The coil-to-globule-to-coil transition of linear polymer chains in dilute aqueous solutions: Effect of intrachain hydrogen bonding

Our previous studies of the captioned transition have shown that thermally sensitive poly(Nisopropylacrylamide) (PNIPAM) in water can form stable individual single-chain globules, but not for polystyrene (PS) in cyclohexane. In the current study, using poly(N,N-diethylacrylamide) (PDEAM) (M_w = 1.7 × 10⁷ g/mol and M_w/M_n = 1.06) with no hydrogen donator site, we intend to find whether the intrachain hydrogen bonding plays a role in stabilizing individual collapsed PNIPAM single-chain globules. We found that PDEAM can also form stable single-chain globules in water even though the transition is less sharp. The resultant individual PDEAM single-chain globules are less compact, reflecting in a lower chain density and a higher ratio of the radius of gyration to hydrodynamic radius, presumably due to the lack of intrachain hydrogen bonding. Our result also shows that, unlike PNIPAM, there is no hysteresis in the transition, indirectly supporting our previous assumption that the hysteresis observed for PNIPAM is due to the formation of some intrachain additional hydrogen bonds formed in the collapsed state.