1,2-Polybutadiene Latices by Catalytic Polymerization in Aqueous Emulsion

Catalytic aqueous polymerization of butadiene by the cobalt catalyst system [Co(C8H13)(C4H6)]/CS2 affords colloidally stable latices of highly crystalline syndiotactic 1,2-polybutadiene (Tm ) 190 °C, ∆Hc ) 60 J/g, Mw ∼ 105 g/mol, 97% 1,2, 3% 1,4-cis). Catalyst modification with reagents containing electrophilic carbon atoms (e.g., aromatic formamides) strongly decreases polymer crystallinity (Tm ) 60-100 °C, ∆Hc ) 11 J/g, Mw ∼ 8 × 104 g/mol for 85% 1,2). Latices of typically 150-200 nm particles are prepared. During polymerization affording low crystalline polymers the number of particles stays constant. Microstructures were analyzed by 13C NMR of hydrogenated polymers. In all polymers the 1,4-units are largely isolated. Crystallinity decrease results from an increase of 1,4-insertion frequency and the resulting decrease of 1,2-block length. Considerations on the nature of the active species are discussed. Copolymerization of butadiene with isoprene by [Co(C8H13)(C4H6)]/CS2 affords low crystalline copolymers; styrene is not incorporated as a comonomer.