Abstract
Converting biomass-based feedstocks into polymers not only reduces our reliance on fossil fuels, but also furnishes multiple opportunities to design biorenewable polymers with targeted properties and functionalities. Here we report a series of high glass transition temperature (Tg up to 184 °C) polyesters derived from sugar-based furan derivatives as well as a joint experimental and theoretical study of substituent effects on their thermal properties. Surprisingly, we find that polymers with moderate steric hindrance exhibit the highest Tg values. Through a detailed Ramachandran-type analysis of the rotational flexibility of the polymer backbone, we find that additional steric hindrance does not necessarily increase chain stiffness in these polyesters. We attribute this interesting structure-property relationship to a complex interplay between methyl-induced steric strain and the concerted rotations along the polymer backbone. We believe that our findings provide key insight into the relationship between structure and thermal properties across a range of synthetic polymers.
Highlights
Converting biomass-based feedstocks into polymers reduces our reliance on fossil fuels, and furnishes multiple opportunities to design biorenewable polymers with targeted properties and functionalities
We found that the addition of methyl substituents to the anhydride comonomers has a non-linear influence over the observed Tg values, despite the widely accepted notion that Tg values increase upon methyl substitution due to the additional steric hindrance near the polymer backbone[8,10]
Since the monomethyl-substituted polyesters have both larger Vh and larger Tg values, these findings provide a direct correlation between intrinsic chain flexibility and the anomalous Tg relationship observed in these polyesters
Summary
Converting biomass-based feedstocks into polymers reduces our reliance on fossil fuels, and furnishes multiple opportunities to design biorenewable polymers with targeted properties and functionalities. Aromatic and aliphatic rings are often found as components of high-Tg polymers such as aromatic polycarbonates, polynorbornenes, and polyimides[8] Another common way to increase Tg is by introducing substituents along/ near the polymer backbone to hinder main-chain rotations through steric interactions[8,10]. Notable examples of such polymers include poly(α-methylstyrene), poly(2-methylstyrene), and poly (2,6-dimethylstyrene), all of which are characterized by Tg values that are significantly higher than their less substituted analogs[11]. On the basis of these findings, we propose several simple and intuitive design principles for how methyl substitution can be used to rationalize and tune Tg trends across a range of synthetic polymers
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