Synthesis Of Diene Oligomers By Anionic Polymerization And Its Rheological Properties

Liquid rubber is a polymer with fluidity at room temperature and low glass transition temperature,and has the potential to be used as synthetic base oil.The construction of the relationship between the structure and rheology of liquid rubber has profound guiding significance for its future application in synthetic base oil and so on.In this paper,a series of liquid polyisoprene,liquid polybutadiene and their copolymers with different topological molecular structures were designed and synthesized by anionic living polymerization,and some liquid rubbers were hydrogenated to obtain saturated diene liquid rubbers.The relationship between their structure and molecular chain flexibility and rheology was further explored,and the relationship between structure-molecular chain flexibility and structure-rheology of diene liquid rubber was established.The main research results are as follows:1.Synthesis of diene oligomers.The linear liquid polyisoprene with molecular weight of 1100～11700 g/mol,PDI of 1.17～1.52 and1,4-Ip structure content of 93.9～94.8% was designed and synthesized.Then,by adding tetrahydrofuran or tetrahydrofurfuryl alcohol ethyl ether to adjust the microstructure of the polymer,linear liquid polyisoprene with molecular weight of 1100-3100 g/mol and PDI of 1.17-1.44 was synthesized.After adding the modifier,the 1,4-Ip structure content of the liquid polyisoprene was greatly reduced by only 18.1～40.2%,while the3,4-Ip structure was greatly increased,and a small amount of 1,2-Ip structure appeared.The ability of tetrahydrofurfuryl alcohol ethyl ether to adjust the microstructure is greater than that of tetrahydrofuran.Star liquid polyisoprene with 3-4 arms and 5-6 arms with a single-arm molecular weight of 300-4200 g/mol was designed and synthesized.Adding 5 equivalents of tetrahydrofuran after the completion of the polymerization reaction would make the arm number and coupling efficiency simultaneously improve.Linear liquid polybutadiene with molecular weights of 2400-11400 g/mol,PDI of 1.07-1.34 and 1,4-Bd structure content of 88.9-92.9% was designed and synthesized.The star liquid polybutadiene with 3-4 arms and low,medium and high 1,4-Bd unit structure content with single-arm molecular weight of 960-8000g/mol was designed and synthesized.And the star liquid polybutadiene with medium and low 1,4-Bd structure was hydrogenated,and the hydrogenation degree reached 89.9～96.1%.Linear and star block copolymers with Bd:Ip=3:7,1:1,4:1,19:1 were designed and synthesized.Their molecular weights were 2600～4200 g/mol and PDI was 1.26～1.40,The content of 1,4-Ip and 1,4-Bd is about 90%.2.Studies on the rheology and glass transition temperature of dienes.When other structural parameters are similar,the glass transition temperature,kinematic viscosity and viscosity index of liquid polyisoprene and liquid polybutadiene with high 1,4-structure content all increase gradually with the increase of molecular weight.However,linear polymers show a plateau in the graph of kinematic viscosity and molecular weight when the molecular weight is in the range of6000～8000 g/mol.The kinematic viscosity and molecular weight before and after the plateau show a linear relationship,but the slopes of the two are different,and the kinematic viscosity and viscosity index of linear liquid polyisoprene and butadiene are higher than the corresponding star polymers.The increase of short chain branches will make the glass transition temperature and kinematic viscosity of liquid polyisoprene and liquid polybutadiene increase significantly,while the viscosity index decreases significantly.When the total molecular weight is similar,the single arm of the polymer with more arms has lower molecular weight,and its kinematic viscosity and viscosity index are lower than those of the polymer with fewer arms,and when the molecular weight of the single arm is similar,the polymer with more arms has higher kinematic viscosity and viscosity index.Compared with the star polymer with more short-chain branches in the molecular chain,the star polymer with fewer short-chain branches on the periphery and more short-chain branches near the star core has a lower kinematic viscosity and a higher viscosity index.The decrease in the content of double bonds in the molecular chain will also increase the glass transition temperature and kinematic viscosity of the polymer and decrease the viscosity index significantly.When the molecular chain is relatively smooth,the increase in the content of the pendant methyl group will reduce the viscosity index of the polymer.The increase of the butadiene unit content and the decrease of the isoprene unit content will make the glass transition temperature and kinematic viscosity of the butadiene-isoprene block copolymer decrease,and make the viscosity index increase.When other structural parameters are similar,the order of kinematic viscosity is polyisoprene>butadiene-isoprene block copolymer>polybutadiene,while the order of viscosity index is polyisoprene<butadiene-isoprene block copolymer < polybutadiene.