Two eugenol-based aromatic dimethyl terephthalate (DMT)-like monomers were prepared via thiol-ene click reaction and subsequent nucleophilic substitution reactions with methyl chloroacetate or 1,4-dibromobutane. Two series of thermoplastic polyesters derived from renewable eugenol and linear aliphatic α,ω-diols HO-(CH2)n-OH (n = 2, 3, 4, 6, 10, 12) were successfully synthesized. These prepared polyesters have weight-average molecular weights in the range of 18500-90500 g mol -1 , and polydispersities (PDI) between 1.8 and 2.2. Their chemical structures were all accurately characterized by 1 H NMR, 13 C NMR and FTIR. The random microstructures of synthetic polyesters were also explored by 13 C NMR. The obtained polyesters all exhibit thermal stability above 330°C. More importantly, the thermal stability, the maximum degradation rate and residue weight are intimately associated with the length of the linear aliphatic α,ω-diol. Their thermo-mechanical properties were studied by the differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The length of linear aliphatic α,ω-diol shows crucial influence on the glass transition temperature (Tg). With the gradually increase of the α,ω-diol length, the Tg of the synthesized polyester uniformly exhibits a tendency of decreasing. The polyesters are all amorphous materials at room temperature, whose Tg values range from -28.4 to 7.6°C. The incorporation of aromatic eugenol into the polyester chains reduces the crystallinity obviously, as well as the mechanical properties compared with conventional PET or PBT. The Young's modulus and ultimate strength are just in the range of 1.2-6.9 MPa and 0.96-3.37 MPa, respectively. On the contrary, the elongation at break reaches up to 840-1000%, indicating the excellent viscosity properties for such unmanageable viscous materials.
As a major class of mechanically interlocked molecules, not only are catenanes topologically intriguing targets that challenge the chemical synthesis to the efficient formation of mechanical bonds, but also the mechanical properties arising from the topology offer unique and attractive features for the development of novel functional molecular materials. Despite advancements in templated methods for different types of interlocked architectures, [ n]catenane possessing multiple numbers of interlocked macrocycles still remains a difficult synthetic target with very few reported examples. If the unique mechanical properties of catenanes are to be fully exploited, reliable, controllable, and efficient strategies for accessing [ n]catenanes will be necessary. In this Viewpoint, challenges, considerations, and strategies to [ n]catenanes are discussed.
A primary amine-thiourea organocatalyzed intramolecular Michael addition access was developed for the synthesis of trans-dihydrobenzofurans. Under the catalysis of an (R,R)-1,2-diphenylethylamine derived primary amine-thiourea bearing a glucosyl scaffold, the corresponding trans-dihydrobenzofurans were obtained in high yields with excellent level of enantioselectivities (94 to >99% ee). Moreover, an in situ isomerization occurring at high temperature gave good to excellent trans/cis ratios as well (trans/cis: 84/16-96/4).
Renewable monomers derived from eugenol and 10-undecenoic acid were synthesized via thiol-ene click and nucleophilic substitution reactions. With these monomers in hand, a series of thermoplastic polyesters with tunable thermo-mechanical properties were prepared via two-step melt polycondensation. The prepared polyesters exhibit weight-average molecular weights in the range of 21 000-48 000 g mol À1 , together with polydispersity values between 1.8 and 2.1. Experiments involving thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were carried out in order to study the thermal and mechanical properties of the polymers. All prepared polyester species prove to be thermally stable at temperatures up to 300 C. Furthermore, the aromatic and semi-aromatic polyesters exhibit fully amorphous behaviours with glass transition temperatures (T g s) ranging between À34.13 and 6.97 C. Herein, the density of the rigid aromatic rings along the main chains of the polyester has a distinct influence on the T g values. Furthermore, the fully aliphatic polyesters prove to be semi-crystalline with inconspicuous T g . The incorporation of aromatic eugenol into the polyester chains and the density of the benzene rings were also found to result in a significant improvement in the mechanical properties, including Young's modulus and elongation at break in the range of 11.6 to 44.2 MPa and 33.6-106.7%, respectively. The relatively high tan d and the low storage modulus indicate that eugenol-based polyesters feature superior viscosity properties and may therefore find future applicability in a variety of high-tech materials.
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