Synthesis of dual thermo‐ and pH‐sensitive poly(N‐isopropylacrylamide‐co‐acrylic acid)‐grafted cellulose nanocrystals by reversible addition‐fragmentation chain transfer polymerization

• Published in: Journal of biomedical materials research. Part A 2018-01, Vol.106 (1), p.231-243
• Main Authors: Zeinali, Elnaz, Haddadi‐Asl, Vahid, Roghani‐Mamaqani, Hossein
• Format: Article
• Language: English
• Subjects: Acrylic acid; Acrylics; Addition polymerization; Block copolymers; Calorimetry; Cellulose; cellulose nanocrystal; Chain transfer; Chains (polymeric); Chemical synthesis; Copolymers; Crystals; Differential scanning calorimetry; dual stimuli‐responsive polymers; Electron microscopy; Fourier transforms; Fragmentation; Graft copolymers; Gravimetric analysis; Hydrogen ions; Infrared analysis; Isopropylacrylamide; Light scattering; Low temperature; Microscopy; Nanocrystals; NMR; Nuclear magnetic resonance; pH effects; Photon correlation spectroscopy; poly(acrylic acid); poly(N‐isopropylacrylamide); Polymerization; Polymers; RAFT polymerization; Resonance scattering; Scanning electron microscopy; Temperature; Thermal analysis; Thermodynamic properties; Transmission electron microscopy; X-ray diffraction
• ISSN: 1549-3296; 1552-4965
• DOI: 10.1002/jbm.a.36230

Free and cellulose nanocrystals (CNCs)‐grafted block copolymers of acrylic acid and N‐isopropylacrylamide with various poly(N‐isopropylacrylamide) (PNIPAAm) block lengths as dual temperature‐ and pH‐sensitive materials were synthesized by reversible addition‐fragmentation chain transfer polymerization via an R‐approach method. Controlling lower critical solution temperature (LCST) of the products by changing the PNIPAAm block length, addition of CNC, and variation of pH was studied. The free and CNC‐grafted block copolymers were analyzed by Fourier transform infrared and proton nuclear magnetic resonance. LCST of copolymers was measured by dynamic light scattering using their hydrodynamic diameters. The block copolymers reversibly form core–corona structure with PNIPAAm as core and poly(acrylic acid) (PAA) as shell above LCST at higher pH values. LCST point shifts to higher temperatures by increasing pH and CNC content and also lowering PNIPAAm block length. By decreasing pH below 4 at certainly low temperatures, PAA becomes core and PNIPAAm forms corona. Thermal behavior of the CNC‐grafted polymers was studied by thermal gravimetric analysis and differential scanning calorimetry. Morphology of the polymer‐grafted CNC was examined by X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 231–243, 2018.