Prepn. of latex and emulsion SBR samples from rubber latex samples, to be used to det. n(25), was reduced from -20 to 1-3 hrs., by pptg. SBR from latex with EtOH to remove stabilizers (free acids, soaps, etc.) or by extg. oil-modified SBR with EtOH-toluene, and pressing the purified SBR at temp., time, and pressure related to elastomer or latex type, viz., to Mooney viscosities (ML (1 + 4) 100 degrees C) of 29-140 and to styrene contents of 22-45%, to prep. transparent < 0.50-mm SBR films. A review with 38 refs. covers oxidn. of SBR to p-nitrobenzoic acid, detn. of the acid by UV spectrometry and of n(25) in thin SBR films, and further Raman, FT-Raman, IR, FTIR, UV, H-1 and C-13 NMR spectroscopies, pyrolysis mass spectroscopy, pyrolysis gas chromatography, and elemental analysis used to det. bound styrene content in emulsion and soln. SBRs.