Dendrimer-like Star Block and Amphiphilic Copolymers by Combination of Ring Opening and Atom Transfer Radical Polymerization

Abstract

A new type of macromolecular architecture, denoted as dendrimer-like star block copolymers, is reported. These block copolymers are described by a radial geometry where the different generations or layers are comprised of high molecular weight polymer emanating from a central core. A hexahydroxyl functional core was used as an initiator for the “living” ring opening polymerization (ROP) of ε-caprolactone producing a hydroxyl terminated six arm star polymer with controlled molecular weight and narrow polydispersities (PD < 1.1). Capping these chain ends with dendrons containing activated bromide moieties produced “macro-initiators” for atom transfer radical polymerization (ATRP). Methyl methacrylate was polymerized from these “macro-initiators” in the presence of an organometallic promoter to produce the requisite dendrimer-like star polymers. High molecular weight was obtained with low polydispersities (<1.2). Alternatively, amphiphilic character could be introduced by designing the different layers or generations to be either hydrophobic or hydrophilic. For example, methyl methacrylate (MMA) with either hydroxyethyl methacrylate (HEMA) or methacrylate functional ethylene oxide macromonomers (EO) were polymerized from these “macro-initiators” to provide a hydrophilic outer layer. The use of macromolecular building blocks allows rapid attainment of high polymer in a limited number of steps with purification between transformation requiring only polymer precipitation.

New methodologies in the construction of dendritic materials

“…For instance, Frechet et al devised hybrid PEG-unsymmetrical dendrimers with covalently attached cancer drugs and the resulting branched structure affords greater solubility and bioavailability which allows maximized performance in physiological environments. 34 One approach to obtain hybrid structures is by turning the core or the multiple end-groups of the dendritic polymer into initiating moieties for ATRP, 39 RAFT, 40 nitroxide-mediated polymerization, 41 ringopening polymerization 39 or ring-opening metathesis polymerization, 42 for example, and subsequent grafting-from polymerization. However, this approach is coupled with potential problems.…”

Synthesis of Amphiphilic Tadpole-Shaped Linear-Cyclic Diblock Copolymers via Ring-Opening Polymerization Directly Initiating from Cyclic Precursors and Their Application as Drug Nanocarriers

“…[1][2][3] It has been well-established that the topological structures and chemical composition of nonlinearshaped block copolymers can exhibit dramatic effects on the solution properties and self-assembling morphologies as compared with their linear counterpart. [4][5][6][7][8][9] It is worthy of noting that the developments of a variety of controlled radical polymerization techniques 10 such as atom transfer radical polymerization (ATRP), [11][12][13] reversible addition-fragmentation chain transfer (RAFT) polymerization, [14][15][16] and nitroxide-mediated polymerization (NMP) 17,18 have facilitated the synthesis of nonlinear-shaped polymers with varying chain architectures such as cyclic, 8,9,[19][20][21][22][23] (miktoarm) star, [24][25][26] star block copolymers, 27,28 comb, [29][30][31][32] sun-shaped, [33][34][35] H-shaped, [36][37][38] and θ-shaped 39,40 polymers. Among these nonlinear chain topologies, tadpole-shaped linearcyclic diblock copolymers [41]…”

Synthesis and Single Molecule Force Spectroscopy of Graft Copolymers of Poly(2-hydroxyethyl methacrylate-g-ethylene glycol)

“…PHEMA is also expected to have some hydrophobic interactions between -CH 2 -groups and a high van der Waals attractive interaction, since it is reported to have a high refractive index of 1.512. 23 The technique of atom transfer radical polymerization (ATRP) [26][27][28][29][30][31][32][33][34][35] was chosen to synthesize the poly(HEMAg-EG) model system described in this paper for a number of reasons. ATRP is an excellent general method to synthesize statistical, gradient, block, and graft copolymers as well as star and hyperbranched polymers due to the facile availability of functional monomers, halogen initiators, and catalysts.…”