Hybrid hydrogels self-assembled from HPMA copolymers containing peptide grafts

Graft copolymers were designed that self-assemble into hydrogels mediated by the interaction of coiled-coil peptide domains. A linear hydrophilic polymer of HPMA was chosen as the backbone, and coiled-coil forming peptides, covalently attached to the backbone, formed the grafts. Microrheology was used to evaluate the self-assembly of graft copolymers into hydrogels. The results revealed that the length and the number of coiled-coil grafts per chain had a significant influence on the gelation process. At least 4 heptads were needed to achieve the association of graft copolymers into hydrogels. CD spectra of the copolymer containing 5 heptad grafts further suggested that coiled-coil formation may contribute to the self-assembly. Gelation of graft copolymers containing CC4 peptides indicated that a threshold amount of grafts per macromolecule is needed to form a three-dimensional structure. These studies demonstrated a potential of the graft copolymers to create self-assembling hydrogels with desirable and controllable structures.     

Effect of molecular architecture on phase behavior of graft copolymers

Influence of molecular architecture on phase behavior of graft copolymer melts was studied by using a reciprocal-space self-consistent filed theory (SCFT). The phase diagrams were examined as functions of the architectural parameters describing the graft copolymers (i.e., the number of grafts and the position of first junction). In comparison with the well-known phase diagram of diblock copolymers, the phase diagrams of the graft copolymers are asymmetric. When the number of grafts or the position of first junction varies, the boundaries of order-order transitions have shifts due to the variation in the chain stretching energy. The change in molecular architecture also significantly alters the domain spacing of ordered structures but has weak impact on the density distributions of graft copolymers. For comparison of the theoretical predictions with the existing experimental results, the phase diagrams of graft copolymers were also calculated at strong segregation. The SCFT calculations can accurately capture the characteristics of the phase behavior of graft copolymer melts.     

Synthesis and characterization of graft copolymers containing poly(p-phenylene) main chains and mesogen-jacketed liquid-crystalline polystyrene side chains

A series of novel comblike mesogen-jacketed liquid-crystalline graft copolymers, poly(p-phenylene)-g-poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PPP-g-PMPCS) copolymers, have been designed and successfully synthesized by a Yamamoto coupling reaction and subsequent atom transfer radical polymerization (ATRP). ¹H NMR spectroscopy, ultraviolet–visible spectra, and gel permeation chromatography (GPC) have been used to confirm the molecular structure of the macroinitiator and the copolymers. A study of the polymerization kinetics of ATRP has shown that the molecular weight of the copolymer increases linearly with the conversion of the monomer, whereas the polydispersity remains narrow (≤1.28), indicating that the ATRP of 2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene is well controlled. Thermogravimetric analysis and differential scanning calorimetry (DSC) measurements have indicated that the PPP-g-PMPCS copolymers have better thermal stabilities than the macroinitiator, and their thermal stabilities increase with increasing molecular weight. The liquid-crystalline behavior has been examined with polarized optical microscopy, DSC, one-dimensional wide-angle X-ray diffraction (1D WAXD), and two-dimensional wide-angle X-ray diffraction (2D WAXD). The results show that all the comblike copolymers exhibit obvious liquid-crystalline behaviors, even though the GPC molecular weight of the segments of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) have been determined to be far less than the critical value of linear PMPCS. Moreover, 1D WAXD measurements show that the temperature at which the comblike mesogen-jacketed liquid-crystalline copolymers can transform into a liquid-crystalline phase is low; about 20 °C in comparison with the linear ones. 2D WAXD analysis has revealed that these comblike copolymers should be assigned to a hexatic columnar nematic (Φ_HN) phase. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2543–2555, 2007     

Amphiphilic graft copolymers - preparation and interfacial properties

Amphiphilic graft copolymers containing poly(ethylene oxide) (PEO) grafts have been prepared by various methods, for example, by coupling of reactive hydrophobic backbone polymers with end-functionalised PEO, by macromonomer copolymerisation, and by anionic graft polymerisation of EO onto polymer backbones carrying functional groups as initiator precursors. The graft copolymers are amphiphilic and were shown to accumulate at surfaces and interfaces in solution and in the solid state. Amphiphilic starch derivatives were prepared by reaction of amylose and starch with aliphatic α-epoxides.     

Hybrid thermotropic liquid-crystalline block copolymers

A new approach to the preparation of two classes of block copolymers containing liquid-crystalline segments is reported. Copolymers 1 and 2 are constituted by polytetrahydrofuran and side-chain liquid-crystalline polymethacrylate blocks, whereas block copolymers 3 consist of polystyrene and main-chain liquid-crystalline polyester blocks. The synthetic procedures leading to copolymers 1-3 are extremely versatile and can be used to prepare a great variety of block copolymer architectures. In both copolymer classes the chemically different blocks are strongly segregated in the solid and melt phases and undergo individual phase transitions. The mesophase transition temperatures of the liquid-crystalline blocks are very similar to those of the corresponding homopolymers, and their enthalpies are directly proportional to the content of the liquid-crystalline block.     

Banded texture in sheared a semiflexible thermotropic liquid-crystalline polyester and its graft copolymers with polyolefins

The formation of banded texture both in a semiflexible thermotropic liquid-crystalline polyester (SBH 112, synthesized from sebacic acid, 4,4′-dihydroxybiphenyl and 4-hydroxybenzoic acid, from Eniricerche, Milan) and in a blend of SBH with graft copolymers, consisting of a polyolefin (polyethylene or polypropylene) backbone and SBH grafts (COPPE, COPPP) has been studied by polarization microscopy and by scanning electron microscopy. The influence of the preparation conditions upon the perfection, characteristics and thermal stability of the banded texture has been investigated. The results show that the banded texture formed in SBH sheared films possesses greater perfection, smaller band width and larger angle of deviation, and higher thermal stability than the banded texture formed in COPPE and COPPP prepared under similar conditions. It has been assumed that the chain rigidity of the macromolecules of the system is mainly responsible for the formation and perfection of the banded texture. Received: 17 March 2000 Accepted: 26 July 2000     

Some Recent Advances in Pure and Applied Aspects of Graft Copolymers

In recent years more attention has been given to the preparation and characterization of graft copolymers and an examination of their properties than to developing novel methods of synthesis. In particular, these property studies can be used to develop applications of graft copolymers. The methods used to prepare and characterize better defined grafts are briefly reviewed. The structure of most graft copolymers is such that considerable amounts of one polymer can be grafted to another without affecting greatly the main properties of that polymer. In this way, the properties of one polymer such as higher water absorption can be imparted to another without changing the mechanical properties, for example, of the second polymer.

Some other inherent properties of graft copolymers are discussed, including their compatibility with the parent homopolymers, their possible con-formational changes, and other features. Finally, the use of the special nature of graft copolymers for the modification of the barrier properties of film and membranes is discussed as one possible general field of application.     

Temperature-induced chiral nematic phase changes of suspensions of poly(N,N-dimethylaminoethyl methacrylate)-grafted cellulose nanocrystals

Temperature-induced copolymers of poly(N,N-dimethylaminoethyl methacrylate)-grafted cellulose nanocrystals (PDMAEMA-grafted CNC) were synthesized by surface-initiated atom transfer radical polymerization (ATRP). The graft copolymers were characterized by thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), and gel permeation chromatography (GPC). The size of the original CNC was 10–40 nm in width and 100–400 nm in length, as characterized by atomic force microscopy (AFM). The liquid-crystalline properties of the graft copolymers were investigated by using polarizing optical microscopy (POM). The graft copolymers exhibited fingerprint texture in lyotropic state. The temperature-induced fingerprint texture changes of PDMAEMA-grafted CNC aqueous suspensions were investigated at various temperatures. With increasing temperature, the spacing of the fingerprint lines decreases. Temperature-induced changes of PDMAEMA polymer chains result in changes of fingerprint texture.     

含聚氧乙烯链段的两亲嵌段共聚物及接枝共聚物的分子设计,合成及性能

论述了由聚烯链段与聚苯乙烯或聚（甲基）丙烯酸酯链段组成的各种嵌段或接枝共聚物（包括二嵌段、两种三嵌段、星型嵌段、多嵌段、二种规整接枝共聚物等）的分子设计及合成,并总结了其两亲性质、络合碱金属离子性及微观相分离等特性。     

Synthesis and properties of poly(ethylene oxide)‐grafted polyethylene copolymer and terpolymer

A series of graft copolymers were synthesized based on ethylene‐co‐m,p‐methylstyrene (EMS) (backbone copolymer), ethylene‐1‐hexene‐m,p‐methylstyrene (EHMS) (backbone terpolymer), and polyethylene glycol monomethyl ethers (PEGM) (grafts) in this study. The PEGMs with molecular weights of 750 and 2000 were used. The chemical composition of the graft copolymers was analyzed by NMR and DSC measurements. The graft copolymers exhibited a phase‐separated morphology with the backbone and the methoxy polyethylene glycol (MPEG) grafts forming separate crystalline phases. The MPEG phase had a melting temperature lower than the corresponding MPEG homopolymer, as determined by DSC. The melting point of the crystalline phase formed by the EMS and EHMS main chains was lower than that of pure polymer backbone. Copyright © 2009 John Wiley & Sons, Ltd.     

Cellulose acetate graft copolymers with nano-structured architectures: Synthesis and characterization

Cellulose acetate is a very good film-forming polymer with major applications in cigarette filters, photographic films, cosmetics and pharmaceutics formulations and membrane separation processes. Nevertheless, its rigidity and relative hydrophobic character can be limiting drawbacks for some applications. In this work, new cellulose acetate materials with highly flexible and hydrophilic grafts were obtained with different hydrophilic/hydrophobic balances. Cellulose acetate was grafted with methyl diethylene glycol methacrylate (MDEGMA) from brominated macroinitiators by atom transfer radical polymerization (ATRP) in two steps. The first step consisted of introducing ATRP initiator groups on cellulose acetate by reacting hydroxyl side groups with 2-bromoisobutyryl bromide. A preliminary study was then carried out to determine the experimental conditions for the controlled ATRP of MDEGMA homopolymerization in a solvent (cyclopentanone) compatible with cellulose acetate grafting. In these conditions, the MDEGMA homopolymerization followed Hanns Fischer’s kinetics model accounting for the radical persistent effect. The ATRP grafting was then investigated for two cellulose acetate macroinitiators differing in the number of their ATRP initiator groups. Two families of graft copolymers with nano-structured architectures were obtained. The first family corresponded to copolymers with a high number of short grafts. The copolymers of the second family had almost the same graft weight fractions but a small number of long grafts. The morphology of the graft copolymers was then investigated by synchrotron X-ray scattering. The most informative results showed that the phase segregation depended upon the number and length of the poly(MDEGMA) grafts. The copolymer with 44 wt.% of long grafts showed a segregated morphology of nano-domains with sharp interfaces and a radius of gyration of 11.5 nm (from Guinier’s law). These cellulose acetate copolymers eventually led to strong films with potential applications in membrane separations.     

接枝共聚物EPR-g-PS作PS/EPDM共混体系增容剂的探讨

使用了由大分子单体共聚合制备的以乙丙橡胶(EPR)为主干、聚苯乙烯(PS)为支链的接枝共聚物EPR-g-PS作为PS/EPDM共混体系的增容剂。实验结果表明,共混体系的组成、增容剂加入量以及增容剂分子结构对共混体系冲击强度有很大影响。将这些因素与相差显微镜及扫描电镜研究所揭示的共混物形态的变化相联系,对此类接校共聚物作为不相容体系增容剂的机理作了探讨。     

Modification of EVOH copolymers with ϵ‐caprolactone: synthesis and compatibilization effects in PE/PVC blends

Polyethylene‐polycaprolactone graft copolymers with different chemical structures (i.e. different number and length of PCL grafts and molecular weight of PE backbone) were synthesized from various EVOH copolymers and ϵ‐caprolactone, using Aluminum isopropoxide as catalyst, and were tested for their compatibilizing capability in PE/PVC blends. PE and PCL segments in the graft copolymers were found completely immiscible, while PCL segments of the graft copolymers were found completely miscible with PVC. When graft copolymers were added to PE/PVC blends they proved to be good agents for the dispersion of PVC phase in the PE matrix. SEM showed also improved adhesion between the dispersed PVC phase and PE matrix. Moderate improvements in mechanical properties were also observed in preliminary tensile tests.     

Grafted and segmented hydrophilic polyimides for microfiltration membranes: Part I. Synthesis and characterisation

This paper describes the synthesis of two series of hydrophilic copolyimides. Polyimides were prepared with a variety of aromatic units. The copolyimides described are graft and segmented copolymers; the hydrophilic grafts and hydrophilic main-chain segments are both derived from amine-terminated poly(ethylene oxide)s (PEO). Graft copolymers were prepared by reacting mono-amine terminated PEO with pre-formed polyimide having pendant carboxyl groups activated by 1,1-carbonyl diimidazole (CDI). High molecular weight graft copolyimides with significant degrees of grafting were produced using commercial mono-functional Jeffamine^®, long-chain PEO; restricted solubility in appropriate solvents limited detailed characterisation. Segmented copolyimides were prepared using Jeffamine diamines in combination with aromatic diamines to form suitable copolymers for use in membrane applications. Equilibrium water uptakes were determined for both grafted and segmented copolyimides. The copolymers were prepared for investigations of fouling in microfiltration membranes the results of which are described in an accompanying paper.     

羧酸型接枝共聚物的合成及其络合物做化学阀

用大单体技术合成了带规整聚苯乙烯支链的聚丙烯酸接枝共聚物 .研究了各种聚合条件包括温度、时间、单体浓度、大单体分子量及大单体与小单体的投料比等对接枝效率、共聚物分子量的影响 .纯化的共聚物表现出良好的乳化性质及高吸水率 ,在稀溶液中的行为如同聚电解质 .此接枝共聚物与含规整聚氧乙烯支链的聚丙烯酸乙酯络合生成的大分子间络合物膜呈现化学阀的作用 ,水通过它的渗透速率能通过调节pH加以可逆地控制 .     

Multicenter polyester initiators for the synthesis of graft copolymers with oligo(2-ethyl-2-oxazoline) side chains

Multicenter alkylene-aromatic polyester initiators for the cationic polymerization of oxazolines are synthesized via the high-temperature polycondensation of 2-[4-(2-Br-ethyl)]phenylsulfonyl hydroquinone with 4,4'- (alkanoyldioxydibenzoyl)dichlorides. The Kuhn segment values, liquid-crystalline properties, and molecularmass characteristics of the macroinitiators are determined. It is shown that the obtained polyesters may be used as initiators for the cationic polymerization of 2-ethyl-2-oxazoline. The graft copolymers form aqueous micellar solutions with a narrow particle-size distribution and possess a lower critical solution temperature.     

Stabilization of carbon black with ionic-hydrophobic polyelectrolytes

The mode of action and efficiency of amphipolar copolymers of different molecular architectures with copolymers consisting of ionic (acrylic acid) and hydrophobic (styrene) constitutional units and sequences (segments, blocks, grafts) as stabilizers of carbon black dispersion are discussed. The pigment-copolymer interactions were investigated by the ESA method as well as lumifuge and rheological measurements. The results indicate that there are distinctive differences in the stabilization behavior depending on the molecular architecture with better results being achieved for block and graft copolymers.     

Grafting polymerization of styrene onto alternating terpolymers based on chlorotrifluoroethylene,hexafluoropropylene, and vinyl ethers,and their modification into ionomers bearing ammonium side‐groups

The grafting polymerization of styrene initiated by the alkyl chloride groups of poly(CTFE‐alt‐VE) and poly[(CTFE‐alt‐VE)‐co‐(HFP‐alt‐VE] copolymers (where CTFE, HFP, and VE stand for chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), and vinyl ether (VE), respectively) followed by the chemical modification of the polystyrene grafts are presented. First, the fluorinated alternating copolymers were produced by radical copolymerization of CTFE (with HFP) and VE. Second, atom transfer radical polymerization enabled the grafting polymerization of styrene in the presence of the poly(CTFE‐alt‐VE)‐macroinitiator using the alkyl chloride group of CTFE as the initiation site. Kinetics of the styrene polymerization indicated that such a grafting had a certain controlled character. For the first time, grafting of polystyrene onto alternating fluorinated copolymers has been achieved. Differential scanning calorimetry thermograms of these graft copolymers exhibited two glass transition temperatures assigned to both amorphous domains of the polymeric fluorobackbone (ranging from ?20 to +56 °C) and the polystyrene grafts (ca. 95 °C). The thermostability of these copolymers increased on grafting. Thermal degradation temperatures at 5% weight loss were ranging from 193 to 305 °C when the polystyrene content varied from 81 to 27%. Third, chloromethylation of the polystyrene grafts followed by the cationization of the chloromethyl dangling groups led to original ammonium‐containing graft copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Water-Soluble Copolymers. II. Synthesis and Characterization of Model Dextran-g-Acrylamides by Ce(lV)/HNO3-lnduced Initiation

In order to develop polymers useful as mobility control agents in enhanced oil recovery processes, water-soluble acrylamide grafted polysaccharide copolymers have been synthesized in water at 25° C using a ceric ammonium nitrate/nitric acid system. The effects of varying concentrations of ceric ion, monomer, and substrate on conversion, graft length, and molecular structure of the reaction products have been examined. The crude reaction products were purified by fractional precipitation and then were analyzed for nitrogen content using a micro-Kjeldahl method. The chemical structures of the graft copolymers were studied by selective hydrolysis of the carbohydrate backbones. Intrinsic viscosity and grafting length data were used to predict solution behavior of the graft copolymers prepared under controlled conditions. Aqueous size exclusion and viscosity studies showed direct correlations between hydrodynamic volume and length of the polyacrylamide side-chain grafts.     

Graft copolymers composed of high molecular weight poly(ethylene oxide) backbone and poly(N-isopropylacrlylamide) side chains and their thermoassociating properties

Novel, water-soluble thermoassociative graft copolymers based on high molecular weight (HMW) poly(ethylene oxide-co-glycidol) backbone and relatively short grafts of poly-N-isopropyl acrylamide (NIPAAm) were prepared. The copolymer precursors with two architectures (block and graft) were synthesized using Ca-amide-alkoxide initiators. The OH groups in the copolymer precursors have been utilized for grafting NIPAAm using ceric ion (Ce⁴⁺) redox initiation. The idea was to imprint the “smart” properties of PNIPAAm grafts into common HMW poly(ethylene oxide). The sensitive moieties undergo reversible association transitions by changing the temperature of dilute and semidilute aqueous solutions of the copolymers. Associative properties were studied by viscosity and rheology measurements. Two types of interactions, induced by heating, depending on the copolymer concentration namely intra- and intermolecular association were observed.