Synthesis and characterization of copolymeric aliphatic–aromatic esters derived from terephthalic acid, 1,4‐butanediol, and ε‐caprolactone by physical, thermal, and mechanical properties and NMR measurements

In this study, a series of aliphatic–aromatic poly(butylene terephthalate‐ co ‐ε‐caprolactone) (PBTCL) copolyesters were synthesized from various monomeric compositions of terephthalic acid (TPA), 1,4‐butanediol (BDO), and ε‐caprolactone (CL) in the presence of tetrabutyl titanate (Ti(Obu) 4 ) and stannous octoate (Sn(Oct) 2 ) as catalysts through a combination of polycondensation and ring opening polymerization. A significant increase in the melting temperature ( T m ) of copolyesters was observed by increasing the TPA/(CL+TPA) molar ratio, starting from the low end ( T m 66.2°C) of pure poly‐ε‐caprolactone PCL upward. We found that PBTCL‐50, which has a TPA/(CL+TPA) 50% molar ratio and polycondensation at 260°C for 1.5 h, resulted in a proper T m of 139.2°C that facilitates thermal extrusion from biomass or other biodegradable polymers of similar T m . The number–average molecular weight ( M n ) of 7.4 × 10 4 for PBTCL‐50 was determined from the intrinsic viscosity [η] by using the Berkowitz model of M n = 1.66 × 10 5 [η] 0.9 . Good mechanical properties of PBTCL‐50 have been shown by tensile stretching experiment that indicates tensile strength, elongation, and Young's modulus are 11.9 MPa, 132%, and 257 MPa, respectively. Polymers with aforementioned properties are suitable for manufacturing biodegradable plastic films for downstream agricultural applications or merely for trash bag. This article reveals that the PBTCL‐50 contains all five monomers with different molar ratios and characteristical linkages between each other. The novel structure was furthermore analyzed by 1 H‐ and 13 C‐NMR spectroscopy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013