Poly(vinylamine), PVA, complexes with cobalt chloride hexahydrate exhibit a 45 degrees C enhancement in the glass-transition temperature per mol % of the d-block metal cation. Poly(ethylene imine), PEI, complexes with CoCl2(H2O)(6) exhibit a 20 degrees C enhancement in T-g per mol % Co2+. Since the basicities of primary and secondary amines are comparable (i.e., pK(b,PVA) approximate to 3.34 vs. pK(b,PEI) approximate to 3.27) and the rates at which each polymeric ligand displaces waters of hydration in the coordination sphere of Co2+ are similar, transition metal compatibilization is operative in blends of both polymers with CoCl2(H2O)(6). These two polymers are immiscible in the absence of the inorganic component. Infrared spectroscopy suggests that nitrogen lone pairs in PVA and PEI coordinate to Co2+. The stress-strain response of a 75/25 blend of PVA and PEI with 2 mol % Co2+ reveals a decrease in elastic modulus from 4.4 x 10(9) N/m(2) to 5.7 x 10(7) N/m(2), a decrease in fracture stress from 3.7 x 10(7) N/m(2) to 2.0 x 10(6) N/m(2), and an increase in ultimate strain from 1.3 to 12% relative to the 75/25 immiscible polymer-polymer blend. A plausible explanation for this effect is based on the fact that cobalt chloride hexahydrate compatibilizes both polymers by forming a coordination bridge between nitrogen lone pairs in dissimilar chains. Hence, poly(ethylene imine), which is very weak with a T-g near -40 degrees C, is integrated into a homogeneous structure with poly(vinylamine) and the mechanical properties of the individual polymers are averaged in the compatibilized ternary complex.