Fluorescence studies of cellulose ethers: synthesis, characterization, and spectroscopic properties of labeled polymers
1996
Examples are given of the use of pyrene-labeled polymers as models for the study of solution properties of hydrophobically modified polymers acting as gelling agents or associative thickeners in waterborne fluids. Labeled polymers were obtained from three commercial cellulose ethers: Tylose M-300 (hydroxyethylmethylcellulose), Methocel-50-F (hydroxypropylmethylcellulose), and Klucel-L (hydroxypropylcellulose). The polymers contain on average one to five pyrene groups per chain. Procedures for labeling, purification, and characterization of the polymers are described. Spectroscopic parameters such as pyrene excimer-to-monomer intensity ratios, absorption spectra, excitation spectra, and excited-state lifetimes are reported for solutions of the polymers in water and in an organic medium (dichloromethane-methanol). These parameters present evidence that in water pyrene groups form hydrophobic clusters that are destroyed at the temperature corresponding to the cloud point. These clusters form in samples that undergo heat-induced phase separation, such as pyrene-labeled hydroxypropylcellulose in water.
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