Polymer blend usage has increased in recent years as the blends provide a convenient means for modifying polymer properties. It is often necessary to determine the percents or ratios of the polymers present in a blend. One blend of interest is the immiscible blend of polystyrene (PS) and poly(4-methylstyrene) (P4MS). The percentages were determined by two methods: Fourier transform infrared (FTIR) spectroscopy and second derivative ultraviolet (UV) spectroscopy. The peak ratio versus percent polymer technique was used in both methods. For the FTIR, the ratio of the absorbance values for the out-of-plane C-H para-substituted bending vibration of P4MS at 813 cm(-1) and the out-of-plane monosubstituted C-H bending vibration for PS at 757 cm(-1) were ratioed. For derivative UV, the vibrational structures of the aromatic secondary,bands were used: the 269 nm minimum for PS and 275 nm minimum for P4MS. The derivative UV method gave considerably better results and also had the advantage of requiring less sample due to its greater sensitivity. (c) 2006 Wiley Periodicals, Inc.