Hydrophilic polymers structure

Carbopol is widely used in cosmetic and pharmaceutical practice as a gel-former. Carbopol resins are hydrophilic polymers which swell in water solutions and transform into the gel form at neutralization. At the elaboration of special cosmetic preparations in which carbopol is used, the problem of raw materials compatibility appears. For example, some extracts of aromatic pectin containing materials destroy the gel structure of carbopol. High contents of bivalent metal ions, in particular calcium ions, destructively influence onto the gel-making ability of the system too. 

In the last few years there have been new creative methods of preparation of novel hydrophilic polymers and hydrogels that may represent the future in drug delivery applications. The focus in these studies has been the development of polymeric structures with precise molecular architectures. Stupp et al. (1997) synthesized self-assembled triblock copolymer, nanostructures that may have very promising applications in controlled drug delivery. Novel biodegradable polymers, such as polyrotaxanes, have been developed that have particularly exciting molecular assemblies for drug delivery (Ooya and Yui, 1997). 

The "catch-22" of these systems is their dependence on liquid water as the working fluid. In contact with water, hydrophobic and hydrophilic polymer constituents self-organize into phase-segregated random structures that... 

The structure of this interface determines fhe sfabilify of PEMs, the state of water, the strength of interactions in the polymer/water/ion system, the vibration modes of side chains, and the mobilities of wafer molecules and protons. The charged polymer side chains contribute elastic ("entropic") and electrostatic terms to the free energy. This complicated inferfacial region thereby largely contributes to differences in performance of membranes wifh different chemical architectures. Indeed, the picture of a "polyelectro-lyfe brush" could be more insighttul than the picture of a well-separated hydrophobic or hydrophilic domain structure in order to rationalize such differences. ... 

A second interesting class of amphiphilic polymers is the polysoaps or miceUar polymers as they are often referred to. Such polymers are composed of hydrophilic and hydrophobic fragments leading to various molecular architectures that have been discussed in detail by A. Laschewsky [78]. The precise structure of the resulting micelles, that is, whether they are intra- or intermolecular assembhes, is still subject to discussion because the polymer structure is so versatile. Possible micellar structures are depicted in Fig. 6.8. The most interesting feature of such polymers with respect to their application in catalysis is (i) their remarkable abil-... 

Hydrophilic Groups. Water solubility can be achieved through hydrophilic units in the backbone of a polymer, such as O and N atoms that supply lone-pair electrons for hydrogen bonding to water. Solubility in water is also achieved with hydrophilic side groups (e.g., OH, NHi,C02, SOy ). Truly unique in its ability to interact and promote water solubility is the -O-CH2-CH2- group. The interactions of these groups with water and their placement in the polymer structure influence the waler solubility of the polymer and its hydrodynamic volume. 

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