124 H. E. SCHROEDER AND S. N. BOYD 



MYDROGEN-BONOING GROUPS 

 (o) ELECTRON- DONORS (b) ELECTRON- ACCEPTORS 



Fig. 12 



A similar picture is obtained with polyacrylonitrile which can be basified by 

 copolymerization of acrylonitrile with vinyl pyridine. A cationic site is created 

 by treatment with acid, or by dyeing at low pH. Dye anions are then iixed on 

 the cationic sites. The case of the polyacrylonitrile is interesting in that it has 

 been necessary to assume for absorption of proton the existence of two types of 

 site, differing in basicity. At very low pH where all the basic sites will appear 

 equivalent, an excellent fit with straight line results. At higher pH it has been 

 necessary to calculate a new expression for two types of site. The fit of data with 

 the derived two site expressions is excellent. 



The primary attraction of anionic dyes to basic polymers is thus ascribable 

 to ionic forces functioning in the same way as in the absorption of simple acids. 



A whole class of dyes, the so-called '"acid dyes," dye wool or nylon by just 

 this simple process. These colors consist of a very simple organic chromophore 

 with attached negative charge (Fig. 14). Despite considerable variety in their 

 chemistry, they have no particular structural features promoting dyeing other 

 than their anionic nature. Simple coulombic forces result in athxation of dye 

 anion on the protonated fiber cation. Indeed, this process is practical for dyeing 



S03~ 





SOj" 



_A. SHOWS GREATER AFFINITY THAN J_ 



Fig. 13 



