The morphology of the triblock copolymers (TBC) containing chemically complementary poly(ethylene oxide) (M(vPEO) = 3.10(3)divided by 1.10(5)) and polyacrylamide (M(PAAm) = 4.5.10(4)divided by 9.07.10(5)) of different chain lengths is studied. The loss of the PEO ability to crystallize in TBC at M(vPEO) <= 4.10(4) is established. At the same time, PEO blocks with M(v) = 1.10(5) form small crystalline domains in the TBC structure, but their crystallinity degree turns out to be by 2.8 times less than that in individual poly(ethylene oxide). A microphase separation in amorphous regions of the TBC structure at high values of M(PAAm) is revealed. It is shown that the main reason for the effects observed is the formation of a complex between PEO and PAAm blocks by hydrogen bonds.