Self-assembly of well-defined block copolymers in solution has gained attention not only for its scientific value but also for its potential application in nanotechnology. In this study, we present a comprehensive series of synthesized block copolymers that allows conclusions to be drawn how to design micelles by ROMP with defined core−shell geometry and controlled size. We used a general route for the preparation of well-defined block copolymers by ring opening metathesis polymerization (ROMP) with “Grubbs first generation catalyst” RuCl2(PCy3)2(CHPh) (Cy = cyclohexyl). In a first step, we sequentially polymerized endo,exo[2.2.1]bicyclo-2-ene-5,6-dicarboxylic acid dimethylester with endo,exo[2.2.1]bicyclo-2-ene-5,6-dicarboxylic acid di-tert-butyl ester, to obtain a high control of polymerization and complete characterization of the block copolymers. The polymers were characterized by 1H- and 13C NMR spectroscopy, FT-IR spectroscopy, by GPC, and by DSC. By cleavage of the tert-butyl group, the polymer was transformed into an amphiphilic block copolymer. In two series of polymers, we investigated the micelle formation in ethanol by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS). In the first series, the influence of the block ratio on the size of the micelle, the aggregation number, and the core−shell dimensions were investigated while the overall polymer length was kept constant. In the second series, the block ratio was fixed to 1:1 and the overall polymer length was varied, leading to direct proportionality of the micelle size to the polymer length, while the core-to-shell ratio was constant.

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Well‐defined amphiphilic block copolymers were prepared by ring opening metathesis polymerization and their stimuli responsive behavior of formed micelles in aqueous solution was investigated. The hydrophobic core of the micelles consists of either a poly[5,6‐bis(ethoxymethyl)bicyclo[2.2.1]hept‐2‐ene]‐block with a glass transition Tg at room temperature or a poly[endo,exo[2.2.1]bicyclohept‐5‐ene‐2,3‐diylbis (phenylmethanone)] with a Tg of 143 °C. For the polyelectrolyte shell, the precursor block poly[endo,exo[2.2.1]bicyclohept‐5‐ene‐2,3‐dicarboxyclic tert‐butylester] was transformed into the free acidic block by cleavage of the tert‐butyl groups using trifluoroacetic acid. Micellar solutions were prepared by dialysis, dissolving the copolymers in dimethyl sulfoxide which was subsequently replaced by water. All polymers form micelles with radii between 10 and 20 nm at a pH‐value below 5, where the carboxylic acid groups are in the protonated state. The block copolymer micelles show a strong increase of the hydrodynamic radius with increasing pH‐value, due to the repulsion among the formed carboxylate anions resulting in a stretching of the polymer chains. In this state, the micelles exhibit responsive behavior to ionic strength where a contraction of the micelles is observed as the carboxylate charges are balanced by sodium ions, whereas no changes of the hydrodynamic radius on addition of salt are observed at low pH. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1178–1191, 2009

The self-assembly of block copolymers to form well-ordered structures is of great interest for the design of hierarchical materials. In this contribution, the morphologies and properties of well-defined block copolymers with narrow molecular weight distributions prepared by ring-opening metathesis polymerization are studied. Two series of amphiphilic AB-block copolymers poly [(endo,exo[2.2.1]bicyclohept-5-ene-2,3-dicarboxylic acid dimethyl ester)-b-(endo,exo[2.2.1]bicyclohept-5-ene-2,3-dicarboxylic acid)] of different block ratios and lengths were investigated by thermal analysis, small-angle X-ray scattering, and transmission electron microscopy. As observed by thermal gravimetric analysis and FTIR spectroscopy, the free carboxylic acid functionalities lead to anhydride formation at higher temperatures so that direct observation of the melt morphologies is not possible. However, by drop-casting polymer solutions in THF, which is a nonselective solvent for this type of block copolymer, well-ordered films were prepared. A variety of structured morphologies of block copolymers with different compositions was obtained. Perfectly ordered lamellar phases can be observed for AB-block copolymers where both blocks are of equal size. For block copolymers with ratios that deviate from 1:1, morphologies like lamellae with different lamella size, hexagonal cylinders, and globules with liquidlike packing were found.