L. Paternostre

Morphology and crystal structure of the poly(ethylene oxide)–hydroquinone molecular complex

The occurrence of a molecular complex between poly(ethylene oxide) (PEO) and p-dihydroxybenzene (hydroquinone) has been determined using different experimental techniques such as differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and Fourier transform infrared spectroscopy (FTIR). From DSC investigations, an ethylene oxide/hydroquinone molar ratio of 2/1 was deduced. During the heating, the molecular complex undergoes a peritectic reaction and spontaneously transforms into a liquid phase and crystalline hydroquinone (incongruent melting). A triclinic unit cell (a = 1.17 nm, b = 1.20 nm, c = 1.06 nm, α = 78°, β = 64°, γ = 115°), containing eight ethylene oxide (EO) monomers and four hydroquinone molecules, has been determined from the analysis of the X-ray diffraction fiber patterns of stretched and spherulitic films. The PEO chains adopt a helical conformation with four monomers per turn, which is very similar to the 72 helix of the pure polymer. A crystal structure is proposed on the basis of molecular packing considerations and X-ray diffraction intensities. It consists of a layered structure with an alternation of PEO and small molecules layers, both layers being stabilized by an array of hydrogen bonds. The morphology of PEO–HYD crystals was studied by small angle X-ray scattering and DSC. As previously shown for the PEO–resorcinol complex, PEO–HYD samples crystallize with a lamellar thickness corresponding to fully extended or integral folded chains. The relative proportion of lamellae with different thicknesses depends on the crystallization temperature and time. Finally, the observed morphologies are discussed in terms of intermolecular interactions and chain mobility.

Metastabilities of lamellar crystals of molecular complexes

Abstract The molar stoichiometry and the crystal structure of four molecular complexes between poly(ethylene oxide) (PEO) and p -dichlorobenzene (PDCL), resorcinol (RES), hydroquinone (HYD) and p -nitrophenol (PNP) are compared. Even with a polymer weight fraction of 0.5, these molecular compounds form lamellar crystals when crystallized from the melt. The morphology of the lamellar crystals of these four PEO molecular complexes has been investigated in the early stages and after prolonged times of crystallization from the melt by time-resolved small-angle X-ray scattering coupled with wide-angle X-ray diffraction and differential scanning calorimetry. Non-integral-folded chain (NIFC) crystals are observed in the early stage of crystallization of PEO–RES and PEO–PNP molecular complexes from the melt. NIFC crystals of PEO–RES transform into integral-folded chain (IFC) and extended chain (EC) lamellar crystals with time. NIFC, 1-IFC and EC crystals can coexist in a sample of PEO–RES molecular complex. NIFC crystals of PEO–PNP do not transform into IFC or EC crystals even after long crystallization times or after heating until they melt. Stacks of IFC and EC crystals are present in the early stage of crystallization of PEO–HYD complexes at all the range of crystallization temperatures studied. The relative proportion of EC crystals of PEO–HYD increases with the crystallization temperature. PEO–PDCL forms only EC crystals at high crystallization temperatures ( T c >50°C). The type and magnitude of the interactions between host and guest molecules account for the different lamellar morphologies of these four molecular complexes. PEO–RES forms banded and unbanded spherulites in the temperature range 20 to 55°C. Banded spherulites are metastable and transform into unbanded spherulites through a solid-phase transition.

New dynamical effects in spherulitic growth

Abstract Two unexpected phenomena have been observed during the study of the growth of α and β spherulites of a poly(ethylene oxide)-resorcinol complex: an overgrowth rate (denoted as G i ) of the fastest, namely the α-form, along the interface of the β-form, and a transformation of the β-form into the α-form, which propagates as a dynamic front at a constant rate G t . The evidence for these two phenomena is demonstrated, and possible explanations are discussed. Measurements of the two rates, G i and G t , are also reported.

The use of an imaging plate as a detecting system in X-ray diffraction of polymers

Abstract We present in this paper some applications of X-ray diffraction to polymer studies, using an imaging plate as the detector. The advantages of this system make it very attractive for a number of experimental measurements (WAXS and SAXS), especially on oriented polymer samples.

Interspherulitic Limits and Transformation between the β and α Forms of the Poly(Ethylene Oxide)-Resorcinol Molecular Complex

Study of the growth rate of spherulites of the two allotropie forms of the poly(ethylene oxide)-resorcinol complex has revealed two unexpected phenomena: an interfacial “overgrowth” rate of the fastest kind when they are in contact with the slow one, and a transformation of this last form. This phase transformation propagates as a dynamic front characterized by a constant rate for given experimental conditions.

Morphology and crystallization kinetics of the two allotropic forms of the poly(ethylene oxide)-resorcinol molecular complex

PEO forms various crystalline molecular complexes with organic and inorganic molecules. Crystalline complexes with PEO and paradihalogenobenzene have been discovered and investigated in our laboratory(1). In these complexes, the interactions between PEO and the organic molecules are of the type Van der Waals. The present study deals with an other molecular complex of PEO and resorcinol, in which the interactions between the polymer and the guest molecules are larger (hydrogen bonding). The occurrence of a PEO-resorcinol complex has been reported by (2) and (3). The phase diagram (figure 1) shows clearly two eutectic points and a molecular complex. Its stoichiometry is 2 PEO monomers for 1 molecule of resorcinol. This complex present the particularity to have two allotropie forms, named α and β. The melting temperature of the α and β forms are around 90°C and 70°C respectively. Theα and β forms crystallize as unhanded and banded spherulites respectively. The banded spherulites (β form) transform into unhanded spherulites (α form) at room temperature. By a WAXS study, (4) has shown that the unit cell was orthorhombic (a= 1.05 nm b= 1.132 nm c= 0.9776 nm) and had a space group of Pna21.From FTIR study, the orientation of the resorcinol molecule in the unit cell was the benzenic plane is perpendicular to the chain axis (c) and the 2–5 axis of the resorcinol molecule is oriented along the radius of the unhanded spherulitic wich is parallel to the crystallographic parameter a of the unit cell.