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1.
Christopher Barner‐Kowollik Johan P. A. Heuts Thomas P. Davis 《Journal of polymer science. Part A, Polymer chemistry》2001,39(5):656-664
The free‐radical copolymerization of itaconic acid (IA) and styrene in solutions of dimethylformamide and d6‐dimethyl sulfoxide (50 wt %) has been studied by 1H NMR kinetic experiments. Monomer conversion versus time data were used to estimate the ratio kp · kt−0.5 for various comonomer mixture compositions. The ratio kp · kt−0.5 varies from 5.2 · 10−2 for pure styrene to 2.0 · 10−2 mol0.5 L−0.5 s−0.5 for pure IA, indicating a significant decrease in the rate of polymerization. Individual monomer conversion versus time traces were used to map out the comonomer mixture–composition drift up to overall monomer conversions of 60%. Within this conversion range, a slight but significant depletion of styrene in the monomer feed can be observed. This depletion becomes more pronounced at higher levels of IA in the initial comonomer mixture. The kinetic information is supplemented by molecular weight data for IA/styrene copolymers obtained by variation of the comonomer mixture composition. A significant decrease in molecular weight of a factor of 2 can be observed when increasing the mole fraction of IA in the initial reaction mixture from 0 to 0.5. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 656–664, 2001 相似文献
2.
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
3.
Leonie Barner Senake Perera Sam Sandanayake Thomas P. Davis 《Journal of polymer science. Part A, Polymer chemistry》2006,44(2):857-864
The γ‐initiated reversible addition–fragmentation chain transfer mediated free‐radical graft copolymerization of styrene and m‐isopropenyl‐α,α′‐dimethylbenzyl isocyanate (TMI) from a polypropylene (PP) solid phase was performed with cumyl phenyldithioacetate (CPDA) as the chain‐transfer agent. The initial CPDA concentration was 8 × 10?3 mol L?1. Polymerizations were performed with a dose rate of 0.18 kGy h?1 at the ambient temperature. Initial comonomer mixtures with 15, 30, and 50 mol % TMI were used. Depending on the amount of TMI in the initial comonomer mixture, the plot of the grafting ratio versus the time showed two grafting regimes (for 15 and 50 mol % TMI) or one (for 30 mol % TMI). Scavenger lanterns with 15 and 50 mol % TMI featured two isocyanate loading regimes, the second with higher loading capacities. The scavenger lanterns with 30 mol % TMI showed a linear loading capacity over the full grafting ratio. A maximum loading capacity of 110 μmol per scavenger lantern was achieved with 50 mol % TMI at a grafting ratio of approximately 60 wt %. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 857–864, 2006 相似文献
4.
Wannida Apisuk Naohiro Suzuki Hyun Joon Kim Dong Hyun Kim Boonyarach Kitiyanan Kotohiro Nomura 《Journal of polymer science. Part A, Polymer chemistry》2013,51(12):2565-2574
Aryloxo‐modified half‐titanocenes, Cp′TiCl2(O‐2,6‐iPr2C6H3) [Cp′ = Cp* ( 1 ), tBuC5H4 ( 2 )], catalyze terpolymerization of ethylene and styrene with α‐olefin (1‐hexene and 1‐decene) efficiently in the presence of cocatalyst, affording high‐molecular‐weight polymers with unimodal distributions (compositions). Efficient comonomer incorporations have been achieved by these catalysts. The content of each comonomer (α‐olefin, styrene, etc.) could be controlled by varying the comonomer concentration charged, and resonances ascribed to styrene and α‐olefin repeated insertion were negligible. The terpolymerization with p‐methylstyrene (p‐MS) in place of styrene also proceeded in the presence of [PhN(H)Me2][B(C6F5)4] and AliBu3 cocatalyst, and p‐MS was incorporated in an efficient matter, affording high‐molecular‐weight polymers with uniform molecular weight distributions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2565–2574 相似文献
5.
Hongxia Feng Mohamad Al‐Sheikhly Joseph Silverman Douglas E. Weiss Pedatsur Neta 《Journal of polymer science. Part A, Polymer chemistry》2003,41(1):196-203
The bulk polymerization of 2‐ethylhexyl acrylate (2‐EHA), induced by a pulsed electron beam, was investigated with pulse radiolysis, gravimetry, and Fourier transform infrared spectroscopy. The roles of the dose rate, pulse frequency, and added acrylic acid (AA) in the polymerization of 2‐EHA were examined at ambient temperature. In the range of 12.6–71.2 Gy/pulse, the polymerization of 2‐EHA was dose‐rate‐dependent: at the same total dose, a lower dose rate yielded a higher conversion. Also, a lower pulse rate gave a higher conversion at the same total dose. The addition of up to 10 wt % AA showed no increase in the conversion of 2‐EHA at a low conversion (8 kGy), but at a higher conversion (16 kGy), a 20 wt % increase in the conversion of 2‐EHA was observed. The estimated values (1.6 ± 0.3) × 10?3 (dm3 s)3/2 mol?1 s?1/2 for kp(G/2kt)1/2 and 2.6 ± 0.8 dm3 s J?1 for 2ktG (where kp is the rate constant of propagation, kt is the rate constant of bimolecular termination, and G is the yield of free radicals) were obtained at relatively low conversions. The reaction rate constant of the addition of 2‐EHA· free radicals to the monomer was measured by pulse radiolysis and found to be 2.8 × 102 mol?1 dm3 s?1. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 196–203, 2003 相似文献
6.
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
7.
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
8.
Nathalie Charton Achim Feldermann Alexander Theis Martina H. Stenzel Thomas P. Davis Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2004,42(20):5170-5179
An Erratum has been published for this article in J. Polym. Sci. Part A: Polym. Chem. (2004) 42(21) 5559 . The initiator efficiency, f, of 2,2′‐azobis(isobutyronitrile) (AIBN) in dodecyl acrylate (DA) bulk free‐radical polymerizations has been determined over a wide range of monomer conversion in high‐molecular‐weight regimes (Mn ? 106 g mol?1 [? 4160 units of DA)] with time‐dependent conversion data obtained via online Fourier transform near infrared spectroscopy (FTNIR) at 60 °C. In addition, the required initiator decomposition rate coefficient, kd, was determined via online UV spectrometry and was found to be 8.4 · 10?6 s?1 (±0.5 · 10?6 s?1) in dodecane, n‐butyl acetate, and n‐dodecyl acetate at 60 °C. The initiator efficiency at low monomer conversions is relatively low (f = 0.13) and decreases with increasing monomer to polymer conversions. The evolution of f with monomer conversion (in high‐molecular‐weight regimes), x, at 60 °C can be summarized by the following functionality: f60 °C (x) = 0.13–0.22 · x + 0.25 · x2 (for x ≤ 0.45). The reported efficiency data are believed to have an error of >50%. The ratio of the initiator efficiency and the average termination rate coefficient, 〈kt±, (f/〈kt〉) has been determined at various molecular weights for the generated polydodecyl acrylate (Mn = 1900 g mol?1 (? 8 units of DA) up to Mn = 36,500 g mol?1 (? 152 units of DA). The (f/〈kt〉) data may be indicative of a chain length‐dependent termination rate coefficient decreasing with (average) chain length. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5170–5179, 2004 相似文献
9.
Christopher Barner‐Kowollik Philipp Vana Thomas P. Davis 《Journal of polymer science. Part A, Polymer chemistry》2002,40(5):675-681
Pulsed laser polymerization (PLP) experiments were performed on the bulk polymerization of methyl methacrylate (MMA) at ?34 °C. The aim of this study was to investigate the polymer end groups formed during the photoinitiation process of MMA monomer using 2,2‐dimethoxy‐2‐phenylacetophenone (DMPA) and benzoin as initiators via matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectrometry. Analysis of the MALDI‐TOF spectra indicated that the two radical fragments generated upon pulsed laser irradiation show markedly different reactivity toward MMA: whereas the benzoyl fragment—common to both DMPA and benzoin—clearly participates in the initiation process, the acetal and benzyl alcohol fragments cannot be identified as end groups in the polymer. The complexity of the MALDI‐TOF spectrum strongly increased with increasing laser intensity, this effect being more pronounced in the case of benzoin. This indicates that a cleaner initiation process is at work when DMPA is used as the photoinitiator. In addition, the MALDI‐TOF spectra were analyzed to extract the propagation‐rate coefficient, kp, of MMA at ?34 °C. The obtained value of kp = 43.8 L mol?1 s?1 agrees well with corresponding numbers obtained via size exclusion chromatography (kp = 40.5 L mol?1 s?1). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 675–681, 2002; DOI 10.1002/pola.10150 相似文献
10.
Bart Dervaux Thomas Junkers Maria Schneider‐Baumann Filip E. Du Prez Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2009,47(23):6641-6654
Pulsed laser polymerization (PLP) coupled to size exclusion chromatography (SEC) is considered to be the most accurate and reliable technique for the determination of absolute propagation rate coefficients, kp. Herein, kp data as a function of temperature were determined via PLP‐SEC for three acrylate monomers that are of particular synthetic interest (e.g., for the generation of amphiphilic block copolymers). The high‐Tg monomer isobornyl acrylate (iBoA) as well as the precursor monomers for the synthesis of hydrophilic poly(acrylic acid), tert‐butyl acrylate (tBuA), and 1‐ethoxyethyl acrylate (EEA) were investigated with respect to their propagation rate coefficient in a wide temperature range. By application of a 500 Hz laser repetition rate, data could be obtained up to a temperature of 80 °C. To arrive at absolute values for kp, the Mark‐Houwink parameters of the polymers have been determined via on‐line light scattering and viscosimetry measurements. These read: K = 5.00 × 105 dL g−1, a = 0.75 (piBoA), K = 19.7 × 105 dL g−1, a = 0.66 (ptBA) and K = 1.53 × 105 dL g−1, a = 0.85 (pEEA). The bulky iBoA monomer shows the lowest propagation rate coefficient among the three monomers, while EEA is the fastest. The activation energies and Arrhenius factors read: (iBoA): log(A/L mol−1 s−1) = 7.05 and EA = 17.0 kJ mol−1; (tBuA): log(A/L mol−1 s−1) = 7.28 and EA = 17.5 kJ mol−1 and (EEA): log(A/L mol−1 s−1) = 6.80 and EA = 13.8 kJ mol−1. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6641–6654, 2009 相似文献
11.
Yohann Guillaneuf Jean‐Philippe Lamps Jean‐Marie Catala Didier Gigmes Eric Drockenmuller 《Journal of polymer science. Part A, Polymer chemistry》2012,50(18):3750-3757
A new dialkylated α‐hydrogenated linear nitroxide and the corresponding 1‐phenylethyl alkoxyamine were synthesized in two and three steps, respectively. The alkoxyamine was involved in the polymerization of styrene at 60 °C, and the in situ concentration of nitroxide was monitored by electron spin resonance spectroscopy. The enhanced characteristics of these new alkylated alkoxyamine and nitroxide (k = 1.5 × 10?4 s?1 and k = 5.7 × 104 L mol?1 s?1) yielded a monomer consumption one order of magnitude higher than styrene thermal polymerization. This resulted in well‐defined polystyrenes up to 70,000 g mol?1 and the observation of a control occurring through the establishment of the radical persistent effect, that is, ln([M]0/[M]) = t2/3. Experimentally determined kinetic constants were involved in PREDICI modelings to investigate the influence of temperature and initial alkoxyamine concentration on the kinetics as well as on the livingness and the controlled character of the polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
12.
Makiko Seno Toshiya Ikezumi Takafumi Sumie Yasuhito Masuda Tsuneyuki Sato 《Journal of polymer science. Part A, Polymer chemistry》2000,38(11):2098-2105
The radical polymerization of N‐tert‐butyl‐N‐allylacrylamide (t‐BAA) was carried out in a dimethyl sulfoxide/H2O mixture in the presence of β‐cyclodextrin (β‐CD). The polymerization proceeded with the complete cyclization of the t‐BAA unit and yielded optically active poly(t‐BAA). The IR spectrum of the obtained polymer showed that the cyclic structure in the polymer was a five‐membered ring. The optical activity of poly(t‐BAA) increased with an increasing molar ratio of β‐CD to the t‐BAA monomer. The interaction of β‐CD with t‐BAA was confirmed by 1H NMR and 13C NMR analyses of the polymerization system. It is suggested that interaction of the t‐BAA monomer with the hydrophobic cavity of β‐CD plays an important role in the asymmetric cyclopolymerization of t‐BAA. The radical copolymerization of t‐BAA with styrene (St), methyl methacrylate, ethyl methacrylate, or benzyl methacrylate (BMA) also produced optically active copolymers with a cyclic structure from the t‐BAA unit. St and BMA carrying a phenyl group were predicted to compete with t‐BAA for interaction with β‐CD in the copolymerization system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2098–2105, 2000 相似文献
13.
Yulia A. Piskun Irina V. Vasilenko Sergei V. Kostjuk Kirill V. Zaitsev Galina S. Zaitseva Sergei S. Karlov 《Journal of polymer science. Part A, Polymer chemistry》2010,48(5):1230-1240
The titanium complexes with one ( 1a , 1b , 1c ) and two ( 2a , 2b ) dialkanolamine ligands were used as initiators in the ring‐opening polymerization (ROP) of ε‐caprolactone. Titanocanes 1a and 1b initiated living ROP of ε‐caprolactone affording polymers whose number‐average molecular weights (Mn) increased in direct proportion to monomer conversion (Mn ≤ 30,000 g mol?1) in agreement with calculated values, and were inversely proportional to initiator concentration, while the molecular weight distribution stayed narrow throughout the polymerization (Mw/Mn ≤ 1.2 up to 80% monomer conversion). 1H‐NMR and MALDI‐TOF‐MS studies of the obtained poly(ε‐caprolactone)s revealed the presence of an isopropoxy group originated from the initiator at the polymer termini, indicating that the polymerization takes place exclusively at the Ti–OiPr bond of the catalyst. The higher molecular weight polymers (Mn ≤ 70,000 g mol?1) with reasonable MWD (Mw/Mn ≤ 1.6) were synthesized by living ROP of ε‐caprolactone using spirobititanocanes ( 2a , 2b ) and titanocane 1c as initiators. The latter catalysts, according MALDI‐TOF‐MS data, afford poly(ε‐caprolactone)s with almost equal content of α,ω‐dihydroxyl‐ and α‐hydroxyl‐ω(carboxylic acid)‐terminated chains arising due to monomer insertion into “Ti–O” bond of dialkanolamine ligand and from initiation via traces of water, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1230–1240, 2010 相似文献
14.
Lucas Martins Monica Arrais Alexandre de Souza Anita Marsaioli 《Magnetic resonance in chemistry : MRC》2014,52(11):665-672
Binary and ternary systems composed of dapsone, sulfobutylether‐β‐cyclodextrin (SBE‐β‐CD), β‐CD and egg phosphatidylcholine (EPC) were evaluated using 1D ROESY, saturation transfer difference NMR and diffusion experiments (DOSY) revealing the binary complexes Dap/β‐CD (Ka 1396 l mol?1), Dap/SBE‐β‐CD (Ka 246 l mol?1), Dap/EPC (Ka 84 l mol?1) and the ternary complex Dap/β‐CD/EPC (Ka 18 l mol?1) in which dapsone is more soluble. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
15.
Vasilios Kotzabasakis Konstantinos Kostakis Marinos Pitsikalis Nikos Hadjichristidis David J. Lohse Thomas Mavromoustakos Constantinos Potamitis 《Journal of polymer science. Part A, Polymer chemistry》2009,47(17):4314-4325
The Cs‐symmetry hafnium metallocene [(p‐Et3Si)C6H4]2C(2,7‐di‐tert‐BuFlu)(C5H4)Hf(CH3)2 and tetrakis(pentafluorophenyl) borate dimethylanilinium salt ([B(C6F5)4]?[Me2NHPh]+) were used as the catalytic system for the polymerization of higher α‐olefins (from hexene‐1 to hexadecene‐1) in toluene at 0 °C. The evolution of the polymerization was studied regarding the variation of the molecular weight, molecular weight distribution and yield with time. The effect of the monomer structure on the polymerization kinetics was established. The role of trioctylaluminum in accelerating the polymerization was investigated. 13C NMR spectroscopy was used to study the microstructure of the poly(α‐olefins) by the determination of the pentad monomer sequences. The thermal properties of the polymers were obtained by differential scanning calorimetry, DSC. The results were discussed in connection with the polymer microstructure. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4314–4325, 2009 相似文献
16.
Yu‐Yang Liu Xiao‐Dong Fan YA‐Bing Zhao 《Journal of polymer science. Part A, Polymer chemistry》2005,43(16):3516-3524
A novel linear poly(N‐isopropylacrylamide) (PNIPA) with β‐cylodextrin (β‐CD) moiety (PNIPA‐β‐CD) was synthesized by the conjugation of β‐CD carrying amino groups (EDA‐β‐CD) onto PNIPA with epoxy groups (P(NIPA‐co‐GMA), Mn = 3.86 × 104), and the related reaction conditions are investigated. PNIPA‐β‐CD was characterized by means of IR, NMR and UV spectroscopes, element analysis, and differential scanning calorimetry (DSC). The number‐average molecular weight (Mn) and the β‐CD content of the obtained PNIPA‐β‐CD are 4.87 × 104 and 18.8 wt %, respectively. PNIPA‐β‐CD can not only respond to temperature stimuli but also include guest molecules. Lower critical solution temperature (LCST) of aqueous PNIPA‐β‐CD solution is similar to that of PNIPA. The association constant (Ka) for PNIPA‐β‐CD with methyl orange (MO) is 2.4 × 103 L mol?1 at pH 1.4, which is comparable to that of EDA‐β‐CD (Ka = 2.9 × 103 L mol?1). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3516–3524, 2005 相似文献
17.
Per B. Zetterlund Kazuki Miyake Kunihiro Goto Bunichiro Yamada 《Journal of polymer science. Part A, Polymer chemistry》2004,42(11):2640-2650
A detailed investigation of addition–fragmentation chain transfer (AFCT) in the free‐radical polymerization of methyl methacrylate (MMA) in the presence of methyl α‐(bromomethyl)acrylate (MBMA) was carried out to elucidate mechanistic details with efficient macromonomer synthesis as an underlying goal. Advanced modeling techniques were used in connection with the experimental work. Curve fitting of simulated and experimental molecular weight distributions with respect to the rate coefficient for addition of propagating radicals to MBMA (kadd) over 60–120 °C resulted in Eadd = 21.7 kJ mol?1 and Aadd = 2.18 × 106 M?1 s?1 and a very weak temperature dependence of the chain‐transfer constant (Eadd ≈ Ep). The rate coefficient for fragmentation of adduct radicals at 60 °C was estimated as kf ≈ 39 s?1 on the basis of experimental data of the MMA conversion and the concentration of 2‐carbomethoxy‐2‐propenyl end groups. The approach developed is generic and can be applied to any AFCT system in which copolymerization does not occur and in which the resulting unsaturated end groups do not undergo further reactions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2640–2650, 2004 相似文献
18.
Reiko Saito Yoshiki Okuno Hiroaki Kobayashi 《Journal of polymer science. Part A, Polymer chemistry》2001,39(20):3539-3546
A novel template monomer with multiple methacryloyl groups was synthesized with β‐cyclodextrin by the acetylation of primary hydroxyl groups and the esterification of secondary hydroxyl groups with methacrylic acid anhydride. The average number of methacryloyl groups in the monomer was 11. The radical polymerization of the monomer was carried out with the following initiators: α,α′‐azobisisobutylonitrile, H2O2? Fe2+ redox initiator, p‐xylyl‐N,N‐dimethyldithiocarbamate (XDC), and α‐bromo‐p‐xylyl‐N,N‐dimethyldithiocarbamate (BXDC). When the concentration of the monomer was less than 4.12 × 10?3 M, polymerization was limited inside the molecule, and gelation of the system was hindered. For controlled radical photopolymerization with XDC and BXDC, the methacryloyl groups of the monomer were homogeneously polymerized, and poly(methacrylic acid) with a narrow molecular weight distribution was obtained by the hydrolysis of the polymerized products. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3539–3546, 2001 相似文献
19.
β‐Bromo‐α,β‐unsaturated ketones are condensed with arylhydrazines to form hydrazones, which are in situ intramolecularly cyclized into 3‐substituted 1‐aryl‐1 H‐pyrazoles under a catalytic system of Pd(OAc)2/1,3‐bis(diphenylhosphino)propane (dppp)/NaOtBu. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
20.
Enrique Saldívar‐Guerra Jos Bonilla Gregorio Zacahua Martha Albores‐Velasco 《Journal of polymer science. Part A, Polymer chemistry》2006,44(24):6962-6979
Mechanisms and simulations of the induction period and the initial polymerization stages in the nitroxide‐mediated autopolymerization of styrene are discussed. At 120–125 °C and moderate 2,2,4,4‐tetramethyl‐1‐piperidinyloxy (TEMPO) concentrations (0.02–0.08 M), the main source of radicals is the hydrogen abstraction of the Mayo dimer by TEMPO [with the kinetic constant of hydrogen abstraction (kh)]. At higher TEMPO concentrations ([N?] > 0.1 M), this reaction is still dominant, but radical generation by the direct attack against styrene by TEMPO, with kinetic constant of addition kad, also becomes relevant. From previous experimental data and simulations, initial estimates of kh ≈ 1 and kad ≈ 6 × 10?7 L mol?1 s?1 are obtained at 125 °C. From the induction period to the polymerization regime, there is an abrupt change in the dominant mechanism generating radicals because of the sudden decrease in the nitroxide radicals. Under induction‐period conditions, the simulations confirm the validity of the quasi‐steady‐state assumption (QSSA) for the Mayo dimer in this regime; however, after the induction period, the QSSA for the dimer is not valid, and this brings into question the scientific basis of the well‐known expression kth[M]3 (where [M] is the monomer concentration and kth is the kinetic constant of autoinitiation) for the autoinitiation rate in styrene polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6962‐6979, 2006 相似文献