Homogeneous reactive coupling of terminally functional polymers

The rates of nine melt coupling reactions were measured by reacting terminally functional polymer chains. The functional groups are carboxylic acid, oxazoline, epoxy, aromatic primary amine, aliphatic primary amine, hydroxyl and cyclic anhydride. The functional groups were attached to the end of polystyrene (PS) and poly(methyl methacrylate) (PMMA) chains with most experiments performed at molecular weights of about 25,000 g/mol and temperature of 180°C. Reactions were performed homogeneously by blending stoichiometric amounts of the same type of polymer containing complementary functional groups. Reaction rates were determined from the amount of coupled chains via gel permeation chromatography. The functional group pairs, in order of increasing reactivity, are acid/amine, hydroxyl/(anhydride or acid), aromatic amine/epoxy, aliphatic amine/epoxy, acid/oxazoline, acid/epoxy, aromatic amine/anhydride, aliphatic amine/anhydride. This is in general agreement with results for very dilute small molecule analogs. Some experiments performed at higher molecular weights gave similar results. Coupling between aliphatic amine terminal and cyclic anhydride terminal chains was found to be extremely fast; complete conversion occurred in <30 s. Dilution studies and comparison to theory indicate that this reaction was not diffusion controlled. Mixing and diffusion are rapid enough to bring every chain end in contact within 15 s.