Plasma Polymerization sequences

The reaction mechanisms of plasma polymerization processes are not understood in detail. Poll et al [34] (figure C2.13.6) proposed a possible generic reaction sequence. Plasma-initiated polymerization can lead to the polymerization of a suitable monomer directly at the surface. The reaction is probably triggered by collisions of energetic ions or electrons, energetic photons or interactions of metastables or free radicals produced in the plasma with the surface. Activation processes in the plasma and the film fonnation at the surface may also result in the fonnation of non-reactive products. 

Considering that the system pressure continues to increase after most of the polymerizable species are exhausted in the gas phase, plasma polymerization of TMS in a closed system can be visualized as a time-delayed, consecutive application of three fundamental processes. The sequence takes the order (1) deposition of Si species, (2) deposition of C species, and (3) H2 plasma treatment of the deposited plasma polymer. 

In order to modify favorably the interaction balance at PE/PS contacts, mica was subjected to LMP treatments using E and S monomers in sequence. In principle, the generation of plasma-polymerized ethylene (PPE) and styrene (PPS) on the mica surface might... 

The extent of reversed monomeric units is routinely determined by high-resolution NMR methods, using predominately F spectra and, less frequently, C spectra [580-582]. F-NMR can also be used to measure chain branching in head to-tail sequences. Plasma polymerized samples yield more complex spectra as a result of extensive cross-linking, branching, and unsaturation [554]. 

Figure 3. Schematic of reaction sequences in plasma polymerizations.

Fibrin polymerization is initiated by the enzymatic cleavage of the fibrinopeptides, converting fibrinogen to fibrin monomer (Fig. 1). Then, several nonenzymatic reactions yield an orderly sequence of macromolec-ular assembly steps. Several other plasma proteins bind specifically to the resulting fibrin network. The clot is stabilized by covalent ligation or crosslinking of specific amino acids by a transglutaminase, Factor XHIa. 

Wzy-dependent pathway is most widespread in O polysaccharide biosynthesis. Following the assembly of O repeating units, the individual und-PP-linked O units are exported to the site of polymerization at the periplasmic face of the plasma membrane (Figure 2). This process requires a Wzx protein, the O unit transporter (flippase), which is highly hydrophobic with 12 potential transmembrane domains. Although the Wzx proteins share little primary sequence similarity, they do share structural features with bacterial permeases... 

Polymeric materials are used in a wide range of medical applications, because of their unique physical properties such as strength, elasticity, and pliability. A potential application could include small diameter vascular implants if one of the major problems of polymeric biomaterials in contact with blood, thrombus formation, could be overcome. Although the underlying processes are not completely understood, an initial step in the thrombogenic sequence is the adsorption of plasma proteins to the surface of a material followed by adhesion of platelets and/or leukocytes.2 3 The extent of thrombosis, in turn, is related to the... 

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