Living Polymer Chains with Predictable Molecular Weight and Dispersity via Carbanionic Polymerization in Continuous Flow: Mixing Rate as a Key Parameter

Aiming at systematic variation of the parameter dispersity, D (or "polydispersity"), living polymers with predictable dispersity (D = 1.15-2.20) and controlled molecular weights (M-n = 3200-18 500 g mol(-1)) were prepared via carbanionic polymerization. The approach relies on a continuous flow reactor equipped with a tangential four-way jet micromixing device. By varying the total flow rate, the mixing efficiency of the initiator (sec-BuLi) and the corresponding vinyl monomers is controlled, resulting in polymers with predefined dispersity, while the number-average molecular weight, Mn, is kept constant. In this manner living polystyrene (PS), poly(p-methylstyrene) (PpMeS), and poly-(2-vinylpyridine) (P2VP) samples with systematically varied D (studied by SEC) were prepared. All polymerizations were carried out at room temperature in a 50:50 solvent mixture of THE with either hexane for PS and PpMeS or with benzene for the polymerization of 2VP. To prove the living character of all polymer chains of the distributions obtained, all carbanionic chains were labeled, i.e., end functionalized via addition of an epoxide (benzyl glycidyl ether, BGE) as a termination reagent, when full conversion of the monomer was reached. Subsequent MALDI-ToF characterization confirmed the living character of all chains of the distributions. This is key for the further generation of complex polymer architectures with tailored polydispersity. Using the living carbanions with different dispersity, in an exploratory study, PS-b-PI block copolymers with controlled dispersity of the styrene block have been prepared via direct addition of isoprene as a second monomer.