Abstract
A new type of aggregation behavior of block ionomers, i.e. functionalized polystyrene‐block‐poly[ethylene‐co‐(1‐butene)]‐block‐polystyrene (SEBS) with respective contents of 3.2 mol‐% and 8.3 mol‐% sodium carboxylate groups in polystyrene blocks has been studied using steady‐state fluorescence techniques. It is found that the block ionomers could form a stable dispersion in water although both the slightly ionized polystyrene block and the ethylene/1‐butene block are hydrophobic. The intensity ratio of the first to third vibronic band (I~1~/I~3~) of pyrene varies from 1.8, characteristic of the aqueous medium, to about 0.8, characteristic of hydrophobic microenvironment when the ionomer concentration in water is increased from 8 × 10^−4^ g/L to 2 × 10^−1^ g/L. Meanwhile, the emission intensity ratio of excimer to monomer (I~e~/I~m~) of pyrene increases with increasing polymer concentration first, then passes through a maximum and eventually falls off to zero. Both of the methods show the same critical aggregation concentration (8 × 10^−4^ g/L). Besides the non‐radiative energy transfer efficiency between naphthalene and anthracene shows a considerable increase when the concentration reaches 0.01 g/L. All of these three approaches lead to the fact that the block ionomers could form hydrophobic aggregates in water stabilized by the rare ionic groups.