A novel thermosensitive poly(methyl 2-acetamidoacrylate)

The thermosensitive properties of aqueous poly(methyl 2-acetamidoacrylate) (PMAA) solutions were investigated in the absence or presence of sodium sulfate. Poly(methyl 2-acetamidoacrylate) with a molecular weight of 23,000 (PMAA-1) exhibited the cloud point. On heating the PMAA-1 solution, the transmittance began to decrease from near 34 °C and increased again after the minimum value was shown at 36.0 °C. The minimum transmittance increased linearly with an increasing concentration of the polymer although the minimum-transmittance temperature did not depend on polymer concentration. The minimum transmittance was affected by the pH and the 1-butanol added. This finding suggests that the cloudiness is controlled by a delicate balance of hydrophilicity and hydrophobicity and by intra- and/or inter-molecular hydrogen bonding. Poly(methyl 2-acetamidoacrylate) with a molecular weight of 15,000 (PMAA-2) did not exhibit cloudiness in distilled water. However, the addition of sodium sulfate caused cloudiness to appear. The cloud point of a PMAA-2 solution depended on concentrations of polymer and salt added. It decreased with an increase in polymer and salt concentrations. The salting-out constants were determined from the relationship between the cloud point and concentrations of polymer and salt.