Individual Block Length Distributions of Block Copolymers of Polystyrene-block-Poly(α-methylstyrene) by MALDI/TOF Mass Spectrometry

Abstract

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...

Microstructural and conformational studies of polyether copolymers

“…The MALDI-ToF spectra from these copolymers (data not shown) are dominated by peaks from singly charged ions, even for the oligomers of highest molecular weights. The overlapping distributions of peaks from oligomers with different initiating (␣) end groups (i.e., from the tridecanol and pentadecanol mixtures of alcohols used as the initiator for the copolymers) mean that deconvolution of the data would be required for three-dimensional intensity plots to be produced, as previously shown for other copolymers (also from MALDI-ToF data) [27][28][29][30].…”

MALDI-TOF mass spectrometry in the analysis of synthetic polymers

“…Wilczek-Vera et al [69] investigated block copolymers of PS-block-(p-a-methylstyrene). For polymers in the mass range up to 10 000 Da interesting details could be obtained from the data.…”

Characterization of poly(ethylene oxide)-b-poly(L-lactide) block copolymer by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

“…Therefore this type of attempts has been made only for low molecular weight copolymers whose monomer molecular weights are appropriately different to minimize the peak overlap. 25,26 For an example, Wilczek-Vera et al analyzed the MALDI-TOF mass spectra up to m/z~4000 of a poly(α-methylstyrene)-b-poly(4-vinylpyridine) diblock copolymers of varying poly(4-vinylpyridine) block length. 26 From the analysis, they could monitor the progression of the growing block chain length.…”