Bio-Based Poly(butylene 2,5-thiophenedicarboxylate-co-butylene 4,4′-biphenyldicarboxylate) with Excellent Ultraviolet Shielding Properties and Barrier Properties

To improve the glass transition temperature and ultraviolet shielding properties of poly(butylene 2,5-thiophenedicarboxylate) (PBTF), a series of poly(butylene 2,5-thiophenedicarboxylate-co-butylene 4,4′-biphenyldicarboxylate) (PBTFBs) were synthesized from 2,5-thiophenedicarboxylic acid (TDCA), 1,4-butanediol (BDO), and dimethyl 4,4′-biphenyldicarboxylate (BDD). The composition and molecular weights of PBTFBs were investigated by ¹H NMR, .¹³C NMR and GPC. The results showed that the glass transition temperature of PBTFBs gradually increased, and the thermogravimetric analysis results also showed that the thermal stability gradually increased with increasing the BDD content. Compared with PBTF, the polyester with 40% butylene 4,4′-biphenyldicarboxylate unit (PBTFB40) showed a higher Young’s modulus (1166.8 MPa) and tensile strength (25.8 MPa). In addition, the ultraviolet (UV) shielding ability of PBTF was greatly enhanced, and the UV transmittance at 350 nm decreased from 19.66% (PBTF) to 6.22% (PBTFB30). The average transmittance at wavelengths of 320–400 nm decreased from 26.25 to 15.20%. The gas permeability coefficient of CO₂ decreased from 0.3120 barrer to 0.0321 barrer. Because the biphenyl structure was successfully introduced into PBTF, the rigidity of the chain segment was improved, and excellent thermal stability, mechanical properties and UV shielding properties were obtained. PBTFB30 has potential application in outdoor products.