The aggregation of block copolymer dissolved in methyl ethyl ketone (MEK) as well as toluene was observed. The aggregation of molecules leads to micelles and clusters of micelles. Between micelles and clusters a dynamical equilibrium exists. Inside the micelles lyophobic chains of PEO are combined and the outer layer of micelles is formed by lyophilic chains of PMMA. This is observed particularly in samples with triblock or diblock structure and high portions of PEG. In these cases, there are great differences between molecular weights obtained by light scattering, SEC or vapour pressure osmometry (VPO). We introduce a factor A to study the relation of the PEO content in diblock or triblock structure, and the measured M-w.