Although great successes have been achieved, the preparation of closed-loop recyclable polyesters with high working temperatures still remains as a big challenge. Herein, we present the syntheses of a series of enantiopure bicyclic ether-ester monomers by upcycling of poly(3-hydroxybutyrate) bioplastic. The "living"/controlled ring-opening polymerizations of these enantiopure monomers to produce stereoregular polyesters with controlled molecular weights and welldefined chain ends were achieved. The effects of stereoconfiguration and substituent on polymerization kinetics and thermodynamics as well as the thermal properties of resultant polyesters were investigated. Of note, the stereoregular polyesters are semi-crystalline materials with melting temperatures up to 176 °C, even higher than the commodity polyolefin plastics. These polyesters can be depolymerized back to recover pristine monomers, thus successfully establishing a closed-loop life cycle.
The upcycling of plastic waste into value-added products
is a promising
strategy to reduce plastic pollution and create a sustainable style
for polymeric materials. We report here the synthesis of a novel N-heterocyclic lactone, 5-methyl-N-Boc-1,4-oxazepane-7-one
(MeOxPBoc) and corresponding poly(amine-alt-ester) through upcycling of the poly(3-hydroxybutyrate) (P3HB) biopolymer.
Specifically, tens of grams of MeOxPBoc can be easily prepared
from P3HB waste in a satisfactory yield. Well-controlled ring-opening
polymerization (ROP) of MeOxPBoc was achieved to give an
amorphous poly(amine-alt-ester) P(MeOxPBoc) with a targeted molecular weight, narrow molecular weight dispersity,
and well-defined terminal groups in toluene using stannous 2-ethyl
hexanoate (Sn(Oct)2) as a catalyst. The obtained P(MeOxPBoc) could be depolymerized back to its pristine monomer either
in trimethylbenzene at 120 °C using Sn(Oct)2 as a
catalyst or in bulk at 150 °C in the presence of ZnCl2 as the catalyst. After simple purification by recrystallization,
the recycled MeOxPBoc could be repolymerized to produce
virgin-quality polymers. Remarkably, the obtained P(MeOxPBoc) can be converted to the corresponding cationic polymer by simply
removing the pendent t-butoxycarbonyl protecting
group. This study provides a new insight to address the end-of-use
problem of plastic by upcycling the plastic waste to value-added functional
poly(amine-alt-ester) with a closed-loop life cycle.
The
development of chemically recyclable polymers with closed-loop
life cycles is believed to be the most attractive strategy in creating
the circular plastic economy. Here, we successfully prepared a pair
of enantiopure O-heterocyclic lactones bearing with
pendent phenyl substituent, which are named (2S,7R)-7-methyl-2-phenyl-1,4-dioxepan-5-one (SR-M1) and (2R,7R)-7-methyl-2-phenyl-1,4-dioxepan-5-one
(RR-M2), respectively, by using the methanolysis
product of poly(3-hydroxybutyrate) (P3HB) as the raw material. The
well-controlled ring-opening polymerizations of SR-M1 and RR-M2 were achieved in the presence of MeAl[salen]
as the catalyst to produce poly(ether-ester)s with controlled molecular
weights, narrow dispersities, and well-defined terminal groups. The
monomer stereoconfiguration has a big impact on their polymerization
kinetics and thermodynamics as well as the thermal and mechanical
properties of resultant polyesters. Both the resultant P(SR-M1) and P(RR-M2) exhibited closed-loop recyclability.
The depolymerization of resultant polyesters back to pristine monomers
can be easily realized using stannous octoate as the catalyst in solution.
Although great successes have been achieved, the preparation of closed‐loop recyclable polyesters with high working temperatures still remains as a big challenge. Herein, we present the syntheses of a series of enantiopure bicyclic ether‐ester monomers by upcycling of poly(3‐hydroxybutyrate) bioplastic. The “living”/controlled ring‐opening polymerizations of these enantiopure monomers to produce stereoregular polyesters with controlled molecular weights and well‐defined chain ends were achieved. The effects of stereoconfiguration and substituent on polymerization kinetics and thermodynamics as well as the thermal properties of resultant polyesters were investigated. Of note, the stereoregular polyesters are semi‐crystalline materials with melting temperatures up to 176 °C, even higher than the commodity polyolefin plastics. These polyesters can be depolymerized back to recover pristine monomers, thus successfully establishing a closed‐loop life cycle.
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