Styrene–isoprene and styrene–1,3-pentadiene copolymerisation catalyzed by titanium [OSSO]-type catalysts

Abstract

The synthesis of styrene–isoprene and styrene–1,3-pentadiene binary copolymers promoted by the titanium complexes dichloro{1,4-dithiabutanediyl-2,2′-bis(4,6-di-tert-butylphenoxy)}titanium (1) and dichloro{1,4-dithiabutanediyl-2,2′-bis[4,6-bis(2-phenyl-2-propyl)phenoxy]}titanium (2) activated by methylaluminoxane (MAO) is reported. Both copolymers were obtained in a wide range of compositions and the molecular weight distributions obtained from GPC analysis of the copolymers are coherent with the material being copolymeric in nature. DSC analysis shows an increase of T_g by increasing the amount of styrene in the copolymers, for both binary copolymers. Furthermore, ¹³C NMR analysis of the copolymer microstructure allowed the assessment of the monomer block lengths and distribution in the polymer chain revealing a random distribution with the catalyst 1 and 2 for both binary copolymers and a low tendency to form long styrene homosequences. Intriguingly, both in styrene–isoprene and in styrene–1,3-pentadiene copolymers, the catalyst 2 produces polymers with higher vinyl (3,4 for isoprene and 1,2 for 1,3-pentadiene) content with respect to catalyst 1 giving interesting insights about the mechanism of stereocontrol for this class of catalysts.