Evidence of sidewall covalent functionalization of single-walled carbon nanotubes and its advantages for composite processing

Single-walled carbon nanotubes (SWCNTs) were functionalized in a three-step procedure. The first step is a radical reaction creating a covalent bond between the carbon nanotube surface and grafted p-methoxyphenyl functional groups. In a second step, a deprotection of the methoxy functions generates free alcohol groups and in the final step an esterification is done in order to install a double bond for further polymerization. Evidence that functionalization has actually occurred on the SWCNT sidewalls is furnished through investigations involving several complementary techniques (visual dispersion tests, transmission electron microscopy, thermal gravimetric analysis and adsorption volumetry). We show that surface properties of SWCNTs are changed throughout the chemical treatments and that the obtained level of functionalization is low. Incorporation of functionalized SWCNTs in a polymer (poly(methyl methacrylate)) matrix was done through an in situ polymerization process. Observations of the obtained composites using scanning and transmission electron microscopy illustrate that interactions between the SWCNT surface and the polymer matrix are improved.     

Facile synthesis of magnetic nanoparticle–coated single‐walled carbon nanotubes and its functional modification in epoxy resin

Magnetic single‐walled carbon nanotubes (SWCNTs) were synthesized in a process consisting of two steps: (a) covalent in situ polymerization and grafting of poly (acrylic acid) (PAA) on the surface of SWCNTs, followed by (b) thermal decomposition of ferric triacetylacetonateto produce magnetite nanoparticles on the PAA‐grafted SWCNTs. It was demonstrated that magnetic nanoparticle–coated SWCNTs dispersed in water by sonication would respond to an external magnetic field. On such functionalization, the reorientation of SWCNTs in an epoxy matrix could be produced using a magnet. This endowed the composites with desirable magnetic and mechanical properties. POLYM. COMPOS., 31:2035–2041, 2010. © 2010 Society of Plastics Engineers     

Improvement single-wall carbon nanotubes (SWCNTs) based on functionalizing with monomers 2-hydroxyethylmethacryate (HEMA) and N-vinylpyrrolidone (NVP) for pharmaceutical applications as cancer therapy

The functionalized carbon nanotubes play significant roles in the fields such as preparation of composite materials and biological technologies. This paper explains the covalent functionalization of single-wall carbon nanotubes (SWCNTs) with biomedical important monomers, 2-hydroxyethylmethacryate (HEMA) and N-vinylpyrrolidone (NVP) by chemical grafting of HEMA and PVP monomers via free radical polymerization. To get carboxylic acid functionalized SWCNTs, first the nanotubes were oxidized with a mixture of nitric acid and sulfuric acid (1:3). Then, the binding of HEMA and NVP onto the surface of SWCNTs was performed by chemical functionalization of HEMA, NVP with acid chloride-bound carbon nanotube by esterification reaction. These results were confirmed by FT-IR and SEM. The cell culture experiments conducted for pharmaceutical applications were used as cancer therapy.     

Raman spectroscopic evidence for interfacial interactions in poly(bithiophene)/single-walled carbon nanotube composites

Electrochemical polymerization of 2,2′-bithiophene (BTh) on single-walled carbon nanotube (SWCNT) films has been studied by Raman scattering and infrared absorption spectroscopy. Covalent functionalization of SWCNTs with poly(bithiophene) (PBTh) in its un-doped and doped states is demonstrated. The occurrence of a charge transfer process at the interface of PBTh and SWCNTs, is shown by: (i) an up-shift of the Raman lines associated with the radial breathing modes of SWCNTs that reveals both a doping process and an additional twisting together as a rope with the conducting polymer as binding agent; (ii) a new Raman band in the range 1430-1450 cm⁻¹ indicating the functionalization of SWCNTs with PBTh in doped and un-doped states; (iii) strong absorption bands situated in the interval 600-800 cm⁻¹ resulting from steric hindrance produced by the nanotube binding to the polymeric chain. Treatment of the PBTh/SWCNT composite with aqueous NH₄OH solution forms un-doped PBTh covalently functionalized SWCNTs. At the resonant excitation of the metallic tubes, an additionally enhanced Raman process is generated by plasmon excitation in the metallic nanotubes. It is evidenced by a particular behavior in the Stokes and anti-Stokes branch of the PBTh Raman line at 1450 cm⁻¹.     

Soft Immobilization of Proteins onto Single-Walled Carbon Nanotubes through Nickel Complexed Nitrilotriacetic Acid-End Functionalized Polystyrenes

We describe the immobilization of histidine-tagged green fluorescent protein (His₆-GFP) specifically and reversibly onto single-walled carbon nanotubes (SWCNTs) using nickel complexed nitrilotriacetic acid-end functionalized polystyrene (Ni-NTA-PS) by conjugation between the protein and the polymer in phosphate buffer solution (PBS). We synthesized Ni-NTA-PS by atom transfer radical polymerization (ATRP) using a nitrilotriacetic acid (NTA) initiator. The SWCNTs were dispersed in PBS along with Ni-NTA-PS and His₆-GFP aided by sonication. The diameter of the dispersed SWCNTs was measured by transmission electron microscope (TEM). The immobilization of His₆-GFP and dispersion of SWCNTs were controlled by addition of excess imidazole. It was found that the immobilized His₆-GFP was more stable than free His₆-GFP in organic solvent (PBS/DMF, 1/1, v/v).     

VAc聚合过程工艺条件对链支化的影响

研究了以甲醇为溶剂、偶氮二异丁腈(AIBN)为引发剂的VAc聚合过程,通过比较醇解前后PVAc和PVA聚合度的变化研究过程参数如溶剂、引发剂量和分段加入方式以及反应时间对PVAc链支化程度的影响。结果表明,在溶剂总量为20%(wt)、引发剂总量为0.00013%~0.0013%范围内,分段加入引发剂使PVAc链支化程度增加,醇解后PVA聚合度与PVAc聚合度相比有所下降;过低的引发剂浓度虽然可以获得比较高的PVAc聚合度,但醇解后的PVA聚合度相比PVAc下降可达27.0%。在引发剂总量为0.000 63%情况下分批加入溶剂,在合适的反应时间内可控制PVAc支链化程度,缩小PVAc和PVA聚合度的差异并获得相对较高PVA聚合度。无论是一次性加入溶剂或分段加入溶剂,过长的反应时间都使PVAc的支链化程度增加,醇解后PVA聚合度与PVAc聚合度相比差异增大。     

Thiol-ene “clickable” carbon-chain polymers based on diallyl cyclopropane-1,1-dicarboxylate

A novel type of clickable polymers with a very high local density of allyl side groups was developed. These polymers were obtained by the anionic ring-opening (co)polymerization of diallyl cyclopropane-1,1-dicarboxylate using as an initiating system a protic precursor whose acid–base reaction with the t-BuP₄ phosphazene base generated the initiator in situ. The obtained polymers display geminated allyl groups on every third carbon alongside the macromolecular backbone. Homopolymers as well as block and statistical copolymers have been synthesized, with controlled molecular weights and narrow molecular weight distributions. The coupling of mercaptans with the allyl CC double bonds has been investigated both thermally and photochemically, with the influence of the type of initiation on the efficiency of the polymer modification being discussed in comparison with other “clickable” systems. Further functionalization by several thiols was performed, leading to a range of functional poly(cyclopropane-1,1-dicarboxylate)s.     

The synthesis of covalent bonded single‐walled carbon nanotube/polyvinylimidazole composites by in situ polymerization and their physical characterization

Single‐walled carbon nanotube (SWCNT) polyvinylimidazole (PVI) composites have been prepared by in situ emulsion polymerization. Dispersion of raw SWCNTs in the PVI matrix was improved by surface modification of the SWCNTs using nitric acid treatment and air oxidation. The carbonyl‐terminated SWCNTs were covalently bonded to PVI by in situ polymerization and the SWCNT/PVI composite was thus obtained. The morphological and structural characterizations of the surface‐functionalized SWCNTs and SWCNT/PVI composites were carried out by Fourier transform infrared spectroscopy, X‐ray diffraction, conductivity measurements, scanning, and transmission electron microscopy. Thermograms of the materials were determined by the differential scanning calorimetry technique. The characterization results indicate that PVI was covalently bonded to SWCNTs and a new material was then obtained. The functionalized SWCNTs showed homogenous dispersion in the composites, whereas purified SWCNT resulted in poor dispersion and nanotube agglomeration. SWCNT/PVI composites exhibited chemical stability enhancement in many common solvents. I–V curves of the samples exhibit an ohmic character. Conductivity values for pure SWCNTs, pure PVI and SWCNT/PVI composite were measured to be 3.47, 2.11 × 10⁻⁹, and 2.3 × 10⁻³ S/m, respectively. Because of resonance, a large dielectric constant is obtained for SWCNT/PVI composite, which is not observed for ordinary materials. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Continuous Dosing of a Fast Initiator during Suspension Polymerization of Vinyl Chloride for Enhanced Productivity: Mathematical Modeling and Experimental Study

An adopted mathematical model was developed to reduce the batch time required for the suspension polymerization of vinyl chloride in order to improve the productivity by continuous dosage of a fast initiator during polymerization reaction. The model was accompanied by a particle swarm optimization (PSO) algorithm, so as to optimize the initiator dosage rate during the process for a certain conversion. A pilot scale reactor was employed to verify the mathematical model predictions. This showed that the model predictions are in very good agreement with the experimental data. A proper initiator dosage trajectory during the course of the reaction was obtained in such a way that the reaction rate over the course of polymerization was constant and corresponded to the maximum rate in the conventional case (non-continuous addition of a mild initiator). The maximum reduction in reaction time relative to conventional polymerization for the predefined conversion was 53%. Analyzing the molecular characteristics of the samples showed that the molecular characteristics of the final poly(vinyl chloride) (PVC) product remained relatively unchanged under an optimum initiator dosage trajectory compared with the conventional process.     

Electrical conductivity and tensile properties of block‐copolymer‐wrapped single‐walled carbon nanotube/poly(methyl methacrylate) composites

Poly(methyl methacrylate) (PMMA) composites containing raw or purified single‐walled carbon nanotubes (SWCNTs) are prepared by in situ polymerization and solution processing. The SWCNTs are purified by centrifugation in a Pluronic surfactant, which consists of polyethyleneoxide and polypropyleneoxide blocks. Both the effects of SWCNT purity and non‐covalent functionalization with Pluronic are evaluated. Electrical conductivity of PMMA increases by 7 orders of magnitude upon the integration of raw or purified SWCNTs. The best electrical properties are measured for composites made of purified SWCNTs and prepared by in situ polymerization. Strains at fracture of the SWCNT/PMMA composites are nearly identical to those of the neat matrix. A certain decrease in the work to fracture is measured, particularly for composites containing purified SWCNTs (?31.6%). Fractography and Raman maps indicate that SWCNT dispersion in the PMMA matrix improves upon the direct addition of Pluronic, while dispersion becomes more difficult in the case of purified SWCNTs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41547.     

乳液法AES的研究

以歧化松香酸钾为乳化剂，过硫酸钾为引发剂，乳液接枝法合成了三元乙丙橡胶-丙烯腈-笨乙（AES）．测定了反应条件时乳胶粒直径分布、接枝率、接枝效率的影响。结果表明，该聚合体系为常规乳液聚合，而不是细乳液聚合；引发剂浓度上升．乳胶粒直径下降，但对接枝率和接枝效率影响不明显；所得AES树脂的力学性能指标优良。     

Modification of Polychloroprene Rubber Latex by Grafting Polymerization and Its Application as a Waterborne Contact Adhesive

Grafting of methyl methacrylate (MMA) onto polychloroprene rubber latex (CRL) was carried out by emulsion polymerization using a redox initiator. The effects of the principal factors such as emulsifier, initiator and their concentrations and monomer/polymer ratio on monomer conversion, and grafting efficiency were studied. Infrared (FTIR) spectra, proton nuclear magnetic resonance (HNMR), and differential scanning calorimetry (DSC) analysis of the graft copolymer showed the occurrence of grafting. The surface-diffusion controlled process model was proposed to describe the grafting mechanism. The graft copolymer was blended with tackifier and filler for waterborne contact adhesive applications. The 180 degree peel strength of the above adhesive for canvas to other decoration materials was investigated.     

Preparation of polymeric microcapsules enclosing microbial cells by radical suspension polymerization via water-in-oil-in-water emulsion

Polymeric microcapsules enclosing Saccharomyces cerevisiae were prepared by radical suspension polymerization via water-in-oil-in-water emulsion. Trimethylolpropane trimethacrylate and 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) were used as monomer and radical initiator, respectively. A culture medium with suspended yeast cells, monomer solution with the dissolved radical initiator, and poly(vinyl alcohol) aqueous solution were used as inner aqueous phase, oil phase, and outer aqueous phase, respectively. The influence of microcapsule preparation parameters on the viability of encapsulated cells and encapsulation efficiency was investigated. The radical polymerization process did not cause significant damage to encapsulated yeast cells. Decreased weight ratio of aqueous phase to oil phase resulted in increased encapsulation efficiency of the cells. The diameter of the microcapsules could be controlled by varying the agitation rate.     

Radical thermo‐ and sonopolymerization of methyl methacrylate initiated by iodobenzene 1,1‐diacetate

The efficiency of iodobenzene 1,1‐diacetate or (diacetoxyiodo)benzene (DAIB) as a thermo‐ and sono‐initiator of methyl methacrylate (MMA) in radical bulk polymerization is tested. The polymerization kinetics and molecular‐mass characteristics support an assumption for a combined polymerization mechanism including a classical bimolecular termination with chain transfer reaction and iniferter quasi‐living polymerization. In addition to the equilibrium formation and degradation of the ‘dormant’ polymer ends, other possible decomposition reactions of the hypervalent iodine bond are the probable reason for the deviation of this polymerization from the iniferter polymerization mechanism. These reactions bear some similarity to the two‐step addition–fragmentation chain transfer mechanism of controlled radical polymerization. The application of the poly(MMA) obtained as a macroinitiator is evidence of ‘dormant’ chain end formation. © 2001 Society of Chemical Industry     

High-efficiency synthesis of dendrimer-like poly(ethylene oxide) via “arm-first” approach

In this study, a dendrimer-like polymer based on poly(ethylene oxide) (PEO) was synthesized through a combination of anionic ring-opening polymerization (AROP) and click reaction via arm-first method. Firstly, the polymeric arm, a linear PEO with one alkynyl group and two bromo groups, was synthesized by AROP of ethylene oxide followed by functionalization with propargyl bromide and esterified with 2-bromopropionic bromide. Second, a star PEO carrying three azide groups was synthesized though AROP of ethylene oxide used 1,1,1-tris(hydrosymethyl) ethane as initiator followed esterificated with 2-bromopropionic acid and azidation. By azide–alkyne click reactions between the azide-terminated PEO star polymer and linear PEO with functionalization alkynyl group, a three generation dendrimer-like PEO, G3-PEO-24Br, was successfully synthesized. The resulting polymers were observed to have precisely controlled molecular weights and compositions with narrow molecular weight distributions.     

Primary amine functionalized polystyrenes by atom transfer radical polymerization

Primary amine functionalized polystyrenes were prepared in quantitative yields by atom transfer radical polymerization using the adduct of 1‐(bromoethyl)benzene with 1‐(4‐aminophenyl)‐1‐phenylethylene as initiator for styrene polymerization in the presence of a copper(I) bromide/N,N,N′,N′,N″‐pentamethyldiethylenetriamine catalyst system. The polymerizations proceeded via a controlled free radical polymerization process to afford quantitative yields of the corresponding primary amine functionalized polystyrenes with predictable molecular weights (M_n = 2 × 10³ to 10 × 10³ g mol^?1), relatively narrow molecular weight distributions (M_w/M_n = 1.03–1.49), well defined chain‐end functionalities and initiator efficiencies as high as 0.92. The polymerization process was monitored by gas chromatographic analysis. The primary amine functionalized polymers were characterized by thin layer chromatography, size exclusion chromatography, potentiometry and spectroscopy. Experimental results are consistent with quantitative functionalization via the 1,1‐diphenylethylene derivative. Polymerization kinetic measurements show that the polymerization reaction follows first order rate kinetics with respect to monomer consumption and the number average molecular weight increases linearly with monomer conversion. © 2003 Society of Chemical Industry     

Nitroxide-mediated polymerization of styrene initiated from the surface of fumed silica. Comparison of two synthetic routes

Nitroxide-mediated free radical polymerization of styrene was performed from 13 nm diameter fumed silica in two steps. First, an alkoxyamine, based on N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide (DEPN) was covalently attached onto silica. Polystyrene chains with controlled molecular weights and narrow polydispersities were then grown from the alkoxyamine-functionalized nanoparticles surface in the presence of a ‘free’ sacrificial styrylDEPN alkoxyamine. Two strategies were investigated in order to immobilize the alkoxyamine initiator on the silica surface. In a first route, we synthesized a unimolecular alkoxyamine initiator carrying triethoxysilyl end groups reactive towards the silica surface. In a second route, the alkoxylamine was formed in situ by the simultaneous reaction of a polymerizable acryloxy propyl trimethoxysilane (APTMS), azobisisobutyronitrile (AIBN) and DEPN used as radical trap. In both cases, the grafting of both the initiator and the polystyrene chains was characterized and quantified by several techniques which allowed us to evaluate and compare the two strategies.     

Atom transfer radical bulk polymerization of methyl methacrylate under microwave irradiation

Microwave irradiation (MI) was applied to the atom transfer radical bulk polymerization of methyl methacrylate. The influence of the amount of the refluxing solvent used for controlling the polymerization temperature, irradiation power, irradiation time, and initiator concentration on the conversion, molecular weight, and molecular weight distribution of the polymers was studied with a benzyl chloride/cuprous chloride/2,2′‐bipyridyl initiation system and compared with the corresponding conventional heating (CH) process. In comparison with CH, the results can be summarized as follows. The polymerization rate for reaching 70% conversion increased 2.6–5.1 times under an irradiation power of 270–630 W. The apparent increasing rate constant was much larger than that with CH and increased with the irradiation power. MI produced a higher polymerization rate and conversion even if the concentration of the initiation system was very low (initial monomer concentration/initial initiator concentration = 200:0.33 mol/mol) and the polydispersity index (DI) was narrower; however, CH yielded almost no polymers. MI promoted the activities of the catalyst and monomer, and its initiation efficiency was higher than that with CH and increased with the irradiation power. MI obviously played an important role in promoting the polymerization rate of atom transfer radical polymerization (ATRP). MI reduced the concentration of the initiation system and perhaps made ATRP controlled (cf. uncontrolled ATRP with CH); at the same time, it made the DI values of the polymers narrower. In comparison with the initiation efficiencies found with benzyl bromide and 2,2′‐azobisisobutyronitrile used as initiators, the initiation efficiency with p‐toluene sulfonyl chloride used as an initiator was higher; moreover, DI was much narrower (1.17), and the polymerization rate was greater. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1787–1793, 2003     

Thermal polymerization of styrene in the presence of TEMPO

To investigate aspects of the contribution of (thermal) self-initiation in nitroxide-mediated radical polymerization (NMRP) of styrene, selective styrene polymerizations with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) in the absence of initiator were carried out at 120 and 130 °C. The results of these experiments (including conversion data, molecular weight averages, polydispersity and molecular weight distribution information) were compared with regular thermal polymerization of styrene and NMRP of styrene in the presence of a bimolecular initiator (benzoyl peroxide; BPO). It was observed that although the thermal polymerization of styrene can be controlled to some extent in the presence of TEMPO to provide polystyrene with low polydispersity, the polymerization was never as controlled as that obtained by a BPO-initiated NMRP.     

Fe‐mediated ARGET atom transfer radical polymerization of methyl methacrylate in ionic liquid‐based microemulsion

Poly(methyl methacrylate) (PMMA) was synthesized by activator regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) of MMA in ionic liquid‐based microemulsion with polyoxyethylene sorbitan monooleate (Tween 80) as surfactant. The polymerization was carried out at 25°C with CCl₄ as initiator, FeCl₃·6H₂O/N,N,N′,N′‐tetramethyl‐1,2‐ethanediamine (TMEDA) as catalyst complex in the presence of reducing agent ascorbic acid (VC). The polymerization kinetics showed the feature of controlled/″living″ process as evidenced by a linear first‐order plot. The well‐controlled polymers were obtained with narrow polydispersity indices and the ionic liquid‐based microemulsions were transparent with a particle size less than 30 nm. The obtained polymer was characterized by ¹H NMR and gel permeation chromatography. The chain extension was successfully achieved by the obtained PMMA macroinitiator/FeCl₃·6H₂O/TMEDA/VC initiator system based on ARGET ATRP method. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013