Micellization of non-ionic amphiphilic block copolymers

Most of the amphiphilic block copolymers of this type comprise PEO as hydrophilic block(s), 

In this section, we intend to examine successively the micellization behavior in aqueous medium of PEO-poly(oxyalkylene), and PEO-PS block copolymers which have been studied the most extensively up to now, then that of PEO-based block copolymers with other hydrophobic blocks and finally that of block copolymers with hydrophilic non-ionic sequences other than PEO, mainly AB, ABA and BAB structures are considered at this point, whereas more elaborate block architecture will be examined in Section 7.3.12. 

PEO-PPO, and later on PEO-PBO copolymers, represent the link between classical low molecular weight non-ionic surfactants and polymeric surfactants. These commercially available products (formerly known as POLOXAMERS, PLURICARE, PLURONICS, SYN-PERONICS), mainly with di- and triblock structures can form, depending on temperature and concentration, true solutions, micelles of different shapes and physical gels. Their micellization behavior has been studied quite extensively and the experimental as well as the theoretical results were summarized in the review articles of Nace [10], Chu and Zhou [116], Ahngren etal. [147], Hamley [11], Booth and co-workers [79,148] and Wanka etal. [149]. 

In the most recent ones. Booth and co-workers [79, 148] outlined the correlations between the molecular characteristics (composition, structure, molecular weight) and the corresponding micellar characteristics, such as the CMC and GMT, the micellization enthalpy, the micelle size and association number, etc. These characteristic features were studied by SLS, DLS, SAXS, SANS, NMR, etc. 

By SAXS it could for instance be demonstrated that not only spherical but, depending on molecular weight, composition, temperature, concentration, salt content, also rod-like micelles are formed [116,147]. Mortensen and Pedersen [150] have shown that in case of spherical micelles the PPO core is surrounded by a dense layer of PEO and an outer corona of flexible PEO chains. 

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