A New Approach for the Synthesis of Miktoarm Star Polymers Through a Combination of Thiol–Epoxy “Click” Chemistry and ATRP/Ring‐Opening Polymerization Techniques

Abstract

A new approach was developed for synthesis of certain A3B3‐type of double hydrophilic or amphiphilic miktoarm star polymers using a combination of “grafting onto” and “grafting from” methods. To achieve the synthesis of desired miktoarm star polymers, acetyl protected poly(ethylene glycol) (PEG) thiols (Mn = 550 and 2000 g mol−1) were utilized to generate A3‐type of homoarm star polymers through an in situ protective group removal and a subsequent thiol–epoxy “click” reaction with a tris‐epoxide core viz. 1,1,1‐tris(4‐hydroxyphenyl)ethane triglycidyl ether. The secondary hydroxyl groups generated adjacent to the core upon the thiol–epoxy reaction were esterified with α‐bromoisobutyryl bromide to install atom transfer radical polymerization (ATRP) initiating sites. ATRP of N‐isopropylacrylamide (NIPAM) using the three‐arm star PEG polymer fitted with ATRP initiating sites adjacent to the core afforded A3B3‐type of double hydrophilic (PEG)3[poly(N‐isopropylacrylamide)] (PNIPAM)3 miktoarm star polymers. Furthermore, the generated hydroxyl groups were directly used as initiator for ring‐opening polymerization of ε‐caprolactone to prepare A3B3‐type of amphiphilic (PEG)3[poly(ε‐caprolactone)]3 miktoarm star polymers. The double hydrophilic (PEG)3(PNIPAM)3 miktoarm star polymers showed lower critical solution temperature around 34 °C. The preliminary transmission electron microscopy analysis indicated formation of self‐assembly of (PEG)3(PNIPAM)3 miktoarm star polymer in aqueous solution. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 146–156

Surface-Initiated Atom Transfer Radical Polymerization for the Preparation of Well-Defined Organic–Inorganic Hybrid Nanomaterials

“…Hybrid polymer materials are based on the covalent linkage of the polymer chain to the various inorganic substrates including nanoparticles (NPs), flat and cylindrical surfaces or the inner surface of the nanopores [30]. Such surface modification can be achieved via different techniques including (a) grafting-from [31,32,33,34,35]; (b) grafting-through [36,37,38]; (c) grafting-onto [39,40,41].…”

Click chemistry strategies for the accelerated synthesis of functional macromolecules

“…Furthermore, the resulting three β-hydroxyl groups in the star core can be further polymerized through ATRP or ROP to obtain a miktoarm star polymer. 714 Multiple click reactions have also been applied to prepare star-BCPs by sequential coupling of endfunctionalized arm (co)polymers. Tunca demonstrated sequential CuAAC and DA coupling of arm polymers to prepare star-diblock, star-triblock, and miktoarm star BCPs.…”

“…Gadwal reported star polymer synthesis by clicking a thiol‐terminated PEG to a tri‐epoxide core through thiol‐epoxy chemistry. Furthermore, the resulting three β‐hydroxyl groups in the star core can be further polymerized through ATRP or ROP to obtain a miktoarm star polymer 714 …”

Thiol-epoxy ‘click’ chemistry: a focus on molecular attributes in the context of polymer chemistry

“…This strategy is developed by Gadwal and coworkers for the synthesis of star polymers. 50 It can be extended to the preparation of AB and AB 2 monomers to access linear and hyperbranched polymers, respectively.…”