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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]

Comprehensive Summary Copolymerization as an efficient strategy can provide an opportunity to create new closed‐loop recyclable polymeric materials with tailored properties that are generally inaccessible to the individual homopolymers. In this contribution, the bulk ring‐opening copolymerization of bio‐renewable δ‐caprolactone and trans‐hexahydro‐(4,5)‐benzofuranone was achieved to produce closed‐loop recyclable copolyesters by using an organobase/urea binary catalyst at room temperature. The obtained copolyesters exhibited composition‐dependent thermal properties. Remarkably, the obtained copolyesters were able to depolymerize back to recover the corresponding monomers under mild conditions. The copolyesters with suitable compositions can be directly used as pressure‐sensitive adhesives (PSAs) that possessed comparable peel strength with the commercially available PSA scotch tapes. When the copolyesters were mixed with plasticizers, the as‐prepared PSAs exhibited desirable adhesive failure and can be used as removable post‐it note. [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]