Study On Anionic Polymerization Of Styrene And Methyl Methacrylate Using Dodecylbenzenesulfonate As Additive

Dodecylbenzenesulfonate was widely used thanks to its amphipathic molecular structure. Used dodecylbenzenesulfonate as μ-type ligand in anionic polymerization, the polymerization rate and microstructure of polymer could be adjusted. In this paper, we prepared n-butyllithium (naphthalene sodium)/alkyl sulfonate initiating system in various ways, and then we focused on status of active center and polymerization behavior of styrene and methyl methacrylate. Tracking analysis on alkyl sulfonate solution, initiating system, polymerization process was investigated by means of LPS, UV, NMR, GPC, SEM and TG. Our purpose was to further clarify the influence of alkyl sulfonate on anionic polymerization. The main conclusions were as follows:Dodecylbenzenesulfonate barium prepared by neutralization reaction, dissolved directly in cyclohexane and the particle size of the solution was micron. Experimental results revealed that polymer mixed with alkyl sulfonate. Dodecylbenzenesulfonate lithium solution was obtained through substitution reaction, whose particle size was nanometer level. After introduction of equimolar n-BuLi active center, the particle size distribution of aggregate became wider. There existed various active centers in polymerization system because of the presence of residual metal powder in preparation process, so that the characteristics of anionic living polymerization were missing.The LDBS/n-BuLi initiating system was prepared through "in situ" method of dropping n-butyllithium into dodecylbenzenessulfonic acid (DBSA)/cyclohexane solution. Polymer was composed of soluble and insoluble section. The reasons why the insoluble phenomenon occurred were the high degree of isotacticity and that LDBS was tightly including to polystyrene. The isotactic triad content in soluble section was41%, while the isotactic pentad content reached21%. With the increasing concentration of LDBS and [LDBS]/[n-BuLi] ratio, the activity of initiator and polymerization conversion reduced, and molecular weight distribution of polystyrene broadened.Owing to the low initiating activity of LDBS/n-BuLi, the polymerization of methyl methacrylate at0℃was proved to be available. Reaction temperature has less influence on the polymerization, so that the molecular weight and molecular weight distribution made little difference. Isotactic triad structure content (mm) of PMMA was about80%, and in tetrahydrofuran (mm) was smaller (44%). A trace amount of styrene was added dropwise into alkyl sulfonate system, short-chain polystyrene was polymerized, which was equivalent to hooded process. PSLi/n-BuLi could initiate the polymerization of methyl methacrylate, and PMMA achieved a narrow molecular weight distribution (2.39).In study on polymerization of styrene initiated by alkyl sulfonate/naphthalene lithium (sodium) system, the existence of equilibrium of naphthalene lithium (sodium) active center was confirmed. It formed a heterogeneous system, and this system did not have the characteristics of living polymerization.