Novel copolymers consisting of poly(N-isopropylaminoethyl-co-6-hydroxyhexyl aspartamide) and poly (N-isopropylaminoethyl-co-hexyl aspartamide) were prepared from polysuccinimide, which was the thermal polycondensation product Of L-aspartic acid, via a ring-opening reaction with 6-amino-L-hexanol (AH) or hexylamine (HA) and N-isopropylethylenediamine at different ratios. The copolymers, containing 75-90 mol % of AH and 35-45 mol % of HA, produced thermoresponsive polymers through their lower critical solution temperatures (LCSTs) in aqueous solution. We could control the LCST could be controlled by modifying the hydrophobic-hydrophilic balance by changing the content of AH or HA. The pH dependencies of the LCST were opposite in these two different copolymer systems. (C) 2007 Wiley Periodicals, Inc.