bluuebunny/crossref_metadata_2025_split huggingface dataset:
Styrene–maleic anhydride copolymerization through polar transition states in polar solvents
Authors: Lin Q. , Talukder M. , Pittman C. U. 
Published: April 2003

AbstractRadical copolymerization of styrene (M1) and maleic anhydride (M2) was performed in highly polar, oxygen lone‐pair donor solvents (N, N‐dimethylformamide, N‐methylfor‐mamide) at high temperatures (135 and 145°C) and in strong π‐electron donor solvents (1,3‐dimethoxybenzene and 1,2,4‐trimethoxybenzene) at 60‐145°C. The corresponding reactivity ratios were evaluated by Fineman–Ross, Kelen Tüdos, and error‐in‐variables model (RREVM) methods. The reactivity ratios obtained (r1r2 < 1) show that alternating copolymers were produced. These results are best explained if the copolymerizations proceed through highly polarized radical transition states rather than styrene–maleic anhydride charge‐transfer complexes. Polar solvents stabilize highly polarized radical transition states thereby promoting alternating polymerization at higher temperatures than can be observed in nonpolar solvents. Donor solvents might also stabilize the electrophilic maleic anhydride radical more than the nucleophilic styryl radical thereby tending to depress k21 relative to k12. The copolymerizations were also studied in decalin (a nonpolar, nondonor solvent) at 60‐145°C. At lower temperatures alternating copolymers were combined. However, at temperatures > 120°C, random copolymers were obtained in decalin. Thus, in decalin, styrene–maleic anhydride charge‐transfer complexes are present at lower temperatures where they might play a role in alternation. In decalin the solvation of the polar transition states (relative to the macroradicals and monomers) does not favor copolymerization through such dipolar structures. Thus, at low temperatures growing chains could add to charge‐transfer complexes. However, at temperatures above 120°C the concentration of charge‐transfer complexes becomes so small that they can no longer be kinetically important contributions to the copolymerization. Thus, random copolymers with high styrene mole ratios are produced in decalin. The equilibrium constants for complex formation between maleic anhydride and both 1,3‐dimethoxybenzene and 1,2,4‐trimethoxybenzene were de‐termined in 1 : 1 (v/v) CCl4/CDCl3 using a technique based on changes in the NMR chemical shifts of the maleic anhydride protons. © 1995 John Wiley & Sons, Inc.
Chemoselective hydrosilations. I. Synthesis and photopolymerization of 1‐propenyl ether functionalized siloxanes
Authors: Crivello James V. , Yang Bo , Kim Whan‐Gi 
Published: April 2003

AbstractThe synthesis of 1‐propenyl ether‐functionalized siloxanes (PFS) has been achieved by the controlled, rhodium‐catalyzed, chemoselective hydrosilation of 1‐allyloxy‐4(1‐propen‐oxy) butane with various H‐functional siloxanes. It was shown that the hydrosilation pro‐ceeds exclusively at the allyl ether group of 1‐allyloxy‐4(1‐propenoxy) butane without par‐ticipation at the 1‐propenyl ether group. The photoinduced cationic polymerization of these monomers was studied using various analytical techniques and found to take place very rapidly. © 1995 John Wiley & Sons, Inc.
Mechanistic study of the reactivity of 3,4‐epoxycyclohexylmethyl 3′,4′‐epoxycyclohexancarboxylate in photoinitiated cationic polymerizations
Authors: Crivello James V. , Varlemann Ulrike 
Published: April 2003

AbstractAn investigation of the reactivity of the cycloaliphatic diepoxide, 3,4‐epoxycyclohexyl 3′, 4′‐epoxycycloexane carboxylate (I) in photoinitiated cationic polymerization was carried out with the aid of model compounds. It was shown that the presence of the ester group greatly retards the rate of polymerization of this bisepoxide. Molecular modeling studies indicate that the ester carbonyl group can interact in a number of ways with the initially formed protonated or alkylated oxiranium cation to give bicylic dialkoxycarbenium ions. These latter species are both more sterically hindered and less reactive than the oxiranium cation precursors and undergo propagation at a considerably reduced rate. Reactivity studies em‐ploying model compounds also showed that epoxy monomers that contain ester groups undergo polymerization at much slower rates than those in which the ester group is absent. © 1995 John Wiley & Sons, Inc.
Synthesis and characterization of poly(amide sulfonamide)s (PASAs)
Authors: Chan Winghong , Lam‐Leung Suei Yee , Ng Chingfai , Ding Junqi , Xi Shiping 
Published: April 2003

AbstractNew diamino monomers IIa–IIg were synthesized in a two‐step reaction sequence starting from p‐acetamidobenzenesulfonyl chloride. Solution polymerization of these monomers in DMAC with terephthaloyl or isophthaloyl chloride resulted in the formation of a series of 14 poly(amide sulfonamide)s (PASAs) in excellent yield (> 95%). The polymers have in‐trinsic viscosities of 0.32–1.11 dL g−1. Except for polymers IIIa−p and IIId‐p, all other PASAs were readily soluble in aprotic polar solvents including DMAC, DMF, and DMSO. Thermogravimetric analyses of the polymers showed moderate thermal stability with 10% weight loss being recorded in the range of 325–408°C. In addition, these polymers exhibit moderate chemical stabilities toward alkali, acidic, and chromic acid solution. © 1995 John Wiley & Sons, Inc.
Fundamental studies of grafting reactions in free radical copolymerization. I. A detailed kinetic model for solution polymerization
Authors: Huang Nai‐Jen , Sundberg Donald C. 
Published: April 2003

AbstractGraft site initiation occurs by primary radical and/ or polymeric radical attack on the back‐bone polymer. The controlling mechanism is determined by the structure of the backbone and the activity of the free radicals. The efficiency of incorporating monomer into the graft chains depends upon the graft site initiation mechanism and the mode of polymer chain termination (recombination or disproportionation). A kinetic analysis results a series of uniquely different expressions describing the graft efficiency, ϕ corresponding to different combinations of graft site initiation and chain termination mechanisms. The dependency of ϕ upon monomer, initiator, and backbone concentrations is different from case to case. The complete kinetic model is capable of predicting reaction rate, graft efficiency, graft frequency, graft ratio, and molecular weight averages and distributions. Simulations are provided to compare predicted results with experimental data for two different systems which show contrasting mechanisms of graft site initiation and mode of termination. © 1995 John Wiley & Sons, Inc.
Enzyme‐catalyzed synthesis of aliphatic polyesters in organic media: Study of transesterification equilibrium shift and characterization of cyclic compounds
Authors: Mezoul G. , Lalot T. , Brigodiot M. , Maréchal E. 
Published: April 2003

AbstractEnzyme‐catalyzed synthesis of aliphatic polyesters in organic media from methyl diesters and diols was carried out at stoechiometric ratio in the presence of supported lipases (li‐pozyme® and novozyme®). Two systems were studied to shift the thermodynamic equilibrium which limits the conversion. In the first one, the solution flows through a molecular sieve in which methanol is adsorbed. In the second one, methanol is eliminated by nitrogen bubbling. The system with nitrogen bubbling in hydrophobic solvents at 60°C works best when novozyme® is used as catalyst. Despite a high fractional conversion (p> 0.99), the number‐average molar mass is not very high (M̄;n = 3050 eq. PS). In relation to the nature of monomers, cycles with DP = 2–20 were characterized by chromatographic analyses and mass spectrometry. Their formation explains why high polycondensates cannot be obtained. © 1995 John Wiley & Sons, Inc.
Synthesis of novel macromonomers and telechelics of poly(2‐alkyl‐2‐oxazoline)s
Authors: Shimano Yasuo , Sato Kumiko , Kobayashi Shiro 
Published: April 2003

AbstractNovel macromonomers and telechelics of poly(2‐alkyl‐2‐oxazoline) (PROZO) were syn‐thesized by utilizing termination of propagating species (2‐oxazolinium ions) in the living polymerization of 2‐alkyl‐2‐oxazoline (ROZO) with suitable nucleophiles. Two types of p‐vinylbenzyl–type macromonomers were obtained by terminating living PROZO with sodium p‐vinylbenzyl alkoxide or with sodium p‐vinylbenzyl mercaptide. The synthesis of telechelics having a functional group (SH, COOH) on both ends of PROZO was achieved by using a bis(2‐oxazolinium salt) initiator. The PROZO dithiol was synthesized by two methods: (1) termination of the living species on both ends with NaSH, and (2) aminolysis of PROZO bis(O‐ethyldithiocarbonate) given by treatment of the living PROZO with potassium O‐ethyldithiocarbonate. Termination of the living PROZO with the sodium salt of di‐t‐butyl malonate yielded a PROZO with di‐t‐butyl malonate moieties on both polymer ends, from which the PROZO dicarboxylic acid was derived via free tetracarboxylic acid. © 1995 John Wiley & Sons, Inc.
Characterization and comparison of poly(aryl ether ketone)s containing dibenzoylbiphenyl moieties: Effects of changes in biphenyl substitution pattern on thermal and mechanical properties
Authors: Moulinié Pierre , Paroli Ralph M. , Wang Zhi Yuan 
Published: April 2003

AbstractA monomer, 3,3′‐bis (4‐fluorobenzoyl) biphenyl, was prepared in high yield in two steps from inexpensive 3‐chlorobenzoyl chloride and fluorobenzene, and polymerized by nucleophilic displacement reaction with various bisphenol monomers in tetramethylene sulfone to produce a series of high molecular weight poly(aryl ether ketone)s containing 3,3′‐dibenzoylbiphenyl (DBBP) moieties. The spectroscopic, thermal, and thermomechanical properties of these polymers and related isomeric polymers having 2,2′‐and 4,4′‐DBBP units were determined and compared to study the effects of changes in the substitution pattern of the biphenyl unit. Except for the 2,2′‐DBBP series of polymers, Tgs were found to increase with increasing linearity of the DBBP unit. The 2,2′‐DBBP series of polymers had exceptionally high Tgs due to the sterically restricted motions in the biphenyl unit caused by the 2,2′‐substitution. In addition, they also showed evidence for torsion with the 2,2′‐DBBP unit, whereas in other isomeric polymers the DBBP units are believed to be relatively coplanar. Thermal stabilities and tensile moduli for these polymers proved to be independent of substitution patterns. © 1995 John Wiley & Sons, Inc.
Olefin terpolymerizations. II. 4‐vinylcyclohexene and cyclooctadiene
Authors: Marques Maria , Yu Zhengtian , Rausch Marvin D. , Chien James C. W. 
Published: April 2003

Abstract4‐Vinylcyclohexene (VCH) and cyclooctadiene (COD) were investigated as termonomers in EPDM (ethylene/propylene/diene) synthesis by using rac‐ethylenebis (1‐η5‐indenyl) zir‐conium dichloride (1) as a catalyst precursor. Homopolymerizations of VCH, vinylcycloh‐exane and cyclohexene were compared. The parameter Kπκp, which is the apparent rate constant for Ziegler‐Natta polymerization, is about the same for VCH and vinylcyclohexanebut is 10 times smaller for cyclohexene. Therefore, the linear olefinic double bond is more active than the cyclic internal double bond. VCH reduces ethylene polymerization rate but not propylene polymerization rate in copolymerizations. In terpolymerizations, VCH tends to suppress ethylene incorporation especially at elevated polymerization temperature and Lowers the polymer MW by about two‐fold. COD has very low activity as a termonomer. © 1995 John Wiley & Sons, Inc.
Preparation of polyamides derived from 1,6‐diamantane dicarboxylic chloride by solution polycondensation and interfacial polycondensation
Authors: Chern Yaw‐Terng , Fang Jea‐Shih , Kao Shen C. 
Published: April 2003

Abstract1,6‐Diamantane dicarboxvlic acyl chloride (I) was used as a monomer with various aromatic diamines to synthesize polyamides by interfacial polycondensation and solution polycon‐densation. The polyamides prepared by interfacial polycondensation had inherent viscosities between 0.38 and 0.15 dL/g. The polyamides prepared by solution polycondensation had inherent viscosities between 0.62 and 0.25 dL/g. The polyamides IIIa prepared by solution polycondensation showed the main melting transition at 380°C by dynamic mechanical analysis. In addition, it was quite temperature‐stable and maintained good mechanical properties (G′⋐108 Pa) up to high temperatures close to the main transition well above 350°C. The polyamide IIIA had a tensile strength of 35 MPa, elongations to break of 10%, and initial modulus of 0.8 GPa. Some of the polyamides were soluble in NMP, DMAc, and DMSO, depending on soft segment moiety of diamine (II). The polyamides prepared by interfacial polycondensation have a greater tendency to form crystal than those prepared by solution polycondensation, as evidenced by x‐ray diffraction studies. These polyamides had glass transition temperatures in the 270–300°C range, and 5% weight loss temperatures up to 435°C in nitrogen. © 1995 John Wiley & Sons, Inc.
Novel copolyesters containing naphthalene structure. II. Copolyesters prepared from 2,6‐dimethyl naphthalate, 1,4‐dimethyl terephthalate, and ethylene glycol
Authors: Lu Tsu‐Shang , Sun Yih‐Min , Wang Chun‐Shan 
Published: April 2003

AbstractCopolyesters containing rigid segments (naphthalene and terephthalene) and flexible seg‐ments (aliphatic diol) structure were synthesized from DMN/DMT/EG (2,6‐dimethyl naphthalate/1,4‐dimethyl terephthalate/ethylene glycol) ternary monomers with various mole ratios. Copolyesters having intrinsic viscosities of 0.52–0.65 dL/g were obtained by melt polycondensation in the presence of metallic catalysts. The effect of reaction tem‐perature and time on the formation of the copolyesters was investigated to obtain an op‐timum condition for copolyester manufacturing. The optimum condition for PNT (poly‐ethylene naphthalate terephthalate) copolyester manufacturing is the transesterification under nitrogen atmosphere for 4 h at a temperature of 185±2°C followed by polymerization under 2 mm Hg for 2 h at a temperature of 280°C. Most copolyesters have better solubilities than poly(ethylene naphthalate) (PEN) and poly(ethylene terephthalate) (PET) in various solvents. The effect of the starting mole ratio of DMN, DMT, and EG on the thermal properties of the resulted copolyesters was also investigated using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Glass transition temperatures of copolyesters were in the range of 70.7–115.2°C, and 10% weight loss in nitrogen were all above 426°C. © 1995 John Wiley & Sons, Inc.
Pyrolysis chemical ionization mass spectrometry of cellulose ethers
Authors: Arisz P. W. , Boon J. J. 
Published: April 2003

AbstractPyrolysis ammonia chemical ionization (PyCI) mass spectrometry was performed on hy‐droxyethyl‐, hydroxypropyl‐,methyl‐, hydroxypropylmethyl‐, and ethylhydroxyethyl cel‐luloses. The mass peaks in the PyCI mass spectra of these cellulose ethers could be assigned to the ions of pyrolytic dissociation products which form via the [2 + 2 + 2] cycloreversion and the Ei elimination pyrolysis pathway. Structural information about the residual amount of nonderivatized cellulose, the relative chain length distributions of the substituents in hydroxyalkyl celluloses, and the end‐capping of hydroxyalkyl substituents by alkyl groups in the mixed cellulose ethers is obtained. Interference of secondary pyrolysis products in the PyCI mass spectra is found to be of minor importance, especially in the lower mass regions. © 1995 John Wiley & Sons, Inc.
Amine‐quinone polyurethanes. I. Preparation of polyurethane block copolymers containing 2,5–bis(N‐2‐hydroxyethyl‐N‐methylamino)‐1,4–benzoquinone diol monomer
Authors: Nikles David E. , Liang Jeng‐Li , Cain Jason L. , Chacko Antony P. , Webb Russell I. , Belmore Ken 
Published: April 2003

AbstractThe amine‐quinone monomer, 2,5–bis(N‐2‐hydroxyethyl‐N‐methylamino)‐1,4‐benzoqui‐none (AQM‐1), was prepared by the multiple‐step condensation of 2‐(N‐methylam‐ino)ethanol with benzoquinone in the presence of oxygen. This crystalline monomer was used to prepare a series of amine‐quinone polyurethanes by condensation polymerization, either in the melt or in solution (THF or DMF), with a diisocyanate (MDI, TDI, or IPDI) and an oligomeric diol [poly(caprolactone) or poly(1,2‐butylene glycol)]. The amine‐quinone functional group was stable under the polymerization conditions, and was incorporated into the main chain, giving red‐brown polyurethanes that had molecular weights in the range of 11,000–90,000 and were soluble in THF, MEK, DMF, and DMSO. The thermal properties were consistent with a two‐phase morphology with an amorphous soft segment, containing the oligomeric diol, and a microcrystalline hard segment, containing AQM‐1. The polymers having a low hard segment content (<50%) were rubbery (soft segment Tg <−25°C); polymers having a high hard segment content (>50%) were thermoplastic (hard segment Tg>150°C). © 1995 John Wiley & Sons, Inc.
Redox polymerization process: An efficient tool for the synthesis of block copolymers
Authors: Nagarajan Soundappan , Srinivasan Kalathur Sabdham Vangepuram 
Published: April 2003

AbstractThe synthesis of poly(acrylonitrile)‐block‐poly‐(ethylene glycol)‐block‐poly(acrylonitrile) copolymers has been carried out using a redox system consisting of ceric ion and poly(ethylene glycol)s of various molecular weights in aqueous medium. The generation of intermediate radicals in the redox process has been confirmed by ESR spectroscopy and the polymerization progressing through ‘blocking from’ mechanism has been postulated. The formation of the block copolymers has been confirmed by chemical tests and fractional precipitation technique as well as by FT‐IR and FT‐NMR [1H and 13C–(1H)] spectroscopic techniques. The triblock nature of the block copolymers has been ascertained through the cleavage of ether linkage of the PEG segment. TG/DTA studies of the block copolymers with PEG molecular weights of 1000 and above revealed two‐stage decomposition, while their DSC traces exhibited a shift in the melting peak of PEG. GPC investigations of the block copolymers manifested a high homogeneity with unimodal distribution of molecular weights. SEM studies indicated significant changes in the morphological characteristics of the block copolymers. © 1995 John Wiley & Sons, Inc.
LuCaP 35: A new model of prostate cancer progression to androgen independence
Authors: Corey Eva , Quinn Janna E. , Buhler Kent R. , Nelson Peter S. , Macoska Jill A. , True Lawrence D. , Vessella Robert L. 
Published: April 2003

AbstractBackgroundGeneration of suitable in vivo models is critical for understanding of processes associated with development and progression of prostate cancer (CaP).MethodsLymph nodes containing metastatic androgen‐independent CaP were implanted into athymic mice. A xenograft designated LuCaP 35 and its hormone‐independent variant LuCaP 35V were established and characterized.ResultsLuCaP 35 is an androgen‐sensitive, prostate‐specific antigen (PSA)‐producing xenograft. It expresses the wild‐type androgen receptor and exhibits deletions in chromosome 8p, but not in chromosome 10. The response of LuCaP 35 to androgen ablation is similar to that observed in man. Using recurring LuCaP 35 tumors we have also established an androgen‐insensitive variant of LuCaP 35.ConclusionsThe availability of hormone‐dependent and ‐independent variants of LuCaP 35, which exhibit many properties analogous to those of CaP in man, provides an excellent model system to study the processes associated with development of androgen independence and to evaluate new treatment modalities. Prostate 55: 239–246, 2003. © 2003 Wiley‐Liss, Inc.
Suppression of LNCaP prostate cancer xenograft tumors by a prostate‐specific protein tyrosine phosphatase, prostatic acid phosphatase
Authors: Igawa Tsukasa , Lin Fen‐Fen , Rao Prathibha , Lin Ming‐Fong 
Published: April 2003

AbstractBackgroundAlthough the molecular mechanism of androgen‐independent prostate cancer growth and progression has been gradually elucidated, there is limited effective treatment for this prevalent disease. Human prostatic acid phosphatase (PAcP), a major protein tyrosine phosphatase in prostate epithelium, plays a critical role in regulating the growth of prostate cancer cells. In prostate carcinomas, the expression of cellular PAcP decreases. To explore directly the possible therapeutic potential of cellular PAcP, we investigated the suppression effect of PAcP by utilizing cDNA direct intratumoral administration in androgen‐independent LNCaP xenograft tumors.MethodsAn androgen‐independent LNCaP cell model (C‐33 and C‐81 cells) and stable subclones of PAcP cDNA‐transfected C‐81 cells (LNCaP‐23 and LNCaP‐34 cells) were used for the experiments. We examined the growth property and expression of PAcP and c‐ErbB‐2 of these different LNCaP cells in vitro and in vivo. We subsequently investigated the growth suppression effect of PAcP cDNA intratumoral injection in pre‐established C‐81 xenograft tumors, and analyzed the expression of PAcP, prostate‐specific antigen (PSA), proliferating cell nuclear antigen (PCNA), and c‐ErbB‐2 in the tumors by immunohistochemistry and Western blotting.ResultsThe different LNCaP cells exhibited different growth property and tumorigenicity, both in cell culture and xenograft. Biochemical characterizations revealed that the level of cellular PAcP correlated negatively with the growth property of different LNCaP cells, while the level of tyrophosphorylated c‐ErbB‐2 had an inverse correlation with cellular PAcP. The single intratumoral administration of the wild type PAcP cDNA showed a significant suppression effect on C‐81 xenograft tumor growth, compared to vector alone‐injected control (P <0.05). In the tumors injected with this PAcP cDNA, the PAcP expression was detected 1 week (wk) after injection, but was undetectable at 6 wk, which inversely correlated with the level of tyrophosphorylated c‐ErbB‐2 and the degree of cell proliferation indicated by PCNA staining.ConclusionsOur results clearly demonstrated that cellular PAcP has a suppression effect on the growth of androgen‐independent LNCaP xenograft tumors. This effect occurs at least partly through the dephosphorylation of c‐ErbB‐2 by PAcP, the prostate‐specific protein tyrosine phosphatase. The data indicates that human PAcP could be utilized in the corrective gene therapy for a subgroup of androgen‐independent human prostate cancer cells that lack cellular PAcP expression. Prostate 55: 247–258, 2003. © 2003 Wiley‐Liss, Inc.