M. Tardi

The mechanism of the polymerization of n.butyl acrylate initiated with N,N-diethyl dithiocarbamate derivatives

Abstract The kinetics of the photo-initiated polymerization of n.butyl acrylate by p -xylylene bis-( N , N -diethyldithiocarbamate) have been investigated in order to check the living character of this polymerization initiated with an “iniferter”. The reaction shows some features of a living system viz. growth of the molecular weight during the reaction under chosen conditions (high [M]/[I] ratios) and preparation of block copolymers. This confirms the existence of a reversible termination reaction between the growing chains and the dithiocarbamyl radicals. However, evidence has been found for the intervention of side reactions (formation of tetraethylthiuram disulphide, and decrease of the functionality of the polymers during the polymerization), indicating that the polymerization is not strictly living.

Synthesis of di- and triblock copolymers of styrene and butyl acrylate by controlled atom transfer radical polymerization

Di- and triblock copolymers of styrene and butyl acrylate with controlled molar masses (Mn up to ≈ 105) were sequentially prepared by radical atom transfer polymerization in a homogeneous medium using chlorine end capped polymers as initiators and the copper(I) chloride/bipyridine complex as catalyst, in the presence of dimethylformamide. Random poly(styrene-co-butyl acrylate) was synthesized and the cross-over reactions between Cl end capped polystyrene and poly(butyl acrylate) to the opposite monomers were examined.

Homopolymerization and copolymerization of methyl methacrylate in the presence of complexing agents—III. Investigation of the composition of copolymers of methyl methacrylate with styrene

Abstract The influence of monomer concentration on copolymer composition and on its evolution during reaction has been investigated for the alternating copolymerization of styrene with methyl methacrylate (MMA), in the presence of ethylaluminium sesquichloride and diethylaluminium chloride, in toluene solution at 20°. The results are in agreement with the hypothesis of a statistical copolymerization involving the uncomplexed monomers and complexed MMA. Using this scheme, the reactivity ratios have been calculated in the particular case in which the concentration of styrene varies, those of the other reagents being kept constant. The copolymer compositions derived from these ratios are in good agreement with the experimental data.

Homopolymerization and copolymerization of methyl methacrylate in the presence of complexing agents—I: Investigation of the complexation of methyl methacrylate with organochloroaluminium compounds

Abstract Methyl methacrylate (MMA) and organochloroaluminium dimers (Al)2 form strong complexes. An investigation by cryometry and 1H-NMR led to the conclusion that the association can be formulated thus: (Al) 2 +2MMA⇄2(Al, MMA) . The value of the equilibrium constant, in bulk at 20°, is 25 l mol−1 for AlEt2Cl and 70 l mol−1 for Al2Et3Cl3. In the case of AlEtCl2, the constant is too high to be measured, the association being practically quantitative. No ternary association of styrene with the Al-MMA complex could be detected using these methods; in any case, the formation constant of such a complex would be lower than 0.1 l mol−1.

Homopolymerization and copolymerization of methyl methacrylate in the presence of complexing agents. IV: Influence of the nature of the complexing agent

Abstract The kinetics of the alternating copolymerization of styrene and methyl methacrylate (MMA), in the presence of ethylaluminium sesquichloride or diethylaluminium chloride, in carbon tetrachloride solution, have been investigated in order to compare the results with those previously obtained in toluene. Cryometric measurement established that in CCl 4 the binary association of the MMA with the complexing agent involves a dimeric molecule of the organochloroaluminium compound. When the concentration of one of the monomers is increased, the polymerization rate goes through a maximum for a nearly equimolar feed of the monomers, and the usual deviations from the equimolar composition at extreme feed ratio have been observed. The kinetic schemes proposed in the literature only partially account for the experimental data and the maximum value for the polymerization rate could be only qualitatively explained.

Préparation de copolymères greffés par voie cationique—5. Intervention éventuelle de réactions de greffage par terminaison

The possibility of cationic grafting through a termination reaction of the active species with an aromatic backbone (“grafting onto”) has been considered. When the polymerization of styrene is initiated with AlEt2Cl and C6H5CH2Cl at −50°, in a methylene chloride methylcyclohexane mixture in the presence of poly(isobutylene-co-styrene), no graft copolymer is formed during the reaction. Grafting occurs subsequently, probably through a slow reaction with the aromatic rings of the backbone. In the case of backbones containing benzyl chloride groups [poly(isobutene-co-p-chloromethylstyeren)] the graft copolymer formed during the polymerization results mainly from initiation grafting (“grafting from”). Grafting onto, if it eventually occurs at high conversion or high monomer concentration, is only a side reaction.

Transfer and Termination Reactions in “Living” Carbocationic Polymerizations

Abstract The available data concerning the polymerization of three classes of monomers deemed to yield living polymers, vinyl ethers, styrenic monomers and isobutylene, are discussed from the point of view of transfer and termination reaction. In the case of vinylethers, linearity of [Mbar]n with a yield up to 30,000 has been obtained, but when higher [Mbar]n are planned, there is evidence for the occurrence of transfer reactions. In the case of isobutylene, indene, and p-Me-styrene, the linearity (up to [Mbar]n ∼ 105) of [Mbar]n with the amount of monomer polymerized which has been observed (but only at low temperature) is compatible with values of transfer constants to monomer measured in “conventional” systems. In these living systems, irreversible terminations are often not very important but may become significant toward the end of monomer consumption. The main termination process is reversible termination which may lead to narrow molecular weight distributions. The linearity of [Mbar]n with yield is...