Methods for preparing substantially non-antigenic polymers having lone electron pair-containing moieties in high purity are disclosed. The polymers are useful as intermediates for synthesis of amine-based polymers and in the formation of activated polymers for conjugation with nucleophiles. Conjugates and methods of preparation and treatment with the conjugates are also disclosed. The resultant polymer-amines are of sufficient purity so that expensive and time consuming purification steps required for pharmaceutical grade polymers are avoided.