Preparation of novel acrylamide‐based thermoresponsive polymer analogues and their application as thermoresponsive chromatographic matrices

New thermoresponsive polymers based on poly(N‐(N′‐alkylcarbamido)propyl methacrylamide) analogues were designed with increased hydrophobic content to facilitate temperature‐dependent chromatographic separations of peptides and proteins from aqueous mobile phases. These polymer solution exhibited a lower critical solution temperature (LCST) when the alkyl group is methyl, ethyl, isopropyl, propyl, butyl, and isobutyl. However, larger alkyl groups such as hexyl and phenyl were not soluble in aqueous solutions at any temperature. Phase transition temperatures were lower for larger alkyl groups and increased with decreasing polymer molecular weight and concentration in solution. LCST dependence on polymer molecular weight and concentration is more significant compared with well‐studied poly(N‐isopropylacrylamide) (PIPAAm). Partition coefficient (log P) values for N‐(N′‐butylcarbamide)propylmethacrylamide and N‐(N′‐isobutylcarbamide)propyl methacrylamide (iBuCPMA) monomers are larger than that for IPAAm monomer, suggesting higher hydrophobicity than IPAAm. Chromatographic evaluation of poly(N‐(N′‐isobutylcarbamide)propyl methacrylamide) (PiBuCPMA) grafted silica particles in aqueous separations revealed larger k′ values for peptides, insulin, insulin chain B, and angiotensin I than PIPAAm‐grafted silica beads. In particular, k′ values for insulin obtained from PiBuCPMA‐grafted silica separations were much larger than those from PIPAAm‐grafted surface separations, indicating that PiBuCPMA should be more hydrophobic than PIPAAm. These results support the introduction of alkylcarbamido groups to efficiently increase thermoresponsive polymer hydrophobicity of poly(N‐alkylacrylamides) and poly(N‐alkylmethacrylamides). Consequently, poly(N‐(N′‐alkylcarbamido)propyl methacrylamide) analogues such as PiBuCPMA and poly(N‐(N′‐alkylcarbamido)alkylmehacrylamide) are new thermoresponsive polymers with appropriate hydrophobic partitioning properties for protein and peptide separations in aqueous media, depending on selection of their alkyl groups.