Side groups

Mono- and multilayers may be fonned by the LB technique from polymers bearing both hydrophilic and hydrophobic side groups that are already spread as a polymer at the water-air interface. 

Another approach to the fabrication of LB films from prefonned polymers is to fonn a hydrophobic main chain by reacting monomers tenninated by a vinyl group [102, 103, 104, 105 and 106]. The side groups studied also included perfluorinated hydrocarbon chains, which tilt with respect to the nonnal to the plane of the film, whereas the analogous ordinary hydrocarbon chains do not [105]. 

Strike can t believe Strike can actually quote Strike s own book. That is so freaky )]. Most of these things will make amphetamines that are much more potent than X. It is also possible to play around with some of the little side groups on these to eventually make X or some other interesting psychotomimetics. With few exceptions these precursors are all substituted allylbenzenes just like safrole. They are all found in the same kind of legal oils and sold in the same kinds of places as sassafras. Finally, these precursors are turned into their own respective amphetamines using the exact same conversion recipes used for safrole. 

Polybutylene. Polybutylene is composed of linear chains having an isotactic arrangement of ethyl side groups along the chain backbone. 

The sequence of amino acids in a peptide can be written using the three-letter code shown in Figure 45.3 or a one-letter code, both in common use. For example, the tripeptide, ala.ala.phe, could be abbreviated further to AAF Although peptides and proteins have chain-like structures, they seldom produce a simple linear system rather, the chains fold and wrap around each other to give complex shapes. The chemical nature of the various amino acid side groups dictates the way in which the chains fold to arrive at a thermodynamically most-favored state. 

Hydrocarbons without bulky side groups are held together by London forces, the weakest of intermolecular attractions. This means that the free volume tends to be large for these compounds, so a relatively large amount of cooUng is necessary before the free volume collapses. Thus Tg is low for these compounds. 

Incorporation of cyclic aliphatic (aUcycHc) side groups markedly improves the plasma etch resistance of acryhc polymers, without reduciag optical transparency at 193 nm (91). Figure 32 presents stmctures of some acryhc polymers currendy under study for use ia 193-nm CA resists (92—94). Recendy, polymers with main-chain aUcycHc stmctures have been described that offer similar properties (95,96). 

Hydrophilic Groups. Water solubiUty can be achieved through hydrophilic units in the backbone of a polymer, such as O and N atoms that supply lonepair electrons for hydrogen bonding to water. SolubiUty in water is also achieved with hydrophilic side groups (eg, OH, NH2, CO2, SO3 ). 

Solution Properties. Typically, if a polymer is soluble ia a solvent, it is soluble ia all proportions. As solvent evaporates from the solution, no phase separation or precipitation occurs. The solution viscosity iacreases continually until a coherent film is formed. The film is held together by molecular entanglements and secondary bonding forces. The solubiUty of the acrylate polymers is affected by the nature of the side group. Polymers that contain short side chaias are relatively polar and are soluble ia polar solvents such as ketones, esters, or ether alcohols. As the side chaia iacreases ia length the polymers are less polar and dissolve ia relatively nonpolar solvents, such as aromatic or aUphatic hydrocarbons. 

Both side-chain and main-chain scission products are observed when polyacrylates are irradiated with gamma radiation (60). The nature of the alkyl side group affects the observed ratio of these two processes (61,62). 

During the vulcanization, the volatile species formed are by-products of the peroxide. Typical cure cycles are 3—8 min at 115—170°C, depending on the choice of peroxide. With most fluorosihcones (as well as other fluoroelastomers), a postcure of 4—24 h at 150—200°C is recommended to maximize long-term aging properties. This post-cure completes reactions of the side groups and results in an increased tensile strength, a higher cross-link density, and much lower compression set. 

FiaaHy, the use of photoreversible change of the circular dichroism for optical data storage is of iaterest. This technique offers an advantage over photochromic materials ia that the data can be read ia a way that does not damage the stored information. These chirooptic data storage devices have been demonstrated with the example of chiral peptides with azobenzene side groups (155). 

The birefringence for phenyl-substituted PC (4) (T = 176 C) is reduced to about 50%, for benzyl substituted PC (5) (T = 138 C) to about 25%, and for four-ring bisphenol PC (6) to 8% of the value for BPA-PC (183,190,195,197,198) on condition of an optimum conformation of the phenyls in the side groups perpendicular to the aromatic rings in the backbone. In reaUty, however, these low birefringence values are not achieved, because the optimum conformation of the phenyl rings cannot be achieved in injection-stamped disks. 

Phosphazene polymers are inherently good electrical insulators unless side-group stmctures allow ionic conduction in the presence of salts. This insulating property forms the basis for appHcations as wire and cable jackets and coatings. Polyphosphazenes also exhibit excellent visible and uv radiation transparency when chromophoric substituents are absent. 

Polymers Bearing Metal Complexes. A large number of polymers with side groups containing metal complexes have been reported. The... 

Liquid crystal polymers are also used in electrooptic displays. Side-chain polymers are quite suitable for this purpose, but usually involve much larger elastic and viscous constants, which slow the response of the device (33). The chiral smectic C phase is perhaps best suited for a polymer field effect device. The abiHty to attach dichroic or fluorescent dyes as a proportion of the side groups opens the door to appHcations not easily achieved with low molecular weight Hquid crystals. Polymers with smectic phases have also been used to create laser writable devices (30). The laser can address areas a few micrometers wide, changing a clear state to a strong scattering state or vice versa. Future uses of Hquid crystal polymers may include data storage devices. Polymers with nonlinear optical properties may also become important for device appHcations. 

Silicones. SiHcoae fluids coasist of an alternating siHcon—oxygen backbone (sdoxane), with two organic side groups branching off from each of the siHcon atoms. Although there are many possibiHties, methyl and phenyl side chains have been the most common (46,47). 

Welan is produced by 2is Pilcaligenes species (ATCC-31555) by aerobic fermentation, and marketed under the trade name BIOZAN (Merck and Co., Inc.) early reports also referred to it as S-130 (229). The polymer is stmcturaUy similar to geUan, sharing the same backbone sequence. It has an additional side group of an a-L-rhamnopyranosyl or an a-L-maimopyranosyl (Man ) unit linked (1— 3) to a P-D-glucopyranosyl unit in the backbone of the polymer ... 

Scleroglucan exists in a triple hehcal conformation that is highly stable (314). The D-glucopyranosyl side groups project to the outside of the helix (312) and prevent the aggregation of hehces, which would result in insolubiUty, as in the case of curdlan vide infra). The transition from helix to coil occurs... 

Thermal, Thermooxidative, and Photooxidative Degradation. Polymers of a-olefins have at least one tertiary C-H bond in each monomer unit of polymer chains. As a result, these polymers are susceptible to both thermal and thermooxidative degradation. Reactivity in degradation reactions is especially significant in the case of polyolefins with branched alkyl side groups. For example, thermal decomposition of... 

Reaction with Phosgene. This reaction of amino acid esters is used for preparing the corresponding isocyanates, especially lysine diisocyanate [4460-02-0] (LDI). LDI is a valuable nonyellowing isocyanate with a functional side group for incorporation in polyurethanes. 

This compound is soluble in most organic solvents and may be easily copolymerized with other vinyl monomers to introduce reactive side groups on the polymer chain (18). Such reactive polymer chains may then be used to modify other polymers including other amino resins. It may be desirable to produce the cross-links first. Thus, A/-methylolacrylamide can react with more acrylamide to produce methylenebisacrylamide, a tetrafunctional vinyl monomer. 

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