Leveraging the Enantiomeric Excess of Catalyst for Precise Stereocontrol in Poly(3-hydroxybutyrate).

Abstract

The properties of polymers are governed by multi-level structural parameters, with tacticity being particularly critical for crystallization, thermal, and mechanical performance. Conventional approaches to modulate tacticity-such as tuning monomer enantiomeric excess or synthesizing distinct catalysts-are often complex and lack precise control. To address this challenge, we present a stereocontrol strategy by exploiting an enantiopure catalyst governed by an enantiomorphic site control (ESC) mechanism and polymeric exchange between the enantiomer pair. As a result, the enantiopure DiMeBiPh-BINOL-salen catalysts (R, R)-Y1 and (S, S)-Y1 were designed and demonstrated outstanding isoselectivity for the ROP of rac-BBL via the ESC mechanism. Their racemic pair rac-Y1 exhibited high syndioselectivity (P_r = 0.93) due to polymeric exchange. Ultimately, a series of P3HB products with streamlined tacticity (P_m: 0.07-0.90) was readily prepared by simply adjusting the enantiomeric excess (ee) values of the catalyst. A systematic investigation of the relationship between tacticity and material properties was performed. This work not only establishes an efficient and controllable route to tailor-made P3HB but also provides a scalable pathway for precise stereocontrol in polymer synthesis.