Analysis of diblock copolymers of poly(α-methylstyrene)-block-polystyrene by mass spectrometry

The individual block length distributions of a series of diblock copolymers, polystyrene-b-poly(alpha-methylstyrene), were determined by the MAC MALDI/TOF MS method of analysis of copolymers which combines matrix-assisted laser desorption/ionization time-of-flight mass spectrometry with computational data treatment. The robustness of the calculation technique was evaluated. The presence of unreacted homopolymer was observed as well bimodal and trimodal distributions for the poly(amethylstyrene) segments. A new method to verify the random coupling hypothesis has been proposed. The hypothesis was verified to hold within the experimental error of the technique for all the correct assignments of polymers studied. The experimental distributions have been compared with the Poisson, Schulz-Zimm, Tung, and logarithmic-normal models, modified to account for the change of variables. The equations of the Tung model, which was found to have the best predictive capability for the P alpha MS blocks, were transformed into the analytical form. Overall, the Schulz-Zimm model remains the most flexible of all models.