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1.
Vishal Sipani Alec B. Scranton 《Journal of polymer science. Part A, Polymer chemistry》2003,41(13):2064-2072
We have characterized the effective rate constants for termination/trapping (kt/t) and propagation (kp) for solvent‐free cationic photopolymerizations of phenyl glycidyl ether for conversions up to 50%. We have performed dark‐cure experiments in which active centers are produced photochemically for a specified period of time until the initiating light is shuttered off, and then the polymerization rate is monitored in the dark. This method is especially well suited for characterizing cationic polymerizations because of the long active center lifetimes. Our analysis provides profiles of the instantaneous kinetic rate constants as functions of conversion (or time). For photopolymerizations of phenyl glycidyl ether initiated with iodonium photoinitiators, kt/t and kp remain essentially invariant for conversions up to 50%. For the photoinitiator (tolycumyl) iodonium tetrakis (pentafluorophenyl) borate (IPB), the values of kt/t at 50 and 60 °C are 0.027 and 0.033 min?1, respectively. The corresponding values of kt/t for diaryliodonium hexafluoroantimonate (IHA) are 0.041 and 0.068 min?1. The values of kp at 50 °C for IPB and IHA are 0.6 and 0.4 L mol?1 s?1, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2064–2072, 2003 相似文献
2.
Tsuneyuki Sato Shin‐Ichi Tada Makiko Seno Tomohiro Hirano 《Journal of polymer science. Part A, Polymer chemistry》2000,38(22):4137-4146
The polymerization of α‐N‐(α′‐methylbenzyl) β‐ethyl itaconamate derived from racemic α‐methylbenzylamine (RS‐MBEI) by initiation with dimethyl 2,2′‐azobisisobutyrate (MAIB) was studied in methanol kinetically and with ESR spectroscopy. The overall activation energy of polymerization was calculated to be 47 kJ/mol, a very low value. The polymerization rate (Rp ) at 60 °C was expressed by Rp = k[MAIB]0.5±0.05[RS‐MBEI]2.9±0.1. The rate constants of propagation (kp ) and termination (kt ) were determined by ESR. kp was very low, ranging from 0.3 to 0.8 L/mol s, and increased with the monomer concentration, whereas kt (4–17 × l04 L/mol s) decreased with the monomer concentration. Such behaviors of kp and kt were responsible for the high dependence of Rp on the monomer concentration. Rp depended considerably on the solvent used. S‐MBEI, derived from (S)‐α‐methylbenzylamine, showed somewhat lower homopolymerizability than RS‐MBEI. The kp value of RS‐MBEI at 60 °C in benzene was 1.5 times that of S‐MBEI. This was explicable in terms of the different molecular associations of RS‐MBEI and S‐MBEI, as analyzed by 1H NMR. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4137–4146, 2000 相似文献
3.
Ewa Andrzejewska Mariusz B. Bogacki Maciej Andrzejewski 《Macromolecular theory and simulations》2001,10(9):842-849
This work was aimed at studying variations in the termination mechanism occurring during the after‐effects of a light‐induced polymerization of a dimethacrylate monomer after the irradiation had been discontinued. The experimental method was based on differential scanning calorimetry. The initiation was stopped at various moments of the reaction corresponding to different degrees of double‐bond conversion (starting conversions). Three termination models: monomolecular, bimolecular, and mixed were used to calculate the ratio of the bimolecular termination and propagation rate coefficients ktb/kp and/or the monomolecular termination rate coefficient ktm. The models were determined over short time intervals (conversion increments) of the dark reaction giving different values of rate coefficients for each time interval (interval approximation method). Two‐stage statistical analysis was used to find the model that best reproduced the experimental data obtained for each conversion increment. This enabled variations in the termination mechanism during the after‐effects to be followed. It was found that the termination mechanism changed with the time of the dark reaction from the bimolecular reaction to the mixed reaction when the light was cut off at low and medium double‐bond conversions. At higher starting conversions a monomolecular termination mechanism dominated from the beginning of the dark reaction. The mixed termination model was the only model to describe correctly the variations of rate coefficients in the dark, i. e., the increase in ktm and the decreasein the ktb/kp ratio. 相似文献
4.
Thomas Junkers Lin Zang Edgar H.H. Wong Nico Dingenouts Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2011,49(22):4841-4850
The preparation of ABA‐type block copolymers via tandem enhanced spin capturing polymerization (ESCP) and nitroxide‐mediated polymerization (NMP) processes is explored in‐depth. Midchain alkoxyamine functional polystyrenes (Mn = 6200, 12,500 and 19,900 g mol?1) were chain extended with styrene as well as tert‐butyl acrylate at elevated temperature NMP conditions (T = 110 °C) generating a tandem ESCP‐NMP sequence. Although the chain extensions and thus the block copolymer formation processes function well (yielding in the case of the chain extension with styrene number average molecular weights of up to 20,800 g mol?1 (PDI = 1.22) when the 6200 g mol?1 precursor is used and up to 67,500 g mol?1 (PDI = 1.36) when the 19,900 g mol?1 precursor is used and 21,600 g mol?1 (PDI = 1.17) as well as 37,100 g mol?1 (PDI = 1.21) for the tert‐butyl acrylate chain extensions for the 6200 and 12,500 g mol?1 precursors, respectively), it is also evident that the efficiency of the block copolymer formation process decreases with an increasing chain length of the ESCP precursor macromolecules (i.e., for the 19,900 g mol?1 ESCP precursor no efficient chain extension with tert‐butyl acrylate can be observed). For the polystyrene‐block‐tert‐butyl acrylate‐block‐polystyrene polymers, the molecular weights were determined via triple detection SEC using light scattering and small‐angle X‐ray scattering. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011. 相似文献
5.
Tsuneyuki Sato Masahiko Hashimoto Makiko Seno Tomohiro Hirano 《Journal of polymer science. Part A, Polymer chemistry》2003,41(12):1819-1830
The polymerizations of α‐ethyl β‐N‐(α′‐methylbenzyl)itaconamates carrying (RS)‐ and (S)‐α‐methylbenzylaminocarbonyl groups (RS‐EMBI and S‐EMBI) with dimethyl 2,2′‐azobisisobutyrate (MAIB) were studied in methanol (MeOH) and in benzene kinetically and with electron spin resonance (ESR) spectroscopy. The initial polymerization rate (Rp) at 60 °C was given by Rp = k[MAIB]0.58 ± 0.05[RS‐EMBI]2.4 ± 0.l and Rp = k[MAIB]0.61 ± 0.05[S‐EMBI]2.3 ± 0.l in MeOH and Rp = k[MAIB]0.54 ± 0.05[RS‐EMBI]1.7 ± 0.l in benzene. The rate constants of initiation (kdf), propagation (kp), and termination (kt) as elementary reactions were estimated by ESR, where kd is the rate constant of MAIB decomposition and f is the initiator efficiency. The kp values of RS‐EMBI (0.50–1.27 L/mol s) and S‐EMBI (0.42–1.32 L/mol s) in MeOH increased with increasing monomer concentrations, whereas the kt values (0.20?7.78 × 105 L/mol s for RS‐EMBI and 0.18?6.27 × 105 L/mol s for S‐EMBI) decreased with increasing monomer concentrations. Such relations of Rp with kp and kt were responsible for the unusually high dependence of Rp on the monomer concentration. The activation energies of the elementary reactions were also determined from the values of kdf, kp, and kt at different temperatures. Rp and kp of RS‐EMBI and S‐EMBI in benzene were considerably higher than those in MeOH. Rp of RS‐EMBI was somewhat higher than that of S‐EMBI in both MeOH and benzene. Such effects of the kinds of solvents and monomers on Rp were explicable in terms of the different monomer associations, as analyzed by 1H NMR. The copolymerization of RS‐EMBI with styrene was examined at 60 °C in benzene. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1819–1830, 2003 相似文献
6.
Donor property of cobalt(II) Schiff base complexes toward triphenyltin(IV)‐chloride: A kinetic study
In this study, some cobalt(II)tetraaza Schiff base complexes were used as donors in coordinating to triphenyltin(IV)chloride as acceptors; the kinetics and mechanism of the adduct formation were studied spectrophotometrically. Co(II)tetraaza Schiff base complexes used were [Co(amaen)][N,N′‐ethylene‐bis‐(o‐amino‐α‐methylbenzylideneiminato)cobalt(II)] ( 1 ), [Co(appn)] [N,N′‐1,2‐propylene‐bis‐(o‐amino‐α‐phenylbenzylideneiminato)cobalt(II)] ( 2 ), [Co(ampen)] [N,N′‐ethylene‐bis‐(o‐amino‐α‐phenylbenzylideneiminato)cobalt‐(II)] ( 3 ), [Co(cappn)][N,N′‐1,2‐proylene‐bis‐(5‐chloro‐o‐amino‐α‐phenylbenzylideneiminato)cobalt(II)] ( 4 ), and [Co(campen)] [N,N′‐ethylene‐bis‐(5‐chloro‐o‐amino‐α‐phenylbenzylid‐eneiminato)cobalt(II)] ( 5 ). The reactivity trend of the complexes in interaction with triphenyltin(IV)chloride was Co(amaen) > Co(appn) > Co(ampen) > Co(cappn) > Co(campen). The linear plots of kobs versus the molar concentration of the triphenyltin(IV)chloride, a high span of the second‐order rate constant k2 values, and large negative values of ΔS≠ and low ΔH≠ values suggest an associative (A) mechanism for the acceptor–donor adduct formation. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 635–640, 2012 相似文献
7.
Renate Gessmann Hans Brückner Kyriacos Petratos 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(11):1046-1049
The title achiral peptide N‐benzyloxycarbonyl‐α‐aminoisobutyryl‐α‐aminoisobutyryl‐α‐aminoisobutyrylglycine tert‐butyl ester or Z‐Aib‐Aib‐Aib‐Gly‐OtBu (Aib is α‐aminoisobutyric acid, Z is benzyloxycarbonyl, Gly is glycine and OtBu indicates the tert‐butyl ester), C26H40N4O7, is partly hydrated (0.075H2O) and has two different conformations which together constitute the asymmetric unit. Both molecules form incipient 310‐helices. They differ in the relative orientation of the N‐terminal protection group and at the C‐terminus. There are two 4→1 intramolecular hydrogen bonds. 相似文献
8.
Yongjun Li Sen Zhang Hao Liu Qingnuan Li Wenxin Li Xiaoyu Huang 《Journal of polymer science. Part A, Polymer chemistry》2010,48(23):5419-5429
A series of perfluorocyclobutyl (PFCB) aryl ether‐based amphiphilic diblock copolymers containing hydrophilic poly(acrylic acid) (PAA) and fluorophilic poly(p‐(2‐(p‐tolyloxy)perfluorocyclobutoxy)phenyl methacrylate) segments were synthesized via successive atom transfer radical polymerization (ATRP). 2‐MBP‐initiated and CuBr/N,N,N′,N′,N″‐pentamethyldiethylenetriamine‐catalyzed ATRP homopolymerization of the PFCB‐containing methacrylate monomer, p‐(2‐(p‐tolyloxy)perfluorocyclobutoxy)phenyl methacrylate, can be performed in a controlled mode as confirmed by the fact that the number‐average molecular weights (Mn) increased linearly with the conversions of the monomer while the polydispersity indices kept below 1.38. The block copolymers with narrow molecular weight distributions (Mw/Mn ≤ 1.36) were synthesized by ATRP using Br‐end‐functionalized poly(tert‐butyl acrylate) (PtBA) as macroinitiator followed by the acidolysis of hydrophobic PtBA block into hydrophilic PAA segment. The critical micelle concentrations of the amphiphilic diblock copolymers in different surroundings were determined by fluorescence spectroscopy using N‐phenyl‐1‐naphthylamine as probe. The morphology and size of the micelles were investigated by transmission electron microscopy and dynamic laser light scattering, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
9.
Yukihiko Tomioka Chie Nagahiro Yumiko Nomura Hiroshi Maruoka 《Journal of heterocyclic chemistry》2003,40(1):121-127
Arylnitroso compounds 1–3 easily reacted with dimethyl bromomalonate to give the corresponding N‐aryl‐C,C‐dimethoxycarbonylnitrones ( 4–6 ). Treatment of C,C‐dimethoxycarbonyl‐N‐( 1‐naphthyl)nitrone ( 4 ) with acetylene compounds (dimethyl acetylenedicarboxylate, methyl 2‐butynoate or ethyl phenylpropiolate) caused 1,3‐dipolar cycloaddition to furnish the corresponding 1H‐benz[g]indolines ( 7a‐c ). In a similar manner, the reactions of nitrones 5 and 6 with acetylene compounds afforded the corresponding indolines 9a‐c and 11a‐c together with 4‐oxazolines 13a‐c and 14a‐c . 相似文献
10.
The kinetics and mechanism of the adduct formation of diorganotin(IV)dichlorides with Co(II) tetraaza Schiff base complexes, such as [Co(ampen)] {[N,N′‐ethylenebis‐(o‐amino‐α‐phenylbenzylideneiminato)cobalt(II)]}, [Co(campen)] {[N,N′‐ethylenebis‐(5‐chloro‐o‐amino‐α‐phenylbenzylideneiminato)cobalt(II)]}, and [Co(amaen)] {[N,N′‐ethylenebis‐(o‐amino‐α‐methylbenzylideneiminato)cobalt(II)]}, were studied spectrophotometrically. The kinetic parameters and the rate constant values show the following acceptor tendency trend for the diorganotin(IV)dichlorides: Ph2SnCl2> Me2SnCl2> Bu2SnCl2. Adducts have been separately synthesized and fully characterized by 119SnNMR, IR, UV–vis spectra, and elemental microanalysis (C,H,N) methods. The trend of the rate constants for the adduct formation of the cobalt complexes with a given tin acceptor decreases as follow: Co(amaen) > Co(ampen) > Co(campen). The linear plots of kobs vs. the molar concentration of the diorganotin(IV)dichlorides, the high span of the second‐order rate constant k2 values, and the large negative values of AS≠ suggest an associative (A) mechanism for the acceptor–donor adduct formation. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 499–507, 2010 相似文献
11.
Matthew I. Gibson Neil R. Cameron 《Journal of polymer science. Part A, Polymer chemistry》2009,47(11):2882-2891
It is demonstrated here that three different α‐amino N‐carboxyanhydrides (NCAs), including for the first time O‐benzyl‐L ‐threonine NCA, can be polymerized in a controlled/“living” fashion without the need for transition metal catalysts or complex custom‐made glassware. Homopolymerizations in tetrahydrofuran gave monomodal distributions, high conversions, predictable Mn values and displayed first‐order kinetics. Chain extension experiments from poly(benzyl‐L ‐threonine), using N,N‐dimethylacetamide to avoid the formation of insoluble β‐sheets, was used to create a range of block copolypeptides of controlled structure. Monomodal molecular weight distributions are observed throughout and molecular weights agree well with predicted values, although polydispersities are generally higher than those observed using more experimentally challenging techniques. This method therefore represents a practical approach to the synthesis of well‐defined polypeptides without the requirement for specialized glassware or glove‐box techniques. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2882–2891, 2009 相似文献
12.
Ugo Chiacchio Filippo Genovese Vito Librando Antonio Rescifina Antonio Procopio 《Tetrahedron》2004,60(2):441-448
A new class of homo-N,O-nucleosides has been designed, based on the 1,3-dipolar cycloaddition of C-substituted nitrones with allyl nucleobases. The N-methyl-C-ethoxycarbonyl nitrone 1, and the C-α-silyloxymethyl-N-methyl nitrone 7 have been exploited: the stereochemical features of the obtained nucleosides are dependent on the nature of the dipole. The results obtained with DFT calculations fully agree with the experimental results and successfully reproduce the experimentally observed reversal of endo/exo selectivity for nitrones 1 and 7. 相似文献
13.
Wei Ding Chongfu Lv Ying Sun Xiaojun Liu Tao Yu Guangmiao Qu Huoxin Luan 《Journal of polymer science. Part A, Polymer chemistry》2011,49(2):432-440
The Cu0‐mediated single electron transfer‐living radical polymerization of acrylamide and N,N‐dimethyl‐N‐methacryloyloxyethyl‐N‐sulfobutyl ammonium in aqueous at 25 °C using 2‐chloropropionamide as initiator with Cu0 powder/tris‐(2‐dimethylamino ethyl)amine (Me6‐TREN) as catalyst system is studied. The results showed the characteristic of the “living” polymerization that were the Mn of polymers increased linearly with monomer conversion and the ln([M]0/[M]) increased linearly with time too, meanwhile the narrow molecular of weight distributions were found at most cases. Because of the high rate constant of propagation and bimolecular termination of the acrylamide, the external addition of CuCl2 is required to mediate deactivation the early stage of polymerization. In addition, the disproportionation constant of CuIX/L in H2O is higher than in other solvents and the coordination of amino group and CuII takes place easily, so the isopropanol or N,N‐dimethylformamide is added to control the polymerization. High conversions were achieved within short time and the polymers prepared showed good antipolyelectrolyte properties in inorganic salts solutions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
14.
Anna Gawlicka‐Chruszcz Katarzyna Stadnicka 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(7):o416-o420
Three crystal structures have been analysed from the point of view of intermolecular interactions: N,N′‐diphenyl‐1,4‐benzoquinone diimine, C18H14N2, (I), its reduced form N,N′‐diphenyl‐1,4‐phenylenediamine, C18H16N2, (II), and N,N′‐diphenyl‐1,4‐phenylenediammonium bis(p‐toluenesulfonate), C18H18N22+·2C7H7O3S?, (III), which contains fully protonated (II) with p‐toluenesulfonic acid. The local molecular Ci symmetry is preserved in all three structures and the packing seems to be dominated by the mutual arrangement of the simple polyaniline oligomers in the different protonation states. In (I), the most significant molecular interactions are stacking forces, forming columns of molecules along [001]. Close packing of the columns results in C‐centring of the structure. In (II), only van der Waals interactions can be observed. In the structure of (III), the p‐toluenesulfonate ions serve as acceptors in relatively strong N—H?O hydrogen bonds. The N,N′‐diphenyl‐1,4‐phenylenediammonium cation intercalates between two anions related by a centre of symmetry. 相似文献
15.
Yusuke Sugihara Padraig O'connor Per B. Zetterlund Fawaz Aldabbagh 《Journal of polymer science. Part A, Polymer chemistry》2011,49(8):1856-1864
Chain transfer to solvent has been investigated in the conventional radical polymerization and nitroxide‐mediated radical polymerization (NMP) of N‐isopropylacrylamide (NIPAM) in N,N‐dimethylformamide (DMF) at 120 °C. The extent of chain transfer to DMF can significantly impact the maximum attainable molecular weight in both systems. Based on a theoretical treatment, it has been shown that the same value of chain transfer to solvent constant, Ctr,S, in DMF at 120 °C (within experimental error) can account for experimental molecular weight data for both conventional radical polymerization and NMP under conditions where chain transfer to solvent is a significant end‐forming event. In NMP (and other controlled/living radical polymerization systems), chain transfer to solvent is manifested as the number‐average molecular weight (Mn) going through a maximum value with increasing monomer conversion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
16.
Pavel Buzin Gert Schwarz Hans R. Kricheldorf 《Journal of polymer science. Part A, Polymer chemistry》2008,46(14):4777-4784
Acidic bismuth salts, such as BiCl3, BiBr3, BiJ3, and Bi‐triflate catalyzed the ring‐opening polymerization of 2‐methoxazoline (MOZ) in bulk at 100 °C, whereas less acidic salts such as Bi2O3 or Bi(III)acetate did not. Bi‐triflate‐catalyzed polymerizations of 2‐ethyloxazoline (EtOZ) were performed with variation of the monomer–catalyst ratio (M/C). It was found that the molecular weights were independent of the M/C ratio. The formation of cationic chain ends and the absence of cycles was proven by reactions of virgin polymerization products with N,N‐dimethyl‐4‐aminopyridine or triphenylphosphine. The resulting polymers having modified cationic chain ends were characterized by 1H NMR spectroscopy and MALDI‐TOF mass spectrometry. The polymerization mechanism including chain‐transfer reactions is discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4777–4784, 2008 相似文献
17.
Christophe Detrembleur Jean‐Louis Clément Valérie Sciannaméa Christine Jérôme Jean‐Marie Catala Didier Gigmes Laurent Autissier Edith Botek Natalia Zarycz Benoît Champagne 《Journal of polymer science. Part A, Polymer chemistry》2013,51(8):1786-1795
The styrene polymerization initiated by benzoyl peroxide (BPO) in the presence of N‐tert‐butyl‐α‐isopropylnitrone as nitroxide precursor is well‐controlled provided that a prereaction between the nitrone and BPO is carried out in suitable conditions prior to polymerization at a higher temperature. Electron spin resonance (ESR) spectroscopy was implemented to probe the nitroxides formed during both steps, that is, the prereaction and polymerization, and to get crucial information regarding the structure of the nitroxides responsible for the polymerization control. ESR studies combined with first principles calculations have evidenced that nitroxides observed during the prereaction in the presence of styrene and during the polymerization steps consist of a mixture of two macronitroxides. One is formed by the addition of a growing polystyrene chain to the nitrone as would be expected. However, the second one results from the addition of a polystyrene chain to tert‐butyl nitroso that is in situ formed presumably by decomposition of the first macronitroxide type. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
18.
Shobu Hiraoka Tsutomu Matsumoto Koki Matsuzaka Takaaki Sato Noritaka Chida 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(13):4425-4429
An approach to cyclic nitrones from N‐hydroxylactam derivatives is documented. The nucleophilic addition of an organolithium reagent to an N‐OSEM [SEM=2‐(trimethylsilyl)ethoxymethyl] lactam forms a five‐membered chelated intermediate, which undergoes both elimination and deprotection to give a fully substituted nitrone in a one‐pot process. When combined with the N‐oxidation of easily available chiral lactams, this method becomes especially useful for the quick synthesis of chiral nitrones in enantio‐pure form, enabling the concise total synthesis of cylindricine C. 相似文献
19.
Charles U. Pittman Hookun Lee 《Journal of polymer science. Part A, Polymer chemistry》2003,41(12):1759-1777
β‐Methyl‐α‐methylene‐γ‐butyrolactone (MMBL) was synthesized and then was polymerized in an N,N‐dimethylformamide (DMF) solution with 2,2‐azobisisobutyronitrile (AIBN) initiation. The homopolymer of MMBL was soluble in DMF and acetonitrile. MMBL was homopolymerized without competing depolymerization from 50 to 70 °C. The rate of polymerization (Rp) for MMBL followed the kinetic expression Rp = [AIBN]0.54[MMBL]1.04. The overall activation energy was calculated to be 86.9 kJ/mol, kp/kt1/2 was equal to 0.050 (where kp is the rate constant for propagation and kt is the rate constant for termination), and the rate of initiation was 2.17 × 10?8 mol L?1 s?1. The free energy of activation, the activation enthalpy, and the activation entropy were 106.0, 84.1, and 0.0658 kJ mol?1, respectively, for homopolymerization. The initiation efficiency was approximately 1. Styrene and MMBL were copolymerized in DMF solutions at 60 °C with AIBN as the initiator. The reactivity ratios (r1 = 0.22 and r2 = 0.73) for this copolymerization were calculated with the Kelen–Tudos method. The general reactivity parameter Q and the polarity parameter e for MMBL were calculated to be 1.54 and 0.55, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1759–1777, 2003 相似文献
20.
Toshiaki Taniike Binh Tien Nguyen Shougo Takahashi Thang Quoc Vu Mitsuhiro Ikeya Minoru Terano 《Journal of polymer science. Part A, Polymer chemistry》2011,49(18):4005-4012
We have kinetically elucidated the origins of activity enhancement because of the addition of comonomer in Ziegler‐Natta propylene polymerization, using stopped‐flow and continuously purged polymerization. Stopped‐flow polymerization (with the polymerization time of 0.1–0.2 s) enabled us to neglect contributions of physical phenomena to the activity, such as catalyst fragmentation and reagent diffusion through produced polymer. The propagation rate constant kp and active‐site concentration [C*] were compared between homopolymerization and copolymerization in the absence of physical effects. kp for propylene was increased by 30% because of the addition of a small amount of ethylene, whereas [C*] was constant. On the contrary, both kp (for propylene) and [C*] remained unchanged by the addition of 1‐hexene. Thus, only ethylene could chemically activate propylene polymerization. However, continuously purged polymerization for 30 s resulted in much more significant activation by the addition of comonomer, clearly indicating that the activation phenomenon mainly arises from the physical effects. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献