Bio-Based Degradable Poly(ether-ester)s from Melt-Polymerization of Aromatic Ester and Ether Diols

Abstract

Vanillin, as a promising aromatic aldehyde, possesses worthy structural and bioactive properties useful in the design of novel sustainable polymeric materials. Its versatility and structural similarity to terephthalic acid (TPA) can lead to materials with properties similar to conventional poly(ethylene terephthalate) (PET). In this perspective, a symmetrical dimethylated dialkoxydivanillic diester monomer (DEMV) derived from vanillin was synthesized via a direct-coupling method. Then, a series of poly(ether-ester)s were synthesized via melt-polymerization incorporating mixtures of phenyl/phenyloxy diols (with hydroxyl side-chains in the 1,2-, 1,3- and 1,4-positions) and a cyclic diol, 1,4-cyclohexanedimethanol (CHDM). The polymers obtained had high molecular weights (Mw = 5.3–7.9 × 104 g.mol−1) and polydispersity index (Đ) values of 1.54–2.88. Thermal analysis showed the polymers are semi-crystalline materials with melting temperatures of 204–240 °C, and tunable glass transition temperatures (Tg) of 98–120 °C. Their 5% decomposition temperature (Td,5%) varied from 430–315 °C, which endows the polymers with a broad processing window, owing to their rigid phenyl rings and trans-CHDM groups. These poly(ether-ester)s displayed remarkable impact strength and satisfactory gas barrier properties, due to the insertion of the cyclic alkyl chain moieties. Ultimately, the synergistic influence of the ester and ether bonds provided better control over the behavior and mechanism of in vitro degradation under passive and enzymatic incubation for 90 days. Regarding the morphology, scanning electron microscopy (SEM) imaging confirmed considerable surface degradation in the polymer matrices of both polymer series, with weight losses reaching up to 35% in enzymatic degradation, which demonstrates the significant influence of ether bonds for biodegradation.

Synthesis and properties of biodegradable aliphatic–aromatic polyesters derived from 4‐hydroxybenzaldehyde

“…The glass transition temperature increased for the rigid copolyesters, the largest increase being observed when the isosorbitol content reached 20 mol%. While the addition of rigid units improved the melt strength of the copolymers, 19 their low crystallization rate was not conducive to processing by film extrusion. The modulus also increased with the rigid monomer content 20 .…”

Synthesis by Melt-Polymerization of a Novel Series of Bio-Based and Biodegradable Thiophene-Containing Copolyesters with Promising Gas Barrier and High Thermomechanical Properties

“…The semi-crystalline films were melt-pressed into thin films and tested on a gas permeability tester (Labthink VAC-V2, Medford, Massachusetts, USA UK). The morphology and degree of entanglement of the multiphase (semi-crystalline) affected the diffusion path of the permeating molecules [ 19 , 48 ]. The permeability coefficients were determined according to the ASTM D3985 standard and measured at 23 °C.…”

“…This enzymatic degradation follows a two-step process in which extracellular enzymes produce microorganisms (mostly sulfur-loving bacteria) that induce hydrolysis of ester bonds, resulting in the cleavage of the polymer chains into water-soluble hydrolysates such as monomers and oligomers. Afterwards, the microorganisms metabolize the water-soluble hydrolysates, in a process known as mineralization, into by-products such as methane, CO 2 , and H 2 O [ 19 , 30 , 70 ]. The enzymatic biodegradation is strongly correlated to properties such as chain composition, molecular weight, and crystallinity of the copolyesters [ 47 , 71 , 72 ].…”

“…Polymeric materials consist of aliphatic polyesters or aliphatic/aromatic polyesters, which may break down more quickly when they reach the end of their useful life. This is because macromolecules have potentially hydrolyzable ester bonds and short aliphatic chains that can be broken down by bacteria, fungi, or algae in the environment [ 19 , 20 , 21 ].…”