Hybrid Block Copolymers Research Articles

Synthesis and characterization of organic-inorganic hybrid block copolymers containing a fully condensed ladder-like polyphenylsilsesquioxane

A series of inorganic–organic hybrid block copolymers were synthesized via atom transfer radical polymerization using a fully condensed, ladder-like structured polyphenylsilsesquioxane end-functionalized macroinitiator. The inorganic portion, ladder-like polyphenylsilsesquioxane, was synthesized in a one-batch, base-catalyzed system, whereas organic hard and soft monomers, styrene, and n-butyl acrylate, were polymerized and copolymerized on the ends of the linear, inorganic backbone. Synthesized hybrid diblock, triblock, and random copolymers were characterized by 1H NMR, 29Si NMR, gel permeation chromatography, static light scattering, Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. Hybrid block copolymers were well-defined with low polydispersity (<1.4) and exhibited enhanced thermal properties in the form of increased glass transition and degradation onset temperatures over their organic analogues.© 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Interfacial Interactions of Single-Walled Carbon Nanotube/Conjugated Block Copolymer Hybrids for Flexible Transparent Conductive Films

Nanohybrids consisting of single-walled carbon nanotubes (SWCNTs) and a conductive block copolymer, perchlorate-doped poly(3,4-ethylenedioxythiophene)-block-poly(ethyleneoxide) (P-PEDOT-b-PEO), were successfully prepared. Individual exfoliation of SWCNTs and high solution processability were simultaneously achieved in the supramolecular assembly. The assembly at the molecular level was driven by the interfacial interaction between SWCNT walls and the PEDOT block, as characterized by various spectroscopic analyses (UV–Vis, FT-IR, PL, and Raman). The exfoliation of SWCNTs and the solubility of the nanohybrids, which are facilitated by the soluble PEO block, were confirmed by Raman spectroscopy and a range of other microscopy techniques (AFM, TEM, and SEM). Flexible transparent conductive films of the nanohybrids were fabricated using a vacuum-assisted filtration method. The films displayed high electrical conductivity with good mechanical integrity due to the strong interaction between the SWCNT and the con...

Production and characterization of poly(3-hydroxybutyrateco-3-hydroxyhexanoate)-poly(ethylene glycol) hybird copolymer with adjustable molecular weight

A novel natural-synthetic hybrid block copolymer was synthesized by Aeromonas hydrophila 4AK4 in poly(ethylene glycol) (PEG, Mn = 200) modified fermentation. This hybrid biomaterial consists of the natural hydrophobic polymer poly(3-hydroxybutyrat-co-3-hydroxyhexanoate) (PHBHHx) end-capped with hydrophilic PEG, which has the increased flexibility as well as the improved thermal stability. Addition of diethylene glycol (DEG) and ethylene glycol could not result in the accumulation of hybrid block copolymer. DEG and ethylene glycol, together with PEG-200, could cause a reduction of molar mass of PHBHHx, resulting in a series of low molecular weight polymer and the reduction of the polymer yield as well as the cellular productivity. In vitro degradation of PHBHHx and PHBHHx-PEG with different molecular weight showed that the decrease of molecular weight accelerated the degradation of copolymers, but PEG modification has little effect on its degradation rate. The results in this study provided a convenient and direct method to produce a series of PHBHHx and PHBHHx-PEG materials with adjustable molecular weight and broad molecular weight distribution which will be very useful for the biomedical applications.

Sub-10 nm Nanofabrication via Nanoimprint Directed Self-Assembly of Block Copolymers

Directed self-assembly (DSA) of block copolymers (BCPs), either by selective wetting of surface chemical prepatterns or by graphoepitaxial alignment with surface topography, has ushered in a new era for high-resolution nanopatterning. These pioneering approaches, while effective, require expensive and time-consuming lithographic patterning of each substrate to direct the assembly. To overcome this shortcoming, nanoimprint molds--attainable via low-cost optical lithography--were investigated for their potential to be reusable and efficiently template the assembly of block copolymers (BCPs) while under complete confinement. Nanoimprint directed self-assembly conveniently avoids repetitive and expensive chemical or topographical prepatterning of substrates. To demonstrate this technique for high-resolution nanofabrication, we aligned sub-10 nm resolution nanopatterns using a cylinder-forming, organic-inorganic hybrid block copolymer, polystyrene-block-polydimethylsiloxane (PS-b-PDMS). Nanopatterns derived from oxidized PDMS microdomains were successfully transferred into the underlying substrate using plasma etching. In the development phase of this procedure, we investigated the role of mold treatments and pattern geometries as DSA of BCPs are driven by interfacial chemistry and physics. In the optimized route, silicon molds treated with PDMS surface brushes promoted rapid BCP alignment and reliable mold release while appropriate mold geometries provided a single layer of cylinders and negligible residual layers as required for pattern transfer. Molds thus produced were reusable to the same efficacy between nanoimprints. We also demonstrated that shear flow during the nanoimprint process enhanced the alignment of the BCP near open edges, which may be engineered in future schemes to control the BCP microdomain alignment kinetics during DSA.

Morphological Variation of Peptide-synthetic Hybrid Block Copolymer Assemblies in Nonaqueous Media

Abstract In this communication, we demonstrate that significantly different aggregation morphologies are readily generated from a simple poly(γ-benzyl l-glutamate)/polystyrene hybrid block copolymer in nonaqueous media. These nanostructural variations were governed basically by both the solubility of each block to solvents and the character of the polypeptide block such as helix rod–coil transition.

Linear‐dendritic polymeric amphiphiles as carriers of doxorubicin—In vitro evaluation of biocompatibility and drug delivery

AbstractIn our recent work, we have explored the formation of chemotherapeutic delivery vehicles constructed from four different amphiphilic linear‐dendritic hybrid block copolymers. These micelles were found to form about 100‐nm‐sized structures that were capable of sequestering doxorubicin at loading efficiencies up to 22%. Here, the cellular toxicity of these biocompatible and biodegradable linear‐dendritic hybrid materials was evaluated on two breast cancer cell lines and primary human macrophages. The micelles were found not to affect the cellular viability at concentrations below 35 μg mL−1. After drug loading, these constructs could deliver an efficient dose of drugs, resulting in significant decreases in cell viability. Kinetic studies indicated that the drug formulation in the polymer micelles slowed down the cell uptake compared with the nonformulated drug, but similar efficacy in viability reduction and cell apoptosis were found. Taken together, these linear‐dendritic hybrid materials represent an interesting novel architecture for the construction of drug delivery systems. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Selective Enzymatic Degradation of Self-Assembled Particles from Amphiphilic Block Copolymers Obtained by the Combination of N-Carboxyanhydride and Nitroxide-Mediated Polymerization

Combining controlled radical polymerizations and a controlled polypeptide synthetic technique, such as N-carboxyanhydride (NCA) ring-opening polymerization, enables the generation of well-defined block copolymers to be easily accessible. Here we combine NCA polymerization with the nitroxide-mediated radical polymerization of poly(n-butyl acrylate) (PBA) and polystyrene (PS), using a TIPNO and SG1-based bifunctional initiator to create a hybrid block copolymer. The polypeptide block consists of (block) copolymers of poly(L-glutamic acid) embedded with various quantities of L-alanine. The formed superstructures (vesicles and micelles) of the block copolymers possessed varying degrees of enzyme responsiveness when exposed to elastase and thermolysin, resulting in controlled enzymatic degradation dictated by the polypeptide composition. The PBA containing block copolymers possessing 50% L-alanine in the polypeptide block showed a high degradation response compared to polymers containing lower L-alanine quantities. The particles stabilized by copolypeptides with L-alanine near the hydrophobic block showed full degradation within 4 days. Particles containing polystyrene blocks revealed no appreciable degradation under the same conditions, highlighting the specificity of the system and the importance of synthetic polymer selection. However, when the degradation temperature was increased to 70 °C, degradation could be achieved due to the higher block copolymer exchange between the particle and the solution. A number of novel biohybrid structures are disclosed that show promise as enzyme-responsive materials with potential use as payload release vehicles, following their controlled degradation by specific, target, enzymes.

Nanostructured hybrid polymer networks from in situ self‐assembly of RAFT‐synthesized POSS‐based block copolymers

AbstractA series of well‐defined hybrid block copolymers PMACyPOSS‐b‐PMMA and PMAiBuPOSS‐b‐PMMA exhibiting high POSS weight contents have been synthesized by RAFT polymerization and further studied as modifiers for epoxy thermosets based on diglycidyl ether of bisphenol A. The hybrid block copolymers self‐assembled within the epoxy precursors into micelles possessing an inorganic core and a PMMA corona. Thanks to the presence of the PMMA blocks that remain miscible until the end of the reaction, curing of the resulting blends afforded nanostructured hybrid organic/inorganic networks with well‐dispersed inorganic‐rich nanodomains with diameters on the order of 20 nm. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Linear and non-linear viscoelastic rheology of hybrid nanostructured materials from block copolymers with gold nanoparticles

A polystyrene-b-poly-4-vinypyridine (PS-b-P4VP) diblock copolymer is modified with a gold precursor to obtain an organic–inorganic (hybrid) block copolymer in bulk with gold nanoparticles selectively incorporated in the P4VP block. In the linear viscoelastic regime, temperature sweep tests over a series of these hybrid block copolymer systems revealed consistent shifts (ΔT) in the glass transition temperatures (both T\(_{\rm g\text{-}PS}\) and T\(_{\rm g\text{-}P4VP}\)) of the hybrid materials in comparison to the pristine polymers. Studying different volume fractions of the pyridine block, a level-off point was found for block copolymers with fP4VP > 0.26, where the shifts in T\(_{\rm g\text{-}P4VP}\) consistently increased up to ΔT = 25°C. By artificially increasing the volume fraction of the pyridine block, the nanoparticles reduce the transition regime determined in master curves. At higher volume fractions of the pyridine block, crossover frequencies were not detected after the entanglement regime, indicating that the material does not relax from topological constraints (entanglements and nanoparticles) into the terminal regime. Above a specific volume fraction of nanoparticles (ΦP = 0.05), the flow behaviour of the hybrid materials becomes increasingly elastic, exhibiting wall-slip from the geometry at lower strain values in comparison to the pristine material. In the non-linear viscoelastic regime, Fourier-transformed rheology was used to analyse the raw signals from strain sweep experiments. It was clearly demonstrated the nanoparticle effect by following the second and third harmonic (I2/1, I3/1) of the stress response. Comparing the behaviour of the third and second harmonics provided an unambiguous fingerprint for the effect of the nanoparticles.

Tailoring Micelle Formation and Gelation in (PEG−P(MA-POSS)) Amphiphilic Hybrid Block Copolymers

We demonstrate that hydrophobic POSS (polyhedral oligomeric-silsesquioxane) nanoparticles, added to block copolymer solutions of poly(ethylene glycol) (PEG) and poly(methacrylisobutyl polyhedral oligomericsilsesquioxane) P(MA-POSS) as the hydrophilic and hydrophobic blocks respectively, could be employed to tailor their micelle formation, gelation, and rheological performance. For example, the hydrodynamic size of the micelles, formed by PEG5k-b-P(MA-POSS)3.6, increased from 13.6 ± 1.0 to 56.9 ± 3.7, an increase of more than four times, with 0.1 wt % (with respect to block copolymer) POSS nanoparticles in solution. However, the micelles retain their spherical morphology with core−shell structure as evidenced by calculating the values of dimensionless ratios, Rg/Rh for micelles as a function of added POSS nanoparticles content. For P(MA-POSS)-b-PEG10k-b-P(MA-POSS) triblock copolymers, which is associative in nature, addition of POSS nanoparticles resulted in formation of more robust and stronger hydrogels with a significantly higher storage modulus, G′, yield strengths, σy, and lower critical gelation concentration, cg, as compared with those for the pristine triblock copolymer. The presence of eight vinyl groups, attached to the POSS nanoparticles under investigations, is also exploited for further enhancement of rheological properties of the hydrogels with UV treatment. Finally, gel formation is induced in aqueous solutions of PEG5k-b-P(MA-POSS)3.6 diblock copolymer by introducing P(MA-POSS)-b-PEG10k-b-P(MA-POSS) triblock copolymer chains, and the rheological performance of the produced hydrogels, with certain compositions, is even superior to that of pure triblock copolymer gel.

Synthesis of hybrid block copolymers via integrated ring-opening metathesis polymerization and polymerization of NCA

Linear hybrid block copolymers with well controlled molecular weights and narrow polydispersities were synthesized via ring-opening metathesis polymerization (ROMP) followed by ring-opening polymerization of amino acid N-carboxyanhydrides.

Preparation and photo/chemical-activation of wormlike network micelles of core–shell quantum dots and block copolymer hybrids

Poly(styrene-b-4-vinylpyridine) diblock copolymers PS404-b-P4VP76 and PS317-b-P4VP76 (the subscripts indicate the degree of polymerization) self-assemble into spherical “crew-cut” micelles with a PS core and P4VP corona when prepared in a mixture of chloroform and 2-propanol. When the micelles are formed in the presence of quantum dots (QDs), the nature of the structures formed depends upon the polymer and the type of QDs. In our previous report [Macromolecules, 2010, 43, 5066–5074], PS404-b-P4VP76 + CdSe QDs formed stable spherical hybrid micelles, but prolonged vigorous stirring of the solutions led to a rearrangement into wormlike networks and loss of photoluminescence (PL) from the QDs. Here we report that PS317-b-P4VP76 + CdSe/ZnS core–shell QDs behave differently. Partial loss of PL intensity occurred upon addition of 2-propanol to the chloroform solution of the components, and the rearrangement to a network structure occurred spontaneously. We describe two strategies for recovery of the PL intensity for the QDs within the network, photo-activation and chemical activation with elemental sulfur.

Responsive hybrid block co-polymer conjugates of proteins–controlled architecture to modulate substrate specificity and solution behaviour

Responsive co-polymers based on polyethyleneglycol methacrylate (PEGMA) monomers have been grown by aqueous phase ATRP from a model protein, trypsin, to generate hybrid polymer-protein block conjugates. The conjugates (Hybrids I and II) both contained the same segment of grafted responsive co-polymer to afford a phase transition at 37 °C, Hybrid II however differed from Hybrid I by having a second block of hydrophilic pPEGMA monomer grown from the end of the responsive block. The resultant ‘diblock’ and ‘triblock’ hybrids were characterised in terms of their temperature-dependent behaviour in solution by dynamic light scattering, small-angle neutron scattering and pulsed-gradient spin-echo NMR, and their structures at surfaces examined by aqueous phase atomic force microscopy and cryo transmission electron microscopy. These data showed that Hybrids I and II differed in their solution behaviour with temperature, dependent on the arrangement of their grafted polymer blocks. Hybrid I self-assembled into higher-order structures above 37 °C before precipitating reversibly, whereas Hybrid II remained essentially constant in size across a similar temperature range even when its attached intermediate polymer block underwent a phase transition. The differences in polymer-protein hybrid behaviour were also manifest in enzyme activity assays with temperature-dependent hydrolysis of both peptide and protein substrates varying with hybrid architecture. Overall the data show that it is possible to grow responsive polymer-protein block co-polymers of varied structures, architectures and solution behaviour and that these can be used to control bioconjugate activity.

Precision Synthesis of Hybrid Block Copolymers by Organotellurium‐Mediated Successive Living Radical and Cationic Polymerizations

Living cationic polymerization reactions using organotellurium compounds as initiators are reported. Polymerization of vinyl ethers in the presence of an organotellurium initiator and a Lewis acid, such as In(OTf)(3) and BF(3)·OEt(2), affords well-controlled poly(vinyl ether)s with predetermined molecular weights and narrow molecular-weight distributions. Poly(meth)acrylates possessing organotellurium group at the ω-polymer end, which are prepared using organotellurium-mediated controlled/living radical polymerization (TERP), are used as macroinitiators for living cationic polymerization. The one-pot, two-step reaction of the macroinitiator with vinyl ether under radical and cationic conditions gives well-controlled AB diblock copolymers. ABA triblock copolymers with controlled structures are also synthesized from a bifunctional organotellurium initiator.

Synthesis of Poly(methyl methacrylate)-Block-Poly(L-histidine) and Its Use as a Hybrid Silver Nanoparticle Conjugate

Poly[(methyl methacrylate)-block-poly(L-histidine)] (PMMA-b-PHIS) was synthesized by combining atom transfer radical polymerization and living ring-opening polymerization of alpha-amino acid-N-carboxyanhydride. The resulting hybrid block copolymer forms reverse micelles in the mixture solution of water and N,N-dimethylformamide (DMF) and self-assembles into PHIS/PMMA core/shell spheres with controllable size in the range of 80 to 250 nm depending on the micellization temperature. The self-assembly of PMMA-b-PHIS was carried out in H2O/DMF (3/7) mixture in the presence of AgNO3. Reduction of the resulting Ag ions encapsulated inside of the reverse micelles yielded an attractive Ag nanoparticle core/polymer shell conjugate system.

Calcium phosphate/block copolymer hybrid porous nanospheres: Preparation and application in drug delivery

Calcium phosphate (CaP)/block copolymer hybrid porous nanospheres were synthesized by a simple solution method using CaCl2 and (NH4)2HPO4 in the presence of a block copolymer at room temperature. X-ray diffraction showed that the sample consisted of amorphous calcium phosphate (ACP). The BET specific surface area and the pore size distribution of the CaP/PLLA-mPEG hybrid porous nanospheres were also characterized. The as-prepared CaP/PLLA-mPEG hybrid porous nanospheres were explored as drug carriers, and showed a high ibuprofen loading capacity and in vitro prolonged drug release behavior in a simulated body fluid. These CaP/block copolymer hybrid porous nanospheres exhibit a great potential for application in drug delivery.

Microstructure characterization and thermal analysis of hybrid block copolymer α-methoxy-poly(ethylene glycol)- block-poly[ ε-(benzyloxycarbonyl)- l-lysine] for biomedical applications

Hybrid block copolymers, which combine the economy and processibility of synthetic polymers with the functionality and highly ordered structures of polypeptides, can enhance control over structure formation at the nanoscale, as well as afford interesting materials that interface with Nature for a diversity of biomedical applications, such as drug delivery, tissue engineering and bioimaging. Hybrid block copolymer, α-methoxy-poly(ethylene glycol)- b-poly[ ε-(benzyloxycarbonyl)- l-lysine], MPEG- b-PLL(Z), was synthesized by anionic ring-opening polymerization in excellent yield, and fully characterized using IR, 1H, 13C and 2-D NMR, GPC, TGA, DTGA, DSC, MDSC and polarimetry. Its precursor NCA, ε-(benzyloxycarbonyl)- l-lysine N-carboxyanhydride, l-Lys(Z)-NCA, was prepared in 97% yield; and a double doublet observed in the 1850–1750 cm −1 absorption region of its infrared spectrum, for the characteristic NCA carbonyl absorption bands, is discussed.

Supramolecular structures from self-assembled poly(γ-benzyl- l-glutamate)–polydimethylsiloxane–poly(γ-benzyl- l-glutamate) triblock copolypeptides in thin films

We describe the self-assembly of A–B–A triblock copolymers in thin films composed of a soft polydimethylsiloxane (PDMS) central block (B) and two polypeptidic (A) blocks, poly(γ-benzyl)- l-glutamate (PBLG). The PBLG segment exhibits depending on the chain length two distinct secondary conformations either a β-sheet or a α-helical conformation. The direct relationship between the surface morphology and the secondary conformation of the polypeptide segment has been evidenced by atomic force microscopy. For chain lengths below 20 U the polypeptide segments adopt preferentially a β-sheet secondary structure and the triblock copolymer self-assembled in fibers. Moreover, the fiber diameters increased with the chain length of the triblock copolymer. For chain lengths above 20, the α-helical structure is stabilized and a lamellar morphology is formed driven by rod–rod interactions in spite of the very asymmetric composition of the triblock copolymer. However, decreasing the film thickness from 25 to 8 nm, i.e., below the L/2 and due to the preferential attraction of the polypeptide block for the hydrophilic substrate employed, instead of a lamellar morphology a rod-like morphology could be found. Thus, the use of hybrid block copolymer containing polypeptides with particular secondary structures offers novel alternatives to control the self-assembly in thin films compared to traditional amorphous block copolymers.

Bending of Lamellar Microdomains of Block Copolymers on Nonselective Surfaces

Symmetric diblock copolymers self-assemble into lamellar microdomains which can be used to create line and space patterns on substrates by controlling the orientation of microdomains. Previously, it has been reported that the orientation of lamellar microdomains can be controlled perpendicular to the surface by modifying the substrate surface to become nonselective to each domain. For practical use of the block copolymer based patterns for nanofabrications, of great interest is precise control over the lateral placement of lamellar microdomains. Commonly predefined guiding patterns containing chemical and/or topographical contrast have been used to direct the lateral placement of lamellae on substrates. In the absence of guiding patterns, the lamella microdomains produce fingerprint-like surface patterns on nonselective substrates as reported previously with a variety of model diblock copolymers, where the most well-studied diblock copolymer is poly(styrene-b-methyl methacrylate) (PS-b-PMMA). The fact that this fingerprint-like pattern contains many regions of high curvature of bent lamellae suggests the cost of lamellae bending may be relatively small. Previously, Nealey and co-workers reported that the lamellar microdomains of PS-bPMMA faithfully follow the lithographically predefined surface patterns of chemical contrast. They showed that bent block copolymer lamellae could be obtained when homopolymers were added to the copolymer. More recently, Wilmes et al. examined the extent to which patterns with different curvatures can be created within the same block copolymer thin films. They showed that the lamellae conform to patterns with radii of curvature equal to the equilibrium domain spacing. In this Note, we report our investigation on the bending characteristics of lamellar microdomains resulting from directed assembly using topographic guiding patterns. We designed the topographic guiding patterns as elbows with varying corner angles. By controlling the surface of guiding patterns nonselective to the microdomains, we rendered the orientation of lamellae perpendicular to the surfaces of bottom and sidewalls of the guiding patterns. Detailed experimental observation of the degree of bending and tilting of lamellae at the sidewall surface is reported along with a theoretical investigation using self-consistent-field calculations, which provide additional knowledge regarding the free energy and interfacial characteristics of the experimentally observed morphologies. We also extended our investigation to a block copolymer hybrid system which is a mixture of an organic diblock copolymer, poly(styrene-b-ethylene oxide) (PS-b-PEO), and an organosilicate (OS) resin. The effect of larger orientational correlation length of the hybrid system on the bending property of lamellar microdomains will be discussed.

Electroactive Linear–Hyperbranched Block Copolymers Based on Linear Poly(ferrocenylsilane)s and Hyperbranched Poly(carbosilane)s

A convenient two-step protocol is presented for synthesis of linear-hyperbranched diblock copolymers consisting of a linear, organometallic poly(ferrocenylsilane) (PFS) block and hyperbranched poly(carbosilane) (hbPCS) segments. Linear PFS diblock copolymers were synthesized through photolytic ring-opening polymerization of dimethyl[1]silaferrocenophane as the first block and methylvinyl[1]silaferrocenophane as the second. These block copolymers served as polyfunctional cores in a subsequent hydrosilylation polyaddition of different silane-based AB(2) monomers. Three AB(2) monomers (methyldiallylsilane; methyldiundecenylsilane, and ferrocenyldiallylsilane) were investigated; they introduced structural diversity to the hyperbranched block and showed variable reactivity for the hydrosilylation reaction. In the case with the additional ferrocene moiety in the ferrocenyldiallylsilane monomer, an electroactive hyperbranched block was generated. No slow monomer addition was necessary for molecular-weight control of the hyperbranching polyaddition, as the core had much higher functionality and reactivity than the carbosilane monomers. Different block ratios were targeted and hybrid block copolymers with narrow polydispersity (<1.2) were obtained. All the resulting polymers were investigated and characterized by size exclusion chromatography, NMR spectroscopy, cyclic voltammetry, and TEM, and exhibited strongly anisotropic aggregation.