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Mechanistic aspects of palladium-catalyzed insertion copolymerizations of ethylene and R-olefins with methyl acrylate to give high molar mass polymers are described.dNAr, e.g., Ar t 2,6-C 6 H 3 (i-Pr) 2 , R t H (a), Me (b); Ar′ t 3,5-C 6 H 3 (CF 3 ) 2 ) with bulky substituted R-diimine ligands were used as catalyst precursors. The copolymers are highly branched, the acrylate comonomer being incorporated predominantly at the ends of branches as -CH 2 CH 2 C(O)OMe groups. The effects of reaction conditions and catalyst structure on the copolymerization reaction are rationalized. Lowtemperature NMR studies show that migratory insertion in the η 2 -methyl acrylate (MA) complex [(N ∧ N)-PdMe{H 2 CdCHC(O)OMe}] + (5) occurs to give initially the 2,1-insertion product [(N ∧ N)PdCH(CH 2 CH 3 )C-(O)OMe] + (6), which rearranges stepwise to yield 2 as the final product upon warming to -20°C. Activation parameters (∆H q ) 12.1 ( 1.4 kcal/mol and ∆S q ) -14.1 ( 7.0 eu) were determined for the conversion of 5a to 6a. Rates of ethylene homopolymerization observed in preparative-scale polymerizations (1.2 s -1 at 25°C, ∆G q ) 17.4 kcal/mol for 2b) correspond well with low-temperature NMR kinetic data for migratory insertion of ethylene in [(N ∧ N)Pd{(CH 2 ) 2n Me}(H 2 CdCH 2 )] + . Relative binding affinities of olefins to the metal center were also studied. For [(N ∧ N)PdMe(H 2 CdCH 2 )] + + MA h 5a + H 2 CdCH 2 , K eq (-95°C) ) (1.0 ( 0.3) × 10 -6 was determined. Combination of the above studies provides a mechanistic model that agrees well with acrylate incorporations observed in copolymerization experiments. Data obtained for equilibriashows that chelating coordination of the carbonyl group is favored over olefin coordination at room temperature. Formation of chelates analogous to 2 during the copolymerization is assumed to render the subsequent monomer insertion a turnover-limiting step.

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Plastics are a key component of virtually any technology today. Although their production consumes enormous feedstock resources, plastics are largely disposed of after their useful service life. In terms of a circular economy, 1-8 desirable re-utilisation of post-consumer sorted polymers ('mechanical recycling') is hampered by deterioration of materials performance. 9,10 Chemical recycling 1,11 via depolymerisation to monomer offers an alternative to retain high performance properties. The linear hydrocarbon chains of polyethylene 12 enable crystalline packing and provide excellent materials properties. 13 Their inert nature hinders chemical recycling, however, necessitating temperatures > 600 °C and recovering ethylene with < 10 % yield. 3,11,14 Here, we show that renewable polycarbonates and polyesters with a low-density of in-chain functional groups as break points in a polyethylene chain can be recycled chemically by solvolysis with > 96 % recovery. At the same time, the break points do not disturb the crystalline polyethylene structure, and the HDPE (high density polyethylene)-like materials properties are fully retained upon recycling. Processing can be performed by common injection moulding and the materials are well-suited for additive manufacturing. Selective removal from model polymer waste streams is possible. The virgin polymers result from polycondensation of long-chain building