Fast Hydrolyzable Constitutional Isomer of Poly(butylene terephthalate) and Its Copolyesters with 1,4-Butanediol

Abstract

Fast hydrolyzable polyesters are promising candidates as biodegradable plastics degrading to carbon dioxide, water, and biomass in the presence of oxygen in a suitable environment. The rate-determining step of biodegradation is the fragmentation of polyesters to lower mass fragments by hydrolysis, which in the second step undergo bioassimilation. Polyesters with a balance of good mechanical properties and fast hydrolyzability are urgently needed as a sustainable solution to the problem of plastic pollution and persistent microplastics when used in packaging and agricultural applications. Aromatic polyesters, such as poly(butylene terephthalate) (PBT), are mechanically strong but require harsh hydrolysis conditions, making them nonbiodegradable. The trend is mostly the opposite for aliphatic polyesters. We present in this work an aromatic polyester, a constitutional isomer of PBT [poly(1,4-benzenedimethylene succinate) (PBDMS)], and its copolymers (PB x BDM y S) in which aliphatic ester units balance the mechanical, thermal, and hydrolysis properties. PBDMS was prepared from 1,4-benzenedimethanol (BDM) and succinic acid (S) via two-step polycondensation. Its copolyesters with 1,4-butanediol (B) as a comonomer are also presented. High-molecular-weight PBDMS showed a glass-transition temperature of 6 °C and a melting temperature around 100 °C, very high thermal stability, and melt processability. The structure−property relationship of such polyesters was intensively studied, focusing on the impact of molecular composition. The stress−strain behavior of these (co-)polyesters largely depended on the content of BDM and covered a wide range from ductile to elastic to brittle materials. The films of these polyesters showed much faster hydrolysis under basic conditions, making them promising for future detailed degradation studies under different environmental conditions.

Stretchable and Fast Composting Polyester Films with High-Performance Oxygen Barrier

“… c Rates of enzymatic hydrolysis were calculated by the slope of the linear fit of each data set (Figures S2 and S16). d Residue mass of the polyester films without the addition of enzyme sampled after the last measuring point of each composition. e Data was taken from ref . …”

“…Therefore, in the second heating cycle, no melting peak was seen. Therefore, before using polyester films for any testing in this work, as mentioned in the experimental part, annealing was performed according to a previously published procedure …”

“…The material features a cation exchange capacity of 1.27 mmol g –1 . According to our recently published procedure, the polyesters were synthesized in a two-step melt polymerization process using 1,4-butanediol, 1,4-benzenedimethanol, and succinic acid . The polymers are designated as PB x BDM y S, where x and y are the molar ratios of the 1,4-butanediol and 1,4-benzenedimethanol in the feed, respectively.…”

“…For example, aromatic monomer units could be combined with degradable aliphatic units in a single polymer, as is the case for the commercial poly­(butylene adipate- co -butylene terephthalate) (PBAT), but such polymers still display slow degradation kinetics in many environmental conditions. , The combination of hydrolyzable ester groups and an aromatic group into the backbone of a polymer in a way that maintains degradability and desirable mechanical properties was recently investigated by us. Poly­(1,4-benzenedimethylene succinate) (PBDMS) is a constitutional isomer of PBT in which the carbonyl carbon is more electrophilic due to the aromatic unit being separated from the ester carbonyl carbon, thus limiting the delocalization of electron density through resonance structures . PBDMS and its copolymers with 1,4-butanediol were prepared, showing fast hydrolysis under basic conditions, good mechanical properties, and thermal stability.…”

“…Poly(1,4-benzenedimethylene succinate) (PBDMS) is a constitutional isomer of PBT in which the carbonyl carbon is more electrophilic due to the aromatic unit being separated from the ester carbonyl carbon, thus limiting the delocalization of electron density through resonance structures. 21 PBDMS and its copolymers with 1,4-butanediol were prepared, showing fast hydrolysis under basic conditions, good mechanical properties, and thermal stability. Such material has great potential to be a suitable replacement as a biodegradable food packing material if only it also demonstrated the other requirements of fast degradation and high barrier performance.…”