V. A. Rozentsvet

Microstructure of polyisoprene produced by cationic polymerization: NMR spectroscopic study

High-resolution 1H and 13C NMR spectroscopy, including two-dimensional heteronuclear experiments, has been used to study the microstructure of polyisoprene produced by cationic polymerization. It is shown that macromolecules resulting from both regular and inverse additions are predominantly composed of trans-1,4-units, while 1,2- and 3,4-units are present in small amounts. NMR spectra demonstrate the absence of cis-1,4-units in the polymer, whereas broad signals (pedestals) are related to the presence of saturated structures. It is proposed to determine the content of trans-1,4-, 1,2-, and 3,4-units in cationic polyisoprene via the combined measurements of intensities of signals in the olefinic regions of 1H and 13C NMR spectra.

Cationic polymerization of isoprene in the presence of the TiCl4-trichloroacetic acid catalyst system

Cationic polyisoprene characteristic of different molecular parameters can be obtained with high yields in the presence of the TiCl4-trichloroacetic acid catalyst system. At low monomer concentrations, polyisoprene has a unimodal molecular-mass distribution. At elevated monomer concentrations, the polydispersity of polyisoprene increases significantly with conversion because of chain transfer to the polymer and branching. As the TiCl4/trichloroacetic acid ratio in the catalyst and the total concentration of the catalytic complex increase, the average molecular masses of the produced cationic polyisoprene decrease as a result of chain transfer to trichloroacetic acid.

Cationic polyisoprene: Synthesis, structure, and some properties

The effect of the catalyst composition and temperature on the cationic polymerization of isoprene in the presence of the catalytic system TiCl4-trichloroacetic acid was examined. The molecular heterogeneity, microstructure, and some properties of the resulting cationic polymer were determined.

Molecular Heterogeneity of Cationic Polyisoprene

Abstract The effect of polymerization conditions on the molecular parameters and unsaturation of cationic polyisoprene synthesized with the BF3·O(C2H5)2-trichloroacetic acid catalytic system has been studied. It has been shown that regardless of the initial monomer concentration, formation of the high-molecular-mass fraction in the polymer was observed when the first characteristic (threshold) concentration of the polymer was achieved. Further transformation of this fraction into the insoluble fraction took place when the second characteristic concentration of the polymer was achieved. The level of threshold concentrations of the polymer was determined by the component ratio in the catalytic system and the temperature of polymerization.

New insight into the polymerization mechanism of 1,3-dienes cationic polymerization. IV. Mechanism of unsaturation loss in the polymerization of isoprene

The cationic polymerization of isoprene with the tBuCl/TiCl4 initiating system in the presence of a high excess of tBuCl over TiCl4 ([tBuCl]/[TiCl4] > 100) in CH2Cl2 is reported. It is shown that the polymerization follows first-order kinetics, which indicates that the main chain-breaking process is the chain transfer to the initiator. The number-average functionalities with respect to the tert-butyl head group and chlorine-containing end group are determined to be considerably higher than unity. In addition, unsaturation of the polymer chain is found to be always less than 100%. It is also shown that unsaturation of the polyisoprene chain decreases with a simultaneous increase in polydispersity upon treatment of the polymer using the tBuCl/TiCl4 initiating system. Based on these observations, the mechanism to obtain a polymer with reduced unsaturation is proposed, which includes multiple interactions of growing cations with double bonds of “own” or/and “alien” macromolecules with the formation of branched structures.

Synthesis of cationic poly-1,3-pentadiene under the action of Gustavson complex

Polymerization of 1,3-pentadiene was performed using the Gustavson complex (AlCl2.xylene.0.5HCl) at a nearly full conversion of the monomer. The possibility of control over molecular characteristics of the polymer was demonstrated. Recommendations for application of the poly-1,3-pentadiene synthesized are given.

Kinetics and mechanism of 1,3-pentadiene cationic polymerization

Abstract1,3-Pentadiene cationic polymerization under the action of titanium tetrachloride-carboxylic acid (CF3COOH, CF3COOD, CCl3COOH, CHCl2COOH, CH2ClCOOH, CH3COOH, and (CH3)3CCOOH) catalytic systems has been studied. The highest activity in the 1,3-pentadiene polymerization is shown by the TiCl4-trifluoroacetic or deuterated trifluoroacetic acids system. Poly-1,3-pentadiene synthesized over these catalytic systems is characterized by a relatively low Mn, which changes slightly with an increasing monomer conversion, while Mw of the polymer increases substantially. The polymer chain propagation rate constants and the concentration of active species at various initial 1,3-pentadiene concentration have been determined using a deuterium-containing initiator. The reduced unsaturation of poly-1,3-pentadiene synthesized via the cationic polymerization method is due to chain transfer to the polymer and does not result from the cyclization reaction with the formation of six-membered cyclic structures.

On the issue of the propagation rate constant for the cationic polymerization of 1,3-dienes

119 A characteristic feature of the cationic polymeriza tion of conjugated dienes is the ability of the double bonds of a macromolecule to undergo further trans formations, which result in branched structures and a decrease in the unsaturation of polydienes [1, 2]. Moreover, the cationic polymerization of 1,3 dienes as a rule has a pronounced non stationary character [2–5]. This feature hinders the correct use of known methods for the calculation of propagation rate con stants [1, 6, 7] based on the measurement of number average polymerization degree. At the same time, there is no information in the literature on the propa gation and termination rate constants of the cationic polymerization of 1,3 dienes.

Kinetic parameters of cationic polymerization of 1,3-dienes

A new technique for the determination of the concentration of active centers of polymerization and propagation rate constants for processes of cationic polymerization of conjugated dienes was proposed. The method consists of the quantitative calculation from the 13C NMR spectra of the concentration of the initial units of the polymer chain polydienes synthesized at different monomer conversions and the subsequent extrapolation of the obtained values to the zero monomer conversion. Using the proposed procedure, the chain propagation rate constants were determined for the cationic polymerization of isoprene and 1,3-pentadiene in the presence of a titanium tetrachloride–tert-butyl chloride catalytic system.

Cationic polymerization of butadiene using a titanium tetrachloride—tert-butyl chloride catalytic system

Cationic polymerization of butadiene using a titanium tetrachloride—tert-butyl chloride catalytic system allows one to synthesize with high rates and yield fully soluble polybutadiene with controlled molecular characteristics. It was shown that the obtained cationic polybuta diene is characterized by predominantly 1,4-trans-structure and reduced unsaturation. The macromolecules of the cationic polybutadiene contain the initial tert-butyl and end chlorine-containing units.