Cui Shuquan, Jeong Daun, Shi Yukai, Jahan Nusrat, Lodge Timothy P, Bates Frank S, Ellison Christopher J
Department of Chemistry, University of Minnesota, Minneapolis, MN 55455.
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455.
Proc Natl Acad Sci U S A. 2025 Jul 22;122(29):e2508921122. doi: 10.1073/pnas.2508921122. Epub 2025 Jul 18.
Plastics offer innumerable societal benefits but simultaneously contribute to persistent environmental pollution, dominated by polyethylene (PE) and isotactic polypropylene (PP). Melt blending and reformulating postconsumer PE and PP into useful materials presents a promising recycling approach. However, such repurposed plastics are generally mechanically inferior due to an inability to efficiently separate polyolefins in mixed waste streams; phase separation of PE and PP results in brittleness as a consequence of poor interfacial strength. Recently, we demonstrated that a small amount (1 wt%) of a poly(ethylene)--poly(ethyl ethylene--ethylene)--poly(ethylene) (EXE) triblock copolymer, synthesized by low-cost anionic polymerization of 1,3-butadiene followed by solution hydrogenation, restores tensile toughness to levels equivalent to virgin polyolefins. Unfortunately, low-temperature solvent insolubility of EXE, driven by crystallization of the E blocks containing 1.5 ethyl branches per 100 backbone repeat units (EB), presents a challenge for industrial hydrogenation. Comparable toughness (ca. > 400% strain at break) was achieved in the present work with 1.5 ≤ EB ≤ 6.5, accompanied by reduced EXE crystallinity and dissolution in cyclohexane down to room temperature at the highest EB content. This remarkable toughening behavior is attributed to a synergy between chain entanglements between the E end blocks and semicrystalline PE homopolymer and formation of E block "crystal nodules" that prevent chain pullout, along with topological constraints between the X loops and semicrystalline PP. Our findings overcome barriers to commercial production of EXE with existing industrial facilities, providing a cost-effective strategy for recycling PE and PP.
塑料给社会带来了无数益处，但同时也造成了持续的环境污染，其中以聚乙烯（PE）和等规聚丙烯（PP）为主。将消费后的PE和PP熔融共混并重新配方制成有用材料是一种很有前景的回收方法。然而，由于无法有效分离混合废物流中的聚烯烃，这些重新利用的塑料通常机械性能较差；PE和PP的相分离会导致界面强度差，从而产生脆性。最近，我们证明了一种由1,3 - 丁二烯通过低成本阴离子聚合然后溶液加氢合成的少量（1 wt%）聚（乙烯）-聚（乙基乙烯 - 乙烯）-聚（乙烯）（EXE）三嵌段共聚物，能将拉伸韧性恢复到与原始聚烯烃相当的水平。不幸的是，由每100个主链重复单元含有1.5个乙基支链（EB）的E嵌段结晶驱动的EXE在低温下的溶剂不溶性，给工业加氢带来了挑战。在本工作中，当1.5≤EB≤6.5时，实现了可比的韧性（约>400%的断裂应变），同时EXE结晶度降低，并且在最高EB含量下在室温下可溶于环己烷。这种显著的增韧行为归因于E端嵌段与半结晶PE均聚物之间的链缠结以及防止链拔出的E嵌段“晶体结节”的形成之间的协同作用，以及X环与半结晶PP之间的拓扑约束。我们的研究结果克服了利用现有工业设施商业化生产EXE的障碍，为回收PE和PP提供了一种经济有效的策略。
