Study On The Appliczation Of New Explanation Of Anionic Polymerization Theory To The Structure Control Of Polyisoprene

Anionic polymerization has made significant breakthroughs in scientific research and industrial application over the last half century. Maturity theory of polymerization also is eatlabished. There is a kinetic equilibrium among free-ion, solvent-separated ion-pairs, contact ion-pairs and aggregated ion-pairs. However the problem that if this equilibrium will still exist in the chain propagation reaction has seemed an open question.In this paper, through the investigation of initiation process of n-BuLi and the effection of THF and P-Complex on the anionic polymerization of Ip, a new explanation of anionic polymerization theory to the structure control of PI is established.First, the bulk micro-flow polymerization of Ip is carried out below 35℃. Results show that the conversion is less than 2% within 3min and it introduces inaccuracy in the calculation of conversion and the purification of PI. In order to increase accuracy, the polymerization of Ip is operated in flask with three necks with cyclohexane as solvent and the conversion, relationship between the cis-1,4 content of PI and temperature, dosage of n-BuLi and reaction time is discussed. In the reaction, n-BuLi which occurs as hexameric-sturcture will dissociate to free ion-pairs. Because the distance between Li+ and carbanion when forming cis-1,4 and trans-1,4 which can be transformed each other through the rotation of single bond are almost the same and the energy of cis-1,4 is higher than trans-1,4, the content of cis-1,4 would decline as the temperature grows or dosage of n-BuLi reduces.Then the effection of THF and P-Complex on the polymerization of Ip is investaged. Results show the ionpair interspace is enlarged with the addition of THF and anionic polymerization of Ip can take place in 15℃and 25℃. When P-Complex was added in the polymerization system initiated by n-BuLi, the reaction between them was intensified because the lithium was shared by both P-Complex and n-BuLi. Therefore, the content of poly-3,4 isoprene increased to 66.1% and 57.9% respectively at 40℃and 70℃in the polymerization since the interspace between the ion pairs was blocked by P-Complex with big bulk.Finally, a new polymerization method of being initiated at a higher tempeture(50℃) and polymerized at a lower temperature(30℃) is studied.Meanwhile the difference of initiation between freshly-prepared and long-time stored n-BuLi is also investigated. Results show that the reaction rate initiated by freshly-prepared n-BuLi is a little faster but the microstructure of PI is still the same compared to that initiated by long-tome stored n-BuLi. The conversion reaches to 49% and the content of cis-1,4 remains unchanged through this new polymerization mothod.