Titanium-mediated [CpTiCl₂(OEt)] ring-opening polymerization of lactides: a novel route to well-defined polylactide-based complex macromolecular architectures

Among three cyolopentadienyl titanium complexes studied, CpTiCl ₂(OEt), containing a 5% excess CpTiCl₃, has proven to be a very efficient catalyst for the ring-opening polymerization (ROP) of L-lactide (LLA) in toluene at 130 °C Kinetic studies revealed that the polymerization yield (up to 100%) and the molecular weight increase linearly with time, leading to well-defined PLLA with narrow molecular weight distributions [M _w/M_n ≤ 1.1). Based on the above results, PS-b-PLLA, PI-b-PLLA, PEO-b-PLLA block copolymers, and a PS-b-PI-b-PLLA triblock terpolymer were synthesized. The synthetic strategy involved: (a) the preparation of OH-end-functionalized homopolymers or diblock copolymers by anionic polymerization, (b) the reaction of the OH-functionalized polymers with CpTiCl₃ to give the corresponding Ti-macrocatalyst, and (c) the ROP of LLA to afford the final block copolymers. PMMA-gPLLA [PMMA: poly(methyl methacrylate)] was also synthesized by: (a) the reaction of CpTiCl₃ with 2-hydroxy ethyl methacrylate, HEMA, to give the Ti-HEMA-catalyst, (b) the ROP of LLA to afford a PLLA methacrylic-macromonomer, and (c) the copolymerization (conventional and ATRP) of the macromonomer with MMA to afford the final graft copolymer. Intermediate and final products were characterized by NMR spectroscopy and size exclusion chromatography, equipped with refractive index and two-angle laser light scattering detectors.