Well-defined nanofiberous polystyrene nanocomposites with twofold chains by ATRP

Polystyrene nanocomposites, being a combination of nanoclay-attached and free polystyrene chains were prepared using in situ atom transfer radical polymerization. Subsequently, they were electrospun to form fibers with diameter varying from 450?C700 nm according to scanning electron microscopy data; in addition, the transmission electron microscopy and x-ray diffraction analysis revealed that nanoclay layers were oriented along the nanofiber axis during the electrospinning process. Molecular weight of the extracted free polymer chains from the nanocomposites is higher than the attached chains. However, Anchored chains are characterized by higher polydispersity index in comparison with the free ones. Polydispersity index of polymer chains increases by the addition of nanoclay. Thermogravimetric analysis results shows that increasing clay content leads to a decrease in the quantity of polymer chains attached to the clay surface.     

Preparation of well-defined polystyrene/silica hybrid nanoparticles by ATRP

Immobilization of the atom transfer radical polymerization (ATRP) macroinitiators at the silica nanoparticle surfaces was achieved through surface modification with excess toluene-2,4-diisocynate (TDI), after which the residual isocyanate groups were converted into ATRP macroinitiators. Structurally well-defined polystyrene chains were grown from the nanoparticle surfaces to yield individual particles composed of a silica core and a well-defined, densely grafted outer polystyrene by ATRP, which was initiated by the as-synthesized silica-based macroinitiator. FTIR, NMR and gel permeation chro-matography (GPC) were used to characterize the polystyrene/silica hybrid particles.     

Modification of the halogen end groups of polystyrene prepared by ATRP

The stabilization modification of the halogen end groups of polystyrene prepared by atom transfer radical polymerization (ATRP) has been attempted. The reaction mechanism adopted is radical chain transfer reaction, and iso-propylbenzene is employed as not only the chain transfer agent but also the solvent. Moreover, Cu⁰ is used as the acceptor of the transformed halogen atom in some experiments. As evidenced by ¹H NMR analysis of the modified products, the halogen end group can really be converted into the much more stable carbon-hydrogen structure. When Cu⁰ is not used, the conversion of the halogen end groups rises rapidly during the early stage and the increase rate slows down after about 8 h reaction. In view of the influence of reaction temperature on the modification, the conversion increases almost exponentially with temperature in the range of 80-100 °C, and the increase rate slows down at higher temperature. ¹H NMR and SEC analyses prove that the modification reaction does not destroy the polymer backbone and the molecular weights remain almost the same as those of the unmodified samples. When Cu⁰ is introduced, the modification reaction proceeds much rapidly, the conversion of the halogen end groups rises almost linearly at the early stage and the nearly complete (>95%) dehalogenation of the polymeric chains is observed after only 12 h reaction. However, the molecular weights rise and the polydispersities become wider after the modification, which implies that the modification is accompanied with the couple termination of the polystyrene radicals besides chain transfer reaction. Furthermore, the couple termination can be restrained at some lower catalyst concentration. Indeed, the modified polymers show improved thermal stability, the initial weight loss temperatures is increased from 196 °C to 378 °C for the linear polystyrene and from 203 °C to 261 °C for the hyperbranched polystyrene.     

Synthesis of branched polystyrene by ATRP exploiting divinylbenzene as branching comonomer

Branched polystyrenes have been synthesized using atom transfer radical polymerization (ATRP) of styrene in the presence of divinyllbenzene (DVB) as branching comonomer. The synthesis was completed via facile one pot approach. Mole ratio of styrene to DVB in range of 5:1-30:1 was employed to obtain soluble polymers. The kinetics of the polymerization and evolution of polymer compositions were revealed by determining the conversions of reactants by gas chromatography (GC). The growth of molecular weight was monitored by GPC and the results indicate that the branched polymers were formed by self-condensing vinyl polymerization (SCVP) of AB^∗ monomer or macromonomers. The branched structure of the resulting polymers was confirmed by the remarkable discrepancies of the weight average molecular weights determined by GPC and multi angle laser light scattering (MALLS). The specific viscosity of the resulting polymer is also much lower compared with that of linear analogues. The influence of dosage of initiator and catalyst on the yield and molecular weights of the resulting polymers was also investigated.     

Synthesis of high molecular weight polystyrene using AGET ATRP under high pressure

High molecular weight polystyrene (PS) was synthesized by ATRP. Under atmospheric pressure (1 bar), PS with M_n up to 200,000 was prepared using either ARGET or ICAR ATRP. Under high pressure (6 kbar), higher molecular weight PS could be obtained due to accelerated radical propagation and diminished radical termination in polymerization of styrene. Therefore, it was possible to synthesize PS with M_n > 1,000,000 and M_w/M_n < 1.25 using AGET ATRP under a pressure of 6 kbar at room temperature. This is the highest molecular weight linear PS prepared by a controlled radical polymerization.     

MALDI‐TOF mass spectrometry characterization of C60 end‐capped polystyrene prepared by ATRP

The ATRP (atom‐transfer radical polymerization) process was used to synthesize C₆₀ end‐capped polystyrene. GPC data demonstrated that fullerene (C₆₀) was chemically bonded to polystyrene, and C₆₀ was most likely monosubstituted. Matrix‐assisted laser desorption/ionization‐time of flight (MALDI‐TOF) mass spectrometry (MS) analysis (with 1,8‐dihydroxy‐9(10H)‐anthracenone (dithranol)/silver trifluoroacetate as the matrix) of this copolymer proved that C₆₀ was monosubstituted.     

Synthesis of temperature responsive polymer brushes from polystyrene latex particles functionalized with ATRP initiator

Thermally responsive poly(N-isopropylacrylamide) (PNIPAAM) brushes were grafted from polystyrene particles synthesized with surfactant free emulsion polymerization and functionalized with a thin shell of ATRP initiator on the surface. The ATRP initiator was present in the shell either alone or along with copolymerized styrene and also a crosslinker. The grafted brushes were characterized with transmission electron microscopy before and after negative staining with uranyl acetate. Cryo-scanning electron microscopy confirmed the growth of extremely long PNIPAAM layers from the surface, which otherwise looked shrunken in the transmission electron microscope owing to dehydration and possibly the effect of staining agent. The amount of grafted polymer also increases proportionally to the increase of the monomer concentration in the initial reaction system. The change in character from hydrophilic to hydrophobic with temperature and salt was found to be reversible and fast. The adsorption of protein complexes (tobacco mosaic virus) could be readily achieved at higher temperatures indicating the potential of the grafted particles to be used as stationary phases in temperature regulated chromatographic separations.     

Oligopeptide‐based amide functional initiators for ATRP

Polymer–peptide conjugates are receiving significant interest. Here, we show that, under the appropriate conditions, a small family of oligopeptide‐based initiators can be used successfully to initiate the polymerization of methacrylic monomers by atom transfer radical polymerization (ATRP), generating new examples of such materials. However, the use of the peptidic amide‐based initiators results in polymers which have a higher molecular weight than expected and a significantly higher polydispersity than those prepared from ester‐based initiators. In many cases significant initiator remains, suggesting that either not all peptides successfully initiate polymerization or that significant termination reactions occur early in the reaction. This low initiator efficiency agrees with other reports for amino acid‐based initiators. It therefore appears that such amide‐based initiators can be used successfully, but have a significantly lower applicability than the more commonly used ester‐based initiators. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6082–6090, 2008     

Polystyrene microspheres having epoxy functional dangling chains linked by hydrolytically stable bonds via ATRP

We report application of copper‐mediated atom transfer radical polymerization in graft copolymerization of glycidyl methacrylate (GMA) from N‐bromosulfonamide groups on polystyrene‐divinyl benzene (PS‐DVB) microspheres (210–420 μm). The surface initiator groups were introduced by simple modification of crosslinked PS‐DVB (10% mol/mol) beads in three steps: (i) chlorosulfonation, (ii) sulfamidation with propylamine, and (iii) bromination. Initiation from surface‐bound N‐bromosulfonamide groups showed first‐order kinetics (k = 1.04 × 10^?4 s^?1 in toluene at 70 °C) and gave poly(GMA) graft chains linked to the surface by hydrolytically stable sulfonamide bonds. High graft yields were attained (up to 294.4% within 21 h) while retaining the epoxy groups. Epoxy content of the resulting product (5.41 mmol g^?1) revealed an average 17 GMA repeating units in the graft per initiation site. Taking advantage of the hydrolytic stability of sulfonamide linkages and well‐known reactivity of the epoxy groups on dangling chains, “the hair‐like structure” of the polymer beads prepared can be considered when devising more efficient functional polymers as catalysts or reagent carriers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6708–6716, 2006     

Surface initiated ATRP in the synthesis of iron oxide/polystyrene core/shell nanoparticles

A method to prepare magnetic nanoparticles with a covalently bonded polystyrene shell by surface initiated atom transfer radical polymerization (ATRP) was reported. First, the initiator for ATRP was covalently bonded onto the surface of magnetic nanoparticles through our novel method, which was the combination of ligand exchange reaction and condensation of triethoxysilane having an ATRP initiating site, 2-bromo-2-methyl-N-(3-(triethoxysilyl)propyl) propanamide. Then the surface initiated ATRP of styrene mediated by a copper complex was carried out and exhibited the characteristics of a controlled/“living” polymerization. The as-synthesized nanoparticles were coated with well-defined PS of a target molecular weight up to 45 K. These hybrid nanoparticles had an exceptionally good dispersibility in organic solvents and were subjected to detailed characterization using DLS, GPC, FTIR, XPS, UV-vis, TEM and TGA.     

End‐functionalized polystyrene by ATRP: A facile approach to primary amino and carboxylic acid terminal groups

Monoamino‐terminated and monocarboxylic acid‐terminated polystyrenes containing active halogenated end groups were prepared by atom transfer radical polymerization (ATRP) using the so‐called initiator method and protective group chemistry. α‐Chloropropionates were synthesized and utilized as initiators containing the tert‐butoxycarbonyl (t‐BOC)‐protected amino and the tert‐butyl (t‐Bu)‐protected carboxylic acid function, respectively. Optimum polymerization conditions were attained using CuCl/N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDETA) as catalyst and 10 vol % n‐butanol as homogenizing agent at 110 °C. However, targeting larger quantities an alternative route was established employing 50 vol % N,N‐dimethylformamide (DMF). Subsequent hydrolysis of the ω‐tert‐butoxycarbonyl polystyrenes afforded well‐defined polymers with quantitative deprotection of the functional groups. Comparatively, thermolytic cleavage of the protective sites was studied. ¹H NMR verified the quantitative removal of the t‐BOC‐protecting groups. Furthermore, the resulting α‐amino‐ω‐chloro polystyrenes were reacted with Sanger reagent to confirm the existence of the thereby converted primary amino groups. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3845–3859, 2009     

Synthesis of bis-allyloxy functionalized polystyrene and poly (methyl methacrylate) macromonomers using a new ATRP initiator

A new bis-allyloxy functionalized ATRP initiator, viz, 4,4-bis (4-(allyloxy) phenyl) pentyl-2-bromo-2-methylpropanoate was synthesized starting from commercially available 4,4-bis (4-hydroxyphenyl) pentanoic acid. Atom transfer radical polymerization of styrene in bulk and that of methyl methacrylate in anisole using CuBr/N,N,N′,N′,N″-pentamethyldiethylenetriamine system was carried out. The kinetic study of styrene polymerization showed controlled polymerization behavior. Bis-allyloxy functionalized well-defined polystyrene (M_n^GPC: 13,600–28,250, PDI: 1.07–1.09) and poly (methyl methacrylate) (M_n^GPC: 10,100–18,450, PDI: 1.23–1.34) macromonomers were obtained. The presence of allyloxy functionality was confirmed by ¹H NMR spectroscopy. The reactivity of allyloxy functionality was demonstrated by carrying out organic reactions such as addition of bromine and hydrosilylation on polystyrene macromonomer. Polystyrene macromonomer with bis-allyloxy functionality was transformed into bis-epoxy functionalized polystyrene macromonomer using 3-chloroperoxybenzoic acid.     

Surface and interfacial segregation in blends of polystyrene with functional end groups and deuterated polystyrene

The effect of chain-end chemistry on surface and interfacial segregation in symmetric blends of polystyrene (hPS)/deuterated polystyrene (dPS) has been investigated by X-ray photoelectron and secondary ion mass spectroscopy in conjunction with neutron reflectivity measurements. Alpha,omega-fluoroalkyl- and alpha,omega-carboxy-terminated polystyrenes (alpha,omega-hPS(Rf)2 and alpha,omega-hPS(COOH)2) were used as end-functionalized polymers; the former possesses chain ends with lower surface energies, and the latter possesses higher surface energies compared with that of the main chain. In the case of an alpha,omega-hPS(Rf)2/dPS blend film, alpha,omega-hPS(Rf)2 was enriched at the surface owing to the surface localization of the Rf groups, although the surface energy of the hPS segments was slightly higher than that of the dPS ones. On the contrary, in the case of an alpha,omega-hPS(COOH)2/dPS blend film, dPS was preferentially segregated at the surface. This may be due to a surface depletion of COOH ends and an apparent molecular weight increase of alpha,omega-hPS(COOH)2 produced by a hydrogen-bonded intermolecular association of COOH ends in addition to the surface energy difference between hPS and dPS segments. Interestingly, both Rf and COOH chain ends were partitioned to the substrate interface for the alpha,omega-hPS(Rf)2/dPS and alpha,omega-hPS(COOH)2/dPS blend films, resulting in the segregation of the hPS component at the substrate interface for both blends. The results presented imply that surface and interfacial segregation in polymer blends could be regulated by incorporating functional groups into the end portions of one component.     

'Supramolecular wrapping chemistry' by helix-forming polysaccharides: a powerful strategy for generating diverse polymeric nano-architectures

We have exploited novel supramolecular wrapping techniques by helix-forming polysaccharides, β-1,3-glucans, which have strong tendency to form regular helical structures on versatile nanomaterials in an induced-fit manner. This approach is totally different from that using the conventional interpolymer interactions seen in both natural and synthetic polymeric architectures, and therefore has potential to create novel polymeric architectures with diverse and unexpected functionalities. The wrapping by β-1,3-glucans enforces the entrapped guest polymer to adopt helical or twisted conformations through the convergent interpolymer interactions. On the contrary, the wrapping by chemically modified semi-artificial β-1,3-glucans can bestow the divergent self-assembling abilities on the entrapped guest polymer to create hierarchical polymeric architectures, where the polymer/β-1,3-glucan composite acts as a huge one-dimensional building block. Based on the established wrapping strategy, we have further extended the wrapping techniques toward the creation of three-dimensional polymeric architectures, in which the polymer/β-1,3-glucan composite behaves as a sort of amphiphilic block copolymers. The present wrapping system would open several paths to accelerate the development of the polymeric supramolecular assembly systems, giving the strong stimuli to the frontier of polysaccharide-based functional chemistry.     

Construction of regulated nanospace around a porphyrin core

A series of 1,3,5-phenylene-based rigid dendritic porphyrins were synthesized by Suzuki coupling between a porphyrin core and dendron units. The intramolecular energy transfer was studied by absorption and fluorescence spectroscopies. The encapsulation of the porphyrin core within the 1,3,5-phenylene dendron units was found to provide highly efficient energy transfer from the dendron units to the porphyrin core. The dendritic wedge structure affected the energy transfer efficiency. The 1,3,5-phenylene-based rigid dendron units act as highly efficient light-harvesting antennae. These dendritic porphyrins have also been examined as C(60) hosts and substrate-selective oxidation catalysts. The attachment of the second generation of 1,3,5-phenylene-based dendron units with the porphyrin core enabled a stable inclusion of C(60) in toluene. Furthermore, the size and shape of the nanospace in the rigid dendritic porphyrins were found to affect the selectivity of substrates in the catalytic olefin oxidations.     

Grafting of amino functional monomer onto initiator-modified polystyrene particles

Polystyrene nanoparticles with grafted chains of an amino functionalized polymer were prepared by a two-step polymerization process. In the first step, the polystyrene seed particles were synthesized by the conventional batch emulsion polymerization using terpolymer HAS (hydroperoxide monomer, acrylic acid, and styrene) as a surface-active initiator. The surface of the obtained particles contains carboxyl groups, which are responsible for the latex stability, and residual undecomposed hydroperoxide groups. Therefore, in the second step, an amino functional monomer was grafted onto the hydroperoxide modified polystyrene particles by a "grafting from" approach. X-ray photoelectron spectroscopy, NMR, and scanning electron microscopy were used to examine the surface of the amino functionalized particles. The amount of incorporated amino groups onto the particles was determined by fluorescenometric titration. In general, the number of amino groups on the particle surface increased with the increase of the functional monomer content in the reaction mixture. The incorporation of the functional monomer was also confirmed by electrophoretic measurements. Final particles possess amphoteric character due to the presence of amino and carboxyl groups on the surface. Adsorption of human immunoglobulins G onto the amino functionalized particles was studied as a function of pH and ionic strength. The covalent binding of human IgG was performed using the glutaraldehyde preactivation method. The immunoreactivity of the latex-IgG complex was examined by the latex agglutination test.     

原子转移自由基活性聚合合成PS-PMA-PS嵌段聚合物

本文采用氯化亚铜/α,α'-联吡啶配位化合物作催化剂.首先在130℃时用1-苯基氯乙烷在引发苯乙烯(St)进行原子转移自由基聚合,再以其产物PS-Cl作为大分子引发剂引发丙烯酸甲酯(MA)在反应温度为120℃时进行聚合,得到两嵌段聚合物PS-PMA-Cl.此两嵌段共聚物在特殊混合溶剂--丙酮/正丙醇(体积比7:3)中仍然可以作大分子引发剂引发苯乙烯进行原子转移自由基聚合,由于聚合体系接近于均相.所以表现出了较高的反应活性,并且合成的聚苯乙烯一聚丙烯酸甲酯一聚苯乙烯(PS-PMA-PS)三嵌段聚合物的分子量与设计值接近、分子量分布比较窄,反应的条件温和,可控性好.最后通过NMR技术对三元嵌段共聚物的结构迸行了表征.     

Construction of a comb-like glycosylated membrane surface by a combination of UV-induced graft polymerization and surface-initiated ATRP

Carbohydrate residues are found on the extracellular side of the cell membrane. They form a protective coating on the outer surface of the cell and are involved in intercellular recognition. Synthetic carbohydrate-based polymers, so-called glycopolymers, are emerging as important well-defined tools for investigating carbohydrate-based biological processes and for simulating various functions of carbohydrates. In this work, the surface of a polypropylene microporous membrane (PPMM) was modified with comb-like glycopolymer brushes by a combination of UV-induced graft polymerization and surface-initiated atom-transfer radical polymerization (ATRP). 2-Hydroxyethyl methacrylate (HEMA) was first grafted to the PPMM surface under UV irradiation in the presence of benzophenone and ferric chloride. ATRP initiator was then coupled to the hydroxyl groups of poly(HEMA) brushes. Surface-initiated ATRP of a glycomonomer, D-gluconamidoethyl methacrylate, was followed at ambient temperature in aqueous solvent. Water had a significant acceleration effect on the ATRP process; however, loss of control over the polymerization process was also observed. The addition of CuBr2 to the ATRP system largely increased the controllability at the cost of the polymerization rate. The grafting of HEMA, the coupling of ATRP initiator to the hydroxyl groups, and the surface-initiated ATRP were confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.     

电化学方法构筑直结型卟啉高分子

利用电化学方法成功地合成了不含其它连接基团的卟啉高分子,循环伏安图谱中发现该高分子在电极上的沉积为紧密型沉积,所得产物的紫外-可见吸收光谱表明相邻的卟啉环在该高分子链中均成平面直角结构,FT-IR图谱表明卟啉环之间是通过C-C键在meso位上相连,质谱图证明该高分子的链长可以达到13个卟啉环以上。