Synthesis and Investigation of Chiral Polycarbodiimides with Reversible Dynamic Properties (2010)

Ever since the pioneering idea of macromolecules was introduced by Staudinger in the 1920â€™s, the interdisciplinary field of synthetic polymer chemistry has grown tremendously and has now emerged into the mature subject that it is today. During this maturation, polymers have globally incorporated themselves into the everyday lives of humanity. Although, in most instances, polymers have been reveled for being lightweight, strong, chemically inert, flexible, and relatively inexpensive materials, a new breed of functional polymers are now being synthesized by polymer chemists and creating frontline attention within peer-reviewed journals. These new polymers are specialty materials designed to perform a function and otherwise interact in some way with their surroundings. The breadth of functionality being investigated is too long to list, ranging from something as complicated as biomimetic or conductive polymers to something as simple as improved degradation or â€œgreenâ€ polymers. Along with these new functionalities comes new challenges faced by polymer chemists with regards to the synthesis and characterization of such systems and although many significant advances have been made, this field is generally considered to be within the early stages of discovery. This manuscript will discuss a particular class of functional polymers known as polycarbodiimides and their application as specialty materials will be outlined as well as significant advances made to the synthesis and characterization of these polymers. Focus is placed on particular types of helical polycarbodiimides containing polyarene and aliphatic pendant groups. Through chiro-optical analysis, these polymers display a low energy solvo- and thermo-controllable conformational switching which is believed to arise from reorientation of the polyarene pendant groups fixed to the helical polycarbodiimide backbone scaffold. In essence, these polymers act as molecular shutters and, through their chirality, can greatly alter the polarization of light under very mild conditions. Structure activity relationships were performed and a library of over twenty new polymers was created to further understand the limitations and driving forces behind this unique phenomenon. In addition, synthetic optimization and property relationships of a new hallmark polymer, N-(1-naphthyl)-Nâ€™-(n-octadecyl) polycarbodiimide, is explored with the inclusion of solvation, molecular weight, regioregularity, and enantiomeric studies and their effect on this switching behavior.\nIn addition to the reversible dynamic properties of these polycarbodiimides, this manuscript will also explore new approaches towards better understanding and controlling fundamental properties of polycarbodiimides in general. Regioregularity of asymmetric carbodiimide polymers will be discussed and select polymers from within this new library reveal evidence of potentially controlling regioselectivity of these polymer systems through pendant group substituent effects. New improvements and clarification to analytical techniques for determination of the amount of regioirregularity within these polymer systems are also discussed.