Collisionally polymers

The efficiency of these radiative processes often increase at low temperatures or in solvents of high viscosity. Consequently emission spectra are generally run in a low-temperature matrix (glass) or in a rigid polymer at room temperature. The variation in efficiency of these processes as a function of temperature and viscosity of the medium indicates that collisional processes compete with radiative and unimolecular nonradiative processes for deactivation of the lowest singlet and triplet states. 

Lemak, A. S. and Balabaev, N. K. (1996). Molecular dynamics simulation of a polymer chain in solution by collisional dynamics method, J. Comput. Chem., 17, 1685-1695. 

The data demonstrate the existence of a collisional process that leads to ejection of CO2 (and CO) from an oxidized polymer surface upon impingement of hyperthermal inert atoms or molecules and show that the rate of release of these carbon oxide molecules from the surface rises dramatically with incident kinetic energy above 800 kJ mol. The fact... 

Applications of FAB have been succesfully performed in the characterization of a wide range of compounds (dyes, surfactants, polymers...) but little attention has been devoted to the capabilities of this technique to solve environmental concerns, such as organic pollutants identification in water. The widespread use of surfactants in the environment has required the emplo yment of both sensitive and specific methods for their determination at trace levels. GC/MS and HPLC procedures has been used for the determination of anionic (LAB s) and non ionic surfactants (NPEO) in water (1-4). Levsen et al (5) identified cationic and anionic sirrfactants in surface water by combined field desorption/ collisionally activated decomposition mass spectrometry (FD/CAD), whereas FAB mass spectrometry has been used for the characterization of pine industrial surfactants (6-8). 

There is one additional mechanism for momentum transfer which does not seem to have been mentioned in the polymer literature. A bead of one dumbbell may collide with a bead of another dumbbell in such a way that their centers at the time of collision are on opposite sides of the plane at which the stress is being calculated. Such collisions would result in an instantaneous transfer of momentum between the two dumbbell centers and thus contribute to the stress at the plane. For very dilute solutions the contribution of this collisional momentum transfer would clearly be much smaller than those associated with mechanisms (i) and (ii) above. 

Photoluminescence quenching may arise from either a static process, by the quenching of a bound complex, or a dynamic process, by collisionally quenching the excited state [47,48]. For the former mechanistic case, Ksg represents an association constant for analyte binding to the polymer chain in... 

The purpose of this chapter is to review the kinetics and mechanisms of photochemical reactions in amorphous polymer solids. The classical view for describing the kinetics of reactions of small molecules in the gas phase or in solution, which involves thermally activated collisions between molecules of approximately equivalent size, can no longer be applied when one or more of the molecules involved is a polymer, which may be thousands of times more massive. Furthermore, the completely random motion of the spherical molecules illustrated in Fig. la, which is characteristic of chemically reactive species in both gas and liquid phase, must be replaced by more coordinated motion when a macromolecule is dissolved or swollen in solvent (Fig. b). Furthermore, a much greater reduction in independent motions must occur when one considers a solid polymer matrix illustrated in Fig. Ic. According to the classical theory of thermal reactions the collisional energy available in the encounter must be suificient to transfer at least one of the reacting species to some excited-state complex from which the reaction products are derived. The random thermal motion thus acts as an energy source to drive chemical reactions. 

Several desorphon and spray ionization methods can be used to convert S5mthehc polymers into intact molecular or quasimolecular ions (vide supra), whose exact m/z ratio identifies the composition of the polymer. For structural informahon about the polymer, the dissociation behavior or ion-molecule reactions of the polymer ions must be studied. Such reactions, which rarely take place during the soft ionization processes necessary to generate intact gas phase ions from synthetic macromolecules, are most conveniently assessed by tandem mass spectrometry (MS/MS). With MS/MS, a specific precursor ion is mass-selected, so that its reactivity can be investigated without perturbation from the other ions formed upon ionization. The reaction products of this ion are then mass-analyzed and collected in the MS/MS spectrum. MS/MS studies on polymer ions have so far focused on their spontaneous ("metastable") or collision-induced fragmentation. The fragments arising in these reactions are displayed in metastable ion (MI) or collisionally activated dissociation (CAD) spectra, respectively. Customarily, MI spectra acquired with a TOF mass analyzer have been named "postsource decay (PSD)" spectra similarly, CAD is often referred to as CID (collision-induced dissociation). ... 

Studies concerning the structural determination of some synthetic homopolymers by MALDI, combined with post-source decay or collisional-induced dissociation fragment ion analysis, show that the masses of individual end-groups can be determined from ion peaks generated by cleavage of the polymer backbone. ... 

The interactions of polymer surfaces with atoms of high velocity on collisions has been examined in order to try and elucidate relevant information to sur ce degradation [20]. The collisional dynamics were examined for various impact... 

The values of t (i.e., the critical exponent for electrical conductivity versus fluence), obtained from the slope of logftr) versus log(4> - j) linear dependences for various ion-implanted polymers (polyacrylonitrile [11], polyimide [87], poly-2,6-dimethyl-polyphenyleneoxide [11], perylene derivatives [12]), are 4-5 when the energy is deposited predominantly by the collisional mechanism and 7-8 when electronic stopping prevails. These values of the critical exponent for conductivity are substantially higher than those observed for metal nanoparticles in a dielectric matrix [88], which can be apparently explained by the effects of the conducting phase ordering during the implantation. 

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