Morphologies in solvent-annealed thin films of symmetric diblock copolymer

We have systematically studied the thin film morphologies of symmetric poly(styrene)-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer after annealing to solvents with varying selectivity. Upon neutral solvent vapor annealing, terraced morphology is observed without any lateral structures on the surfaces. When using PS-selective solvent annealing, the film exhibits macroscopically flat with a disordered micellar structure. While PMMA-selective solvent annealing leads to the dewetting of the film with fractal-like holes, with highly ordered nanoscale depressions in the region of undewetted films. In addition, when decreasing the swelling degree of the film in the case of PMMA-selective solvent annealing, hills and valleys are observed with the coexistence of highly ordered nanoscale spheres and stripes on the surface, in contrast to the case of higher swelling degree. The differences are explained qualitatively on the basis of polymer-solvent interaction parameters of the different components.

Ring-opening polymerization and block copolymerization of L-lactide with divalent samarocene complex

Divalent samarocene complex [(C5H9C5H4)(2)Sm(tetrahydrofuran)(2)] was prepared and characterized and used to catalyze the ring-opening polymerization of L-lactide (L-LA) and copolymerization of L-LA with caprolactone (CL). Several factors affecting monomer conversion and molecular weight of polymer, such as polymerization time, temperature, monomer/catalyst ratio, and solvent, were examined. The results indicated that polymerization was rapid, with monomer conversions reaching 100% within 1 h, and the conformation of L-LA was retained. The structure of the block copolymer of CL/L-LA was characterized by NMR and differential scanning calorimetry. The morphological changes during crystallization of poly(caprolactone) (PCL)-b-P(L-LA) copolymer were monitored with real-time hot-stage atomic force microscopy (AFM). The effect of temperature on the morphological change and crystallization behavior of PCL-b-P(L-LA) copolymer was demonstrated through AFM observation.

Self-assembly of star block copolymers by dynamic density functional theory

The dynamic mean-field density functional method, driven from the generalized time-dependent Ginzburg-Landau equation, was applied to the mesoscopic dynamics of the multi-arms star block copolymer melts in two-dimensional lattice model. The implicit Gaussian density functional expression of a multi-arms star block copolymer chain for the intrinsic chemical potentials was constructed for the first time. Extension of this calculation strategy to more complex systems, such as hyperbranched copolymer or dendrimer, should be straightforward. The original application of this method to 3-arms block copolymer melts in our present works led to some novel ordered microphase patterns, such as hexagonal (HEX) honeycomb lattice, core-shell HEX lattice, knitting pattern, etc. The observed core-shell HEX lattice ordered structure is qualitatively in agreement with the experiment of Thomas [Macromolecules 31, 5272 (1998)].

Preparation and characterization of PSt-b-PHEMA metal hybrids

The block copolymer polystyrene-b-poly[2-(trimethylsilyloxy)ethylene methacrylate] (PSt-b-PTMSEMA) was synthesized using atom-transfer radical polymerization (ATRP). The hydrolysis of PSt-b-PTMSEMA led to the formation of an amphiphilic block copolymer, polystyrene-b-poly(2-hydroxylethyl methacrylate) (PSt-b-PHEMA), which was characterized by GPC and H-1-NMR. TEM showed that the PSt-b-PHEMA formed a micelle, which is PSt as the core and PHEMA as the shell. Under appropriate conditions, the nickel or cobalt ion cause chemical reactions in these micelles and could be reduced easily. ESCA analysis showed that before reduction the metal existed as a hydroxide; after reduction, the metal existed as an oxide, and the metal content of these materials on the surface is more than that on the surface of the copolymer metal ion. XRD analysis showed that the metal existed as a hydroxide before reduction and existed as a metal after reduction.

Observation of inverted phases in poly(styrene-b-butadiene-b-styrene) triblock copolymer by solvent-induced order-disorder phase transition

We report observation of inverted phases consisting of spheres and/or cylinders of the majority fraction block in a poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer by solvent-induced order-disorder phase transition (ODT). The SBS sample has a molecular weight of 140K Da and a polystyrene (PS) weight fraction of 30%. Tapping mode atomic force microscopy (AFM) and transmission electron microscopy (TEM) were utilized to study the copolymer microstructure of a set of solution-cast SBS films dried with different solvent evaporation rates, R. The control with different R leads to kinetic frozen-in of microstructures corresponding to a different combination parameter chi (eff)Z of the drying films (where chi (eff) is the effective interaction parameter of the polymer solution in the cast film and Z the number of "blobs" of size equal to the correlation length one block copolymer chain contains), for which faster evaporation rates result in microstructures of smaller chi (eff)Z. As R was decreased from rapid evaporations (similar to0.1 mL/h), the microstructure evolved from a totally disordered one sequentially to inverted phases consisting of spheres and then cylinders of polybutadiene (PB) in a PS matrix and finally reached the equilibrium phase, namely cylinders of PS in a PB matrix. We interpret the formation of inverted phases as due to the increased relative importance of entropy as chi (eff)Z is decreased, which may dominate the energy penalty for having a bigger interfacial area between the immiscible blocks in the inverted phases.

Controlled synthesis of L-lactide-b-epsilon-caprolactone block copolymers using a rare earth complex as catalyst

Well-defined block copolymers of L-lactide-b-epsilon-caprolactone were synthesized by sequential polymerization using a rare earth complex, Y(CF3COO)(3)/Al(iso-Bu)(3), as catalyst system. The compositions of the block copolymers could be adjusted by manipulating the feeding ratio of comonomers. The characterizations by GPC, H-1 NMR, C-13 NMR, and DSC displayed that the block copolymer, poly(epsilon-caprolactone-b-L-lactide) [P(CL-b-LLA)], had a narrow molecular weight distribution and well-controlled sequences without random placement.

Syndiotactic polystyrene/thermoplastic polyurethane blends using poly(styrene-b-4-vinylpyridine) diblock copolymer as a compatibilizer

The effect of adding diblock copolymer poly(styrene-b-4-vinylpyridine) (P(S-b-4VPy), to immiscible blends of syndiotactic polystyrene (sPS)/thermoplastic polyurethane (TPU) on the morphology, thermal transition, crystalline structure, and rheological and mechanical properties of the blends has been investigated. The diblock copolymer was synthesized by sequential anionic copolymerization and was melt-blended with sPS and TPU. Scanning electron microscopy (SEM) showed that the added block copolymer reduced the domain size of the dispersed phase in the blends. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) revealed that the extent of compatibility between sPS and TPU affected the crystallization of the sPS in the blends. Tensile strength and elongation at break increased, while the dynamic modulus and complex viscosity decreased with the amount of P(S-b-4VPy) in the blend. The compatibilizing effect of the diblock copolymer is the result of its location at the interface between the sPS and the TPU phases and penetration of the blocks into the: corresponding phases, i.e. the polystyrene block enters the noncrystalline regions of the sPS, and the poly(4-vinylpyridine) block interacts with TPU through intermolecular hydrogen bonding. (C) 1999 Elsevier Science Ltd. All rights reserved.

Effect and mechanism in compatibilization of poly(styrene-b-2-ethyl-2-oxazoline) diblock copolymer in poly(2,6-dimethyl-1,4-phenylene oxide) poly(ethylene-ran-acrylic acid) blends

The compatibilization effect of poly(styrene-b-2-ethyl-2-oxazoline) diblock copolymer, P(S-b-EOx), on immiscible blends of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and poly(ethylene-co-acrylic acid) (EAA) is examined in terms of phase structure and thermal, rheological and mechanical properties, and its compatibilizing mechanism is investigated by Fourier-transform infrared spectroscopy. The block copolymer, synthesized by a mechanism transformation copolymerization, is used in solution blending of PPO/EAA. Scanning electron micrographs show that the blends exhibit a more regular and finer dispersion on addition of a small amount of P(S-b-EOx). Thermal analysis indicates that the grass transition of PPO and the lower endothermic peal; of EAA components become closer on adding P(S-b-EOx), and the added diblock copolymer is mainly located at the interface between the PPO and EAA phases. The interfacial tension estimated by theological measurement is significantly reduced on addition of a small amount of P(S-b-EOx). The tensile strength and elongation at break increase with the addition of the diblock copolymer for PPO-rich blends, whereas the tensile strength increases but the elongation at break decreases for EAA-rich blends. This effect is interpreted in terms of interfacial activity and the reinforcing effect of the diblock copolymer, and it is concluded that the diblock copolymer plays a role as an effective compatibilizer for PPO/EAA blends. The specific interaction between EAA and polar parts of P(S-b-EOx) is mainly hydrogen bonding. (C) 1998 Elsevier Science Ltd. All rights reserved.

Molecular dynamics simulation of polystyrene-block-poly(methyl methacrylate)

Molecular dynamics is applied to the system of polystyrene-block-poly(methyl methacrylate). The simulation shows that for the block copolymer system, a layered structure, which reflects microphase separation, is obtained and this structure is stable. In order to elucidate that the formation of the layered structure is reasonable, some static properties such as the radial distribution function and the dipole moment are analyzed in some detail.

Poly(vinyl methyl ether) poly(methyl methacrylate) blends using diblock copolymer of styrene and methyl methacrylate as compatibilizer

Blends of poly(vinyl methyl ether) (PVME) and poly(methyl methacrylate) (PMMA) compatibilized by poly(styrene-block-methyl methacrylate) (P(S-b-MMA)) ale studied by FT-IR, DSC, excimer fluorescence spectrometry, and scanning electron microscopy (SEM). In FT-IR measurement the ratio of absorption intensity at 1107 cm(-1) to that at 1085 cm(-1) (I-1107/I-1085) reaches a minimum at about 10wt% block copolymer content. DSC results show that the glass transition temperature of PVME in the blends has a maximum at 10 wt% copolymer content. In plots of the ratio of excimer-to-monomer fluorescence emission intensities (I-E/I-M) VS block copolymer content, I-E/I-M increases rapidly above 10%. Ail these phenomena show that PS block chains penetrate into PVME: domains on addition of block copolymer. Above 10% copolymer content, block copolymer chains tend to form micelles in bulk phase.

Crystallization and intriguing morphologies of compatible mixtures of tetrahydrofuran-methyl methacrylate diblock copolymer with poly(tetrahydrofuran)

The crystallization and unusual crystalline morphologies of compatible mixtures of tetrahydrofuran-methyl methacrylate diblock copolymer with tetrahydrofuran homopolymer were studied. It is shown that the PTHF [poly(tetrahydrofuran)] block of the copolymer cocrystalizes with the PTHF homopolymer in the PTHF microphase of the blend. However, the degree of crystallinity of the PTHF block is always lower than that of the PTHF homopolymer in the PTHF microphase. The crystallizability of the PTHF microphase increases appreciably with increasing PTHF microphase size and PTHF homopolymer weight fraction in the microphase. The morphology study of the blends shows that the crystalline morphology is strongly dependent on blend composition, copolymer composition and PTHF block length, as well as crystallization temperature. When alternating PTHF and PMMA [poly(methyl methacrylate)] lamellae are formed, the macroscopic crystalline morphology could be only observed when the thickness of the PTHF lamellae is large enough (similar to 20 nm). In the blend where PMMA spherical or cylindrical microphases are formed, the crystalline morphology changes dramatically with the change in the PTHF microdomain size and PMMA interdomain distance. Many unusual crystalline morphologies have been observed. A study of the solution-crystallized morphology of the blends at different temperatures shows that the morphology is also strongly dependent on the isothermal crystallization temperature, suggesting that the PMMA microdomains may have different effects on the morphology formation when the blend is crystallized at different rates.

Poly(epsilon-caprolactone)/poly(ethylene oxide) diblock copolymer .1. Isothermal crystallization and melting behavior

The isothermal crystallization and melting behavior of the poly(epsilon-caprolactone) (PCL)/poly(ethylene oxide)(PEO) diblock copolymer has been studied by WAXD, SAXS, and DSC methods. Only the PCL block is crystallizable; the PEO block of weight fraction 20% cannot crystallize, although its corresponding homopolymer has strong crystallizability. The long period, amorphous layer, and crystalline lamella of the PCL/PEO block copolymer all increase with the rise in the crystallization temperature, and the thickness of the amorphous layer is much larger than that of crystalline lamella due to the existence of the PEO block in the amorphous region. The isothermal crystallization of the PCL/PEO block copolymer is investigated by using the theory of Turnbull and Fischer. It is found that the amorphous PEO block has a great influence on the nucleation of PCL block crystallization, and the extent of this influence depends on crystallization conditions, especially temperature. The outstanding characteristics are the phenomenon of the double melting peaks in the melting process of the PCL/PEO block copolymer after isothermal crystallization at different temperatures and the transformation of melting peaks from double peaks to a single peak with variations in the crystallization condition. They are related mainly to the existence of the PEO block bonding chemically with the PCL block. In summing up results of investigations into the crystallization and melting behavior of the PCL/PEO block copolymer, it is interesting to notice that when the PCL/PEO block copolymer crystallizes at three different crystallization temperatures, i.e., below 0 degrees C, between 0 and 35 degrees C, and above 35 degrees C, the variation of peak melting temperature is similar to that of overall crystallization rates in the process of isothermal crystallization. The results can be elucidated by the effect of the PEO block on the crystallization of the PCL block, especially its nucleation. (C) 1996 John Wiley & Sons, Inc.

NMR-STUDY ON THE RELATIONSHIP BETWEEN MISCIBILITY AND ANTIAGING PERFORMANCE OF BLENDS CONTAINING BLOCK-COPOLYMERS

The anti-aging performance of blends of polystyrene (PS), styrene-butadiene triblock copolymers (SBS), and PS/styrene-butadiene (SB)-4A (Carm star SE block copolymer) has been studied by means of C-13 NMR techniques. It is found that the anti-aging performance of these kinds of blends largely depends on their miscibility with PS of different molecular weight M(PS). The larger the quantities of PS solubilized in polybutadiene (PBD) domains, the better the anti-aging performance of the blends. It is also found that the anti-aging performance of these blends has dependence on molecular architectures of the SE block copolymers. For the aged blends, the double bonds of PBD were broken, meanwhile serious cross-linking networks formed in the blends. The proposed anti-aging mechanism is that the PS solubilized in PBD domains can efficiently prevent oxygen molecules from diffusing into PBD domains, therefore, successfully stop the oxidative process of PBD.

COMPATIBILITY AND CRYSTALLIZATION OF TETRAHYDROFURAN-METHYL METHACRYLATE DIBLOCK COPOLYMER/POLYTETRAHYDROFURAN BLENDS

The compatibility and crystallization of tetrahydrofuran-methyl methacrylate diblock copolymer (PTHF-b-PMMA)/tetrahydrofuran homopolymer (PTHF) blends were studied. Our results showed that the crystallization and morphology of compatible PTHF-b-PMMA/PTHF

Crystallization Behavior of Poly(tetrahydrofuran-b-methyl methacrylate) Diblock Copolymer

Crystallization behavior of a series of newly synthesized poly (tetrahydrofuran-b-methyl methacrylate) diblock copolymer has been studied by differential scanning calorimetry (DSC) and X-ray scattering and diffraction techniques. The results show that the