Analysis of diblock copolymers of poly(alpha-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 las er desorption/ionization time-of-flight mass spectrometry with computationa l data treatment. The robustness of the calculation technique was evaluated . The presence of unreacted homopolymer was observed as well bimodal and tr imodal distributions for the poly(amethylstyrene) segments. A new method to verify the random coupling hypothesis has been proposed. The hypothesis wa s verified to hold within the experimental error of the technique for all t he correct assignments of polymers studied. The experimental distributions have been compared with the Poisson, Schulz-Zimm, Tung, and logarithmic-nor mal models, modified to account for the change of variables. The equations of the Tung model, which was found to have the best predictive capability f or the P alpha MS blocks, were transformed into the analytical form. Overal l, the Schulz-Zimm model remains the most flexible of all models.