Controlling crystallinity in degradable poly(ethylene carbonate) polymers by precision carbonate placement

In this report, we show that precision placement of hydrolyzable carbonate units enables chemical deconstruction without compromising crystallinity. The crystallinity of polyethylene underlies its exceptional mechanical, thermal, and barrier properties. However, the non-polar, crystalline structure of polyethylene materials renders it resistant to backbone degradation. Incorporating degradable functionalities along the backbone offers a potential solution, provided crystallinity can be retained. Here we report the synthesis of precision carbonate-containing polyethylene-like (PE-like) polymers by acyclic diene metathesis (ADMET) polymerization followed by mild hydrogenation. This generates PE-like materials where the density and placements of carbonate units is precisely controlled. Thermal analysis shows that the melting behavior and crystallinity are retained by the methylene-rich domains, where melting temperatures increase (35, 50, 76 °C) as uninterrupted methylene sequences lengthen (PCO3-10C, PCO3-14C, and PCO3-18C, respectively). X-ray scattering reveals that carbonates are excluded from the interior of lamellae and are positioned at the termini of orthorhombic crystallites, indicating that the carbonates are the dominant source of chain-folding in these semicrystalline materials. Surface-localized carbonates provide a route for acid-catalyzed hydrolytic cleavage, which we exploit to degrade these materials into small molecules. These results provide a mechanistic understanding of how dipolar, hydrolyzable groups interact with polyethylene domains and offer design principles for embedding degradable units into polyolefins without compromising bulk crystallinity. We expect that future efforts to control the crystallinity of polyethylene materials could provide a route to sustainable materials with tunable thermal, mechanical, or chemical characteristics.