Biologically active drug polymer derivatives and method for preparing same

New biologically active drug polymer derivatives, namely peptides or protein derivatives, are useful medicaments and are represented by the generic formula: wherein R represents a lower alkyl group, n is an integer comprised between 25 and 250, X when combined with adjacent NH and CO groups represents an amino acid or a dipeptide or tripeptide residue, and Z when combined with the adjacent NH group represents a biologically active peptide or protein or NH or NH.sub.2 containing drug residue.