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

Abstract

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 γ‐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 γ‐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 (Tg) of about 150 °C; when cast from tetrahydrofuran solutions, PC is semicrystalline with a melting temperature (Tm) of about 230 °C; and after PC/γ‐CD‐IC is washed with hot water for the removal of the host γ‐CD and for the coalescence of the guest PC chains, it is semicrystalline but has an elevated Tm value of about 245 °C. PC crystals formed upon the coalescence of highly extended and segregated PC chains from the narrow channels in the γ‐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/γ‐CD‐IC produces a normal amorphous PC melt that, upon cooling, results in typical glassy PC. PET coalesced from its γ‐CD‐IC crystals, although also semicrystalline, displays a Tm value only marginally elevated from that of typical bulk or solution‐crystallized PET samples. However, after the melting of γ‐CD‐IC‐coalesced PET crystals, it is difficult to quench the resultant PET melt into the usual amorphous PET glass, characterized by a Tg value of about 80 °C. Instead, the coalesced PET melt rapidly recrystallizes during the attempted quench, and so upon reheating, it displays neither a Tg nor a crystallization exotherm but simply remelts at the as‐coalesced Tm. This behavior is unaffected by the coalesced PET sample being held above Tm 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 γ‐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. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 992–1012, 2002

Molecular Processing of Polymers with Cyclodextrins

“…8) of as-received and solution-cast PET samples, although very similar, are clearly distinct from the spectrum of coalesced PET. The most noticeable difference is the much improved resolution observed in the spectrum of PET coalesced from its γ-CD-IC, in which nearly every vibrational absorption, [21]), solution-cast PET, and ICcoalesced PET samples, from bottom to top, respectively [21] except those likely contributed by residual γ-CD or H 2 O above 3,200 cm −1 , is resolved to the baseline. This improved resolution may be a result of the already suggested improved order in the noncrystalline regions of the sample; the chains are not as nearly randomly coiling or interpenetrating as those in the noncrystalline regions of the as-received and solution-cast samples and, as a result, do not exhibit a glass transition (DSC and solid-state NMR [33] below).…”

“…Thus, it appears that the PET chains in the noncrystalline regions of the coalesced PET film are more densely packed (by ∼1.4%) than in the amorphous regions of the annealed PET film, even though each film is ∼65% noncrystalline. The coalesced PET film has a higher density noncrystalline phase, because there the chains are more extended and tightly packed, and possibly more oriented, with a higher trans conformer content for the -CH 2 -CH 2 -bonds (FTIR results presented below [21]). In fact, the density estimated for the noncrystalline regions in coalesced PET (ρ nc = 1.354 g cm −3 ) exceeds slightly the overall density of the annealed PET film (1.3497 g cm −3 ).…”

“…However, we can currently conclude that electrostatic, van der Waals, and hydrogen-bonding interactions and relief of conformational strain in CDs are not important, while hydrophobic interactions, exclusion of high energy, cavitybound water, and crystalline packing of host CDs are important in the formation of polymer-CD-ICs. [33] ∼40% crystallinity (see Table 1, for typical levels of crystallinity in PET), while solid-state FTIR and NMR observations presented later [21,33] indicate that the PET chains in the noncrystalline regions of coalesced PET largely retain their included kink conformations.…”

“…6 both the all trans crystalline conformation of PET and noncrystalline, though also highly extended, kink conformation of PET are drawn. PET chains in the narrow channels of its γ-CD-IC crystals adopt the kink conformations, which after coalescence were also demonstrated to persist in the noncrystalline regions [21,33,59]. PET kink conformers have been suggested to occupy only ∼2/3 of the volume occupied by the all trans crystalline PET conformation [78].…”

“…In addition, the kink conformations adopted by PET included in its γ-CD-IC may upon coalescence be easily and rapidly converted into the crystalline all trans conformation solely by facile counter rotations about the -O-CH 2 -and -CH 2 -O-bonds, a conformational transformation producing little swept out volume and resulting in a highly crystalline sample. Largely amorphous as-received PET, on the other hand, is slow to crystallize, because its largely gauche -CH 2 -CH 2 -bonds must be rotated to the trans conformation during crystallization, a conformational transformation that must sweep out a large volume [21].…”