Low-molecular-weight HOOC-terminated poly(butylene adipate) prepolymer (PrePBA) and poly(butylene succinate) prepolymer (PrePBS) were synthesized through melt-condensation polymerization from adipic acid or succinic acid with butanediol. The catalyzed chain extension of these prepolymers was carried out at 180-220 C with 2,2 0 -(1,4-phenylene)-bis(2-oxazoline) as a chain extender and p-toluenesulfonic acid (p-TSA) as a catalyst. Higher molecular weight polyesters were obtained from the catalyzed chain extension than from the noncatalyzed one. However, an improperly high amount of p-TSA and a high temperature caused branching or a crosslinking reaction. Under optimal conditions, chain-extended poly (butylene adipate) (PBA) with a number-average molecular weight up to 29,600 and poly(butylene succinate) (PBS) with an intrinsic viscosity of 0.82 dL/g were synthesized. The chain-extended polyesters were characterized by IR spectroscopy, 1 H-NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis, wide-angle X-ray scattering, and tensile testing. DSC, wide-angle X-ray scattering, and thermogravimetric analysis characterization showed that the chain-extended PBA and PBS had lower melting temperatures and crystallinities and slower crystallization rates and were less thermally stable than PrePBA and PrePBS. This deterioration of their properties was not harmful enough to impair their thermal processing properties and should not prevent them from being used as biodegradable thermoplastics. The tensile strength of the chain-extended PBS was about 31.05 MPa. V C 2009 Wiley Periodicals, Inc. J Appl Polym
This paper provided an easy and flexible method to synthesize high molecular weight polyesters by polycondensation and chain extension. Low molecular weight polybutylene adipate, polybutylene succinate, and poly(butylene succinate‐co‐butylene adipate) (PBSA) were synthesized through melt condensation polymerization from adipic acid and/or succinic acid with butanediol. The prepolyesters obtained had different amount of COOH and OH terminal groups. Chain extension of them was carried out at 180–240°C using 2,2′‐(1,4‐phenylene)‐bis(2‐oxazoline) and adipoyl biscaprolactamate as combined chain extenders. The influencing factors of the chain extension were studied. At the optimal conditions, chain‐extended polybutylene adipate with Mn up to 39,100, polybutylene succinate with intrinsic viscosity of 0.99 dl/g, and PBSA with intrinsic viscosity from 0.73 to 0.81 dl/g were synthesized. The chain‐extended polyesters were characterized by IR spectrum, 1H NMR spectrum, differential scanning calorimetry, thermogravimetric analysis (TGA), wide angle X‐ray scattering, and tensile test. The thermal analysis showed that chain extension often led to slight decrease of the regularity, the crystallinity, and the melting point. This deterioration of the properties is not harmful enough to impair their thermal properties and obstruct them from being used as biodegradable thermoplastics. The TGA showed that the chain‐extended polyesters were stable with initial decomposition temperature over 354.7°C. The tensile strength of the chain extended PBS and PBSAs with butylene adipate units less than 20 mol% was in the range of 18.95–31.22 MPa. Copyright © 2010 John Wiley & Sons, Ltd.
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