V. G. Kozlov

Diene polymerizations with lanthanide coordination catalysts. II. The effects of catalytic system component types and polymerization conditions on molecular characteristics of 1,4-cis-Polybutadienes

Abstract Molecular inhomogeneity has been investigated for 1,4-cis-polybutadienes obtained with a lanthanide- containing catalytic system; some kinetic parameters have been estimated for polymerizations. Gel-permeation chromatography was chosen as the main method to find out the average molecular weights (MW) and molecular weight distributions (MWD). The catalyst composition has been shown to effect MW and MWD. The molecular characteristics are determined by both the catalyst composition and the polymerization conditions (reagent concentration, temperature). The broad MWD is considered a peculiarity of butadienes prepared with lanthanide- containing catalysts. The data obtained lead to the assumption that the distribution of the polymerization centres by reactivity is responsible for the broad MWD of the polybutadienes formed.

Cationic polymerization of 1,3-pentadiene in the presence of vanadium oxychloride

The cationic polymerization of 1,3-pentadiene in the presence of vanadium oxytrichloride is studied. 1,3-Pentadiene is shown to polymerize at a high rate to high monomer conversions in the absence of proton-donor compounds in the catalytic system. The initial rate of 1,3-pentadiene polymerization is proportional to the concentration of VOCl3 in the system and demonstrates an extremal dependence on the initial concentration of 1,3-pentadiene. The polymerization process is distinguished by an induction period whose duration increases with a decrease in the reaction temperature. Regardless of polymerization conditions, with an increase in the monomer conversion, the molecular-mass distribution of the polymer widens owing to formation of a high-molecular-mass fraction, which, depending on reaction conditions, can be consumed in formation of the gel fraction. It is shown that the degree of unsaturation and the microstructure of poly(1,3-pentadiene) are almost independent of the polymerization conditions.

Effect of temperature on the cationic polymerization of 1,3-pentadiene in the presence of the TiCl4-trichloroacetic acid catalytic system

117 The existing views on the effect of temperature on the cationic polymerization of 1,3-dienes are largely debatable and contradictory [1, 2]. This study is devoted to the description and discussion of the elucidated unusual kinetic features of the cationic polymerization of 1,3-pentadiene (PD) as a function of the process temperature. The procedures for monomer and solvent (hexane) purification and the polymerization experiments and measurement of molecular parameters of PPD were reported previously [3].

Polymerization of butadiene during the action of the catalytic system neodymium versatate-diisobutylaluminum hydride-hexachloro-p-xylene

The polymerization of butadiene in the presence of the neodymium versatate-diisobutylaluminum hydride-hexachloro-p-xylene catalytic system is studied. Quantitative information on the kinetic parameters of the process is obtained. The effects of the monomer concentration, the catalyst, and temperature on the molecular-mass characteristics and microstructure of PB are studied.

Long-chain branching of “lanthanide” 1,4-cis-polybutadiene and conditions of its polymerization☆

The degree of branching of 1,4-cis-polybutadiene synthesized on a lanthanide-containing catalytic system has been investigated. The values of [η], the molecular mass and molecular-mass distribution of specimens synthesized under various conditions and having a wide polydispersity have been determined, together with the same properties of fractions of these specimens with a narrow molecular-mass distribution. It has been established that, depending on the conditions of synthesis on the lanthanide-containing catalytic system, specimens of polybutadiene may be obtained that are either linear or have a branched structure. A change in the proportions of Al and Nd has hardly any effect on the degree of branching whereas an increase in the temperature of polymerization leads to the appearance of long-chain branching.

Molecular weight and molecular weight distribution of 1,4-cis-polyisoprene obtained under various conditions with the system TiCl4Al(C7H15)3☆

Abstract Gel permeation chromatography and accelerated sedimentation have been used to study the way in which the molecular characteristics of 1,4- cis -polyisoprene depend on the polymerization conditions on the catalytic system TiCl 4 Al(C 7 H 15 ) 3 . It is shown that the polymer contains a gel fraction of from 7 to 15% and that changing the polymerization conditions enables the molecular characteristics of the poly-isoprene to be regulated. Satisfactory agreement is reported in the determination of molecular mass and molecular weight distribution by sedimentation and gel permeation chromatography.

Nature of the active centres of the catalytic system VOCl3TiCl4Al(iso-C4H9)3 on polymerization of piperilene☆

Abstract The polymerization of piperilene has been studied on exposure to the catalytic system VOCl 3 TiCl 4 Al( iso -C 4 H 9 ) 3 prepared with a fractionated supply of the organoaluminium component. It is known that the stereospecificity of the action and reactivity of the active centres and the molecular mass of the polymer obtained depend in a complex fashion on the relative concentration of the first portion of the organoaluminium compound. It was found that change in the content of V 3+ and Ti 3+ in the catalytic system correlates with the activity and stereospecificity of the action. It is assumed that in conditions of formation of the catalyst active centres form including, simultaneously, V and Ti atoms in trivalent forms.

Molecular weight distribution of 1,2-polybutadiene obtained under the influence of catalytic systems based on tetra-π-allylmolybdenum☆

Abstract The molecular weight characteristics of samples of 1,2-polybutadiene obtained under the influence of catalytic systems based on tetra-π-allylmolybdenum have been investigated by the GPC method. The mean MW and MWD of the samples have been calculated and the effect of the different conditions of polymerization on the MW of the polymer studied.