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1. Photooxidation of Polyolefins to Produce Materials with In‐Chain Ketones and Improved Materials Properties

   https://doi.org/10.1002/anie.202418411  

   Liu, Xin; Hu, Zhitao; Portela, Brandon S; Rettner, Emma M; Pineda, Agustin; Miscall, Joel; Rorrer, Nicholas A; Krummel, Amber T; Paton, Robert S; Miyake, Garret M (January 2025, Angewandte Chemie International Edition)

   Abstract Herein, we report a selective photooxidation of commodity postconsumer polyolefins to produce polymers with in‐chain ketones. The reaction does not involve the use of catalyst, metals, or expensive oxidants, and selectively introduces ketone functional groups. Under mild and operationally simple conditions, yields up to 1.23 mol % of in‐chain ketones were achieved. Installation of in‐chain ketones resulted in materials with improved adhesion of the materials and miscibility of mixed plastics relative to the unfunctionalized plastics. The introduction of ketone groups into the polymer backbone allows these materials to react with diamines, forming dynamic covalent polyolefin networks. This strategy allows for the upcycling of mixed plastic waste into reprocessable materials with enhanced performance properties compared to polyolefin blends. Mechanistic studies support the involvement of photoexcited nitroaromatics in consecutive hydrogen and oxygen atom transfer reactions. 

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2. Synthesis of telechelic polyolefins

   https://doi.org/10.1039/d1py00819f  

   Yan, Tianwei; Guironnet, Damien (September 2021, Polymer Chemistry)

   Telechelic polymers, polymers with two reactive end-groups, are sought after for their role in synthesizing macromolecules with complex structures such as multiblock copolymers and graft polymers. Many strategies for the synthesis of telechelic polymers from vinyl monomers using controlled radical polymerizations and anionic polymerizations exist. However, polyolefins—which account for the major fraction of polymer production—are not easily synthesized with two reactive end-groups. This difficulty is related to the sensitivity of olefin polymerization catalysts and their propensity for intramolecular chain transfer reactions. As a result, the most common strategies to access telechelic polyethylene and polypropylene (the two major polyolefins) do not rely on the insertion polymerization of ethylene nor propylene but rather on the polymerization of dienes or cyclic olefins. Nonetheless, recent advances in insertion polymerization and post-polymerization functionalization have resulted in the emergence of novel synthetic methods to access telechelic polyolefins. We here present a comprehensive review of all of these strategies to synthesize telechelic polyolefins. 

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3. Resilient Poly(α-hydroxy acids) with Improved Strength and Ductility via Scalable Stereosequence-Controlled Polymerization

   https://doi.org/10.1021/jacs.1c08802  

   Xiaoqian Wang, Ai Lin (September 2021, Journal of the American Chemical Society)

   null (Ed.)

   Despite the degradability and biocompatibility of poly(α-hydroxy acids), their utility remains limited because their thermal and mechanical properties are inferior to those of commodity polyolefins, which can be attributed to the lack of side-chain functionality on the polyester backbone. Attempts to synthesize high-molecular-weight functionalized poly(α-hydroxy acids) from O-carboxyanhydrides have been hampered by scalability problems arising from the need for an external energy source such as light or electricity. Herein, we report an operationally simple, scalable method for the synthesis of stereoregular, high-molecular-weight (>200 kDa) functionalized poly(α-hydroxy acids) by means of controlled ring-opening polymerization of O-carboxyanhydrides mediated by a highly redox reactive manganese complex and a zinc-alkoxide. Mechanistic studies indicated that the ring-opening process likely proceeded via the Mn-mediated decarboxylation with alkoxy radical formation. Gradient copolymers produced directly by this method from mixtures of two O-carboxyanhydrides exhibited better ductility and toughness than their corresponding homopolymers and block copolymers, therefore highlighting the potential feasibility of functionalized poly(α-hydroxy acids) as ductile and resilient polymeric materials. 

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4. Functionalized chalcogenide hybrid inorganic/organic polymers (CHIPs) via inverse vulcanization of elemental sulfur and vinylanilines

   https://doi.org/10.1039/c8py00270c  

   Zhang, Yueyan; Kleine, Tristan S.; Carothers, Kyle J.; Phan, David D.; Glass, Richard S.; Mackay, Michael E.; Char, Kookheon; Pyun, Jeffrey (January 2018, Polymer Chemistry)

   In this report, a new class of functional chalcogenide hybrid inorganic/organic polymers (CHIPs) bearing free aryl amine groups that are amenable to post-polymerization modifications were synthesized. These functional CHIPs were synthesized via the inverse vulcanization of elemental sulfur with 4-vinylaniline without the need for functional group protection of amines. This polymer is the first example of a polysulfide or CHIP material to carry a useful primary amine functional group which can be successfully post functionalized with acid chlorides and isocyanates to improve the mechanical properties. 

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5. Selective electrochemical degradation of bottlebrush elastomers

   https://doi.org/10.1002/pol.20240393  

   Albanese, Kaitlin R; Morris, Parker T; Roehrich, Brian; Read_de_Alaniz, Javier; Hawker, Craig J; Bates, Christopher M (July 2024, Journal of Polymer Science)

   <sc>A</sc>bstract We introduce a simple synthetic strategy to selectively degrade bottlebrush networks derived from well‐defined poly(4‐methylcaprolactone) (P4MCL) bottlebrush polymers. Functionalization of the hydroxyl groups present at the terminal ends of P4MCL side chains withα‐lipoic acid resulted in bottlebrush polymers having a range of molecular weights (M_n = 45–2200 kg mol⁻¹) and a tunable number of reactive dithiolane chain ends. These functionalized chain ends act as efficient crosslinkers due to radical ring‐opening of the dithiolane rings under UV light. The resulting redox‐active disulfide crosslinks enable mild electrochemical or chemical degradation of the SS crosslinks to regenerate the starting bottlebrush polymer. P4MCL side chains and the disulfides can be degraded simultaneously using harsher reducing conditions. This combination of bottlebrush architecture with facile disulfide crosslinking presents a versatile platform for preparing highly tunable elastomers that undergo controlled degradation under mild conditions. 

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