Poly MALDI spectra

The MALDI spectrum of a polymer sample in which all chains possess the same backbone allows identification of the end-groups present at the chain ends. This type of analysis is referred to as end-group analysis. An example will be helpful. Figure 15.1 reports the MALDI spectrum of a poly(bisphenolA carbonate) (PC for short) sample [7], It displays a series of peaks from 2 up to 16 kDa, the most intense ones in the region from 5 up to 7 kDa. It also displays peak assignment and an expansion of the spectral region from 3.0 up to 3.7 kDa. Peaks at 3034, 3288, and 3542 are labeled as A and are due to PC chains terminated with phenolcarbonate on both sides. Peaks at 3168, 3422, and 3676 are labeled as B and are due to PC chains terminated with phenolcarbonate on one side and bisphenol-A on the other. Peaks at 3048, 3302, and... 

Figure 15.1. MALDI spectrum of a polycarbonate sample along with peak assignment. In the inset, an expansion of the spectral region from 3.0 up to 3.7 kDa is shown. (Reproduced from Puglisi, C. et al., 1999. Analysis of Poly(bisphenol A Carbonate) by Size Exclusion Chromatography/Matrix-Assisted Laser Desorption/lonization. I. End Group and Molar Mass Determination. Rapid Communications in Mass Spectrometry, 13 2260-2267. With permission of John Wiley Sons, Inc.)...

Figure 8.12 MALDI mass spectra of poly(styrene) 7000 obtained (a) under the optimal condition and (b) under the same conditions except that LiOH was added to the sample preparation, (c) Individual peak areas of oligomers from the MALDI spectrum shown in (a) are plotted as the function of m/z. The result of Gaussian curve...

They noted that the extent of fragmentation decreases when the laser power is lowered and also when a large excess of matrix is used in sample preparation. Thus, the protocol features the use of a low laser power (close to the threshold th) and a matrix-to-analyte ratio of at least 10,000 1. As a matter of fact, the effect of the matrix-to-analyte ratio on the appearance of the MALDI spectrum of an equimolar mixture of four poly(ethylene oxide)s PEG2k + PEG4k + PEG6k +... 

FIGURE 45.9 MALDI spectrum of PI8300, a poly(isoprene) standard. Recorded by Jaber and Wilkins [50], copyright 2005 with permission. 

Kuran et al. [60] polymerized neopentyl carbonate using a catalyst prepared from water and diethylzinc and obtained a poly(neopentyl carbonate). The analysis by SEC yielded the average molar masses, namely Mr, = 3.0 kDa and = 6.3 kDa. The polydispersity index is close to 2, a typical value for a condensation polymer. The MALDI spectrum of the poly(neopentyl carbonate) displays almost 70 equally spaced peaks. The envelope is bell shaped. The abundances of chain with different sizes follows a Gaussian curve (sigma = 17) and centered at DP = 28. An accurate calculation was done by the authors using experimental peak intensities. Inserting these peak intensity values in Equations 45.1 and 45.2, they obtained Mr, = 3.5 kDa and M = 4.0 kDa. The polydispersity index associated with these values is 1.14. These three values are unacceptable since they are clearly affected by a large error. 

Polymers with a peroxide bond are interesting since they are very reactive. They are used as fuels and initiators. Kishore and coworkers [61] analyzed PSOX, a poly (alpha-methylstyrene peroxide), by SEC and found Mr, = 2.5 kDa and M = 4.0 kDa. The MALDI spectrum of PSOX displayed an acceptable spectral quality, with more than 50 peaks, due to poly(alpha-methylstyrene peroxide) chains. However, the upper limit of the mass range is very low, about 3.0 kDa, and the strongest peaks fall at 1.5 kDa. It was quite apparent that MALDI strongly underestimates the molar mass averages. In fact, the calculation (Equations 45.1 and 45.2) yielded... 

MALDI spectral quality is important, and thus, many authors have collected SEC fractions, recorded their MALDI spectra, and compared them with the spectra of the unfractionated polymer. To the best of our knowledge, there are no reports that quality worsens when using SEC. Vice versa, very often quality increases. For instance, the MALDI spectra of SEC fractions of Poloxamer407 (see above) possess a better spectral quality than the unfractionated sample. Moreover, a poly(bisphenol-A-carbonate) sample [64] with a poly-dispersity index of around 2 was analyzed by SEC and fractions were collected. Figure 45.11 contains the MALDI spectrum of PCF22 corresponding to the SEC... 

FIGURE 45.11 MALDI spectrum of PCF22, a poly(bisphenol A carbonate) sample, obtained collecting the SEC fraction eluting at 22 mL. Reproduced from Montaudo et al. [64], copyright 2002 with permission. 

FIGURE 45.13 SEC-MALDI spectra of PDMS-HB, a poly(siloxane) sample. Labels A-H are used to identify each SEC-MALDI spectrum. Reproduced from Nanda et al. [61], copyright 2002 with permission. GPC, gel permeation chromatography. 

Liquid chromatography at the critical condition (LCCC) is performed at the elution-adsorption transition. It can be used to separate macromolecules with different functionalities such as chains with different chain ends or to separate linear chains from cycles. LCCC was used [77] to separate cycles from linear chains in poly(bisphenol-A-carbonate) PC. Figure 45.20 contains the LCCC trace. The trace is bimodal, with two bands, Z1 and Z2. The MALDI spectrum of Z1 displayed a large number of peaks, ranging approximately from 2.0 to 10 kDa, due to PC chains terminated with n-butyl on one side or on both sides. The MALDI spectrum of Z2 was far less crowded. It is made of cycles and one can note the systematic absence of linear chains. This implies that the LCCC separation is perfect. 

FIGURE 45.22 MALDI spectrum of RLS80, a copolyethersulfones of the type P(ESES-co-EES) (polyethersulfone ether sulfone poly ether ether sulfone). Reproduced from Puglisi et al. [84], copyright 2006 with permission. 

The MALDI spectrum of a pure polymer resembles a comb and the spacing between the comb s teeth equals the mass, Tr, of the repeat unit. This quantity is often diagnostic and it suggests an almost trivial use of MALDI, namely spectral identification of polymers. The reason is that if one computes LIr values for common polymers, most values are different, the number of superpositions being very low. For instance, the most common polyethers are poly (ethylene oxide), poly (propylene oxide), poly(tetrahydrofuran), and poly(2,5-dimethyl phenylene oxide), and some common aliphatic polyesters are poly(caprolactone),poly(lactic acid), poly (hydroxy-butyrate), and poly(hydroxyvalerate). No superposition occurs (Pr values are 44, 58, 72, 120, 114, 72, 86, and 100 Da, respectively). 

Figure 6.8 shows the MALDI spectrum of the fraction of copolymer eluted at 27.9 ml. The MALDI spectrum of a fraction of copolymer eluted at 27.9 ml is well resolved and this allows the characterisation of the end groups. All the peaks were assigned to sodium alkoxide terminated oligomers of poly(EO-co-PO) copolymers. Nevertheless vinyl/hydroxyl and allyl/hydroxyl terminated oligomers with different ratios of EO to PO and, more unlikely, cyclic species are also possible. 

A first generation poly(amido amine) dendrimer has been functionalized with three calyx[4]arenes, each carrying a pyrene fluorophore (4) [30]. In acetonitrile solution the emission spectrum shows both the monomer and the excimer emission band, typical of the pyrene chromophore. Upon addition of Al3+ as perchlorate salt, a decrease in the excimer emission and a consequent revival of the monomer emission is observed. This can be interpreted as a change in the dendrimer structure and flexibility upon metal ion complexation that inhibits close proximity of pyrenyl units, thus decreasing the excimer formation probability. 1H NMR studies of dendrimer 4 revealed marked differences upon Al3+ addition only in the chemical shifts of the CH2 protons linked to the central amine group, demonstrating that the metal ion is coordinated by the dendrimer core. MALDI-TOF experiments gave evidence of a 1 1 complex. Similar results have been obtained for In3+, while other cations such as Ag+, Cd2+, and Zn2+ do not affect the luminescence properties of... 

MALDI is the method of choice for the analysis of synthetic polymers because it usually provides solely intact and singly charged [62] quasimolecular ions over an essentially unlimited mass range. [22,23] While polar polymers such as poly(methylmethacrylate) (PMMA), [83,120] polyethylene glycol (PEG), [120,121] and others [79,122,123] readily form [M+H] or [M+alkali] ions, nonpolar polymers like polystyrene (PS) [99,100,105,106] or non-functionalized polymers like polyethylene (PE) [102,103] can only be cationized by transition metal ions in their l-t oxidation state. [99,100] The formation of evenly spaced oligomer ion series can also be employed to establish an internal mass calibration of a spectrum. [122]... 

Fig. 9.30 a) Normalized MALDI TOF mass spectrum of all fractions (taken after 2 h to 72 h of polymerization time) of poly(2-phenyl-2-oxazoline) freed by dissolving the gold core with NaCN solution and collection of the polymer. The calculated mass of the monomer unit (147.17) is in good agreement with the spacing of the mass signals (AM = 146.93) of the most prominent peaks. Based on ear-... 

Fig. 2.12. MALDI mass spectrum of a side-chain substituted poly(p-phenylene). The splitting of the mass peaks of the respective -mers is caused by the different combinations of end groups, i.e., H,H, H,Br, or Br,Br...

The MALDI-TOF spectrum of [G-3] poly(benzyl ether) dendrimer-po-ly(ethylene glycol) triblock copolymer shows a broad band of peaks between 4300 and 6100 D with resolution of the individual ethyleneoxide (44 D) units. The MALDI-TOF spectrum of a [G-3] dendrimer with two polystyrene blocks (molecular peak=8073 D) shows material with 6000-11,000 D and a broad band corresponding to material with 2 M+Ag+. SEC can be used to prove that the latter species is indeed an artifact of the mass spectroscopic method. The authors claim almost exact agreement between the polydispersities derived from MALDI-TOF and SEC [40]. This does, however, not leave any room for the unavoidable column spreading in the latter method. Furthermore, anionically prepared low MW polymers have a minimum polydispersity given by (1 + 1/DP) [41]. 

Figure 1.30a depicts the MALDI-CAD spectrum of [M + Na] of the 9-mer of poly(butyl methacrylate), PBMA A, measured on an EBE-TOF instrument. In this sector-orthogonal acceleration-TOF hybrid, the EBE and TOP sections are used for precursor ion selection (MS-1) and fragment ion analysis (MS-2), respectively, and CAD takes place in an intermediate collision cell at 800 eV collision energy. The CAD spectrum contains several series of fragments separated by 142 Da (repeat unit). Series A and B arise by charge-remote direct cleavages at either end, as shown in Figure 1.30b. Series C/D and E/F...

FAB and MALDI mass spectrometric analyses of both polymers reveals that only macromolecules having hydroxy end-groups are formed by this interesting synthetic procedure. Figure 7.10 reports the FAB spectrum of the oligomers present in the unfractionated poly(l,2-dihydroxy-4-methylbenzene phthalate). Remarkably, the spectrum shows peaks up to m/z values of 6000,... 

MALDI-TOF mass spectrum of poly(lactic acid). In the region 1300-2600 peaks due to cyclic are stronger than peaks due to linear, whereas in the region 2600-4000 peaks due to cyclic are weaker. 

LCCC can be used to separate macromolecules with different end-groups. Wachsen et al. used LCCC to separate the products obtained by partially degrading poly(lactic acid). The MALDI-TOF spectra of the LCCC fractions turned out to display a smaller number of peaks compared to the MALDI-TOF spectrum of the whole sample, and this feature made tire peak assignment procedure for MS peaks simpler and more reliable. ... 

The positive ions MALDI-TOF spectrum of poly(butylene adipate diol)s, made by bulk polymerization of terephthaloyl chloride with a molar excess of 1,4 butanediol, shows only one series of peaks, extending over mass range 1000-6000 Da. These may be assigned to dihydroxyl-terminated oligomers. ° ... 

PSD-MALDI-TOF mass spectrum of the trimer from poly(bisphenol-A carbonate) (PC). (Reprinted with permission from Ref. 242)... 

Polyelectrol5des require desalting and conversion to the "hydrogen" form prior to MALDI analysis. Sinapinic acid is often used as a matrix for polylectrolytes such as poly(styrenesulfonic acid) and poly(acrylic acid). Figure 10.36 reports the MALDI-TOF mass spectrum (recorded in the negative-ion mode) of poIy(styrenesuIfonic acid), which possesses a narrow MM distribution. The most intense peaks are those at 130,000 and 200,000 due respectively to... 

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