Comprehensive structural characterization of polyisoprene synthesized via cationic mechanism

Abstract

The microstructure of polyisoprene synthesized with t BuCl/TiCl 4 initiating system is investigated using 1D and 2D (HSQC and HMBC) NMR spectroscopy. It is found that trans-1,4-units with regular (head-to-tail) and inverse (tail-totail) and (head-to-head) enchainments are predominant structures of unsaturated part of polymer chain, while 1,2-and 3,4-units are presented in minor amounts. The new methodology for the quantitative calculation of the content of different structural units in polyisoprene chain including both types of inverse trans-1,4-addition (tail-to-tail and head-to-head) is proposed. It is shown that head groups consist of tert-butyl group connected to trans-1,4-unit of polyisoprene chain. In addition, two types of chlorine-containing end groups are found (trans-4,1-Cl and 4,3-Cl), while conjugated double bonds at the chain end are totally absent. The methodology for the calculation of number-average functionality by tertbutyl head and chlorine end groups, respectively, is developed.

The Structure of Cationic Polyisoprene: Branching versus Cyclization

“…Figure shows 13 C NMR spectra of original sample as well as polyisoprene fractions 2F and 7F. The unsaturation and microstructure of polymer chain as well as the content of head and end groups for each fraction (Table and Table ) were calculated based on the analysis of intensities of carbon atoms of corresponding structural units …”

“…The unsaturation and microstructure of polymer chain as well as the content of head and end groups for each fraction ( Table 1 and Table 2 ) were calculated based on the analysis of intensities of carbon atoms of corresponding structural units. [ 27 ] As it is seen from Table 1 , the unsaturated part of polymer chain consists of trans -1,4-units (92-95 mol%) and the content of this structural unit almost does not depend on molecular weight of corresponding fraction. Some decrease of the amount of trans -1,4-units in lowmolecular-weight fractions (1F and 2F) is consistent with high content of chlorine-containing 3,4-units at the chain end (structure TII in Figure 2 ) due to the low degree of polymerization for these fractions.…”

“…Polyisoprene sample was synthesized by cationic polymerization using t BuCl/TiCl 4 initiating system according to procedure reported in work . Polymerization conditions: [TiCl 4 ] = 1.5 × 10 −2 m ; [ t BuCl] = 4.5 m ; [C 5 H 8 ] = 4.0 m ; temperature: −20 °C; time: 16 min; yield: 76.5%.…”

“…Polyisoprene sample was synthesized by cationic polymerization using t BuCl/TiCl 4 initiating system according to procedure reported in work. [ 27 ]…”

“…In this work, polyisoprene with broad MWD synthesized using t BuCl/TiCl 4 initiating system was used for the fractionation. Importantly, polydienes obtained using above‐mentioned catalytic system contain tert ‐butyl ( t Bu) head and chloride end groups, respectively, which can be quantitatively determined by 13 C NMR spectroscopy . This, in turn, facilitates the precise characterization of polymer as well as its fractions.…”