Thiol–ene addition enables tailored synthesis of poly(2-oxazoline)-graft-poly(vinyl pyrrolidone) copolymers for binder jetting 3D printing

The continued interest in graft copolymer architectures arises from their unique solution properties and potential for a myriad of applications ranging from drug delivery to adhesives. Poly(vinyl pyrrolidone) (PVP) represents a popular amorphous, water-soluble polymer used as a polymeric binder in binder jetting additive manufacturing, as fillers in cosmetic products, and for subcutaneous drug delivery systems. This report describes the synthesis of poly(2-oxazoline) and PVP graft copolymers using a ‘grafting to’ methodology with an efficient thiol–ene ‘click’ reaction. Copolymerization of 2-methyl-2-oxazoline and 2-(3-butenyl)-2-oxazoline introduced pendent vinyl grafting sites with a predictable absolute number-average molecular weight. In parallel, reversible addition-fragmentation chain-transfer polymerization and subsequent aminolysis yielded well-defined, oligomeric, thiol-terminated PVP. Thiol–ene click chemistry enabled the formation of poly(2-oxazoline)-graft-poly(vinyl pyrrolidone) (PMeOx-g-PVP) copolymers with varying mole percent grafting sites and PVP graft length. ¹H NMR spectroscopy, aqueous SEC with multiangle light scattering (SEC-MALS), and bromine titrations confirmed chemical structure, and DSC with TGA elucidated thermal transitions. Aqueous SEC-MALS and ¹H NMR spectroscopy also determined absolute number- and weight-average molecular weights and average grafting levels, which revealed optimal reaction conditions. Zero-shear viscosities of 5 and 10 wt% solutions in deionized water for each graft copolymer compared to their linear analogs demonstrated a significant (ca 31%) decrease in viscosity at the same number-average molecular weight. This decrease in solution viscosity suggested PMeOx-g-PVP copolymers as exceptional alternatives to linear analogs for aqueous-based, binder jetting additive manufacturing.