Suppressing gas permeation in cross-linkable biobased polyester elastomers via isophthalate-induced free-volume reduction and segmental confinement

Isophthalate-rich copolyesters form amorphous cross-linked elastomers. • PPeSATI60 shows O 2 /N 2 permeabilities of 0.24/0.18 Barrer. • PALS reveals smaller free-volume holes at higher DMI contents. • DMA and LF-NMR indicate stronger constraints on local chain mobility. Suppressing gas permeation while retaining elastic deformability remains a key challenge in the design of barrier elastomers. Here, a series of poly(1,5-pentylene succinate- co -itaconate- co -terephthalate- co -isophthalate) elastomers (PPeSATI) was prepared by transesterification, melt polycondensation, and peroxide curing via the carbon–carbon double bonds in the itaconate units. Dimethyl isophthalate was incorporated as a nonlinear aromatic comonomer into a flexible polyester backbone derived from dimethyl succinate, dimethyl itaconate, dimethyl terephthalate, and 1,5-pentanediol. The isophthalate fraction was systematically varied to examine its influence on the mechanical and gas-barrier properties of the resulting elastomers. The resulting copolyesters showed no melting or crystallization transitions in the DSC thermograms, while retaining glass-transition temperatures below room temperature and exhibiting 5% weight-loss temperatures above 356 °C. PPeSATI 60 exhibited O 2 and N 2 permeability coefficients of 0.24 and 0.18 Barrer, respectively, approximately one order of magnitude lower than those of the laboratory-prepared unfilled BIIR reference vulcanizate. Low-field NMR spectroscopy indicated an overall increase in apparent network constraints across the PPeSATI series. As the isophthalate fraction and total aromatic content increased, DMA results showed an overall shift of the β -relaxation peak toward higher temperature. PALS results indicated decreases in the mean free-volume hole size and relative fractional free volume ( f v ) across the same series. These results demonstrate that incorporating isophthalate units is an effective strategy for developing gas-barrier polyester elastomers. Download: Download high-res image (352KB) Download: Download full-size image