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Abstract The catalytic system of azo-bis-isobutyronitrile (AIBN) combined with (SiMes)Ru(PPH 3)(Ind)Cl 2 [M 20 ] was investigated for the controlled radical polymerization of methyl methacrylate (MMA) in solution. Various factors that may influence the catalytic polymerization process, such as the aging time of the initiating system, AIBN/M 20 ratio, concentration of monomer, polymerization time, temperature, and the nature of solvent were examined. The results showed that the yield, molecular weight, and molecular distribution are practically unaffected by these parameters; however, the syndiotactic stereo-structure tendency that characterizes the produced poly(methyl methacrylate) (PMMA) varied with temperature. The optimum conditions for PMMA synthesis were determined to produce an essentially syndiotactic material with uniformly high molecular weights. It was also revealed that the kinetics of MMA polymerization is of first order with respect to the concentration of monomer. A comparison was also made for some vinylic polymers synthesized either with the AIBN alone or with the AIBN/M 20 initiating system under the same conditions. [ABSTRACT FROM AUTHOR]

Abstract: Density functional theory (DFT) calculations were used to predict and rationalize the effect of the modification of the structure of the prototype 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) (IPr) N-heterocyclic carbene (NHC) ligand. The modification consists in the substitution of the methyl groups of ortho isopropyl substituent with phenyl groups, and here we plan to describe how such significant changes effect the metal environment and therefore the related catalytic behaviour by simple steric maps. Bearing in mind that there is a significant structural difference between IPr and IPr* ligands, that translated in different reactivity for several olefin metathesis reactions, here by means of DFT we characterize where the NHC ligand plays a more active role and where it is a simple spectator, or at least its modification does not significantly change its catalytic role/performance. Furthermore, this communication endeavours to modify further the skeleton of the IPr NHC ligand. The optimization of these bulky new systems go to the limits of the DFT computational method. [Copyright &y& Elsevier]