Cyclo-depolymerization of olefin-containing polymers to give macrocyclic oligomers by metathesis and the entropically-driven ROMP of the olefin-containing macrocyclic esters

A range of olefin-containing polyesters were prepared by acyclic diene metathesis (ADMET) and were then subjected to cyclo-depolymerization (CDP). CDP involves metathesis of the 1,2-disubstituted olefinic linkages and gives a homologous family of strainless macrocyclic oligomers (MCOs). When Grubbs' “first generation” catalyst was used at 23 °C the CDPs were sluggish and required reaction times of several days, but with the “second generation” Grubbs' catalyst at 40 °C CDPs were complete in only 2-4 h. Macrocyclic olefin-containing lactones were also prepared by ring-closing metathesis. Under appropriate reaction conditions (i.e. neat cyclics or very concentrated solutions of cyclics) the strainless macrocycles successfully underwent ring-opening metathesis polymerizations (ROMPs). Unlike most ROMPs reported in the literature, which are usually enthalpically-driven, these ROMPs are entropically-driven (ED-ROMPs). The results obtained clearly demonstrate that 21-, 24-, 27-, 28-, 38-, 45-, 52-, 63-, 64-, 68- and 84-membered macrocycles polymerized successfully. Two of the ED-ROMPs were carried out in films. These ROMPs appeared to proceed in part in the solid phase, i.e. were examples of solid state polymerization.