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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 (Tm) of copolyesters was observed by increasing the TPA/(CL+TPA) molar ratio, starting from the low end (Tm 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 Tm of 139.2°C that facilitates thermal extrusion from biomass or other biodegradable polymers of similar Tm. The number–average molecular weight (Mn) of 7.4 × 104 for PBTCL-50 was determined from the intrinsic viscosity [η] by using the Berkowitz model of Mn = 1.66 × 105[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 1H- and 13C-NMR spectroscopy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013