Branching Effect on Butylene Succinate and Ethylene Terephthalate Copolyesters: Synthesis and Properties

Research subject: 

In the present study, a number of linear and long-chain branched copolyesters, poly (butylene succinate-co-ethylene terephthalate) (PBSET), were synthesized. Hence, effect of branching agent introduction was studied. Such a copolyesters, mostly aliphatic polyesters, may be applied in biomaterial fields. Adding aromatic section and branching agent have great effects on properties.

Research approach: 

All polyesters were synthesized via a two-step method esterification and polycondensation. All samples were produced in a laboratory scale set-up. First, prepolymers of two monomers were produced, separately. Then, required amount of each prepolymer were poured in the reactor and catalyst and thermal stabilizer were added and polycondensation reaction was performed. Pentaerythritol (PER) and trimellitic anhydride (TMA) were used as branching agents during synthesis. Microstructure of the copolyesters were characterized by ATR-FTIR and 13CNMR. Crystallinity, using XRD, and mechanical properties were studied, too.  Even small amount of branching agent has a great effect on properties. 0.4 mol% of PER and 0.4 and 0.6 mol% of TMA were incorporated.

Intrinsic viscosities of samples indicate that high molecular weight, about 38000 g/mol, were reached. ATR-FTIR spectra proves polyester synthesis. 13CNMR spectra shows incorporation of branching agent in polyester chain. Based on the XRD spectra, branching has no effect on the crystal type and type of crystal was unchanged. However, Crystallinity is decreased with branching. Mechanical properties are under serious effect of branching agent addition. It was observed that elongation at break and tensile strength were increased up to 400% and 200%, respectively. Hence, these branched copolyesters were synthesized and structure, crystallinity and mechanical properties were studied.