A number of excellent techniques for precision end-functionalization of ring-opening metathesis polymerization (ROMP) polymers have been reported by the Kilbinger group and collaborators in recent years (including an excellent review), but a recent publication takes the concept to a logical next step by combining two very different techniques to create heterotelechelic metathesis polymers. First-generation Grubbs catalyst was used to create a di-block copolymer featuring an initial sacrificial poly(dioxepine) block which transitioned to a standard poly(norbornene imide) block. The polymerization was terminated by addition of a lactone – metathesis of the lactone creates an unstable acyl carbene which decomposes to a functional-group terminated polymer and a deactivated ruthenium-carbido complex. A hydroxyl functionality is created at the other end of the telechelic polymer through acidic hydrolysis of the acetals within the initial sacrificial ROMP block. The resulting telechelic poly(norbornene imide) contains hydroxyl groups at one end, and either aldehyde or carboxylic acid groups at the other. A series of poly(norbornene imide) telechelics were investigated, and molecular weights, PDI values, and functional group characterizations are presented, giving a wider picture of the utility of these functionalization reactions.
Given the intense interest in polymer architectures with well-placed functional groups, expect functionalized metathesis polymers to continue to impact a wide range of applications at an ever-increasing rate.