Modification of carbon nanotubes with well-controlled fluorescent styrene-based polymers using the Diels-Alder reaction

A simple and single-step “grafting to” approach based on the Diels-Alder (DA) reaction is described to functionalize multi-wall carbon nanotubes (MWCNTs) with polystyrene (PSt). Thus, several fluorescent and furfuryl functionalized PSts, synthesized by the atom transfer radical polymerization (ATRP) of styrene, furfuryl methacrylate and low proportion of a fluorescent monomer, were covalently attached onto the pristine nanotubes. Furfuryl (diene) groups allowed the chemical attachment of the PSt polymer onto the as-synthesized MWCNTs by a DA reaction. On the other hand, the incorporation of fluorescent groups in the polymer has two main advantages. It permits to determine the attachment of the polymer onto the nanotubes and, in further applications, it will allow to follow the dispersion of these modified MWCNTs in a matrix. The efficiency of the functionalization was verified by FTIR, Raman spectroscopy, TEM, AFM and fluorescence techniques.     

Rigid-chain polyesters grafted with flexible-chain vinyl polymers

The concept of “molecular reinforcement” has been advanced, in the last decade, as an alternative to conventional fibre reinforcement of thermoplastics: In blends with normal (flexible-chain) thermoplastics, rigid chains of main-chain LC polymers (PLC) can act as strengthening fibres on the molecular scale. However, the rigid PLC chains must be well dispersed which is improbable since PLC and normal polymers are usually incompatible. A related concept is “micellar reinforcement”: Graft copolymers made of a rigid-chain PLC backbone and flexible-chain grafts can form a microphase morphology of cylinderic micelles where the PLC chains act as reinforcing fibres on a micellar scale. Such rigid-flexible graft copolymers are discussed in this study. They were pepared from a polyester of terephthaloyl, dihexoxyterephthaloyl and phenylhydroquinone moieties with special comonomer units carrying a double bond onto which styrene was grafted via radical copolymerisation. Grafting occurred with high efficiency, leading to products with the desired morphology of cyclindric micelles.     

Mechanism of alkali-thickening of acid-containing emulsion polymers. II. Examination of latexes with the light microscope

The mechanism of alkali thickening of acid-containing emulsion polymers has been confirmed by visual examination of the swelling and disappearance of latex particles with the light microscope. Specially prepared large particle-sized latexes were used in this study. Each latex was examined from 0%–200% neutralization with base. The particle swelling and dissolution behavior correlated with viscosity measurements, high viscosity being present for swollen particle systems and low viscosity for true solutions. The neutralized state of all acid-containing latexes can be pictured in a cube with the important variables being per cent acid, hydrophilicity of the comonomers, and T_g. At the bottom will be latexes only slightly affected by neutralization, above this will be a swollen particle zone, and the largest area will be a true solution zone. The true solution zone will be enlarged by lowering the molecular weight of the latex polymer.     

Crosslinking systems and film properties for surfactant-free latexes based on anhydride-containing polymers

In this paper, we report novel crosslinking systems for surfactant-free artificial latexes based on anhydride-containing polymers. Surfactant-free latexes with average particle diameters of about 150 nm and a ζ-potential of −70 mV have been successfully obtained from anhydride-containing polymers with various T_gs and polarities, including poly(octadecene-alt-maleic anhydride) (POMA) and maleinized polybutadiene (PBDMA). When adipic dihydrazide (ADH), a water-soluble crosslinker, was added to these latexes, no differences in particle size or ζ-potential were found; the presence of ADH did not affect the latex stability. In contrast, when 1,6-diaminohexane (DAH) was added to these latexes, it was found to interact with the polymer particles, indicated by a decrease in absolute ζ-potential for the latex particles and even gelation in the case of POMA. From ¹H NMR and LC-MS studies, it has been shown that no free DAH was present after being added to the latex, while free, unreacted ADH was present in aqueous phase upon its addition to the latex. Kinetic studies revealed that irreversible imide formation between anhydride and ADH took place at temperatures of 90 °C and above. In comparison, DAH only formed imides with the copolymers at significantly higher curing temperatures, i.e. >130 °C. Furthermore, the film formation of these latexes was studied; for the different copolymer latexes, curing at temperatures above the T_g of the respective copolymers led to homogeneous film formation. These systems based on surfactant-free latexes crosslinked with ADH have displayed promising properties for future coating applications.     

Mechanism of alkali thickening of acid-containing emulsion polymers. I. Examination of latexes by means of viscosity

Viscosity-versus-pH relationships for a large number of methacrylic acid-containing emulsion polymers have been measured. The monomers chosen for this study were so selected because they represent synthesized latexes of high and low T_g and comparative hydrophilicity. These were styrene, methyl methacrylate, ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate. The postulated mechanism involved in the transition from an unneutralized latex particle to the neutralized species is accounted for in terms of varying degrees of particle swelling. In the limiting case, particle swelling is followed by complete solution of the polymer. The most important variables are the per cent methacrylic acid and the polymer T_g and hydrophilicity as determined by the comonomers present. The degree of particle swelling ranges from none for high styrene-containing latexes to high degrees of swelling followed by polymer solubilization for high ethyl acrylate-containing latexes.     

氢键酸性接枝聚硅氧烷的合成及应用

应用硅氢化反应将具有氢键酸性的间三氟甲基苯酚接枝在聚甲基氢硅氧烷上,合成了一种用于有机磷化合物检测的新型氢键酸性敏感材料,并通过IR、1HNMR、GPC和GC-MS进行表征.在此基础上,制备了声表面波(SAW)气体传感器,并对甲基膦酸二甲酯(DMMP)进行了检测,效果良好.     

表面接枝二分散聚合物的自洽场理论

建立了表面接枝多分散聚合物的自洽场理论.通过对二分散聚合物进行自洽场模拟,研究了排除体积参数对分子链密度分布的影响,考察了分子链的摩尔分数与自由端分布的关系并将模拟结果与强伸展理论进行了比较.通过计算分子链的链段密度分布和伸展轨迹,讨论了二分散聚合物分子链的伸展行为.     

Cytocompatibility of polymers grafted by activated carbon nano-particles

Carbon nano-structures find their application in bio-medicine. In this work we functionalized carbon nano-particles (CNPs) with nitrogen (amine) groups. The CNPs were then chemically grafted onto the surface of polyethyleneterephthalate (PET) and high density polyethylene (HDPE) previously treated (activated) in argon plasma. Transmission electron microscopy (TEM) was used for investigation of the size and form of reactivated CNPs. Chemical composition of the modified polymer surfaces was determined by Raman and X-ray photoelectron (XPS) spectroscopies and by an electrokinetic analysis (zeta potential) as well. Surface contact angle was measured by goniometry. Surface roughness and morphology of polymers grafted with CNPs was studied using atomic force microscopy (AFM). Adhesion and proliferation of vascular smooth muscle cells (VSMC) on CNPs grafted HDPE and PET surfaces were studied in vitro. TEM results show that CNPs aggregate in water solution. Successful grafting of CNPs on the HDPE and PET surfaces was proved by XPS and Raman spectroscopies (amorphous carbon in the form of sp² hybridization) and by AFM. CNPs grafting of polymer surfaces leads to a decrease of contact angle and also to a change in surface zeta potential. Grafting with CNPs has a positive effect on adhesion and proliferation of VSMC on polymers’ surface.     

Towards anti-corrosion coatings from surfactant-free latexes based on maleic anhydride containing polymers

We report on the film formation of surfactant-free, artificial latexes based on copolymers containing maleic anhydride. Different metallic substrates, such as aluminum, steel and magnesium alloys, were coated with three different latexes. A commercial polyester based coating was used as a comparative sample. Two of the latexes were based on polymer with a high T_g (resp. 100 and 130 °C), and one on a polymer with a T_g of −70 °C. The wetting of the substrates could be optimized by etching the metal substrate, acidic or alkaline, leading to homogenous film formation and improved adhesion. For aluminum substrates an alkaline pretreatment improved the adhesion with the polymer films, whereas for magnesium the acidic pretreatment improved the adhesion. Furthermore, acid pretreatment increased the corrosion resistance of the coated magnesium substrate, when compared to an alkaline pretreatment. The films formed from latex displayed comparable or better anti-corrosive properties when compared to the commercial polyester.     

Encapsulation of fillers with grafted polymers for model composites

Glass beads were encapsulated by grafted polymers: polybutylacrylate and polystyrene. Grafting was performed by the polymerization initiated from the particle surface with preliminary adsorbed polyperoxide initiator. Grafting procedure and properties of grafted film were studied using model substrates: powders, plates, and wafers by wetting technique and SEM. Conditions of grafting affect the film structure. They are porous, and due to some sort of pores the wetting liquid is able to penetrate into covering and reach the substrate. Model epoxy composites were prepared with covered glass beads. The coverings allowed a decrease of adhesion between the matrix and bead surface to detect acoustic emission caused by the debonding process. The dependence of debonding stress from covering the structure and nature was studied. © 1996 John Wiley & Sons, Inc.     

Barrier and adhesion properties of anti-corrosion coatings based on surfactant-free latexes from anhydride-containing polymers

We have successfully obtained surfactant-free latexes from anhydride-containing polymers, including poly(styrene-alt-maleic anhydride) (PSMA), maleinized polybutadiene (PBDMA), and poly(octadecene-alt-maleic anhydride) (POMA). Here we report barrier and adhesion properties of the coatings made from these surfactant-free latexes, which were crosslinked with adipic acid dihydrazide (ADH). The barrier property of these coatings was studied with electrochemical impedance spectroscopy in NaCl solutions on pretreated aluminum substrates. PSMA and PBDMA-based coatings demonstrated good barrier property, indicated by the absence of corrosion after 1-month immersion in NaCl solutions, which was comparable to that of a commercially available polyester coating. The polyester coating, however, was found to hydrolytically degrade when immersed in a NaCl solution, which was not observed for our latex-based coatings. The POMA-based coating showed inferior barrier property on un-pretreated aluminum, likely due to inhomogeneous film formation and poor adhesion to the substrate, but the adhesion could be improved by an alkali pretreatment of the substrate. In comparison, PBDMA and PSMA-based coatings showed much better adhesion toward the aluminum substrates. The anti-corrosion behavior appeared to be closely related to both the barrier and adhesion properties of the coatings on the metal substrate.     

Functional polymers supported on porous silica. II.Radical polymerization of vinylbenzyl chloride from grafted precursors

Vinylbenzyl chloride was chosen as a model monomer for grafting a functional polymer onto silica carrying radical active precursors, such as monomer, transfer agent or initiator, previously grafted onto silica via a suitable coupling agent. The grafting efficiency was studied as a function of the texture of the initial silica, the nature of the active precursor and the polymerization conditions. Evidence for grafting was obtained from FTIR and ²⁹Si CP-MAS NMR spectra, and the thickness of the grafted layer was estimated from surface area and porosimetry measurements. From molecular weight measurements of nongrafted polymer it can be deduced that there is a trend toward the elongated conformation of the grafted polymer. Attempts to separate the grafted polymer through digestion of the silica with HF, failed to give a soluble linear polymer except when the active precursor was a transfer agent; in the two other cases a crosslinked polymer with a low crosslink density was obtained, which kept the morphology of the initial silica.     

Electrical properties of carbon-black grafted with polymers using an anionic catalyst

The polymer-grafted carbon black (GC) was prepared by an anionic polymerization of methyl methacrylate in the presence of carbon black previously treated with n-butyl lithium. The electrical properties of the resistors obtained using the GC material were studied. For a comparison with the above resistors, resistors with a smaller grafting ratio or without grafting were also prepared. It was found that the resistivity increased with an increase of the grafting ratio and that, by comparing resistors with similar resistivities, resistivity variation with temperature was less for higher grafting ratios. The resistors with a resistivity in the range of ca. 10³–10⁶ Ω·cm showed a remarkably large positive anomaly, but, for a resistivity larger than 10⁷ Ω·cm, the temperature coefficient was negative.     

Using dispersion/flocculation phase diagrams to visualize interactions of associative polymers, latexes, and surfactants

The colloidal interactions of associative polymers and latexes in the presence of surfactant are complex. This is because, in addition to good particle dispersion, both brid-ging and depletion flocculation can occur. Therefore, we have developed phase diagrams to help visualize these interactions. The various phases have a significant effect on coatings and applications properties. Examples of phase diagrams are presented for a model HEUR nonionic associative polymer and latexes in the presence of sodium dodecylsulfate. The major variables affecting phase behavior were found to be associative polymer concentration, latex particle size, latex surface hydrophobicity, and electrolyte, cosolvent, and surfactant concentrations. Presented at the PMSE Waterborne Coatings Symposium at the ACS Meeting, August 26–30, 2001, in Chicago IL. P.O. Box 904, Spring House, PA 19477-0904, E-mail: ekostansek@rohmhaas.com.     

Flame-retardant thermoplastics. I. Polyethylene–red phosphorus

Red phosphorus is a highly effective flame retardant for polyolefins. The low additive levels of red phosphorus in polyethylene make it an attractive route to nonhalogen flame-retardant systems. The mode of action of the red phosphorus has been investigated. Results indicate that the red phosphorus is effective both in the vapor and condensed phase. In the gas phase, PO species produced from the combustion of red phosphorus quench radical processes. In the condensed phase, the red phosphorus substantially lowers the heat of oxidation and traps radicals. This improved thermal stability results in a decrease in fuel production during burning.     

Synthesis of polyurethane/polyethylene grafted polymers using cyclotriphosphazene as a coupling agent

The reaction between a dihydroxyphenoxycyclotriphosphazene containing allylic functions, 3, and hexamethylene‐1,6‐diisocyanate (HDI) leads to a new cyclotriphosphazene‐substituted polyurethane 4. The structures of both classes of compounds involved in that synthesis were investigated by ³¹P‐, ¹³C‐, and ¹H‐NMR, infrared, and mass spectrometries, size‐exclusion chromatography, and elemental analysis. The thermal behavior of 4 was investigated and compared to that of hexaphenoxycyclotriphosphazene, N₃P₃(OC₆H₅)₆, and of a polyurethane synthesized from 1,3‐bis(hydroxy)benzene and HDI. The free‐radical‐promoted grafting of 4 onto the polyethylene surface is described. The resultant surface was studied by ATR–IR, XPS, and contact‐angle techniques. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1925–1934, 2003     

Solvent and temperature effects on chain conformations in interfaces of polymers grafted on silica. Study by H NMR

The ¹H NMR technique is used to study the behaviour of the poly(ethylene oxide) chains grafted chemically on silica in presence or not of solvent. A noticeable influence of the different physicochemical parameters on the conformation of the grafted macromolecules is evinced. The grafting ratio, the temperature, the solvent can all in well chosen situations modify the configurations of the chains. The macromolecules can lay flat on the surface, or be swollen and spread out. Depending on the conformations the dipolar interactions between monomer detected by NMR are different and inform on the behaviour of the chains. In particular a static contribution also called pseudo-solid effect is measured, which is an indication of the local concentration of segments in the vicinity of the surface.     

Polymerization of organic compounds in an electrodeless glow discharge. X. Internal stress in plasma polymers

Owing to the unique mechanisms operative in plasma polymerization, a thin layer of plasma polymer deposited on the surface of a substrate shows a tendency to expand, indicating an internal stress in the layer. This stress, σ_s, has been estimated from the observed curling of composite membranes in which the thickness of the plasma coating, d, is much smaller than the thickness of a flexible substrate, D, according to the relation where R is the radius of the roll into which the composite films curl up and E is the modulus of the substrate polymer. The stress σ_s is found to depend on the kind of monomer used and to be of the order of magnitude 10⁸–10⁹ dynes/cm² with most of the monomers here employed.     

Morphology of glassy polymers grafted onto polybutadiene in relation to monomer diffusivity and initiator solubility

The morphology of polybutadiene grafted in emulsion with vinylchloride, methylmethacrylate, styrene, was examined by transmission electron microscopy. The morphology depends on synthesis conditions. Solubility of initiators in the monomers or in water, diffusivity of monomers in the rubber and transfer mechanism during the polymerization were found to be important factors in determining the morphology. New experimental data of diffusion coefficients of the monomers in polybutadiene are given. A special technique was used for liquid VC diffusivity measurements.