End Of Block Research Articles

Temperature and light-induced self-assembly changes of a tetra-arm diblock copolymer in an ionic liquid

A tetra-arm diblock copolymer ([PEG-b-P(AzoMA-r-NIPAm)]4) was synthesized by reversible addition–fragmentation chain transfer copolymerization of N-isopropylacrylamide (NIPAm) and 4-phenylazophenyl methacrylate (AzoMA), initiating from the ends of functionalized tetra-arm polyethylene glycol (tetra-PEG). The resulting tetra-arm diblock copolymer consists of two segments: tetra-PEG (the center block; compatible with 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim]PF6)) and P(AzoMA-r-NIPAm) (the end blocks; temperature- and photosensitive compatibility with [C4mim]PF6 due to photoresponsive upper critical solution temperature phase behavior). We found that [PEG-b-P(AzoMA-r-NIPAm)]4 underwent high-temperature unimer and low-temperature micelle (upper critical micellization temperature (UCMT)) transitions in [C4mim]PF6. The UCMT of the tetra-arm diblock copolymer depended on photoisomerization states of the azobenzene groups within the copolymer. The UCMT of the trans-form polymer in dark conditions was higher than that of the cis-form polymer under UV-light irradiation. We demonstrated photoinduced self-assembly changes of the tetra-arm diblock copolymer in [C4mim]PF6 at a ‘bistable’ temperature. Reversible photoinduced unimer/micelle transitions were also demonstrated. A tetra-arm diblock copolymer, consisting of tetra-PEG as central block and random copolymer of N-isopropylacrylamide (NIPAm) and 4-phenylazophenyl methacrylate (AzoMA) as four end blocks, exhibit high-temperature unimers and low-temperature micelles in a hydrophobic ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim]PF6). The upper critical micellization temperature depends on photoisomerization states of azobenzene in the copolymer. Photoinduced unimer/micelle transition was reversible at a suitable temperature.

Preparation, properties, and structure of polysiloxanes by acid-catalyzed controlled hydrolytic co-polycondensation of polymethyl(methoxy)siloxane and polymethoxysiloxane

Polysiloxanes were prepared by acid-catalyzed controlled hydrolytic co-polycondensation of polymethyl(methoxy)siloxanes (PMS) and polymethoxysiloxanes (PMOS) obtained as macromonomers by acid-catalyzed controlled hydrolytic polycondensation of methyl(trimethoxy)silane and tetramethoxysilane, respectively. Co-polycondensation of the macromonomers with molecular weights M w 2000 (PMS) and 400 (PMOS) provided polymethylsiloxane copolymers with molecular weights M w 6500–15,000. The structure was confirmed to consist of block copolymers poly(PMS-block-PMOS) based on the results of gel permeation chromatography, isolation by fractional precipitation with THF and hexane, and 1H and 29Si NMR spectral analyses. The copolymers were soluble in organic solvents, except for hexane, and were fairly stable to self-condensation even without an end block. Transparent and flexible free-standing films were obtained from a 20 wt% THF solution of polymers. The surface morphology of films by FE-SEM and IR microscopic spectral analyses revealed cross-shaped crystalline materials on the film surface of poly(PMS-block-PMOS); these materials consisted of silsesquioxane unit structures depending on the compositions of PMS and PMOS. Polysiloxanes were prepared by acid-catalyzed controlled hydrolytic co-polycondensation of polymethyl(methoxy)siloxanes (PMS) and polymethoxysiloxanes (PMOS). The structure was confirmed to consist of block copolymers poly(PMS-block-PMOS). The surface morphology of transparent and flexible free-standing films revealed cross-shaped crystalline materials on the film surface of poly(PMS-block-PMOS); these materials consisted of silsesquioxane unit structures depending on the compositions of PMS and PMOS.

End Block Design Modulates the Assembly and Mechanics of Thermoresponsive, Dual-Associative Protein Hydrogels

Polymers exhibiting lower critical solution behavior in water have found broad use as thermoresponsive moieties in soft materials, particularly in biomedical applications for triggered actuation, gelation, accumulation, or release. In this work, changing the thermoresponsive block in a self-assembling hydrogel is shown to be a useful approach to control the viscoelastic behavior and mechanical reinforcement of the gel above its transition temperature. Triblock copolymers were prepared with artificial associative protein midblocks from either site-specific bioconjugation of narrowly disperse poly(N-isopropylacrylamide) (PNIPAM) or as biosynthetic genetic fusions to monodisperse elastin-like polypeptide (ELP) sequences. Both synthetic approaches yield responsively reinforceable hydrogels that can be stiffened by up to an order of magnitude to approximately 105 Pa at 30% (w/w). However, end block chemical composition and linear block copolymer architecture could be manipulated to yield high-temperature plate...

Bulk morphologies of polystyrene-block-polybutadiene-block-poly(tert-butyl methacrylate) triblock terpolymers

The self-assembly of block copolymers in the bulk phase enables the formation of complex nanostructures with sub 100 nm periodicities and long-range order, both relevant for nanotechnology applications. Here, we map the bulk phase behavior of polystyrene-block-polybutadiene-block-poly(tert-butyl methacrylate) (SBT) triblock terpolymers on a series of narrowly distributed polymers with widely different block volume fractions, ϕS, ϕB and ϕT. In dependence of ϕ, we find the lamella–lamella, core-shell cylinder, cylinder-in-lamella and core-shell gyroid morphology, but also a rarely observed cylinder-in-lamella phase. The bulk morphologies are thoroughly characterized by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) and display unusually broad stability regions, i.e. morphologies are observed over a broad range of compositions. We attribute this phase behavior to the asymmetric distribution of block–block incompatibilities, along the SBT block sequence, which are relatively large for S/B and S/T interfaces, but small for B/T. The higher enthalpic penalties at the S/B and S/T interface cause B to preferentially spread on the T microdomain thereby adopting its geometry. The morphological behavior of SBT is thus dominated by the volume ratio of the end blocks, ϕS and ϕT, which reduces the number of potential morphologies to only a few, mostly the core-shell analogue of diblock copolymer morphologies. In general, a simplified terpolymer bulk behavior with large stability regions for morphologies offers straightforward synthetic targeting of specific morphologies that usually only appear in a small parameter space as demonstrated here on the core-shell gyroid.

Effects of shading and blocking in linear Fresnel reflector field

In a linear Fresnel reflector field, parallel rows of reflectors in a collector direct the incident sun rays towards a common linear receiver. Some portion of reflector aperture remains unused due to end effect, inter-row shading and blocking. In addition to these factors, cosine effect, cleanliness factor, reflectivity of reflectors, intercept factor, transmissivity of receiver cover, reflectivity of secondary reflector, absorptivity of absorber tube and thermal losses are other factors that contribute to energy losses and thus affect net energy collection by the heat transfer fluid in the absorber, electricity generation and cost of electricity. Conventionally, the collectors are oriented either along North–South or East–West directions in most cases. However the energy collection, electricity generation and cost of electricity need to be found out for all possible collector-orientations lying between North–South and East–West. This can be used in designing collectors for places where the available land strip does not align with any of these two directions. In this work, explicit analytical expressions for energy losses due to cosine effect, end effect, shading and blocking are derived for any desired time interval as functions of length (L) and width (w) of aperture of reflector-row, spacing between adjacent reflector-rows (p), number of reflector-rows in a collector (n), height of receiver (H), collector-orientation angle (Ω) and location. The expressions for the net energy collected by the working fluid, electricity generated by a collector and the cost of electricity are presented. The effects of L, w, p, n, H, Ω and location on energy losses, net energy collection by fluid, electricity generation and cost of electricity are studied. The minimum cost of electricity is found out for different collector-orientations at various locations and relative comparisons have been made. The corresponding collector parameters, annual energy collection by fluid and the annual electricity generation are also found out.

Equivalent pathways in melting and gelation of well-defined biopolymer networks.

We use multiple particle tracking microrheology to study the melting and gelation behavior of well-defined collagen-inspired designer biopolymers expressed by the transgenic yeast P. Pastoris. The system consists of a hydrophilic random coil-like middle block and collagen-like end block. Upon cooling, the end blocks assemble into well-defined transient nodes with exclusively 3-fold functionality. We apply the method of time-cure superposition of the mean-square displacement of tracer beads embedded in the biopolymer matrix to study the kinetics and thermodynamics of approaching the gel point from both the liquid and the solid side. The melting point, gel point, and critical relaxation exponents are determined from the shift factors of the mean-square displacement and we discuss the use of dynamic scaling exponents to correctly determine the critical transition. Critical relaxation exponents obtained for different concentrations in both systems are compared with the currently existing dynamic models in literature. In our study, we find that, while the time scales of gelation and melting are different by orders of magnitude, and show inverse dependence on concentration, that the pathways followed are completely equivalent.

Controlled synthesis of poly(neopentyl p‐styrene sulfonate) via reversible addition‐fragmentation chain transfer polymerisation

AbstractThe controlled synthesis of poly(neopentyl p‐styrene sulfonate) (PNSS) using reversible addition‐fragmentation chain transfer polymerisation has been studied under a wide range of experimental conditions. PNSS can be used as an organic‐soluble, thermally labile precursor for industrially valuable poly(p‐styrene sulfonate), widely employed in technologies such as ionic exchange membranes and organic electronics. The suitability of two different chain transfer agents, three solvents, three different monomer concentrations and two different temperatures for the polymerisation of neopentyl p‐styrene sulfonate is discussed in terms of the kinetics of the process and characteristics of the final polymer. Production of PNSS with systematically variable molecular weights and low dispersities (Đ ≤ 1.50 in all cases) has been achieved using 2‐azidoethyl 2‐(dodecylthiocarbonothioylthio)‐2‐methylpropionate in anisole at 75 °C, with an initial monomer concentration of 4.0 mol L−1. Finally, a poly(neopentyl p‐styrene sulfonate)‐b‐polybutadiene‐b‐poly(neopentyl p‐styrene sulfonate) (PNSS‐b‐PBD‐b‐PNSS) triblock copolymer has been synthesised via azide‐alkyne click chemistry. Moreover, subsequent thermolysis of the PNSS moieties generated poly(p‐styrene sulfonate) end blocks. This strategy allows the fabrication of amphiphilic copolymer films from single organic solvents without the need for post‐deposition chemical treatment. © 2014 Society of Chemical Industry

Multiresponsive Hydrogels Formed by Interpenetrated Self-Assembled Polymer Networks

It is shown how interpenetrated polymer networks can be formed by self-assembly in water of two different amphiphilic triblock copolymers, which preserve and combine the properties and stimuli-responsiveness of each polymer. Aqueous solutions of a pH and a UV-sensitive triblock copolymer spontaneously formed a self-assembled interpenetrated network when mixed. The polymers were based on poly(acrylic acid) and poly(ethylene oxide), respectively, and had different hydrophobic end blocks. The structure of the mixed networks was studied with light scattering and the dynamic mechanical properties were studied by oscillatory shear measurements. Synergy led to reduction of the percolation concentration of the individual polymer networks within the interpenetrated network.

Physical Hydrogels via Charge Driven Self-Organization of a Triblock Polyampholyte – Rheological and Structural Investigations

We investigate the conformational properties of stimuli-responsive hydrogels from triblock polyelectrolytes PtBA-b-P2VP-b-PtBA (PtBA and P2VP are poly(tert-butyl acrylate) and poly(2-vinylpyridine)) and the corresponding polyampholytes PAA-b-P2VP-b-PAA (PAA is poly(acrylic acid)), the latter with nonquaternized or quaternized P2VP blocks. The block lengths are the same in all three polymers with relatively short end blocks and long middle blocks. The mechanical properties of the hydrogels have previously been found to depend strongly on the pH value and on the nature of the blocks (Polymer 2008, 49, 1249). Here, we present results from rheological studies and small-angle neutron scattering revealing the underlying hydrogel structures. The hydrogel structure of the polyampholyte depends on the charge asymmetry, controlled by the pH value, and reveals several transitions with increasing charge ratio. A low charge asymmetry causes the collapse of the chains into large globular structures due to the fluctuati...

The effect of carbon black reinforcement on the dynamic fatigue and creep of polyisobutylene-based biomaterials

This paper investigates the structure–property relationship of a new generation of poly(styrene-b-isobutylene-b-styrene) (SIBS) block copolymers with a branched (dendritic) polyisobutylene core with poly(isobutylene-b-para-methylstyrene) end blocks (D_IBS), and their carbon black (CB) composites. These materials display thermoplastic elastomeric (TPE) properties, and are promising new biomaterials. It is shown that CB reinforced the block copolymer TPEs, effectively delayed the oxidative thermal degradation of the D_IBS materials, and greatly improved their dynamic fatigue performance. Specifically, the dynamic creep of a CB composite was comparable to that of chemically crosslinked and silica-reinforced medical grade silicone rubber, used as a benchmark biomaterial.

Phase Behavior of a Single Structured Ionomer Chain in Solution

Structured polymers offer a means to tailor transport pathways within mechanically stable manifolds. The building block of such a membrane is examined, namely a single large pentablock co-polymer that consists of a center block of a randomly sulfonated polystyrene, designed for transport, tethered to poly-ethylene-r-propylene and end-capped by poly-t-butyl styrene, for mechanical stability, using molecular dynamics simulations. The polymer structure in a cyclohexane-heptane mixture, a technologically viable solvent, and in water, a poor solvent for all segments and a ubiquitous substance is extracted. In all solvents the pentablock collapsed into nearly spherical aggregates where the ionic block is segregated. In hydrophobic solvents, the ionic block resides in the center, surrounded by swollen intermix of flexible and end blocks. In water all blocks are collapsed with the sulfonated block residing on the surface. Our results demonstrate that solvents drive different local nano-segregation, providing a gateway to assemble membranes with controlled topology.

Calorimetric and Scattering Studies on Micellization of Pluronics in Aqueous Solutions: Effect of the Size of Hydrophilic PEO End Blocks, Temperature, and Added Salt

Micellar behavior of five ethylene oxide–propylene oxide (EO–PO) triblock copolymers, called Pluronics, with similar molecular weights of middle block PPO (∼2250 g/mol) and varied percentages of poly(ethylene oxide) (10%, 40%, 50%, 70%, and 80%, referred to as L81, P84, P85, F87, and F88, respectively) was examined by thermal (isothermal titration calorimetry and high-sensitivity differential scanning calorimetry), spectral (UV–vis), and dynamic light scattering (DLS) techniques. Micellization was decreased with increasing hydrophilicity of copolymer but induced in the presence of salt. Critical micelle temperatures (CMTs) of copolymers at different concentrations, with and without sodium chloride, are reported. Viscosity and DLS results reveal that highly hydrophilic copolymers (F87 and F88) did not show significant change in micelle size even at temperatures close to cloud point, whereas micelle growth and sphere-to-rod transition occurred for P84 and P85. Surface tension of solutions in water and salt also show enhanced surface activity and salt-induced micellization. The CMTs for different systems using different methods are compared.

Characteristics of Lamellar Mesophases in Strongly Segregated Broad Dispersity ABA Triblock Copolymers

We report the synthesis and characterization of a series of 13 strongly segregated poly(lactide-b-1,4-butadiene-b-lactide) (LBL) triblock copolymers, in which a broad dispersity center B segment (Đ = Mw/Mn ∼ 1.7–1.9) is embedded between two narrow dispersity L end blocks (Đ ≤ 1.20). Derived from chain transfer ring-opening metathesis polymerization (ROMP-CT) of 1,5,9-cyclododecatriene in the presence of 1,4-diacetoxy-2-butene, α,ω-dihydroxytelechelic poly(1,4-butadienes) serve as ring-opening transesterification polymerization (ROTEP) macroinitiators for the parallel synthesis of LBL triblock copolymers with Mn = 12.4–28.7 kg/mol and volume fractions fB = 0.44–0.79. By determining the Flory–Huggins interaction parameter χLB = 0.192 at 155 °C from mean-field theory analyses of synchrotron X-ray scattering profiles for a narrow dispersity LB diblock copolymer, we estimate that the segregation strengths associated with the broad dispersity LBL copolymers range χLBN = 35.1–83.6. As compared to their narrow di...

Synthetic strategies for the generation of ABCA' type asymmetric tetrablock terpolymers

We report the synthesis of poly(lactide)-b-poly(styrene)-b-poly(butadiene)-b-poly(lactide) (LSBL′) and poly(styrene)-b-poly(isoprene)-b-poly(ethylene oxide)-b-poly(styrene) (SIOS′) tetrablock terpolymers with asymmetrically sized end blocks. A combination of anionic polymerization and ring opening transesterification polymerization (ROTEP) of (±)-lactide was used to synthesize LSBL′ while SIOS′ was prepared by a combination of anionic polymerization and reversible addition–fragmentation chain transfer (RAFT) polymerization. All intermediate and final products were characterized by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) techniques and specific control experiments for the LSBL′ tetrablock confirmed the successful synthesis.

Aliphatic polyester block polymers: renewable, degradable, and sustainable.

Nearly all polymers are derived from nonrenewable fossil resources, and their disposal at their end of use presents significant environmental problems. Nonetheless, polymers are ubiquitous, key components in myriad technologies and are simply indispensible for modern society. An important overarching goal in contemporary polymer research is to develop sustainable alternatives to "petro-polymers" that have competitive performance properties and price, are derived from renewable resources, and may be easily and safely recycled or degraded. Aliphatic polyesters are particularly attractive targets that may be prepared in highly controlled fashion by ring-opening polymerization of bioderived lactones. However, property profiles of polyesters derived from single monomers (homopolymers) can limit their applications, thus demanding alternative strategies. One such strategy is to link distinct polymeric segments in an A-B-A fashion, with A and B chosen to be thermodynamically incompatible so that they can self-organize on a nanometer-length scale and adopt morphologies that endow them with tunable properties. For example, such triblock copolymers can be useful as thermoplastic elastomers, in pressure sensitive adhesive formulations, and as toughening modifiers. Inspired by the tremendous utility of petroleum-derived styrenic triblock copolymers, we aimed to develop syntheses and understand the structure-property profiles of sustainable alternatives, focusing on all renewable and all readily degradable aliphatic polyester triblocks as targets. Building upon oxidation chemistry reported more than a century ago, a constituent of the peppermint plant, (-)-menthol, was converted to the ε-caprolactone derivative menthide. Using a diol initiator and controlled catalysis, menthide was polymerized to yield a low glass transition temperature telechelic polymer (PM) that was then further functionalized using the biomass-derived monomer lactide (LA) to yield fully renewable PLA-PM-PLA triblock copolymers. These new materials were microphase-separated and could be fashioned as high-performing thermoplastic elastomers, with properties comparable to commercial styrenic triblock copolymers. Examination of their hydrolytic degradation (pH 7.4, 37 °C) revealed retention of properties over a significant period, indicating potential utility in biomedical devices. In addition, they were shown to be useful in pressure-sensitive adhesives formulations and as nucleating agents for crystallization of commercially relevant PLA. More recently, new triblocks have been prepared through variation of each of the segments. The natural product α-methylene-γ-butyrolactone (MBL) was used to prepare triblocks with poly(α-methylene-γ-butyrolactone) (PMBL) end blocks, PMBL-PM-PMBL. These materials exibited impressive mechanical properties that were largely retained at 100 °C, thus offering application advantages over triblock copolymers comprising poly(styrene) end blocks. In addition, replacements for PM were explored, including the polymer derived from 6-methyl caprolactone (MCL). In sum, success in the synthesis of fully renewable and degradable ABA triblock copolymers with useful properties was realized. This approach has great promise for the development of new, sustainable polymeric materials as viable alternatives to nonrenewable petroleum-derived polymers in numerous applications.

A Comparison of Posterior and Medial Cord Stimulation for Neurostimulation-Guided Vertical Infraclavicular Block

We investigated whether medial cord stimulation is inferior to posterior cord stimulation for vertical infraclavicular block with respect to block success. Ninety-six patients scheduled for upper limb surgery were randomly elicited a medial or posterior cord response for infraclavicular block using 40 mL of 0.5% ropivacaine. We assessed block success (complete sensory block of the 5 nerves in the forearm at 50 minutes) as the primary end point and block procedure characteristics and adverse events as secondary end points. The block success rates did not differ significantly between medial and posterior cord stimulation (95.7% [44/46] vs 91.7% [44/48], 95% CI of difference, -7.4% to 15.6%), while the secondary end points were comparable in both groups. Needle manipulation to elicit medial cord response is noninferior to posterior cord response of block success during neurostimulation-guided vertical infraclavicular block.

Poly(methyl methacrylate)-block-polyethylene-block-poly(methyl methacrylate) Triblock Copolymers as Compatibilizers for Polyethylene/Poly(methyl methacrylate) Blends

Poly(methyl methacrylate)-block-polyethylene-block-poly(methyl methacrylate) (PMMA–PE–PMMA) triblock copolymers were prepared by a combination of ring-opening metathesis polymerization (ROMP), hydrogenation, and reversible addition–fragmentation chain-transfer (RAFT) polymerization. The number-average molar masses of the PMMA end blocks were varied (Mn = 1, 4, 12, and 31 kg mol–1), whereas that of the PE middle block was kept constant at Mn = 13 kg mol–1. The copolymers were evaluated as compatibilizers in PE/PMMA homopolymer blends containing PE in a 4:1 excess by weight. The compatibilized blends displayed significant improvements in elastic modulus, hardness, and scratch resistance as compared to uncompatibilized binary blends. The effects of the PMMA end-block molar mass and compatibilizer concentration on the blend morphology and mechanical properties were investigated. The triblock copolymer with the highest-molar-mass PMMA end blocks was most effective, presumably because of enhanced stress transfer between phases by virtue of a higher degree of entanglement of the end blocks with the PMMA dispersed phase.

Subtle Charge Balance Controls Surface-Nucleated Self-Assembly of Designed Biopolymers

We report the surface-nucleated self-assembly into fibrils of a biosynthetic amino acid polymer synthesized by the yeast Pichia pastoris. This polymer has a block-like architecture, with a central silk-like block labeled SH, responsible for the self-assembly into fibrils, and two collagen-like random coil end blocks (C) that colloidally stabilize the fibers in aqueous solution. The silk-like block contains histidine residues (pKa≈6) that are positively charged in the low pH region, which hinders self-assembly. In aqueous solution, CSHC self-assembles into fibers above a pH-dependent critical nucleation concentration Ccb. Below Ccb, where no self-assembly occurs in solution, fibril formation can be induced by a negatively charged surface (silica) in the pH range of 3.5-7. The density of the fibers at the surface and their length are controlled by a subtle balance in charge between the protein polymer and the silica surface, which is evidenced from the dependence on pH. With increasing number density of the fibers at the surface, their average length decreases. The results can be explained on the basis of a nucleation-and-growth mechanism: the surface density of fibers depends on the rate of nucleation, while their growth rate is limited by transport of proteins from solution. Screening of the charges on the surface and histidine units by adding NaCl influences the nucleation-and-growth process in a complicated fashion: at low pH, the growth is improved, while at high pH, the nucleation is limited. Under conditions where nucleation in the bulk solution is not possible, growth of the surface-nucleated fibers into the solution--away from the surface--can still occur.

The effect of side chains on the reactive rate and surface wettability of pentablock copolymers by ATRP

AbstractThe reactive rate and surface wettability of three pentablock copolymers PDMS‐b‐(PMMA‐b‐PR)2 (R = 3FMA, 12FMA, and MPS) obtained via ATRP for coatings are discussed. Poly(dimethylsiloxane) (PDMS) is used as difunctional macroinitiator, poly(methyl methacrylate) (PMMA) as the middle block, while poly(trifluoroethyl methacrylate) (P3FMA), poly(dodecafluoroheptyl methacrylate) (P12FMA) and poly(3‐(trimethoxysilyl)propyl methacrylate) (PMPS) as the end block, respectively. Their reactive rates obtained by gas chromatography (GC) analysis indicate that 3FMA gains 8.053 × 10−5 s−1 reactive rate and 75% conversion, higher than 12FMA (4.417 × 10−5 s−1, 35%), but MPS has 1.9389 × 10−4 s−1 reactive rate and 96% conversion. The wettability of pentablock copolymer films is characterized by water contact angles (WCA) and hexadecane contact angles (HCA). The PDMS‐b‐(PMMA‐b‐P12FMA)2 film behaves much higher advancing and receding WAC (120° and 116°) and HCA (60° and 56°) than PDMS‐b‐(PMMA‐b‐P3FMA)2 film (110° and 106° for WAC, 38° and 32° for HAC) because of its fluorine‐rich surface (20.9 wt % F). However, PDMS‐b‐(PMMA‐b‐PMPS)2 film obtains 8° hysteretic contact angle in WAC (114°–106°) and HAC (32°–24°) due to its higher surface roughness (138 nm). Therefore, the fluorine‐rich and higher roughness surface could produce the lower water and oil wettability, but silicon‐rich surface will produce lower water wettability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40209.

Fabrication pentablock copolymer/silica hybrids as self-assembly coatings

Novel organic/inorganic hybrid for coating material is prepared by the pentablock copolymer PDMS-b-(PMMA-b-PMPS)2 (PMMDMM) and SiO2 nanoparticles. PMMDMM is obtained via atom transfer radical polymerization (ATRP) by using polydimethylsiloxane (PDMS) as bifunctional macroinitiator. Poly 3-(trimethoxysilyl)propyl methacrylate (PMPS) is designed as the end block for facilitating the chemical bond of triethoxysilane (Si(OCH3)3) groups with SiO2 nanoparticles produced by tetraethyl orthosilicate (TEOS), and poly (methyl methacrylate) (PMMA) is designed as the middle block for improving the solubility and the film-forming ability of copolymer. The homogeneous dispersion of SiO2 nanoparticles in the pentablock copolymer matrix enables PMMDMM/SiO2 to self-assemble into 210nm SiO2 core/PMMDMM shell elliptic or spherical micelles in tetrahydrofuran (THF) solution. This self-assembled aggregate could provide the film surface with uniform distribution of SiO2 nanoparticles, obvious hydrophobicity (101–102° water contact angles), lower surface free energy (22.3–21.8nN/m) and lower viscoelasticity. SiO2 involved into the copolymer matrix could increase the nanostructures roughness. When TEOS is controlled as 20wt.%, the hybrid performs higher glass transition temperature (Tg=113°C) and excellent thermostability (520°C) than PMMDMM (Tg=87°C, 295°C) due to the introduction of SiO2 nanoparticles. These excellent properties promise PMMDMM/SiO2 hybrid as the candidate for coating material.