Arm-First Approach toward Cross-Linked Polymers with Hydrophobic Domains via Hypervalent Iodine-Mediated Click Chemistry.

Saikat Maiti,Dibakar Dhara,Pousali Samanta,Gargi Biswas

doi:10.1021/acsomega.7b01632

Saikat Maiti, Dibakar Dhara + Show 2 more

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https://doi.org/10.1021/acsomega.7b01632

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Journal: ACS omega	Publication Date: Jan 17, 2018
Citations: 11	License type: cc-by

Affiliation: Indian Institute of Technology Kharagpur

Abstract

In this work, synthesis of two cross-linked polymeric systems through isoxazoline ring formation using nitrile oxide–acrylate click chemistry has been described. In the first system, styrenic block copolymer with oxime-functionalized middle block was synthesized using S,S′-bis(α,α′-dimethyl-α″-acetic acid)trithiocarbonate as chain-transfer agent using reversible addition fragmentation chain-transfer technique. This block copolymer was further utilized to prepare core cross-linked star polymers by reacting with a four-arm acrylic cross-linker by employing environment-friendly, nontoxic PhI(OAc)2-mediated “click reaction” via the formation of isoxazoline ring. In the second system, two linear styrenic block copolymers, one containing oxime and another containing acrylate group, were reacted to form a cross-linked (CS) polymeric system. Formation of cross-linked polymers and isoxazoline ring was confirmed by Fourier transform infrared spectroscopy, gel permeation chromatography, NMR spectroscopy, and dynamic light scattering studies. Later, we also demonstrated that in aqueous medium these CS polymers produced polymeric nanoparticles (NPs), which can be used as potential carriers of hydrophobic drug molecules. The loading capacity of the hydrophobic domains has been investigated using coumarin dyes with varying hydrophobicity through steady-state and time-resolved spectroscopy studies. The polymeric NPs were also shown to successfully encapsulate a hydrophobic drug doxorubicin.

Highlights

Cross-linked polymeric systems are a promising field of interest due to their compact architecture, aggregation behavior in selective solvent(s), and unique properties toward the delivery of drugs or dye molecules
Core cross-linked star (CCS) polymers, in which the polymer chains emerge from a single core, have found applications in the field of chemical sensing, tissue engineering, cosmetics, catalysis, etc.[1−4] Tremendous efforts have been made over the last few years to develop a facile and efficient route to synthesize a new class of cross-linked polymer structures, including core cross-linked star using dynamic covalent chemistry,[5−7] alkyne−azide click chemistry,[2−48−11] and thiol−ene click chemistry.[12−14] In this context, 1,3-dipolar cycloaddition[15] (1,3-DC) has been successfully utilized as synthetic tool for the formation of complex architectures, owing to its effectiveness in producing functionalized organic compounds
We have reported a unique method toward the synthesis of (i) core cross-linked star (CCS) polymers and (ii) cross-linked (CS) polymeric systems having polystyrene backbone via the formation of isoxazoline ring through nitrile oxide−acrylate 1,3-dipolar cycloaddition (1,3-DC) reactions.[43−45] Reversible addition fragmentation chain transfer (RAFT), one of the most diverse controlled polymerization techniques,[47−49] has been implemented to synthesize welldefined, controlled block copolymers using styrene, chlorobenzyl, and aldehyde-functionalized monomers

Summary

Introduction

Cross-linked polymeric systems are a promising field of interest due to their compact architecture, aggregation behavior in selective solvent(s), and unique properties toward the delivery of drugs or dye molecules. Synthesis of star polymers was reported using click chemistry as major pathway, as coppercatalyzed alkyne−azide cycloaddition was carried out, leading to the formation of 1,2,3-triazole systems.[6,7,18] complete removal of metals from the residue is often challenging, and considering the cytotoxicity of metals, a significant amount of work based on metal-free procedure for the synthesis of CCS polymers has been carried out in recent years by Sumerlin et al.,[19−21] Wiltshire and Qiao,[22−25] Fulton et al.,[26−28] and Otsuka et al.[29−31] In this context, hypervalent iodine(III) reagents,[32−35] such as iodobenzenediacetate [PhI(OAc)2], have drawn considerable attention due to their fairly high activity toward various oxidative organic reactions. We have reported the synthesis of polystyrene-based CCS polymer assembly with acrylic functionality at the polymer backbone with oxime-functionalized cross-linker via 1,3-dipolar cycloaddition.[36]

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