Thermo thickening behavior of MPEG-b-PCL grafted Poly(acrylic acid): A molecular insight

• Published in: Polymer (Guilford) 2018-07, Vol.148, p.138-148
• Main Authors: Tiwari, Neha, Shedge, Aarti, Fayis, K.P., Bhat, Suresh K., Ravindranathan, Sapna, Rajamohanan, P.R., Badiger, Manohar V.
• Format: Article
• Language: English
• Subjects: Acrylic acid; Aqueous solutions; Block copolymers; Chemical synthesis; Critical temperature; Ethylene glycol; Gelation; Graft copolymers; Grafts; Heating; Hydrophobically modified poly (acrylic acid); Hydrophobicity; Light scattering; Methoxy polyethylene glycol-b-polycaprolactone (MPEG-b-PCL) copolymer; MPEG encoders; NMR; Nuclear magnetic resonance; Polyethylene glycol; Polymers; Rheological properties; Rheology; Scattering; Thermo gelation; Thickening; Video compression
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2018.06.031

We report on the synthesis and characterization of a new thermothickening polymer (PAA-g-(MPEG-b-PCL)) based on the grafting of a block copolymer of mono methoxy poly (ethylene glycol)–b-poly (caprolactone) (MPEG-b-PCL) onto poly (acrylic acid) (PAA). Rheological experiments reveal that aqueous solutions of PAA-g-(MPEG-b-PCL) exhibit interesting irreversible thermothickening behavior above a certain polymer concentration and critical temperature. Light scattering experiments show that increasing temperature induces hydrophobic associations and subsequent aggregation leading to gel formation which is irreversible. The mechanism of thermo thickening was examined at the molecular level by NMR methods which indicated unassembled and assembled environments of the MPEG-b-PCL grafts. On heating, interactions between the graft side chains are significantly enhanced and molecular mobility in the assembled microdomains is reduced. The stable well ordered microdomains that are formed on heating are retained on cooling thus, leading to irreversible gelation. [Display omitted] •A thermo-associating polymer PAA-g-(MPEG-b-PCL) was designed and synthesized.•The thermogelation was studied by rheology, light scattering and NMR spectroscopy.•PAA-g-(MPEG-b-PCL) exhibited irreversible thermogelation.•Both hydrophobic associations and stable partial micro ordering of MPEG-b-PCL drives the gelation.•2D NMR spectroscopy revealed the molecular insight in to the irreversible gelation.