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Heterogeneous catalysis offers opportunities to enhance valorization of plastic waste via chemical recycling through control of the upcycled product distributions. Minimizing low-value light hydrocarbons is desired; however, fundamental insights into how to control selectivity are lacking. Here we use contrast variation with small-angle neutron scattering (SANS), model perdeuterated polyethylenes (dPEs), and a model liquid hydrocracking product (tetradecane) to quantify polymer partitioning within mesoporous silica (SBA-15). Polyethylene concentration within the mesopores is increased relative to the bulk solution, and this partitioning increases as the temperature increases. However, this polyethylene partitioning is maximized when the radius of gyration of the polymer chains is comparable to the SBA-15 pore size (10 nm). An increased partitioning at higher temperatures is attributed to entropically driven adsorption of PE within the mesopores. There is no observed preferential partitioning of hexatriacontane (a model oligomer) within the mesopores at the temperatures examined. These results suggest that pore size could promote the selective partitioning of polymer species into the mesopores by size. For plastic upcycling, pore-size-dependent partitioning should increase the probability for the reaction of long polymers over oligomeric and small-molecule polyolefin depolymerization products. 

Polyolefins, which dominate the plastics marketplace, require high-temperature size exclusion chromatography (HT-SEC) to characterize their molar masses. Chemical recycling methods designed to deconstruct plastic waste into smaller molecules (i.e., depolymerization methods) rely on HT-SEC to characterize their products, but depolymerization methods often yield a complex mixture, including components below the typical separation range of commercial HT-SEC columns. Herein, we report the accuracy and limitations of triple detection HT-SEC to analyze model chemical recycling products. We examined the chromatographic separation and quantification of individual components and mixtures of short polyethylenes (apparent Mn = 465 and 2722 g/mol), hexatriacontane (C36H74, M = 507 g/mol), dotriacontane (C32H66, M = 451 g/mol), and octadecane (C18H38, M = 254 g/mol). Despite short alkanes exhibiting molar masses below the lower molar mass limit of the columns (500 g/mol), the separation of their mixtures was resolved via refractive index (RI) detection. However, the determined molar masses of these alkane mixtures did not agree with the known molar masses of the short alkanes or their prepared mixtures. Similarly, the SEC analysis of mixtures containing discrete alkanes with low molar mass PE revealed that their individual components are easily resolved in the HT-SEC chromatogram. No obvious shift in the elution volume of the blend components versus the elution volume of the pure components was observed. However, inaccurate molar masses and molar mass distributions for these alkane-PE mixtures are calculated from the HT-SEC data. These inaccuracies are attributable to two factors: (1) molar mass-dependent ∂n/∂c for low molar mass components and (2) the small size of the molecules in solution that limits light scattering. These results highlight the importance of considering measurement limitations for quantitative interpretation of triple detection HT-SEC data obtained from chemical recycling and depolymerization experiments that commonly contain complex mixtures of polymeric, oligomeric, and small molecule alkanes. 

Comparing blockyversusgradient chlorinated polyethylene compatibilizer performance for polyolefin elastomer/polyvinyl chloride blends. The effects of crystallinity and sequence distribution on compatibilizer performance. 

Depolymerization of post-consumer PET yields telechelic oligomers that enable upcycling into novel multiblock copolymers. 

Conjugated copolymers containing electron donor and acceptor units in their main chain have emerged as promising materials for organic electronic devices due to their tunable optoelectronic properties. Herein, we describe the use of direct arylation polymerization to create a series of fully π-conjugated copolymers containing the highly tailorable purine scaffold as a key design element. To create efficient coupling sites, dihalopurines are flanked by alkylthiophenes to create a monomer that is readily copolymerized with a variety of conjugated comonomers, ranging from electron-donating 3,4-dihydro-2 H -thieno[3,4- b ][1,4]dioxepine to electron-accepting 4,7-bis(5-bromo-3-hexylthiophen-2-yl)benzo[ c ][1,2,5]thiadiazole. The comonomer choice and electronic nature of the purine scaffold allow the photophysical properties of the purine-containing copolymers to be widely varied, with optical bandgaps ranging from 1.96–2.46 eV, and photoluminescent quantum yields as high as ϕ = 0.61. Frontier orbital energy levels determined for the various copolymers using density functional theory tight binding calculations track with experimental results, and the geometric structures of the alkylthiophene-flanked purine monomer and its copolymer are found to be nearly planar. The utility of direct arylation polymerization and intrinsic tailorability of the purine scaffold highlight the potential of these fully conjugated polymers to establish structure–property relationships based on connectivity pattern and comonomer type, which may broadly inform efforts to advance purine-containing conjugated copolymers for various applications.