The present invention relates to a novel group of copolymers comprising a soluble carbohydrate polymer (SCP), which typically is a non-starch carbohydrate, and a macromolecule covalently attached to the SCP. The macromolecule may e.g. be a hydrophobic copolymer, a polyelectrolyte polymer or a biodegradable polymer. The present invention furthermore relates to a method of preparing the copolymer, products comprising the copolymer, and to methods of preparing the products comprising the copolymer. The products comprising a copolymer are for example a polymeric carbohydrate material (PCM) modified by attachment of a copolymer, and a composite material comprising the modified PCM.