Hydrophilic comonomer

For the characterization of Langmuir films, Fulda and coworkers [75-77] used anionic and cationic core-shell particles prepared by emulsifier-free emulsion polymerization. These particles have several advantages over those used in early publications First, the particles do not contain any stabihzer or emulsifier, which is eventually desorbed upon spreading and disturbs the formation of a particle monolayer at the air-water interface. Second, the preparation is a one-step process leading directly to monodisperse particles 0.2-0.5 jim in diameter. Third, the nature of the shell can be easily varied by using different hydrophilic comonomers. In Table 1, the particles and their characteristic properties are hsted. Most of the studies were carried out using anionic particles with polystyrene as core material and polyacrylic acid in the shell. 

K. Barthold, R. Baur, S. Crema, K. Oppenlaender, and J. Lasowski. Method of demulsifying crude oil and water mixtures with copolymers of acrylates or methacrylates and hydrophilic comonomers. Patent US 5472617, 1995. 

Evidently, there are a number of factors that determine which of the above-mentioned pathways of polymerization occurs. One of these is the enrichment of final copolymers with the more hydrophilic comonomer (in comparison with the composition of the initial feeds), due to a higher reactivity of NVIAz. The higher (than for NVC1) reactivity of NVIAz is determined by a stronger polarization of the double bond of the vinyl group by the imidazole moiety as compared with the caprolactam cycle. Furthermore, a good solubility of hydrophilic NVIAz can also contribute to its higher reactivity in aqueous media. 

Thermoresponsive polymeric micelles with PIPAAm block copolymers can be expected to combine passive spatial targeting specificity with a stimuli-responsive targeting mechanism. We have developed LCSTs of PIPAAm chains with preservation of the thermoresponsive properties such as a phase transition rate by copolymerization with hydrophobic or hydrophilic comonomers into PIPAAm main chains. Micellar outer shell chains with the LCSTs adjusted between body temperature and hyperthermic temperature can play a dual role in micelle stabilization at a body temperature due to their hydrophilicity and initiation of drug release by hyperthermia resulting from outer shell structural deformation. Simultaneously, micelle interactions with cells could be enhanced at heated sites due... 

Biodegradable amphiphilic networks have been synthesized by free radical copolymerization of PCL or PD,L-LA dimacromonomers with a hydrophilic comonomer, i.e., 2-hydroxyethylmethacrylate (HEMA) [45, 46, 114]. Well-defined a,cD-methacryloyl PCL and PD,L-LA oligomers were synthesized by the living ROP of the parent monomers initiated by diethyl alimiinum 2-hydroxyethyl-... 

The surface of polymer particles obtained by emulsion polymerization is occupied by emulsifier molecules, initiator fragments, and hydrophilic comonomer units. Therefore, desirable design of the surface ought to be done by choosing the emulsifier, initiator, and comonomer. Some of them are employed in aiming for postreaction at the surface to convert it into a functional one. When any change is necessary on the particle surface, modification of surface can be done by the following means ... 

Fig. 44a. Side group spacer (hydrophilic segments), b Main chain spacer (hydrophilic comonomers), c Main chain spacer and side group spacer (spacer combination) [346]...

Improved Comfort Properties. Wear comfort generally means cotton-like properties, The ability lo absorb moisture from the skin and ihe softness of cotton fabrics are considered to be the two key properties for comfort. The extremely line denier of cotton fibers accounts for its softness. Both properties can be achieved in acrylic fibers. Improved moisture retention can be achieved by incorporating hydrophilic comonomers that decrease ultimate fiher density, by modifying the fiber spinning process, ur by using after-treatments such as modified finishes. 

A means to avoid such tedious optimization can be envisaged by employing stoichiometric monomers to develop strong interactions with the template as mentioned above. The other way is to incorporate hydrophilic comonomers (2-hydroxyethyl methacrylate (HEMA), acrylamide) or cross-linkers (pentaerythri-toltriacrylate, methylene bisacrylamide) in the polymer. This results in an increase of the hydrophilicity of the polymer. Indeed, the use of HEMA for a MIP directed towards the anesthetic bupivacaine resulted in high imprinting factors due to reduced non-specific hydrophobic adsorption in aqueous buffer. This was not the case when HEMA was omitted from the polymerization mixture [27]. These conditions were exploited for the direct and selective extraction of bupivacaine from blood plasma samples. 

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. 

The First Stage. The preferential polymerization of AA at the initial stage of copolymerization means that the main reaction locus is the aqueous phase just as Juang and Krieger pointed it out for the aqueous copolymerization of St with sodium styrenesul-fonate ( SSS ) (9). In the St-SSS system, SSS polymerized preferentially up to a few percent conversion under the condition of SSS/St (w/w) - 0.014. Copolymerization of hydrophobic monomer with a large amount of hydrophilic comonomer was considered to yield a greater amount of information with respect to the reaction mode. By use of a relatively large amount of AA or its derivatives the characteristic reaction mode of the copolymerization of St with acrylamides could be clarified. 

Linear NIPAM-co-VP copolymers As discussed in the Experimental Section, hydrophilic comonomer, vinyl pyrrolidone (VP), can be purposely copolymerized into PNIPAM at two different temperatures, 30 °C and 60 °C, respectively, below and above the LCST of PNIPAM homopolymer. At each temperature, the copolymers with two different VP/NIPAM ratios (5 and 10 mol%) were prepared. A proper fractionation of resultant copolymers led to narrowly-distributed long NIPAM-co-VP copolymer chains with a similar length and VP/NIPAM ratio, but different comonomer distributions. 

It is not surprising to see that the chains with a higher hydrophilic comonomer VP content have a higher transition temperature. However, it is rather interesting to see that for each pair of the copolymers with a similar VP content, the copolymer prepared at 60 °C has a lower transition temperature than its counterpart prepared at 30 °C. In order to check this shift in the transition temperature, we also measured the partial heat capacity (Cp) of these copolymers in solution using a micro-calorimeter. Figure 7 shows that for the two copolymers prepared at 60 °C, the temperatures at which the maximum... 

The comonomer distribution can be alternated by controlling the synthesis conditions, such as the copolymerization at different reaction temperatures at which the thermally sensitive chain backbone has different conformations (extended coil or collapsed globule). In this way, hydrophilic comonomers can be incorporated into the thermally sensitive chain backbone in a more random or more segmented (protein-like) fashion. On the other hand, short segments made of hydrophobic comonomers can be inserted into a hydrophilic chain backbone by micelle polymerization. One of the most convenient ways to control and alternate the degree of amphiphilicity of a copolymer chain, i.e., the solubility difference of different comonomers in a selective solvent, is to use a thermally sensitive polymer as the chain backbone, such as poly(N-isopropylacrylamidc) (PNIPAM) and Poly(N,N-diethylacrylamide) (PDEA). In this way, the incorporation of a hydrophilic or hydrophobic comonomer into a thermally sensitive chain backbone allows us to adjust the degree of amphiphilicity by a temperature variation. 

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. 

The thin NIPAAm hydrogel layers were covalently attached to the surface, therefore the swelling was confined to one direction perpendicular to the substrate. The degree of anisotropy was calculated from ratio of l/0p and swelling ratio. This ratio was found to be between 1.2-1.3. Such a study describing the effect of hydrophilic comonomer on Tc of PNIPAAm provides an opportunity to formulate thermoresponsive hydrogel layers with desired transition temperature and swelling behavior for various applications. 

Musyanovych A, Rossmanith R, Tontsch C, Landfester K (2007) Effect of hydrophilic comonomer and surfactant type on the colloidal stability and size distribution of carboxyl-and amino-functionalized polystyrene particles prepared by miniemulsion polymerization. Langmuir 23(10) 5367-5376... 

Aqueous dispersions of crosslinked crystalline polymers containing both hydrophobic and hydrophilic components have been prepared. The hydrophobic components consist of Cg-, Ci2-, C14-, and Cig-acrylates while methyacryhc acid constituted the hydrophilic comonomer. These dispersions are useful as coatings, particularly on human hair. 

Copolymerization of the CD-complexed macromonomer 8a with hydrophilic comonomers 2-acrylamido-2-methylpropansulfonate (AMPS) and A,A-dimethyl-acrylamide (DMAA) leads to formation of hydrophobically associative polymers (Fig. 14) [48],... 

Nafion membranes are composed of hydrophobic-hydrophilic comonomers. When the ionic form of Nafion is exposed to water, some swelling takes place. However, in order to minimize the free energy of the system, water will be taken up in such a way as to avoid contact with the hydrophobic TFE units of the copolymer. At equilibrium, for a fixed structure, there will be a balance between the free energy of dilution (osmotic swelling) and the free energy of hydration of the TFE units. As a result of these two opposing effects, water of hydration is contained in ion clusters which reduces the necessity of water-TFE interaction and yields a system of minimum energy. Several models... 

Covenient and versatile as well, the preferred technique at present seems to be copolymerization. Either polymerizable surfactants are copolymerized with small, often polar or hydrophilic, comonomers, creating rather well defined surfactant fragments in the polysoaps [73, 77, 78, 156-168] (Fig. 3e). This strategy is more versatile than exclusive homopolymerization and allows the use of polymerizable surfactants whose homopolymers are not water-soluble, but it still requires considerable synthetic effort. Or, much more facile, simple hydro-phobic monomers are copolymerized with small hydrophilic ones (Fig. 3f), taking full advantage of the choice of commercial or easily accessible monomers [39, 53-55, 153, 169-218]. 

---