Synthesis of Novel Linear PEO-b-PS-b-PCL Triblock Copolymers by the Combination of ATRP, ROP, and a Click Reaction

Synthesis and Characterization of ABA-Type Triblock Copolymers Using Novel Bifunctional PS, PMMA, and PCL Macroinitiators Bearing p-xylene-bis(2-mercaptoethyloxy) Core

Syntheses of novel bifunctional poly(methyl methacrylate) (PMMA)-, poly(styrene) (PS)-, and (poly ε-caprolactone) (PCL)-based atom transfer radical polymerization (ATRP) macroinitiators derived from p-xylene-bis(1-hydroxy-3-thia-propanoloxy) core were carried out to obtain ABA-type block copolymers. Firstly, a novel bifunctional ATRP initiator, 1,4-phenylenebis(methylene-thioethane-2,1-diyl)bis(2-bromo-2-methylpropanoat) (PXTBR), synthesized the reaction of p-xylene-bis(1-hydroxy-3-thia-propane) (PXTOH) with α-bromoisobutryl bromide. The PMMA and PS macroinitiators were prepared by ATRP of methyl methacrylate (MMA) and styrene (S) as monomers using (PXTBR) as the initiator and copper(I) bromide/N,N,N',N″,N″-pentamethyldiethylenetriamine (CuBr/PMDETA) as a catalyst system. Secondly, di(α-bromoester) end-functionalized PCL-based ATRP macronitiator (PXTPCLBr) was prepared by esterification of hydroxyl end groups of PCL-diol (PXTPCLOH) synthesized by Sn(Oct)2-catalyzed ring opening polymerization (ROP) of ε-CL in bulk using (PXTOH) as initiator. Finally, ABA-type block copolymers, PXT(PS-b-PMMA-b-PS), PXT(PMMA-b-PS-b-PMMA), PXT(PS-b-PCL-b-PS), and PXT(PMMA-b-PCL-b-PMMA), were synthesized by ATRP of MMA and S as monomers using PMMA-, PS-, and PCL-based macroinitiators in the presence of CuBr/PMDETA as the catalyst system in toluene or N,N-dimethylformamide (DMF) at different temperatures. In addition, the extraction abilities of PCL and PS were investigated under liquid-liquid phase conditions using heavy metal picrates (Ag+, Cd2+, Cu2+, Hg2+, Pb2+, and Zn2+) as substrates and measuring with UV-Vis the amounts of picrate in the 1,2-dichloroethane phase before and after treatment with the polymers. The extraction affinity of PXTPCL and PXTPS for Hg2+ was found to be highest in the liquid-liquid phase extraction experiments. Characterizations of the molecular structures for synthesized novel initiators, macroinitiators, and the block copolymers were made by spectroscopic (FT-IR, ESI-MS, 1H NMR, 13C NMR), DSC, TGA, chromatographic (GPC), and morphologic SEM.

Poly (Ethylene Oxide)-Based Block Copolymer Electrolytes Formed via Ligand-Free Iron-Mediated Atom Transfer Radical Polymerization

The Br-terminated poly (ethylene oxide) (PEO-Br) is used as a green and efficient macroinitiator in bulk Fe-catalyzed atom transfer radical polymerization (ATRP) without the addition of any organic ligands. The polymerization rate is able to be mediated by PEO-Br with various molecular weights, and the decrease in redox potential of FeBr₂ in cyclic voltammetry (CV) curves indicates that an increased coordination effect is deteriorated with the depressing reaction activity in the longer ethylene oxide (EO) chain in PEO-Br. In combination with the study of different catalysts and catalytic contents, the methyl metharylate (MMA) or poly (ethylene glycol) monomethacrylate (PEGMA) was successfully polymerized with PEO-Br as an initiator. This copolymer obtained from PEGMA polymerization can be further employed as a polymer matrix to form the polymer electrolyte (PE). The higher ionic conductivity of PE was obtained by using a high molecular weight of copolymer.

Strategies to combine ROP with ATRP or RAFT polymerization for the synthesis of biodegradable polymeric nanoparticles for biomedical applications

The available strategies to combine CRPs and ROP in the synthesis of highly engineered polymer nanoparticles are here critically discussed.

Folic acid-functionalized AIE Pdots based on amphiphilic PCL-b-PEG for targeted cell imaging

Folic acid-functionalized polymer dots with aggregation induced emission features (AIE Pdots), which show high fluorescence efficiency and little toxicity to living cells, which possess a good capability for targeted HeLa intracellular imaging.

Poly(ethylene oxide) (PEO)-based ABC triblock terpolymers – synthetic complexity vs. application benefits

This review presents a short summary of possible synthetic routes for the synthesis of poly(ethylene oxide) (PEO) containing triblock terpolymers, as well as different applications in the bulk or in solution – including the preparation of porous materials, hybrid systems, and carriers for controlled drug delivery.

pH-dependent, thermosensitive polymeric nanocarriers for drug delivery to solid tumors

Polymeric micelles are promising carriers for anti-cancer agents due to their small size, ease of assembly, and versatility for functionalization. A current challenge in the use of polymeric micelles is the sensitive balance that must be achieved between stability during prolonged blood circulation and release of active drug at the tumor site. Stimuli-responsive materials provide a mechanism for triggered drug release in the acidic tumor and intracellular microenvironments. In this work, we synthesized a series of dual pH- and temperature-responsive block copolymers containing a poly(ε-caprolactone) (PCL) hydrophobic block with a poly(triethylene glycol) block that were copolymerized with an amino acid-functionalized monomer. The block copolymers formed micellar structures in aqueous solutions. An optimized polymer that was functionalized with 6-aminocaproic acid (ACA) possessed pH-sensitive phase transitions at mildly acidic pH and body temperature. Doxorubicin-loaded micelles formed from these polymers were stable at blood pH (~7.4) and showed increased drug release at acidic pH. In addition, these micelles displayed more potent anti-cancer activity than free doxorubicin when tested in a tumor xenograft model in mice.

Functional Polyether-based Amphiphilic Block Copolymers Synthesized by Atom-transfer Radical Polymerization

This review deals with the synthesis, physical properties, and applications of amphiphilic block copolymers based on hydrophilic poly(ethylene oxide) (PEO) or hydrophobic poly(propylene oxide) (PPO). Oligomeric PEO and PPO are frequently functionalized by converting their OH end groups into macroinitiators for atom-transfer radical polymerization. They are then used to generate additional blocks as part of complex copolymer architectures. Adding hydrophobic and hydrophilic blocks, respectively, leads to polymers with amphiphilic character in water. They are surface active and form micelles above a critical micellization concentration. Together with recent developments in post-polymerization techniques through quantitative coupling reactions (‘click’ chemistry) a broad variety of tailored functionalities can be introduced to the amphiphilic block copolymers. Examples are outlined including stimuli responsiveness, membrane penetrating ability, formation of multi-compartmentalized micelles, etc.

Utilization of micelles formed from poly(ethylene glycol)-block-poly(epsilon-caprolactone) block copolymers as nanocarriers to enable hydrophobic red two-photon absorbing emitters for cells imaging

A hydrophobic two-photon absorbing (2PA) red emitter (R) was successfully incorporated into micelles formed from two block copolymers, poly(epsilon-caprolactone)-block-poly(ethylene glycol)s, for imaging and toxicity studies. In micelles, the chromophore R exhibits a 2PA cross-section of 400 GM (1 GM = 1 x 10(-50) cm(4) s photon(-1) molecule(-1)) at 820 nm, which is among the highest values reported for red 2PA emitters. The micelles with a cationic amino moiety-containing poly(ethylene glycol) corona showed an enhancement of cell internalization and delivered the dye into the cytoplasmic regions of the mouse macrophage RAW 264.7 cells. In comparison, the dye in micelles with neutral poly(ethylene glycol) as corona could not be delivered into the cells. Cytotoxicity of the micelle-R constructs was studied using a 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. More than 90% of the cells were viable after they were stained with the dye-containing micelles at different concentrations (dye concentrations of 2-6 muM and polymer concentrations of 0.05-0.15 mg/mL) for 16 h. This is the first reported application of a hydrophobic 2,1,3-benzothiadiazole-containing 2PA red emitter delivered into the cytoplasm of cells for bioimaging and toxicity assessment.

2,1,3-Benzothiadiazole (BTD)-moiety-containing red emitter conjugated amphiphilic poly(ethylene glycol)-block-poly(epsilon-caprolactone) copolymers for bioimaging

2,1,3-Benzothiadiazole (BTD)-containing red emitter was chemically conjugated onto amphiphilic poly(ethylene glycol)-block-poly(epsilon-caprolactone) (PEG-b-PCL) copolymers to form two new fluorophore-conjugated block copolymers (P5 and P7). P5 is a cationic amino group-containing polymer, whereas, P7 is a neutral polymer. The polymers formed micelles in aqueous solution with average diameters of 45 nm (P7) and 78 nm (P5), which were characterized using dynamic light scattering (DLS) and atomic force microscopy (AFM). Cell internalization of the micelles using mouse macrophage RAW 264.7 was investigated. The micelles formed from P5 were endocytosed into the cell's cytoplasm through a non-specific endocytosis process, which was affected by temperature and calcium ions. Micelles formed from P7 could not be endocytosed. The dramatic difference of cell uptake between P5 and P7 indicated the cationic amino groups had a strong influence on the cell internalization to enhance the endocytosis pathway. 3-(4,5-Dimethyl thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) viability assay was used to evaluate the cytotoxicity of the P5 micelle and no significant toxicity was observed. This study is the first report regarding the synthesis of BTD-conjugated block copolymers and the application of the biomacromolecules for bioimaging.