The chain transfer to monomer constants (C-m) in styrene bulk polymerizations have been determined in the temperature range between 25 and 90 degreesC using both thermal polymerization and the novel pulsed laser polymerization (PLP) with extended dark times. This novel technique determines transfer to monomer rate coefficients by combining a pulsed laser setup with a rotating reactor/cuvette assembly. The resulting transfer controlled molecular weight distributions (MWD) were analyzed by the well-known Mayo and chain length distribution (CLD) methods. The results of both experimental methods agree well, which indicates that PLP with extended dark times is a reliable technique to determine transfer to monomer constants. For this reason, we report average values for the activation parameters determined from both thermal and extended dark times PLP experiments: E-a = 21.6 kJ mol(-1) and A = 0.22 L mol(-1) s(-1). These numbers are in excellent agreement with those reported in the literature.