Volume phase transition induced by temperature sensitive DL-amino acid methyl ester side chain based copolymer gels

Polymer gels based on methacryloyl-DL-amino acid methyl esters with different alkyl groups on the alpha-carbon (MA-DL-AA-OMe) were synthesized to evaluate the apparent lower critical solution temperature (LCST) from the composition-induced volume phase transition behavior of their copolymer gels as a function of the temperature. Methacryloyl-DL-alanine methyl ester (MA-DL-AlaOMe) gel showed a thermo-responsive volume phase transition around 22 degrees C, which is close to its LCST of 25 degrees C. In contrast with this, methacryloyl-DL-amino acid methyl ester (MA-DL-AAOMe) gels with alkyl groups on the alpha-carbon larger than ethyl (Et) collapsed without a volume phase transition. Based on an extrapolated linear plot between the volume phase transition temperatures (VPTTs) estimated using data from the composition-induced volume phase transition at a given temperature and composition for the copolymer gels MA-DL-AlaOMe/MA-DL-AbuOMe and MA-DL-AlaOMe/methacryloyl-norvaline methyl ester (MA-DL-nValOMe), the apparent LCST was estimated to be 22 degrees C for MA-DL-AlaOMe, -35 degrees C for MA-DL-AbuOMe, and -58 degrees C for MA-DL-nValOMe.