Polymer groups hydrophilic

The generally low chemical, mechanical and thennal stability of LB films hinders their use in a wide range of applications. Two approaches have been studied to solve this problem. One is to spread a polymerizable monomer on the subphase and to polymerize it either before or following transfer to the substrate. The second is to employ prefonned polymers containing hydrophilic and hydrophobic groups. 

Schneider J, Erdelen C, Ringsdorf H and Rabolt J F 1989 Structural studies of polymers with hydrophilic spacer groups. 2. Infrared-spectroscopy of Langmuir-Blodgett multilayers of polymers with fluorocarbon side-chains at ambient and elevated temperatures Macromolecules 22 3475-80... 

For some applications, such as for repulpable type PSAs, it may be advantageous to incorporate high levels of acrylic acid because this makes the polymer more hydrophilic. At the same time, high levels of acid also improve the water-dispersibility of the adhesive, especially at higher pH where the acid groups are converted to the more water-soluble neutralized salt form. Since the high level of acid increases the of the resulting polymer, a non-tacky material results. To make the adhesive pressure sensitive, the polymer can be softened with water-dispersible or soluble plasticizers, such as polyethers [68]. 

The hydroxylic content of the dextran sugar backbone makes the polymer very hydrophilic and easily modified for coupling to other molecules. Unlike PEG, discussed previously, which has modifiable groups only at the ends of each linear polymer, the hydroxyl functional groups of dextran are present on each monomer in the chain. The monomers contain at least 3 hydroxyls (4 on the terminal units) that may undergo derivatization reactions. This multivalent nature of dextran allows molecules to be attached at numerous sites along the polymer chain. 

The affinity of the polymer-bound catalyst for water and for organic solvent also depends upon the structure of the polymer backbone. Polystyrene is nonpolar and attracts good organic solvents, but without ionic, polyether, or other polar sites, it is completely inactive for catalysis of nucleophilic reactions. The polar sites are necessary to attract reactive anions. If the polymer is hydrophilic, as a dextran, its surface must be made less polar by functionalization with lipophilic groups to permit catalytic activity for most nucleophilic displacement reactions. The % RS and the chemical nature of the polymer backbone affect the hydrophilic/lipophilic balance. The polymer must be able to attract both the reactive anion and the organic substrate into its matrix to catalyze reactions between the two mutually insoluble species. Most polymer-supported phase transfer catalysts are used under conditions where both intrinsic reactivity and intraparticle diffusion affect the observed rates of reaction. The structural variables in the catalyst which control the hydrophilic/lipophilic balance affect both activity and diffusion, and it is often not possible to distinguish clearly between these rate limiting phenomena by variation of active site structure, polymer backbone structure, or % RS. 

Whether or not the surface of a polymer is hydrophilic or hydrophobic is not determined by whether hydrophilic or hydrophobic moieties exist in a polymer molecule but by what kind of moieties actually occupy the top surface of the polymer. Namely, the surface properties are controlled by the surface configuration but not by the configuration of polymer molecules. The configuration of PVA can be represented by -[CH2-CH(OH)] -, which indicates that the polymer is highly hydrophilic, and PVA is water soluble. However, the surface characteristics of a film of PVA depend entirely on how many OH groups exist on the top surface or buried in the bulk phase of the polymer that is described by the surface configuration. 

PVP is a nonionic water-soluble polymer that interacts with water-soluble dyes to form water-soluble complexes with less fabric substantivity than the free dye. Additionally, PVP inhibits soil redeposition and is particularly effective with synthetic fibers and synthetic cotton blends. The polymer comprises hydrophilic, dipolar imido groups in conjunction with hydrophobic, apolar methylene and methine groups. The combination of dipolar and amphiphilic character make PVP soluble in water and organic solvents such as alcohols and partially halogenated alkanes, and will complex a variety of polarizable and acidic compounds. PVP is particularly effective with blue dyes and not as effective with acid red dyes. 

Moisture relations in textile polymers are concerned mostly with the hydrophilic fibers, such as the cellulose groups of cotton, flax, hemp, jute, viscose, modal, and acetates. This is not to say however that the essentially hydrophobic fibers, which fall into the synthetic polymer group (see Fig. 1) have zero moisture imbibition or are totally unaffected by moisture, although this will be true for some of the fibers in this group. 

For regulation of the biocompatibiUty, it is desirable when the total number of sulfonic acid groups in the polymer, and also their distribution in the polymer chain, can be influenced. By the selective introduction of, domains with high and low degrees of sulfonation, the variational possibilities with respect to the functional polymer groups can be increased and thus, the hydrophilicity properties can be graded even more selectively. For this reason, block copolymers containing blocks of sulfonated and un-sulfonated polyether sulfones are more suitable than sulfonated PES. 

In this linkages are covalent bonds. They are influenced by the chemical linkages and functional groups present in the gel networks. Hydrophilic polymers and hydrophilic-hydrophobic copolymers are examples of chemically crosslinked gels obtained by the polymerization of vinyl monomers in fhe presence of multifunctional crosslinkers. These crosslinkers are the crosslinking points within and between the polymeric chains allowing modification of the entire physicochemical properties of the gel systems... 

In the course of the investigation illustrated in Scheme 2.25, stimuli-responsive polymers were discovered, in particular, those that exhibit thermally-induced phase separation. A transparent aqueous solution of a polymer with hydrophilic oxyethylene chains and a hydrophobic co-alkyl group (POEVE) became cloudy upon heating to a certain critical temperature. This phase separation was found to... 

---