Investigation Of The Living Anionic Alternating Copolymerization Of DPE-SiH And Isoprene

Polymer materials have had a profound impact on the development of the national economy.But nowadays,it is necessary for meet the needs of booming economy to synthesize more high-performance,multifunctional polymers.As we all know,the structure of a polymer is closely related to its properties,especially the primary structure of the polymer—the sequence distribution.Therefore,the synthesis of polymers with a well-defined sequence distribution is particularly important for studying the structure-function relationship between polymer structure and properties.Living anionic polymerization has good controllability in molecular weight,molecular weight distribution,micro structure,etc.,and which is widely used in the synthesis of sequence-controlled polymers.Due to its unique advantages,DPE derivatives have been widely used in anionic polymerization to synthesize alternating copolymers.The DPE derivative/styrene polymerization system needs to broaden the range of comonomers due to the difficulty of functionalization of comonomer styrene and the single main chain structure.Dienes,as a kind of monomer with diverse structures,ha ve attracted widespread attention.However,dienes monomers such as isoprene(Ip)and butadiene(Bd)copolymerized with DPE in non-polar solvents all show a high reactivity ratio,which makes it difficult to achieve sequence control.Based on the above problems,this subject adopts 1-(4-dimethylsiloxphenyl)-1-styrene(DPE-SiH)highly reactive DPE derivative as a comonomer,which is combined with Ip through living anionic polymerization.Synthesized copolymers with different sequence distributions and microstructures,and achieving the controlled of the monomer sequence distribution in the copolymer chain.The main findings are as follows:1.The DPE-SiH with weak electron-withdrawing group was synthesized and copolymerized with Ip in solvent benzene by living anionic polymerization.By changing the monomer feed ratio of DPE-SiH and Ip and the types of modifiers,copolymers with different sequence distributions are obtained.The in situ ¹H NMR real-time monitoring technology was used to study the kinetics of DPE-SiH/Ip copolymerization without additives.The results showed that the conversion rate of Ip in the copolymer is much higher than that of DPE-SiH without additives.DPE-SiH is mainly distributed at the end of the polymer chain,and a gradient copolymer is obtained.The Ip reactivity ratio(r _Ip)is 9.28.It exhibits high copolymerization activity without additives.2.The sequence control of DPE-SiH and Ip units in the copolymer chain was realized by introducing additives,The addition of the additives greatly improves the relative copolymerization activity of DPE-SiH.It was found that there was no significant difference in the cis-trans content of Ip units in the alternating copolymer chain when studied the microstructure of the alternating copolymer.Based on density functional theory(DFT),the mechanism of the additive's action on the active center is simulated.Under the action of the additives,the active center with DPE-SiH as the subterminal has no selectivity to the Ip cis-trans structure.In the DPE-2Si H/Ip alternating copolymerization of the research group,when DPE-2Si H is the secondary terminal,the microstructure of Ip shows significant selectivity.It indicates that the growth behavior of the active center(D-M-Li·A)was obviously affected by the structure of the DPE derivative from the subterminal in the alternating copolymerization of DPE derivatives.The structure of the secondary terminal unit plays an important role in stereo control.