Composition and Particle Diameter for Styrene/Methyl Methacrylate Copolymer Latex Using UV and NIR Spectroscopy

The properties of a polymer latex were measured over the course of a semi-batch polymerization with the use of ultraviolet (UV) and near-infrared (NIR) spectroscopy. The spectra were very complex, and their characteristics changed dramatically throughout the course of a batch, so linear calibration models were constructed for groups of similar spectra using Partial Least-Squares (PLS). Principal Component Analysis (PCA) was used as a pattern recognition tool to group spectra before calibration or prediction. UV spectra from 190 to 800 nm were taken of diluted latex. The weight fractions of styrene monomer and poly(styrene) were predicted with a standard error less than 0.5 wt%. NIR spectra from 900 to 1800 nm were taken of undiluted latex with a transflectance fiber-optic probe. Calibrations could predict the concentrations of all the major components [water, poly(styrene), poly(methyl methacrylate), styrene, methyl methacrylate] with a standard error of less than 0.5 wt%. Mean particle size was also well predicted for some of the calibration sets.