bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radical alternating copolymerization of vinyl ethers
Authors: Kharas G. B. , Ajbani H. 
Published: April 2003

AbstractNew alternating equimolar copolymers of electrophilic trisubstituted ethylenes, methyl 3‐phenyl‐2‐cyanopropenoate and 2‐phenyl‐1,1‐dicyanoethene, with ethyl, n‐butyl, i‐butyl, t‐butyl, 2‐chloroethyl, and phenyl vinyl ethers were prepared by free radical initiation. Chemical compositions of the copolymers are 1 : 1 in broad ranges of monomer ratios. The copolymerization rate of both electrophilic monomers with the vinyl ethers increase in the series 2‐chloroethyl > ethyl > phenyl > n‐butyl > i‐butyl > t‐butyl. These variations in the reactivity of the vinyl ethers are discussed in terms of their preferred conformations in donor‐acceptor complexes with electrophilic trisubstituted ethylenes. © 1993 John Wiley & Sons, Inc.
Polyesters, polyurethanes and epoxy resins derived from 2,2′‐(1,4‐phenylenedivinylene)bis‐8‐hydroxyquinaldine and 6‐(4‐hydroxystyryl)‐3‐hydroxypyridine
Authors: Diakoumakos Constantinos D. , Mikroyannidis John A. 
Published: April 2003

AbstractNew polyesters and polyurethanes as well as diepoxides bearing styrylpyridine segments were prepared utilizing 2,2′‐(1,4‐phenylenedivinylene)bis‐8‐hydroxyquinaldine (PBHQ) and 6‐(4‐hydroxystyryl)‐3‐hydroxypyridine (HSHP) as starting materials. The polyesters were prepared by reacting PBHQ or HSHP with terephthaloyl dichloride in the presence of an acid acceptor utilizing the solution polycondensation method. The polyurethanes were prepared from the reactions of PBHQ and HSHP with tolylene diisocyanate and methylenebis(4‐phenylisocyanate). In addition, model diesters and diurethanes were synthesized by reacting PBHQ and HSHP with benzoyl chloride and phenyl isocyanate, respectively. Model compounds and polymers were characterized by FT‐IR and 1H‐NMR spectroscopy as well as by DTA and TGA. Diepoxides were also prepared from the reactions of PBHQ and HSHP with epichlorohydrin which were polymerized in the presence of 4,4′‐diaminodiphenylsulfone. The polyesters were the most thermostable polymers obtained. After curing at 240°C for 20 h, they were stable in N2 up to 345–370°C and afforded anaerobic char yields of 65–75% at 800°C. © 1993 John Wiley & Sons, Inc.
Exchange reactions occurring through active chain ends: Melt mixing of nylon 6 and polycarbonate
Authors: Montaudo Giorgio , Puglisi Concetto , Samperi Filippo 
Published: April 2003

AbstractThe chemical reactions occurring in the melt mixing of nylon6/polycarbonate (Ny6/PC) at 240°C were investigated. The reaction of equimolar Ny6/PC blends can be reconciled within the overall scheme of an exchange reaction occurring with the attack of active amino terminals on the inner carbonate groups. We have performed the synthesis of low molecular weight amino‐terminated nylon 6 and the effect of the active amino terminal groups on the exchange kinetics was investigated. The exchange reaction yields sizeable amounts of copolymer, in fact after 75 min of melt mixing the (initially equimolar) blend contains 30 mol of unreacted PC and 70 mol of Ny6/PC copolymer (all the Ny6 was therefore incorporated in the copolymer). Trifluoroacetylation of nylon 6 was used to produce CHCl3‐soluble Ny6/PC copolymers, that could be analyzed by NMR. The NMR analysis yielded, beside the copolymer composition, evidence of the presence of urethane units interconnecting the Ny6 and PC blocks. The amount of urethane units increased with the reaction time, indicating a reduction of the block size as a function of the extent of exchange. Our study established the structure of the products formed, provided the materials balance of the process, and investigated some salient kinetic aspects. A thermal degradation study was also performed by thermogravimetry and direct pyrolysis mass spectrometry, to identify the products formed in the thermal treatment of the blends and to investigate the possible role of the inner amide groups in the intermolecular exchange reactions occurring between Ny6 and PC. Our results prove that these reactions occur above 300°C, and that only the cleavage of carbonate groups, by means of Ny6 amino end groups, is actually occurring at 240°C. © 1994 John Wiley & Sons, Inc.
Preparation and characterization of acrylates and polyacrylates having variable fluorine contents and distributions
Authors: Guo X. Andrew , Hunter Allen D. , Chen Jie 
Published: April 2003

AbstractFive acrylic esters having different fluorine contents and distributions in their side‐groups (i.e., CH2=CHC(O)OR, where R = C(CH3)2C6F4H, C(CH3)2C6F5, C(CF3)2C6F5, C(CF3)2C6H5, and C(CH3)2C6H5) have been prepared from the reactions of the lithium salts of their corresponding alcohols with acryloyl chloride. These monomers are polymerized under identical conditions by the radical initiator AIBN and five polyacrylates were prepared having the structure of  [ CH2CHC(O)OR]n. These addition polymers were compared and fully characterized by GPC, VPO, DSC, TGA, NMR, IR, and UV‐visible spectroscopies, and they showed potential for practical applications. Significant differences in their thermal stabilities were found with respect to fluorine contents and distributions in these polyacrylates, and the highest stability arises from CF3 substitutions in the side‐chains of the polymers. © 1994 John Wiley & Sons, Inc.
Preparation and characterization of fluorine‐containing aromatic condensation polymers. II. Preparation and characterization of fluorine‐containing aromatic polyformal and copolyformals by solution polycondensation of 2,2‐bis (4‐hydroxyphenyl)‐1,1,1,3,3,3‐hexafluoropropane and/or 2,2‐bis‐(4‐hydroxyphenyl)propane with dichloromethane
Authors: Saegusa Yasuo , Kuriki Minoru , Kawai Akihiro , Nakamura Shigeo 
Published: April 2003

AbstractA series of fluorine‐containing aromatic homopolyformal and copolyformals with a wide range of unit ratio were synthesized by the solution polycondensation of 2,2‐bis (4‐hydroxyphenyl)‐1,1,1,3,3,3‐hexafluoropropane (Bisphenol AF) and/or 2,2‐bis (4‐hydroxyphenyl)propane (Bisphenol A) with dichloromethane, and the effect of the fluorine substitution on the preparation and properties of these polymers was investigated by comparing with those of Bisphenol‐A‐based homopolyformal without fluorine. Irrespective of the ratio of Bisphenol AF, high‐molecular‐weight, fluorine‐containing polyformals with reduced viscosities of 1.4–5.3 dL/g were obtained in high yields by using dichloromethane as both comonomer and solvent, potassium hydroxide as a base, and N‐methyl‐2‐pyrrolidone as a comedium at 75°C for 4 h. Their solubility increased markedly by the introduction of fluorine atom. Colorless, transparent, and tough films were cast from chloroform solution irrespective of fluorine content. These films had good mechanical properties comparable to that of Bisphenol‐A‐based homopolyformal. The contact angles by water were larger than 90°, regardless of their fluorine contents, at 25°C. The glass transition temperature and thermal stability increased monotonically with increasing fluorine content. © 1994 John Wiley & Sons, Inc.
High modulus polyimide/polyimide molecular composite films that utilize acetylene unit as a crosslink site
Authors: Takeichi Tsutomu , Takahashi Nobuyuki , Yokota Rikio 
Published: April 2003

AbstractPolyimide/polyimide molecular composite (MC) films comprised of a rigid polyimide derived from biphenyltetracarboxylic dianhydride (BPDA) and p‐phenylenediamine (PDA) and a flexible polyimide derived from BPDA and bis (3,3'‐diaminodiphenyl) acetylene (intA) and/or oxydianiline (ODA) were prepared by blending the polyamic acid solutions in 7 : 3 weight ratio, and then imidizing the blend films. Acetylene content in the flexible polyimide backbone was controlled by the ratio of intA and ODA. Cold‐drawing of the blend polyamic acid films, followed by imidization, gives high modulus polyimide/polyimide MC films. The modulus of the MC films increased almost linearly with the draw ratio, reaching 25.5 GPa for the 40% drawn film. Acetylene groups in the flexible polyimide can be thermally cured to crosslink. The onset of exotherm appeared at 340°C on DSC, reaching maximum at 398°C. After the thermal crosslinking, the MC films maintained the high modulus, though elongation became small. Taking advantage of the crosslinkable acetylene units, two MC films were laminated and processed at 400°C for 20 min under 100 kg/cm2 to give a good‐quality laminate film. The interface of the two films was strongly bonded through the crosslinking of acetylene groups. Laminate films maintained the high modulus afforded by the cold‐drawing. © 1994 John Wiley & Sons, Inc.
A study on the mechanism of dissolution of the cellulose/NH3/NH4SCN system. I
Authors: Cuculo J. A. , Smith C. B. , Sangwatanaroj U. , Stejskal E. O. , Sankar S. S. 
Published: April 2003

AbstractAmmonia/ammonium thiocyanate (NH3/NH4SCN) is an excellent swelling agent and solvent for cellulose, even at a high degree of polymerization. Because polymorphic conversion in cellulose has been a long‐standing, perplexing, troublesome problem, we have undertaken to study that mechanism. Solid state CP/MAS 13C‐NMR and X‐ray analysis proved to be very useful analytical techniques for the task. It appears that during temperature cycling, specific cellulosic inter‐ and intramolecular hydrogen‐bonds are broken as polymorphic conversion proceeds sequentially from the polymorph I to III, and finally at total solvation to amorphous. This proceeds correspondingly via transformation of the polymorph conformations of CH2OH from trans‐gauche, “tg,” to gauche‐trans, “gt,” to gauche‐gauche, “gg.” © 1994 John Wiley & Sons, Inc.
A study on the mechanism of dissolution of the cellulose/NH3/NH4SCN system. II.
Authors: Cuculo J. A. , Smith C. B. , Sangwatanaroj U. , Stejskal E. O. , Sankar S. S. 
Published: April 2003

AbstractIn a previous article,1 we reported on the interaction of cellulose with NH3/NH4SCN by using solid state CP / MAS 13C‐NMR, wide‐angle X‐ray and other techniques. It appears that during an imposed temperature cycling sequence, specific cellulosic inter‐ and intramolecular hydrogen bonds are broken as polymorphic conversion and, ultimately, dissolution occurs. Cellulose is converted from the polymorph I to II to III and, finally, to amorphous. We speculate that these changes proceed via transformation of the polymorph conformations of CH2OH from trans‐gauche, “tg,” to gauche‐trans, “gt,” to gauche‐gauche, “gg.” Remarkably, the temperature cycling effectively and rapidly effects these changes, seemingly, by invoking at two different temperatures (22°C and −78°C), a subtle but powerful temperature‐related interplay of enthalpic and entropic forces. At the higher of the cycling temperature limits, entropy and van der Waals forces dominate, causing NH3 to partition in favor of the liquid phase. At the lower of the temperature cycling limits, enthalpy dominates and the situation is reversed favoring NH3 partition toward the cellulose, resulting in breakage of inter‐ and intracellulosic H‐bonds by the interpenetrating ammonia to form new H‐bonds between cellulose and ammonia, leading ultimately to conformational changes and, ultimately, even dissolution. © 1994 John Wiley & Sons, Inc.
Stability of chemical sequence in a periodic polymeric nematogen
Authors: Wu J. L. , Stupp S. I. 
Published: April 2003

AbstractThe stability of a polymeric nematogen's chemical sequence was studied by differential scanning calorimetry, optical microscopy, and 13C‐NMR; the nematogen studied was a thermotropic polyester and had a periodic chemical structure. Model compounds were used to investigate transesterfication in the melt at different temperatures with the addition of phenol or benzoic acid as analogues of polymer end groups. Ester interchange reactions at high temperature were found to be partly suppressed when acidic end groups of the periodic nematogen were capped. However, sequence reorganization was completely suppressed in capped nematogens when temperatures remained below the isotropization transition of the nematogen investigated. Rapid disordering of the periodic nematogen was observed above the nematic‐isotropic transition, suggesting that both chemical and physical factors play a role in sequence redistribution of periodic nematogens. © 1994 John Wiley & Sons, Inc.
Template polymerization of multiacrylate
Authors: Jantas R. , Szumilewicz J. , Strobin G. , Połowiński S. 
Published: April 2003

AbstractBy reacting poly (2‐hydroxyethyl methacrylate) with acryloyl chloride, multiacrylate connected through a covalent bond with polymethacrylate chain (template) has been obtained. The free‐radical polymerization of multiacrylate in dilute dioxane solutions at 75°C and 85°C was examined by IR spectrophotometry and the distribution of molecular weights of the resultant products was evaluated by gel permeation chromatography. The findings show that under selected conditions the polymerization proceeds along ordered acrylic double bonds on the template and results in a ladder‐type polymer. At a temperature of 85°C, in addition to the intramolecular cyclopolymerization, intermolecular reactions proceed to a minor extent. © 1994 John Wiley & Sons, Inc.
Synthesis and properties of aromatic poly (ether sulfone)s and poly (ether ketone)s based on methyl‐substituted biphenyl‐4,4′‐diols
Authors: Keitoku Fumio , Kakimoto Masa‐Aki , Imai Yoshio 
Published: April 2003

AbstractNovel methyl‐substituted aromatic poly (ether sulfone)s and poly (ether ketone)s were synthesized from combinations of 3,3′,5,5′‐tetramethylbipheny‐4,4′‐diol and 2,2′,3,3′,5,5′‐hexamethylbiphenyl‐4,4′‐diol, and 4,4′‐dichlorodiphenyl sulfone and 4,4′‐difluorobenzo‐phenone by nucleophilic aromatic substitution polycondensation. The polycondensations proceeded quantitatively in a N‐methyl‐2‐pyrrolidone‐toluene solvent system in the presence of anhydrous potassium carbonate to afford the polymers with inherent viscosities between 0.86 and 1.55 dL/g. The methyl‐substituted poly (ether sulfone)s and poly (ether ketone)s showed good solubility in common organic solvents such as chloroform, tetrahydrofuran, pyridine, m‐cresol, and N,N‐dimethylacetamide. The tetramethyl‐ and hexamethyl‐substituted aromatic polyethers had higher glass transition temperatures than the corresponding unsubstituted polymers, and did not decompose below 350°C in both air and nitrogen atmospheres. The films of the methyl‐substituted poly (ether ketone)s became insoluble in chloroform by the irradiation of ultraviolet light, indicating the occurrence of photochemical crosslinking reactions. © 1994 John Wiley & Sons, Inc.
Fully aromatic thermotropic liquid crystalline polyesters of 3,4′‐dihydroxybenzophenone
Authors: Han Haesook , Bhowmik Pradip K. , Lenz Robert W. 
Published: April 2003

AbstractA series of fully aromatic, thermotropic polyesters, derived from 3,4′‐dihydroxybenzophenone and various aromatic dicarboxylic acids, was prepared by the high‐temperature solution polycondensation method and examined for thermotropic behavior by a variety of experimental techniques. The aromatic dicarboxylic acids used in this study were 2,6‐naphthalenedicarboxylic acid, 4,4′‐bibenzoic acid, and terephthalic acid.The two homopolymers of 3,4′‐DHB with either 2,6‐NDA or 4,4′‐BBA formed nematic LC phases at 285°C and 255°C and also exhibited isotropization transitions (Ti) at 317°C and 339°C, respectively. The copolymer of 3,4′‐DHB with 50% TA and 50% 2,6‐NDA also formed a nematic LC phase and had a broader range of LC phase than that of its respective homopolymers. Two other copolymers of 3,4′‐DHB, both containing 50% 4,4′‐BBA, also formed nematic LC phases at low Tf values. All of the thermotropic polyesters had high thermal stabilities. © 1994 John Wiley & Sons, Inc.
Synthesis and characterization of poly (2‐vinylpridine)‐b‐poly (t‐butyl methacrylate)
Authors: Yin Rui , Hogen‐Esch Thieo E. 
Published: April 2003

AbstractThe synthesis of well defined and monodisperse (Mw/Mn ≤ 1.2) narrow molecular weight distribution poly (2‐vinylpyridine)‐poly (t‐butyl methacrylate) (P2VP‐PTBMA) AB block copolymers is carried out by initiation of 2‐vinylpyridine polymerization by 1,1‐diphenylhexyllithium in THF at‐78°C, followed by addition of TBMA and termination at −78°C using MeOH. The formation of the BAB block copolymer is carried out in a similar fashion except that 1,4‐dilithio‐1,1,4,4‐tetraphenylbutane is used as initiator. The corresponding synthesis of P2VP‐PMMA block copolymers is carried in a similar manner, except that 1‐2 equivalents of TBMA is used to end‐functionalize the living P2VP before the addition of MMA. Without the addition of TBMA, trimodal molecular weight distributions in P2VP‐b‐PMMA are obtained. All the block copolymers are characterized by Size Exclusion Chromatography (SEC), Nuclear Magnetic Resonance (NMR), and Differential Scanning Calorimetry (DSC). © 1994 John Wiley & Sons, Inc.
Synthesis of polyester and copolyesters having amino acid moieties in the main chain
Authors: Wang Chonghui , Nakamura Shigeo 
Published: April 2003

AbstractN, N‐di (2‐hydroxyethyl)‐3‐aminopropionic acid (M3) was synthesized and used for the preparation of a series of polyesters having amino acid moieties in the main chain and carboxyl groups as the side group. Polycondensation of M3, diols, bisphenol A, and isophthaloyl dichloride were performed in the presence of tertiary amine by solution and interfacial methods. Molecular weights of the polymers obtained by the solution method were not high, because oligomers produced at the early stage of reaction are ionized by H+ ions from the by‐product, and become nonreactive triethylamine hydrochloride. Polymers with high M̄w (1–10 × 104) were obtained in a high yield by organic/organic two‐phase interfacial polycondensation using DMAc and n‐heptane as solvents. The combined nucleophilic and basic complex catalytic action of N, N, N′, N′‐tetramethyl ethyiene diamine (TEMED) is suggested for the present organic phase/organic phase interfacial polycondensation. This method can be applied for the preparation of novel functional polyesters. © 1994 John Wiley & Sons, Inc.
Polymerization of surface‐active monomers. VIII. Tacticity of polymers prepared by radical polymerization of quaternary salts of dimethylaminoethyl methacrylate in micellar and isotropic media
Authors: Nagai Katsutoshi , Ohishi Yoshiyuki 
Published: April 2003

AbstractThe effect of monomer micellization on the polymerization was studied from the standpoint of stereochemistry in the polymerization. Quaternary salts (CnBr) of dimethylaminoethyl methacrylate with n‐alkyl bromide having N (=4, 8 and 12) carbon atoms were polymerized with radical initiators in isotropic and anisotropic media and the resulting polymers were converted to poly (methyl methacrylate) (PMMA) to determine their tacticity. Tacticities of poly (C12Br)s were little affected by initiators and solvents used for their preparations. There was little dependence of the tacticities on alkyl chain length (N) for poly (CnBr)s prepared in water and dimethylformamide (DMF). Most of polymers produced here conformed to Bernoullian propagation statistics and a definite difference was not found in the tacticities between the polymers prepared in isotropic and anisotropic media. From the results obtained here it was deduced that the micellar aggregation has little influence upon the stereochemistry in the polymerization of the quaternary monomers. © 1994 John Wiley & Sons, Inc.
Solid‐state polyamidation of hexamethylenediammonium adipate. II. The influence of acid catalysts
Authors: Katsikopoulos P. V. , Papaspyrides C. D. 
Published: April 2003

AbstractLoss of diamine and distinct transition phenomena from the solid to the melt state restrain solid‐state polymerization (SSP) of nylon salts from industrial application. To depress these phenomena temperatures well below the melting point of the starting material are employed, resulting however in low reaction rates. The need to use catalysts arises and accordingly in this study hexamethylenediammonium adipate (HMA) particles were polymerized containing a strictly controlled amount of uniformly distributed catalyst. The catalysts included boric, sulphuric, and phosphoric acids with boric acid being the most effective in accelerating the reaction while eliminating the tendency to agglomeration. In general, catalyst concentration up to a critical value plays a considerable role in the overall behavior. Furthermore, in agreement with non catalytic processes, the reaction temperature remains an influential parameter. © 1994 John Wiley & Sons, Inc.
Synthesis and electronic properties of poly (E, E)‐[6.2]‐(2,5) thiophenophane‐1,5‐diene)
Authors: Guerrero Douglas J. , Glatzhofer Daniel T. 
Published: April 2003

AbstractCationic cyclopolymerization of (E, E)‐[6.2]‐(2,5) thiophenophane‐1,5‐diene (2) gave polymer 3 which has bridged thiophene rings pendant to the polymer backbone. The structural, thermal, and electronic properties of polymer 3 were compared to those of its benzene analogue (1) and its nonbridged analogue poly (2‐vinylthiophene) (5). The onsets of thermal degradation for polymers 3 and 5 under helium were 425 and 382°C, respectively. Polymer 3 exhibited conductivity in the 10−3−10−4 S/cm range when exposed to iodine vapor, four orders of magnitude higher than for 5 treated in the same manner. Apparent energies of activation for conductivity in iodine saturated polymers 3 (0.57 eV) and 5 (0.61 eV) were calculated from conductivity temperature dependence measurements. Conductivity parameters for iodine saturated 3 show both a higher level of conductivity and weaker temperature dependence than for the corresponding cyclopolymer 1 which has benzene rather than thiophene moieties, suggesting that greater charge generation occurs in 3, due to the lower oxidation potential of the thiophenophane repeat units. Differences in conductivity behavior for iodine saturated polymers 1, 3, and 5 are discussed in terms of both charge generation and mobility. © 1994 John Wiley & Sons, Inc.
Synthesis of polyphosphazenes bearing alkoxyethoxy and trifluoroethoxy groups
Authors: Matyjaszewski Krzysztof , Lindenberg Michael S. , Moore Mary K. , White Michael L. 
Published: April 2003

AbstractThe synthesis of various phosphoranimines including (CH3OCH2CH2O) (CF3CH2O)2PNSi(CH3)3, (CH3OCH2CH2OCH2CH2O) (CF3CH2O)2PNSi (CH3)3, (CH3OCH2CH2O)2(CF3CH2O) PNSi(CH3)3, and (CH3OCH2CH2OCH2CH2O)(CF3CH2O) PNSi(CH3)3 via the Staudinger reaction of (CH3)3SiN3 with the suitably substituted phosphite is reported. These monomers were polymerized using tetra‐n‐butylammonium fluoride and N‐methylimidazole in various solvents at several temperatures. In situ 31P‐NMR kinetic studies and Mn versus time studies were also performed for the monomers to understand the propagation mechanism. © 1994 John Wiley & Sons, Inc.
Syntheses and properties of related polyoxadiazoles and polytriazoles
Authors: Hensema E. R. , Sena M. E. R. , Mulder M. H. V. , Smolders C. A. 
Published: April 2003

AbstractNew aromatic poly‐1,2,4‐triazoles and poly‐1,3,4‐oxadiazoles are studied as thermally stable membrane materials. Various groups were introduced onto the pendant phenyl groups of poly‐1,2,4‐triazoles. Glass transition temperature, degradation temperature, and cold crystallization behavior were studied as a function of these groups. Cold crystallization appeared to be highly sensitive to macromolecular regularity. The solubility of poly‐1,3,4‐oxadiazoles was highly improved upon incorporation of 5‐t‐butylisophthalic, 1,1,3‐trimethyl‐3‐phenylindane, 4,4′‐(2,2′‐diphenyl) hexafluoro propane, and diphenyl ether groups into the polymeric main chain, whereas the high glass transition temperatures and degradation temperatures typical for aromatic poly‐1,3,4‐oxadiazoles were maintained. © 1994 John Wiley & Sons, Inc.