Well-Defined Polyisoprene-b-Poly(acrylic acid)/Polystyrene-b- Polyisoprene-b-Poly(acrylic acid) Block Copolymers: Synthesis and Their Self-Assembled Hierarchical Structures in Aqueous Media Xiaojun Wang, † Jihua Chen, ‡ Kunlun Hong, ‡ and Jimmy W. Mays* ,†,‡,§ † Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996, United States ‡ Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States § Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States * S Supporting Information ABSTRACT: The synthesis and characterization of well-defined polyacid based block copolymers containing polyisoprene (PI) are reported. The challenge of maintaining the integrity of the polydiene while producing polyacid from the tert-butyl ester precursor is addressed in this communication. A general purification method was also developed, taking advantage of the different polarities of each block. The polystyrene-b-polyisoprene-b-poly- (acrylic acid) (PS-b-PI-b-PAA) triblock terpolymers form multicompartmental micelles via aqueous self-assembly. Our work reveals the morphological consequences of unique balances among global and local interactions. A mphiphilic block copolymers hold great potential for applications in the biomedicine and nanotechnology fields owing to their surfactant behavior, that is, self-assembly into micelles in a selective solvent. 1 Such micelles can exhibit an array of morphologies dictated by multiple interactions among the hydrophilic, hydrophobic segments, and solvent (typically water). 1,2 Although much progress has been made over the past two decades, 2-7 it is still challenging to predict structure- property relationships for many block copolymer-based micelles, which is critical in utilizing their characteristic properties in various applications. When amphiphilic block copolymer micelles are employed as a delivery vehicle, the core of the micelle should provide a suitable microenvironment for the incorporation of hydro- phobic ingredients, while the corona stabilizes this hydrophobic core. Due to the potential differences in solubility of these ingredients, it may be advantageous to use micellar cores with multiple compartments, which can solubilize different ingre- dients. Such “multi-compartment micelles” may be formed through self-assembly of block copolymers containing multiple immiscible hydrophobic components. 8-10 The majority of studies to date have focused on glassy materials such as polystyrene (PS) as the hydrophobic constituents in block copolymer-based micelles. Poly(acrylic acid) (PAA), a commonly used hydrophilic block, conjugated with a PS block, has been well-studied. 11,12 In contrast, PAA-based diblock copolymers containing polydienes (polyisoprene (PI) or polybutadiene (PBD)), which can self-assemble to create micelles having hydrophobic soft cores, are rarely studied, mainly due to challenges in synthesis and purification of such block copolymers. 13-16 Well-defined polydienes are readily obtained using anionic polymerization, but this method is not applicable directly to acrylic acid. Synthetic difficulties in creating well-defined PI- b-PAA and PBD- b-PAA block copolymers center around the intrinsically unstable nature of polydienes under strongly acidic conditions (40% loss of double bonds was reported when HCl catalyzed hydrolysis was carried out 17 ), which are necessary for hydrolysis of poly(tert- butyl acrylate) (PtBuA), the commonly used anionically polymerizable precursor to PAA. No spectroscopic evidence for the structural integrity of these polydiene components in block copolymers with PtBuA (or poly(tert-butyl methacrylate), PtBuMA) after converting to PAA through hydrolysis has been furnished. 13-17 It is critical to ascertain that the polydiene remain intact after the ester hydrolysis, since retention of the residual double bonds of the polydienes in the self-assembled structures will provide further opportunities for functionaliza- tion and chemical modification. For example, cross-linking can be carried out to stabilize the as-formed structures, 8 or sacrificial degradation (e.g., by ozonolysis) can be employed to create cavities for bioactive reagent encapsulation. 17,18 Here, we report the synthesis of well-defined block copolymers of isoprene and acrylic acid with the carbon- carbon double bonds in the PI block remaining intact after Received: April 20, 2012 Accepted: May 30, 2012 Published: June 1, 2012 Letter pubs.acs.org/macroletters © 2012 American Chemical Society 743 dx.doi.org/10.1021/mz300192u | ACS Macro Lett. 2012, 1, 743-747