The
discovery and prosperous growth of synthetic polymers have
presented both significant advantages and daunting challenges in the
last century. To address the issues of environmental pollution and
fossil consumption, recyclable, degradable, and/or biobased polymers
have been given much attention in the polymer science community. This
viewpoint focuses on the emerging fully chemical recyclable poly(γ-butyrolactone)-based
polymers. The breakthrough from nonpolymerizable to efficient polymerization
is highlighted by the benefits of the development of a series of catalysis
for ring-opening polymerization of γ-butyrolactone. Subsequently,
the design of γ-butyrolactone derivatives and synthesis of more
recyclable polymers are summarized together with the discussions about
the structure and property relationship. Finally, the remaining challenges
and promising opportunities are suggested in order to provide insights
into the further direction for sustainable polymers.
A novel metal-free and protecting-group-free synthesis method to prepare telechelic thiol-functionalized polyesters is developed by employing organocatalysis. A scope of Brønsted acids, including trifluoromethanesulfonic acid (1), HCl.Et2O (2), diphenyl phosphate (3), γ-resorcylic acid (4) and methanesulfonic acid (5), are evaluated to promote ring-opening polymerization of ε-caprolactone with unprotected 6-mercapto-1-hexanol as the multifunctional initiator. Among them, diphenyl phosphate (3) exhibits great chemoselectivity and efficiency, which allows for simply synthesis of thiol-terminated poly(ε-caprolactone) with near-quantitative thiol fidelity, full monomer conversion, controlled molecular weight and narrow polydispersity. Kinetic study confirms living/controlled nature of the organocatalyzed chemoselective polymerizations. Density functional theory calculation illustrates that the chemoselectivity of diphenyl phosphate (3) is attributed to the stronger bifunctional activation of monomer and initiator/chain-end as well as the lower energy in hydroxyl pathway than thiol one. Moreover, series of tailor-made telechelic thiol-terminated poly(δ-valerolactone) and block copolymers are efficiently generated under mild conditions.
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