Reorganization of the structures, morphologies, and conformations of bulk polymers via coalescence from polymer-cyclodextrin inclusion compounds

摘要

Bulk poly(ethylene terephthalate) (PET) and bisphenol A polycarbonate (PC) samples have been produced by the coalescence of their segregated, extended chains from the narrow channels of the crystalline inclusion compounds (ICs) formed between the gamma-cyclodextrin (CD) host and PET and PC guests, which are reported for the first time, Differential scanning calorimetry, Fourier transform infrared, and X-ray observations of PET and PC samples coalesced from their crystalline gamma-CD-ICs suggest structures and morphologies that are different from those of samples obtained by ordinary solution and melt processing techniques. For example, as-received PC is generally amorphous with a glass-transition temperature (T-g) of about 150 degreesC; when cast from tetrahydrofuran solutions, PC is semicrystalline with a melting temperature (T-m) of about 230 degreesC; and after PC/gamma-CD-IC is washed with hot water for the removal of the host gamma-CD and for the coalescence of the guest PC chains, it is semicrystalline but has an elevated T-m value of about 245 degreesC. PC crystals formed upon the coalescence of highly extended and segregated PC chains from the narrow channels in the gamma-CD host lattice are possibly more chain-extended and certainly more stable than chain-folded PC crystals grown from solution. Melting the PC crystals formed by coalescence from PC/gamma-CD-IC produces a normal amorphous PC melt that, upon cooling, results in typical glassy PC. PET coalesced from its gamma-CD-IC crystals, although also semicrystalline, displays a T-m value only marginally elevated from that of typical bulk or solution-crystallized PET samples. However, after the melting of gamma-CD-IC -coalesced PET crystals, it is difficult to quench the resultant PET melt into the usual amorphous PET glass, characterized by a T-g value of about 80 degreesC. Instead, the coalesced PET melt rapidly recrystallizes during the attempted quench, and so upon reheating, it displays neither a T-g nor a crystallization exotherm but simply remelts at the as-coalesced T-m. This behavior is unaffected by the coalesced PET sample being held above T-m for 2 h, indicating that the extended, unentangled nature of the chains in the noncrystalline regions of the coalesced PET are not easily converted into the completely disordered, randomly coiled, entangled melt. Apparently, the highly extended, unentangled characters of the PC and PET chains in their gamma-CD-ICs are at least partially retained after they are coalesced. Initial differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared, and X-ray observations are described here. (C) 2002 Wiley Periodicals, Inc. [References: 40]