Synthesis and characterization of the well-defined polypentadiene via living anionic polymerization of (E)-1,3-pentadiene

Abstract

The well-defined anionic polymerization of (E)-1,3-pentadiene (EP) using various RLi initiators in nonpolar solvent was studied. The results of the polymerization kinetics with n-BuLi initiator in cyclohexane confirmed the expected living nature of the anionic polymerization of EP. An apparent activation energy of 86.17 ± 2.93 kJ/mol has been achieved for the poorly reactive EP polymerization, while an apparent activation energy close to 80 kJ/mol has been gained for the polymerization of IP under the same conditions. The obtained homopolymer with predictable molecular weights and narrow molecular weight distributions (1.05 ≤ Đ ≤ 1.19) was completely characterized by GPC, DSC, 1H NMR and quantitative 13C NMR. It was found that the trans-1,4 structure is predominant in the amorphous polymer and the portion of 1,2-structure is relatively fixed. The relatively low Tgs values ranging from −53 to −38 °C indicate that the polypentadiene is one of the potential candidates for a new elastomeric middle block, for example, polybutadiene and polyisoprene, in TPEs. Meanwhile the quantitative NMR results showed that the microstructure isomeric units as well as diad sequence distributions can be strongly affected by the polarity of solvent and the concentration of polar additives (THF, TMEDA, etc.). Finally an interpretation of the polymer's formation is proposed, moreover, an allylic-methylene zwitterionic intermediates mechanism is applied to rationalize the available polymerization results.