Selective Long-Range Isomerization Carbonylation of a Complex Hyperbranched Polymer Substrate

Hyperbranched oligoethylenes are rewarding and extremely challenging substrates for functionalization. They contain one double bond per molecule which offers itself for long-range isomerization carbonylation; however, these are present in various substitution patterns and high degrees of substitution render them unreactive, and furthermore different branch sites need to be passed in an isomerizing functionalization approach. Studies of Pd(II) catalysts with different bulky-substituted diphosphines on hyperbranched oligomers (M_n 1000-3000 g mol^-1) amended by low-molecular-weight model substrates show that with 1,2-bis(4-phosphorinone)xylene alkoxycarbonylation occurs with high selectivity at the ends of branches to form primary esters with high conversions. The key to this is the retention of selectivity in long-range isomerization/carbonylation even at elevated temperatures that promote reaction rates. By a tandem cross-metathesis/long-range isomerization functionalization approach, difunctional esters were obtained. As a demonstration of their synthetic utility, these were polycondensed to semicrystalline all-aliphatic polyesters in which they serve as soft segments.