Synthesis and Biodegradation Studies of Low‐Dispersity Poly(acrylic acid)

Abstract

Poly(acrylic acid) (PAA) is produced on an industrial scale and widely‐used in applications such as personal care products and cleaning formulations that end up “down‐the‐drain.” Relatively high molecular weight PAA is considered poorly biodegradable, but little is known about the biodegradability of low molecular weight PAA at the wastewater treatment plant according to current regulatory and industrial Organization for Economic Co‐operation and Development (OECD) standards. The synthesis, separation, and characterization of a series of ultralow dispersity PAA oligomers (i.e., Đ < 1.10) in the molecular weight range Mn ≈ 350–1200 Da and the results of biodegradability testing are reported. Miniaturized, high‐throughput screening studies in a parallel respirometer reveals a strong trend toward lower biodegradation at higher molecular weight; these results are confirmed and expanded using standardized method OECD 301F. Biodegradability reaches ≈40% at Mn = 380 Da, ≈26% at Mn = 770 Da, and ≈17% at Mn = 1190 Da for discrete polyacid oligomers. These data not only shed light on potential biodegradation mechanisms for linear PAA, but also may inspire the future design of biodegradable PAA‐containing macromolecules.

Biodegradability as an Off-Ramp for the Circular Economy: Investigations into Biodegradable Polymers for Home and Personal Care

“…Rapid Commun. 2022 , 43 (13), 2100773 . An exploration of the biodegradability of ultralow molecular weight poly­(acrylic acid), vital to predicting the ultimate biodegradation of polymeric electrolytes. Yang, P.; Gao, W.; Zhang, T.; Pursch, M.; Luong, J.; Sattler, W.; Singh, A.; Backer, S. Two-dimensional liquid chromatography with active solvent modulation for studying monomer incorporation in copolymer dispersants.…”

“…Rapid Commun. 2022 , 43 (13), 2100773 . An exploration of the biodegradability of ultralow molecular weight poly­(acrylic acid), vital to predicting the ultimate biodegradation of polymeric electrolytes.…”

“…As most polymers are too large to be taken up by macrophages for direct consumption, understanding the pathway from macromolecule to digestible segment is paramount to following the end of life for a polymeric material. 1,2 Molecular weight is the most significant property for primary biodegradation, as the macromolecule can be reduced in size such that mineralization is more likely to occur. It has been demonstrated that in the absence of extracellular degradation, polymers with MW greater than 500−1000 Da are unlikely to significantly degrade under aerobic conditions found in a wastewater treatment plant.…”

“…Many nontoxic small molecules can be taken in and engulfed by cells, converted into a usable material or energy, and ultimately eliminated by the organism as CO 2. As most polymers are too large to be taken up by macrophages for direct consumption, understanding the pathway from macromolecule to digestible segment is paramount to following the end of life for a polymeric material. , …”

“…Molecular weight is the most significant property for primary biodegradation, as the macromolecule can be reduced in size such that mineralization is more likely to occur. It has been demonstrated that in the absence of extracellular degradation, polymers with MW greater than 500–1000 Da are unlikely to significantly degrade under aerobic conditions found in a wastewater treatment plant. , Both small molecules and primary degradants can be mineralized depending on structural factors such as the carbon chain length, the charge type/density, and a myriad of other subtle factors. Predicting the biodegradability of small molecules is a difficult task being explored using techniques such as quantitative structure–activity relationship (QSAR) modeling and deep-learning approaches …”