Ring-Opening Polymerization of Cyclic Esters in an Aqueous Dispersion

Abstract

Aqueous polymer dispersions are commodity materials produced on a multimillion-ton scale annually. Today none of these materials are biodegradable because the process by which they are made is not compatible with the synthesis of biodegradable polymers. Herein, we report a droplet microfluidic encapsulation strategy for protecting a water incompatible ring-opening polymerization (ROP) catalyst from the aqueous phase, yielding biodegradable polymer particles dispersed in water. Polymerization yields 300 μm sized particles comprised of biodegradable poly­(δ-valerolactone) with molecular weights up to 19.5 kg mol–1. The success of this approach relies on simultaneous precise control of the kinetics of polymerization, the rate of mass transfer, and fluid mechanics. The power of this methodology was demonstrated by the synthesis of cross-linked polymer particles through the copolymerization of bis­(ε-caprolactone-4-yl)­propane and δ-valerolactone, producing cross-linked polymer particles with molecular weights reaching 65.3 kg mol–1. Overall, this encapsulation technique opens the door for the synthesis of biodegradable polymer latex and processable, biodegradable elastomers.

Plastic Pollution: A Material Problem?

“…Current research in the development of compostable, synthetic biodegradable polymers primarily focuses on aliphatic and aliphatic–aromatic polyesters . These polymers are prepared by ring-opening polymerization and condensation polymerizations. − For example, poly­(butylene adipate–terephthalate) (PBAT), synthesized by condensation of 1,4-butanediol with terephthalic acid and adipic acid, is a commercially available polyester that shows ∼75% biodegradation in industrial compost in 8 weeks that increases to more than 90% in 12 weeks. , Like PBAT, the ester functional group in several other aliphatic and aliphatic–aromatic polyesters has the capability of undergoing biodegradation under industrial composting conditions. Polyesters, such as polycaprolactone (PCL) and PHB (polyhydroxybutyrate), reach more than 90% biodegradation in about 4 weeks, whereas PLA and poly­(butylene succinate) (PBS) take ∼8 and >18 weeks, respectively. − These polymers reach the benchmark of the present biodegradation standard (ASTM 5388/ISO 14588), according to which biodegradation of at least 90% of the reference material (cellulose) in 180 days certifies the polymer as compostable.…”

Design rules for performing water-sensitive ring-opening polymerizations in an aqueous dispersion

“…[6][7][8][9][10] In previous work, we encapsulated water-sensitive ROP catalysts via droplet-based microfluidics, which temporarily shielded the catalyst and allowed polymerization to proceed in an aqueous dispersion. 11 The microfluidic encapsulation strategy separately supplies a catalyst solution and a monomer solution in a hydrophobic solvent, which are fed into a narrow tube where the polymerization starts before meeting the immiscible continuous aqueous phase at a co-flowing junction to form micrometersized droplets, Fig. 1a.…”

“…† The fast quench configuration allows us to precisely determine the reaction extent at the end of the hypodermic tubing outlet tip responsible for droplet generation for each flowrate before droplet formation. This technique allows us to access particles that could not be directly synthesized using any other polymerization technique, specifically we will show production of spherical crosslinked polyester 11 and polyether particles in flow.…”

“…6–10 In previous work, we encapsulated water-sensitive ROP catalysts via droplet-based microfluidics, which temporarily shielded the catalyst and allowed polymerization to proceed in an aqueous dispersion. 11…”

Balancing Degradability and Physical Properties of Amorphous Poly(d,l‐lactide) by Making Blends

“…The ester functional groups in polymer backbone repeat units can be hydrolyzed under appropriate environments leading to the breakage of the polymer chain (fragmentation) followed by bio‐assimilation of fragmented oligomers and monomers to carbon dioxide (CO 2 ), water, and biomass. [ 4–9 ] This two‐step process is called biodegradation. The first step of biodegradation, the process of fragmentation to oligomers and monomers, is highly critical for the whole process of biodegradation as long macromolecule chains with high molar mass cannot be bio‐assimilated.…”