This communication details the successful synthesis of low polydispersity core cross‐linked star (CCS) polymers via DPE‐mediated polymerisation. We demonstrate the ability to produce poly(methyl methacrylate) and poly(acrylonitrile) CCS polymers that are currently inaccessible via the two most common non‐metal‐based controlled radical polymerisation techniques (NMP and RAFT polymerisations).
Reversible addition fragmentation chain transfer (RAFT) polymerization is one of the most extensively studied reversible deactivation radical polymerization methods for the production of well‐defined polymers. After polymerization, the RAFT agent end‐group can easily be converted into a thiol, opening manifold opportunities for thiol modification reactions. This review is focused both on the introduction of functional end‐groups using well‐established methods, such as thiol‐ene chemistry, as well as on creating bio‐cleavable disulfide linkages via disulfide exchange reactions. We demonstrate that thiol modification is a highly attractive and efficient chemistry for modifying RAFT polymers.
The preparation of hairy core–shell nanoparticles including (crosslinked) micelles, unimolecular micelles such as star polymers with block structures in each arm and surface grafted nanoparticles such as inorganic particles via the RAFT process are discussed. The RAFT process is certainly a highly versatile process. However, it should not be forgotten that RAFT polymerization is a process, i.e., superimposed on a conventional free radical process. Furthermore, the livingness of the process is dependent on the accessibility of the RAFT group, which can be hampered in certain approaches such as star synthesis and surface grafting from nanoparticles. Nevertheless, the RAFT process is a versatile toolbox that offers good solutions to a range of problems in the preparation of hairy nanoparticles.
The synthesis of water soluble star‐block copolypeptides and their encapsulation properties are described. The star‐block copolypeptides, obtained by ring‐opening polymerization of amino acid N‐carboxyanhydrides, consist of a PEI core, a hydrophobic polyphenylalanine or polyleucine inner shell, and a negatively charged polyglutamate outer shell. The encapsulation study showed that these water soluble, amphiphilic star‐block copolypeptides could simultaneously encapsulate versatile compounds ranging from hydrophobic to anionic and cationic hydrophilic guest molecules.
A combination of reversible addition fragmentation chain transfer (RAFT) polymerization and hetero Diels‐Alder (HDA) chemistry has been utilized to successfully generate functional core‐shell microspheres. Initially, precipitation polymerization in conjunction with the RAFT technique has been employed to synthesize divinylbenzene (DVB) microspheres with surface expressed RAFT groups. Subsequently, HDA cycloaddition has been performed under mild reaction conditions (50 °C, 24 h) with a diene‐functionalized poly(ε‐caprolactone) (PCL). While the successful grafting is immediately evident by optical inspection of the microspheres (color change from purple to white), X‐ray photoelectron spectroscopy (XPS), and attenuated total reflectance spectroscopy (ATR) were additionally employed to characterize the chemical composition and surface functionalization of the microspheres. Further, confocal microscopy was used to confirm the presence of grafted PCL chains after labeling them with rhodamine B.
Summary: We propose and demonstrate the utility of an interfacial living/controlled (reversible addition fragmentation chain transfer, RAFT) radical miniemulsion polymerization in nano‐encapsulation. The principles and methodology behind this technique are readily scalable and highly efficient. The living/controlled nature of the system offers great opportunities to tune the properties of the polymer shell‐like thickness, surface functionality, molecular weight, and inner‐wall functionality by simply using a semi‐continuous polymerization technique.
Illustration of encapsulation principles by RAFT interfacial miniemulsion polymerization. 相似文献
A trithiocarbonate RAFT agent was modified with a pyridyl disulfide group and used in the direct synthesis of endgroup pyridyl disulfide‐functionalized homo‐ and amphiphilic block copolymers of oligo(ethyleneglycol) acrylate (PEG‐A) and butyl acrylate (BA). Both the homo‐ and copolymerizations were found to be well controlled via the RAFT mechanism. The NMR analysis indicated that both the homopolymers of PEG‐A and the amphiphilic diblock copolymers of PEG‐A and BA possessed pyridyl disulfide terminal groups. A UV‐Vis absorption test revealed that the pyridyl disulfide endgroup of the polymer could be efficiently used to couple thiol‐bearing molecules to the polymer without the need for any post‐polymerization modification. This communication presents the first efficient direct synthesis of thiol‐reactive endgroup‐functionalized well‐defined polymers via the RAFT technique.
A dextran‐based dual‐sensitive polymer is employed to endow gold nanoparticles with stability and pH‐ and temperature‐sensitivity. The dual‐sensitive polymer is prepared by RAFT polymerization of N‐isopropylacrylamide from trithiocarbonate groups linked to dextran and succinoylation of dextran after polymerization. The functionalized nanoparticles show excellent stability under various conditions and can be stored in powder‐form. UV and DLS measurements confirm that the temperature‐induced optical changes and aggregation behaviors of the particles are strongly dependent on pH.
A Y‐shaped amphiphilic fluorinated monomer, 1‐(1H,1H,2H,2H‐perfluorodecyloxy)‐3‐(3,6,9‐trioxadecyloxy)‐propan‐2‐yl acrylate has been synthesized and its polymerization by reversible addition–fragmentation chain transfer (RAFT) homopolymerization has been investigated. The results show that the molecular weights of the polymers are controlled and all the molecular weight distributions are lower than 1.4. Well‐defined copolymers with 2‐(N,N‐dimethylamino)ethyl methacrylate have been prepared by RAFT polymerization, and the surface properties of the block and random copolymers have been examined by contact angle measurement for water and hexadecane. It has been found that the surfaces of the block copolymers simultaneously exhibit excellent anti‐fog and oil‐repellent properties.
Supramolecular self‐assembly of block copolymers in aqueous solution has received ever‐increasing interest over the past few decades due to diverse biological and technological applications in drug delivery, imaging, sensing and catalysis. In addition to relative block lengths, molecular weights and solution conditions, chain architectures of block copolymers can also dramatically affect their self‐assembling properties in selective solvents. This feature article mainly focuses on recent developments in the field of supramolecular self‐assembly of amphiphilic and double hydrophilic block copolymers (DHBCs) possessing nonlinear chain topologies, including miktoarm star polymers, dendritic–linear block copolymers, cyclic block copolymers and comb‐shaped copolymer brushes.
The use of the reversible addition fragmentation chain transfer—hetero Diels–Alder (RAFT‐HDA) click reaction for the modular construction of block copolymers is extended to the generation of high molecular weight materials. Cyclopentadienyl end‐functionalized polystyrene (PS‐Cp) prepared via both atom transfer radical polymerization (ATRP) and the RAFT process are conjugated to poly(isobornyl acrylate) (PiBoA) (also prepared via RAFT polymerization) to achieve well‐defined block copolymers with molecular weights ranging from 34 000 to over 100 000 g · mol−1 and with small polydispersities (PDI < 1.2). The conjugation reactions proceeded in a very rapid fashion (less than 10 min in the majority of cases) under ambient conditions of temperature and atmosphere. The present study demonstrates—for the first time—that RAFT‐HDA click chemistry can provide access to high molecular weight block copolymers in a simple and straight‐forward fashion.
The synthesis of new star‐shaped polymers, prepared by atom transfer radical polymerization of methyl methacrylate with tris(dialkylaminostyryl‐2,2′‐bipyridine) zinc(II) and iron(II) metalloinitiators, is reported. Their thermal and optical (absorption and emission) properties are discussed.
Summary: A well‐defined homopolymer of 2‐(diethylamino)ethyl methacrylate has been synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization using (4‐cyanopentanoic acid)‐4‐dithiobenzoate as a chain transfer agent. The corresponding protonated homopolymer with a very reactive dithiobenzoate end group has been used as a water‐soluble macromolecular chain transfer agent in the batch emulsion polymerization of styrene without any surfactant. The reaction leads to a stable latex, as a result of the in‐situ formation of an amphiphilic block copolymer stabilizer, via transfer reaction to the dithioester functions during the nucleation step. The work does not intend to apply controlled free‐radical polymerization in an aqueous dispersed system but takes advantage of the RAFT technique to create a well‐defined polyelectrolyte, with a high chain‐end reactivity.
Schematic of the formation of the stabilized latex by the in situ formation of an amphiphilic block copolymer stabilizer. 相似文献
A thermoresponsive block copolymer, namely poly(acryloyl glucosamine)‐block‐poly(N‐isopropylacryamide) (PAGA180‐b‐PNIPAAM350) was simultaneously self‐assembled and crosslinked in aqueous medium via RAFT polymerization at 60 °C to afford core‐crosslinked micelles exhibiting a glycopolymer corona and a PNIPAAM stimuli‐responsive core. An acid‐labile crosslinking agent, 3,9‐divinyl‐2,4,8,10‐tetraoxaspiro[5.5]undecane, was employed to generate thermosensitive and acid‐degradable core‐shell nanoparticles. Stable against degradation at pH = 6 and 8.2, the resulting core crosslinked micelles readily hydrolyzed into well‐defined free block copolymers at lower pH (30 min and 12 h respectively at pH = 2 and 4).
A clickable alkyne monomer, PgMA, was successfully polymerized in a well‐controlled manner via single electron transfer initiation and propagation through the radical addition fragmentation chain transfer (SET‐RAFT) method. The living nature of the polymerization was confirmed by the first‐order kinetic plots, the linear relationships between molecular weights and the monomer conversions while keeping relatively narrow (≤1.55), and the successful chain‐extension with MMA. The better controllability of SET‐RAFT than other CRP methods is attributed to the less competitive termination in view of the presence of the CTA as well as the Cu(II) that is generated in situ. Moreover, a one‐pot/one‐step technique combining SET‐RAFT and “click chemistry” methods has been successfully employed to prepare the side‐chain functionalized polymers.
We have developed a novel strategy for the preparation of ion‐bonded supramolecular star polymers by RAFT polymerization. An ion‐bonded star supramolecule with six functional groups was prepared from a triphenylene derivative containing tertiary amino groups and trithiocarbonate carboxylic acid, and used as the RAFT agent in polymerizations of tert‐butyl acrylate (tBA) and styrene (St). Molecular weights and structures of the polymers were characterized by 1H NMR and GPC. The results show that the polymerization possesses the character of living free‐radical polymerization and the ion‐bonded supramolecular star polymers PSt, PtBA, and PSt‐b‐PtBA, with six well‐defined arms, were successfully synthesized.
Summary: Computational chemistry is a valuable complement to experiments in the study of polymerization processes. This article reviews the contribution of computational chemistry to understanding the kinetics and mechanism of reversible addition fragmentation chain transfer (RAFT) polymerization. Current computational techniques are appraised, showing that barriers and enthalpies can now be calculated with kcal accuracy. The utility of computational data is then demonstrated by showing how the calculated barriers and enthalpies enable appropriate kinetic models to be chosen for RAFT. Further insights are provided by a systematic analysis of structure‐reactivity trends. The development of the first computer‐designed RAFT agent illustrates the practical utility of these investigations.
Well‐defined amphiphilic PCL‐b‐PDMAEMA block copolymers were successfully synthesized by a combination of ATRP and “click” chemistry following either a commutative two‐step procedure or a straightforward one‐pot process using CuBr · 3Bpy as the sole catalyst. Compared to the traditional coupling method, combining ATRP and click chemistry even in a “one‐pot” process allows the preparation of PCL‐b‐PDMAEMA diblock copolymers characterized by a narrow molecular weight distribution and quantitative conversion of azides and alkynes into triazole functions. Moreover, the amphiphilic character of these copolymers was demonstrated by surface tension measurements and critical micellization concentration was calculated.
This review covers the literature concerning the modification of polysaccharides through controlled radical polymerizations (NMP, ATRP and RAFT). The different routes to well‐defined polysaccharide‐based macromolecules (block and graft copolymers) and graft‐functionalized polysaccharide surfaces as well as the applications of these polysaccharide‐based hybrids are extensively discussed.
Biotinylated polymers with side‐chain aldehydes were prepared for use as multifunctional scaffolds. Two different biotin‐containing chain transfer agents (CTAs) and an aldehyde‐containing monomer, 6‐oxohexyl acrylate (6OHA), are synthesized. Poly(ethylene glycol) methyl ether acrylate (PEGA) and 6OHA are copolymerized by reversible addition‐fragmentation chain transfer (RAFT) polymerization in the presence of the biotinylated CTAs. The resulting polymers are analyzed by GPC and1H NMR spectroscopy. The polymer end groups contained a disulfide bond, which could be readily reduced in solution to remove the biotin. Reactivity of the aldehyde side chains is demonstrated by oxime and hydrazone formation at the polymer side chains, and conjugate formation of fluorescently labeled polymers with streptavidin is investigated by gel electrophoresis.
