Synthesis of amphiphilic diblock copolymers of isotactic polystyrene-block-isotactic poly(p-hydroxystyrene) using a titanium complex with an [OSSO]-type bis(phenolate) ligand and sequential monomer addition

Abstract

A series of isotactic diblock copolymers of polystyrene-block-poly(p-tert-butyldimethylsilyloxystyrene) (iPS-b-iP(p-TBDMSOS)) were successfully synthesized using living coordination polymerization techniques with a kind of titanium dichloro complex containing a 1,4-dithiabutandiyl-linked [OSSO]-type bis(6-cumyl-4-methyl phenolato) ligand (complex 1) activated by methylaluminoxane (MAO) as a catalyst. Nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), infrared spectroscopy (IR), and differential scanning calorimetry (DSC) were used to characterize the copolymers. iPS-b-iP(p-TBDMSOS) had a higher molecular weight than that of the iPS prepolymer, and a narrow molecular weight distribution below 1.35. The diblock copolymers displayed two glass transition temperatures (T_g) at ∼97 and ∼117 °C, originating from iPS and iP(p-TBDMSOS) blocks, respectively. Furthermore, a novel well-defined amphiphilic diblock copolymer consisting of iPS (nonpolar block) and isotactic poly(p-hydroxystyrene) (iP(p-HOS), polar block), was achieved through hydrolysis of iP(p-TBDMSOS) block of iPS-b-iP(p-TBDMSOS) in the presence of hydrochloric acid. The obtained amphiphilic diblock copolymers self-assembled into spherical micelles with size of approximately 70 nm in methanol.