Study On Synthesis Of High Trans-1,4-polybutadiene And Its Copolymers By Anionic Polymerization

High trans-1,4-polybutadiene(HTPB) and its copolymers exhibit desirable dynamic properties,such as excellent antifatigue,low rolling resistance,low heat buildup,good green strength and low abrasion loss.These properties make HTPB and its copolymers the idea materials for the production of high performance tires.HTPB can be prepared with Ziegler-Natta catalysts of Ti,Ni,Co,V,or anionic polymerization initiators.Due to the living nature,anionic polymerization is able to well design the macromolecules to meet different requirements.Fully recognizing the significant advantages of anionic polymerization,the syntheses of HTPB and its copolymers by anionic polymerization are surveyed.The preparation of HTPB and its copolymers were investigated,a series of block copolymers containing HTPB were also designed and synthesized.The initiation system was composed of di(ethylene glycol) ethyl ether(BaDEGEE), triisobutylaluminium(TIBA),and alkyllithium(RLi).The homopolymerization of Butadiene (Bd),Isoprene(Ip),or Styrene(St) and the copolymerization of Bd and Ip were studied.The effect of Al/Li ratio on the microstructure of the polymer and the kinetic behavior were both carefully investigated.Last,but not least,a series of block copolymers containing HTPB were synthesized and characterized.The main results and conclusions are as follows:The trans-1,4 content of polybutadiene(PB) increased from 50%to 89%along with the increasing of Al/Li ratio;the trans-1,4 content of polyisoprene(PI) increased from 24%to 46%as well as 3,4 content along with the increasing of Al/Li ratio;the microstructure of polystyrene(PS) was invariable and atactic.In addition,the trans-1,4 content of PB was promoted to 92.1%by lowering the polymerization temperature.The morphology of PB transformed from amorphous phase to crystalline phase through the intermediate state of semicrystalline phase with the increasing trans-1,4 content of PB.The kinetic behavior of Bd, Ip,or St was significantly influenced by Al/Li ratio,especially for St,the retarding effect was obvious when Al/Li ratio was bigger than 1.0;when using different RLi,the effect of Al/Li ratio on the kinetic behavior of Bd and Ip was different.For Bd-Ip copolymerization,the value of r_Bd was bigger than that of r_Ip and decreased with the increasing of polymerization temperature or Al/Li ratio,however,the value of r_Ip increased.The value of r_Bdr_Ip increased and approaching to constant,which indicated the random nature of the copolymer. Furthermore,the copolymerization of Bd and Ip tended to be constant copolymerization by lowering the polymerization temperature or raising Al/Li ratio.The anionic polymerization of St using BaDEGEE/TIBA/n-BuLi as initiation system was investigated.The molecular weight distribution of PS obtained by BaDEGEE/PSLi was bimodal distribution.Simultaneous promoted-retarded polymerization was supposed and proved to be responsible for the bimodal distribution:the polymerization was promoted when 0＜Ba/PSLi＜0.17,the polymerization was simultaneous promoted and retarded when 0.17≤Ba/PSLi＜0.33,and the polymerization was retarded when Ba/PSLi≥0.33.Noncrystalline-crystalline stereo diblock PB(LCPB-b-HTPB),crystalline-noncrystalline -crystalline stereo triblock PB(HTPB-b-LCPB-b-HTPB),and crystalline-noncrystalline star-shaped stereoblock PB were well designed.Attributed to the lubricant-effect of flexible LCPB,cold crystallization was observed in stereoblock PB.Bd-Ip block copolymers(HTPB-b-PI,C-(PI-b-HTPB)n,C-(HTPB-b-PI)n,and PI-b-HTPB -b-PI) and Bd-St block copolymers(HTPB-b-PS,C-(PS-b-HTPB)n,C-(HTPB-b-PS)n, and PS-b-HTPB-b-PS ) containing crystallizable HTPB were well synthesized,the microstructures and properties of the copolymers were investigated in detail.When the chain length of PI segments was long enough,cold crystallization was observed in Bd-Ip block copolymers,however it was not observed in Bd-St block copolymers.When the chain length of PS segments in Bd-St block copolymers was long enough,micro phase separation took place and two glass transition temperatures were observed and belonged to amorphous PB phase and PS phase,respectively.As a consequence of the above,the requirements of cold crystallization were list as follows:the segments were soft and long enough.Because the PS segments were hard,which resulted in no lubricant effect,cold crystallization was not observed although the chain length of PS segments was long enough.In the same way,the soft PI segments with insufficient chain length could not induce cold crystallization;however,the cold crystallization took place when the length of soft PI segments was long enough.