Relationship between Sequence Length and Thermal Properties of Poly(ethylene Terephthalate-Co-4, 4’-Bibenzoate) (PETBB)

Abstract

Poly(ethylene terephthalate-co-4,4’-bibenzoate)s (PETBBs) with 0-25mol% bibenzoate unit were prepared from terephthalic acid (PTA), 4,4'- bibenzoic acid (BBA) and ethylene glycol (EG). The chemical composition and number-average sequence length of the resultant PETBBs were investigated by 13C-NMR. It was improved that the chemical composition of PETBBs is identical with the feed ratio, and the number-average sequence length of PET segment (LPET) becomes reduced with increasing BBA unit. The molecular weights of PETBBs reaches the high level for practical use. DSC analysis explains that the glass transition temperature (Tg) increases almost linearly and the crystallization becomes difficulty with increasing content of BBA unit. X-ray diffraction also illustrates that both crystallinity and crystal size reduced as more BBA unit is incorporated. Moreover, the relationship between the number-average sequence length and the melting temperature was investigated. The linear correlation between the number-average sequence length (LPET) and the melting temperature was observed.