Development of Anti-Shrinkage and High-Elastic Thermoplastic Poly(Ether-Ester) Elastomer Foams Via Supercritical Carbon Dioxide Foaming

The demand for thermoplastic poly(ether ester) elastomer (TPEE) foams with ecofriendly performance, superior mechanical attributes, and cost-effectiveness has garnered significantly. However, TPEE is challenging to foam and attain the ideal cellular texture before chemical cross-linking owing to its poor melting strength. In this study, we developed a lightweight sustainable TPEE foam system with tunable cellular textures and excellent performance by supercritical carbon dioxide (scCO2) foaming. First, a biobased TPEE library with improved melting strength was synthesized using renewable monomers, namely, 1,3-propanediol, 2-methyl-1,3-propanediol, triblock poly(propylene oxide) (PPO)-poly(ethylene oxide) (PEO)-PPO (PEP), and dimethyl terephthalate. Results showed that the melting temperature (Tm) decreased from 230.2 to 170.5 °C and the initial degradation temperature (Td5%) was higher than 340 °C. The mechanical modulus and strength of TPEEs were within the regime of 16.7 ± 0.5–61.6 ± 0.3 MPa and 7.2–10.8 MPa, respectively, with strain at break reaching 1032.8 ± 2.1%. It was found that incorporating a side methyl group structure improved scCO2 solubility and melt strength against cell growth elongation stresses and led to lower Tm and crystallinity (Xc%) of PTT-b-PEP-M (PTT = poly(trimethylene terephthalate)), improving the foaming temperature window. The synergistic effect offered by the side methyl groups steers to the successful construction of foam specimens with average cell size (27–34 μm), high expansion rate (3.5–7.1), cell density ((1.96–2.59) × 108 cell/cm3), and strong dimensional stability, effectually surpassing the foaming complications of inadequate melt strength in the traditional TPEE system. These unique benefits and the green scCO2 foaming method make the TPEE foams favorable for flexible, high-performance cellular polymeric materials.