Structure and characterization of random aliphatic–aromatic copolyester

• New aliphatic–aromatic copolyester was synthesized from petrochemical raw materials.
• 1H NMR analysis indicated random distribution of aliphatic and aromatic comonomers.
• Solidification of copolyester is by crystallization of aromatic component only.
• Small angle X-ray scattering does not indicate the existence of “long period”.
• Fibrous crystals are arranged in spherulites filling completely the material volume.

New aliphatic–aromatic copolyester containing three different aliphatic comonomers: butylene adipate, butylene succinate and butylene glutarate, and one aromatic butylene terephthalate comonomer, all of petrochemical origin, has been synthesized (PBASGT) and its molecular characteristic, crystallization aptitude and morphology were examined by various techniques. Using the assignment of 1H NMR resonances due to homogeneous and heterogeneous dyads, the average block lengths were determined and it was found that PBASGT is a nearly random copolymer. During solidification only butylene terephthalate blocks are able to crystallize. However, some of the reflections from crystal planes are shifted towards lower diffraction angles as compared to butylene terephthalate homopolymer. Nonisothermal crystallization revealed the peak of crystallization at 37 °C while melting of those crystals occurred at 108 °C, in contrast to a homopolymer of butylene terephthalate (228 °C). PBASGT crystallizes in the form of thin fibrous crystals, few nanometers thick, which is the main factor influencing the depression of its melting temperature. Although the crystallinity degree is low (around 20%) the crystals form spherulitic aggregates filling the entire volume of the material. The chemical structure, morphology and crystallization behavior of PBASGT were compared with commercial aliphatic–aromatic copolyester of butylene terephthalate and butylene adipate (PBAT), Ecoflex. It appeared that, in contrast to aliphatic part of PBAT, aliphatic part of PBASGT is unable to crystallize, when annealed below room temperature. It appeared also that, similarly as PBAT, PBASGT is biodegradable.

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