Structural Basis for the Different Mechanical Behaviors of Two Chemically Analogous, Carbohydrate-Derived Thermosets

Abstract

Two renewable, structurally analogous monomers, isosorbide undecenoate (IU) and glucarodilactone undecenoate (GDLU) reacted with pentaerythritol tetrakis(3-mercaptopropionate) (PETT) via thiol−ene photopolymerization to form IU− PETT and GDLU−PETT thermosets. Despite their chemical similarity, uniaxial tensile testing showed that GDLU−PETT exhibited a strain-hardening behavior and is significantly tougher than IU−PETT. To understand this observation, in situ tensile testing and wide-angle X-ray scattering experiments (WAXS) were conducted. While the 2D WAXS patterns of IU−PETT displayed an isotropic halo during uniaxial deformation, they exhibited a change from an isotropic halo to a pair of scattering arcs for the GDLU− PETT samples. Density functional theory calculations further revealed that the GDLU alkyl chains are less angled than the IU alkyl chains. Based on these results, we postulate that the GDLU molecules can more easily order and align during uniaxial deformation, hence increasing intermolecular interactions between the GDLU molecules and contributing to the observed strain hardening behavior of their thermosets. This study exemplifies how molecules with subtle differences in their chemical structures can alter the structures and thermophysical properties of the resulting polymers in unpredictable ways.

Sugar-Based Polymers with Stereochemistry-Dependent Degradability and Mechanical Properties

“…The observed divergence in properties between isoidide- and isomannide-based materials highlights the power of controlling supramolecular interactions via stereochemistry (especially ring-induced geometric isomerism) in renewable monomer feedstocks. This is in line with a recent study of chemically analogous, carbohydrate-derived isosorbide- and glucarodilactone-based thermosets that demonstrated significant mechanical differences as a consequence of divergent chain interactions; however the samples both displayed elastomeric behavior …”

“…This is in line with a recent study of chemically analogous, carbohydrate-derived isosorbide-and glucarodilactone-based thermosets that demonstrated significant mechanical differences as a consequence of divergent chain interactions; however the samples both displayed elastomeric behavior. 39 The disparity of mechanical properties juxtaposed against the chemical similarity between IIPU and IMPU presented the opportunity to finely manipulate material mechanical properties by combining the stereoisomers either in physical blends or by copolymerization. Statistical copolymers (co-II x IM y ) with controlled stereochemical composition were obtained by varying the relative quantity of isoidide and isomannide monomer in the feed and copolymerizing with 1,8octanedithiol to afford polymers.…”

Ultra‐Tough Elastomers from Stereochemistry‐Directed Hydrogen Bonding in Isosorbide‐Based Polymers

“…Other reports have shown that the dynamic rupture and reformation of the reversible bonds releases residual stress and promotes effective energy dissipation, simultaneously enhancing both the strength and elasticity of the material [3a, 16] . A recent study reported thermoset isohexide polyesters, however the mechanical performance was typical for crosslinked materials and moreover, was inferior to a dilactone analogue [17] …”

“…[3a, 16] A recent study reported thermoset isohexide polyesters, however the mechanical performance was typical for crosslinked materials and moreover, was inferior to a dilactone analogue. [17] We have recently shown that regioregular isoidide (exo/ exo isomer) and isomannide (endo/endo isomer) could be incorporated into alternating polyurethanes to create materials in which the stereochemistry of the isohexide determined if the material displayed plastic or elastic behavior. [18] We were interested to study the effect of isosorbide on the resultant materials' properties on account of its endo/exo stereochemistry that we postulated would break up the regioregularity of the other isohexide materials to potentially deliver materials with improved strength and/or ductility to either of the other isohexide isomer-based polymers.…”

Renewable Photopolymers: Transformation of Biomass Resources into Value-Added Products Under Light

“…Chemical differences between similar molecules can be observed at the nanometer scale, as seen in the formation of thiol−ene photopolymerized thermosets using biobased monomers IU and GDLU (Scheme 17). 165 Isosorbide in IU contains cyclic ether functionalities, while GDLU contains cyclic ester groups. Density functional theory calculations showed that GDLU had better alignment in the elongation direction due to less angled alkyl chains, resulting in contrasting properties of their thermosets.…”