Copolymerization of Myrcene with Styrene Catalyzed by Half-sandwich Scandium Complexes

The copolymerization of myrcene with styrene by the half-sandwich scandium complexes (C5H5) Sc(CH2SiMe3)(2)(THF) (1) and (C5Me4SiMe3) Sc(CH2SiMe3)(2)(THF) (2) was studied. The structures and thermal properties of the obtained copolymers were characterized by NMR, GPC and DSC. The copolymerization of myrcene with styrene at room temperature had been achieved and the copolymerization activity reached up to 104 g polymer molSc - 1 h(-1). The myrcene-styrene copolymers with controllable compositions (myrcene content = 22 mol% -83 mol%), high molecular weight (M-n = 4.8 x 10(4) - 11.3 x 10(4)) and narrow molecular weight distribution (Mw/Mn = 1.49 - 1.99) were conveniently obtained by changing the feed ratio of myrcene and styrene. Significant influence of catalyst structure on the stereoselectivity and comonomer distribution sequences in the resulting copolymers was observed. In the copolymerization of myrcene and styrene catalyzed by scandium complex 1, styrene started to incorporate into chains after myrene was almost completely consumed, and diblock copolymers containing cis-1,4-polymyrcene (selectivity 95%) block and atactic polystyrene block were obtained. The obtained copolymers with different myrcene contents possessed two glass transition temperatures (T-g, -63 and 96 degrees C), close to those of cis-1,4-polymyrcene and atactic polystyrene. In contrast, in the copolymerization of myrcene and styrene catalyzed by scandium complex 2, myrene content showed a gradient decline accompanied by styrene content increasing gradually, producing gradient copolymers containing 3,4-polymyrcene (3,4-selectivity 75%, cis-1,4-selectivity 25%) and syndiotactic polystyrene. The obtained copolymers with different myrcene contents possessed a T-g at - 35 degrees C and a melting temperature (Tm) at 254 degrees C, originating from polymyrcene block and syndiotactic polystyrene block, respectively. There is a great difference in the reactivity ratios between myrcene and styrene in the copolymerization catalyzed by scandium 1 (r(My) >> rSt). However, the gap between the reactivity ratios of myrcene and styrene in the copolymerization catalyzed by scandium complex 2 was much smaller (rMy = 8.47, r(St) = 0.76) and gradient copolymers were generated.