Hydroxyl group reactions urethanes

Faster oxide addition rates Lower polyol viscosity Primary hydroxyl groups Faster urethane reaction Poor himidity aging properties Propylene Oxide... 

Secondary hydroxyl groups Slower urethane reaction Better humidity aging stability Mixture of Ethylene and Propylene Oxide ( ) Faster oxide addition Primary and secondary hydroxyls Lower polyol viscosity Good humidity aging properties... 

Preparation of the polymer can be carried out in glass equipment at atmospheric pressure at temperatures typically above 100°C, but the higher pressures in an autoclave result in much faster reaction rates. Each polymer molecule which used butanol as a starter contains one hydroxyl end group as it comes from the reactor diol-started polymers contain two terminal hydroxyls. Whereas a variety of reactions can be carried out at this remaining hydroxyl to form esters, ethers, or urethanes, this is normally not done and therefore lubricant fluids contain at least one terminal hydroxyl group (36). 

This process is based on the very high reactivity of the isocyanate group toward hydrogen present ia hydroxyl groups, amines, water, etc, so that the chain extension reaction can proceed to 90% yield or better. Thus when a linear polymer is formed by chain extension of a polyester or polyether of molecular weight 1000—3000, the final polyurethane may have a molecular weight of 100,000 or higher (see Urethane polymers). 

Surface Concentration of Hydroxyl Groups. Since it has been concluded that the urethanation with monoisocyanates in toluene is limited to the hydroxyl groups present at the film surface, we can evaluate the concentration of the hydroxyl groups that are present at the surface, more strictly, accessible to the reaction with isocyanates. The amounts of hydroxyl groups urethanated to saturation, obtained from Figures 7, 9 and 11 are summarized in Table I, which also contains the values obtained from experiments not shown here. These are expressed as surface concentration per cm of films, which are assumed to have a perfectly flat... 

Many of the common condensation polymers are listed in Table 1-1. In all instances the polymerization reactions shown are those proceeding by the step polymerization mechanism. This chapter will consider the characteristics of step polymerization in detail. The synthesis of condensation polymers by ring-opening polymerization will be subsequently treated in Chap. 7. A number of different chemical reactions may be used to synthesize polymeric materials by step polymerization. These include esterification, amidation, the formation of urethanes, aromatic substitution, and others. Polymerization usually proceeds by the reactions between two different functional groups, for example, hydroxyl and carboxyl groups, or isocyanate and hydroxyl groups. 

The three secondary hydroxyl groups in the 12-posihon are somewhat slow to react with diisocyanates and generally require heat for the completion of reaction. This can be of advantage or disadvantage depending upon the specific application. Modifications of CO and particularly of ricinoleic acid through esterification results in products that are of considerable interest as polyols for various urethane applications [88, 89]. 

If the hydroxyl group (-OH) in a conventional diol is replaced by an amine group (-NH2), polyamines are formed. The polyamines can be used in a similar manner to polyols to form a polyurea on reaction with diisocyanate. These polymers do not have any urethane groups, only urea groups. Because... 

In the present work we have used, therefore, dextran as the water-soluble macromolecule to be coupled and a film of an ethylene-vinyl alcohol copolymer (EVAL) as the substrate material. This copolymer has hydroxyl groups but is insoluble in water and can be injection-molded to yield a material with good mechanical properties. The coupling reaction of dextran onto the film surface will be achieved by using diisocyanate, since dextran, as well as EVAL, has hydroxyl groups which readily react with isocyanate under formation of urethane linkage. 

Urethane adhesives take their name from the product of the most common step-growth polymerization reaction used to generate the adhesive polymers. Isocyanates react with hydroxyl groups to create urethane (or carbamate) linkages ... 

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