Transition metal compatibilization of poly(vinylamine) and poly(ethylene imine)

Poly(vinylamine), PVA, complexes with cobalt chloride hexahydrate exhibit a 45 °C enhancement in the glass‐transition temperature per mol % of the d‐block metal cation. Poly(ethylene imine), PEI, complexes with CoCl 2 (H 2 O) 6 exhibit a 20 °C enhancement in T g per mol % Co 2+ . Since the basicities of primary and secondary amines are comparable (i.e., pK b,PVA ≈ 3.34 vs. pK b,PEI ≈ 3.27) and the rates at which each polymeric ligand displaces waters of hydration in the coordination sphere of Co 2+ are similar, transition metal compatibilization is operative in blends of both polymers with CoCl 2 (H 2 O) 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 Co 2+ . The stress–strain response of a 75/25 blend of PVA and PEI with 2 mol % Co 2+ reveals a decrease in elastic modulus from 4.4 × 10 9 N/m 2 to 5.7 × 10 7 N/m 2 , a decrease in fracture stress from 3.7 × 10 7 N/m 2 to 2.0 × 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 °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. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 552–561, 2000