Block copolymer Blocked isocyanate

Fluorourethanes can also be applied using powder coating technology. Resins suitable for this should have Tg values between 35°C and 120°C (95°F and 248°F) to optimize flow out and cure at the annealing temperature. Blocked isocyanates, which form free isocyanates after being heated above certain temperatures, are frequently used [50]. Certain FEVE copolymers with hydroxyl and carboxyl functionalities combined with blocked isophorone diisocyanate are suitable for powder coating technology [51]. 

Devise a copolymer containing blocked isocyanate groups, such that on reaction with a difunctional reagent to cure it, no reblocking would occur, and no volatile compound would come off. 

The use of blocked isocyanates for aqueous systems is of special interest. The sodium bisulfite blocking of hexamethy1ene diisocyanate was already described in Petersen s classic paper on blocked isocyanates ( ). Its application in cross-linking paper (75) and acrylamide copolymers (76) has been described. The stability of bisulfite-blocked aromatic isocyanates in water can present a difficulty, and various stabilizer systems have been proposed. Peters and Reddie (77) have made an extensive study of the various factors affecting stability and have found that optimum stability was obtained at pH of 2-3 in aqueous ethanol with excess hydrogen peroxide. 

The majority of the currently used coating systems is based on copolymers prepared from epoxy resins, polyfunctional amines, and partially blocked isocyanates (84-87). The resins are generally solubilized by the formation of cationic derivatives of amines by aminolysls of the carbamate in the partially blocked isocyanate. The principal applications of these cationic electrocoating systems are as automotive primers, in appliances, as primers and one-coat system.s, and in various other industrial applications. The main... 

A number of methods such as ultrasonics (137), radiation (138), and chemical techniques (139—141), including the use of polymer radicals, polymer ions, and organometaUic initiators, have been used to prepare acrylonitrile block copolymers (142). Block comonomers include styrene, methyl acrylate, methyl methacrylate, vinyl chloride, vinyl acetate, 4-vinylpyridine, acryUc acid, and -butyl isocyanate. 

Step-Growth Gopolymerization. A sample of a block copolymer prepared by condensation polymerisation is shown in equation 30 (37). In this process, a prepolymer diol (HO—Z—OH) is capped with isocyanate end groups and chain extended with a low molecular-weight diol (HO—E—OH) to give a so-called segmented block copolymer, containing polyurethane hard blocks and O—Z—O soft blocks. 

When polyols, di-isocyanates and glycols are reacted together as described in the previous section they do in fact tend to produce block copolymers as can be seen from the following reaction mechanism ... 

Isocyanates can be added to solvent-borne CR adhesive solutions as a two-part adhesive system. This two-part adhesive system is less effective with rubber substrates containing high styrene resin and for butadiene-styrene block (thermoplastic rubber) copolymers. To improve the specific adhesion to those materials, addition of a poly-alpha-methylstyrene resin to solvent-borne CR adhesives is quite effective [76]. An alternative technique is to graft a methacrylate monomer into the polychloroprene [2]. 

Polyaddition reactions based on isocyanate-terminated poly(ethylene glycol)s and subsequent block copolymerization with styrene monomer were utilized for the impregnation of wood [54]. Hazer [55] prepared block copolymers containing poly(ethylene adipate) and po-ly(peroxy carbamate) by an addition of the respective isocyanate-terminated prepolymers to polyazoesters. By both bulk and solution polymerization and subsequent thermal polymerization in the presence of a vinyl monomer, multiblock copolymers could be formed. 

The block lengths and the final polymer molecular weight are again determined by the details of the prepolymer synthesis and its subsequent polymerization. An often-used variation of the one-prepolymer method is to react the macrodiol with excess diisocyanate to form an isocyanate-terminated prepolymer. The latter is then chain-extended (i.e., increased in molecular weight) by reaction with a diol. The one- and two-prepolymer methods can in principle yield exactly the same final block copolymer. However, the dispersity of the polyurethane block length (m is an average value as are n and p) is usually narrower when the two-prepolymer method is used. 

Furukawa et al. 67) have synthesised block copolymers with polystyrene and polyether segments from azo group-containing prepolymers, which were prepared by reaction of a low-molar-mass azobis-alcohol with polyether glycols containing isocyanate endgroups ... 

Aluminum isopropoxide has been used for the preparation of block copolyesters [147, 148]. Tri-block poly(e-CL-b-DXO-e-CL) was prepared by the sequential addition of different monomers to a living polymerization system initiated with aluminum isopropoxide in THF or toluene solution [95]. An alternative route for the preparation of the tri-block copolymer was to react the diblock poly(e-CL-b-DXO) containing an -OH functionality at the chain end using a difunctional coupling agent such as isocyanate or acid chloride (Scheme 18). However, the molecular weights were low and full conversion of monomers was not achieved. 

This reaction is often employed in the production of flexible urethane foams, which are frequently block copolymers of polyether or polyester segments joined to polyurea segments. (The polyester or polyether segments terminate in urethane segments resulting from reaction of polyether or polyester hydroxyl end groups with the isocyanate.)... 

Starting from these aminofunctional siloxanes, PDMS-urea block copolymer can be obtained easily [6]. The synthesis is performed by polyaddition of aminoaikyl-terminated polydimethylsiloxanes with diisocyanates to yield thermoplastic silicone elastomers (TPSE). The reaction between the amino and the isocyanate group gives highly polar urea groups, which solidify at room temperature (Scheme 1). 

The synthesis of siloxane-urea block copolymers can be performed either in solution or in the melt at elevated temperatures up to 200 °C. We favor the use of dynamic mixers or extruders to ensure intensive mixing of the components. Surprisingly, adding aminosiloxane and isocyanate to get the block copolymers (2K process) is not the only possibility. We can also add the silanol fluid, the cyclic aminosilane, and the diiosocyanate consecutively to the extruder for a successful solventless preparation of siloxane-urea block copolymers (3K process). 

Nylon block copolymers were previously synthesized from the anionic polymerization of caprolactam in the presence of polyurethane prepolymers. (11) The prepolymers, prepared from the reaction of diisocyanates with polyether glycols, contained Isocyanate end groups which initiated caprolactam polymerization. Sodium caprolactam was used to catalyze the reaction. This copolymer system is the basis for some current areas of nylon 6 RIM research. (12) NYRIM nylon block copolymers are formed from stoichiometric mixtures of polymeric polyols and caprolactam using poly acyllactam initiation which was described previously. The reactions are as follows ... 

Ober and Thomas et al. reported on rod—coil diblock copolymers consisting of poly(hexyl isocyanate) as the rod block and polystyrene as the coil block (Scheme 2).51 53 The polymers (2) were synthesized... 

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