This work presents an in-depth study of the interrelation between the junction potential

The block length distributions of two block copolymers of R-methylstyrene and styrene, of different molecular weights and relative block lengths, were analyzed by matrix-assisted laser desorption/ ionization time-of-flight (MALDI/TOF) mass spectrometry. A method for the treatment of mass spectroscopic data for block copolymers is proposed. The random coupling hypothesis has been verified experimentally and found to hold for this type of triblock copolymers. The experimental distributions have been compared with the Poisson and Schulz-Zimm models modified to accommodate the change of variables. The agreement between the experimental and calculated distributions is very good for the Schulz-Zimm model and fair for the Poisson model. Mass spectrometry proved to be a useful technique providing unique information on the experimental distributions of both constituent parts in a block copolymer. It was confirmed that block copolymers with narrow molecular weight distributions may have broad, complex, and even bimodal composition distributions. The polydispersity factors observed for the individual parts were higher than those for the whole copolymer. IntroductionIn the recent past, there has been a considerable upswing and interest in properties of block copolymers. Micellization, brush formation, and drug delivery are just three examples of the areas in which block copolymers have been receiving extensive attention. For the study of many of these properties, detailed information about the block lengths and compositions of each of the segments is needed. However, while it has been possible to determine the total molecular weight and the molecular weight distribution of the block copolymer, as well as the molecular weight and molecular weight distribution of the first segment to be prepared, 1,2 it has not been possible, with the exception of few cases, 3-5 to determine independently the molecular weight and molecular weight distribution of the second segment. This information can be of considerable importance, since, to pick one example, it has recently been shown that the size of the core of block copolymer micelles is very much a function of the molecular weight distribution of the core forming block. 6 In the above case, the core forming block was composed of vinylpyridinium methyl iodide, while the corona consisted of styrene. In that case, the block length distribution was broadened artificially to obtain very large values of the heterogenity index. However, in general, it has been impossible to obtain detailed data on the second block (e.g., vinylpyridine) independent of the first (e.g., styrene). A number of theoretical treatments exist which make possible the calculation of the molecular weight distribution of the second block from the molecular weight distribution of the first block and of the total block copolymers. These methods are very useful for some compositions, but, if the first block is sizable and the second block is relatively small, the error associated with the applications of this method can be app...

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The individual block length distributions of poly(a-methylstyrene)-b-poly(4-vinylpyridine) diblock copolymers have been determined by the MAC MALDI-TOFMS method of analysis of copolymers, which combines matrix assisted laser desorption/ionization time-of-flight mass spectrometry with computational data treatment. The problem of the possibility of multiple assignments of chemical composition to the mass spectral peaks is discussed in detail. A solution based on the pattern of peak clusters is proposed and verified using the statistical random coupling hypothesis test. The progress of the anionic polymerization in a series of polymers prepared by sequential addition of the second monomer to a living chain system is studied and shown in three-dimensional (3-D) plots of experimental individual blocks length distributions. The presence of unreacted homopolymer has been observed as well as bimodal and trimodal distributions for the poly(amethylstyrene) and the poly(4-vinylpyridine) segments. A depolymerization process of the homopoly(amethylstyrene) in the series of poly(a-methyl-styrene)-b-poly(4-vinylpyridine) diblock copolymers was detected following a temperature rise. It was confirmed that it is impossible to place a single unit of 4VP at the end of each PaMS chain. Copyright # 1999 John Wiley & Sons, Ltd. Received 24 December 1998; Revised 22 February 1999; Accepted 24 February 1999 Matrix-assisted laser desorption/ionization time-of-flight spectrometry (MALDI-TOFMS) is a powerful analytical technique widely used in the characterization of synthetic organic polymers, 1-9 proteins and peptides, 10-13 metabolites, 14 and other biopolymers. 15,16 Recently, block copolymers 17 have also been characterized by this technique. Block copolymers have many interesting properties with applications to drug delivery, micellization and brush formation, 18,19 among others. It is known 20,21 that the properties of block copolymers are determined by the chain lengths of the individual segments and their distributions. In one case, it has been demonstrated that the size of the core of block copolymer micelles depends both on the molecular weight and the molecular weight distribution of the core forming block. 21 Therefore, a general method of independent determination of the chain length distributions for both constituent parts of a block copolymer 17 was developed using the MALDI-TOFMS technique. As the proposed method gives the possibility of direct experimental determination of the composition distribution for block copolymers, it was possible to confirm that block copolymers with narrow molecular weight distributions may have complex and even bimodal composition distributions. It was also found that the polydispersity factors observed for the individual parts were higher than those for the whole polymer. The random coupling hypothesis has been confirmed experimentally. 17 The polymers studied were of the type ABA, where A corresponds to a poly (amethylstyrene) chain and B to a polystyrene chain. The error introduced by the ...

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The individual block length distributions of a series of diblock copolymers, polystyrene-b-poly(α-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(α-methylstyrene) 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 PαMS blocks, were transformed into the analytical form. Overall, the Schulz−Zimm model remains the most flexible of all models.

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This work highlights the main elements of the new thermodynamic approach to electrolyte solutions and demonstrates its ability to make predictions for mixed salt systems. After a review of the state of affairs before the measurement of activities of individual ions, experimental set-ups used for these measurements are described and the essential elements of different methods used to reduce the data are discussed. The results of experiments carried to test a possible bias introduced by uncertainty in the values of the junction potential are emphasized. It is purported that the thermodynamic treatment proposed by Lin and Lee is of general application and ensures the thermodynamic consistency of correlations previously proposed for the individual ionic activities. It is shown that the use of a more complex form for the contribution of long-range interactions to ionic activities leads to a simpler form of the osmotic coefficient. As an example of application, the predictions of the equilibrium pressure over NaCl + KCl, NaBr + KBr, and NaCl + CaCl 2 aqueous solutions, at different temperatures and compositions, are compared with independently measured experimental data.