Phase transition behavior of hydroxypropylcellulose under interpolymer complexation with poly(acrylic acid)

The phase transition behavior of hydroxypropylcellulose (HPC) under interpolymer complexation with poly(acrylic acid) (PAA) has been studied by turbidity and laser light scattering measurements. It has been found that the lower critical solution temperature (LCST) of the HPC was drastically reduced after adding 1 wt % of PAA into the HPC solution. The LCST of the HPC/PAA complexes decreased with the increase of the molecular weight of either the HPC or the PAA. The driving force shifting the LCST is attributed to the hydrogen bonding and hydrophobic interaction of the macromolecules. As the pH value increases from at 4.0 to 6.0, the LCST of the HPC-PAA complex decreases. This may be due to the salt effect of the polyelectrolyte on the nonionic polymer. The HPC/PAA complexation has been observed even at very dilute solution of 1.6 × 10^-5 g/mL at pH = 3.2. The study of complexation between the HPC and the PAA leads to a new method for synthesis of surfactant-free microgels at room temperature. The resultant microgels swell and collapse at the pH value higher and lower than the pK_α value of the PAA, respectively.