Polymer matrix, trapping

To get polyurethane foams the polymer is formed along with gas evolution. When these two processes take place simultaneously the gas bubbles are trapped in polymer matrix yielding a cellular product. Slightly cross-linked products are flexible while highly cross-linked products are rigid. Both flexible and rigid foams are of commercial importance. 

Poly(vinyl alcohol) (PVA) seems to be one of the most efficient polymer matrix for CD-containing membranes owing to its ability to form free-standing films and its hydrophilic character due to the presence of hydroxyl groups. In these membrane materials CDs have been either trapped in PVA [83,84] or covalently linked to the chain [106],... 

A low or high molar mass stabilizing component whenever the polymer matrix of choice does not exert a stabilizing effect on the trapped protein drug. 

An irradiation-induced expansion could conceivably be caused by the ions, formed as precursors of the radicals, or by thermalized electrons trapped within the polymer. Irradiation induces electrical conductivity in polymers, and this conductivity decays after irradiation is ceased (4, 5). The decay process is accelerated by increased temperature or plasticity of the specimen, presumably by facilitating leakage of the trapped electrons or ions to ground. One might speculate that the sample expands upon irradiation because of the local mutual electrical repulsions of like charges which are trapped in the polymer matrix, and that both increased temperature and plasticizer content diminish this expansion because of charge leakage out of the specimen. It is difficult to prove or disprove this hypothesis. 

In the case of filled systems, the two latter effects provide a substantial contribution to C2 compared with the influence of trapped entanglements [80]. For filled systems, the estimated or apparent crosslinking density can be analyzed with the help of the Mooney-Rivlin equation using the assumption that the hard filler particles do not undergo deformation. This means that the macroscopic strain is lower than the intrinsic strain (local elongation of the polymer matrix). Thus, in the presence of hard particles, the macroscopic strain is usually replaced by a true intrinsic strain ... 

It is interesting to note that the efficiency of radical reactions in solid glassy matrices appears to be uninhibited by the presence of the polymer matrix and in fact in many cases we have observed that the efficiency of radical escape when at least one of the radicals is a small molecule is just as great in polymeric glasses as it is in solution. One can deduce from this that polymeric glasses are not particularly good at trapping radical species unless they are cooled to very low temperatures. 

For the development of drug delivery systems it is of fundamental importance to achieve the co-precipitation of drugs and biodegradable polymers. The supersaturation working conditions of S AS allow, in many cases, fast and simultaneous precipitation of both polymer and drugs, so that the drugs can be trapped into the polymer matrix. A list of the coprecipitation experimental results is reported in Table 9.9-5. 

Radiation grafting [83, 84, 85, 86, 87, 88, 89] is a very versatile and widely used technique by which surface properties of almost all polymers can be tailored through the choice of different functional monomers. It covers potential applications of industrial interest and particularly for achieving desired chemical and physical properties of polymeric materials. In this method, the most commonly used radiation sources are high-energy electrons, y-radiation, X-rays, U.V.-Vis radiation and, more recently, pulsed laser [90], infrared [91], microwave [92] and ultrasonic radiation [93]. Grafting is performed either by pre-irradiation or simultaneous irradiation techniques [94, 95]. In the former technique, free radicals are trapped in the inert atmosphere in the polymer matrix and later on the monomer is introduced into... 

Another method to retain cells is to trap the cells inside a polymer matrix. For instance, mammalian cells were entrapped in PEG-based hydrogel fabricated in glass-Si chips (see Figure 8.19). The cells included murine 3T3 fibroblasts and SV-40- transformed murine cells (i.e., hepatocytes, macrophages). A cell adhesion... 

Blowing agent—A chemical added to a monomer or polymer system to generate a gas that becomes trapped inside the polymer matrix, resulting in a foam. 

Jayalekshmy and Mazur illustrated the reduced mobility of polymer-bound reagents by delayed trapping of reactive intermediates generated within a polymer matrix 139). 

Anomalous migration data where the mobility decreases very rapidly with molecular size have been described by an entropic trapping of the molecules within the gel matrix. This effect should be noticeable when the pore size of the polymer matrix corresponds to the radius of gyration of the analyte. However, the electric forces reduce the entropic effect consequently it should contribute only at extremely low field strength. It does not seem relevant under normal CGE conditions, and cannot improve separations. 

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