Modified polymer

Materials that typify thermoresponsive behavior are polyethylene—poly (ethylene glycol) copolymers that are used to functionalize the surfaces of polyethylene films (smart surfaces) (20). When the copolymer is immersed in water, the poly(ethylene glycol) functionaUties at the surfaces have solvation behavior similar to poly(ethylene glycol) itself. The abiUty to design a smart surface in these cases is based on the observed behavior of inverse temperature-dependent solubiUty of poly(alkene oxide)s in water. The behavior is used to produce surface-modified polymers that reversibly change their hydrophilicity and solvation with changes in temperatures. Similar behaviors have been observed as a function of changes in pH (21—24). 

B. D. Bauman, "Novel Polyurethane Composites with Surface-Modified Polymer Particles," paper presented at SPI 32nddnnual Technical Marketing Conference, 1989. 

The extent of the long-chain branching of a series of ethyl xanthogen disulfide modified polymers carried to increasing conversion is shown in Table 1. No branches are found until 56% conversion. The gel point is a Htfle over 82%. Polymer rheology deteriorates between 56 and 82% conversion. 

Table 15.3 Comparison of properties of some rubber-modified polymers with polyimethyl methacrylate)...

Lower cost alternatives to PTFE-modified polymers have also been introduced for low-friction applications. These materials use graphite and chemical lubricants of undisclosed composition. 

Chemically modified polymers have been used to determine polar compounds in water samples (37, 71). Chemical modification involves introducing a polar group into polymeric resins. These give higher recoveries than their unmodified analogues for polar analytes. This is due to an increase in surface polarity which enables the aqueous sample to make better contact with the surface of the resin (35). 

R. Azzam, A. Yasin, and T. Siyam, 6th lUPAC, Bratislava Conf. on Modified Polymers, Czechoslovakia, July 2-5, II, 100-106 (1984). 

Figure 2 The percent recovery of the modified polymer from rat small intestine after 1 h (a), and the schematic representation of in situ loop method using rat small intestine (b).

Fraction Molecular weight Unmodified polymer Modified polymer ... 

Modified PS by use of BF3-OEt2 catalyst had better properties comparised with virgin PS and other modified polymers. High thermostability and photosensitivity of modified PS compared with virgin PS are explained by the crosslinked structure of macromolecules formed during the processes of thermo- and phototreatment. 

Lewis et al. [52,53] have also determined labile chlorines in PVC by a crown ether catalyzed acetoxylation of PVC and the thermal degradation characteristics of the modified polymer. The values were comparable with those obtained by the phenolysis method. 

The modified NBR samples were characterized by differential scanning calorimetry [11,78-80,98]. The glass-transition temperature (T ) decreased with the level of hydrogenation. In the case of HFNBR, Tg increased with an increase in the addition of aldehyde groups to the polymer chain. Thermogravimetric analysis of the modified polymers have also been carried out [15]. 

Blends based on polyolefins have been compatibilized by reactive extrusion where functionalized polyolefins are used to form copolymers that bridge the phases. Maleic anhydride modified polyolefins and acrylic acid modified polyolefins are the commonly used modified polymers used as the compatibilizer in polyolefin-polyamide systems. The chemical reaction involved in the formation of block copolymers by the reaction of the amine end group on nylon and anhydride groups or carboxylic groups on modified polyolefins is shown in Scheme 1. 

Potyimides obtained by reacting pyromellitic dianhydride with aromatic amines can have ladder-like structures, and commercial materials are available which may be used to temperatures in excess of 300°C. They are, however, somewhat difficult to process and modified polymers such as the polyamide-imides are slightly more processable, but with some loss of heat resistance. One disadvantage of polyimides is their limited resistance to hydrolysis, and they may crack in aqueous environments above 100°C. 

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