Ionic comonomers

For this reaction, soluble monomers are needed, e.g. a mixture of N AT-methylene bisacrylamide as crosslinker, methacrylamide as an inert comonomer, methacrylic acid as ionic comonomer for stabilization [309] and methacryl ami-do-AT-acetaldehyde-dimethylacetal as functional comonomer. The coupling with proteins is only possible if the free aldehyde groups are accessible, i.e. if they are not located in the interior of the microgel. This condition can only be fulfilled by a careful choice of the comonomer composition in the reaction mixture [291]. 

Emulsifier-free latices are useful not only for industrial purposes but also for studies on colloidal properties (1, 2) and medical applications (3, h). Various methods have been tried to prepare characteristic emulsifier-free latices (5-8). Among them, copolymerization of hydrophobic monomers with hydrophilic comonomers has been the most applicable one (7, 8). There have been many studies on the effects of ionic comonomers on the kinetics of aqueous copolymerization and the properties of the resulting latices, but nonionic hydrophilic comonomers have rarely been used for these purposes. 

This paper deals with the copolymerization of styrene with acrylamide and its derivatives in emulsifier-free aqueous media. It is expected that the effects of acrylamides on the nucleation and stabilization of particles differ from those of ionic comonomers. The reaction mechanism, the characteristics of the latices prepared, and the effect of the properties of acrylamides on them are discussed. 

For different applications, water-soluble neutral and ionic comonomers can be incorporated into or attached to the PNIPAM chain backbone to form amphiphilic PNIPAM copolymers via free-radical copolymerization. In this section, we will use the folding of neutral PNIPAM amphiphilic copolymer chains in extremely dilute solutions ( pg/mL) to illustrate a general feature of the folding of hydrophilically modified copolymer chains. 

Using this approach, hydrophilic (neutral or ionic) comonomers, such as end-captured short polyethylene oxide (PEO) chains (macromonomer), l-vinyl-2-pyrrolidone (VP), acrylic acid (AA) and N,N-dimethylacrylamide (DMA), can be grafted and inserted on the thermally sensitive chain backbone by free radical copolymerization in aqueous solutions at different reaction temperatures higher or lower than its lower critical solution temperature (LCST). When the reaction temperature is higher than the LOST, the chain backbone becomes hydrophobic and collapses into a globular form during the polymerization, which acts as a template so that most of the hydrophilic comonomers are attached on its surface to form a core-shell structure. The dissolution of such a core-shell nanostructure leads to a protein-like heterogeneous distribution of hydrophilic comonomers on the chain backbone. 

Polyester fibers can be given an additional mechanism for dyeing if an ionic comonomer is added during polymerization. A common additive is an alkali metal salt of dimethyl-5-sulfo-isophthalate, which gives sulfonic (anionic) groups as part of the polymer structure. These groups allow the fiber to absorb... 

PAN, a synthetic fiber, is a polymer of acrylonitrile monomers. Worldwide, 2.73 million tons of PAN are produced per year, of which over 98% are processed as filament yarn serving as material in the textile industry (Tauber et al., 2000). PAN usually has a molecular weight of 55,000-70,000 g mol and is most commonly a copolymer produced by radical polymerization from acrylonitrile, 5-10 mol% vinyl acetate (or similar nonionic comonomers) to disrupt the regularity and crystallinity, and ionic comonomers, such as sulfuric or sulfonic acid salts. PAN is a hydrophobic polymer that affects the processability of the fibers. The surface is not easily wetted. 

Multistage polymerizations These methods include the deferred addition of an ionic comonomer (constituting the basic latex), favoring a highly efficient surface functionalization. 

KUN Kunugi, S., Yamazaki, Y., Takano, K., and Tanaka, N., Effects of ionic additives and ionic comonomers on the temperature and pressure responsive behavior of thermoresponsive polymers in acpieous solutions, Langmuir, 15,4056, 1999. 

Another way to obtain the desired dense-coagulated fiber structure is to add an ionic comonomer to the chain. Terada [269] has used mercury porosimetry to follow the change in the microvoid size distribution that occurs when comonomers of differing polarity and ionic structure are added to PAN. When hydrophobic comonomers such as methyl acrylate (MA) are used, the peak of the pore size distribution is shifted in the direction of increased size. However, ionic comonomers such as SSS or sodium allyl sulfonate (SAS) shift the peak in the direction of decreased size. With a three-component composition containing both the hydro-phobic and ionic comonomers, as in poly(AN-MA-SAS), the distribution has both characteristics. Examples of void size distributions are shown in Figure 12.27. The 5% MA comonomer has a fairly sharp peak near 850 A and the maximum size is extended to 200 A. Moreover, there is only a slight proportion of pores with small sizes present. 

The 1% SA copolymer shows two broad peaks near 300 and 55 A. Other void size characterization methods were used to confirm these results and show that the effect also carries over into the fibers that have gone through the orientational drawing step. These results suggest that the use of ionic comonomers could lead to improved fiber properties. 

The presence of the ionic comonomer influences the drawing behavior [276]. The copolymers containing nonionic comonomers such as AN-methyl acrylate display a moderate decrease in the mercury density upon drawing, but a proportionately larger increase in the internal surface area gives rise to a reduction in the fibril diameter and microvoid size. The... 

We developed a synthesis of monodisperse, highly charged colloidal particles of PNIPAM whose diameter depends on temperature (76). NIPAM was polymerized with the ionic comonomer 2-acrylamido-2-methyl-l-propane sulfonic acid to increase the colloid surface charge which facilitates CCA self-assembly. Figure 4 shows the temperature dependence of the colloidal sphere diameter, which increases from -100 nm at 40°C to -300 nm at 10 C. 

The most widely used theory of the stability of electrostatically stabilized spherical colloids was developed by Deryaguin, Landau, Verwey, and Overbeek (DLVO), based on the Poisson-Boltzmann equation, the model of the diffuse electrical double layer (Gouy-Chapman theory), and the van der Waals attraction [60,61]. One of the key features of this theory is the effective range of the electrical potential around the particles, as shown in Figure 25.7. Charges at the latex particles surface can be either covalently bound or adsorbed, while ionic initiator end groups and ionic comonomers serve as the main sources of covalently attached permanent charges. 

Materials possessing charged surfaces include almost all of the inorganic oxides and salts of technological importance (silica, alumina, titania, etc.), the silver halides, latex polymers containing ionic comonomers, and many natural surfaces such as proteins and cellulosics. It is very important, therefore, to understand the interactions of such surfaces with surfactants or other adsorbates in order to optimize their effects in such applications as paint and pigment dispersions, papermaking, textiles, pharmaceuticals, and biomedical implants. 

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