Polymer studies resistivity

Recently there has been increasing interest in studies of the effects of high energy radiation on polymers. Some of this interest has arisen because of the use of polymers as resists in the microchip industry, and some through the search for radiation resistant polymers for the aerospace and other high technology industries. 

In order to evaluate the possible use of MAGME-polymers in resist applications, crosslinking studies were conducted on thin films (1 ym ), spinn-coated on silicon wafers. Poly-MAGME is water soluble and most of its co-polymers are soluble in alcohols (Table 3) making the materials relatively attractive to work with from a production point of view. 

An 18-20% hydrolyzed polyacrylamide was used in all tests. In all 300 ppm polymer solutions a radioactive C14 tagged polyacrylamide was used. At higher polymer concentrations (600 and 1200 ppm) a commercial product called Calgon Polymer 454 was added to the base 300 ppm radioactive solution. A special study was conducted to develop a radioactive polymer which has properties identical to the commercial product. Several experiments were run on both polymers to check these properties such as, viscosity measurements, friction reduction flow tests, and flow tests in porous media. These special studies showed that performance of the radioactive product was equivalent to that of the commercial product. A typical result of these tests is shown in Figure 1. The small differences in the polymer flow resistance factors are due to small differences in the textures of different sandpacks, rather than to differences in the chemical structures of the polymers. Friction reduction, viscosity, and retention experiments showed even closer agreements between properties of the radioactive and commercial product. 

To date, no attempt has been made to understand the relationship between the adsorption of biomolecules from the complex synovial fluid and the friction between the surfaces of artificial joint materials on a molecular level. There have, however, been a number of studies on the mechanisms of aqueous lubrication in the presence of synthetic macromolecules. A particularly efficient mechanism of lubrication involves the formation of hydrophilic polymer brushes at the surface, which maintain a fluid film between the opposing surfaces [16,17], The low friction between the surfaces has been attributed to the fluidity of the hydration layers around the polymers and resistance to interpenetration between the polymer brushes [18]. 

The chemistry and biological application of PEG (8) have been the subject of intense study both in academia and industry. PEG is a nontoxic, water soluble polymer that resists recognition by the immune system. Traditionally, PEG has been used in biological research as a precipitating agent for proteins. It has been approved for a wide range of biomedical applications, as they are biocompatible, nontoxic, and nonimmunogenic (46). 

Another mode of operation derived from contact AFM that is relevant to polymer studies is the scanning thermal microscope (SThM) [118, 146], In SThM the tip is a special device that has a resistive element. If a current is passed through this resistive element, its temperature depends on the heat transferred to the specimen. It thus acts as a thermal probe, as seen for example in Fig. 5.36. During scanning, thermal control of the probe can be used to generate images based on variation of either sample temperature or thermal conductivity. Filled polymers and polymer blends are candidates for this kind of study, but the resolution is relatively poor. Microfabricated thermal probes can give a resolution of 100 nm. 

Dichromated Resists. The first compositions widely used as photoresists combine a photosensitive dichromate salt (usually ammonium dichromate) with a water-soluble polymer of biologic origin such as gelatin, egg albumin (proteins), or gum arabic (a starch). Later, synthetic polymers such as poly(vinyl alcohol) also were used (11,12). Irradiation with uv light (X in the range of 360—380 nm using, for example, a carbon arc lamp) leads to photoinitiated oxidation of the polymer and reduction of dichromate to Ct(III). The photoinduced chemistry renders exposed areas insoluble in aqueous developing solutions. The photochemical mechanism of dichromate sensitization of PVA (summarized in Fig. 3) has been studied in detail (13). 

Numerous studies have probed how novolac microstmcture influences resist hthographic properties. In one example, a series of resists were formulated from novolacs prepared with varying feed ratios ofpara-jmeta-cmso. These researchers found that the dissolution rate decreased, and the resist contrast increased, as thepara-jmeta-cmso feed ratio increased (33). Condensation can only occur at the ortho position ofpara-cmso but can occur at both the ortho- and i ra-positions of meta-cmso. It is beheved that increased steric factors and chain rigidity that accompany increasedpara-cmso content modify the polymer solubihty. 

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). 

HEXAFLUOROBENZENE The development of commercial routes to hexafluoroben2ene [392-56-3] included an intensive study of its derivatives. Particularly noteworthy was the development of high temperature lubricants, heat-transfer fluids, and radiation-resistant polymers (248). 

Diallyl terephthalate [1026-92-2] is utilized less, but lenses made of copolymers with triaHyl cyanurate and methacrylates have been suggested (62). Diallyl tetrabromophthalate and tetrachlorophthalate polymers have been proposed for electronic circuit boards of low flammabiUty (63). They are uv-curable and solder-resistant. Copolymers with unsaturated polyester, vinyl acetate and DAP have been studied (64). 

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