N-Vinylamides as Structural Isomers of Protein Grafted onto Deproteinized Natural Rubber and Their Mechanical...

This study proposes a novel strategy to enhance the mechanical properties of deproteinized natural rubber (DPNR) through the surface graft polymerization of protein-mimicking N-vinylamide monomers, which are N-vinylformamide (NVF), N-vinylacetamide (NVA), and N-methyl-N-vinylacetamide (MNVA), initiated by oxygen radicals. Although N-vinylamides generally exhibit low reactivity with oxygen radicals, selective grafting was successfully achieved via radical initiation at the polyisoprene surface, as confirmed by Fourier transform infrared spectroscopy and elemental nitrogen analysis. Tensile testing showed that approximately 70% of the modified samples surpassed the mechanical performance of high ammonia natural rubber (HANR), with the best-performing sample achieving a tensile strength of 15.48 ± 0.64 MPa and strain at break of 1361 ± 29%. orphological analyses using TEM and AFM revealed the reformation of the nanophase-separated "island-nanomatrix" structure, which was absent in DPNR. This result highlights the importance of morphology in mechanical reinforcement. To our knowledge, this is the first report demonstrating N-vinylamide grafting onto DPNR with the aim of replicating protein-like functionality. This approach introduces a sustainable, water-compatible method for functionalizing natural rubber by leveraging protein-isomeric vinyl monomers and tailoring nanostructural design.