Abstract
Alternating copolymers consisting of a kind of mild electron-withdrawing 1,1-diphenylethylene (DPE) derivative and di-olefins, such as 1,1-bis(4-dimethylsilylphenyl)ethylene (DPE-2SiH) and isoprene (Ip), were successfully synthesized via anionic copolymerization using N,N,N',N'-tetramethylethylenediamine (TMEDA) as the modifier and benzene as the solvent. Two mild electron-withdrawing groups (binary-SiH) existed in this system. Therefore, the reaction activity of DPE-2SiH was higher than that of dimethyl-[4(1-phenylvinyl)phenyl]silane (DPE-SiH), and DPE-2SiH was expected to be an appropriate co-monomer for polymerization with dienes. The addition of TMEDA was found to not only control the resulting sequence but also regulate the contents of cis- and trans-structures in the Ip units. To further explore the mechanism of polymerizing DPE-2SiH and isoprene with and without the use of the TMEDA additive, the target samples were carefully characterized by SEC, H-1 NMR and in situ H-1 NMR. By examining the results, the apparent rate constants of DPE-2SiH and Ip without TMEDA were 1.19 x 10(-3) min(-1) and 1.29 x 10(-2) min(-1), respectively, while those of DPE-2SiH and Ip with TMEDA were 4.47 x 10(-5) min(-1) and 3.05 x 10(-5) min(-1), respectively. The reactivity ratios r(Ip) of isoprene with and without TMEDA were also calculated by the least square method and found to be 0.65 and 4.21, respectively, which illustrates the mechanisms of the copolymerization of DPE-2SiH and isoprene. By investigating the mechanism of the copolymerization process, the sequence can be controlled the alternating copolymerization, which can be facilely realized in a nonpolar solvent through the use of TMEDA. The alternating copolymers using this method have great significance both to regulation method of the microstructure of isoprene units and to the industrial production of functionalized materials. Then the alternating copolymers of DPE-2SiH and Ip were also applied to synthesize centipede-shaped grafted poly(isoprene)s (Pips). For the existence of bilateral -SiH groups in the chain, hydrosilylation of -SiH and alkynyl groups was performed at room temperature to avoid the unexpected reaction of the -SiH and alkenyl groups from the PIp branches.