Small-angle neutron scattering and differential scanning calorimetry study of associative behaviour of branched poly(ethylene oxide)/poly(propylene oxide) copolymer in aqueous solution

Tetronic RED 9040, a reverse-type [poly(propylene oxide) as terminal blocks] octablock star copolymer with four poly(ethylene oxide)/poly(propylene oxide) arms attached to the ethylenediamine core was studied in D₂O at concentrations between 1 and 60 g dL^-1 in the temperature range from 283 to 353 K. Depending on concentration and temperature, various structures (unimers, random network, micelles, micellar aggregates, micellar networks) were indicated by small-angle neutron scattering (SANS). Some structure characteristics of unimers, micelles and micellar networks have been determined by fitting model scattering functions to the SANS data. A competition between the increasing association number and dehydration of the micelles is suggested as a possible explanation of the observed non-monotonic temperature dependence of the structure parameters of concentrated systems. A partial phase diagram was suggested on the basis of SANS and differential scanning calorimetry (DSC) data and visual inspection of the solutions.