Living free-radical block copolymerization using thio-iniferters

Polymer Grafting and its chemical reactions

Polymer grafting is a technique to improve the morphology, chemical, and physical properties of the polymer. This technique has the potential to improve the existing conduction and properties of polymers other than charge transport; as a result, it enhances the solubility, nano-dimensional morphology, biocompatibility, bio-communication, and other property of parent polymer. A polymer's physicochemical properties can be modified even further by creating a copolymer with another polymer or by grafting. Here in the various chemical approaches for polymer grafting, like free radical, click reaction, amide formation, and alkylation have been discussed with their importance, moreover the process and its importance are covered comprehensively with their scientific explanation. The present review also covers the effectiveness of the graft-to approaches and its application in various fields, which will give reader a glimpse about polymer grafting and its uses.

Synthesis of manganese-incorporated polycaplactone-poly (glyceryl methacrylate) theranostic smart hybrid polymersomes for efficient colon adenocarcinoma treatment

In the current study, a multifunctional nanoscale vesicular system (polymersome) with the ability to accumulate in the site of action, control drug release and integrate diagnostic and therapeutic functions was developed. The theranostic polymersome was engineered as a promising dual-functional nanoplatform, which can be used for tumor therapy and magnetic resonance imaging (MRI). In this regard, the amphiphilic diblock copolymer of poly(ε-caprolactone)-block-poly(glyceryl methacrylate)[(PCL-b-PGMA)] was synthesized by combined ring-opening polymerization (ROP), and reversible addition-fragmentation chain-transfer (RAFT) polymerization techniques followed by hydrolysis of the pendant oxiran rings to hydroxyl groups. Because of the amphiphilic properties and desirable hydrophobic/hydrophilic balance of the synthesized copolymer, it could self-assemble to form a polymersomal structure in an aqueous environment (with diameters about 100 - 145 nm). The hydrophilic anticancer drug, doxorubicin (DOX) and hydrophobic paramagnetic Mn (phenanthroline)₂ complex, being well-represented on T1-weighted magnetic resonance imaging (MRI), were encapsulated in the hydrophilic core (33%±2.3 efficiency) and hydrophobic bilayer membrane (100 %efficient) of a polymersome system, respectively to provide PCL-PGMA@Mn(phen)₂/DOX NPs. It was found that adding aptamer AS1411 to NPs surfaces enhanced their specificity and selectivity towards colorectal cancer cells expressing nucleolin (HT29 and C26). In vivo evaluation after intravenous administration of the prepared platform was performed using subcutaneous C26 tumor-bearing Balb/C mice. The obtained results demonstrated that the prepared targeted platform provided a reduced systemic toxicity in terms of body weight loss and mortality while showing efficient tumor regression. Furthermore, the prepared theranostic platform afforded MRI imaging capability for tumor monitoring. It could be concluded that the biocompatible PCL-PGMA magnetic DOX-loaded polymersomes could serve as a versatile multifunctional system for simultaneous tumor imaging and therapy.

Study of The Reaction Mechanism to Produce Nanocellulose-Graft-Chitosan Polymer

Cellulose and chitin are the most abundant polymeric materials in nature, capable of replacing conventional synthetic polymers. From them, cellulose nano/microfibers (CNFs/CMFs) and chitosan are obtained. Both polymers have been used separately in graft copolymerization but there are not many studies on the use of cellulose and chitosan together as copolymers and the reaction mechanism is unknown. In this work, the reaction mechanism to produce nano/microcellulose-graft-chitosan polymer has been studied. Recycled cellulose pulp was used, with and without a 2,2,6,6-tetramethylpiperidin-1-oxyl-radical (TEMPO)-mediated oxidation pretreatment, to produce CNFs and CMFs, respectively. For chitosan, a low-molecular weight product dissolved in an acetic acid solution was prepared. Grafted polymers were synthesized using a microwave digester. Results showed that TEMPO-mediated oxidation as the cellulose pretreatment is a key factor to obtain the grafted polymer CNF-g-CH. A reaction mechanism has been proposed where the amino group of chitosan attacks the carboxylic group of oxidized cellulose, since non-oxidized CMFs do not achieve the desired grafting. 13C NMR spectra, elemental analysis and SEM images validated the proposed mechanism. Finally, CNF-g-CH was used as a promising material to remove water-based inks and dyes from wastewater.

IMPROVE THE NATIVE CHARACTERISTICS OF POLYSACCHARIDES BY GRAFTING THROUGH THE GAMMA RADIATION: A REVIEW

Polysaccharides are bio-degradable, inexpensive and easily available from consistent agricultural resources. Polysaccharides and their derivatives represent a group of polymer widely used in pharmaceutical and biomedical fields. The biodegradability of natural polymers reduces their shelf life. Grafting copolymerization technique is a most effective fascinating way for chemical modification of native characteristics of polysaccharides with maximum possibilities for improving the properties of polysaccharides and enhanced the range of exploitation.While the major difficulty facing us during synthesizing a graft copolymers reaction, is the lack of commercial methods of synthesis and lower percent graft yield. It is well known that the most important methods of synthesis engage the employ of chemical free radical initiator i.e. conventional based methods. Graft copolymerization through γ-radiation method is a better method of grafting in comparison to a chemical method and exhibits a great potential to synthesize the graft copolymers by virtue of its higher efficiency, low cost, higher thermal stability as well as enhanced the yield of the graft copolymer. Future prospective of irradiation technique would be significant impacts to develop of polymerization.

Iron-Mediated Homogeneous ICAR ATRP of Methyl Methacrylate under ppm Level Organometallic Catalyst Iron(III) Acetylacetonate

Atom Transfer Radical Polymerization (ATRP) is an important polymerization process in polymer synthesis. However, a typical ATRP system has some drawbacks. For example, it needs a large amount of transition metal catalyst, and it is difficult or expensive to remove the metal catalyst residue in products. In order to reduce the amount of catalyst and considering good biocompatibility and low toxicity of the iron catalyst, in this work, we developed a homogeneous polymerization system of initiators for continuous activator regeneration ATRP (ICAR ATRP) with just a ppm level of iron catalyst. Herein, we used oil-soluble iron (III) acetylacetonate (Fe(acac)₃) as the organometallic catalyst, 1,1'-azobis (cyclohexanecarbonitrile) (ACHN) with longer half-life period as the thermal initiator, ethyl 2-bromophenylacetate (EBPA) as the initiator, triphenylphosphine (PPh₃) as the ligand, toluene as the solvent and methyl methacrylate (MMA) as the model monomer. The factors related with the polymerization system, such as concentration of Fe(acac)₃ and ACHN and polymerization kinetics, were investigated in detail at 90 °C. It was found that a polymer with an acceptable molecular weight distribution (Mw/Mn = 1.43 at 45.9% of monomer conversion) could be obtained even with 1 ppm of Fe(acac)₃, making it needless to remove the residual metal in the resultant polymers, which makes such an ICAR ATRP process much more industrially attractive. The "living" features of this polymerization system were further confirmed by chain-extension experiment.

Synthesis of Novel Triazole-Containing Phosphonate Polymers

The objective of this research was to develop novel phosphonate-containing polymers as they remain a relatively under researched area of polymer chemistry. Herein, we report the synthesis and characterization of 2-(1-(2-(diethoxyphosphoryl)ethyl)-1H-1,2,3-triazol-4-yl)ethyl acrylate (M1) and diethyl (2-(4-(2-acrylamidoethyl)-1H-1,2,3-triazol-1-yl)ethyl)phosphonate (M2) monomers using the copper-catalyzed azide–alkyne cycloaddition (CuAAC) ‘click’ reaction, and their subsequent polymerization via both uncontrolled and reversible addition–fragmentation chain transfer (RAFT) polymerization techniques yielding phosphonate polymers (P1–P4).

Biomimetic materials and micropatterned structures using iniferters

In the preparation of biomimetic materials it is often required that efficient methods of polymerization be used, often methods that can lead to biomimetic polymers with relatively narrow molecular weight distribution. Living radical polymerization techniques have successfully been used to create low polydispersity linear polymers by free-radical polymerizations. Although this technique slows down the polymerization of multifunctional monomers, there is little effect on the network structure due to the high concentration of pendent double bonds. There are applications of the living radical polymerization in the synthesis of block copolymers. Essentially, the technique involves polymerizing a single type of monomer first to create a macromonomer that is capable of acting as an initiator because of the reversible bond between the polymer end group and the terminating group. This terminating group may be a thiol or a halogen and, under the right conditions, will dissociate to form radicals. A second monomer is then added to the system and the polymerization proceeds with the second monomer chemically attached to the polymer of the first monomer. We review methods of creating biomimetic block copolymers using the iniferter radical polymerization technique. The block copolymers would be used in the synthesis of micropatterned polymer films for use in biomaterials and other biomedical applications.

Use of Fluorinated Organic Compounds in Living Radical Polymerizations

Controlled/living radical polymerization (LRP) is a field of special interest because it allows tailoring well-defined macromolecular architectures such as telechelic, block, graft or star copolymers. Since the eighties, several techniques have been reported [such as the iniferter method, nitroxide-mediated radical polymerization (NMP), atom transfer radical polymerization (ATRP), iodine transfer polymerization (ITP), and reversible addition-fragmentation chain transfer (RAFT)] giving rise to a huge number of publications and patents. This review aims at illustrating the contribution of fluorinated organic compounds in this area of research through the use of fluorinated initiators (dithiocarbamates, xanthates, tetraphenylethanes, alkoxyamines, fluorinated alkyl halides, and dithioesters) or other fluorinated molecules (ligands, solvents). Another point depicts the LRP of various fluorinated monomers (methacrylates, acrylates, styrenics, and alkenes). Finally, fluorinated block and graft copolymers prepared by LRP have been reported. A review with 165 references.

Micropatterning of biomedical polymer surfaces by novel UV polymerization techniques

The "living" radical polymerization with an iniferter was used to create micropatterned biomedical surfaces. Novel, photosensitive biomedical polymers were created by the incorporation of dithiocarbamate groups from iniferters. A second monomer layer was then irradiated onto the photosensitive polymer substrate created with the iniferter to form a copolymer. Patterns were created on the films by application of modified microfabrication-based photolithographic techniques. The technique was used to create patterns with depths from 5 to 80 microm. In addition, various polymers were incorporated, including polyethylene glycol methacrylates, styrene, and methacrylic acid, to synthesize regions with different physico-chemical properties. Applications include novel surfaces for biosensors and biomaterials for the selective adhesion of cells and proteins.