The first observation of ordered microphase structures in poly(oxyethylene)–poly(oxypropylene) diblock copolymers melts is reported. Two diblock copolymers were synthesised by anionic polymerisation, i.e. E130P58 and E107P69 where E represents an oxyethylene unit, OCH2CH2, and P an oxypropylene unit, OCH2CH(CH3). The volume fractions of the two components were in the range 0.5–0.6. Order in the melt phase was confirmed by small angle X-ray scattering, and order-to-disorder transitions (ODT) were located at 106°C (E130P58) and 114°C (E107P69). In a related experiment, a triblock copolymer with perdeuterated P blocks, E33dP42E33, was synthesised and studied in the melt phase by small-angle neutron scattering. This allowed determination of the temperature dependence of the Flory–Huggins interaction parameter for the poly(oxyethylene)–poly(oxypropylene) system, i.e. χ=20.2/T+0.0221.
