A.V. Olenin

Study of the initiation mechanism of post-radiation graft polymerization of vinyl monomers on solid inorganic materials☆

Abstract ESR was used to study the type of active centre of silica gel exposed to γ-radiation. It was shown that at 20°SiO type radicals are the main initiating centres of polymerization on silica gel exposed to γ-radiation. When carrying out post-radiation graft polymerization of methylmethacrylate on silica gel exposed to γ-radiation high degree and efficiency of grafting cannot be achieved. As a result of the treatment of silica gel and macro-porous glass using chlorosilanes the concentration of active centres formed by the action of γ-radiation can be markedly increased and the yield of graft polymers and the efficiency of grafting, raised.

Synthesis of block copolymers by non-fissile radical polymerization in the presence of o-phosphoric acid☆

It was shown that during polymerization of methyl methacrylate (MMA) or methyl α-chloracrylate (MCA) in the presence of o-phosphoric acid, complex forming agent, long life radicals are formed at room temperature in an external homogenous system, which after excluding the source of initiation, can effect non-fissile polymerization. If, after all the monomer had reacted, further monomer is added, the reaction continues as a result of extension of macroradicals formed. MMA-MCA block copolymers were sythesized. Block copolymers were obtained both by grafting MCA on PMMA macroradicals and by grafting MMA on PMCA macroradicals. Fractionation, sedimentation and turbidimetric titration showed that the polymers synthesized only contain two types of macromolecule, one of which is a block copolymer and the other PEC is observed over a sufficiently wide composition range 2.5<PVPB:PMMA<5, and does not involve dissociation of PEC into components. The mechanism of formation of water-soluble polycomplexes is considered, and a model of such polymcomplexes is suggested.

The kinetics and mechanism of polymerization of methyl methacrylate radical in the presence of ortho-phosphoric acid☆

The photo-initiated homo-polymerization of methyl methacrylate (MMA) has been studied at 25°C in the presence of ortho-phosphoric acid as complex former. Post-polymerization accompanied by a mol.wt. increase has been found to occur in addition to an increase in reaction rate after ceasing photo-initiation in the system MMA-H3PO4. The factor responsible for the continuation of the post-polymerization in such a system has been found to be the macro-radicals whose active life is greatly prolonged in the presence of the complex former. The effects of various factors in the kinetics of the post-illumination process have been studied. A rapid drop of the bimolecular termination rate of the polymethylmethacrylate (PMMA) radicals has been found to be linked with a change of the configurational properties and the associations of the growing chains as a result of the complexing with H3PO4. A mechanism is suggested for the polymerization in the described system.

Graft polymerization of vinyl monomers on the surface of solid inorganic materials photoinitiated by the systems RCCl3-carbonyls of transition metals☆

Abstract Organosilicas containing chemically grafted CCl 3 groups (RCCl 3 ) have been prepared by modification of silica gel and Aerosil by the (methyldichlorosilyl)propyl ester of trichloroacetic acid. Using the initiating system RCCl 3 Mn 2 (CO) 10 it was found that the graft polymerization of methyl methacrylate and styrene may be carried out through the action of visible light. The extent to which the time of the reaction and concentrations of Mn 2 (CO) 10 and CCl 3 groups influence the yield, MW and MWD of the grafted PMMA.

The study of photo-initiated graft polymerization of vinyl monomers on inorganic materials

Abstract The surfaces of silica gel and of Aerosil have been chemically modified with γ-(dimethylaminopropyl) methyldiethoxysilane and (diethylaminomethyl)triethoxysilane. Preliminary activation of silica by silanes permitted achievement of graft polymerization of methyl methacrylate and styrene in the presence of fluorenone, anthraquinone, benzophenone and benzoin methylether, under the action of visible light. The influence of reaction time, fluorenone concentration, solvent polarity and chemical nature of the aromatic ketone on the yields of grafted polymer and of homopolymer, together with the molecular weights of the grafted chains, was studied.

The synthesis of block copolymers from acrylic and methacrylic monomers and the kinetics of the low temperature radical post-polymerization over o-phosphoric acid

Abstract The thawing of the system H 3 PO 4 -methyl methacrylate which had been exposed to gamma rays at −196°C has been found to result in a radical polymerization and a near 100% polymer yield. The effect of the reaction mixture composition on the molecular weight of the polymethylmethacrylate (PMMA) , of the thawing rate, the absorbed dose of γ-rays and of diluent additions, has been investigated.

Mechanism of photoinitiated radical polymerization of styrene in the presence of benzyldithiocarbamate iniferter

The kinetics and mechanism of radical polymerization with participation of iniferter is studied using the styrene-S-benzyl-N,N-diethyldithiocarbamate system as an example. The identity of the photocomposition of S-benzyl-N,N-diethyldithiocarbamate and polystyrene macroiniferter is demonstrated by an ESR method, and the special features of the transformation of the molecular mass distribution during polymerization are revealed by means of GPC. It is shown that polymerization is characterized by the absence of bimolecular termination of the growing macroradicals and a stepped mechanism of the chain propagation reaction. The experimental data are in good agreement with our previously proposed general kinetic scheme for radical polymerization with the participation of iniferter.

Structure of grafted polymer layer and its effect on mechanical properties of composites poly(butyl methacrylate)-Aerosil☆

Abstract Mechanical and ultimate properties of a composite poly(butyl methacrylate)-Aerosil are further substantially improved if the surface of Aerosil particles is first modified by grafting of a layer of poly(butyl methacrylate). The mechanical properties of the composite go through a maximum in dependence on the parameters of polymer chains in the grafted layer.

Synthesis of graft polymers and block-copolymers of acrylic and methacrylic monomers by a “living” radical polymerization☆

It was shown that in the presence of a complex-forming agent—o-phosphoric acid radical graft polymerization of methyl metahacrylate or methyl-α-chloracrylate on a γ-irradiated cellophane film takes place by a mechanism of “living” chains. At the initial stage of the reaction with a practically constant number of graft chains under given conditions graft polymer yield and the molecular weight of graft chains increases in direct proportion to the time of contact of a γ-irradiated film with the reaction system. A study was made of the dependence of graft polymer yield, molecular weight and the number of PMMA graft chains, on the composition of the H3PO4-MMA system. The rate constant of chain propagation was evaluated when carrying out graft post-polymerization of MMA on a γ-irradiated cellophane film. It was shown that the existence of “live” chains in the grafting of methyl methacrylate and methyl-α-chloracrylate in the presence of H3PO4 on to γ-irradiated cellophane film enables graft block-copolymers and graft tri-block copolymers of these monomers to be obtained with control of the molecular composition and the length of each unit. The block structure of individual graft chains was confirmed by turbidimetric titration. Block-copolymers of methyl methacrylate and methyl-α-chloracrylate practically free from homopolymers were obtained by hydrolysis of this modified cellophane film.

Radical graft polymerization of methyl methacrylate on inorganic fillers initiated by surface S-methyl-N,N-diethyldithiocarbanate groups☆

Abstract A comparative study was made of the kinetics and mechanism of the photoinitiated radical graft polymerization in the system Silochrome (containing surface S-methyl-N,N-diethyldithiocarbamate groups)-MMA, and similarly for photopolymerization in the corresponding homogeneous system S-ethyl-N,N-diethyldithiocarbamate-MMA. Photochemical decay of the surface initiator in presence of the monomer causes simultaneous initiation of graft- and homopolymerization. Attachment of the initiator to the filler surface leads to a reduction in the rate of bimolecular termination of kietic chains during the graft polymerization. This reduction is equal to one order compared with polymerization in the homogeneous solution. It also leads to the disappearance of chain transfer to surface S-methyl-N,N-diethyldithiocarbamate groups.