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characterization methods over the past decade. New depth profiling methods can give concentration versus depth information about polymeric additives labelled with deuterium with resolutions ranging from 1 to 100 nm. These methods include neutron and x-ray reflectivity, ion beam analysis (e.g., forward recoil spectrometry), and secondary ion mass spectrometry. When combined with older surface analytical methods, such as x-ray photoelectron spectroscopy and attenuated total reflection infrared spectroscopy and ellipsometry, these methods provide a powerful array of tools for polymer surface and interface characterization.
A number of new surface analysis techniques have also become available with the advent of high-brightness synchrotron x-ray sources. Grazing incidence x-ray diffraction methods now allow one to elucidate the state of order in the 5 nanometers just below polymer surfaces, while near-edge absorption of polarized soft x-rays can interrogate the orientation of molecular segments of polymers at surfaces.
New methods based on the contact mechanics technique promise to make it possible to measure simultaneously the work of adhesion, area of contact, and normal and lateral forces between two elastomer surfaces and thus offer the possibility of providing new insights on microscopic mechanisms of friction, adhesion, and wear.
Finally, new scanning probe microscopies will make a substantial impact on our knowledge of polymer surfaces by revealing the lateral structure of these interfaces with unprecedented resolution. Scanning force microscopy (SFM) (also called atomic force microscopy) is now in common use to reveal surface topology. Lateral force microscopy, a variant of SFM, has been shown to be capable of imaging polymer surfaces with chemical, rather than just topological, resolution. Another variant, tapping-mode SFM, is capable of revealing local differences in near-surface elastic properties. Near-field scanning optical microscopy promises eventually to allow various optical spectroscopies to be done on polymer surfaces with lateral resolutions as small as 10 nm. Perhaps the most intriguing possible development is a scanning probe NMR spectrometer, an instrument that would make it possible to determine directly the lateral chemical structure of polymer surfaces. Since most of these scanning probe microscopies do not require vacuum, or even air, environments, they can be adapted to examine the structure of water-polymer interfaces as well.
SYNTHESIS AND CHARACTERIZATION
Polymer synthesis has seen major advances in regard to the preparation and controlled design of structure to obtain specific properties or improvements in properties. Structural detail and the tailoring of properties depend on factors such as the control of chain length, molecular weight distribution, sequencing of copolymer units, microstructure isomer control, and end groups. The past 10 years have seen developments such as group transfer polymerization, ring-opening metathesis for cyclic hydrocarbons, improved cationic and anionic techniques for molecular weight control, and new biosynthetic routes. Much remains to be done to more exactly control stereochemistry. The understanding and use of new catalysts for architectural control, and for coupled integrated syntheses from monomer through polymer and product, are significant opportunities for further research.
The creation of new techniques for the synthesis of block, telechelic, and functional polymers will be essential for the study and development of new methods to control the interface of polymers with incompatible environments. Although there are now some techniques for the synthesis of block systems, new high-efficiency systems that allow the incorporation of blocks of standard polymers are required. Methods that produce polymers with controlled levels of functionality, as in telechelic polymers, are also needed.