The Role Of Backbone Hydration Of Poly(N-Isopropyl Acrylamide) Across The Volume Phase Transition Compared To Its Monomer

Abstract

Thermo-responsive polymers undergo a reversible coil-to-globule transition in water after which the chains collapse and aggregate into bigger globules when passing to above its lower critical solution temperature (LCST). The hydrogen bonding with the amide groups in the side chains has to be contrasted with the hydration interaction of the hydrophobic main-chain hydrocarbons. In the present investigation we study molecular changes in the polymer poly(N-isopropyl acrylamide) (PNIPAM) and in its monomer N-isopropyl acrylamide (NIPAM) in solution across the LCST transition. Employing Fourier-transform infrared spectroscopy we probe changes in conformation and hydrogen bonding. We observe a nearly discontinuous shift of the peak frequencies and areas of vibrational bands across the LCST transition for PNIPAM whereas NIPAM exhibits a continuous linear change with temperature. This supports the crucial role of the polymer backbone with respect to hydration changes in the amide group in combination with cooperative interactions of bound water along the backbone chain.

Publication Date

12-1-2017

Publication Title

Scientific Reports

Volume

7

Issue

1

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1038/s41598-017-17272-7

Socpus ID

85037154888 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/85037154888

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