Synthesis of PDMAEMA–PCL–PDMAEMA triblock copolymers

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.

Cationic micelles as nanocarriers for enhancing intra-cartilage drug penetration and retention

There is a tremendous unmet medical need for osteoarthritis (OA) treatment around the world, and pharmacological management is the most common option but presents a limited and short efficacy. Insufficient drug delivery to articular cartilage is the key cause. It is widely accepted that the complex structure of articular cartilage and the rapid clearance of joint liquids largely hinder drug penetration and retention in the cartilage. To address these obstacles, we designed and prepared a positively charged micellar system that can effectively deliver a model drug to the deep zone of the cartilage and prolong the drug retention time. In this work, a triblock copolymer composed of cationic poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(ε-caprolactone) (PCL), denoted as PDMAEMA-PCL-PDMAEMA, was synthesized. A triblock copolymer composed of brush poly[poly(ethylene glycol) methacrylate] (pPEGMA) and PCL, denoted as pPEGMA-PCL-pPEGMA, was prepared for comparison. The two types of triblock copolymers were self-assembled in an aqueous environment to form cationic and neutral micelles, respectively. A hydrophobic fluorescent dye as a model drug was loaded into micelle cores, and the dye-loaded micelles were evaluated for intra-cartilage penetration and retention using porcine knee cartilage explants. The PDMAEMA-PCL-PDMAEMA cationic micelles were found to significantly enhance the intra-cartilage penetration and retention capability due to the electrostatic interaction between the micelles and the negatively charged cartilage extracellular matrix. The confocal microscopy study showed that the cationic micelles could penetrate the full-thickness porcine cartilage explants (around 1.5 mm) within 24 hours. Up to 87% of the cationic micelles were taken up by porcine cartilage explants, and 71% of the absorbed micelles were retained in the tissue for at least 4 days. Although the pPEGMA-PCL-pPEGMA neutral micelles were able to penetrate the full-thickness cartilage, this type of micelle showed lower uptake (44%) and retention (44%) rates. This observation implied that the surface charge of micelles could play an important role in efficient intra-cartilage drug delivery. This study verified the feasibility and effectiveness of the PDMAEMA-PCL-PDMAEM cationic micelles in intra-cartilage drug delivery, showing that cationic micelles could be promising carriers for OA treatment.

Ionically Cross-Linked Polymers as Asymmetric Gel Polymer Electrolytes for Enhanced Cycle Performance of Lithium-Sulfur Batteries

Two thermoplastic triblock copolymers of poly(ε-caprolactone)-based acidic (PCL-A) and basic (PCL-B) polymers are synthesized by atom transfer radical polymerization. PCL-A and PCL-B are sequentially electrospun on a sulfur electrode and then ionically cross-linked by an acid-base reaction via hot pressing at 70 °C, which is confirmed by infrared (IR) spectroscopy. The cross-linked PCL-A/PCL-B-electrospun sulfur electrode is assembled as a lithium-sulfur battery with an asymmetric gel polymer electrolyte. The cross-linked polymer is swollen by a liquid electrolyte to form an asymmetric gel polymer electrolyte. The cyclic voltammetry results indicate that the asymmetric gel polymer electrolyte can suppress the dissolution of lithium polysulfides (Li₂S_n) into the electrolyte. Furthermore, the lithium-sulfur battery with the asymmetric gel polymer electrolyte exhibits enhanced cycle-life performance.

Cationic triblock copolymer micelles enhance antioxidant activity, intracellular uptake and cytotoxicity of curcumin

The aim of the present study was to develop curcumin loaded cationic polymeric micelles and to evaluate their loading, preservation of curcumin antioxidant activity and intracellular uptake ability. The micelles were prepared from a triblock copolymer consisting of poly(ϵ-caprolactone) and very short poly(2-(dimethylamino) ethyl methacrylate) segments (PDMAEMA9-PCL70-PDMAEMA9). The micelles showed monomodal size distribution, mean diameter of 145 nm, positive charge (+72 mV), critical micellar concentration around 0.05 g/l and encapsulation efficiency of 87%. The ability of the micellar curcumin to scavenge the ABTS radical and hypochlorite ions was higher than that of the free curcumin. Confocal microscopy revealed that the uptake of curcumin by chronic myeloid leukemia derived K-562 cells and human multiple myeloma cells U-266 was more intensive when curcumin was loaded into the micelles. These results correlated with the higher cytotoxicity of the micellar curcumin compared to free curcumin. Intraperitoneal treatment of Wistar rats indicated that PDMAEMA-PCL-PDMAEMA copolymer, comprising very short cationic chains, did not change the levels of malondialdehyde and glutathione in livers indicating an absence of oxidative stress. Thus, PDMAEMA-PCL-PDMAEMA triblock micelles could be considered efficient and safe platform for curcumin delivery.

Synthesis and properties of antifouling poly(CL-co-zDMAEMA) zwitterionic copolymer by one-step hybrid copolymerization

A novel biocompatible and biodegradable copolymer was synthesized by one-step hybrid copolymerization of ε-caprolactone (CL) and 2-(N,N-dimethylamino) ethyl methacrylate (DMAEMA) employing (1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phophoranylidenamino]-2Λ5,Λ5-catenadi(phosphazene) (t-BuP4) as a catalyst. The as-synthesized copolymer was betainizated resulting in a zwitterionic copolymer poly(CL-co-zDMAEMA) and the structure of the zwitterionic copolymer was confirmed by the FT-IR, NMR, and XPS measurements. The results of dynamic light scattering (DLS) show that this zwitterionic copolymer can self-assemble into stable micelles. The results of quartz crystal microbalance with dissipation (QCM-D) analysis and MTT measurement suggest that this zwitterionic copolymer possess better protein resistance and lower cell cytotoxicity in vitro in comparison with the cationic copolymer. The pyrene solubilization measurement of copolymers poly(CL-co-zDMAEMA) indicates an excellent pyrene solubilization capacity. These zwitterionic polymer micelles can release drugs in response to specific signals, such as temperature, pH, and enzymes and have a potential application in drug delivery and gene therapy due to their good antifouling, low cytotoxicity and high pyrene solubilization.

Physical tuning of cellulose-polymer interactions utilizing cationic block copolymers based on PCL and quaternized PDMAEMA

In this work, the objective was to synthesize and evaluate the properties of a compatibilizer based on poly(ε-caprolactone) aimed at tuning the surface properties of cellulose fibers used in fiber-reinforced biocomposites. The compatibilizer is an amphiphilic block copolymer consisting of two different blocks which have different functions. One block is cationic, quaternized poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and can therefore electrostatically attach to anionic reinforcing materials such as cellulose-based fibers/fibrils under mild conditions in water. The other block consists of poly(ε-caprolactone) (PCL) which can decrease the surface energy of a cellulose surface and also has the ability to form physical entanglements with a PCL surface thereby improving the interfacial adhesion. Atom Transfer Radical Polymerization (ATRP) and Ring-Opening Polymerization (ROP) were used to synthesize three block copolymers with the same length of the cationic PDMAEMA block but with different lengths of the PCL blocks. The block copolymers form cationic micelles in water which can adsorb to anionic surfaces such as silicon oxide and cellulose-model surfaces. After heat treatment, the contact angles of water on the treated surfaces increased significantly, and contact angles close to those of pure PCL were obtained for the block copolymers with longer PCL blocks. AFM force measurements showed a clear entangling behavior between the block copolymers and a PCL surface at about 60 °C, which is important for the formation of an adhesive interface in the final biocomposites. This demonstrates that this type of amphiphilic block copolymer can be used to improve interactions in biocomposites between anionic reinforcing materials such as cellulose-based fibers/fibrils and less polar matrices such as PCL.