Cellulose derivatives and graft copolymers as blocks for functional materials

In this review, recent progresses in the synthesis of new cellulose derivatives and graft copolymers are summarized. Cellulose derivatives synthesized in new cellulose solvents, such as ionic liquids and NaOH/urea, and the regioselective synthesis of cellulose derivatives have attracted increasing attention in recent years and could be a more active field for cellulose in the future. Cellulose graft copolymers with well‐defined architectures synthesized by controlled/living radical polymerizations such as atomic transfer radical polymerization and their stimuli‐induced assembly have been investigated extensively. Stimuli‐responsive functional materials can be fabricated using either cellulose derivatives or graft copolymers, and they can be used as biosensors and carriers for controlled delivery of drugs and genes. The fabrication of functional materials with cellulosic blocks and their applications have a bright future. © 2013 Society of Chemical Industry     

Organic/inorganic hybrid materials from polypeptide-based block copolymers

Novel organic/inorganic hybrid material was synthesized from poly(acrylazapropyl-trimethoxysilane)-b-poly(N_ε-trifluoroacetyl-l-lysine) (P(AAPTMS)-b-P(TLL)) block copolymer using the sol–gel process. The treatment with ammonia solution permitted the hydrolysis of both trifluoro acetyl and trimethoxysilyl groups of the hydride copolymer followed by the condensation of the silanol groups, leading to cross-linked copolymers. The resulting cross-linked hybrid material was characterized using FT-IR, ²⁹Si NMR, DSC, TGA, and environmental scanning electron microscopy. These techniques evidenced that a siloxane network was obtained. Amphiphilic polypeptide/inorganic hybrid copolymers were achieved and self-organized as particles in water.     

Stimuli-responsive tertiary amine methacrylate-based block copolymers: Synthesis,supramolecular self-assembly and functional applications

In the past decade, responsive polymers exhibiting reversible or irreversible changes in physical properties and/or chemical structures in response to external stimuli have been extensively investigated. Among them, tertiary amine methacrylate-based block copolymers represent a unique category considering their responsiveness to multiple external stimuli (e.g., pH, temperature and salts), which are essentially relevant to the biological milieu. These intriguing properties allow for their applications in a variety of fields ranging from drug or gene delivery, imaging, diagnostics, antibacterial coatings, catalysis, and bio-separations. This review article highlights tertiary amine methacrylate-based block copolymers, focusing on recent advances in the synthesis of tertiary amine methacrylate-based block copolymers with varying chemical structures and chain topologies, their supramolecular self-assembly in aqueous media as well as in the bulk state, and the emerging functional applications.     

A model for rod-coil block copolymers

A coarse-grained model for studying the phase behavior of rod-coil block copolymer systems on mesoscopic length scales is proposed. The polymers are represented on a particle level (monomers, rods) whereas the interactions between the system’s constituents are formulated in terms of local densities. This conversion to density fields allows an efficient Monte Carlo sampling of the phase space. We demonstrate the applicability of the model and of the simulation approach by illustrating the formation of typical micro-phase separated configurations for exemplary model parameters.     

Synthesis of POSS-containing fluorosilicone block copolymers via RAFT polymerization for application as non-wetting coating materials

By using a polydimethylsiloxane (PDMS) macro-chain transfer agent with trithiocarbonate groups at both ends, fluorosilicone block copolymers containing polyhedral oligomeric silsesquioxane (POSS) were synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. Acryloisobutyl POSS (APOSS) and 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA) were sequentially introduced into the copolymers. The obtained triblock copolymers PDMS-b-(PAPOSS)₂ exhibited a low polydispersity index (PDI) of less than 1.42 in the first 6 h of polymerization, but the PDI value became broader later because of the steric hindrance of the POSS macromer. The POSS-containing fluorosilicone pentablock copolymers with a PDI of about 2.0, which were prepared by the further RAFT polymerization of HFBA, showed clear microphase separation. The average roughness values of the copolymer films were enhanced by introducing POSS, and a certain POSS content led to a significant decrease of the receding contact angle. Measurements of water contact angles and ice shear strengths demonstrated that the non-wetting properties of the copolymer films were improved by the incorporation of both POSS and fluorine blocks. The block copolymers combine the advantages of POSS, PDMS and fluoropolymers, and can be potentially applied as non-wetting coating materials for anti-icing or anti-frosting.     

Toward a toolbox of functional block copolymers via free-radical addition of mercaptans

This work demonstrates the applicability of the free-radical addition of ω-functional mercaptans onto 1,2-polybutadienes as a modular synthetic pathway toward a toolbox of diverse functional block copolymers. Functional groups included, for instance electrolytes (carboxylic acid and amine), l-amino acid, and fluorocarbon. The number of functional groups attached to the polymer was lower than that of double bonds reacted (degree of functionalization=50–85%, typically 70–80%) due to cyclization of two neighboring units, but the narrow molecular-weight distribution of the parent (co)polymer was always maintained.     

Nanoporous materials from stable and metastable structures of 1,2-PB-b-PDMS block copolymers

Experimental procedures used at the preparation and characterization stages of nanoporous materials (NPM) from 1,2-polybutadiene-b-polydimethylsiloxane (1,2-PB-b-PDMS) block copolymers are presented. The NPM were obtained from self-assembled block copolymers after firstly cross-linking 1,2-PB (the matrix component) and secondly degrading PDMS (the expendable component). Depending on the temperature of the cross-linking reaction different morphologies can be ‘frozen’ from the same block copolymer. Starting with a block copolymer precursor of lamellar morphology at room temperature, the gyroid structure or a metastable structure showing hexagonal symmetry (probably HPL) were permanently captured by cross-linking the precursor at 140 °C or at 85 °C, respectively. PDMS was degraded by reaction with tetrabutylamonium fluoride; considerations on the mechanism of cleaving reaction are presented. The characterization of the materials at different stages of preparation includes gravimetry, infrared spectroscopy, small angle x-ray scattering, electron microscopy and isothermal nitrogen adsorption experiments.     

Hexagonally ordered arrays of metallic nanodots from thin films of functional block copolymers

We demonstrate a new and simple route to fabricate highly dense arrays of hexagonally close packed inorganic nanodots using functional diblock copolymer (PS-b-P4VP) thin films. The deposition of pre-synthesized inorganic nanoparticles selectively into the P4VP domains of PS-b-P4VP thin films, followed by removal of the polymer, led to highly ordered metallic patterns identical to the order of the starting thin film. Examples of Au, Pt and Pd nanodot arrays are presented. The affinity of the different metal nanoparticles towards P4VP chains is also understood by extending this approach to PS-b-P4VP micellar thin films. The procedure used here is simple, eco-friendly, and compatible with the existing silicon-based technology. Also the method could be applied to various other block copolymer morphologies for generating 1-dimensional (1D) and 2-dimensional (2D) structures.     

Polyaldehydes: homopolymers,block copolymers and promising applications

This minireview gives a brief overview on the polymerization of higher aldehydes, discusses current applications of certain polyaldehydes, and points toward potential future applications of these interesting materials. Although it was discovered long ago that several aldehydes can be polymerized, the application potential of these polymers was largely overlooked. This is somewhat surprising as many polyaldehydes show interesting properties such as fast and complete depolymerization triggered by chemical or thermal stimuli. Such stimuli‐responsive polymers can be useful materials in many applications in for example nanotechnology or drug delivery. By incorporating polyaldehydes into functional block copolymers even more versatile materials can be created. The increasing number of recent research examples demonstrates the growing interest in polyaldehydes as smart materials and their potential for novel applications. Copyright © 2012 Society of Chemical Industry     

Alkaline degradation of styrene-acrylonitrile copolymers and formation of block copolymers

The styrene-acrylonitrile (SAN) copolymer, dissolved in dimethylsulfoxide (DMSO), has been degraded in the presence of some bases such as KOH and potassium-t-butoxide at room temperature. The addition of 4-vinylpyridine or propyleneoxide which can be anionically polymerized, has led to the production of copolymers. Their composition has been studied by IR, elemental analysis, and fractionation techniques. The presence of groups in the degraded products has been explained by a scission mechanism which gives rise to anions useful for the formation of block polymers.     

Nanostructuring compatibilizers of block copolymers for organic photovoltaics

The performance and stability of organic photovoltaic (OPV) devices based upon bulk heterojunction blends of donor and acceptor materials have been shown to be highly dependent on the morphology of the active layer. Block copolymers, which naturally self‐assemble into periodic ordered nanostructures, can be utilized in diverse ways to control morphology on a length scale relevant for charge separation, recombination and transportation, which makes them promising candidates for high performance and thermally stable OPV devices. This minireview presents a brief statistical discussion of inter‐study correlations and a summary of past interfacial research on block copolymer nanostructuring compatibilizers for OPVs. © 2013 Society of Chemical Industry     

Morphology of PI-PEO block copolymers for lithium batteries

Polyimide (PI)-polyethylene oxide (PEO) block copolymers have a wide variety of applications in microelectronics, since PI-PEO films exhibit a high degree of thermal and chemical stability. The polymers consist of short, rigid rod T-shaped PI segments, alternating with flexible, PEO coil segments. The highly incompatible PI rods and PEO coils should phase-separate, especially in the presence of lithium ions used as electrolytes for lithium polymer batteries. The rigid rod phase provides a high degree of dimensional stability. In this paper, we provide evidence by DSC that the self-assembled ordered structure of the PI-PEO molecules is formed from concentrated solution rather than the bulk state. Tapping mode AFM and X-ray diffraction are applied to observe the nanodomains in the phase separation of the PI and PEO before and after doping with lithium ions. In addition, we report evidence of the ion transport primary mechanism, in the amorphous phase of the lithium salt-doped PI-PEO block copolymers' multinuclear NMR linewidth, spin-lattice relaxation time, and pulsed field gradient diffusion measurements.     

Synthesis of hybrid linear-dendritic block copolymers with carboxylic functional groups for the biomimetic mineralization of calcium carbonate

A series of carboxylic acid functionalized hybrid linear-dendritic block copolymers (LDBCs) derived from methoxy poly(ethylene glycol) (MPEG) and variant generation dendrons from 2,2-bis(hydroxymethyl) propionic acid were synthesized and employed as CaCO₃ crystallization growth modifiers. Mainly spherical vaterite particles of gradually reduced sizes were produced with the increase of the polymer additive concentration and/or the dendron segment generation number, while the incorporated polymer organic components in the particles increased for the promoted binding efficiency and ever enhanced adsorption ability. A higher mineralization temperature resulted in significantly larger particle size and partly calcite formation. Under the same molar concentration of carboxylic acid, the same size level particles were obtained which manifested the crucial role of the functional group, meanwhile, the slight decrease of the spherical vaterite diameters with increasing generation number and especially the formation of particular pine-cone shaped calcite crystals also revealed the significant effect of the architectural structure of variant generations and some special characters of the hybrid LDBC structures.     

基于RAFT聚合策略合成功能化聚烯烃嵌段聚合物的研究进展

首先介绍了可逆加成-断裂链转移聚合（RAFT）的聚合机理及其常用的RAFT试剂,并与其它两种活性可控自由基聚合[氮氧化合物媒介的自由基聚合（NMP）和原子转移自由基聚合（ATRP）]进行了简单的优缺点对比。其次,介绍了近些年在基于RAFT聚合制备功能化聚烯烃嵌段聚合物研究中取得的进展,重点综述了制备功能化聚烯烃嵌段聚合物时所采用的6种方法,包括①烯烃配位聚合与RAFT聚合相结合;②阴离子聚合与RAFT聚合相结合;③阳离子聚合与RAFT聚合相结合;④Click反应与RAFT聚合相结合;⑤开环聚合与RAFT聚合相结合;⑥叶立德活性聚合与RAFT聚合相结合。最后,对基于RAFT聚合策略设计合成功能化聚烯烃嵌段聚合物的研究前景与实际应用进行了展望。     

Surface active block copolymers: I. The preparation and some surface active properties of block copolymers of tetrahydrofuran and ethylene oxide

A new type of surface active block copolymer (TE type) having the general formula HO(C₂H₄O)_x(CH₂. CH₂CH₂CH₂O)_y-(C₂H₄O)_zH, was obtained by addition of ethylene oxide to polyoxytetramethylene glycols with molecular weight of 1000-3400. TE types in which the polyoxyethylene sections comprised more than 20–25% of the total weight are soluble in water, and the relation between cloud point and oxyethylene content for TE types was similar to that for propylene oxide-ethylene oxide block copolymers (Pluronics). Some surface active properties of TE types were examined in comparison with those of Pluronics and some other surfactants. The surface tension, foaming and antifoaming properties of TE types were comparable to those of Pluronics. Although the wetting power of TE types was poor, their suspending power (for carbon black) was superior to that of Pluronics in both aqueous and nonaqeuous media. The addition of TE types to some conventional detergents enhanced significantly their detergency. TE types showed a remarkable demulsifying action, on addition to some W/O emulsions.     

丙烯腈嵌段共聚物的合成及其自组装研究进展

综述了含聚丙烯腈(PAN)嵌段共聚物的合成方法及其在溶液中的自组装技术。对常用的活性自由基聚合方法,如原子转移自由基聚合(ATRP)、可逆加成断裂链转移(RAFT)聚合、氮氧自由基聚合(NMP)以及钴调介自由基聚合(CMRP)等方面的研究进行了总结,同时对PAN类嵌段共聚物在溶液中的自组装技术进行了概括。最后提出了现有技术存在的问题,并对其今后发展方向进行了展望。     

Graded block and randomized copolymers of butadiene-styrene

Graded block and randomized copolymers of butadiene-styrene were prepared anionically by polymerizing a mixture of butadiene and styrene with n-BuLi, in the absence and in the presence of t-BuOK respectively. Determination of the monomer composition and microstructure of the poly-butadiene sequence was achieved by 300 MHz ¹H n.m.r. and infra-red spectroscopy. ¹H n.m.r. equations developed previously for butadiene-styrene copolymers were modified and extended. In this way, cis, trans butadiene contents were determined from the aliphatic region of the n.m.r. spectra. The monomer sequence distribution of the copolymers has been investigated by examination of the morphology and their dynamic mechanical properties. The experimental conditions have been established for the preparation of random copolymers with inter- and intramolecular composition distribution.     

Novel non-ionic block copolymers tailored for interactions with phospholipids

The bulk of literature on phospholipid membrane interactions with non-ionic amphiphilic block copolymers deals with ABA triblock copolymers of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide). This is partially the result of their commercial availability. In recent years novel block copolymers have been synthesized and their interactions with phospholipids structured as Langmuir monolayers, liposomes, bilayer lipid membranes, tethered bilayers, and living cells have been studied. This review describes some new block copolymers with potential to interact with phospholipids. There is a tremendous progress in synthesis of amphiphilic block copolymers triggered by new controlled polymerization techniques as atom transfer radical polymerization or nitroxide mediated polymerization and by the possibility to ‘click’ preformed blocks together using quantitative reactions of functional endgroups. A special focus is given to novel water soluble amphiphilic triblock copolymers of poly(glycerol monomethacrylate)-b-poly(propylene oxide)-b-poly(glycerol monomethacrylate) and their interactions with phosphatidylcholine lipids. Also block copolymers containing hydrophobic blocks with perfluoroalkyl groups are discussed since they are special in a sense that their fluorophilic blocks are neither hydrophilic nor oleophilic as this is the case for conventional amphiphilic block copolymers. Experimental methods to study block copolymer–phospholipid interactions are summarized and selected results based on special experimental techniques such as isothermal titration calorimetry, infrared reflection absorption spectroscopy and ion conductance are presented. This work is intended to convey a better quantitative understanding of amphiphilic block copolymers used for in vitro and in vivo experiments in medicine and pharmacy.     

Low molecular weight block copolymers as plasticizers for polystyrene

Polystyrene‐b‐alkyl, polystyrene‐b‐polybutadiene‐b‐polystyrene, and polystyrene‐b‐poly(propylene glycol)monotridecyl ether were synthesized using macro initiators and atom transfer radical polymerization or by esterifications of homopolymers. The aim was a maximum molecular weight of 4 kg/mol and minimum polystyrene content of 50 w/w %, which by us is predicted as the limits for solubility of polystyrene‐b‐alkyl in polystyrene. DSC showed polystyrene was plasticized, as seen by a reduction in glass transition temperature, by block copolymers consisting of a polystyrene block with molecular weight of approximately 1 kg/mol and an alkyl block with a molecular weight of approximately of 0.3 kg/mol. The efficiency of the block copolymers as plasticizers increases with decreasing molecular weight and polystyrene content. In addition, polystyrene‐b‐alkyl is found to be an efficient plasticizer also for polystyrene‐b‐polyisoprene‐b‐polystyrene (SIS) block copolymers. The end use properties of SIS plasticized with polystyrene‐b‐alkyl, measured as tensile strength, is higher than for SIS plasticized with dioctyl adipate. The polystyrene‐b‐polybutadiene‐b‐polystyrene and polystyrene‐b‐poly(propylene glycol)monotridecyl ether series were only partially soluble in polystyrene and insoluble in the polystyrene phase of SIS. For the lowest molecular weight samples, this leads to measurable plasticization of polystyrene but no plasticization of SIS. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 981–991, 2005     

Non-reactive and reactive block copolymers for toughening of UV-cured epoxy coating

Reactive and non-reactive diblock copolymers based on polyethylene oxide (PEO) and a poly(glycidyl methacrylate) (PGMA, reactive) or polystyrene (non-reactive) block, respectively, are prepared via ATRP and those are incorporated into a cycloaliphatic epoxy matrix. Crosslinking of the matrix is then performed by cationic UV curing, producing modified thermosets. ¹H NMR and SEC measurements are carried out and used to analyze the composition, the molar mass and dispersity of the prepared block copolymers. The viscoelastic properties and morphology of the modified epoxy are determined using DMTA and FESEM, respectively. The addition of 4 and 8 wt% of the reactive PEO-b-PGMA block copolymer into epoxy resin has only minor effects on the glass transition temperature, T_g. The reactive homopolymer PGMA significantly increases and the non-reactive block copolymer PEO-b-PS slightly decreases the glass transition temperature of the epoxy matrix. The non-reactive block copolymer PEO-b-PS causes a little decrease in T_g values. The measurement of the critical stress factor, K_IC, shows that the fracture toughness of the composite materials is enhanced by inclusion of the non-reactive block copolymer. In contrary, the reactive block copolymer has negative effect on the fracture toughness especially in case of short PEO block. FESEM micrographs studies on the fracture surfaces sustain the microphase separation and the increase in surface roughness in the toughened samples, indicating more energy was dissipated.