Reactivity prepolymer

Following this work, the y -12F-diol was used for the direct reaction with hexamethylene-1,6-diisocyanate in the presence of dibutyltin dilaurate to produce a cross-linked elastomer or a reactive prepolymer which was terminated with either isocyanate or hydroxyl groups, depending on which reactant was in excess (142,143). 

Interfdci l Composite Membra.nes, A method of making asymmetric membranes involving interfacial polymerization was developed in the 1960s. This technique was used to produce reverse osmosis membranes with dramatically improved salt rejections and water fluxes compared to those prepared by the Loeb-Sourirajan process (28). In the interfacial polymerization method, an aqueous solution of a reactive prepolymer, such as polyamine, is first deposited in the pores of a microporous support membrane, typically a polysulfone ultrafUtration membrane. The amine-loaded support is then immersed in a water-immiscible solvent solution containing a reactant, for example, a diacid chloride in hexane. The amine and acid chloride then react at the interface of the two solutions to form a densely cross-linked, extremely thin membrane layer. This preparation method is shown schematically in Figure 15. The first membrane made was based on polyethylenimine cross-linked with toluene-2,4-diisocyanate (28). The process was later refined at FilmTec Corporation (29,30) and at UOP (31) in the United States, and at Nitto (32) in Japan. 

From these, prepolymers are prepared where the diisocyanates may be completely reacted as in the case of the urethane oils which resemble the oil-modified alkyds but have urethane (—NHCOO—) links in place of the ester (—COO—) links of the alkyds, or where one only of the isocyanate groups is combined, leaving the other to participate in crosslinking reactions. Such a reactive prepolymer is the biuret that may be prepared from hexamethylene diisocyanate, has the following structure ... 

The cationic ring-opening polymerization of epichlorohydrin in conjunction with a glycol or water as a modifier produced hydroxyl-terminated epichlorohydrin (HTE) liquid polymers (1-2). Hydroxyl-terminated polyethers of other alkylene oxides (3 4), oxetane and its derivatives (5 6), and copolymers of tetrahydrofuran (7-15) have also been reported. These hydroxyl-terminated polyethers are theoretically difunctional and used as reactive prepolymers. 

Reactive prepolymers used as binders are produced by acrylation of oligomers, such as epoxy resins, urethanes, polyesters, silicones, oligo-buta-diene, melamine derivatives, cellulose, and starches. Prepolymers are the principal ingredients of coating formulations and largely determine the basic properties of the coating. Examples of industrially important acrylated prepolymers are in Table 5.9. 

The chemical structure of the epoxy matrix constituent as well as processing are reported to strongly influence 11 -I3> the thermoset network and hence the properties and durability of the crosslinked polymer 11 ,4-16). The cure of a reactive prepolymer involves the transformation of low-molecular-weight reactive substances from liquid to rubber and solid states as a result of the formation of a polymeric network by chemical reaction of some groups in the system. Gelation and vitrification are the two macroscopic phenomena encountered during this process which strongly alter the viscoelastic behavior of the material. 

Silicone polymers commonly have cross-linked network structures created by reacting a reactive prepolymer with a cross-linking agent. For example, a hydroxy-terminated polydimethylsiloxane is cross-linked with a methoxy-substituted silane and a catalyst as follows ... 

Once the fiber is sufficiently cool, e.g. below 80 C (0, it can be coated, generally with one or two layers of organic polymers. Because the application method must not damage the glass surface, the polymers are applied in the liquid state, commonly as reactive prepolymer or hot melt formulations. The coating diameter and concentricity are monitored and controlled via suitable techniques (5 ). Once applied the coating must solidify very rapidly, before the fiber... 

The alkaline catalyst systems used for caprolactam polymerization are suitable for both the prepolymer and copolymerization reactions. The preferred catalyst Is caprolactam magnesium bromide, prepared by reaction of Grignard reagent with caprolactam. With NYRIM copolymers, a two-package system Is used—reactive prepolymer and catalyst concentrate. These are dissolved in caprolactam to make up the two reactive streams. 

Chemically reactive prepolymers and intermediate products of monomeric substances (1C and 2C adhesives)... 

Liquid State. The liquid state in most thermoplastics is produced by heating until molten in vinyls it is generally obtained by dispersing resin particles in plasticizer to produce a plastisol and in rubber it is obtained by use of latex. In thermosetting plastics, the monomers are reacted only up to low molecular weight reactive prepolymers, which are still liquid or at least readily fusible at low temperature. 

The simplest UV-curable ink or coating formulations may consist of only three components. In practice, however, a typical industrial formulation contains a much greater number of ingredients. The three essential components are (1) a UV-reactive prepolymer which provides the bulk of the desired properties, (2) a diluent system composed of multifunctional acrylate esters (and at times monofunctional acrylic esters) and (3) a photoinitiator system. The most commonly used multifunctional acrylate in an UV-curable ink or coating formulation is an acrylic acid ester of either pentaerythritol (PETA), trimethyl-olpropane (TMPTA) or hexanediol (HDDA). 

UV-reactive prepolymer based on an acrylated aliphatic isocyanate... 

One-component reactive prepolymer that reacts with moisture from the air to give a polymer. 

Another compound which has been found to somewhat imitate the active site of peroxidases is the commercially available Fe(II)-salen catalyst. This catalyst was used successfully to produce phenol polymers, which could be of interest for industrial production [153,154]. For example, cardanol can be polymerized by the Fe(II)-salen catalyst [155]. Due to the unsaturated bonds in the side chain of the cardanol components, the resulting polymers could be thermally cured, or cured by use of cobalt naphthenate to give brilliant films with a high-gloss surface. This reaction proves that reactive prepolymers can be synthesized from renewable resources (cardanol is the main component obtained by thermal treatment of cashew nutshell liquid). This process could be a true alternative to conventional phenol-formaldehyde resins (Scheme 25) [ 155]. Other non-heme iron complexes have been foimd to... 

For the prepartion of networks from reactive prepolymers commercially available monomers were used as received. Glycidyl methacrylate GMA was obtained from the American Aniline and Extract Company. 

The reactive prepolymer and the crosslinking agent were dissolved in acetone and catalyst added. Solvent was evaporated at room temperature under vacuum to form a dry foam which was subsequently powdered and further dried under vacuum at The... 

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