Molecular and Structural Characterization of Polydisperse Polymers and Copolymers by Combining MALDI-TOF Mass Spectrometry with GPC Fractionation

Abstract

Matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) allows detection of large molecules such as those present in synthetic and natural macromolecules. Until recently, it was reported that MALDI-TOF measurements can provide correct molecular weight (MW) averages only for samples with a narrow MW distribution (MJMn < 1.20). We have now developed a methodology for polydisperse samples. We recorded the GPC trace of two polydisperse polymeric samples, namely, poly(butylene adipate) (PBA) and poly(butylene adipate-co-butylene succinate) (PBAS), collecting about 40-50 fractions per run. Selected fractions were analyzed by MALDI-TOF, and the average MW of each fraction was determined, allowing calibration of the GPC curves against absolute MW. The two calibrated GPC traces were then used to compute average MW and molecular weight distributions (MWD) of the unfractionated samples. End group analysis from MALDI-TOF spectra revealed that the PBA sample is composed of seven different types of chains. For the copolymer sample, PBAS, analysis of the MALDI spectra established a random sequence distribution of comonomer units. The succinate/adipate molar ratio calculated from the MALDI spectra is in good agreement with the molar ratio found by NMR.

Employing MALDI-MS on Poly(alkylthiophenes): Analysis of Molecular Weights, Molecular Weight Distributions, End-Group Structures, and End-Group Modifications

“…9,16 Successful analysis of molecular weights and molecular weight distributions for highly disperse polymer samples can be achieved by coupling the GPC data with the MALDI data. 17 Fractionation of the polymer samples by GPC and subsequent analysis of these fractions by MALDI allows for the M n and M w to be determined for each fraction. Once the average molecular weight of all the fractions is determined by MALDI, subsequent calibration of the GPC curve against the MALDI data allows for the calculation of the molecular weight of highly disperse (unfractionated) polymer samples.…”

Comparative studies of poly(dimethyl siloxanes) using automated GPC-MALDI-TOF MS and on-line GPC-ESI-TOF MS

“…Several research groups have illustrated the powerful combination of GPC with MALDI and ESI MS for polymer analysis. In the most traditional sense, GPC can be incorporated by manually collecting GPC fractions in a number of vials for subsequent analysis by ESI [23,31] or MALDI MS [5,6,10,11,23,[32][33][34][35][36]. This approach is relatively time consuming and very tedious since each collected GPC mass fraction requires sample preparation prior to MS analysis.…”

Synthesis and structural characterization of block and random low molecular weight copolymers composed of L-lactic acid and isosorbide succinate moieties

“…The -M n values obtained by MALDI-TOFMS were 42-76% lower than those obtained by SEC. Two possible reasons can explain this difference: (i) SEC data calculations were based on polystyrene as reference, which may not reflect correctly the hydrodynamic volumes of the samples and (ii) lighter molecules can be preferentially desorbed and ionized, 23 especially in the case of synthetic (co)polymers with polydispersity index higher than 1.2. Table 2 also presents the mass compositions of the products I-IV determined by 1 H NMR.…”