Preparation And Study Of Extended-Chain Crystals Of Biodegradable Poly (Butylene Succinate)

Extended-chain crystals(ECC)with high melting point and crystallinity are the most thermodynamically stable structure of crystalline polymers.Traditionally,ECCs are obtained via melt-crystallization under an ultrahigh pressure condition,which however,is too rigorous for wide application.Polymer chains singly isolated in inclusion complex(IC)with extended and ordered conformation provide a new strategy to prepare ECC.Herein,ECC of poly(butylene succinate)(PBS)is prepared by using the IC precursor,and the regulation and properties of ECC are in detail studied.The research contents and main achievements are as follows:Firstly,the inclusion complex of PBS and urea(PBS/urea-IC)was prepared by co-electrospinning PBS with urea and subsequent thermal treatment,in which PBS chains were separately isolated in urea hexagonal channels with a sub-nanometer diameter.After removal of the host urea frameworks with water washing,ECC of PBS with exceptionally high melting point(～136 °C)and crystallinity(～94.4%),whose lamellar thickness was larger than 26 nm,was obtained by rapidly packing of coalescing PBS chains.Comprehensive study had shown that thermal treatment,increase of chain orientation and the decrease of chain entanglements were the three very important factors in the preparation of PBS/urea-IC and ECC.Secondly,the formation process of PBS/urea-IC crystal structure was regulated by adjusting the annealing temperature and time.DSC results show that as the annealing temperature or time increases,the melting point,lamellar thickness and relative content of ECC increase.In addition,a small amount of butylene adipate(BA)heterogeneous units were introduced to PBS chains.As the increase of the content of BA units,the defects of coalesced crystals increased and the thermodynamic properties of the ECCreduced.Adjusting the undercooling for crystallization had weak regulation effect on ECC.Finally,we explored the application of ECC in PBS modification by taking advantages of high melting point,high crystallinity and good mechanical properties of ECC.ECC powders effectively promoted PBS matrix crystallization as nucleating agents based on epitaxial crystallization theory.The mechanical properties of PBS were significantly improved after adding ECC due to the small spherulite size and excellent interfacial compatibility between ECCs and PBS matrix.Furthermore,we fabricated homo-PBS shape memory materials based on the large melting point gap between PBS-ECC and ordinary crystals.