Analysis of reaction kinetics of end-functionalized polymers at a PS/P2VP interface by DSIMS

Abstract

Reactions to produce graft copolymers at polymer interfaces during extruder mixing are important for controlling dispersed phase size by retarding droplet coalescence and reducing interfacial tension while reinforcing the polymer interface. Such reactions are investigated at various temperatures in a model bilayer film system consisting of amine end-functional deuterated polystyrene (dPS-NH2) in PS and anhydride end-functional poly(2-vinylpyridine) (P2VP-ah) in P2VP. The interfacial excess (z*) of block copolymer formed by the reaction of dPS-NH2 and P2VP-ah at the interface is determined by detecting the H-2(-) ion using dynamic secondary ion mass spectrometry (DSIMS). The reaction kinetics is analyzed using a model based on a reaction-controlled mechanism for various reaction temperatures and molecular weights (M-n) of the end-functional chains. At low initial volume fractions phi(0) (similar to 0.01) of dPS-NH2 and P2VP-ah, such that the normalized interface excess (z*/R-g) < 1 and the blocks are unstretched, the forward reaction rate constant (k(+)) decreases as M-n(-0.70), in rough agreement with predictions of the model (k(+) similar to M-n(-0.55)) for this regime. The reaction is thermally activated with an activation enthalpy (similar to 160 kJ/mol) that is independent of M-n. The interfacial reaction, which is carried out under high-vacuum conditions so that any water produced by reaction would be efficiently removed, is reversible with an equilibrium constant K-rxn that has an enthalpy of reaction of -55 kJ/mol. This result means that the interface reaction does not proceed to form the cyclic imide, but likely stops at the amic acid.