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PEO-PPO block copolymer has been found various applications in these fields such as bimolecular separation,soil remediation and drug delivery due to its versatile phase behavior in aqueous solutions.Many literatures have reported that salt ions can exert a great influence on the self-assembly behavior of PEO-PPO copolymer molecules [1].Whereas the mechanism has not been reached and the dispute is mainly focused on whether the salt ions have a direct interaction with PEO-PPO copolymers [2,3].In this study,FTIR and Raman spectroscopy have been employed to provide molecule-level evidences that there is direct interaction between PEO-PPO and the salt ions in aqueous solutions.For EOPO-K2CO3 and EOPO-Na2CO3 systems,the IR v(C-O) of PEO segment first exhibits a red shift and then undergoes a blue shift,while the Raman vas(-CH2-) band first exhibits a blue shift and then undergoes a red shift with increasing salt concentration.Based upon the spectral results and relevant literatures [4],we are convinced that there are direct interactions of potassium ions with the ether oxygen atoms in PEO-PPO molecular chain.In addition,the experimental results on EOPO-KSCN and EOPO-NaSCN systems reveal that the poorly hydrated anoin,thiocyanate,also has a direct interaction with EOPO molecules.This study helps us gain insight into the mechanism of ions modulating the phase behavior of EOPO molecules.