Micellar Morphologies of Poly(ε-caprolactone)-<i>b</i>-poly(ethylene oxide) Block Copolymers in Water with a Crystalline Core

The self-assembly of poly(ε-caprolactone)-b-poly(ethylene oxide) block copolymers (PCLnPEO44 and PCLnPEO113) with narrow polydispersity in aqueous medium was studied using transmission electron microscopy. In this system, the formed micelles are composed of a crystalline PCL core and a soluble PEO corona. We demonstrated that the PCL-b-PEO block copolymers can form micelles with abundant morphologies, depending on the lengths of the blocks and composition. It is observed that for PCLnPEO44 the micellar morphology changes from spherical, rodlike, wormlike, to lamellar, as the length of the PCL block increases. In contrast, most of PCLnPEO113 (n = 21−147) block copolymers form spherical micelles, and only PCL232PEO113 exhibits mixed spherical and lamellar micellar morphologies. The effect of microstructure on micellar morphology was semiquantitatively interpreted in terms of reduced tethering density (σ). It is found that lamellar micelles are formed when σ is smaller than a critical value of between 3.0 and 4.8. A larger σ indicates crowding of the tethered chain, and spherical micelles tend to be formed

Micellar Morphologies of Poly(ε-caprolactone)-<i>b</i>-poly(ethylene oxide) Block Copolymers in Water with a Crystalline Core

The self-assembly of poly(ε-caprolactone)-b-poly(ethylene oxide) block copolymers (PCLnPEO44 and PCLnPEO113) with narrow polydispersity in aqueous medium was studied using transmission electron microscopy. In this system, the formed micelles are composed of a crystalline PCL core and a soluble PEO corona. We demonstrated that the PCL-b-PEO block copolymers can form micelles with abundant morphologies, depending on the lengths of the blocks and composition. It is observed that for PCLnPEO44 the micellar morphology changes from spherical, rodlike, wormlike, to lamellar, as the length of the PCL block increases. In contrast, most of PCLnPEO113 (n = 21−147) block copolymers form spherical micelles, and only PCL232PEO113 exhibits mixed spherical and lamellar micellar morphologies. The effect of microstructure on micellar morphology was semiquantitatively interpreted in terms of reduced tethering density (σ). It is found that lamellar micelles are formed when σ is smaller than a critical value of between 3.0 and 4.8. A larger σ indicates crowding of the tethered chain, and spherical micelles tend to be formed

Cooperative Effect of Electrospinning and Nanoclay on Formation of Polar Crystalline Phases in Poly(vinylidene fluoride)

Poly(vinylidene difluoride)/organically modified montmorillonite (PVDF/OMMT) composite nanofibers were prepared by electrospinning the solution of PVDF/OMMT precursor in DMF. Wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) show that in the bulk of the PVDF/OMMT precursor OMMT platelets are homogeneously dispersed in PVDF and can be both intercalated and exfoliated. It is found that the diameter of the PVDF/OMMT composite nanofibers is smaller than that of the neat PVDF fibers because the lower viscosity of PVDF/OMMT solution, which is attributed to the possible adsorption of PVDF chains on OMMT layers and thus reduction in number of entanglement. The crystal structure of the composite nanofibers was investigated using WAXD and Fourier transform infrared (FT-IR) and compared with that of thin film samples. The results show that the nonpolar α phase is completely absent in the electrospun PVDF/OMMT composite nanofibers, whereas it is still present in the neat PVDF electrospun fibers and in the thin films of PVDF/OMMT nanocomposites. The cooperative effect between electrospinning and nanoclay on formation of polar β and γ crystalline phases in PVDF is discussed. The IR result reveals that electrospinning induces formation of long trans conformation, whereas OMMT platelets can retard relaxation of PVDF chains and stabilize such conformation due to the possible interaction between the PVDF chains and OMMT layers. This cooperative effect leads to extinction of nonpolar α phase and enhances the polar β and γ phases in the electrospun PVDF/OMMT composite nanofibers

Ethylene–Propylene Segmented Copolymer as an in Situ Compatibilizer for Impact Polypropylene Copolymer: An Assessment of Rheology and Morphology

This work aims to probe the roles of ethylene–propylene segmented copolymer (EPS) in impact polypropylene copolymers (IPCs) by rheological and morphological investigations. A series of IPCs with different EPS contents and molecular structures are prepared by an atmosphere-switching polymerization process (ASPP). The Palierne emulsion model is used to describe the relationship between the rheological response to small amplitude oscillatory deformation and the morphology of IPC. It is found that this model describes well the linear viscoelastic responses of IPC, if the role of EPS is taken into account. An increase in the content of EPS and the length of its PP segments leads to a decrease in the size of the ethylene–propylene random copolymer (EPR) phase domains and the interfacial tension. These results strongly confirm the role of the EPS as a compatibilizer in the IPC system. The adhesion between the PP matrix and the EPR phase domains is enhanced by the presence of the EPS that is produced in situ during the ASPP. For this reason, ASPP is capable of making IPC with an excellent rigidity–toughness balance

Chain Structure, Aggregation State Structure, and Tensile Behavior of Segmented Ethylene–Propylene Copolymers Produced by an Oscillating Unbridged Metallocene Catalyst

Segmented ethylene-propylene copolymers (SEPs) with different propylene contents were prepared by an unbridged metallocene bis­(2,4,6-trimethylindenyl)­zirconium dichloride [(2,4,6-Me₃Ind)₂ZrCl₂] catalyst. Due to oscillation of the unbridged ligands in the catalyst, the SEPs are composed of segments with low propylene contents, alternated by the segments with high propylene contents. Such a chain structure was verified by ¹³C NMR and successive self-nucleation and annealing (SSA). As the propylene/ethylene feed ratio during copolymerization increases, the comonomer contents in both segments are increased, leading to noncrystallizability of the high propylene segments and smaller crystallinity of the low propylene segments. Consequently, SEPs may be used as thermoplastic elastomers (TPEs). The aggregation state structures at nano- and micro-scales were characterized with small angle X-ray scattering, transmission electron microscopy and polarized optical microscopy, and compared with those of ethylene–octene multiblocky copolymers (OBCs) with similar crystallinity. It is found that SEPs form thinner lamellar crystals with a lower melting temperature due to shorter length and higher comonomer content of the low propylene segments. Moreover, the short length of the high propylene segments in SEPs results in an evidently thinner amorphous layer among the lamellar crystals, thus lots of amorphous phases are excluded out of the interlamellae. Accordingly, ill-developed spherulites or even bundle crystals are formed in SEPs, as compared with the well-developed spherulites in OBCs. SEPs exhibit the tensile property of typical TPEs with diffused yielding and large strain at break

Influence of Ionic Species on the Microphase Separation Behavior of PCL‑<i>b</i>‑PEO/Salt Hybrids

The microphase separation behavior of the hybrids of poly­(ε-caprolactone)-b-poly­(ethylene oxide) (PCL-b-PEO) with different inorganic salts at various doping ratios (r) was studied by temperature-variable SAXS. It was observed that the salts could induce microphase separation to form ordered structure in the originally miscible melt of PCL-b-PEO. The effects of the metal ion and anion were correlated with the competitive interactions of PEO/salt and PCL/salt, which were characterized by FT-IR and DSC, respectively. It was found that at lower doping ratios the salts preferentially interacted with PEO. The larger association number of the metal ion and stronger association between PEO and salt led to a lower onset doping ratio for formation of ordered structure (r0). At higher doping ratios the salt interacted with PCL as well. When the metal ion exhibited a highly selective interaction toward PEO, a more ordered structure with a higher order–order transition temperature (TODT) tended to be formed. The anion in the salt also affected the interactions of PEO/salt and PCL/salt. Weaker Lewis basicity of the anion would result in a stronger interaction of PEO/salt and thus a lower r0. The results showed that the microphase separation behavior of the PCL-b-PEO/salt hybrids was sensitive to the competitive interactions of the salt with the PCL and PEO blocks

Regulation of Crystallization Kinetics, Morphology, and Mechanical Properties of Olefinic Blocky Copolymers

Two olefinic blocky copolymers (OBCs) were quenched from different mixing states in the melt, and crystallization kinetics and morphology at various crystallization temperatures (<i>T</i>_cs) and corresponding mechanical properties were studied. It is observed that, at lower <i>T</i>_cs, premesophase separation in the melt accelerates crystallization of OBC-A with a weak segregation strength and a larger fraction of the crystalline hard blocks due to enrichment of the hard blocks in the hard-block-rich domains. By contrast, premesophase separation retards crystallization of OBC-B with a stronger segregation strength and lower fraction of the hard blocks because of the prevailing confinement effect at lower <i>T</i>_cs. Moreover, since the hard blocks dissolved in the soft-block-rich domains can crystallize at lower <i>T</i>_cs, which can bridge the crystals formed in different hard-block-rich domains, the crystal growth is not restricted. At higher <i>T</i>_cs, OBC-A crystallizes more slowly from the premesophase-separated melt than that from the homogeneous melt, which is attributed to the weaker crystallizability of the hard blocks dissolved in the soft-block-rich domains and thus the restricted crystal growth. Nevertheless, mesophase separation always takes place prior to crystallization at higher <i>T</i>_cs for OBC-B because of the faster rate of mesophase separation. Therefore, the mixing state in the melt has little effect on crystallization and morphology of OBC-B at higher <i>T</i>_cs. It is found that the mechanical properties of OBCs can be regulated in a wide range by alteration of crystallization conditions. Better mechanical properties can be achieved when OBCs crystallize from the homogeneous melt and at a lower <i>T</i>_c

Competition of Crystalline and Liquid Crystalline Moieties in Self-Assembly of Poly(oxyethylene) Cholesterol Ethers

Self-assembly of a series of poly(oxyethylene) (POE) cholesterol ethers (ChEOn, n = 5, 10, 15, 20, 24, 30, and 45) bearing both liquid crystalline (LC) and crystalline moieties was studied by differential scanning calorimetry, wide-angle X-ray diffraction, Raman spectrometry, and small-angle X-ray scattering. In ChEO5 where POE is amorphous, the LC moiety was found to be dominant in determining morphology, and the repeating lamellar structure of ChEO5 is composed of double layers of cholesterol and a single layer of amorphous POE. In ChEO10 and ChEO15, LC and crystalline phases coexist and polymorphism is observed. The repeating lamellar structures of ChEO10 and ChEO15 are similar to that of ChEO5, except for the crystalline helical conformation of POE. With further increase in the chain length of POE, the crystalline POE becomes dominant in determining morphology, and the LC phase is not detected. The crystalline conformation of POE induces LC moieties to pack more closely, and the two LC layers gradually merge into a single LC layer in the repeating lamellar structure. Nonisothermal and isothermal crystallization experiments show that the preexisting LC phase can nucleate and accelerate POE crystallization, whereas the dimension of crystal growth of POE is reduced

Straight and Rod-like Core–Sheath Crystals of Solution-Crystallized Poly(ε-caprolactone)/Multiwalled Carbon Nanotube Nanocomposites

The crystal morphology of poly­(ε-caprolactone)/multiwalled carbon nanotube (PCL/MWCNT) blends and MWCNT-<i>g</i>-PCL grafting polymers crystallized in <i>n</i>-hexanol was investigated. Two typical morphologies are observed: a straight and rod-like core–sheath structure with embedded MWCNTs as the core and PCL polycrystals of high crystallinity as the sheath, and a bent double-layer structure with MWCNTs covered by a PCL layer of low crystallinity. It is found that thinner (outer diameter <15 nm) and shorter (length <2 μm) MWCNTs are easier to be straightened by PCL crystals, and the grafted PCL chains have weaker crystallizability due to structural confinement and thus a weaker ability of straightening MWCNTs. Electron diffraction and high-resolution transmission electron microscopy reveal that the PCL crystals are randomly orientated with the <i>b</i>-axis perpendicular to the MWCNT surface. The growth direction of the PCL crystals is not perpendicular to the axis of MWCNT, possibly due to the nucleation effect of the preadsorbed PCL chains in the solution, which helically wrap MWCNTs. This leads to wrapping and straightening of MWCNTs by rigid PCL crystals

Effect of Substrate Surface on Dewetting Behavior and Chain Orientation of Semicrystalline Block Copolymer Thin Films

Three symmetrical semicrystalline oxyethylene/oxybutylene block copolymers (EmBn) were spin-coated on different substrates including silicon, hydrophobically modified silicon, and mica. The effects of surface property on the dewetting behavior of EmBn thin films and the chain orientation of the crystalline block were investigated with atomic force microscopy and grazing incidence X-ray diffraction . The EmBn thin films on silicon exhibit an autophobic dewetting behavior, while ordinary dewetting occurs for the thin films on modified silicon. It was observed that the stems of the E crystals in the first half-polymer layer contacting the mica surface were parallel to the surface, in contrast to the perpendicular chain orientation of the other polymer layers and of the first half-polymer layer on silicon. This is attributed to the strong interaction between the E block and mica, verified by infrared spectra