The present disclosure relates to polymer coatings covalently attached to the surface of a substrate and the preparation of the polymer coatings, such as poly(N-(5-azidoacetamidylpentyl)acrylamide-co-acrylamide) (PAZAM), in the formation and manipulation of substrates, such as molecular arrays and flow cells. The present disclosure also relates to methods of preparing a substrate surface by using beads coated with a covalently attached polymer, such as PAZAM, and the method of determining a nucleotide sequence of a polynucleotide attached to a substrate surface described herein.