Preparation and Morphologies of Shell Cross-Linked Micelles Based on Commercial Poly(styrene-block-ethylene-co-butene-block-styrene)

Abstract

ABSTRACT:Chloromethyl groups were introduced into the polystyrene (PS) blocks of hydrogenated poly(styreneblock-butadiene-block-styrene) (SEBS) via Friedel-Crafts reaction. The product (SEBS-CH 2 Cl) formed spherical micelles with PS corona and hydrogenated PB core in THF/ethanol (10/9, v/v). Then, the polystyrene corona carrying CH 2 Cl groups was cross-linked by amination with 1,6-hexanediamine as a cross linker. The shell cross-linked micelles showed spherical core-shell structure and were stable in solution, which was verified by DLS in solution and by TEM in the solid state.KEY WORDS poly(styrene-block-butadiene-block-styrene) (SEBS) / Shell Cross-Linked Micelle / Chloromethylation / Amination / The creation of novel polymeric nanomaterials with the appropriate morphologies and functions for potential applications has become an intensely studied field of nanotechnology. Recently Wooley and coworkers have reported the synthesis of shell crosslinked "knedel" (SCK) micelles. 1-5 SCK's belong to a new class of nanomaterials which resemble polymer micelles in their core-shell morphology as well as dendrimers and arborescent polymers in being covalently bound and stable structures. 2 Various applications in areas as diverse as solubilization, catalysis, fillers, coatings, and delivery have been proposed for these fascinating new materials. 1 The generally applicable synthetic approach to the preparation of SCK nanoparticles involves micellization of amphiphilic block copolymers in aqueous solution, followed by cross-linking the chain segments composing the hydrophilic shell domain via addition of multifunctional cross-linking agents or radical addition polymerization of side groups. 6 Besides, entirely hydrophobic, 7 hydrophilic, 8 and zwitterionic 9 shell cross-linked micelles were reported as well, as a significant extension of the study of SCK's. Some procedures such as designing temperature-variable core hydrophilicity 8 and performing the cross-linking at an intermediate layer within the polymer micelles 10 are also developped to overcome limitations of possible applications and general approaches.Currently, the precursors for SCK's are mainly the block copolymers with a cross-linkable block. All the copolymers were prepared in laboratories by living polymerization, particularly, sequential anionic polymerization. [1][2][3][4][5][6][7][8][9][10] However, the preparation of such re- † To whom correspordence should be addressed. quired block copolymers is usually costly and timeconsuming. On the other hand, although the commercial block copolymers are relatively cheap and immediately available they are hardly used as the precursors for lack of cross-linkable functional groups. As reported previously by us, 11, 12 hydrogenated poly(styreneblock-butadiene-block-styrene) (SEBS) being a thermoelastomer with excellent properties, can be modified by controllably introducing functional groups without changing the original well defined structure. Here we report the preparation of shell cross-linked micelles starting f...

Nanomicellar Formulations for Sustained Drug Delivery: Strategies and Underlying Principles

“…PEG branching in this polymer can be used to create cross-linkable groups in the system to prepare a shell cross-linked micelle system. Thurmond et al [44] and Li et al [45] reported interesting approaches for cross-linking of the micellar shell in order to stabilize the micelles. Thurmond et al [44] prepared micelles from polyvinyl pyridine-b-poly styrene (M n = 52,500 Da) block copolymer, which on self-assembly, forms shell cross-linked knedel-like micelles, which appear to be a hybrid between dendrimers, hollow spheres, latex particles and block copolymer micelles.…”

“…Thurmond et al [44] prepared micelles from polyvinyl pyridine-b-poly styrene (M n = 52,500 Da) block copolymer, which on self-assembly, forms shell cross-linked knedel-like micelles, which appear to be a hybrid between dendrimers, hollow spheres, latex particles and block copolymer micelles. Li et al reported similar stabilization of the micelles by cross-linking the shell of the micelles made from a poly(styrene-b-butadiene-b-styrene) polymer [45]. Their approach involved formation of the micelles in aqueous medium and then cross-linking the hydrophobic portion of the micelles using chloromethylation and amination.…”

Synthesis and characterization of novel phosphonated and sulfonated poly(styrene–isobutylene–styrene) for fuel cell and protective clothing applications

“…SO 3 H SIBS with high IEC values has proton conductivities that are comparable to Nafion ® but higher methanol permeabilities . Incorporation of other functionalities (e.g., amination, benzoylation, naphthylation, among others) prior to sulfonation could enhance the properties (i.e., low water uptake, high transport, thermal, and oxidative) of the material and its potential as an alternative PEM . For example, phosphonic acid is another protogenic functionality that could be effective in improving the performance of SO 3 H SIBS due to its higher degree of self‐dissociation and hydrogen bonding, chemical and thermal stability, and lower acidity …”

“…Poly(styrene‐b‐(ethylene‐co‐butene)‐b‐styrene) (SEBS) (an aromatic block copolymer similar to SIBS) has been chloromethylated in the past, yielding a material with slightly altered monodispersity that can be used as macroinitiator for grafting via atom transfer radical polymerization (ATRP) . The grafting of copolymers via ATRP have been previously studied .…”

Polymeric Micelles in Targeted Drug Delivery

“…Thurmond et al [52] prepared micelles from polyvinyl pyridineb-poly styrene (M n = 52,500 Da) block copolymer, which on self-assembly, forms shell cross-linked knedel-like micelles. Li et al reported similar stabilization of the micelles by cross-linking the shell of the micelles made from a poly(styreneb-butadiene-b-styrene) polymer [53] by first preparing micelles in aqueous medium and then cross-linking the hydrophobic portion of the micelles using chloromethylation and amination.…”