title: Understanding the UCST-type transition of P(AAm-co-AN) in H2O and D2O: dramatic effects of solvent isotopes.
abstract: The UCST-type transition of poly(acrylamide-co-acrylonitrile) (P(AAm-co-AN)) (molar fraction of AN: 13.3%; PDI = 3.2) in H2O and D2O is explored and compared by applying turbidity, DLS as well as FTIR measurements. The transition temperature of P(AAm-co-AN) in D2O is observed to be almost 10 °C higher than that in H2O at the same concentration, demonstrating a dramatic solvent isotope effect. Such a phenomenon could be rooted from a stronger interaction among polymer chains in D2O than in H2O, as indicated from DLS results. It is also observed in second-derivative analysis of FTIR spectra in the ν(C=O) region, where all C=O groups participate in the formation of inter-/intra-chain hydrogen bonds (C=O···H-N) in D2O while there is still part of relatively "free" C=O groups in H2O. Moreover, we find in the temperature-dependent FTIR spectra that C≡N groups exhibit hydrating behavior while C=O groups present increased inter-/intra-molecular hydrogen bonding interaction (C=O···H-N) upon cooling, revealing the later process to be the driving force of the UCST-type transition.
authors.affiliation: The State Key Laboratory of Molecular Engineering of Polymers, Collaborative Innovation Center of Polymers and Polymer Composite Materials, Department of Macromolecular Science, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China. peiyiwu@fudan.edu.cn.
authors.forename: Lei
authors.initials: L
authors.lastname: Hou
authors.forename: Peiyi
authors.initials: P
authors.lastname: Wu