Prog. Polym. Sci. 28 (2003) 1403–1439 www.elsevier.com/locate/ppolysci New polymeric architectures with (meth)acrylic acid segments Hideharu Mori, Axel H.E. Mu¨ller* Makromolekulare Chemie II and Bayreuther Zentrum fu¨r Kolloide und Grenzfla¨chen, Universita¨t Bayreuth, D-95440 Bayreuth, Germany Received 21 July 2003; revised 21 July 2003; accepted 23 July 2003 Abstract This review summarizes recent advances in the design and synthesis of novel complex polymers with (meth)acrylic acid segments using various living and controlled polymerization techniques. As polymeric architectures, we will focus on block copolymers, branched polymers, Janus micelles, and polymer brushes. Characteristic solution behavior and morphologies derived from their amphiphilic properties and three-dimensional architectures will be introduced briefly. q 2003 Elsevier Ltd. All rights reserved. Keywords: Acrylic acid; Methacrylic acid; Controlled/living polymerization; Block copolymers; Branched polymers; Polymer brushes; Polyelectrolytes Contents 1. Introduction ...................................................................1404 2. Homopolymers.................................................................1405 2.1. Anionic polymerization ......................................................1405 2.2. Group transfer polymerization .................................................1407 2.3. Controlled radical polymerization ...............................................1407 2.4. Deprotection ..............................................................1407 2.5. Direct polymerization of acrylic acid ............................................1408 3. Block copolymers...............................................................1408 3.1. Anionic polymerization ......................................................1409 3.2. Group transfer polymerization .................................................1412 3.3. Atom transfer radical polymerization ............................................1412 3.4. Reversible addition–fragmentation chain transfer polymerization........................1413 3.5. Other reactions ............................................................1414 3.6. Multi-mode polymerizations ...................................................1414 3.6.1. Combination of cationic and anionic polymerizations...........................1414 3.6.2. Combination of cationic polymerization and ATRP ............................1415 3.6.3. Combination of anionic polymerization and ATRP ............................1416 4. Branched polymers..............................................................1416 4.1. Homopolymers ............................................................1416 4.1.1. Dendritic (randomly branched and hyperbranched) polymers .....................1417 * Corresponding author. Tel.: þ49-921-55-3393; fax: þ49-921-55-3399. E-mail address: [email protected] (A.H.E. Mu¨ller). 0079-6700/03/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0079-6700(03)00076-5 1404 H. Mori, A.H.E. Mu¨ller / Prog. Polym. Sci. 28 (2003) 1403–1439 4.1.2. Star polymers........................................................1419 4.2. Copolymers ...............................................................1419 4.2.1. Graft copolymers .....................................................1419 4.2.2. Starblock copolymers ..................................................1421 4.2.3. Hetero/miktoarm copolymers ............................................1422 4.2.4. Janus micelles .......................................................1422 5. Polymer brushes ................................................................1425 5.1. 1D (cylindrical) brushes (‘bottle brushes’).........................................1425 5.2. 2D (planar) brushes .........................................................1427 5.3. 3D (spherical) brushes .......................................................1428 6. Summary and perspective .........................................................1428 References .......................................................................1429 1. Introduction unique and attractive properties, potentially connect- ing materials science, pharmacy, biochemistry and Poly(methacrylic acid) (PMAA) and poly(acrylic polymer science, which make them a challenging acid) (PAA) are weak polyelectrolytes, in which the subject for researchers. In particular, much interest degree of ionization is governed by the pH and ionic has been received by the self-assembly of block strength of aqueous solution. For example, PAA copolymers, because of their feasibility to generate is virtually undissociated at low pH (pH # 4), nanostructured materials and their numerous potential whereas a fully charged chain results at pH $ 8. applications in separation technology, controlled drug Poly[(meth)acrylic acid]s are known to form inter- delivery and release, and smart catalyst separation polymer complexes with various non-ionic proton- technology [13–19]. Recent advances of the con- accepting polymers, their derivatives, and with trolled/living polymerization techniques made it cationic polyelectrolytes in aqueous and organic possible to produce well-defined polymer structures, media [1–7]. It has been shown that the nature and such as graft copolymers, star polymers, polymer molecular weight (MW) of the interacting polymers brushes, etc. The interest in synthesis and character- as well as various environmental parameters (the ization of such complex polymer systems containing nature of solvent, pH, ionic strength of solution, (meth)acrylic acid segments has increased enor- temperature, and polymer concentration) have sig- mously. Their chemical structure and three-dimen- nificant influence on the complex formation. Numer- sional (3D) architectures may be tuned for a wide ous studies have been also devoted to the interaction range of applications covering as different aspects as of poly[(meth)acrylic acid]s with metal ions [8–11], stabilization of colloids, crystal growth modification, since knowledge of association phenomena of metal induced micelle formation, components of intelligent ions with charged macromolecules is of importance materials, polyelectrolyte complexing towards novel for the understanding of their physicochemical drug carrier systems. behavior in environmental and biological systems. For the synthesis of well-defined polymers, living PAA could be successfully used as a component of polymerization techniques have been traditionally characteristic ‘intelligen’ organic–inorganic hybrid employed where the polymerizations proceed in the materials [12]. absence of irreversible chain transfer and chain Block copolymers containing (meth)acrylic acid termination. These requirements are met in a nearly segments belong to the class of ionic (or polyelec- ideal way in anionic polymerization, and less ideally, trolyte) block copolymers, which combine structural in cationic polymerization. However, the application features of polyelectrolytes, block copolymers, and of these techniques for the synthesis of functional surfactants. If the ionic block is rather short compared polymers was limited, as most of the systems are not to the non-ionic one, they are also named ‘block tolerant of functional groups. Thus, typically, pro- ionomers’. Ionic block copolymers possess quite tected monomers have been employed, followed by H. Mori, A.H.E. Mu¨ller / Prog. Polym. Sci. 28 (2003) 1403–1439 1405 Nomenclature Pn BuA poly(n-butyl acrylate) EO ethylene oxide AA acrylic acid PEO poly(ethylene oxide) PAA poly(acrylic acid) PPO poly(propylene oxide) MAA methacrylic acid PB polybutadiene PMAA poly(methacrylic acid) PIB polyisobutylene t BuA tert-butyl acrylate PCL poly(1-caprolactone) Pt BuA poly(tert-butyl acrylate) DMAEMA 2-(dimethylamino)ethyl methacrylate t BuMA tert-butyl methacrylate NIPAAm N-isopropylacrylamide Pt BuMA poly(tert-butyl methacrylate) CRP controlled radical polymerization TMSMA trimethylsilyl methacrylate ATRP atom transfer radical polymerization BzMA benzyl methacrylate GTP group transfer polymerization THPMA 2-tetrahydropyranyl methacrylate RAFT reversible addition-fragmentation chain PNPMA p-nitrophenyl methacrylate transfer EEMA 1-(ethoxy)ethyl methacrylate PMDETA N,N,N0,N00,N00-pentamethyldiethylene- BEMA 1-(butoxy)ethyl methacrylate triamine t BEMA 1-(tert-butoxy)ethyl methacrylate DB degree of branching MMA methyl methacrylate MW molecular weight PMMA poly(methyl methacrylate) MWD molecular weight distribution S styrene SCVP self-condensing vinyl polymerization PS poly(styrene) SCVCP self-condensing vinyl copolymerization n BuA n-butyl acrylate a polymer-analogous deprotection, e.g. hydrolysis of monomers are still required to obtain well-defined protecting ester groups. A variety of protected polymers with (meth)acrylic acid segments. Protected monomers have been developed in the past few monomers with masked acid groups involve tert-butyl decades, and various types of tailor-made polymers acrylate (t BuA), tert-butyl methacrylate (t BuMA), with interesting architectures and functional groups trimethylsilyl methacrylate (TMSMA), benzyl metha- have been synthesized by living anionic polymeriz- crylate (BzMA), 2-tetrahydropyranyl methacrylate ation with the protected monomers [20,21]. (THPMA), and p-nitrophenyl methacrylate Recent development in controlled radical polym- (PNPMA) (Fig. 1). After acid hydrolysis, thermolysis, erization (CRP) methods has provided another or catalytic hydrogenolysis, these protective groups