Polymerizations, surface

Studies of the copolymerization of VDC with methyl acrylate (MA) over a composition range of 0—16 wt % showed that near the intermediate composition (8 wt %), the polymerization rates nearly followed normal solution polymerization kinetics (49). However, at the two extremes (0 and 16 wt % MA), copolymerization showed significant auto acceleration. The observations are important because they show the significant complexities in these copolymerizations. The auto acceleration for the homopolymerization, ie, 0 wt % MA, is probably the result of a surface polymerization phenomenon. On the other hand, the auto acceleration for the 16 wt % MA copolymerization could be the result of Trommsdorff and Norrish-Smith effects. 

In these cases, the polymer remains processible in the gelled state, because it is in the form of discrete PSA particles dispersed in the reaction medium. However, once the particles are dried, redispersion may be difficult if strong interactions develop between the particle surfaces. Polymerization of the acrylic PSA directly on the substrate, as in the case of UV polymerization, can also yield a covalently crosslinked polymer that does not require any further coating steps [71]. 

Adsorption reactions on nonporous surfaces are generally quite rapid (unless there is a large activation energy barrier). By contrast, surface polymerization reactions are usually much slower. Thus it is likely that the initial high level of arises from adsorption, while the subsequent small, but continuous, increase in is caused by the thickening polymer film. 

H. Schulz, K. Beck, E. Erich. 1988. Fischer-Tropsch CO-hydrogenation, a non trivial surface polymerization Selectivity of branching. In Proceedings of the 9th International Congress on Catalysis, Calgary, Vol. 2, p. 829. 

For a precipitated iron catalyst, several authors propose that the WGS reaction occurs on an iron oxide (magnetite) surface,1213 and there are also some reports that the FT reaction occurs on a carbide surface.14 There seems to be a general consensus that the FT and WGS reactions occur on different active sites,13 and some strong evidence indicates that iron carbide is active for the FT reaction and that an iron oxide is active for the WGS reaction,15 and this is the process we propose in this report. The most widely accepted mechanism for the FT reaction is surface polymerization on a carbide surface by CH2 insertion.16 The most widely accepted mechanism for the WGS reaction is the direct oxidation of CO with surface 0 (from water dissociation).17 Analysis done on a precipitated iron catalyst using bulk characterization techniques always shows iron oxides and iron carbides, and the question of whether there can be a sensible correlation made between the bulk composition and activity or selectivity is still a contentious issue.18... 

Fischer-Tropsch synthesis can be regarded as a surface polymerization reaction since monomer units are produced from the reagents hydrogen and carbon monoxide in situ on the surface of the catalyst. Hence, a variety of hydrocarbons (mainly n-paraffines) are formed from hydrogen and carbon monoxide by successive addition of C, units to hydrocarbon chains on the catalyst surface (Equation 12.1). Additionally, carbon dioxide (Equation 12.3) and steam (Equations 12.1 and 12.2) are produced C02 affects the reaction just a little, whereas H20 shows a strong inhibiting effect on the reaction rate when iron catalysts are used. 

Surface polymerization of thiophenes was fou d to be affected by both surface impurities and substituent groups on the thiophene ring. The reactions of thiophene on a Ni(lll) surface with sulfur impurities was examined [11]. The sulfur inhibited the polymerization so that the only reactions observed were desorption of thiophene with a small... 

FIGURE 5.5 Synthesis schemes for chromatographic stationary phases (a) monomeric synthesis where X represents reactive (e.g., chloro or alkoxy) or nonreactive (methyl) substituents, (b) solution polymerization, in which water is added to the slurry and (c) surface polymerization, in which water is added to the silica surface. 

Aromatization according to Fig. 11a requires fewer surface sites than coke formation. A high amount of additives [such as Pb (24), Sn (74), and Re (143)] may dilute the catalyst surface to an extent where aromatization still might proceed over a platinum island, but surface polymerization is not possible anymore. 

With the development of enzymatic polymerization in solution, also first accounts for SIP appeared. Loos et al. [350] reported on enzymatic surface polymerization of glucose-l-phosphate with potato phosphorylase as the catalyst resulting in oligo- or poly-(a,l- 4)-D-glucopyranose. As initiator sites, immobilized malto-heptaose was used. Enzymatic grafting of hexyloxyphenol onto chitosan is reported by Payne and coworkers [351]. 

These new data acquired with double-labeled vinyl probes (13CH2=13CHBr and 13CH2=13CH2) determined first on Rh, but found to be similar for more common Fischer-Tropsch catalysts (Ru, Fe, Co) showed that these are readily incorporated into the alkene and the alkane products. In addition, an increase in the rate of hydrocarbon formation was observed during vinylic but not ethyl addition. These data indicate that the participation of vinyl intermediates is an integral part of the surface polymerization mechanism, specifically, vinyl (alkenyl) intermediates couple with surface methylene in hydrocarbon formation ... 

Soil - Floor wax, oil, grease, particulates Surface - Polymeric flooring Application Method - Wipe or mop... 

In the preceeding section we discussed physisorbed polymers. Now we concentrate on chemisorbed polymer layers (review Ref. [424], see also Section 6.7). Chemisorbed polymers on solid surfaces have the advantage of forming thick flexible layers up to several 100 nm thickness. Due to the flexibility of the polymer chains the layer is relativley homogeneous. Additionally, the large variety of the monomers suitable for surface polymerization leads to a large variety in the surface properties. Also, the mechanical flexibility can be manipulated by the polymer chain density. A high density leads to polymer brushes. 

The coagulum deposited on the reactor surfaces may be the result of polymerization in large monomer drops or a separate monomer layer, or it may be the result of polymerization of the monomer in the vapor space above the latex or a surface polymerization on the walls and roof of the reactor. Polymerization in the vapor space of the reactor will form solid polymer in the form of particles which may stick to the reactor surfaces or fall into the latex in the later case, these particles serve as nuclei for the formation of coagulum. Polymerization of monomer on the reactor surfaces will form solid particles that become swollen with monomer and grow by flocculation of the latex particles. The surface polymerization can be related to the smoothness of the reactor surface the smoother the surface, the lesser the tendency for surface polymerization and formation of coagulum. 

As mentioned, polymer hybrids based on POs are effective as a compati-bilizer between the olefinic materials and polar ones. Furthermore, some polymer hybrids, such as PP-g-PMMA, etc., show good mechanical strength as polymer materials. On the other hand, surface modification of the molded polymer is one of the most attractive methods to let polyolefin materials functionalize. In this sense, surface polymerization of functional monomers on polyolefins is an important subject for polyolefin hybrids. As previously referred to, the growth of PS on PP via the RAFT process has been reported [92]. 

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