Solution property of poly(gamma-benzyl-L-glutamate)-b-polyisoprene-b-poly(gamma-benzy-L-gluta mate) (GIG copolymer) was studied by using dynamic light scattering and static light scattering for N,N-dimethylformamide (DMF) solution and DMF/toluene mixed solutions. GIG copolymer proved to aggregate in DMF and under DMF-rich condition, that is, high-polar region. The aggregate decreased in size, and completely disappeared under toluene-rich condition, that is, low-polar region. The correlation between solubility parameter and aggregate size of GIG copolymer in the DMF/toluene solution systems quantitatively demonstrated how strongly polarity caused by hydrogen bond made an impact on the aggregation behavior. Because the main driving force to the aggregation under DMF-rich condition originates with polyisoprene (PIP) blocks, the aggregate in DMF is considered to be a core-shell micelle consisting of flexible PIP core surrounded by rigid poly(gamma-benzy-L-glutamate) (PBLG) shell. The values of dimensionless parameter rho, defined as the ratio of radius of gyration < S2 >(1/2) to hydrodynamic radius RH, revealed that a single chain of GIG copolymer had the form of rigid rod with flexibility, that is, once-broken rod, caused by the incorporation of a flexible PIP chain between two rigid PBLG rods in the DMF/toluene solution system. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1740-1748, 2010