Crystallization of Poly(ethylene oxide) from Solutions of Different Solvents

Abstract

ABSTRACT:The kinetics and crystalline morphology for isothermal crystallization of poly(ethylene oxide) (PEO) from solutions in three different solvents, N, N-dimethylacetamide (DMAc), toluene, and tripropionin (TP), were investigated. The energy barrier A of primary nucleation was highest for PEO/TP, and that of radial growth C was highest for PEO/toluene. Crystallites grew from both the DMAc and toluene solutions as aggregates of small layers of lamellae with branching and splitting. In addition, the crystallites from PEO/DMAc were found to have polygonal-like contours outside the lamella aggregates. This finding suggests that liquid-liquid phase separation occurred before or during the crystallization for PEO/DMAc. Relatively large spherulites were obtained from PEO/TP solutions due to the relatively low primary nucleation rate. The number density of the crystallites from PEO/TP was much lower than those from PEO/DMAc and PEO/toluene. KEY WORDS Poly(ethylene oxide) / Crystallization from Solutions / Primary Nucleation / Radial Growth / Solvent Effect / Morphology / Since polymer crystallization is essentially a kinetically-controlled process, the morphology of polymer crystals grown from solutions is very different from that in the case of bulk or melt crystallization due to the effects of polymer-solvent interaction, solution viscosity, concentration, molecular weight, and various other factors. The effect of solution concentration on the rate of crystallization can be treated by introducing an excess entropy term into the kinetic nucleation theory. 1-3 Nakajima et al. investigated the solvent effect on single crystal formation of polyethylene from various solutions, and they revealed that the thermodynamic interaction with solvent plays a dominant role. 4, 5 However, studies on the solvent effect have been done exclusively for single crystals from very dilute solutions, and the general characteristics of the solvent effect on solution crystallization have not yet been fully elucidated even from the phenomenological point of view. In some cases, strong interaction between a polymer and a solvent results in the formation of a polymersolvent compound 6, 7 or in physical gelation, [8][9][10][11] while in other cases, a liquid-liquid phase separation process may play a role in the crystallization. 10, 12, 13 However, the effects of liquid-liquid phase separation on kinetics and crystalline morphology have not been extensively studied.In our recent research on crystallization of poly(ethylene oxide) (PEO) from non-dilute solutions of a very viscous solvent, tripropionin (TP), we have found that the heterogeneity arising from incomplete dissolution in the initial solution plays an important role in the primary nucleation. 14,15 This is related to the so-called † To whom correspondence should be addressed. melt memory effect reported for melt crystallization. 17 The significance of this phenomenon should be renewedly assessed in the light of recent issue of the crystallization mechanism at very early stages. 16,18 ...

Unusual phase behavior in mixtures of poly(ethylene oxide) and ethyl alcohol

“…6(b)], I ( q ) = I (0)/(1 + q 2 ξ 2 ), where ξ denotes the average correlation length between the polymer coils, yields the value of I ( q ) at q = 0, that is, I (0), at each temperature. I (0) is directly related to the second derivative of the free energy of mixing, Δ G m , in a binary polymer system20, 25 as 1/ I (0) = ∂ 2 Δ G m /∂ϕ 2 , where ϕ is the polymer concentration. On the phase boundary, 1/ I (0) = ∂ 2 Δ G m /∂ϕ 2 = 0.…”

“…Poly(ethylene oxide) (PEO), a semicrystalline polymer and a unique member of the polyepoxides {[(CH 2 ) m O] n with m = 2}, is soluble in both aqueous and organic solvents1, 2 and is, thus, one of the most intriguing polymers whose solution properties have been extensively studied3–20 both experimentally3–11, 17–20 and theoretically12–16 for decades. Recently, there has been a large amount of research interest in the PEO/water system.…”

“…The PEO/water system is a simple model system (synthetic analogue) for studying fundamental biomolecular interactions in which hydrogen‐bonding and hydrophobic interactions play important roles, such as protein folding and stabilization. Consequently, most of the studies have been focused on PEO aqueous solutions,3–16 and relatively few attempts7, 17–20 have been conducted to examine the properties of PEO in organic solvents.…”

“…It has been reported that PEO dissolves in methanol in forms of single molecules and clusters,18 whereas it crystallizes in toluene and N,N ‐dimethylacetamide 20. The understanding of the behavior of PEO in organic solvents is still incomplete, and so it would be interesting and important to perform systematic studies on mixtures of PEO and organic solvents.…”

Formation of Porous Spherulites of Poly(L-lactide) Grown from Solutions

“…For example, crystallization of PEO in a very viscous solvent results in highly swollen spherulites with solvent, while in dimethyl sulfoxide crystallites with outer polygonal contours are formed suggesting that liquid-liquid phase separation occurs during the crystallization. 7 For many biomedical applications of the porous materials, biocompatibility and biodegradability is usually required. In this respect, poly(L-lacide) (PLLA) is one of the most promising materials for the fabrication of porous particles by the solution crystallization method.…”