Effect Of Block Copolymer Architecture Research Articles

Exploring the effect of block copolymer architecture and concentration on the microstructure, electrical conductivity and rheological properties of PP/PS blend nanocomposites

The interface between polymer matrices and nanofillers is critical for efficient interaction to achieve the desired final properties. In this work, block copolymers were utilized to control the interface and achieve optimum interfacial interaction. Specifically, we studied the compatibilizing effects of styrene-ethylene/butadiene-styrene (SEBS) and styrene-ethylene/propylene (SEP) block copolymers on the morphology, conductivity, and rheological properties of polypropylene-polystyrene (PP/PS) immiscible blend with 2 vol% multiwall carbon nanotube (MWCNT) at different blend compositions of PP/PS 80:20, 50:50 and 20:80.MWCNTs induced co-continuity in PP/PS blends and did not obstruct with the copolymer migration to the interface. Copolymers at the interface led to blend morphology refinement. Adding block copolymers at a relatively low concentration of 1 vol% to compatibilize the PP/PS 80:20 blend substantially increased the electrical conductivity from 5.15*10−7S/cm for the uncompatibilized blend to 1.07*10−2S/cm for the system with SEP and 1.51*10−3S/m for the SEBS system. These values for the compatibilized blends are about 4 orders of magnitude higher due to the interconnection of the droplet domains. For the PP/PS 50:50 blend, the SEBS copolymer resulted in a huge increase in conductivity at above 3 vol% concentration (conductivity increased to 3.49*10−3S/cm from 5.16*10−7S/cm). Both the conductivity and the storage modulus increased as the SEBS copolymer content was increased. For the PP/PS 20:80 blend, we observed an initial decrease in conductivity at lower copolymer concentrations (1–3 vol%) and then an increase in conductivity to values higher than the uncompatibilized system, but only at a higher copolymer concentration of 10 vol%. The triblock copolymer (SEBS), which had 60 wt% PS content, shows a more significant increase in rheological properties compared to the diblock copolymer (SEP). The morphology shows that the interaction between MWCNT and PS is stronger than the interaction between MWCNT and PP, hence there is selective localization of the nanofiller in the PS phase as predicted by Young’s equation and by molecular simulation.

Effect of block copolymer architecture and composition on gold nanoparticle fabrication

Gold nanoparticles (AuNPs) fabricatedviathe self-assembly of block copolymers of various architectures.

Effect of Block Copolymer Architecture on Morphology of Self-Assembled Aggregates in Solution

We predict how equilibrium morphology of self-assembled aggregates in dilute solution could be tuned by replacing a linear AB diblock copolymer by a heteroarm star-like or cyclic block copolymer. We demonstrate that in selective solvent AB miktoarm stars or diblock copolymers with cyclic associating block may give rise to cylindrical assemblies or vesicles, while linear diblock copolymers with same composition form only spherical micelles. The theoretical predictions are in line with experimental observations.

Effect of Block Copolymer Architecture on the Thermally Induced Swelling of Micelle-Containing Multilayer Thin Films

We investigate the effect of block copolymer (BCP) molecular weight and connectivity on the morphology and time–temperature dependent swelling of thin film hydrogels created through layer-by-layer (LbL) assembly of BCP micelles with poly(acrylic acid). BCPs of poly(N,N-dimethylaminoethyl methacrylate) (D) and poly(propylene oxide) (P), a P–D diblock, a long D–P–D triblock, and a short D–P–D triblock copolymer, were compared in terms of their temperature response in solution and within micelle–polyelectrolyte multilayers (mPEMs). The critical micellization concentration and micellization temperature of the BCPs in solution, as well as the swelling transition temperature, Tstt, of the mPEMs, decreased with increasing P block length. AFM imaging of dry mPEMs shows regular dimpled surface structures that arise from surface relaxation of micelles. When the mPEMs are cooled below Tstt in water, the thin ∼200 nm films can swell reversibly between 3 and 6 times their dry thicknesses within 2 min. The degree of sw...

Molecular Architecture Effect on Microphase Separation in Supramolecular Comb−Coil Complexes of Polystyrene-block-poly(2-vinylpyridine) with Dodecylbenzenesulfonic Acid: AnBn Heteroarm Star Copolymer

The microphase separation in a supramolecular comb−coil block copolymer formed by the stoichiometric complexation of an amphiphilic surfactant, dodecylbenzenesulfonic acid (DBSA), with the poly(2-vinylpyridine) (P2VP) blocks in a nonlinear heteroarm (PS)5(P2VP)5 star copolymer has been investigated. The hierarchical structure in the ordered state and the relevant order−disorder transitions (ODT) of the complex have been revealed using small-angle X-ray scattering (SAXS). The results were compared with those obtained previously for linear PS-b-P2VP(DBSA) and block-arm (PS-b-P2VP)5(PS)5(DBSA) complexes [Macromolecules 2005, 38, 10117] to illustrate the effect of block copolymer architecture on the self-assembly behavior of the supramolecular comb−coil complexes. The heteroarm (PS)5(P2VP)5(DBSA) complex exhibited structure-within-structure morphology in which the larger-scale PS cylindrical microdomains were embedded in the matrix consisting of the smaller-scale lamellar mesophase organized by the P2VP(DBSA) comb blocks. As observed previously for the linear PS-b-P2VP(DBSA) complex, the ODT temperature (TODT) of the copolymer domain in the heteroarm complex was appreciably higher than that of neat (PS)5(P2VP)5 due to the strong interblock repulsion caused by the increase in the polarity of P2VP blocks upon complexation with DBSA. Most interestingly, a significant increase in the TODT of the smaller-scale lamellar mesophase was observed in the heteroarm complex compared to that of its linear counterpart, and this was attributed to the lower entropy of transition due to the junction constraint. The interdomain distance of the copolymer domains in the heteroarm complex was smaller than that in the linear complex due to lower aggregation number of PS star arms in the cylindrical domains. However, the corresponding interdomain distance was significantly larger than that in the block-arm complex due to different type of intermolecular segregation occurring in the two kinds of star copolymers.

The effect of block copolymer architecture on the coalescence and interfacial elasticity in compatibilized polymer blends

The effect of block copolymer architecture on the suppression of droplet coalescence and on the interfacial elasticity was studied in immiscible blends of polydimethylsiloxane (PDMS) and polyisoprene (PI) with a droplet-matrix morphology. The PDMS-PI diblock copolymers used in this study to compatibilize the blends differ in molecular weight and degree of asymmetry of the blocks. The general Palierne model with an interfacial shear modulus was used to analyze the dynamic measurements performed after different shear histories. It was shown that the coalescence suppression is more effective when the amount of compatibilizer increases and when the overall molecular weight of the block copolymer increases. When comparing the coalescence behavior of a blend and the inverse blend, it was shown that coalescence is suppressed more when the longest block of the block copolymer is located in the matrix. The interfacial relaxation time increases with molecular weight of the blocks for symmetric block copolymers. Asymmetry of the blocks also causes it to increase. A scaling relation is proposed for the interfacial relaxation time of PI/PDMS blends. This master curve is extended for varying viscosity ratios of the blend and with data of a polydimethylsiloxane (PDMS)/polyisobutylene (PIB) blend and a polymethylmethacrylate (PMMA)/polystyrene (PS) blend.

Effect of block copolymer architecture on compatibility: 2. Epoxidized styrene-butadiene star block copolymers with chlorinated polymers

The compatibility behaviour of an epoxidized styrene-butadiene three-arm block copolymer ((ESB) 3) with chlorinated polyethylene (CPE) at two degrees of chlorination (36 and 48 wt%) and with poly(vinyl chloride) was investigated over the complete composition range. The techniques used were dynamic mechanical analysis, differential scanning calorimetry and tensile testing. The results were compared with epoxidized block copolymer blends of different architectures, studied before: a linear ESB, a branched E(SB) n and an SBS. The results indicate that miscibility is reduced along the series ESB>(ESB) 3>E(SB) n , at the same level of epoxidation. Additional data on tensile properties on (ESB) 3 and E(SB) n blends are also reported. A method is also described to obtain epoxidized semicrystalline poly(hydrocarbons), which when blended with CPE showed a T m depression. This allowed the determination of the interaction parameter χ 12 of epoxidized poly(hydrocarbon)/chlorinated polymer using the well established method.

Effect of block copolymer architecture on compatibility: 3. Expoxidized styrene-butadiene block copolymers with polystyrene/chlorinated polymer blends

The compatibilizing efficiency of epoxidized styrene-butadiene block copolymers [E(S- b-B)] of varying architecture for the immiscible polystyrene (PS)/chlorinated polymer (CP) blends [poly(vinyl chloride), chlorinated polyethene] was examined. The copolymers were a diblock (ESB), a three-arm star (ESB) 3 and a random ESBR. The techniques applied were dynamic mechanical analysis and tensile testing of specimens prepared from solvent casting. Compatibilizing efficiency was found to depend on the degree of epoxidation of the butadiene unit in the copolymer, which in turn relates to the degree of chlorination of the CP, and also on the CP/PS ratio in the ternary blend and the molecular architecture of the E(S- b-B) compatibilizer. Other things being equal, this efficiency varies as: ESB > (ESB) 3 > ESBR; thus it parallels the behaviour of the E(S- b-B) towards the CP in the binary blends. The same holds true of for the degree of expodidation of the E(S)- b-B). This is in agreement with recent theoretical compatibilizing efficiency predictions and relates to the relative strength of the interaction parameters among blend constituents. Use of appropriate values for these parameters allowed the determination of the spinodal, approximating successfully the immiscibility gap of the ternary. This procedure could only be applied to the PS/ESBR/CP system, since ESBR, unlike the other E(S- b-B) copolymers, is not microphase separated.

Toughening of polystyrene and poly(phenylene oxide) matrices with elastomeric styrene‐based block copolymers: Role of molecular architecture

AbstractThe effects of the molecular architecture of elastomeric styrene‐based block copolymers on efficiency of toughening a brittle (polystyrene) and a ductile [a miscible blend of 80% phenylene oxide copolymer and 20% polystyrene (80PEC)] polymer were explored experimentally. Toughening appears to be mainly controlled by the blend morphology, which is determined by the rheological characteristics of the block copolymer relative to that of the matrix. The formation of dispersed particles during melt blending in a Brabender Plasticorder is strongly influenced by the ratio of the matrix and block copolymer viscosities (estimated here by Brabender torque). The size of the dispersed particles was found to be proportional to the 1.77 power of the torque ratio when this ratio is greater than unity. Thus, to a first approximation the effect of block copolymer architecture on toughening efficiency is related to how this structure affects the rheological behavior of the copolymer. Excellent toughness of polystyrene was achieved when the particle size was larger than 1–2 μm. The 80PEC resin is best toughened by block copolymers that form a cocontinuous phase morphology. The extent of toughening of this matrix appears to be a strong function of the styrene block molecular weight, whereas this structural feature seems to have no significant effect in toughening polystyrene.

Effect of block copolymer architecture on compatibility: 1. Epoxidized styrene-butadiene copolymers with chlorinated polymers

The compatibility behaviour of epoxidized styrene-butadiene (SB) block copolymers of varying architecture with chlorinated polyethylene at two degrees of chlorination (36 and 48 wt%) and with poly(vinyl chloride) was investigated over the complete composition range. The copolymers were two diblock (SB) copolymers differing in their degree of purity and a multiarm block copolymer (SB) n . For comparison, data obtained previously with an epoxidized (E) triblock (ESBS) were also used. Other parameters examined were the degree of epoxidation to attain miscibility and the degree of chlorination. The techniques used were dynamic mechanical analysis, differential scanning calorimetry and tensile testing. It was demonstrated that epoxidized SB (ESB) is more miscible with chlorinated polymers than ESBS or E(SB) n with the same degree of epoxidation. Also E(SB) n is better in this respect than ESBS. The level of impurities (homopolymers and SBS) accompanying commercial samples of SB did not impair the tensile properties of these blends. The degree of chlorination was found to determine the required degree of epoxidation to obtain a miscible system.