Dispersants acid-functionalized polymers

Solution vehicles consist of water soluble polymers not manufactured by emulsion polymerization. The solution vehicle is an alkali soluble polymer in aqueous solution or a blend of polymers with combined properties into a single waterborne varnish. Soluble polymers are made by free radical polymerization in a processing solvent or as addition or condensation products with heat reaching temperatures up to 265 °C. Solution vehicles are mixtures of soluble resins unlike emulsion polymers. A solution vehicle is used to increase adhesion to film and improve ink printabihty or transfer to meet specific performance requirements. The solution vehicle provides pigment dispersion stabilization, transparency, low film forming temperature, gloss and re-solubility. An alkali soluble resin is a carboxylic acid functional polymer neutralized (solubilized) with ammonia, amine or sodium hydroxide. The add numbers are generally above 100. Ammonia or volatile amines are used in most aqueous inks except for news print inks. After evaporation of the amine, the resin becomes insoluble and resistant to water spray or other water contact. The ink is re-solubilized with alkaline water for the clean-up cycle. For news print ink, the polymers are solubiHzed with sodium hydroxide to maintain re-solubility (open time) of the ink on the press. News print ink pressman prefer unlimited open time and fewer clean-up cycles. Water resistance is not required since ink penetrates the news print paper fibers. 

The polymers are usually applied either from aqueous or from organic solvent. More recently, aqueous dispersions or redispersible powders of the polymers have become available that ensure economical, fast, and environmentally safe processing of the film coatings. In some cases it might be necessary to prevent an interaction between the acidic functional groups and the drug. In these cases a subcoat (e.g., of hydroxypropylmethylcellulose [HPMC]) is recommended. 

A number of studies on CNT-polymer composites have focused on improving the dispersion and load transfer efficiency in other words the compatibility between the CNTs and polymer matrix through covalent chemical functionalization of CNT surface (12,40). Many of the studies reported above have used acid-functionalized CNTs to fabricate MWCNT-PMMA composites with improved mechanical properties using different processing methods (24,25,27,62). Yang et. al (68) modified the acid functionalized CNTs with octadecylam-ine (ODA) to obtain ODA-functionalized CNTs. These CNTs were reinforced in a copolymer P(MMA-co-EMA) to form composites with improved dispersion and mechanical properties. 

An electrochemical method projected for the determination of the effective volume of a colloidally dispersed polyelec-trolyte phase in aqueous media was evaluated. Experiments with the highly flexible Sephadex (carboxymethyldextran) gel and the more rigidly cross-linked polymethacrylic acid resin were performed for this purpose. With the well-defined resin (gel) phase it was possible to measure the polymer volume as a function of every experimental condition used to test fully the fundamental concepts on which the method is based. The results substantiate the validity of concepts developed. Application of this method for estimating the effective volume of weakly acidic (basic) polymers in solution seems worthy of further consideration. However, some modification of the treatment of the electrochemical data is necessary for polymeric sols, and this aspect is discussed briefly. 

Solubilizable Dispersions (19). The chemistry of solubilizable acrylic dispersions is a hybrid of emulsion and water-reducible technology. These polymers are synthesized by emulsion techniques but contain acidic or basic functionality that renders them water soluble upon neutralization with an appropriate titrant. For example, if the solubilizing functionality is acidic, the polymer will behave like an emulsion below a certain critical pH range, like a highly swollen emulsion within the critical pH range, and like a true water-soluble polymer at sufficiently high pH values. Such polymers offer a favorable balance of properties for many coating applications. 

The main difficulties related to electropolymerization processes have been ruled out, and theoretically, no metal specificity is involved in the procedure which could restrict the application, except the case of PANI whose acidity properties can conflict with different metal oxides, as previously stated in Section 16.2. The main problem lies in the fact that all the conducting polymers are generally insoluble and, therefore, mixing them with paint will involve either the fabrication of particle dispersions or functionalization of the polymer in order to make it soluble in an organic solvent. Initially centred on PANI formulations, the process has been progressively extended to other conducting polymers like PPy, PT, and their derivatives. 

The chemical structure of studied polymers is shown in Fig. 2. Three different types of functionalized polymers have been investigated. In the first case (DRGMMA) the copolymer has been got by free radical polymerization of a 1 1 molar ratio mixture of methyl methacrylate and 4 -(N-ethyl-N-(methacryloxyethyl)amino)-4-nitroazobenzene obtained by esterification with methacrylic acid of commercially available Disperse Redttl. It corresponds to... 

Precipitation into submicron-sized particles is another direct approach. Precipitation by pH shifting can be an effective approach for dyes that have weak acid functionality. A number of different families of such dyes have been dispersed by acidification of weakly alkaline dye solutions, in the presence of stabilizers such as surfactants and polymers. Alternatively, solvent shifting has been demonstrated to be an effective method of preparing absorber dye dispersions. Recent work by Brick et al. (14) has shown how such dyes can be very effectively precipitated from a variety of water-miscible organic solvents. Finally, another approach for incorporation of absorber dyes is to precipitate or condense them on the surface of a high-surface-area carrier species, such as colloidal silica. Such preparations can be prepared by pH- and solvent-shifting processes, in the presence of the carrier particles. 

For carbon nanotubes, discussed in detail in Chapter 10, conductivity is achieved at lower loadings (by weight) but these materials are difficult to disperse in molten polymers. Methods of surface functionalization and lower cost manufacturing must be developed before carbon nanotubes will find wider use as conductive fillers [52, 53]. As an alternative to nanotubes, Fukushima and Drzal [54] have observed conductivity thresholds of less than 3 vol% in composites containing acid-etched or othervdse functionalized exfoliated graphite. These composites retain or improve upon their mechanical properties compared to other carbon-filled polymers. 

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