Design of hybrid molecular brushes with reversible surface adaptability on exposure to specific solvents

Hybrid molecular brushes (HMBs) are macromolecules made of a linear backbone and polymeric side chains that differ in their chemical nature. The authors developed a new method of synthesis of HMB with chitosan (CHI) backbone. In the first step, chitosan-graft-polylactide (CHI-g-PLA) was synthesized by interfacial ring opening polymerization of lactide initiated from CHI. CHI-g-PLA is characterized for its molecular weight and structure. In the second step, polyvinylpyrrolidone (PNVP) or polyacrylamide (PAAm) is grafted by radical polymerization from the CHI in CHI-g-PLA to form CHI-g-PLA-g-PNVP and CHI-g-PLA-g-PAAm. This results in the formation of HMB, with hydrophobic PLA and hydrophilic PNVP or PAAm side chains grafted to CHI. The chemical structure and thermal behavior of the HMBs are characterized. The morphology of CHI-g-PLA as well as the HMBs is determined using atomic force microscopy (AFM). Both the HMBs tethered to separate surfaces exhibit reversible switching between the hydrophilic and hydrophobic polymers on exposure to specific solvents. This is studied by AFM and water contact angle measurements. Hence, the authors developed a method for synthesis of HMB that can be applied for surface modification.