Abstract: The invention relates to a polymer composition as well as to a process for the preparation of such a composition wherein two or more essentially incompatible polymers, each containing functional hydroxy groups and/or functional amino groups, are in contact with each other in the presence of at least one compatibilizer, the compatibilizer being a carbonyl bislactam (CBL) having the structure according to formula (I), where n is an integer from 3 to 15 and preferably 5. Preferably, the compatibilizer is carbonyl biscaprolactam. Depending on the ratio of the number of functional —OH or —NH2 groups to the CBL, the composition can be used as a polymer dispersion, for instance for improvement of the impact resistance or of the VICAT, or as a copolymer.