Conformational transitions and dynamics of thermal responsive poly(N-isopropylacrylamide) polymers as revealed by molecular simulation

• Elucidate the conformational changes in polymers using atomistic explicit dynamics simulation.
• Capture the lower critical solution temperature (LCST) for thermal responsive transitions at molecular level.
• Reveal the dynamics of torsional energy of isopropyl acryl tethers and H-bonds in LCST transition.
• Molecular modelling and prediction of LCST agrees well with experimental measurements.
• Demonstrate the robustness of molecular design and simulation for tailor-made responsive polymers.

Stimuli responsive polymers (SRP) have attracted increasing interest for their unlimited potential of molecular capture, separation, purification and delivery particularly at the cutting edge of bio-nano technologies, as well as for the biotechnological, food and medical industries. However, molecular mechanisms of SRPs and their interactions with target materials are little understood at atomistic levels. Based on poly(N-isopropylacrylamide) (pNIPAAm) and poly(NIPAAm-co-AAc-co-tBAAm) polymers, we examined the SRP operating mechanisms and dynamics by all-atom molecular simulation in varying conditions of temperature and chemistry. The LCST conformational transition predicted by simulation agreed well with experimental results, and simulation results notably leads to elucidate mechanism that torsional energy of isopropyl acryl tethers and H-bond play vital roles in driving the transition in response to temperature changes. These insights are helping molecular design and virtual screening of tailor-made SRPs, and harnessing the responsive control of temperature and other stimuli factors (e.g. ions, hydrophobicity).

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