Catalytic Borylation of Poly(vinyl chloride) Produces Adhesive Materials

Abstract

Postpolymerization functionalization of polymers can create new applications for existing materials, while retaining their most favorable, intrinsic properties. Polyvinyl chloride (PVC) is a widely used, commodity polymer that is particularly challenging to modify. We report a copper-catalyzed protocol that replaces a small fraction of the C-Cl bonds in PVC with C-B bonds to boronic esters. The reaction occurs with an inexpensive catalyst comprising copper(II) chloride and an NHC ligand derived from a common ionic liquid that is distinct from the N-heterocyclic carbene (NHC) used for the borylation of small alkyl halides. The resulting materials adhere strongly to common surfaces, such as glass and metals, even more strongly than do commercial glues.

Figure 1.

Evaluation of NHCs and NHC precursors for the borylation of poly(vinyl chloride) and chlorocyclohexane.^a Efficiency refers to the percentage of C─Cl bonds transformed in the starting material relative to the amount of B₂pin₂ added. ^aThe yield of boronic ester 4 was determined by GC analysis with adamantane as an internal standard. ^bAn equal amount of KHMDS to the imidazolium chloride was added.

Figure 2.

Dependency of the degree of functionalization on the loading of diboron reagent and alkoxide base.

Figure 3.

Evaluation of the adhesive strengths of PVC-Bpnd 2c-1 to aluminum and glass surfaces by lap-shear testing.

Scheme 1.

Prior reports of functionalization of PVC and polyethylene, and this work on the catalytic borylation of PVC.