Thiol-Ene Click Functionalization and Subsequent Polymerization of 2-Oxazoline Monomers

Polymers of 2-oxazolines are a class of polymers that can exhibit water solubility and biocompatibility depending upon the N-acyl side-chain functionality and can be readily modified at both the end-groups and backbone, making them appealing alternatives to poly(ethylene glycol) (PEG). Methods to introduce a range of functionality onto oxazoline monomers are of interest due to the limited availability of functionalized oxazoline monomers. Prepolymerization thiol-ene coupling between a side-chain thiol and 2-isopropenyl-2-oxazoline was used to synthesize three different monomers followed by polymerization to yield 2-substituted oxazoline polymers with aryl, ester, protected amine, and protected carboxylic acid side chains. The resulting polymers exhibited molecular weights ranging form 3000 to 8000 and polydispersities typically below 1.3. The deprotection of these polymers was also achieved to yield polymers with reactive functionalities, including a cysteine with either the amine or carboxylic acid exposed on each repeat unit.