Hydrophilic/hydrophobic copolymers

Lens hazing and protein deposition are common problems for wearers of soft contact lenses. Previous experiments with hydrophobic-hydrophilic copolymers exposed to plasma showed protein adsorption to be minimal at intermediate copolymer compositions. Adsorption of proteins from artificial tear solutions to a series of polymers and copolymers ranging in composition from 100% poly (methyl methacrylate) (PMMA) to 100% poly(2-hydroxyethyl methacrylate) (PH EM A) was measured. The total protein adsorption due to the three major proteins in tear fluid (lysozyme, albumin, and immunoglobulins) was at a minimum value at copolymer compositions containing 50% or less PH EM A. The elution of the adsorbed proteins from these polymers and copolymers with various solutions also was investigated to assess the binding mechanism. 

The accumulation of proteins on contact lenses has long been viewed as an undesirable event. In this study, the effect of polymer composition on both the total amount of protein on the materials, and on the specific proteins on each polymer composition was documented. The importance of these factors for biological response is not known, so this situation remains a fertile area for investigation. This study also demonstrated that a linear variation in material composition will not necessarily result in a linear variation in absorbed layer protein composition. The minima and maxima noted at intermediate copolymer compositions have strong implications for both understanding the mechanism of protein adsorption and for biological response. Investigation is underway to explore further protein interaction with hydrophobic-hydrophilic copolymer materials. 

Khokhlov AR, Khalatur PG (2005) Solution properties of charged hydrophobic/hydrophilic copolymers. Curr Opin Colloid Interface Sci 10 22-29. doi 10.1016/j.cocis.2005.04.003... 

The other possibility, at first examined by Wooley and co-workers [231,232] is to crosslink the corona of the micelles. These kinds of nanoparticles are designated by shell cross-linked knedel-Hke (SCK) micelles by these authors. Wooley et al. have applied this concept to a large variety of block copolymers, mainly hydrophobic-hydrophilic copolymers with PAA or quaternized PVP as the water-soluble block, which can be chemically cross-linked in their micellar form. A similar approach has been described by Armes and co-workers [233] for the synthesis of shell cross-linked micelles where core and shell are both hydrophilic. 

The synthesis of block copolymers by macromonotner RAFT polymeriza tion has been discussed in Section 9.5.2 and examples are provide in Table 9.9. RAFT polymerization with thioearbonylthio compounds has been used to make a wide variety of block copolymers and examples arc provided below in Tabic 9.28. The process of block formation is shown in Scheme 9.59. Of considerable interest is the ability to make hydrophilic-hydrophobic block copolymers directly with monomers such as AA, DMA, NIPAM and DMAEMA. Doubly hydrophilic blocks have also been prepared.476 638 The big advantage of RAFT polymerization is its tolerance of unprotected functionality. 

Preparation of polyfethylene oxide) (PEO) and poly(arylene ether) based hydrophilic-hydrophobic block copolymer is of special interest because PEO has been proven to be particularly reliable and versatile for the surface modification of biomaterials. The first poly(ediylene oxide)-/ /oc/c-polysulfonc (PEO-fc-PSF) copolymers were reported by Aksenov et al.217 They employed diisocyanate chemistry to link hydroxy-terminated sulfone oligomers and polyfethylene... 

Although the potassium superoxide route can be universally applied to various alkyl methacrylates, it is experimentally more difficult than simple acid hydrolysis. In addition, limited yields do not permit well-defined hydrophobic-hydrophilic blocks. On the other hand, acid catalyzed hydrolysis is limited to only a few esters such as TBMA, but yields of carboxylate are quantitative. Hydrolysis attempts of poly(methyl methacrylate) (PMMA) and poly(isopropyl methacrylate) (PIPMA) do not yield an observable amount of conversion to the carboxylic acid under the established conditions for poly(t-butyl methacrylate) (PTBMA). This allows for selective hydrolysis of all-acrylic block copolymers. 

Drug Release from PHEMA-l-PIB Networks. Amphiphilic networks due to their distinct microphase separated hydrophobic-hydrophilic domain structure posses potential for biomedical applications. Similar microphase separated materials such as poly(HEMA- -styrene-6-HEMA), poly(HEMA-6-dimethylsiloxane- -HEMA), and poly(HEMA-6-butadiene- -HEMA) triblock copolymers have demonstrated better antithromogenic properties to any of the respective homopolymers (5-S). Amphiphilic networks are speculated to demonstrate better biocompatibility than either PIB or PHEMA because of their hydrophilic-hydrophobic microdomain structure. These unique structures may also be useful as swellable drug delivery matrices for both hydrophilic and lipophilic drugs due to their amphiphilic nature. Preliminary experiments with theophylline as a model for a water soluble drug were conducted to determine the release characteristics of the system. Experiments with lipophilic drugs are the subject of ongoing research. 

KEY TERMS hydrophobic hydrophilic monomer cross-linking polymer copolymer hydrogel... 

Hydrophilic ends, of surfactants, 22 725 Hydrophilic libers, 9 158 11 168 Hydrophilic flavor compounds, 11 551 Hydrophilic fumed silica, 22 368 Hydrophilic head group, 24 137 Hydrophilic-hydrophobic block copolymers, 20 485... 

Hydrophilic surfaces, 1 584—585 Hydrophilic/tunably hydrophilic/ hydrophobic block copolymers, 20 485-487 Hydrophilite, 5 785t Hydrophobic additives, in paper manufacture, 18 113 Hydrophobic alkoxy silanes, as silylating agents, 22 697... 

Since the hydrophobicity of styrene- or alkyl methacrylate-based monolithic matrices is too high to make them useful for hydrophobic interaction chromatography, porous monoliths based on highly hydrophilic copolymers of acrylamide and methylenebisacrylamide were developed [70,135]. The hydrophobicity of the matrix required for the successful separations of proteins is controlled by the addition of butyl methacrylate to the polymerization mixture. The suitability of this rigid hydrophilic monolith for the separation of protein mixtures is demonstrated in Fig. 21, which shows the rapid separation of five proteins in less than 3 min using a steeply decreasing concentration gradient of ammonium sulfate. 

The ethylene oxide block is hydrophilic, whereas the propylene oxide block is (relatively) hydrophobic. The copolymer forms micelles in aqueous solutions with the hydrophilic portions pointing outward, interacting with the water, while the hydrophobic portions form the inner core, shielded from the water by the ethylene oxide-derived block. A micelle is also formed in organic liquids, but here the hydrophobic propylene oxide block faces outward, whereas the ethylene oxide bloek acts as the inner eore. 

In ionic block copolymers, micellization occurs in a solvent that is selective for one of the blocks, as for non-ionic block copolymers. However, the ionic character of the copolymer introduces a new parameter governing the structure and properties of micellar structures. In particular, the ionic strength plays an important role in the conformation of the copolymer, and the presence of a high charge density leads to some specific properties unique to ionic block copolymers. Many of the studies on ionic block copolymers have been undertaken with solvents selective for the ionic polyelectrolyte block, generally water or related solvents, such as water-methanol mixtures. However, it has been observed that it is often difficult to dissolve ionic hydrophilic-hydrophobic block copolymers in water. These dissolution problems are far more pronounced than for block copolymers in non-aqueous selective solvents, although they do not always reflect real insolubility. In many cases, dissolution can be achieved if a better solvent is used first and examples of the use of cosolvents are listed by Selb and Gallot (1985). 

In the mid to late 1990s, Mimotopes was producing rigid injection molded polypropylene devices that were surface grafted with either a hydrophilic copolymer of methacrylic acid/dimethyl acrylamide or the relatively hydrophobic polystyrene.12 The polymer was then suitably deriva-tized to allow the incorporation of a linker system. In contrast to the various commercial resins available at the time, the Crown was a macroscopic, quantized solid phase. As shown in Fig. 2, the Crowns were typically fitted to a polypropylene stem, which in turn could be fitted into a... 

There are many kinds of polymerizing monomers used to make up copolymers. These differ in physical and chemical properties. One of the most important differences (essential features) is their solubility, that is, how much they like or dislike a solvent, e.g., water. Hence the chemical and atomistic details of different monomeric units may not be necessary to understand the properties of many two-letter copolymers. In what follows, we will mainly use the so-called HP model [31]. This two-letter model of a linear hydrophobic/hydrophilic macromolecule reflects the spirit of minimalist models, in that it is simple yet based on a physical principle. 

Fig. 7 Typical snapshot of a hydrophobically modified copolymer. Hydrophilic chain segments are shown in green and hydrophobic side groups in red...

Protein chains generally contain hydrophobic, hydrophilic and/or charged amino acid residues, which can be regarded as amphiphilic copolymers in a broad definition. The coordinate and cooperative interactions, such as... 

Using PNIPAM ionomers as a bridge, we will shift our discussion from the folding of individual copolymer chains in extremely dilute solutions to the formation of the mesoglobular phase of hydrophilically and hydrophobically modified copolymer chains in dilute solutions. The synthesis of PNIPAM-co-xKAA ionomers has been described before. 

Figure 3.5 shows the organized mesoporous structure of one of these materials. The wide variety of organic molecules with self-assembling properties allows for the synthesis of a myriad of solids with controlled porosity. Cationic surfactants, like the hexadecyltrimethylammonium used to synthesize MCM-41 [26], or three-block copolymers (hydrophilic-hydrophobic-hydrophilic) are two good examples. 

Their hydrophobic/hydrophilic content seems to be just right for applications in cancer and gene therapies. Such nanospheres are prepared by dispersing the methylene chloride solution of the copolymer in water and allowing the solvent to evaporate [38]. By attaching biotin to the free hydroxy groups and complexa-tion with avidin, cell-specific delivery may be attained.NMR studies of such systems [39] revealed that the flexibility and mobility of the thus attached PEG chains is similar to that of the unattached PEG molecules dissolved in water. Re-... 

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