Charles M. Kausch

Butyllithium-initiated anionic synthesis of well-defined poly(styrene-block-ethylene oxide) block copolymers with potassium salt additives

Poly(styrene-block-ethylene oxide) (PS-PEO) diblock copolymers have been synthesized with predictable block molecular weights and narrow molecular weight distributions. sec-Butyllithium-initiated polymerization of styrene was effected in benzene solution followed by ω-end-group functionalization with ethylene oxide to form the corresponding polymeric lithium alkoxide (PSOLi). Block copolymerization of ethylene oxide initiated by the unreactive PSOLi was promoted by addition of dimethylsulfoxide and either potassium t-butoxide, potassium t-amyloxide or potassium 2,6-di-t-butylphenoxide. Although the PS-PEO block copolymer product contained some poly(ethylene oxide) homopolymer, the poly(ethylene oxide) block M n was in good agreement with the calculated value and the molecular weight distribution of the final block was generally narrow (M w /M n ≤ 1.1). The amount of PEO homopolymer was minimized using potassium 2,6-di-t-butylphenoxide rather than potassium t-alkoxides.

Adsorption properties of oligo(fluorooxetane)-b-poly(ethylene oxide)-b-oligo(fluorooxetane) triblock copolymers at the air-water interface: comparison of hydroxyl and acetate end groups.

ABA triblock copolymers, where A is an oligo(fluorooxetane) and B is poly(ethylene oxide) (PEO), are prepared easily using an alpha,omega-dihydroxy PEO initiator and cationic, ring-opening polymerization of a fluorinated oxetane monomer. Terminal hydroxyl groups can be converted readily and quantitatively to acetate groups using acetic anhydride. Both types of triblock copolymers are surface active in water. The hydroxyl- and acetate-terminated triblocks exhibit differences in adsorption behavior. Both materials show similar surface tension reduction efficiencies (minimum surface tension at aggregation limit); however, the acetate-terminated triblock copolymer is much more effective (surface tension reduction at a given concentration to the aggregation limit). This behavior is explained by the influence of hydrogen bonding on adsorption properties of the hydroxyl-terminated triblock copolymer compared to the acetate-terminated version.

On the location of the free ends of the insoluble block in micelles formed by diblock copolymers

SummaryNonradiative singlet energy transfer has been used to monitor the formation of micelles by diblock copolymers of poly(styrene) and poly(oxyethylene). The acceptor is placed at the junction between the two blocks in sample A1. The donor is placed either at the junction point between the blocks (D1) or free end of the block of poly(styrene) (D2). The experiment finds similar efficiencies of nonradiative singlet energy transfer in micelles formed by D1 and A1, and micelles formed by D2 and A1. This result implies that the free ends of the insoluble blocks do not seek out the center of mass of the micelle, but instead have a distribution throughout the micelle that is similar to the distribution of the junction points. Therefore the result confirms a crucial prediction from a recent simulation of the internal structure of the micelle formed by diblock copolymers in a selective solvent.