Enzymatic polymerization of vinyl monomers

The possibility of using horse radish peroxidase as a catalyst for polymerization of monomers (vinylformamide and sodium vinylsulfonate) in the presence of hydrogen peroxide and 2,4-pentanedione in aqueous medium at room temperature was studied.     

乙烯类单体预辐照聚合的研究

讨论了在氧存在下辐照乙烯类单体形成的过氧化物在引发聚合及共聚合中的行为及辐照温度对形成过氧化物的速率和性质的影响.主要结果如下:(1)过氧化物的生成及其引发聚合皆按自由基机制进行.V_0∝c~(1/2),G_R=10;(2)过氧化物的生成活化能为:E_(f(MMA)=11,E_f(Sr)=9.6,E_(f(AN))=8.5kcal/mol.聚合过程中的表观活化能E_MMA=11.4,E_(▽A)=11.4kcal/mol.引发活化能E_i(MMA)=E_i_(▽A)=13kcal/mol;(3)过氧化物生成速率随辐照温度的升高而增加,高温辐照的过氧化物的引发性质发生变化;(4)辐照形成的过氧化物在聚合条件下的分解速率较BPO的分解速率缓慢而平稳,保证了聚合进程的平稳性;(5)预辐照一种单体可以引发另一种未辐照单体共聚.预辐照不同单体在共聚中的引发能力主要取决于预辐照单体的化学结构.     

Synthesis and polymerization of heteroaromatic vinyl monomers

Methods of preparing new monomers, 2-vinyl and 2-isopropenyloxazoles and 2-isopropenyl-1,3,4-oxadiazoles are described. New methods were developed to synthesize monomers containing an isoxazole or a thiazole ring. Radical homopolymerization and copolymerization with styrene of these monomers were carried out by using AIBN as an initiator. Monomer reactivity ratios r₁, r₂ and Alfrey-Price Q–e values were determined by the Fineman-Ross and the Mayo-Lewis methods. The localization energy of the β-carbon was calculated by a HITAC-5020 computer, and the monomer reactivity is discussed in terms of L_β.     

Anionic polymerization of vinyl monomers with xanthates

The polymerization of vinyl monomers with various xanthates (potassium tert-butylxanthate, potassium benzylxanthate, zinc n-butylxanthate, etc.) were carried out at 0°C in dimethylformamide. N-Phenylmaleimide, acrylonitrile, methyl vinyl ketone, and methyl methacrylate were found to undergo polymerization with potassium tert-butylxanthate; however, styrene, methyl acrylate, and acrylamide were not polymerized with this xanthate. In the anionic polymerization of methyl vinyl ketone with potassium tert-butylxanthate, the rate of the polymerization was found to be proportional to the catalyst concentration and to the square of the monomer concentration. The activation energy of methyl vinyl ketone polymerization was 2.9 kcal/mole. In the polymerization, the order of monomer reactivity was as follows: N-phenylmaleimide > methyl vinyl ketone > acrylonitrile > methyl methacrylate. The initiation ability of xanthates increased with increasing basicity of the alkoxide group and with decreasing electronegativity of the metal ion in the series, lithium, sodium, and potassium tert-butylxanthate. The relative effects of the aprotic polar solvents on the reactivity of potassium tert-butylxanthate was also determined as follows: diethylene glycol dimethyl ether > dimethylsulfoxide > hexamethylphosphoramide > dimethylformamide > tetrahydrofuran (for methyl vinyl ketone); dimethyl sulfoxide > hexamethylphosphoramide > dimethylformamide ? diethylene glycol dimethyl ether (for acrylonitrile).     

Verification of transfer-suppressed cationic polymerization of vinyl monomers

A general approach to a transfer-suppressed proceeding of cationic vinyl polymerization is put forward. The fundamental principle of the method consists in stabilization of the counter-ion by interaction with acceptors. This results in an orbital controlled cation-anion interaction and by this, suppression of side reactions, for example chain transfer due to lowering the ß-hydrogen acidity of the growing cation and the specific monomer solvation of the propagation transition state. It is shown that picric acid, initiated polymerization of p-methoxyatyrene and vinyl ethers, runs free of transfer in contrast to LEWIS-acid initiated systems. Cationic polymerization, initiated by iodine based systems, are in the same category as demonstrated by molecular weight distributions, monomer addition experiments, thermokinetical data and UV-spectroscopical measurements. The results are discussed in the framework of a general energetic scheme of propagation via cation-anion orbital controlled interactions with propagating ion pairs.     

Statistical model of stereospecific polymerization of vinyl monomers

A statistical model for the stereospecific polymerization of vinly monomers on Ziegler-Natta catalytic systems is presented. The basic assumptions of the model are: (a) the catalytic centers are asymmetric, so that at a given catalytic center the monomer CH₂?CHR is inserted into the chain with two different rates according to the two different configurations of the opening carbon atom having the R group; (b) the insertion of a monomeric unit in the growing chain is affected also by interactions with the previous monomeric unit. Isotactic, syndiotactic, atatic, or stereoblock polymers are obtained according to the relative values of the two energy parameters expressing these two effects.     

Microgels 1: Solution polymerization using vinyl monomers

Theories of gelation predict that the polymerization and copolymerization of polyfunctional monomers having an average functionality of greater than two will form a macrogel. The theories have not been found to accurately predict the degree of reaction at the gel point in the presence of solvents. This paper, the first in a series, explores a concept in which it is postulated that macrogelation in solution in many cases is not the expected outcome and that small and usually soluble internally crosslinked polymer molecules(microgels) will be the product at complete reaction. The monomers methyl methacrylate and diethyleneglycol dimethacrylate were radically copolymerized in various proportions in a range of solvents to test the hypothesis. It was found that, at essentially complete conversion in good solvents below a critical and relatively high concentration, gelation could not be obtained and a general technique for the preparation of “microgels” is thus revealed.     

Comparative study of the absolute reactivity of vinyl monomers: Kinetics of polymerization of vinyl monomers initiated by Mn3+–thiodiglycolic acid redox system

The kinetics and mechanism of polymerization of methacrylic acid (MAA) and ethyl acrylate (EA) initiated by the redox system, Mn³⁺–thiodiglycolic acid (TDGA) were investigated in the 15–35°C temperature range. The polymerization kinetics of both the monomers followed the same mechanism, viz., initiation by primary radical and termination by Mn³⁺–thiodiglycolic acid complex. The rate coefficients k_i/k₀ and k_p/k_t were related to the monomer reactivity and polymer radical reactivity, respectively. It was observed that both monomer reactivity and polymer radical reactivity followed the same order, viz., EA > MAA. The polymer radical reactivity varied inversely with the Q values of the monomers.     

Initiating radical polymerization of vinyl monomers by silicon peroxides

The initiating ability of organosilicon peroxides, Me_4-mSi(OOCMe₃)_mwherem = 1−3, for polymerization of vinyl monomers has been quantitatively characterized. Complex formation between monomers and Lewis acids has been found to activate the polymerization process. The activation effect is observed for a ratio [Lewis acid]/[monomer] of 0.003 to 0.02. The complex formation parameters (equilibrium constant and complex composition) have been determined by PMR, thermochemical and cryoscopic methods. Organosilicon peroxides have been found to influence the composition of copolymers; polyfunctional peroxides can be used to prepare block copolymers.     

Solvation effects in anionic polymerization of polar vinyl monomers

The anionic polymerization (AP) of polar vinyl monomers (PVM) is strongly affected by additives with electron donor and electron acceptor properties. For the purpose of estimating the interactions of the active centers (AC) of chain growth with different ligands, the approach of studying a reference system was adopted, viz. lithium picrate (LiPi) in dioxane (DO). Three types of interaction were distinguished: with electron pair donors (EPD), with Li salts and alkoxides, and with Lewis acids. Spectral evidence was found of charge transfer complexation with Li alkoxides and enolates, leading to modified dianionic Meisenheimer adducts. The experimental procedure was employed in studies of competitive solvation of LiPi by two ligands. The results were related to reviewed literature data on the kinetics and stereochemistry of methyl methacrylate (MMA) and 2-vinylpyridine (2VP) polymerizations by lithium initiators.     

Photoinitiated polymerization of vinyl monomers by benzophenone t-butyl peresters

Benzophenone peresters undergo efficient photodecomposition when irradiated at 366 nm. This article reports peresters derived from benzophenone p,p′-dicarboxylic acid 1 which may produce radicals at two different centers in the same molecule. These peresters represent a unique new example of an efficient photoinitiator for acrylate and styrene polymerization.      

Graft polymerization of vinyl monomers onto nanosized alumina particles

To enhance the interfacial interaction in alumina nanoparticles filled polymer composites, an effective surface modification method was developed by grafting polystyrene and polyacrylamide onto the particles. That is, the alumina surface was firstly treated with silane, followed by radical grafting polymerization in aqueous or non-aqueous systems. Results of infrared spectroscopy and dispersiveness in solvents demonstrated that the desired polymer chains have been covalently bonded to the surface of the alumina particles. They also greatly changed their surface characteristics. In addition, effects of polymerization conditions, including ways of monomer feeding, concentrations of monomer and initiator, and reaction time, on the grafting reaction were presented. It was found that the growing polymer radicals and/or the grafted polymer chains had a blocking effect on the diffusion of radicals or monomers towards the surface of nanoalumina. This was due to the fact that the interaction between the solvent and the grafted polymers was weaker than that between the grafted polymers and the nanoparticles.     

Design and initiators of living cationic polymerization of vinyl monomers

This paper discusses recent developments in living cationic polymerization of vinyl monomers, specifically focusing on (a) new initiating systems, (b) kinetics and mechanism, and (c) controlled polymer synthesis. The new initiating systems were based on nucleophilic stabilization of the growing carbocations, either by counteranions (as in phosphate/ZnI₂ and Me₃SiI/ZnI₂ systems) or by added Lewis bases (as 2,6-dimethylpyridine for EtAlCl₂). The kinetic study included the determination of the lifetime of living cationic polymers. The controlled polymer synthesis by living cationic processes led to not only end- and pendant-functionalized polymers of narrow molecular weight distributions but also star-shaped polymers and sequence-regulated vinyl ether oligomers with functional groups.     

Preparation,stability and reactivity of fluorinated vinyl organometallic compounds

In contrast to the low stability of the fluorinated vinylic lithium or magnesium reagents, the analogous vinylic cadmium, zinc, copper, and silver reagents have been found to exhibit excellent stability. These organometallic substrates are readily prepared from the corresponding vinylic iodides or $\text{via}$ methathesis reaction. Stereochemical integrity is preserved in all organometallic-forming reactions as well as in all

subsequent chemical transformations of these reagents. In some cases (M = Cd), the $\text{bis}$-reagent can be isolated as a stable solid.A variety of chain-extension and/or functionalization reactions of these stable organometallic compounds will be presented and discussed.     

Kinetics of polymerization of vinyl monomers initiated by lead tetraacetate

A systematic study of the thermal polymerization of α-chloroacrylic acid and α-bromoacrylic acid in aqueous nitric acid was carried out. The effect of variation of monomer concentration lead tetraacetate concentration, hydrogen ion concentration, ionic strength, and temperature on the rate of monomer disappearance was carried out. Based on the experimental observations, suitable reaction schemes were proposed for the polymerization of the above monomers. The rate constants and the thermodynamic parameters were evaluated.     

Dicyclopentadienyltitanium chlorides as regulators of free-radical polymerization of vinyl monomers

The free-radical polymerization of styrene and methyl methacrylate in the presence of dicyclopentadienyltitanium chloride and dicyclopentadienyltitanium dichloride has been studied. It has been shown that the process proceeds without autoacceleration up to high conversions and is characterized by a linear increase in molecular mass with conversion. On the basis of quantum chemical calculations and ESR spectroscopic data, a scheme describing the growth of polymer chains with participation of organotitanium compounds is proposed.     

Inhibiting action of sulfur-containing hydroquinolines during polymerization of vinyl monomers

4,5-Dihydro-4,4-dimethyl-2,3-dithiolo[5,4-c]quinoline-1-thiones and gossypol are effective antioxidants in the polymerization of vinyl monomers. Kinetic parameters of inhibition reactions depend on the structure of the monomer and inhibitor and the nature of the initiator. A mechanism is proposed for the reaction of peroxy radicals with sulfur-containing hydroquinolines.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 782–786, April, 1991.     

Oxoaminium salts as initiators for cationic polymerization of vinyl monomers

Oxoaminium salt ( 1 ), derived from 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 2 ) by one-electron oxidation, could be an initiator for cationic polymerization of vinyl monomers such as isobutyl vinyl ether (IBVE), 2,3-dihydrofuran, p-methoxystyrene, N-vinyl pyrrolidone, etc., to give the corresponding polymers, when 1 had a low nucleophilic counter anion. Formation of the adducts of 1 and IBVE as well as ¹H-NMR and IR data suggested the formation of polymers containing N? O? C structure as the polymer head group. In the polymerization of IBVE, the effects of solvent and concentration of 1 were little observed, however the polymerization rate was dependent on temperature. Furthermore, the thermal reaction of the polymers obtained, which were regarded as prepolymers for block copolymerization and polymeric initiators for radical polymerization, was studied. For example, poly(2-benzylidene-1,3-dioxane) obtained by the polymerization of 2-benzylidene-1,3-dioxane with oxoaminium hexafluoroantimonate ( 1, X = SbF₆) was employed as an initiator for radical polymerization of MMA to give its block copolymer with PMMA. © 1993 John Wiley & Sons, Inc.     

硝酸铈铵均相氧化还原体系引发烯类单体聚合

研究了均相氧化还原体系硝酸铈铵/N,N-二甲基甲酰胺(CAN/DMF)在无外加还原剂的条件下,引发丙烯酸甲酯(MA),苯乙烯(St)和甲基丙烯酸甲酯(MMA)等烯类单体的聚合。该氧化还原体系在较低温度下能引发丙烯酸甲酯快速聚合,聚合速度随温度升高而加快。为烯类单体在有机相中聚合提供了新的均相引发剂。将六甲基膦酰三胺(HMPA)作为CAN的络合剂加入到聚合体系中,在较低温度(40℃)下能加速MMA的聚合,对St和MA亦有一定的促进作用。详细讨论了温度和HMPA量对聚合的影响。用1H-NMR对聚合物精细结构进行表征并探讨了引发机理。