°C. The low molecular weight PHO prepared previously by the base‐catalyzed, rearrangement polymerization of glycidol is highly branched.
Thermal stability of poly(methyl methacrylate) as polymerized in aqueous media by using redox systems as initiators
Authors: Fernández M. D. , Fernández M. J. , Guzmán G. M. 
Published: April 2003

AbstractThe thermal degradation of poly(methyl methacrylate) as polymerized in aqueous nitric acid solution using Ce(IV) alone and in combination with isobutyl alcohol, isopropyl alcohol, glucose, maltose, and cellobiose as initiator systems has been investigated using differential thermal analysis (DTA) and thermogravimetry (TGA) in dynamic nitrogen. The kinetic parameters E, n, and A have been obtained following several methods of thermogravimetric analysis. The most stable material was found to be the PMMA sample obtained with Ce(IV), and the Ce(IV)–IBA and Ce(IV)–maltose polymerized samples were the least stable. In the pyrolysis of Ce(IV)–IBA and Ce(IV)–maltose polymerized samples it was found that two reactions occurred, while in the case of the PMMA polymerized with Ce(IV), Ce(IV)–IPA, Ce(IV)–glucose, and Ce(IV)–cellobiose three reactions took place.
Thermal stability of copolymers of vinyl acetate and methyl acrylate
Authors: Fernández M. J. , Fernández M. D. , Casinos I. , Guzmán G. M. 
Published: April 2003

AbstractThe thermal degradation of a series of copolymers of vinyl acetate and methyl acrylate and the two homopolymers poly(vinyl acetate) and poly(methyl acrylate) obtained using Ce(IV) as initiator has been investigated using differential thermal analysis (DTA) and thermogravimetry (TGA) in dynamic nitrogen. The kinetic parameters E, n, and A have been obtained following several methods of thermogravimetric analyses. The stability increases as the methyl acrylate content in the copolymer composition increases. The incorporation of 5 mol % of vinyl acetate in the copolymer produces a marked decrease in stability compared to the homopolymer poly(methyl acrylate). There is evidence for an intramolecular lactonization process in vinyl acetate—methyl acrylate copolymers.
Preparation of highly sulfonated polystyrene model colloids
Authors: Kim J. H. , Chainey M. , El‐Aasser M. S. , Vanderhoff J. W. 
Published: April 2003

AbstractPrevious attempts to prepare monodisperse styrene/sodium styrene sulfonate copolymer latexes by batch, seeded, and semicontinuous emulsion polymerization were unsuccessful at high concentrations of the functional comonomer. Broad, and sometimes bimodal, size distributions, and large amounts of water soluble homopolymer were obtained. After removal of free monomer, solute and adsorbed homopolymer and copolymer, the overall incorporation of the functional comonomer was found to be low. To overcome these problems, a two stage “shot‐growth” or in situ seeding technique was developed. A first stage copolymerization was carried out with a low concentration of sodium styrene sulfonate: the purpose of the functional comonomer was to enhance the stability and regulate the size of the seed particles. When this reaction had reached high conversion (> 90%), a second stage monomer mixture was added. The ratio of styrene to sodium styrene sulfonate in this mixture determined the final surface charge density. The mechanism by which the NaSS is incorporated in the polymer particles is considered to be by solution copolymerization with solute styrene monomer to form surface active oligoradicals. These radicals adsorb on the particle surface, initiate polymerization and become inextricably bound, preventing their transfer back to the aqueous phase. By this means, it was possible to vary independently the particle size and surface charge density. High concentrations of functional comonomer could be polymerized without undue wastage (incorporations were only slightly less than 100%) or loss of monodispersity. In extreme cases, the area per functional group fell below the theoretical minimum, indicating considerable hydration of the surface layers.
Synthesis and characterization of 9‐anthrylmethyl propiolate polymers
Authors: Simionescu Cristofor I. , Grigoras Mircea 
Published: April 2003

AbstractThe polymerization of 9‐anthrylmethyl propiolate using various initiating methods was studied with particular emphasis on the elucidation of the structure of the polymers. A polymer having a pure polyene structure was synthesized by anionic or anionic‐coordination mechanism only. Thermal or transition metal halides polymerization led to a polymer possessing anthrylene methylene groups into the main polymer chain. A plausible mechanism for the obtention of this structure was proposed.
Copolymerization of α‐methylstyrene and N‐phenylmaleimide
Authors: Fleš D. D. , Vuković R. , Ranogajec F. 
Published: April 2003

AbstractIn the copolymerization of α‐methylstyrene (α‐MeSt) and N‐phenylmaleimide (NPMI), the resulting copolymers were found to have a high alternating structure regardless of the ratio of comonomers in the feed. The monomer reactivity ratios were r1 = 0.21 (NPMI) and r2 = 0.03 (α‐MeSt) (Kelen–Tüdös method), the equilibrium constant of CT complex K was 0.02 L mol−1, and the energy of activation EA was 73 kJ mol−1. From the equation Rp = Rp(f) + Rp(CT) proposed by Shirota and coworkers, Rp(f) and Rp(CT) were calculated, and it was found that in toluene the copolymerization proceeds predominantly by the addition of free monomers. Copolymers prepared at an equimolar ratio of comonomers in the feed have a glass transition temperature Tg of 539 K (DSC method).
Synthesis of diblock copolymers containing both polydiene and polyalcohol blocks
Authors: Chung T. C. 
Published: April 2003

AbstractA wide range of functional diblock copolymers containing both functional polymer and hydrocarbon polymer, have been prepared by the combination of anionic polymerization and borane chemistry. The distinctive hydroboration reactivity between various polydienes enables us to selectively functionalize one polydiene segment in diblock copolymers which contain two different polydiene segments. In turn, the hydroborated polymers are valuable intermediate compounds which can be converted to a whole family of functional polymers with a variety of other functionalities under mild reaction conditions. The hydroxylated diblock copolymer is used as an example to demonstrate the chemistry. The two‐phase nature of these copolymers is also shown by the observation of two distinctive glass transition temperatures associated with the individual polymer segments.
Biocatalytic synthesis of polymers. II. Preparation of [AA–BB]x polyesters by porcine pancreatic lipase catalyzed transesterification in anhydrous, low polarity organic solvents
Authors: Wallace J. Shield , Morrow Cary J. 
Published: April 2003

AbstractEnzyme‐catalyzed preparation of polymers offers several potentially valuable advantages over the usual polymerization procedures. (1) Such polymerizations may allow the polymer to retain functionality that would be destroyed under normal polymerization conditions. (2) The selectivity provided by enzyme catalysts may permit polymers, including optically active polymers, to be prepared that are either not accessible or accessible only with difficulty by other methods. (3) The characteristics of the enzyme and the mild polymerization conditions may permit formation of polymers having highly regular sizes and backbone structures. This report describes the first successful use of an enzyme‐catalyzed polycondensation to prepare a chiral (AA–BB)x polyesters of more than a few repeat units. Polymerization of bis(2,2,2‐trichloroethyl) alkanedioates (BB) with diols (AA) using the enzyme porcine pancreatic lipase (PPL) as a catalyst is detailed. The polycondensations were carried out at ambient temperature in anhydrous, low polarity organic solvents such as ether, THF, and methylene chloride. End group analysis by NMR provided Mn values of 1300–8200 daltons while GPC provided Mw values of 2800–14900 daltons for the polymers. Based on proton NMR spectra obtained during the polymerization, relatively rapid formation of an AA–BB “dimer” and an AA–BB–AA “trimer,” slower formation of a BB–AA–BB “trimer,” and subsequent condensation of these to give higher polymers are suggested to be components of the polymerization mechanism.
Polymerization and characterization of nitrile‐terminated diacetylene materials
Authors: Grasso Robert P. , Lando Jerome B. 
Published: April 2003

AbstractA family of nitrile‐terminated diacetylene materials were synthesized. Samples were prepared in various forms and polymerization was performed photochemically and thermally. The resulting materials exhibited low molecular weights and were obtained in low yields. Although the diacetylene group had oligomerized, no evidence was found in support of CN chain formation. Thermochromism was exhibited by the irradiated 8‐nitrile sample and a molecular interpretation of this chromic transition was discussed. Diffraction data implied that strong intermolecular interactions were present between adjacent nitrile groups in the low temperature phase. It is suggested that stresses are built up during polymerization which cause the low degree of polymerization and yield.
Polymeric formamides as liquid–liquid phase transfer catalysts
Authors: Kondo Shuji , Inagaki Yasuhito , Ozeki Masashi , Tsuda Kazuichi 
Published: April 2003

AbstractPolymeric formamides were prepared by free radical polymerization of N‐methyl‐N‐vinyl‐formamide or N‐methyl‐N‐(4‐vinylbenzyl)formamide, and copolymerization of these monomers with styrene. These soluble polymers serve as phase transfer catalysts for several reactions under liquid–liquid biphase conditions. The catalytic activity of copolymers containing styrene unit is affected remarkably by composition, and there are maxima at certain composition in both polymers. However, copolymers with an acrylonitrile co‐unit scarcely exhibit catalytic activity. Furthermore, it was found that these polymers can extract all alkali metal ions employed here, and that the extraction ability increases with increasing the density of active sites. From these results, it is demonstrated that catalytic activity strongly depends on both cation extraction ability of polymers and lipophilicity around the active sites in the polymer.
Surface modification of polymers. IV. UV initiated degradation of polymers with stabilizers grafted onto the surface
Authors: Allmér K. , Hult A. , Rånby B. 
Published: April 2003

AbstractPolypropylene (PP), Polyethylene (PE), and polystyrene (PS) films were grafted with glycidylmethacrylate in thin surface layers. To the oxiran groups thus grafted onto the surface three UV stabilizers were attached, 4‐amino‐2,2,6,6‐tetramethylpiperidine (AP), 2,4‐dihydroxybenzophenone (DHBP), and phenyl 4‐aminosalicylate (PAS). The amount of stabilizer grafted onto the surface varied between 25 and 40 nmol/cm2 depending on the polymer substrate. The samples were exposed to UV radiation in air, and the degradation and oxidation of the polymers were studied with IR, UV, and ESCA spectroscopy and by stress–strain measurements. PP grafted with AP exhibited a near 20‐fold increase in lifetime compared with the unprotected PP, AP did not stabilize the PE or PS samples. DHBP was an efficient stabilizer of PE, the oxidation rate of the grafted sample being 1/2 to 1/3 of the ungrafted. A similar effect was observed when DHBP was grafted onto PP and PS. PAS underwent a rearrangement reaction when irradiated with UV light, and had only a slight stabilizing effect.
A 1H magnetic resonance imaging study of porosity in polyurethane foams
Authors: Perry B. C. , Koenig J. L. 
Published: April 2003

Abstract1H magnetic resonance imaging (MRI) is used to study the distribution of water in polyurethane foams. Flexible open‐celled foams are easily distinguished from the closed‐cell foams as the latter does not absorb any detectable amounts of water. Flexible foams degassed in vacuo revealed no structural detail due to the resolution limitation of approximately 100 μm. Incompletely degassed foams revealed considerable areas of trapped gas which were recorded as a function of distance beneath the water. Samples injected with water indicated that a tortuous flow pathway is taken due to the presence of cell windows. Samples with lower porosity had a higher resistance to flow.