Dual-initiating and living frustrated Lewis pairs: expeditious synthesis of biobased thermoplastic elastomers

Biobased poly(gamma-methyl-alpha-methylene-gamma-butyrolactone) (PMMBL) has attracted interest because it is biorenewable and exhibits superior properties to petroleum-based linear analog poly(methyl methacrylate) (PMMA). Here the authors report the synthesis of well-defined PMMBL-based ABA tri-block copolymers, enabled by dual-initiating and living frustrated Lewis pairs, which have superior mechanical properties compared to those of PMMA-based tri-BCPs. Biobased poly(gamma-methyl-alpha-methylene-gamma-butyrolactone) (PMMBL), an acrylic polymer bearing a cyclic lactone ring, has attracted increasing interest because it not only is biorenewable but also exhibits superior properties to petroleum-based linear analog poly(methyl methacrylate) (PMMA). However, such property enhancement has been limited to resistance to heat and solvent, and mechanically both types of polymers are equally brittle. Here we report the expeditious synthesis of well-defined PMMBL-based ABA tri-block copolymers (tri-BCPs)-enabled by dual-initiating and living frustrated Lewis pairs (FLPs)-which are thermoplastic elastomers showing much superior mechanical properties, especially at high working temperatures (80-130 degrees C), to those of PMMA-based tri-BCPs. The FLPs consist of a bulky organoaluminum Lewis acid and a series of newly designed bis(imino)phosphine superbases bridged by an alkyl linker, which promote living polymerization of MMBL. Uniquely, such bisphosphine superbases initiate the chain growth from both P-sites concurrently, enabling the accelerated synthesis of tri-BCPs in a one-pot, two-step procedure. The results from mechanistic studies, including the single crystal structure of the dually initiated active species, detailed polymerizations, and kinetic studies confirm the livingness of the polymerization and support the proposed polymerization mechanism featuring the dual initiation and subsequent chain growth from both P-sites of the superbase di-initiator.