The Study Of Anionic Polymerization On Controlling The Degree Of Tacticity Of Polymers And Synthesis Of Block Polymers

The investigation on the anionic polymerization was carried out to aim at the lack of control involved with the stereoregularity of polymers, we set out to find a stable compound that might associate with living seeds to induce stereospecific placement. Some anionic homo-and block-polymerization of styrene, isoprene and butadiene have been studied in this paper.Crystalline trans-1 ,-4-polybutadiene (TPBD) and isotactic polystyrene (iPS) was successfully obtained with cyclohexane as solvent, n-BuLi as initiator and organometallic compounds as structure modifier. We also conducted experiments basing the advantage of anionic polymerization on synthesizing block copolymers to provide the production containing at least one iPS sequence.We have employed dodecyl benzene sulfonic acid barium salt in the anionic polymerization of butadiene and, as described below, we have obtained highly TPBD. It has been found that increasing the ratio of [Ba]/[Li] does appear to enhance the retardation effect. TPBD is typically prepared in cyclohexane at high temperature (90℃). The contents of polymerizer contains both cyclohexane soluble PB and about 87．5% precipitated TPBD resin. For the cyclohexane soluble fraction, the ¹H-NMR spectra indicates that its content of 1, 2-, 1, 4-are equal to 18．98%, 81．02% respectively. For the cyclohexane insoluble fraction, the IR spectra displays that its content of 1, 2-, trans-1, 4-, cis-1, 4-are equal to 43．40%, 49．87%, 6．73%.Isotactic polystyrene was prepared using dodecyl benzene sulfonic acid barium salt or dodecyl benzene sulfonic acid sodium salt as ligands. Polymerization reaction was sensitive to solvent, reaction temperature, polymerization method and so on. With MEK reflux,¹³ C-NMR, DSC, GPC the features of iPS chain structures have being analyzed and made quantitative calculations of the Isotactic Index of Polystyrene (IIP). It is revealed that the dodecyl benzene sulfonic acid barium salt as ligand, has a higher content of IIP (83．6%) than dodecyl benzene sulfonic acid sodium salt as ligand (77．4%).Diblock copolymers of isotactic polystyrene and polyisoprene (Pl-b-iPS) were successfully synthesized by sequential anionic synthesis of the isotactic polystyrene followed by the polybutadiene block. In cyclohexane media, when used in very low concentration, gives Pl-b-iPS exhibiting a small size of the polymer particle. Because cyclohexane is a good solvent for PI block , whereas the iPS block is insoluble in it, micelle-like aggregates result from manipulation of the solvent. The expected structure of such an aggregate in the cyclohexane solution is an inner iPS block surrounded by the PI shell. Micelle-like aggregate morphologies were observed by optical microscopy, AFM, SEM, TEM.In addition, guided by the predecessors work, preliminary polymerization mechanisms of TPBD and iPS were discussed briefly.