Film hydroxyl groups urethanated

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... 

Surface Concentration, Cs, of the Hydroxyl Groups Urethanated for Cellulose and PVA Films and Surface Area, As, per Hydroxyl Group... 

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. 

Carboxyl and hydroxyl groups are added also to the polymer chain to increase compatibility with other resinous materials such as melamine, alkyds, urethanes, etc. Some cases of incompatibility between polymers may not originate from polymer chemistry but rather from solvent strength. If a vinyl terpolymer in a ketone solvent system is mixed with another polymer system which is dissolved primarily in (for example) an alcohol, the solvent mixture may be too lean for the vinyl which will precipitate out or develop a hazy film. 

This reaction is associated with the formation of new isocyanate groups, which immediately add to excess hydroxyl groups to form more urethane species. The emergence of carbodiimide is still incomplete after 4 h of post-curing in films on Au and A1 and in the bulk. Only on copper are no carbodiimide bands observed after post-curing, even in thick films (e.g., dpu = 2pm in Fig. 6.7). Instead, a new chemical species develops with an IR band at 1660 cm , which is probably a reaction product of the carbodiimide consumption. 

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