共查询到20条相似文献,搜索用时 31 毫秒
1.
James C. W. Chien Phillipe L. Bres 《Journal of polymer science. Part A, Polymer chemistry》1986,24(10):2483-2505
Polymerizations of ethylene by the MgCl2/ethylbenzoate/p-cresol/AlEt3 TiCl4-AlEt3/methyl-p-toluate (CW-catalyst) have been studied. The initially formed active site concentration, [Ti] has a maximum value of 50% of total titanium at 50°C and lower values at other temperatures. The Ti decays rapidly to Ti sites with conc. ca. 10 mol %/mol Ti. The rate constants for four chain transfer processes have been obtained at 50°C: for transfer with AlEt3, k = 2.1 × 10?4 s?1 and k = 4.8 × 10?4 s?1; for transfer with monomer, k = 3.6 × 10?3 (M s)?1 and K = 8.3 × 10?3 (M s)?1; for β-hydride transfer, k = 7.2 × 10?4 s?1 and k = 4.9 × 10?4 s?1; and transfer with hydrogen, k = 4.0 × 10?3 torr1/2 s? and k = 5.1 × 10?3 torr1/2 s?1. The rate constants for the termination assisted by hydrogen is k = 1.7 (M1/2 torr1/2 S)?1. If monomer is assisting termination as was observed for propylene polymerization, then k = 7.8 (M3/2 s)?1. Values of all the rate constants can be higher or lower at other temperatures. Detailed comparisons were made with the results of propylene polymerizations. There are more than four times as many Ti active sites for ethylene polymerization than there are for stereospecific polymerization of propylene; the difference is more than a factor of two for the Ti sites. Certain rate constants are nearly the same for both monomers while others are markedly different. Some of the differences can be explained by stereoelectronic effects. 相似文献
2.
James C. W. Chien Tsunle Ang 《Journal of polymer science. Part A, Polymer chemistry》1986,24(9):2217-2230
Decene-1 was polymerized with the CW catalyst and fractionated by precipitation technique. Light-scattering and viscometric measurements on these fractions established the relationship [η] = 5.19 × 10?3 M . The unperturbed mean square end-to-end distance is (〈R〉/M)1/2 = (6.17 ± 0.34) × 10?9. Light-scattering data is consistent with a relatively stiff molecule with length of L = 1.75 × 10?5 cm for poly(decene-1) with MW = 397,000. Its mean square radius of gyration 〈R〉 is 2.79 × 10?11 cm.2 The ratio of L2/〈R〉 = 11 is close to the theoretical ratio of 12 for this kind of macromolecule. 相似文献
3.
4.
Hyung Soon Park Joo Hee Cho Junghun Suh 《Journal of polymer science. Part A, Polymer chemistry》1997,35(14):2935-2942
Three molecules of 5-(bromoacetyl)salicylate ( 1 ) complexed to uranyl UO ion were crosslinked with branchy poly(ethylenimine) (PEI) in DMSO by alkylation of amino groups of PEI with 1, leading to the formation of UO2(Sal) PEI. Upon demetalation of UO2(Sal) PEI with HCl, apo(Sal) PEI was obtained. Based on the pH dependence of log Kf for UO2(Sal) PEI, it was concluded that each uranyl binding site in UO2(Sal) PEI or apo(Sal) PEI contains three salicylate moieties. In terms of the equilibrium constant for formation of the uranyl complex, apo(Sal) PEI was found to be comparable to or better than the previously reported effective uranophiles. In terms of the rates for the formation of the uranyl complex, however, apo(Sal) PEI was far superior to those other uranophiles. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2935–2942, 1997 相似文献
5.
Tokio Hagiwara Takamasa Shimizu Tomonori Uda Hiroshi Hamana Tadashi Narita 《Journal of polymer science. Part A, Polymer chemistry》1990,28(1):185-192
The kinetic feature of the anionic polymerization of N-PMI was investigated in THF. The polymerization system initiated with lithium tert-butoxide was revealed to be so-called “slow-initiation” system. The rate constant of the initiation reaction, ki, was obtained to be 4.2 × 10?3 (L mol?1 s?1) at ?72°C. The apparent rate constants of the propagation reaction, k, at ?72°C were individually obtained from each slope of the first-order plots in the later stages of the polymerizations for four different initiator concentrations. Each k is fairly close to that of initiation rate around 10?3. The propagation reaction was concluded to be dominated by ion-pair mechanism from the analysis of the kinetic data and the results of the addition effects of crown ether and common salt. 相似文献
6.
Pierre Lebreton Bernard Boutevin 《Journal of polymer science. Part A, Polymer chemistry》2000,38(10):1834-1843
Acrylamide was polymerized in acetonitrile at 82 °C with a perfluorinated azo‐derivative initiator. The polymerization proceeded heterogeneously. Varying amounts of initiator and monomer were used. The activation energy was deduced from three experiments carried out at 59, 71, and 82 °C. The following kinetic law, deviating a great deal from the classical law, was obtained: R ∼ [I2][M](0.05% < [I2]o/[M]o < 1.00%) and R ∼ [I2][M](1% < [I2]o/[M]o < 7%). These results can be interpreted in light of the contribution of primary radical termination and the emergence of occlusion. The development of a new kinetic relationship allowed us to confirm the existence of both of these termination reactions. The calculation of the kprt /ki · kp ratio was also achieved. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1834–1843, 2000 相似文献
7.
Takashi Nozaki James C. W. Chien 《Journal of polymer science. Part A, Polymer chemistry》1991,29(12):1807-1817
Solvay type S –VCl3 catalyst has 7% of catalytically active vanadium sites ([C*]) with kp (rate constant of propagation) = 31 (M s)?1 for ethylene polymerization. Addition of a comonomer, propylene of 4-methylpentene-1 (4-MP) significantly raised the ethylene polymerization activity. S –VCI3 catalyst has very small amounts of catalytically active vanadium for propylene polymerizations: [C] = 0.19% with kp,i = 857 (M s)?1 and [C] = 0.45% with kp,a = 23 (M s)?1 for isospecific and nonspecific sites, respectively. Addition of a conomer, ethylene or 4-MP. lowered the propylene polymerization activity. S –VCI3 is more easily reduced to the divalent ion by AIR3 than S –TiCl3. Methyl-p-toluate moderates the reducting power of AIR3; it increase the productivity and stereoselectivity of the S –YiCl3 catalyst, VCI3 supported on MgCl2 (CW–V catalyst) has enhanced rate constant of propylene polymerization but has the opposite effects on the S –TiCl3 Catalyst. VCI3 supported on MgCl2 (CW–V catalyst) has enhances rate constant of propylene polymerization but only a minute fraction of the supported vanadiums are catalytically active: [C] = 0.019% and kp,i = 1580 (Ms)?1, [C] = 0.057% and kp,i = 58 (M s)?1. This is compared with far greater number of catalytically active titanium sites in the TiCl3 supported on MgCl2 catalyst: [C] = 6% and kp,i = 200 (M s)?1, [C] = 6% and kp,a = 16(M s)?1. Therefore, both the S –VCI3 and CW–V catalysts are highly stereoselective but low in efficiency with respect to the utilization of the vanadium ion in the catalysis. 相似文献
8.
Norio Tsubokawa Yu Jian Yasuo Sone 《Journal of polymer science. Part A, Polymer chemistry》1988,26(10):2715-2724
The cationic ring-opening polymerization of oxepane was found to be initiated by carbon black having acylium perchlorate (CO+CIO) groups, which were introduced by the reaction of acyl chloride groups with silver perchlorate. It was confirmed that polyoxepane, i.e., poly(oxyhexamethylene), was propagated from CO+CIO groups on carbon black and effectively grafted on the surface. The rate of the polymerization and the percentage of grafting of poly(oxyhexamethylene) remarkably increased by the addition of epichlorohydrin (ECH) as a promoter: the percentage of grafting in the presence of ECH increased to about 100% with an increase in conversion. Furthermore, CO+CIO groups on carbon black have an ability to initiate the cationic ring-opening copolymerization of oxepane with ECH to give poly(oxepane-co-ECH) with various composition. The ring-opening copolymerization of oxepane with phthalic anhydride was also initiated by CO+CIO groups to give polyether ester, i.e., poly(hexamethylene phthalate) containing poly(oxyhexamethylene) sequence. In the copolymerization, polyether or polyether ester was effectively grafted from carbon black based on the propagation of these polymers from CO+CIO groups. 相似文献
9.
The electrosynthesis of polyparaphenylene films (PPP) by oxidation of benzene or biphenyl on a Pt electrode was studied in different organic media. Film formation was possible only if the solvent had acidic properties according to the Lewis concept, and if the water content of this medium was less than 5 × 10?2M. Addition of an excess of P2O5 or CuCl2 into the medium increased the acidity and improved the adherence and the homogeneity of the films considerably. PPP films were electroactive and conductive if the electrolysis was carried out in the presence of salts containing BF, SbF, PF anions; they were insulating with perchlorate salts. IR analysis of these polymers showed highly crosslinked structures and the chains were constituted of about 10 para coupled phenyl moieties. 相似文献
10.
Dan Chen Wei Lu Ganhong Du Liming Jiang Jun Ling Zhiquan Shen 《Journal of polymer science. Part A, Polymer chemistry》2012,50(20):4191-4197
A new kind of polymeric chemosensor containing chiral naphthaldimine moiety in the side chain was synthesized by the reversible addition‐fragmentation chain transfer polymerization of N‐{[2‐(4‐vinylbenzyloxy)‐1‐naphthyl]‐methylene}‐(S)‐2‐phenylglycinol (VNP). The resulting polymers (PVNP) showed high selectivity for hydrogen sulfate relative to other anions including F?, Cl?, Br?, H2PO, CH3CO, and NO in tetrahydrofuran (THF) solution as judged from UV?vis, fluorescence, and circular dichroism spectrophotometric titrations. Compared with its monomer, the polymer has proven to be more attractive for detection of HSO in terms of sensitivity and reproducibility. Upon addition of the anion it gives remarkable spectral responses concomitant with detectable color change from colorless to pale yellow. Furthermore, the HSO‐induced CD or fluorescence signal can be totally reversed with addition of base and eventually recovered the initial state, leading to a reproducible molecular switch with two distinguished “on” and “off” states. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
11.
Gorkem Yilmaz Selim Beyazit Yusuf Yagci 《Journal of polymer science. Part A, Polymer chemistry》2011,49(7):1591-1596
The free radical promoted cationic polymerization cyclohexene oxide (CHO), was achieved by visible light irradiation (λinc = 430–490 nm) of methylene chloride solutions containing thioxanthone‐fluorene carboxylic acid (TX‐FLCOOH) or thioxanthone‐carbazole (TX‐C) and cationic salts, such as diphenyliodonium hexafluorophosphate (Ph2I+PF) or silver hexafluorophosphate (Ag+PF) in the presence of hydrogen donors. A feasible initiation mechanism involves the photogeneration of ketyl radicals by hydrogen abstraction in the first step. Subsequent oxidation of ketyl radicals by the oxidizing salts yields Bronsted acids capable of initiating the polymerization of CHO. In agreement with the proposed mechanism, the polymerization was completely inhibited by 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy and di‐2,6‐di‐tert‐butylpyridine as radical and acid scavengers, respectively. Additionally polymerization efficiency was directly related to the reduction potential of the cationic salts, that is, Ag+PF (E = +0.8 V) was found to be more efficient than Ph2I+PF (E = ?0.2 V). In addition to CHO, vinyl monomers such as isobutyl vinyl ether and N‐vinyl carbazole, and a bisepoxide such as 3,4‐epoxycyclohexyl‐3′,4′‐epoxycyclohexene carboxylate, were polymerized in the presence of TX‐FLCOOH or TX‐C and iodonium salt with high efficiency. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
12.
Koji Ishizu Masataka Nunomura Takashi Fukutomi 《Journal of polymer science. Part A, Polymer chemistry》1987,25(4):1163-1175
Soluble microgels with several pendant vinyl groups were synthesised by radical copolymerization of methyl methacrylate (MMA) with p-divinyl benzene (p-DVB). The competitive reactions of intermolecular and intramolecular crosslinkings of these microgels were carried out at 40°C in the presence of 1-buten-3-ol as a degradative chain transfer agent. The rate constant of intermolecular crosslinking (k) was estimated by GPC (gel permeation chromatography) analysis on the polymer produced from intermolecular propagation between bimolecules. The k depended strongly on the internal structure of microgels. Network formation was discussd inclusive of informations for the rate constant of intramolecular crosslinking (k). 相似文献
13.
Makiko Seno Mizuki Maeda Tsuneyuki Sato 《Journal of polymer science. Part A, Polymer chemistry》2000,38(14):2572-2578
The effect of fullerene (C60) on the radical polymerization of vinyl acetate (VAc) with dimethyl 2,2′‐azobisisobutyrate (MAIB) in benzene was investigated kinetically and by means of ESR. C60 was found to act as an effective inhibitor in the present polymerization. All C60 molecules used were incorporated into poly(VAc) during polymerization. The relationship of induction period and initiation rate reveals that a C60 molecule can trap 15 radicals formed in the polymerization system. The polymerization rate (Rp) after the induction period is given by Rp = k [MAIB]0.6 [VAc]2.0 (60 °C), which is similar to that observed in the absence of C60. Stable fullerene radical (C) was observed in the polymerization system by ESR. The C concentration increased with time and was then saturated. The saturation time well corresponds to the induction period observed in the polymerization. About 20% of C60 molecules added could survive as stable C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2572–2578, 2000 相似文献
14.
Katherine B. Aubrecht Karen Chang Marc A. Hillmyer William B. Tolman 《Journal of polymer science. Part A, Polymer chemistry》2001,39(2):284-293
In quest of new, single‐site catalysts for cyclic ester polymerizations, a series of mononuclear yttrium(III) complexes of N,N′‐bis(trimethylsilyl)benzamidinate ([LTMS]−) and hindered N,N′‐bis‐(2,6‐dialkylaryl)toluamidinates ([LEt]−, aryl = Et2C6H3, and [LiPr]−, aryl = iPr2C6H3) were synthesized and characterized by X‐ray diffraction: LY(μ‐Cl)2Li(TMEDA) ( 1 ), LY(OC6H2tBu2Me) ( 2 ), LY(OC6H3Me2)2Li(THF)4 ( 3 ), LY(μ‐OtBu)2Li(THF) ( 4 ), LiPrY[N(SiMe2H)2]2(THF) ( 5 ), LY(THF)(Cl)(μ‐Cl)Li(THF)3 ( 6 ), and LY[N(SiMe2H)2] ( 7 ). Coordination numbers ranging from five to seven were observed, and they appeared to be controlled by the steric bulk of the supporting amidinate and alkoxide, phenoxide, or amide coligands. Complexes 2 – 5 and 7 are active catalysts for the polymerization of D,L ‐lactide (e.g., with 2 and added benzyl alcohol, 1000 equiv of D,L ‐lactide were polymerized at room temperature in less than 1 h, with polydispersities less than 1.5). The neutral complexes 2 , 5 , and 7 were more effective than the anionic complexes 3 and 4 . In addition, the presence of the more hindered amidinate ligands [LEt]− and [LiPr]− on yttrium‐amides slowed the polymerizations ( 7 < 5 < Y[N(SiMe2H)2]3). © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 284–293, 2001 相似文献
15.
Bin Luan Bao‐Qing Zhang Cai‐Yuan Pan 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):549-560
A well‐defined branched copolymer with PLLA‐b‐PS2 branches was prepared by combination of reversible addition‐fragmentation transfer (RAFT) polymerization, ring‐opening polymerization (ROP), and atom transfer radical polymerization (ATRP). The RAFT copolymerization of methyl acrylate (MA) and hydroxyethyl acrylate (HEA) yielded poly(MA‐co‐HEA), which was used as macro initiator in the successive ROP polymerization of LLA. After divergent reaction of poly(MA‐co‐HEA)‐g‐PLLAOH with divergent agent, the macro initiator, poly(MA‐co‐HEA)‐g‐PLLABr2 was formed in high conversion. The following ATRP of styrene (St) produced the target polymer, poly(MA‐co‐HEA)‐g‐(PLLA‐b‐PS2). The structures, molecular weight, and molecular weight distribution of the intermediates and the target polymers obtained from every step were confirmed by their 1H NMR and GPC measurements. DSC results show one T = 3 °C for the poly(MA‐co‐HEA), T = ?5 °C, T= 122 °C, and T = 157 °C for the branched copolymers (poly(MA‐co‐HEA)‐g‐PLLA), and T = 51 °C, T = 116 °C, and T = 162 °C for poly(MA‐co‐HEA)‐g‐(PLLA‐b‐PS2). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 549–560, 2006 相似文献
16.
Se Geun Lee Jae Pil Kim Ick Chan Kwon Ki Hong Park Seok Kyun Noh Sung Soo Han Won Seok Lyoo 《Journal of polymer science. Part A, Polymer chemistry》2006,44(11):3567-3576
Poly(vinyl alcohol) (PVA)/poly(vinyl acetate) (PVAc) microspheres with a skin/core structure were prepared through the heterogeneous surface saponification of PVAc microspheres suspension‐polymerized. The PVA skin formed through the heterogeneous saponification was hydrogel swellable in water. In addition, to obtain monodisperse PVA/PVAc microspheres having various skin/core ratios and morphologies, the ion‐specificities to the heterogeneous saponification were investigated using SO, Cl?, NO, Br?, and I? for anions and Li+, Na+, and K+ for cations, respectively. The ions were not specific significantly to the rate of the heterogeneous saponification, while were related to the degree of saponification (DS). DSs had different values between by weight loss (DSw) and by proton nuclear magnetic resonance spectroscopy (DSNMR) measurements. The order of DSws was SO < Cl? < NO < Br? < I? for anions and K+ < Na+ < Li+ for cations, and that of DSNMRs, I? < Br? < NO < Cl? < SO for anions and Li+ < Na+ < K+ for cations. The differences in values between DSws and DSNMRs were caused by the dissolution of PVA skin and were significantly decreased for SO. The peaks at melting temperature of PVA were sharp and their areas were large for ions deswelling PVA skins. 相似文献
17.
James C. W. Chien Chi-I. Kuo 《Journal of polymer science. Part A, Polymer chemistry》1986,24(11):2707-2727
The effect of H2 on propylene polymerization initiated by a MgCl2/EB/PC/AlEt3/TiCl4–3 AlEt3/MPT catalyst was studied. Hydrogen increases significantly the initial rate during the early stage of the polymerization to give a higher yield of polymer than reactions without H2. But H2 reduces the yield toward the latter stages so that the net effect on the total yield can be quite small. There is no appreciable effect of H2 on either the isotacticity index or polydispersity of the products. It decreases molecular weight proportional to (pH2)1/2. The chain transfer by H2 resulted in a decrease of total metal polymer bond concentration with time of polymerization. The rate constants of hydrogen chain transfer for the two kinds of isospecific and nonspecific sites are = 5.1 × 10?3, = 2.7 × 10?3, = 7.5 × 10?3, = 4.4 × 10?3, in units of torr1/2 sec?1 at 50°. Hydrogen assists in the deactivation of the catalytic sites as does propylene; rates of the former and the latter vary with (pH2)1/2 and [C3H6]1/2, respectively, with k = (12.1 ± 0.9) M?1 torr?1/2 sec?1 and k = (65.3 ± 3.3) M?3/2 sec?1 at 50° and A/T = 167. The mechanism for deactivation of catalytic sites are discussed. 相似文献
18.
James C. W. Chien Tsunle Ang 《Journal of polymer science. Part A, Polymer chemistry》1987,25(3):919-934
Decene-l was polymerized with the MgCl2/ethylebenzoate/p-cresol/AIEt3/TiCl4-AlEt3/methyl-p-toluate catalyst at 50° using an A/T ratio of 167 and a range of monomer concentration. The concentration of the two kinds of active sites are [Ti] = 12% and [Ti] = 4% of the total titanium. The rate constants of propagation are 24 M?1 s?1. Chain transfers to AIEt3, monomer, and by β-hydride elimination have rate constant values of 1.7 × 10?3 M?1 s?1, 1.34 × 10?2 M?1 s?1, and 1.7 × 10?2 s?1, respectively. Poly(decene-l) have relatively narrow MW which are unchanged during the course of a polymerization. Therefore, the active site concentrations in the CW catalyst for propylene and decene polymerization are identical and their rate constant values agree within a factor of 2. However, the rate of decene polymerization depends on fractional order of monomer concentration and decreases with the increase of activator concentration. Furthermore, the formation of metal polymer bonds has a rate independent of these concentrations. These kinetic behaviors are a manifestation of absorption processes of these species which are not seen in propylene polymerizations. 相似文献
19.
Yeong‐Tarng Shieh Show‐An Chen 《Journal of polymer science. Part A, Polymer chemistry》1999,37(4):483-492
Cationic polymerizations of trioxane in 1,2‐ethylene dichloride and benzene were heterogeneous and reversible. Phase separation accompanying with crystallization occurred during the polymerization. Three morphological changes were found in the course of the polymerization as were investigated by dilatometry and precipitation method. Based on the findings of morphological changes and three reversible processes for the polymerization, a rate equation was proposed to describe the polymerization. The proposed rate equation was fairly good in describing the experimental data, and kinetics constants including Kp, Kd, Kp′, Kd′, M, M, and Kdis/Kcr for the polymerization at 30, 40, and 50°C in 1,2‐ethylene dichloride and benzene were obtained. Factors that affected the kinetics constants were discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 483–492, 1999 相似文献
20.
Li‐Ming Huang Guo Cheng Huang Ten‐Chin Wen 《Journal of polymer science. Part A, Polymer chemistry》2006,44(22):6624-6632
Poly(2,5‐dimethoxyaniline) (PDMA)–Ag composites were successfully obtained through the oxidative polymerization of 2,5‐dimethoxyaniline in poly(styrene sulfonic acid) with CH3SO3Ag and AgNO3 as oxidants. In situ ultraviolet–visible spectroscopy results showed that the growth rate of PDMA was strongly affected by CH3SO and NO. The coupling reaction of PDMA and NO was proposed to explain the lower growth rate of PDMA with AgNO3 as the oxidant in comparison with CH3SO3Ag. X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to validate the proposed coupling reaction through the monitoring of the side products and oxidized state of PDMA. The results showed that there were more side products and lower oxidized states for the composite structure in the presence of NO than in the presence of CH3SO, and this agreed with the proposal. Transmission electron microscopy showed that the Ag nanoparticles had almost the same size, regardless of the anions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6624–6632, 2006 相似文献