Ionization of polymers

In Matrix-assisted laser desorption (MALDI) [13], the sample is allowed to crystallize together with an organic acid. Ionization is achieved by UV-laser shots being absorbed by the matrix with subsequent proton transfer. MALDI allows the ionization of polymers and proteins with molecular masses of up to 500000 Da. The major restriction of the MALDI-technique is its incompatibility with separation methods. 

Electrospray ionization of polymers was introduced in 1968 (7) in an effort to study polystyrene by ms. In 1984, the technique was further developed for biopolymers (8). Spectra of poly(ethylene glycols) (PEG) up to molecular masses of 17,500 were also obtained using esi (9). In 1992, esi techniques were used to obtain ms on a poly(ethylene oxide) (PEO) of about 5,000,000 (2). Since esi techniques multiply charge macromolecules, both these studies were able to get spectra on a quadrupole ms with an miz of less than 2000, where z is the number of charges. However, with many different ra-mers in a normal narrow MMD of a synthetic pol5mier, the effect of z often as high as 40 means that one needs to obtain resolution in mIz of a small fraction of a mass unit to see the entire MMD. 

The principle of a MALDI is schematically shown in Figure 1. For the ionization of polymers, ultraviolet (UV) lasers are typically used. Some (more or less successful) efforts have been made to apply other lasers, for example, working in the infrared or visible wavelength range. Irrespective of the applied laser, the MALDI principle basically requires the use of a matrix that has to fulfill the following tasks ... 

In this section we briefly consider the osmotic pressure of polymers which carry an electric charge in solution. These include synthetic polymers with ionizable functional groups such as -NH2 and -COOH, as well as biopolymers such as proteins and nucleic acids. In this discussion we shall restrict our consideration... 

Anionic Polymerization of Cyclic Siloxanes. The anionic polymerization of cyclosiloxanes can be performed in the presence of a wide variety of strong bases such as hydroxides, alcoholates, or silanolates of alkaH metals (59,68). Commercially, the most important catalyst is potassium silanolate. The activity of the alkaH metal hydroxides increases in the foUowing sequence LiOH < NaOH < KOH < CsOH, which is also the order in which the degree of ionization of thein hydroxides increases (90). Another important class of catalysts is tetraalkyl ammonium, phosphonium hydroxides, and silanolates (91—93). These catalysts undergo thermal degradation when the polymer is heated above the temperature requited (typically >150°C) to decompose the catalyst, giving volatile products and the neutral, thermally stable polymer. 

Internal and External Phases. When dyeing hydrated fibers, for example, hydrophUic fibers in aqueous dyebaths, two distinct solvent phases exist, the external and the internal. The external solvent phase consists of the mobile molecules that are in the external dyebath so far away from the fiber that they are not influenced by it. The internal phase comprises the water that is within the fiber infrastmcture in a bound or static state and is an integral part of the internal stmcture in terms of defining the physical chemistry and thermodynamics of the system. Thus dye molecules have different chemical potentials when in the internal solvent phase than when in the external phase. Further, the effects of hydrogen ions (H" ) or hydroxyl ions (OH ) have a different impact. In the external phase acids or bases are completely dissociated and give an external or dyebath pH. In the internal phase these ions can interact with the fiber polymer chain and cause ionization of functional groups. This results in the pH of the internal phase being different from the external phase and the theoretical concept of internal pH (6). 

The photoelectron spectra of pyridazine have been interpreted on the basis of many-body Green s function calculations both for the outer and the inner valence region. The calculations confirm that ionization of the first n-electron occurs at lower energy than of the first TT-electron (79MI21201). A large number of bands in the photoelectron spectrum of 3,6-diphenylpyridazine in stretched polymer sheets have been assigned to transitions predicted... 

Two relatively new techniques, matrix assisted laser desorption ionization-lime of flight mass spectrometry (MALDI-TOF) and electrospray ionization (FS1), offer new possibilities for analysis of polymers with molecular weights in the tens of thousands. PS molecular weights as high as 1.5 million have been determined by MALDI-TOF. Recent reviews on the application of these techniques to synthetic polymers include those by Ilantoif54 and Nielen.555 The methods have been much used to provide evidence for initiation and termination mechanisms in various forms of living and controlled radical polymerization.550 Some examples of the application of MALDI-TOF and ESI in end group determination are provided in Table 3.12. The table is not intended to be a comprehensive survey. 

Among the various radiation-induced modifications, the EB-processing of polymers has gained special importance as it requires less energy, is simple, fast, and versatile in application. The overall properties of EB-irradiated polymeric materials are also improved compared to those induced by other ionizing radiation. 

Yu, K., Block, E., and Balogh, M., LC-MS Analysis of polymer additives by electron and atmospheric-pressure ionization identification and quantitation,... 

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