Polymer blend usage has increased in recent years as the blends provide a convenient means for modifying polymer properties. It is often necessary to be able to determine the percentages or ratios of polymers present in a blend. One blend of interest is the immiscible blend of polystyrene (PS) and poly(4-vinylpyridine) (P4VP). The percentages were determined by two methods: Fourier transform infrared (FTIR) spectroscopy and second derivative ultraviolet (UV) spectroscopy. The peak ratio versus percentage polymer technique was used in both methods. For FTIR, the ratio of the absorbance values of the out-of-plane C-H bending vibration of P4VP at 822 cm(-1) and the aromatic C = C stretch for PS at 1493 cm(-1) were ratioed. For derivative UV, the vibrational structure of the aromatic secondary bands was used: 269 run minimum for PS and the 271 run maximum for P4VP. Both methods gave excellent and comparable results. The derivative UV determination had the advantage of requiring less sample due to its greater sensitivity. (c) 2005 Wiley Periodicals, Inc.