Synthesis and micelle behavior of (PNIPAm-PtBA-PNIPAm)m amphiphilic multiblock copolymer

A linear amphiphilic multiblock copolymer (PNIPAm-PtBA-PNIPAm)_m was successfully synthesized by a two-step reversible addition-fragmentation transfer (RAFT) polymerization in the presence of a cyclic trithiocarbonate as RAFT agent. The micelle behavior of (PNIPAm-PtBA-PNIPAm)_m multiblock copolymer in aqueous solution was then investigated by means of normal TEM, cryo-TEM, static and dynamic light scattering. The morphology, size, and size distribution of (PNIPAm-PtBA-PNIPAm)_m micelles were found to be dependent on the initial concentration of multiblock copolymer in THF. Spherical micelles, associated aggregates of spherical micelles, cage-like micelles, layered structures, and vesicular micelles were experimentally observed, which were in good agreement with the prediction of theory and simulations on linear amphiphilic multiblock copolymer in selective solvent. The (PNIPAm-PtBA-PNIPAm)_m micelles also exhibit thermo-sensitive behavior in aqueous solution because of the PNIPAm blocks.     

Effects of block length and solution-casting conditions on the final morphology and properties of disulfonated poly(arylene ether sulfone) multiblock copolymer films for proton exchange membranes

The effects of block length and solution-casting conditions on the final microstructures and properties of disulfonated poly(arylene ether sulfone) multiblock copolymer (BPSH100-BPS0) films for proton exchange membranes were investigated based on the basic principles of microstructure formation of block copolymers. Morphological studies using transmission electron microscopy and small angle X-ray scattering demonstrated that as the block length increased, the inter-ionic-domain distance increased, with a subsequent increase in lamellar ordering and long-range continuity. Further enhancement in morphological order was achieved by simply utilizing a selective solvent, dimethylacetamide, which is good and marginal for the sulfonated and unsulfonated blocks, respectively, rather than a neutral solvent, N-metyl-2-pyrrolidone. These morphological enhancements led to higher proton conductivity and water uptake. Drying temperature and/or solvent removal rate were observed to have considerable effects on water uptake and swelling behavior, being coupled with solvent selectivity. Also, the multiblock copolymer consisting of longer blocks was found to be more sensitive to the variation of the processing conditions such as solvent type and film drying temperature.     

Concentric lamella structures of symmetric diblock copolymers confined in cylindrical nanopores

We applied a real-space self-consistent field theory to investigate the concentric lamella structures of symmetric diblock copolymers confined in the cylindrical nanopores with the preferential surfaces. The symmetric diblock copolymers are selected to locate in the very weak and strong segregation regions where the lamellae obviously exhibit the “soft” and “rigid” characteristics, respectively. For the soft lamellae, the cylindrical confinement induces the soft concentric lamella structure with the same thickness as the bulk lamellar period, except that the thickness of the innermost layer depends on the confinement degree. For the rigid lamellae, the cylindrical confinement not only induces the rigid concentric lamella structure having the linear dependence on the confinement degree, but also results in several novel morphologies, such as the connective concentric lamella and the broken concentric lamella structures. The results are quantitatively discussed in a wide range of confinement degree and can be reasonably understood based on symmetry breaking and structural frustration. In addition, our results are quantitatively compared to the available observations from the simulations and experiments, which are in good agreements and may be helpful to experimentally fabricate the ordered nanostructures on the large scale.     

Morphology and thermomechanical properties of main-chain polybenzoxazine-block-polydimethylsiloxane multiblock copolymers

The main-chain polybenzoxazine-block-polydimethylsiloxane multiblock copolymers were synthesized via the Mannich polycondensation among 4,4′-dihydroxyldiphenylisopropane, 4,4′-diaminodiphenylmethane, aminopropyl-terminated polydimethylsiloxane and paraformaldehyde. The multiblock copolymers were characterized by means of Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and size exclusion chromatography (SEC). Atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS) showed that the multiblock copolymers displayed microphase-separated morphology. Owing to the presence of the main-chain polybenzoxazine blocks, the multiblock copolymers are thermally-crosslinkable. The curing behavior of the multiblock copolymers was investigated according to the analysis of non-isothermal curing kinetics. The measurement of static contact angles showed that with the inclusion of polydimethylsiloxane blocks, the polybenzoxazine thermosets resulting from the multiblock copolymers displayed the improved surface hydrophobicity.     

Micromechanical simulation of molecular architecture and orientation effect on deformation and fracture of multiblock copolymers

Multiblock copolymers containing a large number of blocks have distinct microstructures and mechanical responses that are different from that of conventional diblock and triblock copolymers. A combined simulation method that utilized MesoDyn for morphologies and probabilistic lattice spring model (LSM) for mechanical properties was adopted in this work. Simulation results show that tensile strength increases dramatically with an increase in the number of blocks within “hard-soft” multiblock copolymers. This phenomenon can be described by the occurrence of bridging and looping chain conformations in experiment. One-dimensional lamellae were built to provide an ideal morphology for studying the influence of lamellar orientation on multiblock copolymer mechanical properties. During tensile tests different failure processes were observed with two kinds of interface strength that corresponded to a difference in chain structures (diblock, triblock or multiblock copolymers). These studies provide an efficient method for correlating the complex morphologies to the mechanical response of multiblock copolymers.     

Effect of molecular architecture of copolymer template on the morphology of mesoporous methylsilsesquioxane

Hybrid and mesoporous materials derived from methylsilsesquixoane (MSSQ) have been prepared by the evaporation-induced self-assembly (EISA) process using polystyrene-poly(2-vinyl pyridine) (PS-P2VP) block copolymers with linear (LA) and hetero-arm star (HA) molecular architectures as the templates. TEM and SAXS were used to characterize the morphology of the hybrid materials, LA/MSSQ (LB) and HA/MSSQ (HB), and their corresponding porous materials, LP and HP, obtained by pyrolysis. TEM images suggested that the morphology transformed from random spheres in LB hybrid to cylinders in the corresponding LP porous material. However, the sphere morphology was effectively preserved after the pyrolysis of HB. We proposed that MSSQ initially solubilized into the P2VP coronas of the copolymer micelles tended to be excluded from the coronal regions during the extensive curing of MSSQ on heating to the calcination temperature. This dewetting process competed against the crosslinking of MSSQ that could freeze the structure if the network formed readily prior to the abundant exclusion of MSSQ. In the hetero-arm system where several pairs of copolymer chains jointed to a common core, the exclusion of the MSSQ out of the corona regions became more restricted. Consequently, the initial micelle morphology was effectively fixed by the crosslinking reaction. The present study demonstrated that the molecular architecture of the structure-directing agent played an important role in the morphological formation of the MSSQ-based mesoporous materials.     

Synthesis of well-defined poly(styrene)-b-poly(p-tert-butoxystyrene) multiblock copolymer from poly(alkoxyamine) macroinitiator

The stepwise insertion reaction of styrene (St) and p-tert-butoxystyrene (BOSt) into poly(alkoxyamine) macroinitiator was carried out to provide well-defined poly(St)-b-poly(BOSt) multiblock copolymers. Structural confirmation of the multiblock copolymers was accomplished by NMR and IR measurements. The model reaction also supported that the monomer insertion into the macroinitiator proceeded in accordance with a living fashion.     

Structure and dynamics of a pentablock copolymer of polystyrene-polybutadiene in a butadiene-selective solvent

We have examined solutions of a polystyrene-polybutadiene pentablock copolymer in n-heptane, a strongly selective solvent for polybutadiene. Small angle neutron scattering from 7 to 15% samples reveals domains about 10 nm in radius formed by the association of 200 polystyrene blocks. Dynamic light scattering measurements on 8 and 9% samples showed three modes: a fast diffusive mode related to the collective diffusion in semidilute solutions/gels; a relaxational mode related to the local dynamics of polystyrene domains trapped in the gel formed by bridging the domains with the polybutadiene chains; and a very slow diffusive mode. The relaxational dynamics persisted over the entire temperature range, becoming faster with increasing temperature, indicating a decreased microviscosity at higher temperatures. The slow dynamics seems to be connected with heterogeneities in the physical gel due to microsyneresis and almost disappeared above 50 °C. Macroscopic phase separation into two liquid phases was observed in a dilute solution of the un-associated copolymer, and into a liquid and gel phase at higher concentrations. The absence of flower-like micelles in dilute solutions and the macroscopic phase seperation suggest that the gels in the pentablock are formed by random association of multiplet domains and not by bridging of micellar domains.     

Synthesis and applications of triblock and multiblock copolymers using telechelic oligopropylene

Isotactic polypropylene (iPP)-polystyrene (PS) and iPP-poly(methyl methacrylate) (PMMA) multiblock copolymers were synthesized by atom transfer radical coupling (ATRC) of PS-iPP-PS and PMMA-iPP-PMMA triblock copolymers obtained by atom transfer radical polymerization (ATRP) of styrene (St) and methyl methacrylate (MMA), respectively, using α,ω-dibromoisobutyrateoligopropylene (iPP-Br) as a bifunctional macroinitiator. The iPP-Br was prepared by hydroxylation and subsequent esterification of telechelic oligopropylene having terminal vinylidene double bonds at both ends obtained by controlled thermal degradation of iPP. ATRP of St and (meth) acrylic monomers using iPP-Br formed the corresponding triblock copolymers. It was confirmed that the PMMA-iPP-PMMA triblock copolymer was effective as the compatibilizer for the iPP/PMMA blend. An iPP-PS multiblock copolymer (M_n: 25?000 g/mol and M_w/M_n: 4.1) was prepared by ATRC of PS-iPP-PS triblock copolymer (M_n: 8900 g/mol and M_w/M_n: 1.3). ATRC with St of PMMA-iPP-PMMA triblock copolymer (M_n: 13?000 g/mol and M_w/M_n: 1.4) provided an iPP-PMMA multiblock copolymer containing St chains (M_n: 39?000 g/mol and M_w/M_n: 2.8).     

Ordering and microdomain orientation in block copolymer films by thermal deprotection

Ordering and microdomain orientation for the films of symmetric polystyrene-b-poly(tert-butyl methacrylate)s (PS-b-PtBMAs) was investigated by in-situ grazing incidence small-angle X-ray scattering (GISAXS) and the electron microscopy. During thermal deprotection at higher temperature (200 °C), functional tert-butyl ester units in the PtBMA block component are integrated into inter- or intra-molecular anhydride linkages. It was observed that this process causes an increase in the Flory-Huggins interaction parameter (χ) between the two block components for disordered PS-b-PtBMA film, leading to a modulated nonequilibrium structure. Interestingly, for lamella-forming PS-b-PtBMA film, a significant chain stretching in lateral direction during thermal deprotection resulted in a characteristic strain-induced perpendicular orientation in the middle of the film confined between two parallel orientations of lamellar microdomains.     

Synthesis of (ABCB)n type ternary amphiphilic multiblock copolymer via poly(ethylene oxide) macro-chain transfer agent

A novel (ABCB)_n type ternary amphiphilic multiblock copolymer was synthesized by stepwise insertion of monomers into the trithiocarbonate-embedded poly(ethylene oxide) (PEO) macro-chain transfer agent (PEO-CTA)_n. (PEO-CTA)_n was synthesized first by coupling of α,ω-dihydroxyl PEO with dicarboxylic trithiocarbonate, then styrene (St) and t-butyl acrylate (^tBA) were inserted into the (PEO-CTA)_n successively to yield (PEO-b-PS)_n and (PEO-b-PS-b-P^tBA-b-PS)_n, respectively. After hydrolysis of the (PEO-b-PS-b-P^tBA-b-PS)_n, the final product (PEO-b-PS-b-PAA-b-PS)_n was obtained.     

Dynamic study of polystyrene-block-poly(4-vinylpyridine) copolymer in bulk and confined in cylindrical nanopores

AAO template is highly recommended to nanostructure polymers and to study polymer properties under confinement. The dynamic properties of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) under confinement using broadband dielectric spectroscopy are investigated in this work and the results compared to those of the bulk. Anodized aluminum oxide (AAO) membranes, having pore diameters from tens to hundreds of nanometers in size, were used to confine PS-b-P4VP. Moreover, the influence of gold nanoparticles (AuNPs) in the copolymer matrix was also studied. The morphology and structure of the bulk copolymer and the copolymer confined in the AAO templates were characterized by transmission electron microscopy, scanning electron microscopy and Small Angle X-Ray Scattering. For PS-b-P4VP in bulk, dielectric relaxation techniques allowed studying selectively the P4VP segmental dynamics within the diblock. At high temperature this copolymer presents a dominant peak (MWS relaxation), most likely originated by the relatively high conductivity combined with the presence of interfaces emerging in the nanostructured samples. Moreover, a pronounced β-relaxation is observed for the copolymer compared with that of pure P4VP. This is likely due to a non-negligible contribution from the α-relaxation of the PS component. The γ-relaxation is markedly different in the copolymer, which is evidenced by a distinct temperature dependence of the resulting relaxation times. When the copolymer is embedded in alumina nanopores with small pore diameters (25 and 35 nm) there are significant changes, where the tendency is going to a faster dynamics when the pore diameter decreases more likely related to the relevance of surface effects. The presence of the AuNPs in the system enhances this effect. These results are in agreement with segregated structures found in the block copolymer by TEM and SAXS.     

Measurement of molecular orientation in thermotropic liquid crystalline polymers

Procedures for obtaining molecular orientational parameters from wide angle X-ray scattering patterns of samples of thermotropic liquid crystalline polymers are presented. The methods described are applied to an extrusion-aligned sample of a random copolyester of poly(ethylene terephthalate) (PET) and p-acetoxybenzoic acid. Values of the orientational parameters are obtained from both the interchain and intrachain maxima in the scattering pattern. The differences in the values so derived suggest some level of local rotational correlation     

丙烯酸高级酯共聚物组成与其无皂乳液稳定性研究

制备了不同分子结构的丙烯酸高级酯共聚物无皂乳液,测定了丙烯酸和甲基丙烯酸十六酯的竟聚率,考察了共聚物的组成对无皂乳液电解质稳定性、机械稳定性和pH值稳定性的影响。结果显示,丙烯酸竟聚率为2.32,甲基丙烯酸十六酯竟聚率为0.59,随共聚物中丙烯酸组分含量增加,乳液粒子表面羧基含量增大,乳液机械稳定性和pH值稳定性提高,乳液适合在偏碱性条件下使用。     

The determination of molecular orientation in uniaxially compressed PMMA by X-ray scattering

A procedure is presented for obtaining full molecular orientation information from wide angle X-ray scattering patterns of deformed non-crystalline polymers. The method is based on the analysis of experimental and calculated scattering patterns into their spherical harmonics. The results obtained for PMMA are compared with values predicted by the pseudo affine and affine deformation schemes.     

Spatial distribution of molecular orientation in injection molded iPP: influence of processing conditions

In this paper, the influence of processing conditions on the spatial distribution of the molecular orientation was determined within the depth of the thickness of injection molded isotactic polypropylene (iPP) plates. Small 35 μm-thick slices were microtomed from the surface to the core of 1 and 3 mm-thick plates. The orientation functions along the three crystallographic axes were determined on the slices from IR dichroism measurements and WAXS pole figures. It was found that the orientation of the amorphous phase was low and the crystalline orientation had a maximum in the shearing layer, which was solidified during the filling stage. The plate thickness seemed to govern the global level of orientation, while the injection speed determined the thickness of the shearing layer without changing the maximum of orientation. Changing the mold temperature from 20 to 40 °C did not modify the molecular orientation. A specific bimodal crystalline orientation was found in the shearing layer. This crystalline structure continued in the post-filling layer, but the local symmetry axes tilted towards the core.     

Anisotropy of the modulus of elasticity in regenerated cellulose fibres related to molecular orientation

Regenerated cellulose fibres of different origin were tested in tension and by means of nanoindentation. Their degree of molecular orientation was characterised with birefringence measurements. An empirical relationship was set up between the degree of orientation expressed by birefringence and the modulus of elasticity parallel to the fibre direction, and the ratio between this modulus and the modulus transverse to the fibre direction, respectively.     

One step fabrication and characterization of platinum nanopore electrode ensembles formed via amphiphilic block copolymer self-assembly

A novel one-step approach to Pt nanopore electrode ensembles (NEEs) has been developed using an amphiphilic block copolymer [polystyrene-block-poly (acrylic acid)] self-assembly. This procedure is simple and fast, and requires only conventional, inexpensive electrochemical instrumentation. Electrochemical methods are used to characterize the Pt nanopore electrode ensembles prepared using this new procedure. And the capacitance and voltammetric characteristics for the NEEs have been examined. At lower scan rates, it remains the features of a single nanoelectrode, while at high scan rates the nanoelectrodes act independently. This is an important feature for vivo sensing and other electroanalytical applications.     

Correlation between crystallization kinetics and melt phase behavior of crystalline-amorphous block copolymer/homopolymer blends

We show that the phase behavior of the strongly segregated blend consisting of a crystalline-amorphous diblock copolymer (C-b-A) and an amorphous homopolymer (h-A), which depends on the degree of wetting of A blocks by h-A, can be probed by the crystallization kinetics of the C block. A lamellae-forming poly(ethylene oxide)-block-polybutadiene (PEO-b-PB) was blended with PB homopolymers (h-PB) of different molecular weights to yield the blends exhibiting ‘wet brush’, ‘partially dry brush’, and ‘dry brush’ phase behavior in the melt state. The crystallization rate of the PEO blocks upon subsequent cooling, as manifested by the freezing (crystallization) temperature (T_f), was highly sensitive to the morphology and spatial connectivity of the microdomains governed by the degree of wetting of PB blocks. As the weight fraction of h-PB reached 0.48, for instance, T_f experienced an abrupt rise as the system entered from the wet-brush to the dry-brush regime, because the crystallization in the PEO cylindrical domains in the former required very large undercooling due to a homogeneous nucleation-controlled mechanism while the process could occur at the normal undercooling in the latter since PEO domains retained lamellar identity with extended spatial connectivity. Our results demonstrate that as long as the C block is present as the minor constituent the melt phase behavior of C-b-A/h-A blends can also be probed using a simple cooling experiment operated under differential scanning calorimetry (DSC).     

Morphologies of diblock copolymer confined in a slit with patterned surfaces studied by dissipative particle dynamics

Diblock copolymers with ordered mesophase structures have been used as templates for nano-fabrication. Unfortunately, the ordered structure only exists at micromete rscale areas, which precludes its use in many advanced applications. To overcome this disadvantage, the diblock copolymer confined in a restricted system with a patterned surface is proved to be an effective means to prohibit the formation of defects and obtain perfect ordered domains. In this work, the morphologies of a thin film of diblock copolymer confined between patterned and neutral surfaces were studied by dissipative particle dynamics. It is shown that the morphology of the symmetric diblock copolymer is affected by the ratio of the pattern period on the surface to the lamellar period of the symmetric diblock copolymer and by the repulsion parameters between blocks and wall particles. To eliminate the defects in the lamellar phase, the pattern period on the surface must match the lamellar period. The difference in the interface energy of different compartments of the pattern should increase with increasing film thickness. The pattern period on the surface has a scaling relationship with the chain length, which is the same as that between the lamellar period and the chain length. The lamellar period is also affected by the polydispersity of the symmetric diblock copolymer. The total period is the average of the period of each component multiplied by the weight of its volume ratio. The morphologies of asymmetric diblock copolymers are also affected by the pattern on the surface, especially when the matching period of the asymmetric diblock copolymer is equal to the pattern period, which is approximately equal to the lamellar period of a symmetric diblock copolymer with the same chain length.