Thioacetate-Based Initiators for the Synthesis of Thiol-End-Functionalized Poly(2-oxazoline)s

Area of Science:

• Polymer Chemistry
• Materials Science
• Organic Synthesis

Background:

• Cationic ring-opening polymerization (CROP) of 2-alkyl-2-oxazolines is a versatile method for synthesizing poly(2-oxazoline)s (POx).
• Precise control over polymer architecture and end-group functionality is crucial for advanced material applications.
• Introducing specific functional groups, like thiols, at the polymer chain terminus (α-terminus) enables further modifications and surface conjugations.

Purpose of the Study:

• To develop novel functional initiators for the CROP of 2-alkyl-2-oxazolines.
• To introduce a thiol moiety at the α-terminus of the resulting poly(2-oxazoline) chains.
• To demonstrate the utility of these thiol-terminated polymers for subsequent functionalization and surface patterning.

Main Methods:

• Synthesis of tosylate and nosylate initiators bearing a thioacetate group via a two-step process, including phototriggered thiol-ene radical addition.
• Cationic ring-opening polymerization of 2-ethyl-2-oxazoline using the nosylate initiator, achieving controlled polymerization with low dispersity (<1.1).
• Deprotection of the thioacetate end group using triazabicyclodecene to yield the mercapto terminus, followed by Michael addition for α-functionalization and surface patterning via microchannel cantilever spotting (µCS).

Main Results:

• Multigram scale synthesis of novel tosylate and nosylate initiators with thioacetate functionality.
• Highly controlled CROP of 2-ethyl-2-oxazoline, yielding polymers with excellent dispersity and quantitative conversion.
• Successful generation of α-mercapto-poly(2-ethyl-2-oxazoline) and its subsequent functionalization with various moieties (esters, furan).
• Demonstration of covalent surface patterning of the thiol-terminated polymer onto acrylated surfaces using µCS, confirmed by XPS and ToF-SIMS analysis.

Conclusions:

• The developed functional initiators provide an efficient route to α-thiol-functionalized poly(2-oxazoline)s.
• The resulting polymers exhibit high control in polymerization and are amenable to diverse post-polymerization modifications and surface conjugations.
• This methodology opens new avenues for creating advanced functional materials and surfaces with tailored properties.