Molecular Clusters, Gas Phase and Cluster Polymerization

Molecular beam techniques are applied to synthesize different classes of weakly bound molecular clusters and metal atom-doped molecular clusters. Resonant two-photon ionization coupled with time-of-flight mass spectrometry is then applied to study the spectroscopy of size specific clusters. We are interested in measuring the size-dependent spectroscopic lineshifts and lineshapes of a particular atomic or molecular excitation in these clusters.

The study of gas phase and cluster polymerization is an important intellectual and technological frontier which promises unique results not only for a fundamental understanding of polymerization reactions, but also for the development of new materials with unique properties. Using cluster beam techniques we have demonstrated, for the first time, that sequential polymerization reactions can occur on a time scale of a few microseconds following the ionization of the neutral clusters. Our current studies involve photodissociation of mass-selected ions in order to characterize the structures of the polymeric ions, and hence, measure the extent of the propagation reaction. The conversion of vdw clusters into size-specific covalent-bonded polymeric species will lead to the design of novel engineered materials with tailored unique properties.

This research in our laboratory has lead to the discovery of a novel technique for polymerization using metal ions generated in the gas phase by laser vaporization techniques [C&E News, May 24, 1993]. Using this method, high molecular weight polymers (106 units, polyisobutylene) have been synthesized. The polymeric materials also contain submicron-sized metal particles. With this method, it is now possible to incorporate essentially any ultrafine metal particles in essentially any polymer that can be made by cationic polymerization. The extra flexibility introduced by applying an electric field to modulate the polymer morphology makes these composites interesting candidates to explore new conducting, superconducting or magnetic materials. Manufacturing polymers with these properties could enhance the overall electro-optic performance and the efficient use of available materials.