Practical and versatile methods for the preparation of glycopeptide polymers containing base labile moieties were established by use of 1-isobuthoxycarbonyl-2-isobuthoxy-1,2-dihydroquinoline (IIDQ) or 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) as polycondensation agents of glycopeptide units without any protection on the carbohydrate residues. These methods were applied for the synthesis of mucin-like glycoprotein mimics related to antifreeze glycoproteins (AFGPs), giving the target O-acetylated glycopolypeptides efficiently, while the conventional DPPA (diphenylphosphoryl azide) method gave complex mixtures of acyl migrated compounds.