Well-defined Graft Copolymers Research Articles

RAFT/ROP binary polymerization towards well-defined graft copolymers

The RAFT/ROP binary polymerization enables the efficient synthesis of controlled and well-defined poly(N-hydroxyethyl acrylamide)–poly(ε-caprolactone) (PHEAA-g-PCL) as compared to the conventional “two-step” method.

Synthesis and Self-Assembly of Thermoresponsive Biohybrid Graft Copolymers Based on a Combination of Passerini Multicomponent Reaction and Molecular Recognition.

Amphiphilic graft copolymers exhibit fascinating self-assembly behaviors. Their molecular architectures significantly affect the morphology and functionality of the self-assemblies. Considering the potential application of amphiphilic graft copolymers in the fabrication of nanocarriers, it is essential to synthesize well-defined graft copolymers with desired functional groups. Herein, the Passerini reaction and molecular recognition are introduced to the synthesis of functional thermoresponsive graft copolymers. A bifunctional monomer 2-((adamantan-1-yl)amino)-1-(4-((2-bromo-2-methylpropanoyl)oxy)phenyl)-2-oxoethyl methacrylate (ABMA) with a bromo group for atom transfer radical polymerization (ATRP) and an adamantyl group for molecular recognition is synthesized through the Passerini reaction. The graft copolymers are prepared by reversible addition-fragmentation transfer (RAFT) copolymerization of ABMA and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) followed by RAFT end group removal and ATRP of di(ethylene glycol)methyl ether methacrylate (DEGMA) initiated by the ABMA units. The graft copolymer P(OEGMA-co-ABMA)-g-PDEGMA can be functionalized with β-cyclodextrin modified peptides, affording a thermoresponsive biohybrid graft copolymer. At a temperature above its lower critical solution temperature, the biohybrid graft copolymer self-assembles into peptide-modified polymersomes.

Synthesis of Highly Defined Graft Copolymers Using a Cyclic Acetal Moiety as a Two-Stage Latent Initiating Site for Successive Living Cationic Polymerization and Ring-Opening Anionic Polymerization

The synthesis of well-defined graft copolymers with designed intervals between branches was achieved using cyclic acetal moieties as two-stage latent initiating sites. A cyclic acetal was shown to initiate the living cationic polymerization of vinyl ethers (VEs), yielding a polymer with a hydroxy group at the α-end derived from the cyclic acetal. The newly generated hydroxy group was able to efficiently induce the subsequent ring-opening anionic polymerization of l-lactide (LLA), and a diblock copolymer with a narrow molecular weight distribution (MWD) was obtained. For the synthesis of a graft copolymer, a five-membered cyclic acetal moiety was introduced at the ω-chain ends of poly(VE)s, which was employed as the initiating site for the living cationic polymerization of VEs. Repeated polymerization and acetalization generated a macroinitiator with several hydroxy groups on the side chain of a poly(VE) backbone. Graft copolymers possessing branches with narrow MWDs and regular spaces between the branches...

PHEA-g-PMMA Well-Defined Graft Copolymer: ATRP Synthesis, Self-Assembly, and Synchronous Encapsulation of Both Hydrophobic and Hydrophilic Guest Molecules

A series of well-defined amphiphilic graft copolymer bearing a hydrophilic poly(2-hydroxyethyl acrylate) (PHEA) backbone and hydrophobic poly(methyl methacrylate) (PMMA) side chains was synthesized by successive reversible addition-fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) through the grafting-from strategy. A well-defined PHEA-based backbone with Cl-containing ATRP initiating group in every repeated unit (Mw/Mn = 1.08), poly(2-hydroxyethyl 2-((2-chloropropanoyloxy)methyl)acrylate) (PHECPMA), was first prepared by RAFT homopolymerization of 2-hydroxyethyl 2-((2-chloropropanoyloxy)methyl)acrylate (HECPMA), a Cl-containing trifunctional acrylate. ATRP of methyl methacrylate was subsequently initiated by PHECPMA homopolymer to afford the target well-defined poly(2-hydroxyethyl acrylate)-graft-poly(methyl methacrylate) (PHEA-g-PMMA) graft copolymers (Mw/Mn ≤ 1.36) with 34 PMMA side chains and 34 pendant hydroxyls in PHEA backbone using CuCl/dHbpy as catalytic system. The critical micelle concentration (cmc) of the obtained graft copolymer was determined by fluorescence spectroscopy using N-phenyl-1-naphthylamine as probe while micellar morphologies in aqueous media were visualized by transmission electron microscopy. Interestingly, PHEA-g-PMMA graft copolymer could self-assemble into large compound micelles rather than common spherical micelles, which can encapsulate hydrophilic rhodamine 6 G and hydrophobic pyrene separately or simultaneously.

A PHEA-g-PEO well-defined graft copolymer exhibiting the synchronous encapsulation of both hydrophobic pyrene and hydrophilic Rhodamine 6G

This article reports the synthesis of a well-defined PHEA-g-PEO graft copolymer by the combination of RAFT polymerization, Cu(i)-mediated ATNRC, and the grafting-onto strategy, which could encapsulate hydrophilic R6G and hydrophobic pyrene simultaneously.

Novel amphiphilic temperature responsive graft copolymers PCL-g-P(MEO2MA-co-OEGMA) via a combination of ROP and ATRP: synthesis, characterization, and sol-gel transition

A series of well-defined novel amphiphilic temperature-responsive graft copolymers containing PCL analogues P(αCleCL-co-eCL) as the hydrophobic backbone, and the hydrophilic side-chain PEG analogues P(MEO2MA-co-OEGMA), designated as P(αCleCL-co-eCL)-g-P(MEO2MA-co-OEGMA) have been prepared via a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The composition and structure of these copolymers were characterized by 1H NMR and GPC analyses. The self-assembly behaviors of these amphiphilic graft copolymers were investigated by UV transmittance, a fluorescence probe method, dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses. The results showed that the graft copolymers exhibited the good solubility in water, and was given the low critical temperature (LCST) at 35(±1) °C, which closed to human physiological temperature. The critical micelle concentrations (CMC) of P(αCleCL-co-eCL)-g-P(MEO2MA-co-OEGMA) in aqueous solution were investigated to be 2.0 × 10−3, 9.1 × 10−4 and 1.5 × 10−3 mg·mL−1, respectively. The copolymer could self-assemble into sphere-like aggregates in aqueous solution with diverse sizes when changing the environmental temperature. The vial inversion test demonstrated that the graft copolymers could trigger the sol-gel transition which also depended on the temperature.

Ethyl cellulose amphiphilic graft copolymers with LCST-UCST transition: Opposite self-assembly behavior, hydrophilic-hydrophobic surface and tunable crystalline morphologies

Novel and well-defined graft copolymer with block copolymer side chain, ethyl cellulose-graft-(poly(ε-caprolactone)-block-poly(N,N-dimethylaminoethylmeth acrylate)) (EC-g-(PCL-b-PDMAEMA)) with a lower critical solution temperature (LCST) was successfully synthesized via the combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). EC-g-(PCL-b-PDMAEMA) copolymers with various PCL-b-PDMAEMA block lengths were obtained by adjusting the molar ratios of the N,N-dimethylaminoethyl methacrylate monomer to ε-caprolactone. The EC-g-(PCL-b-PDMAPS) with an upper critical solution temperature (UCST) was obtained via facile quaternization reaction of PDMAEMA with 1,3-propane sultone. EC-g-(PCL-b-PDMAEMA) and EC-g-(PCL-b-PDMAPS) micelle solutions showed opposite thermoresponsiviness and hydrophilic-hydrophobic surface. Moreover, the tunable crystalline morphologies could be obtained from these graft copolymers through changing the polymer structure and PDMAEMA contents.

Selective Photoactivation: From a Single Unit Monomer Insertion Reaction to Controlled Polymer Architectures.

Here, we exploit the selectivity of photoactivation of thiocarbonylthio compounds to implement two distinct organic and polymer synthetic methodologies: (1) a single unit monomer insertion (SUMI) reaction and (2) selective, controlled radical polymerization via a visible-light-mediated photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) process. In the first method, precise single unit monomer insertion into a dithiobenzoate with a high reaction yield (>97%) is reported using an organic photoredox catalyst, pheophorbide a (PheoA), under red light irradiation (λmax = 635 nm, 0.4 mW/cm(2)). The exceptional selectivity of PheoA toward dithiobenzoate was utilized in combination with another catalyst, zinc tetraphenylporphine (ZnTPP), for the preparation of a complex macromolecular architecture. PheoA was first employed to selectively activate a dithiobenzoate, 4-cyanopentanoic acid dithiobenzoate, for the polymerization of a methacrylate backbone under red light irradiation. Subsequently, metalloporphyrin ZnTPP was utilized to selectively activate pendant trithiocarbonate moieties for the polymerization of acrylates under green light (λmax = 530 nm, 0.6 mW/cm(2)) to yield well-defined graft co-polymers.

PHEA-g-PDMAEA well-defined graft copolymers: SET-LRP synthesis, self-catalyzed hydrolysis, and quaternization

This article reports the synthesis of well-defined graft copolymers containing a PHEA backbone and degradable PDMAEA side chains, by the combination of RAFT polymerization, SET-LRP, and the grafting-from strategy.

Synthesis and characterization of graft copolymers by photoinduced CuAAC click chemistry

Well-defined graft copolymers were synthesized by a simple photoinduced copper(I) catalyzed 1,3-dipolar cycloaddition click reaction of alkyne-terminated poly(epsilon-caprolactone) (PCL) either side-chain azide-functional polystyrene (PSt) or poly(vinyl chloride) (PVC). The alkyne-terminated PCL was prepared by ring-opening polymerization of epsilon-caprolactone in bulk using Sn(Oct)2 as a catalyst and propargyl alcohol as an initiator. Whereas, the halide groups of PVC and poly(styrene-co-chloromethylstyrene) prepared by nitroxide mediated radical copolymerization were transformed to side chain azide-functional PVC or PSt via nucleophilic substitution reaction using sodium azide. Subsequently, the resulting alkyne and azide functional polymers were mixed in DMF with Cu(II)Br2/PMDETA ligand and 2, 2-dimethoxy-2-phenyl acetophenone and irradiated by UV light to form corresponding graft copolymers. The FT-IR, 1H NMR, GPC and DSC analyzes clearly pointed out an efficient photoinduced CuAAC click reactions between azide- and alkyne-functional precursor polymers.

Well-Defined Poly(γ-benzyl-l-glutamate)-g-Polytetrahydrofuran: Synthesis, Characterization, and Properties

The synthesis of well-defined graft copolymers of poly(γ-benzyl-l-glutamate)-g- polytetrahydrofuran, PBLG-g-PTHF, has been achieved via controlled termination of living PTHF branch chains with −NH– functional groups along PBLG macromolecular backbone. The PBLG backbone with different molecular weights (Mn = 2000–45000 g·mol–1) were prepared by anionic ring-opening polymerization of γ-benzyl-l-glutamate N-carboxyanhydrade (BLG-NCA). Living PTHF chains with predictable chain length (Mn = 720–7000 g·mol–1) were prepared by living cationic ring-opening polymerization of THF with methyl triflate (MeOTf) as an initiator. The grafting efficiency (GE) of living PTHF chains onto PBLG backbone via controlled termination reached to near 100%. The grafting density (GD) along PBLG backbone and average number of PTHF branches (Nb,PTHF) in PBLG-g-PTHF graft copolymers could be mediated by changing the molar ratio of living PTHF chains to −NH– functional groups. Circular dichroism (CD) and FTIR spectra show that some of the graft copolymers maintain α-helical structure from PBLG, and the strength of CD signals for α-helical structure of the graft copolymers also decreased with increasing GD. The crystallization degree and spherulitic growth rate of the PBLG-g-PTHF graft copolymers decreased with increasing GD. The obvious phase separation and reticular state of aggregation morphology in PBLG-g-PTHF graft copolymers could be observed. PBLG-g-PTHF graft copolymers have no cytotoxicity and even conducive for cell survival. These graft copolymers had extremely low bibulous rate, and all the water absorption ratios were kept around 1.02 to maintain the shape and dimensional stability.

Synthesis of thermoresponsive block and graft copolymers via the combination of living cationic polymerization and RAFT polymerization using a vinyl ether-type RAFT agent

A novel vinyl ether-type RAFT agent, benzyl 2-(vinyloxy)ethyl carbonotrithioate (BVCT) was synthesized for various block copolymers via the combination of living cationic polymerization of vinyl ethers and reversible addition−fragmentation chain transfer (RAFT) polymerization. The novel BVCT–trifluoroacetic acid adduct play an important role to produce well-defined block copolymers, which is both as a cationogen under EtAlCl2 initiation system in the presence of ethyl acetate for living cationic polymerization and a RAFT agent for blocks by RAFT polymerization. The resulting polymer, poly(vinyl ether)s, by living cationic polymerization had a high number average α-end functionality (≥0.9) as determined by both 1H NMR and MALDI-TOF-MS spectrometry. In addition, this poly(vinyl ether)s worked well as a macromolecular chain transfer agent for RAFT polymerization. The RAFT polymerization of radically polymerizable monomers was conducted in toluene using 2,2′-azobis(isobutyronitrile) at 70 °C. For example, a double thermoresponsive block copolymer (MOVE61-b-NIPAM150) consisting of 2-methoxyethyl vinyl ether (MOVE) and N-isopropylacrylamide (NIPAM) was prepared via the combination of living cationic polymerization and RAFT polymerization. The block copolymer reversibly formed and deformed micellar assemblies above the phase separation temperature (Tps) of poly(NIPAM) block in water. This BVCT is not only functioned as an initiator, but also acted as a monomer. When BVCT was copolymerized with MOVE by living cationic polymerization, followed by graft copolymerization with NIPAM via RAFT polymerization, well-defined graft copolymers (MOVEn-co-BVCTm)-g-NIPAMx (n = 62–73, m = 1–9, x = 19–214) were successfully obtained. However, no micelle formed in water above Tps of poly(NIPAM) graft chain unlike the case of block copolymers.

V-shaped graft copolymers via triple click reactions: Diels-alder, copper-catalyzed azide-alkyne cycloaddition, and nitroxide radical coupling

We report here a simple and universal synthetic pathway covering triple click reactions, Diels–Alder, copper-catalyzed azide–alkyne cycloaddition (CuAAC), and nitroxide radical coupling (NRC), to prepare well-defined graft copolymers with V-shaped side chains. The Diels–Alder click reaction between the furan protected-maleimide-terminated poly(ethylene glycol) (PEG) and a trifunctional core (1) carrying an anthracene, alkyne, and bromide was carried out to yield the corresponding α-alkyne- and α-bromide-terminated PEG (PEG-alkyne/Br) in toluene at 110 °C. Subsequently, the polystyrene or polyoxanorbornene with pendant azide functionality as a main backbone is reacted with the PEG-alkyne/Br and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-terminated poly(ε-caprolactone) using the CuAAC and NRC reactions in a one-pot fashion in N,N′-dimethylformamide at room temperature to result in the target V-shaped graft copolymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4667–4674

Precision synthesis of graft copolymers via living cationic polymerization ofp-acetoxystyrene followed by friedel-crafts-type termination reaction

This study describes a novel precision synthesis strategy for graft copolymers using Friedel–Crafts-type termination reaction between a cationically prepared poly(styrene derivative) and the naphthyl side groups from a poly(vinyl ether) main chain. The pendant alkoxynaphthyl groups on the poly(vinyl ether) efficiently terminated the living cationic polymerization of p-acetoxystyrene (AcOSt) with SnCl4 in the presence of ethyl acetate as an added base. This research provides the first example of a well-defined graft copolymer prepared using this method. The resulting polymer contained 40 poly-(AcOSt) branches, as calculated from the Mw determined via gel permeation chromatography–MALS analysis, which was in good agreement with the estimated number of branches obtained from 1H NMR analysis. The acetoxy groups in the grafted poly(AcOSt) chains were easily converted into phenolic hydroxy groups under basic conditions. The as-obtained graft copolymer with poly(p-hydroxystyrene) side chains exhibited a pH-sensitive phase separation in water. The synthetic method for preparing the graft copolymers was also effective in the living cationic polymerizations of other styrene derivatives. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4675–4683

SET-LRP synthesis of novel polyallene-based well-defined amphiphilic graft copolymers in acetone

A series of polyallene-based well-defined amphiphilic graft copolymers consisting of hydrophobic poly(6-methyl-1,2-heptadiene-4-ol) (PMHDO) backbone and hydrophilic poly(2-(dimethylamino)ethyl acrylate) (PDMAEA) side chains, was synthesized by the combination of living coordination polymerization and single-electron transfer living radical polymerization (SET-LRP). A double-bond-containing PMHDO backbone with pendant hydroxyls was prepared via [(η3-allyl)NiOCOCF3]2-initiated living coordination polymerization of a hydroxyl-containing allene derivative, 6-methyl-1,2-heptadiene-4-ol (MHDO). The pendant hydroxyls in the homopolymer were then treated with 2-chloropropionyl chloride to provide the PMHDO-Cl macroinitiator. Finally, the target PMHDO-g-PDMAEA well-defined graft copolymers were constructed through the grafting-from technique via SET-LRP of 2-(dimethylamino)ethyl acrylate (DMAEA) in acetone, a nonpolar solvent, initiated by the macroinitiator using CuCl/Me6TREN as catalytic system. The narrow molecular weight distributions (Mw/Mn ≤ 1.18) and kinetics experiment showed the controllability of SET-LRP graft copolymerization of DMAEA. The critical micelle concentrations (cmc) of PMHDO-g-PDMAEA amphiphilic graft copolymers in aqueous solution were determined by fluorescence probe technique and the dependence of cmc on pH or salinity were also investigated. Micellar morphologies were visualized using transmission electron microscopy.

Well-defined graft copolymers of tert-butyldimethylsilyl methacrylate and poly(dimethylsiloxane) macromonomers synthesized by RAFT polymerization

Graft copolymers of hydrolyzable tert-butyldimethylsilyl methacrylate (TBDMSiMA) and low surface energy poly(dimethylsiloxane) methacrylate of 1000 g mol−1 (PDMSMA1k) and 5000 g mol−1 (PDMSMA5k) were synthesized by the RAFT process, using 2-cyanoprop-2-yl-dithiobenzoate (CPDB) as a chain transfer agent, at 70 °C, in xylene. The homopolymerizations of each monomer were first studied, demonstrating their control by the RAFT process. Simultaneous copolymerizations of TBDMSiMA and PDMSMA led to gradient graft copolymers as demonstrated by the determination of monomer reactivity ratios by the Jaacks method. Sequential polymerizations led to diblock or blocky graft copolymers depending on the order of addition of each monomer. All the copolymerizations were controlled by the RAFT process with molecular weight values close to the theoretical values, together with monomodal and narrow distributions (PDI < 1.2). The graft copolymers exhibited two glass transition temperatures, corresponding to the PDMS- and pTBDMSiMA-enriched phases, respectively. The PDMS side chain distribution and length were shown to be significant parameters influencing the thermal behavior of the copolymers, their low surface energy and their erosion properties in artificial seawater. These latter properties make these graft copolymers suitable for applications as binders for self-polishing/fouling release hybrid antifouling coatings.

One-pot synthesis of chitosan-g-(PEO-PLLA-PEO) via “click” chemistry and “SET-NRC” reaction

For the development of biocompatible and degradable biomaterials, a kind of well-defined graft copolymer consisting of chitosan back-bone and amphiphilic PEO-PLLA-PEO branch chains was synthesized by Cu(0) catalyzed one-pot strategy combining “click” chemistry and single electron transfer-nitroxide radical coupling (SET-NRC) reaction. First, the precursors of 6-azide-N-phthaloyl-chitosan, TEMPO-PEO-alkyne and mPEO-PLLA-Br were designed and produced. Then, the one-pot coupling reactions between these precursors were performed in the presence of nanosized Cu and PMDETA. The efficiencies of the coupling reactions were greater than 90% determined by the FTIR and ESR spectra. The structure of graft copolymer with 43% of the grafting ratio was confirmed by the spectral analysis. This work provided a route to prepare chitosan graft copolymer.

Preparation of the Amphiphilic Copolymer of Poly(ethyleneoxid-co-glycidol)-Graft-Poly(lactide) and their Extraction for Dyes

A well-defined graft copolymer poly(ethylene oxide-co-glycidol)-graft-Poly(lactide) [poly(EO-co-Gly)-g-PLA] of poly(ethylene oxide-co-glycidol) [(poly(EO-co-Gly)] as main chain and poly(lactide) (PLA) as the side chain was successfully prepared via combination of anionic polymerization and ring-opening polymerization. The glycidol was protected by ethyl vinyl ether first to form 2, 3-epoxypropyl-1-ethoxyethyl ether (EPEE), and then copolymerized with EO by initiation with the mixture of diphenylmethylpotassium and triethylene glycol to obtain the well-defined poly(EO-co-EPEE). The latter was hydrolyzed in the acidic conditions and then coordination-insertion ring-opening polymerization of lactide(LA) with poly(EO-co-Gly) was completed. The object products and intermediates were characterized by 1HNMR, MALDI-TOF-MS and GPC in detail. The experimental results confirmed that poly(EO-co-Gly)-g-PLA showed strong conjugation ability with the dyes.

Synthesis and evaluation of triazole-linked poly(ε-caprolactone)-graft-poly(2-methyl-2-oxazoline) copolymers as potential drug carriers

Well-defined graft copolymers were obtained using a copper-catalysed azide-alkyne Huisgen's cycloaddition click reaction from both biocompatible and non-toxic poly(ε-caprolactone) and poly(2-methyl-2-oxazoline) homopolymers. Resulting amphiphilic copolymers proved to form micelles that could be used as potential drug carriers.

Design of Π-conjugated Graft and Block Copolymers: A Tool Box for Nanostructured Materials in Optoelectronic Devices

ABSTRACTSemi-conducting conjugated (co)polymers are well soluble and can be processed easily in a large scale. Among these materials, rod-coil block and graft copolymers, show very particular properties of self-assembly, and are very promising in organic electronic, as organic photovoltaic materials for example.The post-functionalization of poly(3-hexylthiophene) (P3HT) from ω-allyl terminated P3HT via various synthetic routes is reported in order to obtain well-defined block and graft copolymers for optoelectronic or photovoltaic applications. First, a well-defined and monofunctional P3HT-based macro-initiator has been obtained through a clean and versatile process. Well-defined rod-coil block copolymers were obtained by nitroxide mediated radical polymerization (NMRP) with various monomers. Finally, three different novel P3HT-based graft copolymers were synthesized following two routes.