suring molecular motion and correlation times through relaxation times (76). These measured correlation times reflect the frequency of the motion. Because the performance of polymers is determined almost entirely by their temperature-transition behavior and energy dissipation properties (brittle, tough, rubbery, etc.), it is critical to be able to relate these dynamic properties to segmental motion in the polymer. Most engineering plastics, such as polyethylene, polypropylene, and others, are semicrystalline. The differences in the relative mobility of the crystalline (rigid) and amorphous (flexible) components allow the NMR spectroscopists to isolate these resonances from each other using "motional domain" techniques. In fact, NMR techniques allow examination of the motion over 5 decades of frequency. Recent studies on polycarbonate of bisphenol A (BPA) suggest that the shear dynamical mechanical loss and the dielectric loss result from the reorientation of the carbonate group. The bulk, shear, and dielectric losses all occur coincident in time, because the same cooperative motion results from the translation of the large BPA unit during the conformational interchange (17). One of the more interesting new textile fibers, poly(butylene terephthaiate), exhibits an unusual crystal-crystal transition, which is induced by strain. This strain-induced transition is remarkable in that it is reversible—it transforms back when the strain is reduced. This property makes it an ideal material for producing the currently
popular stretch jeans. Detailed NMR studies using proton, 13C, and deuterium NMR have mapped the transitional behavior of the various segments of the polymer (Figure 11). From these studies, the reversibility of the crystalcrystal transition is believed to arise from the unique chain packing of the aromatic rings and the low barrier to their slippage past each other under strain. The interaction between the aromatic rings behaves as a pseudocross-link that brings the rings back to their original state of packing when the stress is removed (18).
From I Through Z, Just Some of the Compounds You Can Measure At Low Picogram Levels [•iduli-
PhyHoquinone (Vitamin Κ }
Indole 3 A c r t a l d c h y d e lndolc-.ic-i.lic A n d Indolepy.uv.c A c d Inos.ne lHlm [so-Homovamli ic A c i d [sopuwra de lso-VMA lsoxsupune
Physosligmine PlCOhniC A n d P d y c h l o n n a l e d Phenols PrimaquiD Prochlo.peraune P'OPV' Gallale Piopylparaben Piolocatechuic A c i d Piotryptyline
Kvnureme A n d L-Dopa Lei.-enkephalin Menadione 3 M e i c a p t o v a l i n e (Pen i n I Limine} Metsnaphrine Melaproierenol Mel enkephalin Mclhioiii.it Methotrexate 3 M e l h o s y l Hyd)o.vr>ionyl.ily..-ol
• I •
3 Methony,4 H y d i o i y p h e n y l g l y c o l S Mvh'L· I n d - . W ,„• A n d ! titlfaBtlH—ThvMojW Î HlhmjufamnHriytoman. j - M e l h v l A H y d r o χ ν ρ h en ν I G)y< -Λ 5.MelhoKysflhcylic A c i d M elhyl para bon M H F G . M H P G Sulfate Morph.ne N Moth ν [epinephrine Ν Methylnicot.namide H-Methylserolonm Ν Melhy [tryptophan H Methvllryplamine N MWhyltyramine Nalorphine Naloxone NE ( N o i e p i n e p h n n e ) Nenr.-pep1;dc y Nei ι. -, ,-• ι Nicotmarmiie N.colme Nicotinic A n d
Pioxidme Pleioylglutamic Acid Pyridoxins (Vilsmm Β ] Quinaldic A c i d Quinolinic Acid Reserpine [Methyl Reserpate) Rilodrine Salicylic A c i d Serotonin (5-HT) (5 H y d . o x y l r y p t a m i n e ) Serotonin Sulfate Smapie A c i d Somatostatin , s E Î Substance Ρ Sullides Τ [Triindrtthyromaf?] T, [Thyroxine) Theophylline Thimerosal Thymine Thyroxine ( T J T o c o p h e i o l (Vitamin E] Trilluorperazine Trigonelline 2,4,5-Tn hydroxy b e n W"C A c i d (Gallic Acid) Tri ι m pi .amine Triiodothyronine^] 3,4,5-Tnttiethoxybenîoic A c i d Methyl Tryptsmine Tryptophan Ty.amme Tyrosine
I I • • I
Noradrenaline Norcodeme N o r e p i n e p h r i n e (ME) No.me Normorphtne
Uric Acid Vanillic A c i d Vamllylmandelic A n d Vamlmandelic A n d Vasopressin
Future prospects
The polymers of the future will utilize unified approaches that blend a knowledge of macromolecular design with synthetic methods to achieve new materials having unique and controllable properties for a wide range of new applications. The role of analytical chemistry is to make the necessary structure and dynamic measurements with skill and dispatch. The wealth of ideas and the ingenuity that have characterized the polymer industry in the past will create a sound foundation for dealing with future problems—problems that will be considered insignificant when compared with the opportunities that lie ahead. References
(1) Yau, W. W.; Kirkland, J. J.; Bly, D. D. Modern Size-Exclusion Chromatography; Wiley-Interscience: New York, 1979. (2) Koenig, J. L. Chemical Microstructure of Polymer Chains; Wiley: New York, 1982. (3) Cheng, H. N.; Bennett, M. Anal. Chem. 1984, 56, 2320.
I I
I Β I I 1 I I I I 1 I 1 1 I I I I S I 9 I I • • I
Send for Ihe Couîochem* brochure and a bibliography of current applications.
Prove it for yourself. Call today for a demonstration of the Coulochem in your laboratory.
esa Figure 11. Schematic representation of the motional dynamics of various carbons of the segmented poly(butylene terephthalate) copolymer at ca. 25 °C.
ESA, Inc. 45 Wiggins Avenue Bedford, Massachusetts 01730 (617)275-0100
Adapted with permission from Reference 18. CIRCLE 41 ON READER SERVICE CARD
ANALYTICAL CHEMISTRY, VOL. 59, NO. 19, OCTOBER 1, 1987 · 1153 A
