Self-Association of Hydroxypropylcellulose in Water

The association of hydroxypropylcellulose (HPC) chains above their lower critical solution temperature (LCST, ∼41 °C) leads to metastable nanosphere aggregates instead of precipitation. Laser light scattering (LLS) measurements revealed that the size of the aggregates is dependent not only on temperature and HPC concentration but also on heating history. There existed a narrow temperature range from ∼41 to ∼44 °C in which narrowly distributed metastable nanospheres formed in a few minutes and lasted for a few days without changing their sizes and molar masses. Increasing temperature in this range and increasing HPC concentration resulted in larger and denser nanosphere aggregates. In situ cross-linking of self-associated HPC chains was performed in a LLS sample cuvette at 42 °C using divinyl sulfone as a cross-linker. Formation of HPC gel microspheres was monitored by LLS and demonstrated by allowing the gel microspheres to swell and shrink at temperatures below and above the LCST, respectively.