PEO Block and Graft Copolymers

Block or graft copolymers in a selective solvent can form structures due to their amphiphilic nature. Above the critical micelle concentration (CMC), the free energy of the system is lower if the block copolymers associate into micelles rather than remain dispersed as single chains. Often the micelles are spherical, with a compact core of insoluble polymer chains surrounded by a corona of soluble chains (blocks) [56]. Addition of a solvent compatible with the insoluble blocks (chains) and immiscible with the continuous phase leads to the formation of swollen micelles or polymeric micro emulsion. The presence of insoluble polymer can be responsible for anomalous micelles. 

Several morphological studies of polymeric microemulsion have involved graft and block PSt/PEO copolymers in ternary solvent mixtures containing toluene, water, and either an alcohol or an amine acting as a cosurfactant [57,58]. The co-emulsifier increases the dispersion capacity of the copolymers. 

Cogan and Gast [61] presented dynamic light scattering (DLS) data of polystyrene-polyoxyethylene diblock copolymers in cyclopentane in the presence 

In a solution of a larger polymer, PSt/PEO - 1730/170, with a polymer and water content of 1500 and 28 ppm, respectively, micelles with Rh of 34 nm were observed. Since the micelle Rh values measured at 30,60, and 90 °C were the same within experimental error, it was concluded that the micelles are relatively mon-odisperse. The micelle hydrodynamic radius increases from 34 to 48 nm as the water content is increased from 28 to 98 ppm in a 1500 ppm solution of the 1730/170 block copolymer. 

The smaller block copolymers contain a much higher percentage of PEO and insoluble PSt block. Micelles with Rh of 13 nm in solutions of 5800 ppm of polymer and 155 ppm of water were formed. Rh increases to 18 nm at 1030 ppm of water. It was suggested the single chains have Rh values of the order of 2 nm. 

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