the present invention relates to a process for producing polyhydroxyalkanoate oligomers and / or polymers of reduced molecular weight , which comprises reacting at least one polyhydroxyalkanoate with at least one carbonate salt at a temperature of from 50 ° c . to 300 ° c ., preferably from 120 ° c . to 200 ° c . the above reaction allows a controlled degradation of the pha chains which yields oligomers and / or polymers having a controlled molecular weight , which can be modulated in view of the specific application for which the oligomers and / or polymers are intended . moreover , during the reaction carbon dioxide evolves which produces a foamed material which can be easily processed on an industrial scale . additionally , the above oligomers and / or polymers , having an end - group bearing a double bond c ═ c , particularly a crotonate end - group for phb , can be subjected to subsequent modifications to obtain a wide variety of functional end - groups , for instance carboxyl , carboxylate , hydroxyl , dihydroxyl , oxirane ring , halogen atom . moreover , the low molecular weight phas may be used in the area of controlled delivery systems in agro - chemistry , in the cosmetic industry , in medicine in the form of nano - or microspheres , in household products and in coating systems .