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Borane‐based Lewis acids (LA) play an indispensable role in the Lewis pair (LP) mediated polymerization. However, most borane‐based LPs are moisture‐ and air‐sensitive. Therefore, development of moisture and air‐stable borane‐based LP is highly desirable. To achieve this goal, the concept of "aggregation induced enlargement effects" by chemically linking multiple borane within a nanoscopic confinement was conceived to create macromolecular LA. Accordingly, an extremely moisture and air stable macromolecular borane, namely, PVP‐1B featuring poly(4‐vinylphenol) backbone, was constructed. The concentration of borane active site is greatly higher than average concentration due to local confinement. Therefore, an enhanced activity was observed. Moreover, the local LA aggregation effects allow its tolerance to air and large amount of chain transfer agent. Consequently, PVP‐1B showed remarkable efficiency for propylene oxide (PO) polymerization at 25 °C (TOF=27900 h−1). Furthermore, it enables generation of well‐defined telechelic poly (CHO‐alt‐CO2) diol (0.6–15.3 kg/mol) with narrow Đs via copolymerizing cyclohexene oxide and CO2 at 80 °C. This work indicates unifying multiple borane within a polymer in a macromolecular level shows superior catalytic performance than constructing binary, bi(multi)functional systems in a molecular level. This paves a new way to make functional polyethers. [ABSTRACT FROM AUTHOR]

It is a highly attractive strategy to develop chemically recyclable polymers to establish a circular plastic economy. Despite the recent advancements, chemically recyclable polymers still face challenges including high energy cost for polymer preparation or recycling, poor monomer recovery selectivity and efficiency as well as undesired material performance. In this contribution, we present the chemoselective controlled ring‐opening polymerization of bio‐renewable bifunctional α‐methylene‐δ‐valerolactone (MVL) to produce exclusive functionalizable polyester using strong base/urea binary catalysts. The obtained polyester with high molar mass exhibits good tensile strength comparable to that of some commodity plastics. Remarkably, the obtained polyester can be depolymerized to recover pristine monomer with a 96 % yield by thermolysis, thus successfully establishing a closed‐loop life cycle. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: Substantial progresses have been made toward the development of metal‐free catalysts for stereoselective ring‐opening polymerization (ROP) of rac‐lactide. Yet the discovery of organic catalysts effective at ambient temperature remains a major challenge. Here, the bifunctional H‐bonding catalyst SQ‐1 containing a basic tertiary amine and squaramide motif proved to be good candidate for the stereoselective ROP of rac‐lactide at room temperature, yielding stereoregular polylactide with controlled molecular weights (up to 21.1 kg/mol) and high tacticity (PiESC up to 0.88). Furthermore, binary H‐bonding catalytic system consisting of squaramides (SQ‐2 to SQ‐6) and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) could efficiently promote the ROP of rac‐lactide at room temperature within short reaction time. Among them, the most bulky squaramide SQ‐2 exhibited the best steroselectivity towards the ROP of rac‐lactide without transesterification side reactions during the polymerization process. The resulting polylactides were proved to have controlled molecular weights as high as 22.2 kg/mol and narrow distributions (1.10—1.24). [ABSTRACT FROM AUTHOR]

A new superbase, the cyclic trimeric phosphazene base (CTPB), was prepared with high yield and purity. In the presence of alcohol, the CTPB serves as a highly efficient organocatalyst for ring-opening polymerization of the 'non-polymerizable' γ-butyrolactone to offer well-defined poly(γ-butyrolactone) with high conversions (up to 98 %) at −60 °C. The produced polymers have high molecular weights (up to 22.9 kg mol−1) and low polydispersity distributions (1.27-1.50). NMR analysis of initiation process and the structural analysis of resulting polymers by MALDI-TOF suggest a mechanism involving an activating initiator which leads only to linear polymers with BnO/H chain ends. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: Substantial progresses have been made toward the development of metal‐free catalysts for stereoselective ring‐opening polymerization (ROP) of rac‐lactide. Yet the discovery of organic catalysts effective at ambient temperature remains a major challenge. Here, the bifunctional H‐bonding catalyst SQ‐1 containing a basic tertiary amine and squaramide motif proved to be good candidate for the stereoselective ROP of rac‐lactide at room temperature, yielding stereoregular polylactide with controlled molecular weights (up to 21.1 kg/mol) and high tacticity (PiESC up to 0.88). Furthermore, binary H‐bonding catalytic system consisting of squaramides (SQ‐2 to SQ‐6) and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) could efficiently promote the ROP of rac‐lactide at room temperature within short reaction time. Among them, the most bulky squaramide SQ‐2 exhibited the best steroselectivity towards the ROP of rac‐lactide without transesterification side reactions during the polymerization process. The resulting polylactides were proved to have controlled molecular weights as high as 22.2 kg/mol and narrow distributions (1.10—1.24). [ABSTRACT FROM AUTHOR]

Graphical abstract The binary organocatalytic system comprised of CTPB and ureas is developed and shows both of high activity and selectivity for the ROP of cyclic esters. Highlights • A simple and synergetic binary catalytic system containing CTPB and urea has been developed. • The ROP of ε -CL and δ -VL was highly controlled. • The linear and three-arm star block copolymers were readily prepared. • The synergetic bifunctional mechanism was investigated. Abstract Phosphazenes have attracted considerable attention in the field of ring-opening polymerization (ROP) of cyclic esters. However, the application of phosphazenes as catalyst is subject to a trade-off between activity and selectivity (chain propagation versus transesterification/back-biting reaction, e.g., controlled polymerization). Despite extensive research efforts, the development of a new catalytic system having concurrent high activity and selectivity remains a great challenge. In this work, we report that the binary organocatalytic system comprised of cyclic trimeric phosphazene base (CTPB) and ureas shows both of high activity and selectivity for the ROP of ε -caprolactone (ε -CL) and δ -valerolactone (δ -VL) in the presence of alcohol as initiator. It is found that the introduction of ureas would significantly increase the catalytic selectivity during ROP without sacrificing the catalytic activity of CTPB. Moreover, the polymerizations catalyzed by the title catalytic system exhibit immortal characteristics and thus thousands equivalent of monomer could be converted to polymer efficiently with desired MWs and microstructures. Linear diblock copolymer AB and star copolymers (AB) 3 with three identical diblock arms could be readily synthesized by sequential copolymerization using different alcohols as initiators. [ABSTRACT FROM AUTHOR]