Biocompatible polymers having a molecular weight of at least 5000, comprising polymerized monomer with carboxyl and sulfate or sulfonate groups. The new polymers are of formula (I) A a-X x-Y y (I) A : a monomer； X : a carboxyl group fixed on monomer A and of formula R-COO-R'； R : a bond or aliphatic hydrocarbon chain which may be branched and/or unsaturated and which may contain one or more aromatic rings, other than benzylamine and benzylamine sulfonate； R' : H or a cation； Y : a sulfate or sulfonate group fixed on to A and of formula -R-O-SO 3-R', -R-N-SO 3-R'- or -R-SO 3-R'-； a : the number of units of monomer A, and is such as to give (I) a molecular weight of at least 5000； x : the degree of substitution of all monomers A by groups X and is 20 - 150%, preferably around 50%； y : the degree of substitution of all monomers A by groups Y and is 30 - 150%, preferably around 100% Preferably the monomers A are sugars, esters, alcohols, amino acids or nucleotides, glucose units being especially preferred. The groups R are preferably straight or branched alkyl, allyl, or aryl groups. The polymers may further contain groups Z, which are different to X and Y and which confer supplementary biological or physicochemical properties on the polymer, such as increased solubility or lipophilicity. Suitable such groups Z include amino acids, fatty acids and alcohols, ceramides, and nucleotide sequences.
