Neodymium alk(aryl)oxides–dialkylmagnesium systems for butadiene polymerization and copolymerization with styrene and glycidyl methacrylate

The application of well-defined neodymium alkoxides/aryloxides in combination with dialkylmagnesium reagents for 1,3-butadiene (BD) polymerization and copolymerization with styrene (St) and glycidyl methacrylate (GMA) has been investigated. The trinuclear complex Nd3(Ot-Bu)9(THF)2 (1) provided a low-activity system for BD polymerization, even at high temperature, but with a high trans-1,4 stereospecificity (trans-1,4≈95%). Aryloxide complexes Nd(O-2,6-t-Bu2-4-Me-Ph)3(THF) (2) and Nd(O-2,6-t-Bu2-4-Me-Ph)3 (3) were found to give more active systems. The polymerization displayed a controlled character, i.e. a precise control of the molecular weight and a low polydispersity (Mw/Mn<1.30) for high catalyst concentration, keeping the same level of stereocontrol over the polymerization course. The statistical copolymerization of BD and styrene with those systems was successful. High-molecular weight copolymers (Mn up to 50 000 g mol−1) with noticeable styrene content (3–15 mol%) were synthesized. Determination of the microstructure by 13C-NMR showed exclusively trans-1,4-BD–St sequences. The livingness of BD polymerization encouraged attempts of diblock copolymerization with GMA. In this case, low-molecular weight polymers with variable polydispersities were obtained (Mn<20 000 g mol−1; Mw/Mn=1.4–5.0). The composition of the copolymers was analyzed by 1H- and 13C-NMR and IR spectroscopies. SEC analyses confirmed the true nature of the diblock copolymer. The influence of the alkylating agent on those (co)-polymerizations was briefly studied. Finally, the mechanism of polymerization is also discussed.