Sulfur, bond strengths oxidation states

Metals, like many of the elements discussed in previous chapters, can exist in nature in several different oxidation states. When bonded to other elements, metal ions are almost always assigned a positive oxidation number and are somewhat electrophilic. Because of this, they are stabilized by association with electron-rich atoms. In particular, atoms that have a free electron pair can "donate" some of their electron density to the metal to form a bond. The most common and environmentally important donor atoms are oxygen, nitrogen, and sulfur. The bonds they form with metal ions range in strength from relatively weak associations such as those between a dissolved metal ion and water to very strong covalent bonds. These types of bonds are significant in both aqueous phase reactions and in the formation of insoluble compounds. 

The high lap shear strength of 4,4 -diaminodiphenylsulfide (TDA) with BTDA may be explained by the presence of a less rigid system compared to BTDA-4,4 -MDA due to the greater flexibility of the sulfur-carbon bond when sulfur is in this low oxidation state. BTDA-4,4 -diaminodiphenylsulfone had a lap shear strength of 1860 psi which is comparable to that for the 4,4 -MDA polymer. It is possible that the oxidized sulfur atom may restrict the flexibility of the sulfur-carbon bond. 

---