Abstract
Well-defined amphiphilic, biocompatible and partially biodegradable, thermo-responsive poly(N-vinylcaprolactam)-b-poly(ε-caprolactone) (PNVCL-b-PCL) block copolymers were synthesized by combining reversible addition-fragmentation chain transfer (RAFT) and ring-opening polymerizations (ROP). Poly(N-vinylcaprolactam) containing xanthate and hydroxyl end groups (X–PNVCL–OH) was first synthesized by RAFT/macromolecular design by the interchange of xanthates (RAFT/MADIX) polymerization of NVCL mediated by a chain transfer agent containing a hydroxyl function. The xanthate-end group was then removed from PNVCL by a radical-induced process. Finally, the hydroxyl end-capped PNVCL homopolymer was used as a macroinitiator in the ROP of ε-caprolactone (ε-CL) to obtain PNVCL-b-PCL block copolymers. These (co)polymers were characterized by Size Exclusion Chromatography (SEC), Fourier-Transform Infrared spectroscopy (FTIR), Proton Nuclear Magnetic Resonance spectroscopy (1H NMR), UV–vis and Differential Scanning Calorimetry (DSC) measurements. The critical micelle concentration (CMC) of the block copolymers in aqueous solution measured by the fluorescence probe technique decreased with increasing the length of the hydrophobic block. However, dynamic light scattering (DLS) demonstrated that the size of the micelles increased with increasing the proportion of hydrophobic segments. The morphology observed by cryo-TEM demonstrated that the micelles have a pointed-oval-shape. UV–vis and DLS analyses showed that these block copolymers have a temperature-responsive behavior with a lower critical solution temperature (LCST) that could be tuned by varying the block copolymer composition.
Highlights
Amphiphilic and stimuli-responsive block copolymers have been attracting an extensive scientific interest
PNVCL–OH was synthesized by reversible addition-fragmentation chain transfer (RAFT)/MADIX polymerization of NVCL monomer using OS-4-(hydroxymethyl) benzyl carbonodithioate as the chain transfer agent, followed by xanthate end ethyl S-4-(hydroxymethyl) benzyl carbonodithioate as the chain transfer agent, followed by xanthate group removal (Scheme 1)
The block copolymers were synthesized via a combination of RAFT/MADIX and ring-opening polymerizations
Summary
Amphiphilic and stimuli-responsive block copolymers have been attracting an extensive scientific interest. Amphiphilic block copolymers are capable of self-assembling in aqueous solutions and, depending on their architecture, molar ratio, and chemical composition, ordered nanostructures of various morphologies including spherical micelles, cylindrical micelles, lamellae and vesicles, can be Polymers 2020, 12, 1252; doi:10.3390/polym12061252 www.mdpi.com/journal/polymers. Polymers 2020, 12, 1252 obtained [1] This feature contributes to the potential applications of these materials in many fields including catalysis, microelectronics, nanoreactors and drug delivery systems [2,3]. Stimuli-responsive polymers have been used to incorporate and release active substances for controlled delivery systems [4]. Thermo-responsive polymers are frequently used because the temperature is an important physiological factor in the body, and some disease states manifest themselves by some changes in temperature [5]. Hyperthermia techniques can be used with the intent of improving the targeting ability of the thermo-responsive carriers for the tissues [6]
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