Synthesis and Micellization of Triblock Copolymers Containing MePEG-b-PDMAEMA and Fluoropolymer: Effect of Block Lengths on Self-Assembly

Abstract

A series of triblock copolymer consisting of a double-hydrophilic diblock and a fluorinated block, namely monomethyl end-capped poly(ethylene glycol)-b-poly[2-(dimethylamino)ethyl methacrylate]-b-poly(2, 2, 3, 3, 4, 4, 5, 5-octafluoropentyl methacrylate) (MePEG-b-PDMAEMA-b-POFPMA), was synthesized via oxyanion-initiated copolymerization. The hydroxyl group of poly(ethylene glycol) monomethyl ether (MePEG16, M n = 750 g mol−1 or MePEG45, M n = 2000 g mol−1) reacted with potassium methylsulfinyl carbanion (DMSO−K+) and converted into a potassium alcoholate macroinitiator (MePEGO−K+). The lengths of PDMAEMA and POFPMA blocks could be controlled by the original molar ratio of monomers to the macroinitiator. These triblock copolymers were characterized by the measurements of 1H-NMR, and gel permeation chromatography (GPC). The results indicated that they had relatively low polydispersities (M w/M n:1.15–1.36). A significant investigation in this work was the comparison of the effects of the different block lengths, especially for MePEG and PDMAEMA, on the mecellization of copolymers in aqueous solution by the measurements of surface activities and electrical conductivity. The lower critical solution temperatures (LCSTs) of the di- and triblock copolymers varied with different factors, including the chemical structure, the block lengths, and the concentration. The effects of PDMAEMA length on the two kinds of diblock copolymers MePEG-b-PDMAEMA, which were initiated respectively by MePEG-2000 or MePEG-750 oxyanions, were studied by turbidimetric measurement. Furthermore, the different morphologies of MePEG-b-PDMAEMA-b-POFPMA in aqueous solution at pH 7.0 were observed by transmission electron microscopy (TEM).