Materials Science of Polymers

Extract

This issue of the MRS BULLETIN is devoted to a class of materials undergoing a transition from a period in which they were viewed primarily as cheap substitutes for other materials into a new period where polymers are seen as high tech, value-added materials in their own right. The six articles included here focus on a portion of the wide range of topical areas concurrently at the frontiers of polymer materials science.

Polymers are molecules consisting of a large number of units (mers) covalently connected to form macromolecules of very high molar mass (upwards of 10⁶). Polymer chemists have learned how to make an almost endless variety of highly complex yet well- defined macromolecules utilizing a wide variety of monomers. Once polymer physicists and materials scientists depended on industry to provide samples (which were far from model materials to work on). Today, significant improvements in chemical synthesis and a growing collaborative effort between polymer chemists and materials scientists have resulted in the availability of extremely well-defined materials (molecular weight distribution, composition, sequence of monomer types along the chain backbone, stereochemistry of these units and overall molecular architecture, e.g., branching vs. linear) for the attainment of novel properties and the investigation of structure-property relationships. Given the sophistication of current polymer synthesis, it is now possible to test structure-property hypotheses systematically and to rationally design macromolecules to form specified microstructures and provide desirable physical properties.

The typical mental image conjured by the word polymer is an entangled mass of cooked spaghetti. This is in fact very appropriate for the class of flexible chain polymers in the noncrystalline state. The pioneering work of P.J. Flory in elucidating the nature of such materials, e.g., polymer melts and amorphous polymers above their glass transition temperature, made crucial use of the essentially Gaussian behavior of the end-to-end distance vector of a flexible chain polymer in the condensed state.