Synthesis of Arborescent Isoprene Homopolymers

Abstract

A method was developed for the preparation of isoprene homopolymers with a dendritic architecture using an anionic "grafting onto" methodology. A linear polyisoprene substrate with a high (95%) 1,4-content was first epoxidized to introduce grafting sites randomly along the chain. Coupling of the epoxidized polyisoprene with polyisoprenyllithium yielded a comb-branched or generation G0 arborescent polyisoprene. N,N,N′,N′-Tetramethylethylenediamine, BF 3, Me3Al, LiCl, and LiBr were investigated as promoters for the coupling reaction. Lithium salts were most effective, increasing the grafting yield from 78% to 92% for a linear substrate. Further epoxidation and grafting of the G0 polyisoprene led to arborescent isoprene homopolymers of generations G1 and G2. The attempted synthesis of a G3 arborescent polyisoprene was unsuccessful. The graft polymers were purified by precipitation fractionation and characterized by size exclusion chromatography (SEC), light scattering, and NMR spectroscopy. The products have narrow molecular weight distributions (M w/Mn e 1.05) consistent with a uniform molecular size and display geometric increases in molecular weight and branching functionality for successive generations. The absolute weight-average molecular weight values determined from light scattering measurement are much higher than the apparent SEC values because of the highly branched structure of the molecules.

Synthesis of graft polymers with poly(isoprene) as main chain by living anionic polymerization mechanism

“…The homopolymer PI was obtained by LAP mechanism of isoprene monomers using n ‐Bu − Li + as initiator and end‐capped with methanol. Then, the PI was epoxidized with performic acid generated in situ from H 2 O 2 /HCOOH system,29 which was an excellent reagent due to its low cost and relatively good reproducibility of the substitution level 28. Figure 1 showed the size exclusion chromatography (SEC) traces of PI and EPI, their monomodal peaks and low PDIs confirmed that the LAP and subsequent epoxidation were successful.…”

“…That was, there was about 416 epoxide groups on each EPI main chain. Usually, the PE value could also be adjusted by controlling the temperature, reaction time, and the ratio of H 2 O 2 /HCOOH or H 2 O 2 /CC 28,30…”

Arborescent polymers and other dendrigraft polymers: A journey into structural diversity

“…Thus a technique was developed recently for the synthesis of arborescent homopolymers from polyisoprene chains by partial epoxidation of the polyisoprene substrates and coupling with polyisoprenyl anions in the presence of lithium halides. 19 A one-pot method was also developed for the synthesis of arborescent styrene homo-and copolymers. 20 It relies on the anionic copolymerization of styrene and 1,3-diisopropenylbenzene, and subsequent activation of the pendent double bonds with sec-butyllithium to produce polyfunctional macroinitiators.…”

A rheological study on non-rubber component networks in natural rubber

“…And the natural rubber (NR) latex, collected from the Hevea trees as a colloidal suspension [1], is the main commercial feedstock for rubber and latex dipping industries. Under this circumstance, synthetic analogue polyisoprene with high expectations to replace natural rubber is modified mainly by various molecule design [8][9][10][11][12][13], while the comprehensive properties were disappointing. [2,3] Nowadays, natural rubber has become increasingly important for applications spanning many fields of chemistry, the hygienic and medical sectors, and it is further involved in a broad spectrum of consumer products in our daily life [4][5][6][7].…”