Detailed structural analysis of diblock copolymers by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Abstract

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 ...

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].…”

Compositional analysis of isobutylene/p-methylstyrene copolymers by matrix-assisted laser desorption/ionization mass spectrometry

“…For example, silicone copolymers have been reported to have skewed oligomer ionization efficiencies with regard to either hydromethylsiloxane [8] or perfluoroalkyl content [9]. Wilczek-Vera and coworkers found similar skewing with respect to styrene content with ␣-methylstyrene/4-vinylpyridine copolymers [10]. Even with the structurally similar ethylene oxide/ propylene oxide monomers, compositional biases have been observed in copolymer spectra, even though homopolymers of both are easy to ionize [11].…”

Preparation and aggregation behavior of mannose-terminated poly(ethylene glycol)-b-poly(l-leucine) in water

“…3. Similar to the spectrum of other block copolymers [44,45], detailed analysis of the data is difficult. But we can still observe two main families of peaks in the spectrum: in one family (for example, m/z, 3659, 3546, 3433, and 3320), the m/z difference between adjacent peaks is 113, the molecular weight of a Leu unit; and in another family, the difference is 44, the molecular weight of an EG unit.…”