A process for the production of a polymer containing monomer units of butane-1,4-diamine and 1,10-decanedioic acid (PA-410) comprising the steps of: 1) making a solution of a salt of butane-1,4-diamine and 1,10-decanedioic acid in water, 2) concentrating the solution of the salt at a temperature of between 100 and 180° C. and a pressure of between 1.0 and 3.0 bar to a water content of between 4 and 8 wt %, 3) producing from the salt a prepolymer containing monomer units of butane-1,4-diamine and 1,10-decanedioic acid at a temperature of between 185 and 205° C. and 4) post condensation of the prepolymer. Also claimed is PA-410 having a viscosity number (VN) of at least 100 ml/gram.