Do we need to know and can we determine the complete macrostructures of synthetic polymers?

The complete molecular architectures of synthetic polymers, which may be called their macrostructures, consist of the types and amounts of short-range microstructural elements they contain, such as comonomer, regio- and stereosequences, branches, cross-links etc., as well as their locations along the polymer backbone. While spectroscopic probes that are only sensitive to local polymer structures, like NMR, can identify and quantify short-range microstructural elements, they are unable to locate their positions along the polymer backbone. Consequently, the present situation regarding our ability to characterize the complete chemical structures of synthetic polymers would be analogous to that of proteins if it were only possible to determine their amino acid compositions or possibly the amounts of consecutive pairs or even triplets of constituent amino acids, rather than their complete macrostructures, i.e., their complete amino acid sequences or primary structures. While the genetic DNA code may be read to determine the primary structures of most proteins, we have no such synthetic template for man-made polymers which can be utilized to determine their complete macrostructural architectures. Just as the primary sequences of proteins determine their secondary, tertiary, and even quaternary structures, and of course their resultant biological functions, it can logically be presumed that the behaviors of synthetic polymers are also principally the result of their complete structural architectures. Though important, the types and quantities of short-range microstructures polymers contain and which constitutes our present level of structural knowledge, is insufficient for the development of truly relevant structure-property relations. In addition, the degree of macrostructural heterogeneity among the chains in polymer samples is also expected to strongly influence the behaviors of materials made from them, and so this related issue also needs to be addressed. Here we summarize our recent attempts to develop and demonstrate an experimental approach that can be used to begin to characterize the complete macrostructures of synthetic polymers and to illustrate the relevance of this knowledge to understanding their properties and behaviors.