Secondary globular structure of copolymers containing amphiphilic and hydrophilic units: Computer simulation analysis

The coil-globule transition in copolymers composed of amphiphilic and hydrophilic monomer units has been studied by the computer simulation technique. It has been shown that the structure of globules formed in such systems substantially depends on the rate at which the solvent quality worsens. The globule resulting from slow cooling is cylindrical, and its core contains a large amount of hydrophilic groups. The globule formed upon rapid cooling takes the helical conformation, in which all hydrophilic groups are displaced to the periphery. One helix turn of such globules contains 3–5 units. In both cases, the backbone of the polymer chain forms a typical zigzag-shaped structure with an average angle between neighboring bond vectors of about 60°. This fact implies that globules of copolymers consisting of amphiphilic and hydrophilic units comprise secondary structure components.     

Ring-closing olefin metathesis in the aqueous phase of amphiphilic conetworks consisting of fluorophilic and hydrophilic compartments

A Grubbs-Hoveyda-Type metathesis catalyst bearing a tris(perfluoroalkyl)silyl tag was immobilized in the fluorophilic phase of amphiphilic conetworks (APCNs). This catalytic system was applied to ring-closing metathesis (RCM) reactions in aqueous media. Different substrates were evaluated and with 10 mol% of catalyst at 60 °C good conversions were observed. Reuse of the catalytic system was possible, but resulted generally in lower conversions.     

Biocompatible amphiphilic conetwork based on crosslinked star copolymers: A potential drug carrier

A series of amphiphilic conetworks (APCNs) is synthesized through crosslinking of well‐defined tri‐arm star diblock copolymers via atom transfer radical polymerization. A new three‐arm initiator is synthesized to initiate the polymerization of 2‐hydroxyethyl methacrylate (HEMA) via “core‐first” method. The resulting star HEMA homopolymers with well‐defined molecular weight and narrow polydispersity are used as macroinitiator to incorporate allyl methacrylate to get the star diblock copolymers. Then, the precursors with allyl pendant groups are fully crosslinked with polyhydrosiloxanes through hydrosilylation. The so‐prepared APCNs exhibit unique properties of microphase separation of hydrophilic (HI) and hydrophobic (HO) phases with small channel size, a variable swelling capacity, excellent biocompatibility, and outstanding mechanical strength (2 ± 0.5 MPa). The properties of APCNs depend on the ratio of HI to HO, which can be regulated via precise synthesis of the star diblock copolymers. The APCNs show well‐controlled drug release to choline theophyllinate, suggesting a promising intelligent drug carrier for controlled release. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2537–2545     

Novel amphiphilic fluorescent graft copolymers: synthesis,characterization, and potential as gene carriers

Amphiphilic fluorescent graft copolymer (PVP‐PyATAm) was successfully synthesized by the free radical copolymerizations of hydrophobic monomer N‐acryloyl‐thioureylene‐4‐(1‐pyrene)‐butyryl amide (PyATAm) with hydrophilic precursor polymers of vinyl‐functionalized poly (N‐vinylpyrrolidone) (Acryloyl‐PVP) in DMF. FT‐IR, ¹H NMR, TEM, gel permeation chromatography‐multi‐angle laser light scattering, UV‐vis spectroscopy, viscometric measurement, and fluorescence spectroscopy were used to characterize this copolymer. The TEM observation showed that the copolymer PVP‐ PyATAm formed spherical micelles in an aqueous solution and the size of micelles was between 50 and 70 nm in diameter. The interaction of PVP‐PyATAm copolymer and plasmid DNA was examined by agarose gel electrophoresis and TEM. Results indicated that the copolymer–DNA complexes were self‐assembled and the size of complexes was between 90 and 120 nm in diameter. Cytotoxity studies using MTT colorimetric assays suggested good biocompatibility of PVP‐PyATAm in vitro. These results suggested the potential of this graft copolymer as gene delivery carrier. Copyright © 2007 John Wiley & Sons, Ltd.     

New rod-coil block copolymers consisting of terfluorene segments and electron transporting units as the flexible blocks

A series of new rod-coil block copolymers having a well-defined terfluorene unit as the rigid segment with three different electron transporting moieties as the flexible part, such as side chain oxadiazole (TFPOXD), side chain quinoline (TFPQN) and a molecule containing two oxadiazole rings in the side chain (TFPDOXD), were synthesized using the atom transfer radical polymerization (ATRP) technique. All the synthesized copolymers were extensively examined with respect to their optical properties as pristine films, upon thermal annealing (200 °C for 30 min in air) and photo-oxidation treatment in air. Thermal annealing of the block copolymers resulted in stable blue light emission from TFPOXD and TFPDOXD while TFPQN showed the appearance of the undesired 520 nm emission band. In addition, TFPOXD does not exhibit the low-energy emission band at 520 nm after photo-oxidation under prolonged diffuse UV radiation at ambient atmosphere, despite the fluorenone formation on the terfluorene segment, in contrast to all the other copolymers.     

Dissipative particle dynamics simulations of toroidal structure formations of amphiphilic triblock copolymers

In this paper, the dynamic assembly of toroidal micelle structures of amphiphilic triblock copolymers in dilute solution has been investigated using dissipative particle dynamics simulations. The amphiphilic molecule is represented by a coarse-grained model, which contains hydrophilic and hydrophobic particles. Some microstructures of complex morphology having toroidal micelles have been observed in the simulations; the toroidal micelle formation is in accordance with the theoretical prediction of the toroidal structure in cylindrical micelle suspensions by Pochan et al. (Science 2004, 306, 94). These findings are very interesting, and these complex morphologies enrich our knowledge of the potential products obtained from the self-assembly of block copolymers.     

Preparation, photophysics, and electrochemistry of segmented comonomers consisting of thiophene and pyrimidine units: new monomers for hybrid copolymers

An efficient coupling route to novel pi-conjugated comonomers consisting of pyrimidine, thiophene, and bithiophene units was developed. The novel pi-donor-acceptor-donor and pi-donor-acceptor-acceptor-donor conjugated compounds were prepared by Suzuki heterocoupling and Ni(0)-mediated Ullman homocoupling reactions. Photophysical investigation of these alternating pi-donor and acceptor compounds indicated that the deactivation of their singlet excited state proceeds predominately by fluorescence and results in high fluorescence quantum yields. Intersystem crossing to the triplet state was also present in ca. 10%. Quantification of the triplet manifold by laser flash photolysis further revealed that bithiophene produced its triplet state in only 31%. Cyclic voltammetry studies showed that the comonomers undergo both oxidation and reduction leading to their radical cations and radical anions, respectively. The radical cations are highly reactive and undergo anodic polymerization resulting in mutual p- and n-type dopable polymers. The extended conjugation resulting from polymer formation was confirmed by both absorbance and fluorescence spectroscopy and by GPC. Ruthenium binding with the conjugated homocoupled ligand was also found resulting in a hybrid alternating copolymer with significantly different spectroscopic and electrochemical properties relative to its metal-free counterpart.     

Synthesis and characterization of amphiphilic antibacterial copolymers

Macromolecule antimicrobials have been explored in foundational research and practical application due to their potential merit for reducing the residual toxicity, increasing their efficiency, selectivity, and prolonging the lifetime of the antimicrobial material. In this work, the quaternized poly(styrene)‐b‐poly(DMAEMA) diblock polymers are synthesized by reversible addition‐fragmentation chain transfer polymerization (RAFT). The minimum inhibitory concentration (MIC) evaluation and optical density (OD) method demonstrated that the amphiphilic antibacterial biomaterials have exceptional antibacterial properties. The amphiphilic polycation has an admirable antibacterial property, and these quaternized diblocks are potent biocides and nonhemolytic. The relationship between the structure and activity is discussed with respect to molecular weight of the diblocks and bacteria structural dependence. Copyright © 2011 John Wiley & Sons, Ltd.     

Micellization phenomena of biodegradable amphiphilic triblock copolymers consisting of poly(beta-hydroxyalkanoic acid) and poly(ethylene oxide)

This paper reports the studies on micelle formation of new biodegradable amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide) (PEO-PHB-PEO) triblock copolymer with various PHB and PEO block lengths in aqueous solution. Transmission electron microscopy showed that the micelles took an approximately spherical shape with the surrounding diffuse outer shell formed by hydrophilic PEO blocks. The size distribution of the micelles formed by one triblock copolymer was demonstrated by dynamic light scattering technique. The critical micellization phenomena of the copolymers were extensively studied using the pyrene fluorescence dye absorption technique, and the (0,0) band changes of pyrene excitation spectra were used as a probe for the studies. For the copolymers studied in this report, the critical micelle concentrations ranged from 1.3 x 10(-5) to 1.1 x 10(-3) g/mL. For the same PEO block length of 5000, the critical micelle concentrations decreased with an increase in PHB block length, and the change was more significant in the short PHB range. It was found that the micelle formation of the biodegradable amphiphilic triblock copolymers consisting of poly(beta-hydroxyalkanoic acid) and PEO was relatively temperature-insensitive, which is quite different from their counterparts consisting of poly(alpha-hydroxyalkanoic acid) and PEO.     

Microspheres made of poly(epsilon-caprolactone)-based amphiphilic copolymers: potential in sustained delivery of proteins

Microspheres of amphiphilic multi-block poly(ester-ether)s (PEE)s and poly(ester-ether-amide)s (PEEA)s based on poly(epsilon-caprolactone) (PCL) were investigated as delivery systems for proteins. The interest was mainly focused on the effect of their molecular structure and composition on the overall properties of the microspheres, encapsulating bovine serum albumin (BSA) as a model protein. PEEs and PEEAs were prepared using a alpha,omega-dihydroxy-terminated PCL macromer (Mn= 2.0 kDa) as a hydrophobic component. Hydrophilic oxyethylene sequences were generated using poly(ethylene oxide)s (PEO)s of different molecular mass (Mn= 300-600 Da) in the case of PEEs, or 4,7,10-trioxa-1,13-tridecanediamine (Trioxy) and PEO150 (Mn= 150 Da) in the case of PEEAs. The copolymers showed a decrease of Tm and crystallinity values as compared with PCL. Within each class of copolymers, the bulk hydrophilicity increased with increasing the number of oxyethylene groups in the chain repeat unit. PEEAs were more hydrophilic than PEEs with a similar number of oxyethylene groups. Discrete spherical particles were prepared by both PEEs and PEEAs and their BSA encapsulation efficiency related to copolymer properties. Interestingly, the insertion of short hydrophilic segments is enough to significantly affect protein distribution inside microspheres and its release profiles, as compared to PCL microspheres. Different degradation rates and mechanisms were observed for copolymer microspheres, mainly depending on the distribution of oxyethylene units along the chain. The results highlight that a fine control over the structural parameters of amphiphilic PCL-based multi-block copolymers is a key factor for their application in the field of protein delivery.     

Controlled radical polymerization of tert‐butyl acrylate at ambient temperature: Effect of initiator structure and synthesis of amphiphilic block copolymers

Controlled and very rapid ambient temperature polymerization of tert‐butyl acrylate (tBA) via atom transfer radical polymerization (ATRP) and single electron transfer living radical polymerization (SET‐LRP) conditions is reported. Two initiators, one that would generate a secondary radical and another that would generate a primary radical, upon activation, are used. A very active catalyst CuBr/Me₆TREN was found to initiate rapid polymerization whether it was the primary or the secondary initiator. The polymerization was well controlled and very rapid. The initiator that produces secondary initiating site is found to result in more rapid polymerization than the one that produces primary initiating site. To explore the possibility of rapid ambient temperature polymerization through the SET‐LRP mechanism, the polymerization was also carried out in the presence of DMSO. It was found that the polymerization was much faster compared to the bulk ATRP, without loss of control. Styrene was block copolymerized from PtBA macroinitiators and vice versa. In both the cases, block copolymers with controlled molecular weights were obtained. The tBA block of the polymer was selectively hydrolyzed to get amphiphilic block copolymers. This amphiphilic block copolymer was found to be useful in preparing stable cadmium sulfide (CdS) nanoparticulate dispersion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Physical deposition behavior of charged amphiphilic diblock copolymers: Effect of charge distribution and electric field

Coarse-grained molecular dynamics simulations are used to investigate physical deposition behavior of charged amphiphlic diblock copolymers. The effects of solvent selectivity, charge distribution in amphiphlic diblock copolymers, and electric field strength on deposition conformations are studied qualitatively. Flat amphiphilic bilayers, which consist of hydrophilic monolayer and hydrophobic brush, are formed by physical deposition of charged amphiphlic diblock copolymers in nonselective solvents. For physically deposited amphiphlic diblock copolymers in selective solvents, amphiphilic bilayers consist of disc-shaped hydrophilic monolayers and hydrophobic nanospheres are found. This study sheds light on the formation of various amphiphlic diblock copolymer deposition conformations in different solvents and interaction mechanism of different components. Furthermore, the evolution of physical deposition process of charged amphiphlic diblock copolymers layer offers new insight to the controlling of amphiphilic bilayer thickness, hydrophobic nanosphere size, and interface property of depositional amphiphlic diblock copolymers.     

Novel amphiphilic network polymers consisting of nonpolar,short primary polymer chains and polar,long crosslink units: Influence of characteristic dangling chains on swelling behavior of resulting amphiphilic gels

Novel amphiphilic network polymers consisting of nonpolar, short primary polymer chains and polar, long crosslink units were prepared, and the swelling behavior of resulting amphiphilic gels is discussed by focusing on the influence of characteristic dangling chains; that is, benzyl methacrylate (BzMA) was copolymerized with tricosaethylene glycol dimethacrylate [CH₂?C(CH₃)CO(OCH₂CH₂)₂₃OCOC(CH₃)?CH₂, PEGDMA‐23] in the presence of lauryl mercaptan as a chain‐transfer agent because BzMA forms nonpolar, short primary polymer chains and PEGDMA‐23 as a crosslinker contains a polar, long poly(oxyethylene) unit. The enhanced incorporation of dangling chains into the network polymer was brought by shortening the primary polymer chain length, and copolymerization with methoxytricosaethylene glycol methacrylate, a mono‐ene counterpart of PEGDMA‐23, enforced the incorporation of flexible dangling poly(oxyethylene) chains into the network polymer, although the former dangling chains as terminal parts of primary poly(BzMA) chains were rather rigid. Then, the influence of characteristic dangling chains on the swelling behavior of amphiphilic gels was examined in mixed solvents consisting of nonpolar t‐butylbenzene and polar methanol. The profiles of the solvent‐component dependencies of the swelling ratios were characteristic of amphiphilic gels. The introduction of dangling poly(oxyethylene) chains led not only to an increased swelling ratio but also to sharpened swelling behavior of amphiphilic gels. The swelling response of amphiphilic gels was checked by changing the external solvent polarity. The dangling chains with freely mobile end segments influenced the swelling response of gels. The amphiphilic gels with less entangled, collapsed crosslink units exhibited faster swelling response than the ones with more entangled, collapsed primary polymer chains. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2192–2201, 2004     

新型线状-树枝状两亲嵌段共聚物的合成

本文设计合成了一系列由不同链长的聚丙烯酸(PAA)为亲水嵌段和不同代数聚苄醚树枝体(Dendr.PBE)为疏水嵌段的杂化共聚物(PAA-Dendr.PBE)。     

Synthesis and properties of amphiphilic maleic acid copolymers

New amphiphilic polymers derived from maleic acid copolymers and containing stearyl or oleyl residues were prepared. Their physicochemical properties were studied, and the possibility of using them as carriers for antifungal agents was examined with Amphotericin B as example.     

Thermoresponsive amphiphilic symmetrical triblock copolymers with a hydrophilic middle block made of poly(N-isopropylacrylamide): synthesis, self-organization, and hydrogel formation

Several series of symmetrical triblock copolymers were synthesized by the reversible addition fragmentation chain transfer method. They consist of a long block of poly(N-isopropylacrylamide) as hydrophilic, thermoresponsive middle block, which is end-capped by two small strongly hydrophobic blocks made from five different vinyl polymers. The association of the amphiphilic polymers was studied in dilute and concentrated aqueous solution. The polymer micelles found at low concentrations form hydrogels at high concentrations, typically above 30–35 wt.%. Hydrogel formation and the thermosensitive rheological behavior were studied exemplarily for copolymers with hydrophobic blocks of polystyrene, poly(2-ethylhexyl acrylate), and poly(n-octadecyl acrylate). All systems exhibited a cloud point around 30 °C. Heating beyond the cloud point initially favors hydrogel formation but continued heating results in macroscopic phase separation. The rheological behavior suggests that the copolymers associate into flower-like micelles, with only a small share of polymers that bridge the micelles and act as physical cross-linkers, even at high concentrations.     

Preparation of amphiphilic diblock copolymers with pendant hydrophilic phosphorylcholine and hydrophobic dendron groups and their self‐association behavior in water

Generation 3.5 poly(amido amine) dendron (G3.5) with 16 n‐butyl terminal groups containing an acrylamide monomer (AaUG3.5) was prepared by condensation between an amino focal group in G3.5 and 11‐acrylamidoundecanoic acid. AaUG3.5 was polymerized using poly(2‐methacryloyloxyethyl phosphorylcholine) (pMPC)‐based macro‐chain transfer agent via reversible addition‐fragmentation chain transfer (RAFT) radical polymerization to obtain amphiphilic diblock copolymers with different compositions. The diblock copolymers (P_mD_n) were composed of a hydrophilic pMPC block and hydrophobic pendant dendron‐bearing block, where P and D represent pMPC and pAaUG3.5, respectively, and m and n represent the degree of polymerization for each block, respectively. P₂₉₆D₁ and P₉₈D₃ formed vesicles and large compound micelles and vesicles, respectively, which was confirmed by light scattering measurements and transmission electron microscopic (TEM) observations. The large compound micelles formed from P₉₈D₃ could not incorporate hydrophilic guest polymer molecules, because the aggregates did not have a hydrophilic hollow core. In contrast, the vesicles formed from P₂₆₉D₁ could incorporate hydrophilic guest polymer molecules into the hollow core. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4923–4931