The Consequences of the Incorporation of (Aliphatic/Cycloaliphatic) Sugar-Based Non-Drop-In Monomers into Polyamides:In-Depth Study on Representative Examples
Biomass has been recently intensively exploited to mine new compounds, which potentially might be utilized for polyamide synthesis. Sugar (waste) for example offers a variety of structures including moieties containing hydroxyl groups. A polymerization of molecules with multiple hydroxyl groups is possible; however it requires the application of sophisticated and very often exhausting synthetic methods. In many instances a more effective manner of handling this problem is reduction of functionalities and therefore preparation of bifunctional, step-growth polymerizable compounds. The preparation of bifunctional monomers from multifunctional sugar-derived diacid/diesters can be achieved through dehydration, protection of hydroxyl groups with ether or, frequently intensively researched, the acetalization of those groups. The polymerization of the first type of monomer, dehydrated sugars, results in polymers, which possess cyclic moieties built into the backbone. The second approach leads to a polymer with 4 relatively small pendant groups and the last one leads to a polymer with bulky moieties based on a dioxolane or substituted dioxolane/dioxane rings as pendant groups. The incorporation of all those moieties has major consequences and repercussions for polymer properties. The bulky structures of the cycloaliphatic fragments, which are frequently incorporated into polyamides, induce rigidity, suppress crystallinity and notably influence the interaction of polymeric chains. The additional oxygen atoms in protected and unprotected molecules, usually an inherent part of the abovementioned moieties, disrupt hydrogen bond interactions, influence the thermal properties, but also are an excellent way to introduce new functionalities into the polymer. Furthermore, since polyamides are usually synthesized via polycondensation at high temperatures, which is potentially destructive for those heterofunctional moieties, researchers frequently choose for solution polymerization methods, which are not environmentally friendly nor industrially relevant. It is however possible to perform high temperature melt polycondensation of those moieties after careful consideration of the possible consequences for those structures and by right choice of the starting material. In this chapter, a short review of many literature reports will be covered regarding sugar-based moieties and the consequences of their incorporation into polyamides will be considered. At the beginning, the synthetic approach applied for those type of polymers will be discussed from efficiency point of view. Recent advances in the melt polycondensation of cyclic, protected polyhydroxyacid derivatives will be examined and put in a broader perspective. Furthermore, the influence of those moieties on the properties of polymers therefrom (e.g., thermal stability, hydrogen bonding interaction, crystallinity of the polymer) and the influence of structural parameters in the monomers on the reactivity of the polymerizable functional groups will be discussed. The focus point is to find a global relationship between sugar-based monomer structures and properties of polyamides based on a careful analysis of existing reports for representative examples of typical sugar-based molecules
