Lower critical solution temperatures of thermo‐responsive poly(N‐isopropylacrylamide) copolymers with racemate or single enantiomer groups

Abstract

BACKGROUND: Thermo-responsive copolymers with racemate or single enantiomer groups are attracting increasing attention due to their fascinating functional properties and potential applications. However, there is a lack of systematic information about the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide)-based thermo-responsive chiral recognition systems. In this study, a series of thermo-responsive chiral recognition copolymers, poly[(N-isopropylacrylamide)-co-(N-(S)-secbutylacrylamide)] (PN-S-B) and poly[(N-isopropylacrylamide)-co-(N-(R,S)-sec-butylacrylamide)] (PN-R,S-B), with different molar compositions, were prepared. The effects of heating and cooling processes, optical activity and amount of chiral recognition groups in the copolymers on the LCSTs of the prepared copolymers were systematically studied. LCSTs of PN-S-B and PN-R,S-B during the heating process are higher than those during the cooling process. With similar molar ratios of N-isopropylacrylamide groups in the copolymers, the LCST of the copolymer containing a single enantiomer (PN-S-B) is lower than that of the copolymer containing racemate (PN-R,S-B) due to the steric structural difference. The LCSTs of PN-R,S-B copolymers are in inverse proportion to the molar contents of the hydrophobic R,S-B moieties in these copolymers. CONCLUSION: The results provide valuable guidance for designing and fabricating thermo-responsive chiral recognition systems with desired LCSTs. RESULTS: LCST hysteresis phenomena are found in the phase transition processes of PN-S-B and PN-R,S-B copolymers in a heating and cooling cycle. The

Molecular Approach To Understand the Tacticity Effects on the Hydrophilicity of Poly(N-isopropylacrylamide): Solubility of Dimer Model Compounds in Water

“…This observation is similar to the decrease in T ps by copolymerization of a hydrophobic monomer with NiPA. For example, T ps of poly(NiPA-co- N -sec-butylacrylamide(NsBA)) linearly goes down with increasing NsBA content . When m < 55%, one can expect that two monomer units with the m configuration behave as one hydrophobic unit.…”

“…For example, T ps of poly(NiPA-co-N-secbutylacrylamide(NsBA)) linearly goes down with increasing NsBA content. 31 When m < 55%, one can expect that two monomer units with the m configuration behave as one hydrophobic unit. In the range of m > 55%, however, the descent of T ps is not linearly proportional to the m ratio.…”

Stereoselective partitioning of organic substrates by thermoresponsive polymers in aqueous phases

“…Optically active thermoresponsive polymers have been already reported such as poly(N-(S)-sec-butylacrylamide-coNIPAAm), 14,24 poly(N-methacryloyl-(S)-phenylalanine methyl ester-co-N-(2-hydroxypropyl)methacrylamide), 14 poly(N-acryloyl-L-proline methyl ester), 25 and poly(N-acryloyl-4-transhydroxy-L-proline methyl ester), 26 and most of them are N-acryloylaminoacid methyl ester based polymers. We have also prepared in this study several optically active thermoresponsive polymers by copolymerization of NIPAAm with N-acryloylaminoalcohols (Schemes 1 and 2, Table II, see also Supporting Information).…”

Water-soluble random and alternating copolymers of styrene monomers with adjustable lower critical solution temperature

“…First, the substituents of the moderately hydrophilic motif(s) are modified. For instance, when exchanging the isopropyl group of PNIPAM for the ethyl group, the LCST rises from about 32 C to about 72 C, 18,29 while replacement of the isopropyl group of PNIPAM by the sec-butyl group reduces the LCST to below 0 C. 30 Even when replacing the isopropyl group of PNIPAM by the n-propyl group, a marked drop of the LCST of about 10 C is observed. 31,32 Apparently small changes of the substituents strongly affect the transition temperature.…”