Polymer dispersions of narrow particle size distribution

A process for the manufacture of a polymer dispersion comprising the steps of i) providing a mixture comprising from 2 to 60 parts by weight of a first polypropylene polymer having sufficient carboxylic acid and/or carboxylic acid anhydride groups equivalent to an acid value of from 2 to 50 mg KOH/g nv polymer and from 40 to 98 parts by weight of a second polymer having a molar excess of functional groups capable of reacting with the carboxylic acid and/or carboxylic acid anhydride groups of the polypropylene ii) causing the polymers to melt at a chosen temperature under conditions of high shear in an extruder to form an intimate mixture of the polymers iii) causing some of the carboxylic acid and/or carboxylic acid anhydride groups of the polypropylene to react with at least some of the functional groups of the second polymer to form a reaction mixture, under conditions of high shear in an extruder iv) rapidly cooling the reaction mixture outside the extruder to form a solid product v) optionally breaking up