Crystal and phase morphologies and structures determined by self-organization of crystalline-amorphous diblockcopolymers, crystallization of the crystallizable blocks, and vitrification of the amorphous blocks are reviewed through asystematic study on a series of poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymers. On the base ofcompetitions among these three processes, molecular and supramolecular ordering in confined environments can beinvestigated. In a concentration-fluctuation-induced disordered (D_(CF)) diblock copolymer, the competition between crystalli-zation of the PEO blocks and vitrification of the PS blocks is momtored by time-resolved simultaneous small angle X-rayscattering (SAXS) and wide angle X-ray diffraction (WAXD) techniques. In the case of T_c相似文献
Summary: In a low‐molecular‐weight polyethylene‐block‐poly(ethylene oxide) (PE‐b‐PEO) diblock copolymer, two pathway‐dependent melting processes were observed: Upon slow heating, the PE lamellar crystals melted at ≈97 °C into a disordered state. However, when the temperature rapidly jumped to above the melting point (e.g., 100 °C), the PE lamellar crystals transformed directly into an ordered lamellar melt, followed by an isothermal conversion into a disordered melt. This isothermal order‐to‐disorder transition was explained by superheating of the PE crystals using a G‐T diagram.
A schematic G‐T diagram explaining the pathway‐dependent double melting for a crystalline polyethylene‐block‐poly(ethylene oxide) copolymer. 相似文献
We have been able to prepare a molecular complex between the poly(ethylene oxide) block of a poly(ethylene)-b-poly(ethylene-alt-propylene)-b-poly(ethylene oxide) triblock copolymer and p-nitrophenol (PNP). The composition of the copolymer employed was: 24% PE, 57% PEP and 19% PEO in weight percent. The pure copolymer exhibited a non-conventional thermal behavior since the PEO block displayed a fractionated crystallization process during cooling. The PEO block/PNP complex did not show any apparent crystallization during cooling, instead cold crystallization during heating was observed and an approximately 30°C increase in melting point as compared to the neat PEO block within the copolymer. This caused an overlap in the melting regions of the PE block and the PEO block/PNP complex. The self-nucleation of the PE-b-PEP-b-PEO/PNP complex is very different from that of the neat triblock copolymer. An increased capacity for self-nucleation of the PEO block was produced by the complexation with PNP and therefore the three self-nucleation domains were clearly encountered for both the PE block and for the PEO block/PNP complex. Self-nucleation was able to show that the two crystallizable blocks can be self-nucleated and annealed in an independent way, thereby ascertaining the presence of separate crystalline regions in the triblock copolymer. Through the use of PNP, both the crystallinity and the melting point of the PE-b-PEP-b-PEO block copolymer employed here can be substantially increased. Similar results were obtained by complexation of the same ABC triblock copolymer with resorcinol. 相似文献
Semicrystalline polymer/layered silicate nanocomposites were prepared by solution blending of a low molecular weight poly(ethylene oxide) (PEO) with an organically modified montmorillonite, Cloisite 10A (C10A). The intercalation morphology was studied by temperature-dependent synchrotron wide-angle X-ray diffraction (WAXD). Unlike PEO homopolymers, significant secondary crystallization was observed in the PEO/C10A nanocomposites. Reversible de-intercalation and intercalation processes were detected during secondary crystallization and subsequent melting of secondary crystals. On the basis of two-dimensional WAXD results on oriented samples, an interphase layer between the silicate primary particles and PEO lamellar crystals was proposed. Secondary PEO crystallization in the interphase regions was inferred to be the primary driving force for polymer chains to diffuse out of the silicate gallery. This study provided a useful method to investigate polymer diffusion in nanoconfined spaces, which can be controlled by PEO secondary crystallization and melting outside the silicate gallery. 相似文献
Melting points and lamellar thicknesses have been measured for ethylene oxide–propylene oxide block copolymers (sym-PEP) with central poly(ethylene oxide) block lengths of 70–100 chain units and end poly(propylene oxide) block lengths of 0–30 chain units. Melting points of the block copolymers are lower than those of the corresponding poly(ethylene oxide) homopolymer by an amount (up to 15°C) which increases as the poly(propylene oxide) block length increases. Most samples have more than one melting transition, which can be assigned to variously folded chain crystals. End interfacial free energies σe for the various crystals have been estimated by use of Flory's theory of melting of block copolymers. For a given crystal type (e.g., once-folded-chain) σe is higher the longer the chain length of the end poly(propylene oxide) blocks. For a given copolymer σe is lower, the more highly folded the poly(ethylene oxide) chain. 相似文献
Results of an investigation of isothermal crystallization and thermal behavior of poly(ethylene oxide)/poly(ethyl methacrylate) (PEO/PEMA) blends are reported. The blend composition and the crystallization temperature strongly influence the crystallization process from the melt and the melting temperature of PEO. The addition of PEMA to PEO causes a depression in the spherulite growth rate, in the overall kinetic crystallization constant, and in the melting temperature. Experimental data on the radial growth rate G and overall kinetic rate constant Kn are analyzed by means of the latest kinetic theory. From this analysis it emerges that the crystallization of pure PEO and PEO in the blend conforms to the regime I process of surface secondary nucleation. The depression of the melting temperature cannot be explained only in terms of a diluent effect due to the compatibility of the two components in the melt. Annealing and morphological effects, dependent on composition and time, must also be taken into account. 相似文献
We present a systematic investigation of the crystallization and aggregation behavior of a poly(1,2-butadiene)-block-poly(ethylene oxide) diblock copolymer (PB-b-PEO) in n-heptane. n-Heptane is a poor solvent for PEO and at 70°C the block copolymer self-assembles into spherical micelles composed of a liquid
PEO core and a soluble PB corona. Time- and temperature-dependent light scattering experiments revealed that when crystallization
of the PEO cores is induced by cooling, the crystal morphology depends on the crystallization temperature (Tc): Below 30°C, the high nucleation rate of the PEO core dictates the growth of the crystals by a fast aggregation of the micelles
into meander-like (branched) structures due to a depletion of the micelles at the growth front. Above 30°C the nucleation
rate is diminished and a relatively small crystal growth rate leads to the formation of twisted lamellae as imaged by scanning
force microscopy. All data demonstrate that the formation mechanism of the crystals through micellar aggregation is dictated
by two competitive effects, namely, by the nucleation and growth of the PEO core. 相似文献
We report novel micellar carriers, comprising pendant cinnamyl moieties in the core-forming block, designed to increase the solubilization of caffeic acid phenethyl ester (CAPE) in aqueous media. Amphiphilic poly(ethylene oxide)-block-poly(α-cinnamyl-ε-caprolactone-co-ε-caprolactone) (PEO-b-P(CyCL-co-CL) diblock copolymers were synthesized by ring-opening copolymerization of α-propargyl-ε-caprolactone and ε-caprolactone from a monofunctional PEO macroinitiator and subsequent attachment of cinnamyl groups via click reaction. In addition, a linear PEO-b-PCL diblock copolymer was synthesized and used in this study for comparison. Next, nanosized micelles from PEO-b-P(CyCL-co-CL) and PEO-b-PCL were formed via the solvent evaporation method and then loaded with CAPE. Dynamic and electrophoretic light scattering, and transmission electron microscopy were used to characterize both blank and loaded carriers. The potential of the micelles comprising pendant cinnamyl group to solubilize CAPE in water was evaluated in a comparative fashion to that of nonmodified PEO-b-PCL diblock copolymer. 相似文献
Time-resolved synchrotron wide- and small-angle X-ray scattering experiments were used to investigate crystallization behavior and microstructure development of a nearly monodisperse poly(ethylene oxide) [PEO] (Mw = 53,500), and its melt-miscible blends with two fractionated styrene - hydroxystyrene random copolymers [SHS]. PEO crystallization rates decrease significantly in the presence of the melt-miscible SHS copolymers. All low and high molecular weight SHS blends exhibit a crystallization process at relatively short times characterized by large Avrami exponents (n), followed by a dominant process with n near that of neat PEO. A model for the crystallization of these blends is proposed. 相似文献
In the preparation of the ABC star triblock copolymer of ethylene oxide, styrene and methyl methacrylate (MMA), the photo-induced
charge-transfer complex (CTC) was used to initiate the polymerization of the third monomer MMA. The CTC was composed of the
diblock copolymer of poly(ethylene oxide) (PEO) and polystyrene (PS), PEO-bi-PS, with an aromatic imino group at the conjunction point and benzophenone (BP). It was confirmed that the kinetic behavior
of this macromolecular initiation system is nearly the same with a general small radical initiator: the polymerization rate
Rp ∝ [PEO-bi-PS]0.48[BP]0.45[MMA]0.97. Moreover, if the molecular weight of the PEO block is fixed, Rp is independent of the molecular weight of the PS block. By means of measurements of viscosity and fluorescence, it was
found that the micelles of the diblock copolymer PEO-bi-PS were formed in benzene. The aromatic imino groups were located on the boundary surfaces of the micelles and were fully
exposed, and so the BP and MMA molecules easily approached them and affected the charge-transfer polymerization of MMA.
Received: 18 August 1998 Accepted in revised form: 25 November 1998 相似文献
Infrared spectra in conjunction with calorimetric measurements have been used to follow the crystallization process and microstructural changes of poly(ethylene oxide) (PEO) in poly(ethylene oxide) and poly(methyl methacrylate) (PMMA) blends. We have given particular attention to compositions containing low PEO concentrations. The crystallization behavior and the resultant microstructures of PEO are strongly perturbed by the presence of PMMA. In addition, we found phase separation and trans sequences of PEO to be present, especially at low PEO concentrations. 相似文献
The microstructure evolution of isotactic polypropylene(iPP) during annealing is reported.A few amount of poly(ethylene oxide)(PEO) which exhibits much lower melt temperature compared with /PP was introduced into /PP in this work.The crystalline structure of /PP was detected using differential scanning calorimetry(DSC) and wide-angle X-ray diffraction(WAXD),and the relaxation of /PP was characterized using dynamic mechanical analysis(DMA).The variation of PEO morphology was investigated by scanning electron microscopy(SEM).The results show that the crystallization, including the primary crystallization and second crystallization during annealing,as well as the relaxation of /PP matrix is promoted with the presence of PEO. 相似文献