Organotitanium-Mediated Stereoselective Coordinative/Insertive Homopolymerizations and Copolymerizations of Styrene and Methyl Methacrylate

Abstract

This contribution describes coordinative/insertive stereoregular homopolymerizations and copolymerizations of styrene and methyl methacrylate (MMA) mediated by a highly active single-site organotitanium catalyst. The catalyst system used to effect these polymerizations of nonpolar and polar olefinic monomers is prepared by in situ Zn reduction of the precursor derived from the reaction (Me(5)Cp)TiMe(3) + Ph(3)C(+)B(C(6)F(5))(4)(-). The resulting catalyst produces polystyrene (>95% syndiotactic, 170 000 g/mol molecular weight; s-PS) by the established coordinative/insertive pathway. The same catalyst mediates polymerization of MMA to poly(methyl methacrylate) (>65% syndiotactic, >70 000 g/mol molecular weight; s-PMMA) by a group transfer protocol-like (GTP-like) pathway (1,4 insertion mechanism). Under optimal conditions, this catalyst also mediates the copolymerization of MMA + styrene (1:19 ratio) at 50 degrees C to yield random approximately 80% coisotactic poly[styrene-co-(methyl methacrylate)] (coiso-PSMMA) which contains approximately 4% MMA. Control experiments argue that a single-site Ti catalyst is the active species for the copolymerization. The catalyst formation process is quite general, and a variety of reducing agents can be substituted for Zn and still effect copolymerization. Control experiments also indicate that known noncoordination copolymerization mechanisms (i.e., ionic or radical) cannot explain this copolymerization. We suggest a new mechanism involving sequential conjugate addition steps to explain these copolymerization results.

An environmentally benign room temperature aqueous homo‐ and copolymerization of styrene and methylmethacrylate catalyzed by [Cp2TiCl2]/NaBPh4

“…Group 4 cationic complexes are highly active single‐site catalyst for stereocontrolled polymerization of variety of olefins. Polymerization of monomers with polar functional groups with early transition metal catalyst still remains a challenge even in nonaqueous medium 1. Zirconocenes16–18 and lathanocenes19, 20 have been found to be effective catalysts for polymerization of methacrylate monomers in nonaqueous medium.…”

Synthesis of high molecular weight polymer nanoparticles by [Cp2ZrCl2] catalyzed emulsion polymerization

“…S5) of the copolymer show peaks for the methoxy (OCH 3 ) protons of the enchained MMA units in the region δ 2.1–δ 3.6 ppm. The most intense peak around δ 3.57 ppm is due to cosyndiotactic MMA units 25. Thus, the 1 H NMR studies show clearly that, the copolymers contain atactic polystyrene with cosyndiospecifically enchained MMA units.…”

“…It may be noted that the amount of homopolymers obtained by evaporating the cyclohexane and acetonitrile extracts were negligible. The fraction of styrene was determined by using the formula 3A phenyl /3A phenyl + 5A α‐methyl , where A phenyl = area of the phenyl proton resonances and A α‐methyl = area of MMA α‐methyl proton resonances in 1 H NMR spectra 25. Details of the results of copolymerization are given in Table 5.…”

Ophthalmic changes in severe anorexia nervosa: A case series

“…A clear improvement is observed by increasing the amount of Zn to Ti/Zn = 4/8 with a dramatic drop in polydispersity to about 1.25. This trend reflects the heterogeneous nature of Zn as well as its possible involvement (via fast Ti reduction)53 in both the initiation and reversible termination.…”