Investigation by combined solid-state NMR and SAXS methods of the morphology and domain size in polystyrene- b- polyethylene oxide- b- polystyrene triblock copolymers (original) (raw)
Related papers
European Polymer Journal, 2004
In this work, the behavior of the crystallizable blocks within polystyrene-b-poly(ethylene oxide)-b-poly(e-caprolactone) linear triblock copolymers is studied. The apparent crystallization and melting temperatures of PEO and PCL can be coincident as a result of their close values, their dependence on the molecular weight of the blocks and on the relative amount of each component within the copolymers. When the content of both PEO and PCL is low, typically 20% or less, both blocks crystallized coincidentally upon cooling from the melt at very large supercoolings (T c ¼ À40°C), suggesting that homogeneous nucleation has taken place. A S 63 EO 16 C 20 copolymer (where subscripts denote the weight fraction of the components) exhibited a small angle X-ray scattering (SAXS) pattern at room temperature that suggests a cylindrical morphology for the minor components, where the crystallization of PEO and PCL blocks can take place subsequently near)40°C in a hard confinement fashion within the vitreous PS matrix. We have employed differential scanning calorimetry (DSC) to study the self-nucleation process and the results indicate that the difficulty in generating enough self-seeds to nucleate every isolated microdomain causes the disappearance of Domain II (or exclusive self-nucleation Domain) and therefore a direct transition from complete melting (Domain I) to self-nucleation and annealing (Domain III) is observed. When the content of both PEO and PCL blocks is larger than 35%, a coincident crystallization can be observed as well as coincident melting. For a S 15 EO 37 C 48 triblock copolymer, PS is a minor phase and mixed spherulites composed of both PCL and PEO blocks were observed by Polarized Optical Microscope (POM) at appropriate supercoolings. In this case, the self-nucleation behavior is standard, and through its use the crystallization and melting process of both blocks can be separated. Wide angle X-ray scattering (WAXS) at different temperatures was used to corroborate the sequential melting of both semicrystalline blocks deduced by self-nucleation. Isothermal crystallizations were also followed by WAXS as a function of time and the results showed that depending on the crystallization temperature (T c), only the PCL block crystallizes (at high T c), or the PCL block crystallizes first followed by the PEO at later times (at lower T c).
Microphase-separated tapered triblock copolymers
Le Journal de Physique IV, 1993
The microphase-separated morphologies of a series of four poly[styrene-b-(d-styrene-gradisoprene)-b-isoprene] tapered block copolymers have been explored in this work with smallangle neutron scattering (SANS) and transmission electron microscopy (TEM). Each of the copolymers consists of two pure end blocks and a selectively deuterated statistical middle block, across which exists a composition gradient. The middle-block fraction varies from 10 to 40 wt% in this series. All four materials are found to exhibit ordered lamellar morphologies, in which the microdomain periodicities do not differ significantly from that of the corresponding poly(styrene-b-isoprene) diblock copolymer of equal molecular weight (M=200 kDa). These results are compared with predictions from recent theoretical developments. In contrast, a 100 kDa poly[styrene-b-(styrene-ran-isoprene)-b-isoprene] triblock copolymer, possessing a 40 wt% statistical (random) middle block with an average composition of 50 wt% styrene, is observed to order into a lamellar-spherical three-microphase morphology upon block segregation.
Journal of Colloid and Interface Science, 2006
1 H and 13 C nuclear magnetic resonance (NMR) spectra of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers in D 2 O solutions have been systematically investigated. The detailed assignments of various 1 H and 13 C NMR signals are presented. The hyperfine structure of PO-CH 2-protons was clearly assigned, the arising reason of this hyperfine structure was attributed to the influence of the chiral center of-CHCH 3-groups and the direct coupling between the PO-CH 2-and-CH 3 protons. The external standard 2,2-dimethyl-2-silapentane-5-sulfonate sodium salt (DSS) was firstly applied in this system. Accurate chemical shift values referenced to the external standard DSS were obtained. 1 H NMR chemical shift of PO-CH 2-and-CH 3 signals shows a larger decrease in ppm values than that of EO-CH 2-signal with the increase of PPO/PEO ratio or temperature indicating that PO segments exist in a more hydrophobic microenvironment. A new resonance signal assigned to the PO-CH 2-protons appeared when the temperature is above the CMT, which is attributed to the breakdown of the intra-molecular (C-H)• • •O hydrogen bond between the PO-CH 2-protons and the ester oxygens. The breakdown of this intra-molecular hydrogen bond may result in a decrease of gauche conformers of the PPO chain. The increase of 13 C NMR chemical shift of block copolymers validates this conformational change assumption. It can be inferred that the amount of gauche conformers decreases whereas that of trans conformers increases in both PO and EO chains when elevating the PPO/PEO ratio or temperature. The observed 13 C NMR chemical shifts of PO segments show a bigger increase than those of EO segments, supporting the formation of a nonpolar microenvironment around PO segments.
An intriguing morphology in crystallizable block copolymers
Macromolecules, 1993
The complex and important structures formed by assembly of amphiphilic molecules result from a delicate balance between competing intermolecular forces. In the simplest example, soap molecules surround and divide oil droplets in water. In biological systems the intricate function of selective membranes and cellular structures is determined by such forces. The variety of phases formed by polar lipids are notable for their sensitivity to the intermolecular forces dictating their In polymeric systems, the length of the chain molecules exacerbates this balance of forces, often producing new and unique top~logies.~ While the influence of crystallization of one of the components has been known for some time,5 we have discovered that the unique interplay between hydration and ordering can produce new morphologies, namely, cylindrical structures coexisting with spheres and lamellae. These new structures provide a visual display of the intricate balance between ordering and curvature in self-assembling polymers.
Microphase Separation in Poly(oxyethylene)−Poly(oxybutylene) Diblock Copolymers
Macromolecules, 1998
Twenty-six poly(oxyethylene)-poly(oxybutylene) diblock copolymers were prepared by anionic polymerization. The phase behavior of these copolymers was studied near the order-disorder transition over the composition range from 0.21 to 0.84 poly(oxyethylene) volume fraction. Small-angle X-ray scattering was used to characterize phase transition temperatures and ordered state symmetries. Four distinct microstructures were observed: body-centered cubic, hexagonally packed cylinders (hex), lamellae (lam), and a bicontinuous cubic phase with Ia3 hd symmetry, together with a less well-defined region of the phase diagram comprising either hexagonally perforated layers or biphasic hex and lam. The Flory-Huggins parameter as a function of temperature was estimated using both the mean-field approximation and a fluctuation correction to the mean-field theory. The experimental microphase behavior is compared with the exact mean-field phase diagram calculated using self-consistent-field theory.
PEO-PPO-PEO triblock copolymer in aqueous solution. Micelle formation and crystallization
Le Journal de Physique IV, 1993
The phase behavior of poly(ethy1ene oxide) -poly(propy1ene oxide)poly(ethy1ene oxide), PEO-PPO-PEO, tri-block copolymers dissolved in water has been studied using small-angle neutron scattering, using a Couette device for shear alignments. The structural properties has been studied as a function of polymer concentration and temperature. At low-temperature and low polymer concentrations the unimers are dissolved as individual Gaussian chains. At temperatures close to ambient, the hydrophobic nature of PPO causes aggregation of the polymers into spherical micelles. The aggregation number is relative small close to the critical micellation temperature, and increases markedly with temperature. The micellar volume fraction increases roughly linearly with temperature, until either a saturation is reached, where all polymers are part of a micelle, or the volume fraction reaches the critical value for hard-sphere crystallization. At higher temperatures the aggregates transform from spherical form to rod-like micelles, causing first melting of the cubic structure, and subsequently crystallization into a phase of hexagonally ordered rods.
Chinese Journal of Polymer Science, 2019
Amphiphilic diblock copolymers self-assemble into a variety of micellar structures with diverse shapes in selective solvents. Here, we study the concentration and temperature dependence of the packing structure of spherical micelles of a polyisoprene-b-poly(2vinylpyridine) (PI-b-P2VP) diblock copolymer in toluene using synchrotron radiation small angle X-ray scattering (SR-SAXS) and atomic force microscopy (AFM) techniques. Randomly packed spherical micelles are detected in dilute solutions, while in concentrated solutions, face-centered cubic (FCC), body-centered cubic (BCC) mixed crystal structures, and pure BCC crystal structures are observed with an increase in concentration. In situ SAXS experiments on the FCC/BCC mixed crystal structures reveal a novel FCC/BCC → BCC → Disorder → BCC phase behavior during the thermal annealing process. These results demonstrated that the BCC phase is apparently more stable than the FCC phase in the current sphere-packing system and FCC/BCC is a metastable state. The incompatibility of the PI and P2VP blocks decreases at a higher temperature and renders the variation of domain spacing.
The existence of a tetragonal structure in block copolymers
Polymer
The morphology of AB and BAB block copolymers consisting of one amorphous block (A) and liquid crystalline blocks (B) has been investigated using TEM, low angle electron diffraction and small angle X-ray diffraction. All samples of poly [styrene-block-2-(3-cholsteryl-oxycarbonyloxy)ethyl methacrylate] (PS-PChEMA) with a volume fraction OPS between 0.3 and 0.4 show a morphology consisting of PS rods in a PChEMA matrix. The rods are organized in a tetragonal lattice rather than the expected hexagonal structure.