Chemically Recyclable Ester-Linked Polypropylene

Abstract

Polyolefins represent the largest class of commodity materials due to their excellent material properties; however, they have limited pathways to chemical recycling and are often difficult to mechanically recycle. Here we demonstrate a new catalyst for the isoselective copolymerization of propylene and butadiene capable of favoring 1,4-insertion over 1,2-insertion while maintaining good molecular weights and turnover frequencies. This isotactic propylene copolymer with main-chain unsaturation was depolymerized to a telechelic macromonomer using an olefin metathesis catalyst and 2-hydroxyethyl acrylate. After hydrogenation, the telechelic macromonomer was repolymerized to form an ester-linked polypropylene material. This polymer shows thermal and mechanical properties comparable to linear low-density polyethylene. Finally, the telechelic macromonomer could be regenerated through the depolymerization of the ester-linked polypropylene material, which allows for the chemical recycling to macromonomer. This process provides a route to transform partially unsaturated polyolefins to chemically recyclable materials with similar properties to their parent polymers.

Catalytic Chemical Recycling of Post-Consumer Polyethylene

“…Incorporating cleavable linkages into HDPE can be achieved by introducing tunable amounts of unsaturation. Subsequent CC bond cleavage via oxidation, metathesis, and other approaches would produce telechelic polymers. ,− We have previously demonstrated the copolymerization of propylene and butadiene to incorporate internal CC bonds into the polyolefin backbone and subsequently converted the copolymer into a chemically recyclable ester-linked polypropylene . The catalytic transfer dehydrogenation of polyolefins was reported by Goldman, Coates and co-workers using iridium pincer catalysts and norbornene as a sacrificial hydrogen acceptor (Figure a) .…”

“…CM3 was hydrogenated to remove C�C bonds to prevent cross-linking at the acrylate unsaturation. 45 The hydrogenation was performed using 1 mol % of Wilkinson's catalyst (RhCl-(PPh 3 ) 3 ) and minimal toluene at 140 °C and 48 atm H 2 for 6 h. 60 The alkene signals around 5.91 and 7.05 ppm disappeared, indicating complete hydrogenation to generate telechelic macromonomer P1 (Figure 3). The molecular weights of P1 (M n : 3.5 kDa and M w : 7.9 kDa) remained relatively unchanged compared to CM3 (M n : 3.5 kDa and M w : 7.7 kDa).…”

Synthesis of Ethylene/Isoprene Copolymers Containing Cyclopentane/Cyclohexane Units as Unique Elastomers by Half-Titanocene Catalysts

“…Unique properties observed in the copolymers would be due to their microstructure containing cyclopentane units formed by cyclization after 2,1- or 1,4- My insertion followed by ethylene insertion (Scheme ). The results thus suggest a possibility of the synthesis of ethylene/IP copolymers, although, as described below, the reported examples for ethylene copolymerization with conjugated diene, especially using group 4 transition-metal catalysts, have been limited. − …”

Migratory Insertion into a Hafnium–Phenyl Bond and a Ligand-Assisted Mechanism for Reversible Chain Transfer in the Living Coordinative Polymerization of Olefins

“…In response to the global plastic waste crisis, there is an immediate and critical need for new commercially viable polyolefin materials that can be readily produced from the same small set of industrially relevant olefin monomers, but that are more amenable to safe environmental degradation and energy efficient thermal, photolytic, and chemical recycle or upcycle. − Over the past two decades we have made advances with the development of (stereo­selective) two-, three-, and multi-state living coordinative polymerization (LCP) and living coordinative chain transfer polymerization (LCCTP) of a wide variety of α-olefins and α,ω-nonconjugated dienes that now provide a versatile toolbox of methods for systematically exploring multi-dimensional structure/property relationships of an almost unlimited spectrum of existing, fundamentally new, and yet-to-be-conceived classes of polyolefin materials . Recently, we reported a highly versatile, new synthetic process for the scalable production of practical quantities of α,ω-difunctionalized homo- and hetero­telechelic polyolefins, I and II , respectively, that is based on the (stereo­selective) LCCTP of α-olefins using diphenylzinc (ZnPh 2 ) as a chain transfer agent (CTA: y > 0) in combination with a member of the family of cyclopentadienyl amidinate (CPAM) group 4 metal complexes serving as a pre-initiator that is “activated” by a stoichiometric amount of a borate or borane co-initiator ( B ) according to Scheme .…”

“…The phenyl end-groups of I and II then serve as synthons for a range of different end-group functionalities that can be “unmasked” through a variety of simple post-polymerization processes that proceed in near quantitative fashion, such as aromatic electrophilic substitution. This new library of accessible telechelic polyolefins can now be used for the design of higher molar mass materials that incorporate “weak chemical links” for efficient chemical recycle, as well as di-, tri-, and multi-block co-polymers that can function, for example, as blend compatibilizers for two or more plastic waste streams (e.g., polyolefins and polyesters). , …”