Condensation polymerization cross-linking

Polymerization. Thermal polymerization or curing of an ink film at elevated temperatures can foUow many different chemical paths. Condensation and cross-linking reactions may be accompHshed with or without the use of catalysts. However, this method of drying generally has not been widely used for printing inks, except those used for metal and glass decoration, and some clear coatings. 

The principles of forming furan polymers from the condensation of furfuryl alcohol have become attractive for modifying wood, when ways of controlling the polymerization in dilute systems were discovered. There are several competing reactions condensation and cross-linking reactions of furfuryl alcohol with itself and also the reaction between furfuryl alcohol and lignin units is supposed (Scheme 9.4.10). ... 

PET-PEG copolymers were synthesized by melt-condensation method with a custom made reactor [13-15]. Polymerization was carried out in two steps oligomer was prepared in the first step with DMT, EG, and PEG-200, and the oligomer made in first step was condensed and cross-linked with the agent in the second step at high temperature and high vacuum to shift reaction equilibrium further to product. Detailed synthetic procedime for PET-PEG copolymer can be found in our previous paper [13-15]. Synthetic scheme and characterization of copolymers are shown in the results and discussion section. 

Haward et al.t have reported some research in which a copolymer of styrene and hydroxyethylmethacrylate was cross-linked by hexamethylene diisocyanate. Draw the structural formula for a portion of this cross-linked polymer and indicate what part of the molecule is the result of a condensation reaction and what part results from addition polymerization. These authors indicate that the crosslinking reaction is carried out in sufficiently dilute solutions of copolymer that the crosslinking is primarily intramolecular rather than intermolecular. Explain the distinction between these two terms and why concentration affects the relative amounts of each. 

A unique feature of in situ encapsulation technology is that polymerization occurs ia the aqueous phase thereby produciag a condensation product that deposits on the surface of the dispersed core material where polymerization continues. This ultimately produces a water-iasoluble, highly cross-linked polymer capsule shell. The polymerization chemistry occurs entirely on the aqueous phase side of the iaterface, so reactive agents do not have to be dissolved ia the core material. The process has been commercialized and produces a range of commercial capsules. 

Certain polymeric stmctures can also be blended with other coreactive polymers or multifunctional reactive oligomers that affect curing reactions when exposed to ir radiation. These coreactive polymers and cross-linking oligomers undergo condensation or addition reactions, which cause the formation of network stmctures (Table 9) (4,5,47). 

The well-known condensation between 2-furaldehyde and acetone in a basic medium yields what is usually called furfurylidene acetone monomer composed of a mixture of 2-furfurylidene methyl ketone, di-2-furfurylidene ketone, mesityl oxide and other oligomers derived from further condensation reactions135. This mixture is then polymerized by the action of an acidic catalyst in the first phase of the reaction a polymer of low molecular weight is produced which on further treatment cross-links to a black insoluble and heat-resistant material136. ... 

Vinyl addition polymerizations, being chain reactions, are more complex than condensation polymerizations and they are generally more likely to include minor side reactions leading to branching or cross-linking. The structures of the pol3oneric products are consequently more difficult to establish with certainty. 

Polycondensation pol5mers, like polyesters or polyamides, are obtained by condensation reactions of monomers, which entail elimination of small molecules (e.g. water or a hydrogen halide), usually under acid/ base catalysis conditions. Polyolefins and polyacrylates are typical polyaddition products, which can be obtained by radical, ionic and transition metal catalyzed polymerization. The process usually requires an initiator (a radical precursor, a salt, electromagnetic radiation) or a catalyst (a transition metal). Cross-linked polyaddition pol5mers have been almost exclusively used so far as catalytic supports, in academic research, with few exceptions (for examples of metal catalysts on polyamides see Ref. [95-98]). 

As an alternative, stable high-coverage nonpolar RPC sorbents phases have been prepared by cross-linking hydrophobic polymers at the silica surface, either via free radical 143 or condensation 101 polymerization chemistry. In this case, the underlying silica becomes partly protected from hydrolytic degradation due to the presence of the hydrophobic polymer film coating that effectively shields the support material. Similar procedures have been employed to chemically modify the surface of other support materials, such as porous zirconia, titania, or alumina, to further impart resistance to degradation when alkaline mobile-phase conditions are employed. Porous polystyrene-divinylbenzene sorbents, be-... 

Fig. 23a. Hydration and dehydration reactions of the silica surface and the IR absorption frequencies of the surface species. Chemisorption of water produces surface silanols, which serve as adsorption sites for water, b Reaction of octadecyltrichlorosilane (OTS). Hydrolysis of the chloride group by trace amounts of water in solution to silanol is followed by condensation with surface silanols, resulting in covalent bond formation between the monolayer and the substrate. OTS molecules can also cross-link to form polymeric species during film curing [201]...

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