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 s emi-batch polymerization with the use of ultraviolet (UV) and near-inf rared (NIR) spectroscopy. The spectra were very complex, and their cha racteristics changed dramatically throughout the course of a batch, so linear calibration models were constructed for groups of similar spec tra using Partial Least-Squares (PLS). Principal Component Analysis (P CA) was used as a pattern recognition tool to group spectra before cal ibration or prediction. UV spectra from 190 to 800 nm were taken of di luted latex. The weight fractions of styrene monomer and poly(styrene) were predicted with a standard error less than 0.5 wt%. NIR spectra f rom 900 to 1800 nm were taken of undiluted latex with a transflectance fiber-optic probe. Calibrations could predict the concentrations of a ll the major components [water, poly(styrene), poly(methyl methacrylat e), styrene, methyl methacrylate] with a standard error of less than 0 .5 wt%. Mean particle size was also well predicted for some of the cal ibration sets.