Crosslinked polyols

A water-retaining hydrogel (W. R. Grace s Hypol) illustrates the many possibilities of molecular engineering within the realm of PURs. In this case, a crosslinked polyol is treated with TDI, for example, to give a hydrophilic semisolid that can be employed as a carrier of medicinals for the treatment of surface wounds, fragrances in personal-care products, and so on. 

Uses Blocked catalyst for use in isocyanate-crosslinked polyols like solv.-based and aq. hydroxy acrylates and polyesters, e.g., forced drying two-pack lacquers... 

Chem. Descrip. Catalyst in butyl acetate/polyglycol Uses Catalyst reducing drying time in solv.-based and aq. isocyanate-crosslinked polyols, hydroxy acrylates, and polyesters, lacquers Properties YIsh. clear to si. turbid liq. vise. < 20 mPa s (20 C) flash pt. 34 C 30% act. 

The incorporation of carbohydrates into non-polysaccharide structures is an important strategy to attain i) highly functional polymers U) specific biological functions, and Hi) complex systems that act as smart materials. Polyesters with carbohydrate or polyol repeat units in the chain can be produced by chemical methods. However, elalH)rate protection-deprotection steps are needed to avoid crosslinking between polyol units. Multi-step routes to non-crosslinked polyol polyesters limit the potential of their practical use. 

Vigo T L, Antimicrobial acting of cotton fabrics containing crosslinked polyols , Proc. - Beltwide Cotton Conf, 1993, (3), 1424-5. 

Crosslinked polyols Physical barrier to microbial growth 32... 

Even with elastomers, it is often desirable to phase mix the material for certain combinations of physical properties. For example, elastomers with high hardness and flexural modulus are prepared from polyisocyanates, polyols, and polyamines of high functionality, creating a high crosslink density. Although polyol chains... 

The chemistry of the glycolysis of polyurethanes is complicated by the fact that there are additional groups in the polymer such as ureas, allophanates, and biurets, and die PURs may be crosslinked. In die presence of the appropriate glycols and at about 200°C, PURs undergo transesterification to form polyols. Under the same conditions, ureas undergo glycolysis to form urethanes and amines (Fig. 10.5). 

Figure 5. Weighted concentration of effective strands versus bake temperature for a typical high solids polyol crosslinked with hexamethoxymethylmelamine. The ratio of methoxy to hydroxy groups is given by "R". For the dashed lines, the extent of methoxy self-condensation is assumed to be zero. The solid lines use the self-condensation data of T. Nakamichi, Prog. Org. Coat., 14, 23 (1986).

Crosslinking of polyurethanes proceeds in different ways depending on the stoichiometry and choice of reactants and reaction conditions. For example, an isocyanate-terminated trifunctional prepolymer is prepared by reaction of a polyol and... 

Similarly to the phospholipid polymers, the MPC polymers show excellent biocompatibility and blood compatibility [43—48]. These properties are based on the bioinert character of the MPC polymers, i.e., inhibition of specific interaction with biomolecules [49, 50]. Recently, the MPC polymers have been applied to various medical and pharmaceutical applications [44-47, 51-55]. The crosslinked MPC polymers provide good hydrogels and they have been used in the manufacture of soft contact lenses. We have applied the MPC polymer hydrogel as a cell-encapsulation matrix due to its excellent cytocompatibility. At the same time, to prepare a spontaneously forming reversible hydrogel, we focused on the reversible covalent bonding formed between phenylboronic acid and polyol in an aqueous system. 

These are liquid systems that can be produced either in a one shot system (i.e., the diisocyanate, polyol and chain extender reacted in one stage) or, more usually, as a prepolymer which is chain extended and crosslinked at a later stage. 

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