Anionic Polymerization of 1,3-Cyclohexadiene with Alkyllithium/Amine Systems. Characteristics of n-Butyllithium/N,N,N‘,N‘-Tetramethylethylenediamine System for Living Anionic Polymerization

Abstract

The n-butyllithium (n-BuLi)/N,N,N',N'-tetramethylethylenediamine (TMEDA) system (with the molar ratio of TMEDA to n-BuLi higher than 4/4) has been found to polymerize 1,3-cyclohexadiene to produce "living" polymer having a narrow molecular weight distribution with well-controlled polymer chain length. The rate of polymerization and polymer yield increased with increasing of the ratio of TMEDA to n-BuLi. The molecular weight distribution of obtained polymers became narrower with the ratio of TMEDA to n-BuLi. The formation of benzene generated by termination reaction was found to decrease with the ratio of TMEDA to n-BuLi. In contrast to 1,3-cyclohexadiene, low yield and broad molecular weight distribution were observed in the polymerization of 1,3-hexadiene and 2,4-hexadiene initiated by the n-BuLi/TMEDA (4/5) system. The microstructure of poly(1,3-cyclohexadiene) was determined by 2D-NMR. A high content of 1,2-units was found in the polymerization initiated by the alkyllithium/TMEDA system, while the high content of 1,4-units was observed in the cases of alkyllithium or alkyllithium/1,4-diazabicyclo[2,2,2]octane system. The 7Li NMR signals of the n-BuLi/TMEDA systems and poly(1,3-cyclohexadienyl)lithium /TMEDA were in higher magnetic field than the signals of n-BuLi and poly(1,3-cyclohexadienyl)lithium, respectively, indicating the disaggregation of the lithium species.

Thermal Degradation of Poly(1,3‐cyclohexadiene) and its Dehydrogenated Derivatives: Influence of a Controlled Microstructure

“…In the previous paper, [28] we reported the study of alkyllithium (RLi)/amine and poly(1,3-cyclohexadienyl)-lithium (PCHDLi)/amine systems by measuring Li NMR. The obtained results suggested the disaggregation of RLi and PCHDLi by the coordination of amine to Li atom, and the C-Li bond was thought to be strongly polarized.…”

“…The polymers obtained under these conditions were of low molecular weight or in low yield, and the molar ratio of 1,2-addition (1,2-CHD unit) and 1,4-addition (1, to the polymer chain could not be controlled. [1][2][3][4][5][6][7][8][9][10][11][20][21][22][23][24][25] Before our discovery of the living anionic polymerization of 1,3-CHD, [26][27][28] there had been no successful examples for a method of controlled polymerization of 1,3-CHD, and it has been very difficult to elucidate the relationship between the microstructure and properties of PCHDs and their modified derivatives. In previous papers, [26][27][28][29] we reported the first successful example of living anionic polymerization of 1,3-CHD; homopolymers, copolymers, and block copolymers with narrow molecular weight distribution, controlled molecular weight and a clear polymer chain structure were successfully synthesized.…”

Microphase-separated structure of 1,3-cyclohexadiene/butadiene triblock copolymers and its effect on mechanical and thermal properties

“…Especially, CHD/butadiene triblock copolymers that have various content ratio of PCHD unit, and polybutadiene unit were designed. 3 In this report, we will discuss the effect of molecular design on the microphase-separated structure and the properties of those novel CHD/ butadiene block copolymers. We will also describe the relationship between mechanical and thermal properties and morphology regarding the hydrogenated block copolymers by hydrogenation of CHD and butadiene units in the polymer chains, which is another important object in this report.…”

Hydrogenation of Poly(1,3-cyclohexadiene)

“…The 1,2-CHD units/1,4-CHD units molar ratio can be determined by two dimensional NMR. 5,6 The 1,2-and 1,4-CHD units can be regarded as the derivatives of cyclohexene. Therefore, the result of hydrogenation of cyclohexene (which is the most simple model compound for the 1,2-and 1,4-CHD units) seemed a good model for the initial screening of homogeneous catalysts for the hydrogenation of PCHD.…”

“…The catalytic hydrogenation of PCHD has not been attempted before this paper. 1,2 In previous papers, [3][4][5] we reported the first successful living anionic polymerization of 1,3-CHD with the n-BuLi/N,N,N ,N -tetramethylethylenediamine (TME-DA) system as an initiator, and showed examples of the synthesis of homopolymers and block copolymers with a narrow molecular weight distribution and controlled molecular weight. Furthermore, we prepared PCHE with various molecular weights and their block copolymers by the hydrogenation of PCHD homopolymer and block copolymers with heterogeneous catalysts.…”