Improving crystallization and processability of PBS via slight cross-linking

Abstract

To improve the processability and crystallization of poly(butylene succinate) (PBS), a cross-linkable comonomer containing an alkynyl group, named 5-(2-(trimethylsilyl)ethynyl)isophthalate (DTS) was synthesized and copolymerized with dimethyl succinate and 1,4-butanediol to prepare a series of slightly cross-linked PBS copolyesters (PBDTSx). Due to the very low cross-linking degree, PBDTSx do not form gels when the DTS molar content is lower than 1.0%, and this made them keep good solubility and reprocessability. The cross-linking degree of DTS in PBDTSx is determined by NMR spectra. GPC data show that the M_w values of the copolyesters are higher than 23 × 10⁴ g mol⁻¹, and increase with the increase of DTS content. The thermal stability, crystallization, rheological behaviours, and mechanical properties of PBDTSx were investigated. Compared to neat PBS, PBDTSx have greatly increased crystallization rates because of promoted nucleation of the cross-linking domains. The elongation at break of PBDTSx drops slightly, while the Young's modulus increases. The rheological behaviours indicate that PBDTSx have higher melt viscosity than neat PBS even at a high shear rate, meaning that they will have better blow moulding processability. This work demonstrates that via controlling tiny cross-linking during the polymerization of PBS, the properties and processability of PBS can be improved, and this method overcomes the defects caused by traditional post cross-linking.