The quantum-chemical simulation of possible reactions occurring at the initial stage of the free-radical polymerizations of styrene and methyl methacrylate in the presence of fullerene C60 is performed. The reactions of interaction between initiating and model short-chain growing radicals containing from one to three monomer units with fullerene are considered. It is shown that, at the initial stage of styrene polymerization, the addition of short-chain growing radicals to fullerene predominates (with respect to the reaction of chain propagation). In the case of methyl methacrylate polymerization in the presence of fullerene C60, the induction period is absent because of a higher probability of the initiation and chain propagation reactions (compared with the chain-termination reaction of short growing poly(methyl methacrylate) chains on fullerene C60). The formation of bis- and trisadducts of fullerene C60 with short-chain styrene and methyl methacrylate growing radicals is analyzed. The quantum-chemical simulation results are confirmed by electron spectroscopy and ESR studies. 相似文献
The kinetics and mechanism of the pseudoliving free-radical polymerization of styrene are studied for the first time under the conditions of reversible inhibition by TEMPO nitroxides. An abnormal decline in the reduced rate of polymerization, which is inconsistent with a decrease in the concentration of the monomer, and an increase in the steady-state concentration of the free nitroxide are discovered. The main quantitative characteristics of the pseudoliving process are determined, namely, the rate constants of reinitiation and reversible recombination, and the constant of pseudoliving equilibrium between dormant and growing chains. It is shown that the polarity of a medium and the concentration of the monomer determine the character of polymerization in a solution: With an increase in the polarity of the solvent, the pseudoliving equilibrium constant increases, the reduced rate of styrene polymerization decreases, and the molecularmass-distribution of the polymer formed at initial conversions narrows. The smaller the concentration of styrene in the reaction system, the more pronounced the above differences associated with the solvent nature. 相似文献
Esters or carbonates of N‐hydroxypyridine‐2‐thione (Barton esters) were appended to either carboxymethyl or hydroxypropyl cellulose. Irradiation of the cellulose bound Barton esters in monomer initiated free radical graft copolymerization with minimal concomitant homopolymerization. Grafting of styrene to carboxymethyl cellulose was accompanied by backbone cleavage. The hydroxypropyl spacer group minimized backbone degradation; styrene, acylamide and N‐isopropyl acrylamide could be grafted to hydroxypropyl cellulose in tetrahydrofuran solution. Treatment of Barton carbonate modified hydroxypropyl cellulose with styrene in the presence of TEMPO afforded corresponding TEMPO adducts, which can be used to promote the controlled radical graft polymerization of styrene. Grafts were analyzed independently after hydrolysis of the cellulose backbone. 相似文献
A novel bifunctional monomer, namely maleimide glycidyl ether (MalGE), prepared in a four‐step reaction sequence is introduced. This monomer allows for selective (co)polymerization of the epoxide group via cationic ring‐opening polymerization, preserving the maleimide functionality. On the other hand, the maleimide functionality can be copolymerized via radical techniques, preserving the epoxide moiety. Cationic ring‐opening multibranching copolymerization of MalGE with glycidol was performed, and a MalGE content of up to 24 mol% could be incorporated into the hyperbranched polymer backbone (Mn = 1000–3000 g mol−1). Preservation of the maleimide functionality during cationic copolymerization was verified via NMR spectroscopy. Subsequently, the maleimide moiety was radically crosslinked to generate hydrogels and additionally employed to perform Diels‐Alder (DA) “click” reactions with (functional) dienes after the polymerization process. Radical copolymerization of MalGE with styrene (Mn = 5000–9000 g mol−1) enabled the synthesis of a styrene copolymer with epoxide functionalities that are useful for versatile crosslinking and grafting reactions.
Radical copolymerization reaction of vinyl acetate (VA) and methyl acrylate (MA) was performed in a solution of benzene‐d6 using benzoyl peroxide (BPO) as the initiator at 60°C. Kinetic studies of this copolymerization reaction were investigated by on‐line 1H‐NMR spectroscopy. Individual monomer conversions vs. reaction time, which was followed by this technique, were used to calculate the overall monomer conversion, as well as the monomer mixture and the copolymer compositions as a function of time. Monomer reactivity ratios were calculated by various linear and nonlinear terminal models and also by simplified penultimate model with r2(VA)=0 at low and medium/high conversions. Overall rate coefficient of copolymerization was calculated from the overall monomer conversion vs. time data and kp . kt?0.5 was then estimated. It was observed that kp . kt?0.5 increases with increasing the mole fraction of MA in the initial feed, indicating the increase in the polymerization rate with increasing MA concentration in the initial monomer mixture. The effect of mole fraction of MA in the initial monomer mixture on the drifts in the monomer mixture and copolymer compositions with reaction progress was also evaluated experimentally and theoretically. 相似文献
1-Ethoxy-2,2,2-trifluoroethyl esters of acrylic ( I ) and methacrylic ( II ) acids were synthesized from 1-ethoxy-2,2,2-trifluoroethanol and acryloyl- and methacryloylchloride, respectively, and their densities, mass, 1H- and 13C-NMR spectra were measured and the rate constants of hydrolysis were determined. Poly( I ) and poly( II ) were prepared by radical homopolymerization; the rates of polymerization, specific volume contractions in polymerization, limiting viscosity numbers, average number degrees of polymerization, temperature dependences of the heat capacities both in glass and liquid state, glass transition temperatures, and the initial temperature of the spontaneous thermal decomposition of homopolymers were determined. The monomer reactivity ratios of the styrene (S) copolymerizations, S? I and S? II , and the Alfrey–Price copolymerization constants e and Q for I and II were calculated from the composition of copolymers of I and II with styrene. 相似文献
The kinetic behavior of the 60Co-initiated copolymerization at 25°C of styrene with vinyl acetate at 1100 and 2000 rad/hr was studied. As in the case of thermal and photochemical copolymerizations of these monomers, the growing chains are particularly rich in styrene units, and the overall rate is affected by a diluent effect due to the vinyl acetate monomer. However, in the case of the radiation copolymerization, this effect is partially counterbalanced by an increase of the initiation rate with the vinyl acetate concentration; the polymerization rate curve shows a maximum at a vinyl acetate molar fraction of 0.25. This effect is due to the very different free radical yields of these two monomers. The experimental results may be understood on the basis of a kinetic scheme which involves an energy transfer process from the excited vinyl acetate molecules to the styrene monomer and a termination reaction of the growing chains by very short styrene radicals when the mixture is rich in vinyl acetate. 相似文献
Summary: The anionic copolymerization of styrene and butadiene in hydrocarbon solvents initiated by lithium alkyls was first studied by Korotkov, who reported that the polymerization starts slowly and initially consumes butadiene. On exhaustion of this monomer, the reaction speeds up and then styrene polymerizes rapidly. This peculiar behaviour, which was originally explained by Korotkov by treating the monomers as solvents, butadiene being a preferential solvent for the Li+ cation, was later accounted for by considering the cross-over reactions. In this paper an in dept further explanation is given by admitting that the polymerization reactions occur through coordination of the Li + cation by the monomer followed by insertion of the monomer into the polymer chain. A preliminary MOPAC 93 (PM3) calculation seems to confirm this interpretation. 相似文献