Macroinitiator For Atom Transfer Radical Polymerization Research Articles

Organic nanoparticles with tunable size and rigidity by hyperbranching and cross-linking using microemulsion ATRP

Unlike inorganic nanoparticles, organic nanoparticles (oNPs) offer the advantage of "interior tailorability," thereby enabling the controlled variation of physicochemical characteristics and functionalities, for example, by incorporation of diverse functional small molecules. In this study, a unique inimer-based microemulsion approach is presented to realize oNPs with enhanced control of chemical and mechanical properties by deliberate variation of the degree of hyperbranching or cross-linking. The use of anionic cosurfactants led to oNPs with superior uniformity. Benefitting from the high initiator concentration from inimer and preserved chain-end functionality during atom transfer radical polymerization (ATRP), the capability of oNPs as a multifunctional macroinitiator for the subsequent surface-initiated ATRP was demonstrated. This facilitated the synthesis of densely tethered poly(methyl methacrylate) brush oNPs. Detailed analysis revealed that exceptionally high grafting densities (~1 nm-2) were attributable to multilayer surface grafting from oNPs due to the hyperbranched macromolecular architecture. The ability to control functional attributes along with elastic properties renders this "bottom-up" synthetic strategy of macroinitiator-type oNPs a unique platform for realizing functional materials with a broad spectrum of applications.

Block Copolymers of Polyolefins with Polyacrylates: Analyzing and Improving the Blocking Efficiencies Using MILRad/ATRP Approach.

Despite their industrial ubiquity, polyolefin-polyacrylate block copolymers are challenging to synthesize due to the distinct polymerization pathways necessary for respective blocks. This study utilizes MILRad, metal-organic insertion light-initiated radical polymerization, to synthesize polyolefin-b-poly(methyl acrylate) copolymer by combining palladium-catalyzed insertion-coordination polymerization and atom transfer radical polymerization (ATRP). Brookhart-type Pd complexes used for the living polymerization of olefins are homolytically cleaved by blue-light irradiation, generating polyolefin-based macroradicals, which are trapped with functional nitroxide derivatives forming ATRP macroinitiators. ATRP in the presence of Cu(0), that is, supplemental activators and reducing agents , is used to polymerize methyl acrylate. An increase in the functionalization efficiency of up to 71% is demonstrated in this study by modifying the light source and optimizing the radical trapping condition. Regardless of the radical trapping efficiency, essentially quantitative chain extension of polyolefin-Br macroinitiator with acrylates is consistently demonstrated, indicating successful second block formation.

Multifunctional Block Copolymers, Acting as Recycling Aids, by Atom Transfer Radical Polymerization.

Block copolymers utilizing oligomeric poly(pentylene-co-hexylene carbonate)diol modified with 2,4-diisocyanatotoluene and further with 2-bromo-N-(3-hydroxypropyl)-2-methylpropanamide were synthesized and utilized as Activators ReGenerated by Electron Transfer Atom Transfer Radical Polymerization macroinitiators to obtain a first generation of multifunctional recycling additives with poly(glycidyl methacrylate-co-butyl methacrylate-co-methyl methacrylate) side chains, which could act as chain extenders. Then, chosen additive was reacted with a radical scavenger, 3,5-ditertbutyl-4-hydroxybenzoic acid (DHBA), to obtain a second generation of reactive additives. Those copolymers had different numbers of epoxy groups per polymer chain, and different number of epoxides opened with DHBA, hence showed a range of properties, and were utilized as reactive modifiers for polylactide (PLA) extrusion melting. The first-generation modifiers caused an increase in PLA's blends relative melt viscosity, stabilized material properties, and enhanced impact strength, while the second-generation modifiers with more than 8 % of epoxide ring opened showed worse properties. However, they managed to suppress the UV degradation of PLA blend plates.

Surface Molecularly Imprinted Cellulose‐Synthetic Hybrid Particles Prepared via ATRP for Enrichment of Flavonoids in Olive Leaf

AbstractSurface molecularly imprinted cellulose‐synthetic hybrid particles are prepared via atom transfer radical polymerization (ATRP). The two‐step process involves the immobilization of α‐bromoisobutyryl bromide in the pristine microcrystalline cellulose, to generate ATRP macroinitiator particles, and then the creation of a crosslinked‐imprinted shell in the particles surface considering ATRP of 4‐vinylpyridine (4VP) and ethylene glycoldimethacrylate (EGDMA) with quercetin as imprinting template. Among the polymerization recipes tested, a system with ethanol as solvent preserves a final size of the hybrid particles suitable for application as adsorbent, while also incorporating the 4VP/EGDMA co‐monomers. Testing of imprinted/non‐imprinted particles for sorption/desorption of standard phenolic compounds shows the modification of the surface of the pristine cellulose and also the achievement of molecular imprinting (imprinting factor ≈2.6). Particles are used for the enrichment of flavonoids in olive leaf extracts and the special features of the developed molecularly imprinted adsorbents are again highlighted with this complex mixture of phenolic compounds. It is shown that production of fractions rich in luteolin‐7‐O‐glucoside, apigenin‐7‐O‐glucoside, or quercetin, among other flavonoids is possible (estimated enrichment factors up to 4). These results point up for the usefulness of natural‐synthetic materials with processes to get high‐added value compounds in the framework of circular bio‐economy.

Investigation of the Conditions for the Synthesis of Poly(3,4-ethylenedioxythiophene) ATRP Macroinitiator

One of the most widely used conductive polymers in the growing conductive polymer industry is poly(3,4-ethylenedioxythiophene) (PEDOT), whose main advantages are good thermal and chemical stability, a conjugated backbone, and ease of functionalization. The main drawback of PEDOT for use as wearable electronics is the lack of stretchable and self-healing properties. This can be overcome by grafting PEDOT with flexible side branches. As pure PEDOT is highly stable and grafting would not be possible, a new bromine-functionalized thiophene derivative, 2-(tiophen-3-yl) ethyl 2-bromo-2-methylpropanoate (ThBr), was synthesized and copolymerized with EDOT for the synthesis of a poly(EDOT-co-ThBr) ATRP macroinitiator. After the synthesis of the macroinitiator, flexible polymers could be introduced as side branches by atom-transfer radical polymerization (ATRP) to modify mechanical properties. Before this last synthesis step, the conditions for the synthesis of the ATRP macroinitiator should be investigated, as only functionalized units can function as grafting sites. In this study, nine new copolymers with different monomer ratios were synthesized to investigate the reactivity of each monomer. The ratios used in the different syntheses were ThBr:EDOT = 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1, 0.8:1, 0.6:1, 0.4:1, and 0.2:1. In order to determine the effect of reaction time on the final properties of the polymer, macroinitiator synthesis at a 1:1 ratio was carried out at different time periods: 8 h, 16 h, 24 h, and 48 h. The obtained products were characterized by different techniques, and it was found that polymerizations longer than 24 h yielded practically insoluble macroinitiators, thus limiting its further application. Reactivity ratios of both monomers were found to be similar and close to 1, making the copolymerization reaction symmetrical and the obtained macroinitiators almost random copolymers.

Structurally controllable anisotropic polymer brushes and their application in antifouling nanocoatings

Polymer brushes have garnered widespread attention for their potential applications in some emerging fields such as antifouling coating, drug delivery and high-efficiency catalyst. However, the difficulties in precisely controlling the structure and composition of polymer brushes severely degraded their physicochemical properties and chemical conformation. Herein, we developed an effective strategy to prepare structurally controllable atom transfer radical polymerization (ATRP) macroinitiator using multi-site polydienes as the polymer backbone and chlorine as the modifier. The amount of grafting allyl chloride groups could be effectively adjusted by regulating the reaction time, thereby achieving the programming ATRP macromolecular initiator with high-fidelity terminal chlorine groups. Thereinto, with chlorinated polydienes as the ATRP macroinitiator and polymer backbone, and resultant polystyrene as the side chains, the well-defined polystyrene brushes bearing controlled worm-like and rod-like structures were obtained. Benefiting from the branched structure, polystyrene brushes exhibited low intrinsic viscosity, compact molecular dimensions, and high terminal group functionality. Further, we prepared novel a superhydrophobic nanomaterial, namely, SiO2 nanoparticles (NPs)-polymer brushes, which demonstrated high non-wetting and excellent antifouling performance. Consequently, the approach and results collectively provide a promising avenue and perspective for preparing brush-like polymers with precisely designed structures and functionality.

Vapor Phase Modification for Selective Enrichment of Grafted Styrene/Acrylonitrile onto Carbon Nanotubes Via ATRP

Nitric acid vapor phase oxidation of multi-walled carbon nanotubes (MWCNTs) was proposed as a promising technique to fabricate poly styrene-co-acrylonitrile (SAN)-grafted-CNTs via atom transfer radical polymerization (ATRP). The in-situ ATRP grafting approach was successfully employed to graft polystyrene (PS), SAN and polyacrylonitrile (PAN), onto the convex surfaces of pristine MWCNTs (PCNT) and acid-functionalized MWCNTs (FCNT). Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H-NMR), and thermogravimetric analysis (TGA) confirmed the effectiveness of the modification via the ATRP grafting approach. The molar composition of acrylonitrile in the synthesized copolymer on the surface of CNTs for an FCNTs was calculated to be about 80% and 67.5% by 1H-NMR and TGA respectively, whereas the value is lower for PCNTs. Morphological studies showed that SAN-grafted FCNTs exhibit rougher surface morphology compared to the SAN-grafted PCNTs. Moreover, the higher diameter of the FCNTs indicated the higher polymer content, which was coated onto CNTs functionalized by vapor-phase oxidation. Therefore, the vapor phase oxidation strategy employed in this study could be utilized as a general method to prepare CNTs which can serve as an ATRP macroinitiator for the fabrication of various polymer grafted CNTs.

The “Living” Feature of the ATRP Macroinitiators in Different Catalytic Systems

Atom transfer radical polymerization (ATRP) has achieved widespread use in living polymerization. However, until now there has been little report that macroinitiators initiate polymerization in different catalytic systems. The preparation of bromine-terminated polymethyl methacrylate (PMMA-Br) and chlorine-terminated PMMA (PMMA-Cl) were carried out via reverse atom transfer radical polymerization (RATRP). The PMMA with halogen termination and narrow polydispersity (Mn = 12,000–15,000 g/mol, Mw/Mn = 1.1–1.2) were used as macroinitiators. The block copolymer of polymethyl methacrylate and polyacrylonitrile (PMMA-b-PAN) was prepared in different catalytic systems through normal ATRP. The analyses of the 1H NMR showed that the PMMA prepared by RATRP were end-functionalized by halogen atoms, demonstrated the activities of the PMMA macroinitiators. The molecular weight and polydispersity index (PDI) of the polymers were analyzed using gel permeation chromatography (GPC). The results indicated that the block polymers that the molecular weight of the block copolymer after chain extension has increased significantly and the molecular weight distribution is narrow (Mn = 17,000–25,000 g/mol, Mw/Mn = 1.1–1.3). The kinetics of these polymerization processes were studied as a function of monomers to the macroinitiator molar ratio. It was found that the polymerizations in different catalytic systems coincidence first-order kinetics with respect to monomers. In this paper, we reported that the chain extension in different catalytic systems is practicable. The PMMA-Cl and PMMA-Br were obtained in initiating systems of AIBN/FeCl3·6H2O/triphenylphosphine (PPh3) and AIBN/CuBr2/PMDETA, respectively. As the macroinitiators, the PMMA-Cl and PMMA-Br initiate the polymerization in FeCl2/PPh3 and CuBr/PMDETA catalytic systems, respectively. The molecular weight and PDI of the polymers were analyzed using GPC.

Design and fabrication of dual responsive lignin-based nanogel via \u201cgrafting from\u201d atom transfer radical polymerization for curcumin loading and release

The story of human dreams about curing all diseases, disorders and lesions is as old as human history. In the frontier of medical science, nanomedicine is trying to solve the problem. In this study, inspired by nanotechnology and using “grafting from” approach, a novel lignin-based nanogel was synthesized using atom transfer radical polymerization (ATRP) method. N-isopropylacrylamide (NIPAM) and N,N-dimethylaminoethylmethacrylate (DMAEMA) comonomers were graft copolymerized from fully brominated lignin as ATRP macroinitiator to synthesize lignin-g-P(NIPAM-co-DMAEMA) nanogel (LNDNG). By controlling the initial comonomer compositions and ATRP conditions, four LNDNG systems with different lower critical solution temperatures (LCSTs) of 32, 34, 37 and 42 °C were prepared. The LNDNGs were evaluated by GPC, FT-IR, 1H NMR, UV–Vis, DLS, SEM and TEM analyses. The prepared nanogels exhibited an average diameter of 150 nm with dual temperature and pH responsiveness. Curcumin (CUR) loading capacity and encapsulation efficiency of the LNDNGs were 49.69% and 92.62% on average, respectively. The cumulative release amount of loaded CUR was observed to be 65.36% after 72 h. The new lignin-based NGs proposed in the present work seems to be a promising, safe and comparable system in a near future.

Grafting Poly(Methyl Methacrylate) (PMMA) from Cork via Atom Transfer Radical Polymerization (ATRP) towards Higher Quality of Three-Dimensional (3D) Printed PMMA/Cork-g-PMMA Materials.

Cork is a unique material and its by-products are attracting an ever-growing interest for preparing new materials in an attempt to extend the outstanding properties of cork toward innovative and high value applications. Yet, the miscibility of cork particles with thermoplastic matrices is not easy due to its low density and surface properties. Here, cork is functionalized with poly(methyl methacrylate) (PMMA) via atom transfer radical polymerization (ATRP) to yield cork grafted with PMMA chains particles (cork-g-PMMA). Both the ATRP macroinitiator and the cork-g-PMMA obtained are fully characterized by Fourier-transform infrared spectroscopy (FT-IR), 13C cross-polarized magic-angle spinning solid-state nuclear magnetic resonance (13C CP/MAS solid state NMR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD) and thermogravimetric analyses (TGA). The functionalized cork particles are then blended with commercial PMMA to afford cork-g-PMMA/PMMA. To compare, cork also is mixed with PMMA and the ensuing cork/PMMA sample and its morphology, thermal, and mechanical properties are compared with those of cork-g-PMMA/PMMA and commercial PMMA. The cork surface modification via ATRP of the methyl methacrylate (MMA) yields better dispersion in the matrix. Consequently, a blend with enhanced mechanical performance, higher thermal stability, and a higher melt flow index (MFI) is obtained when compared to the blend prepared using unmodified particles. The similarity of the MFI of cork-g-PMMA/PMMA to that of PMMA suggests good printability. Indeed, a three-dimensional (3D) printed specimen is obtained confirming that grafting using ATRP is a promising route for the preparation of high quality 3D printed products.

Conversion of an Injectable MMP-Degradable Hydrogel into Core-Cross-Linked Micelles.

In this study, a new type of injectable hydrogel called “HyMic” that can convert into core cross-linked (CCL) micelles upon exposure to matrix metalloproteinases (MMP’s), was designed and developed for drug delivery applications. HyMic is composed of CCL micelles connected via an enzyme cleavable linker. To this end, two complementary ABA block copolymers with polyethylene glycol (PEG) as B block were synthesized using atom transfer radical polymerization (ATRP). The A blocks were composed of a random copolymer of N-isopropylacrylamide (NIPAM) and either N-(2-hydroxypropyl)methacrylamide-cysteine (HPMA-Cys) or N-(2-hydroxypropyl) methacrylamide-ethylthioglycolate succinic acid (HPMA-ETSA). Mixing the aqueous solutions of the obtained polymers and rising the temperature above the cloud point of the PNIPAM block resulted in the self-assembly of these polymers into flower-like micelles composed of a hydrophilic PEG shell and hydrophobic core. The micellar core was cross-linked by native chemical ligation between the cysteine (in HPMA-Cys) and thioester (in HPMA-ETSA) functionalities. A slight excess of thioester to cysteine groups (molar ratio 3:2) was used to allow further chemical reactions exploiting the unreacted thioester groups. The obtained micelles displayed a Z-average diameter of 80 ± 1 nm (PDI 0.1), and ζ-potential of −4.2 ± 0.4 mV and were linked using two types of pentablock copolymers of P(NIPAM-co-HPMA-Cys)-PEG-peptide-PEG-P(NIPAM-co-HPMA-Cys) (Pep-NC) to yield hydrogels. The pentablock copolymers were synthesized using a PEG-peptide-PEG ATRP macroinitiator and the peptide midblock (lysine-glycine-proline-glutamine-isoleucine-phenylalanine-glycine-glutamine-lysine (Lys-Gly-Pro-Gln-Gly-Ile-Phe-Gly-Gln-Lys)) consisted of either l- or d-amino acids (l-Pep-NC or d-Pep-NC), of which the l-amino acid sequence is a substrate for matrix metalloproteases 2 and 9 (MMPs 2 and 9). Upon mixing of the CCL micelles and the linker (l/d-Pep-NC), the cysteine functionalities of the l/d-Pep-NC reacted with remaining thioester moieties in the micellar core via native chemical ligation yielding a hydrogel within 160 min as demonstrated by rheological measurements. As anticipated, the gel cross-linked with l-Pep-NC was degraded in 7–45 days upon exposure to metalloproteases in a concentration-dependent manner, while the gel cross-linked with the d-Pep-NC remained intact even after 2 months. Dynamic light scattering analysis of the release medium revealed the presence of nanoparticles with a Z-average diameter of ∼120 nm (PDI < 0.3) and ζ-potential of ∼−3 mV, indicating release of core cross-linked micelles upon HyMic exposure to metalloproteases. An in vitro study demonstrated that the released CCL micelles were taken up by HeLa cells. Therefore, HyMic as an injectable and enzyme degradable hydrogel displaying controlled and on-demand release of CCL micelles has potential for intracellular drug delivery in tissues with upregulation of MMPs, for example, in cancer tissues.

A Novel Strategy for the Synthesis of Amphiphilic and Thermoresponsive Poly(N-isopropylacrylamide)-b-Polystyrene Block Copolymers via ATRP.

A new synthetic approach is presented for the preparation of Poly(N-isopropylacrylamide-block-styrene) PNIPAM-b-PS via an Atom Transfer Radical Polymerization (ATRP) technique. The proposed method is based on application of 2-chloro-N-(2-hydroxyethyl)propanamide (NCPAE) as a bifunctional initiator, which enables ATRP of two monomers, differing in activity and polarity, into two stages. The synthesized copolymer molecules contain two well-defined polymer chains connected by a linker, which is a derivative of the proposed initiator. Using NCPAE led to PNIPAMs with well-planned molecular weight, low polydispersities (PDI=1.1÷1.3) and hydroxyl functionality. Activation of such blocks for initiation of styrene polymerization was performed using α-bromoisobutyryl bromide. After such a modification, the synthesized homopolymers acted as macroinitiators in ARGET ATRP and a well-defined polystyrene block, as the next one in the polymer chain was successfully formed. Both of the synthesized macromolecules, PNIPAM and PNIPAM-b-PS, exhibit a thermoresponsive behavior with explicit lower critical solution temperatures (LCST) in their aqueous solutions. The synthesized homopolymers and subsequently derived block copolymers were characterized using Size-Exclusion Chromatography, Differential Scanning Calorimetry, Dynamic Light Scattering, and NMR spectroscopy.

Synthesis and characterization of electroactive bottlebrush nano-copolymers based on polystyrene and polyaniline as side chains and poly(3-(2-hydroxyethyl)thiophene) as backbone

Electroactive bottlebrush copolymers were synthesized via grafting of polystyrene (PSt) and polyaniline (PANI) from poly(3-(2-hydroxyethyl)thiophene) backbones by atom transfer radical polymerization (ATRP) and chemical oxidation polymerization. The bromoesters were attached to the polymer chains to afford the proper macroinitiators for ATRP of PSt branches. Likewise, some other polymer chains were functionalized with antranilic acid for chemical oxidation polymerization of PANI. Electroactivity behaviors of the synthesized bottlebrushes were approved by the cyclic voltammetry, and their conductivities were determined using the four-probe technique. Thanks to the electrical conductivity and thermal stability, the synthesized bottlebrushes can be appropriate candidates for being used in various systems such as organic solar cells.

Novel block glycopolymers prepared as delivery nanocarriers for controlled release of bortezomib

To explore block glycopolymers as novel polymeric delivery nanocarriers for anticancer drug bortezomib (BTZ), three types of block glycopolymers, poly(ethylene glycol)-block-poly(gluconamido ethyl methacrylate) (PEG113-b-PGAMA20), poly(ethylene glycol)-block-poly(styrene)-block-poly(gluconamido ethyl methacrylate) (PEG113-b-PS50-b-PGAMA20), and poly(ethylene glycol)-block-poly(2-(diethyl amino) ethyl methacrylate)-block-poly(gluconamido ethyl methacrylate) (PEG113-b-PDEA50-b-PGAMA20), were synthesized via atom transfer radical polymerization (ATRP) using a PEG-based ATRP macroinitiator. Three glycopolymers possess the capacity to load BTZ via pH-induced dynamic covalent bonding and/or hydrophobic interaction with their specific self-assembly behaviors, and PEG113-b-PS50-b-PGAMA20 carrier maintains the sustain release behavior of BTZ due to the stable micellar structure; PEG113-b-PDEA50-b-PGAMA20 carrier realizes the abrupt release at pH 5.5 by collapse of micellar structure, while PEG113-b-PGAMA20 carrier exhibits the fastest release at studied solution pHs. This study would provide a light to develop novel block glycopolymer carrier for the delivery of anticancer drug bearing boronic acid groups.Graphical abstractᅟᅟ

Amphiphilic comb-like pentablock copolymers of Pluronic L64 and poly(ethylene glycol)methyl ether methacrylate: synthesis by ATRP, self-assembly, and clouding behavior

Well-defined amphiphilic comb-like pentablock copolymers based on Pluronic L64 (PEO13-b-PPO30-b-PEO13) and poly(ethylene glycol)methyl ether methacrylate (PEGMA) have been successfully synthesized via atom transfer radical polymerization (ATRP). The L64 is transformed into ATRP macroinitiator and chain extended with PEGMA under typical ATRP conditions to achieve comb-like pentablock copolymers of various compositions. Due to their amphiphilic nature, the block copolymers could form self-assembled structures in aqueous solutions as confirmed by dynamic light scattering. At higher PEGMA content in the synthesized copolymer, however, the critical aggregation concentration (CAC) is less pronounced that could be attributed to the increased hydrophilicity and steric hindrance of PEG side chains of the PEGMA, thus preventing the formation of well-defined micellar aggregates, and probably leads to open-shell aggregation mechanism. The lower critical solution temperature (LCST) of the synthesized block copolymers is found higher than the neat L64 and increased with increasing the PEGMA content. Further, tuning the clouding behavior could be achieved with inorganic additives (KBr and K2SO4). The influence of SO42− and Br1− on LCST is according to their position in Hofmeister series. Interestingly, the effect of additives is more pronounced above the CAC of the copolymer, suggesting that the nanoaggregates in solution induce the macrophase separation.

Dual Location, Dual Acidic pH/Reduction-Responsive Degradable Block Copolymer: Synthesis and Investigation of Ketal Linkage Instability under ATRP Conditions

Stimuli-responsive degradation (SRD) undergoing chemical transition through the cleavage of labile linkages has been proved to dramatically increase the versatility of stimuli-responsive block copolymers. In particular, dual or multiple stimuli-responsive degradable block copolymers that can be triggered by two endogenous stimuli of acidic pH and reduction are in high demand. Here, a new strategy utilizing atom transfer radical polymerization (ATRP) is reported to synthesize a dual acidic pH/reduction-responsive degradable block copolymer (DLDSRD) labeled with an acidic pH-labile ketal linkage at the block junction and pendant reductively cleavable disulfide groups in hydrophobic block at dual locations. A robust route with multiple steps utilizing carbamate chemistry to endow stability during protection/deprotection steps enables the synthesis of a novel poly(ethylene glycol)-based ATRP macroinitiator labeled with a ketal linkage (PEG-ketal-Br macroinitiator). Conducting ATRP allows for the synthesis of ...

Polymerization-induced self-assembly of acrylonitrile via ICAR ATRP

Polymerization-induced self-assembly (PISA) has attracted growing interest as facile fabrication process of polymer-based nanomaterials. However, PISA of acrylonitrile (AN) by atom transfer radical polymerization (ATRP) has remained an outstanding challenge due to the high activity of AN and poor solubility of polyacrylonitrile (PAN) in AN monomer. Here the application of PISA by using an initiators for continuous activator regeneration (ICAR) ATRP for the synthesis of PAN-based nano-objects is demonstrated. A highly active ATRP macroinitiator, methoxy-poly(ethylene oxide) 2-bromo-2-phenylacetate (mPEO-BPA) was synthesized by esterification and used also as a stabilizer. The molecular weight of the macroinitiator was found to determine the structure of self-assembled nano-objects. The high molecular macroinitiator (mPEO113-BPA) formed nano-objects with spherical or worm-like morphology, while the lower molecular weight analogue (mPEO45-BPA) resulted in precipitation in most cases due to insufficient stabilization of the nano-objects.

Synthesis of Cellulose-graft-Polychloromethylstyrene-graft-Polyacrylonitrile Terpolymer/Organoclay Bionanocomposite by Metal Catalyzed Living Radical Polymerization and Solvent Blending Method

ABSTRACTA bionanocomposite of grafted cellulose and organo-modified clay was synthesized through solution intercalation method. For this purpose, chloromethylstyrene was grafted onto cellulose using acryloylchloride and the subsequent free radical polymerization. The synthesized cellulose-graft-polychloromethylstyrene was used as an atom transfer radical polymerization macroinitiator of acrylonitrile in the presence of CuCl/2,2′-bipyridine catalyst system, to prepare the cellulose-graft-polychloromethylstyrene-graft-polyacrylonitrile terpolymer. For preparing the modified clay, Na-montmorillonite was mixed with hexadecyl trimethyl ammonium chloride salt. Finally, cellulose-graft-polychloromethylstyrene-graft-polyacrylonitrile/organoclay bionanocomposite was prepared in CCl4 by solution intercalation method.

Straightforward synthesis of well-defined poly(vinyl acetate) and its block copolymers by atom transfer radical polymerization

A facile Atom Transfer Radical Polymerization (ATRP) method based on the use of the complex obtained with CuCl, CuCl2 and the very active ligand 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (Me6CyClam) as catalytic system, was successfully employed for the first time to polymerize vinyl acetate (VAc) with a good control over the polymerization, which showed a living character and monomer conversion up to 90%. The use of such an active ligand allows to maintain a particularly low concentration of propagating species once very reactive radicals, from such monomers, are formed, hence establishing a fast and dynamic ATRP equilibrium. Several kinetic studies on the ATRP of VAc were carried out with the aim to identify the optimized conditions allowing a good control over the process attaining materials with well-defined structure and low polydispersity. The livingness of the macromolecular system was confirmed, among the others, by using the obtained PVAc as ATRP macroinitiator for the synthesis of several block copolymers. Furthermore, the possibility to hydrolyse the VAc block thus attaining amphiphilic materials was studied.

Synthesis and characterization of pentablock copolymers based on Pluronic® L64 and poly(methyl methacrylate)

The synthesis and characterization of amphiphilic pentablock copolymers based on Pluronic® L64 (PEO13-PPO30-PEO13) and poly(methyl methacrylate) (PMMA), synthesized via atom transfer radical polymerization (ATRP) is reported. The L64 is first transformed into a bifunctional ATRP macroinitiator which was subsequently chain extended with MMA by ATRP to afford PMMA-b-L64-b-PMMA pentablock copolymers. The chemical structure of the synthesized amphiphilic block copolymers is characterized by FTIR, 1H NMR spectroscopy, and gel permeation chromatography (GPC). The GPC profiles of the block copolymers clearly show an increase in molar mass after the ATRP of MMA and monomodal molecular weight distributions for all the samples. Finally, preliminary studies on their aggregation behavior in aqueous solution have also been investigated by measuring the scattering light intensity as function of block copolymer concentration to estimate the critical aggregation concentration (CAC). The CAC decreases with increasing of hydrophobic content in copolymer, i.e., ∼25 and ∼15 mg/mL, respectively, is estimated for the pure L64 and PMMA13-b-L64-b-PMMA13. Further, with increase in temperature, the CAC is found to decrease that is attributed to the dehydration of the PEO segments at higher temperatures.