One-Step Synthesis of Linear and Hyperbranched CO2-Based Block Copolymers via Organocatalytic Switchable Polymerization

CO2-based block copolymers are gaining significant momentum as high-value-added and functional materials. However, current synthetic achievements mainly rely on well-designed organometallic catalysts and only give access to linear polymeric products. Herein, we report the organocatalytic three-component polymerization of propylene oxide (PO), phthalic anhydride (PA), and CO2 mediated by commercial Lewis pairs composed of triethyl borane (Et3B) and organic bases, wherein the chemoselectivity over the reaction and Lewis basicity of the cocatalysts exhibit a negative correlation. Notably, the interplay of Et3B and 1,8diazabicyclo[5.4.0]undec-7-ene (DBU) bridges and discriminates the ring-opening copolymerization (ROCOP) of PO/PA and ROCOP of PO/CO2 without interferences, thus affording poly(propylene phthalate)-b-poly(propylene carbonate) (PPE-b-PPC) with linear and hyperbranched topologies by using benzyl alcohol and 1,3,4-benzene tricarboxylic anhydride as the chain transfer agent, respectively. Notably, the formation of undesirable cyclic byproducts was completely circumvented by rationally modulating the Et3B/CTA ratio. Moreover, the effect of topology on the viscosity, glass transition temperature, and thermal stability of PPE-b-PPC has been exploited.

Automated summary

CO2-based block copolymers as high-value-added and functional materials have gained significant attention. This study demonstrates the three-component polymerization of propylene oxide, phthalic anhydride, and CO2 using commercial Lewis pairs as catalysts, leading to the synthesis of linear and hyperbranched poly(propylene phthalate)-b-poly(propylene carbonate). Controlling the Et3B/chain transfer agent (CTA) ratio allows for the suppression of cyclic byproduct formation. The influence of topology on the properties of the copolymers is also investigated.