Miktoarm Star Terpolymers Research Articles

Synthesis of an Amphiphilic Miktoarm Star Terpolymer for Self-Assembly into Patchy Polymersomes.

Herein we report the synthesis of an amphiphilic miktoarm star terpolymer and combine it with an equivalent diblock copolymer to form polymersomes with controlled surface topology. The three branches are ligated onto a central maleimide moiety in a reaction sequence that exploits various "click" chemistries. The final star was self-assembled with a linear block copolymer to generate a "patchy" surface on vesicles.

Phase separation and permeability in polyisobutylene-based miktoarm star polymers

The phase behavior of (PS-PIB)2-s-PAA miktoarm star terpolymers with varying volume fractions of PAA was investigated directly by transmission electron microscopy, atomic force microscopy, and small-angle X-ray scattering, and indirectly by thermogravimetric analysis and degree of water sorption. The microdomains of (PS-PIB)2-s-PAA demonstrate a unique and unexpected progression from highly ordered cylinders, to lower ordered spheres, to gyroid structures with increasing PAA content from 6.6 to 47 wt %. Interestingly, the phase behavior in the miktoarm star polymer system is significantly different from that reported previously for the linear counterpart of similar composition (PAA-PS-PIB-PS-PAA), where a steady progression from cylindrical to lamellar morphology was observed with increasing PAA content. At low PAA concentrations, the morphology is driven primarily by the relative solubility of the components, while at high PAA content the molecular architecture dominates. Thermal annealing demonstrated the thermodynamic stability of the morphologies, indicating the potential for design of novel microstructures for specific applications through precise control of architecture, composition, and interaction parameters of the components. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 916–925

Facile synthesis of well-defined ABC miktoarm star terpolymers bearing poly(ε-caprolactone), polystyrene and stereoregular helical poly(phenyl isocyanide) blocks

A novel method for the synthesis of ABC miktoarm star terpolymers bearing poly(ε-caprolactone), polystyrene and helical poly(phenyl isocyanide) blocks has been developed.

A convenient synthesis of α,α′‐ homo‐ and α,α′‐hetero‐bifunctionalized poly(ε‐caprolactone)s by ring opening polymerization: The potentially valuable precursors for miktoarm star copolymers

ABSTRACTTwo new ring opening polymerization (ROP) initiators, namely, (3‐allyl‐2‐(allyloxy)phenyl)methanol and (3‐allyl‐2‐(prop‐2‐yn‐1‐yloxy)phenyl)methanol each containing two reactive functionalities viz. allyl, allyloxy and allyl, propargyloxy, respectively, were synthesized from 3‐allylsalicyaldehyde as a starting material. Well defined α‐allyl, α′‐allyloxy and α‐allyl, α′‐propargyloxy bifunctionalized poly(ε‐caprolactone)s with molecular weights in the range 4200–9500 and 3600–10,900 g/mol and molecular weight distributions in the range 1.16–1.18 and 1.15–1.16, respectively, were synthesized by ROP of ε‐caprolactone employing these initiators. The presence of α‐allyl, α′‐allyloxy and α‐allyl, α′‐propargyloxy functionalities on poly(ε‐caprolactone)s was confirmed by FT‐IR, 1H, 13C NMR spectroscopy, and MALDI‐TOF analysis. The kinetic study of ROP of ε‐caprolactone with both the initiators revealed the pseudo first order kinetics with respect to ε‐caprolactone consumption and controlled behavior of polymerization reactions. The usefulness of α‐allyl, α′‐allyloxy functionalities on poly(ε‐caprolactone) was demonstrated by performing the thiol‐ene reaction with poly(ethylene glycol) thiol to obtain (mPEG)2‐PCL miktoarm star copolymer. α‐Allyl, α′‐propargyloxy functionalities on poly(ε‐caprolactone) were utilized in orthogonal reactions i.e copper catalyzed alkyne‐azide click (CuAAC) with azido functionalized poly(N‐isopropylacrylamide) followed by thiol‐ene reaction with poly(ethylene glycol) thiol to synthesize PCL‐PNIPAAm‐mPEG miktoarm star terpolymer. The preliminary characterization of A2B and ABC miktoarm star copolymers was carried out by 1H NMR spectroscopy and gel permeation chromatography (GPC). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 844–860

PH-responsive ABC type miktoarm star terpolymers: Synthesis via combination of click reaction and SET-LRP, characterization, self-assembly, and controlled drug release

We report on the one-pot synthesis of well-defined ABC miktoarm star terpolymers consisting of poly(ethyleneglycol)-b-poly(tert-butylacrylate)-b-polycaprolactone, (mPEG-b-PtBA-b-PCL), by using combination of click reaction and single electron transfer living radical polymerization (SET-LRP). Mono-epoxide functionalized mPEG (mPEG-EP) was synthesized and reacted with sodium azide in the presence of NH4Cl to afford mPEG-N3(-OH). Then, a difunctional molecule bearing azide and bromine moieties, mPEG-N3(-Br), was synthesized via the nucleophilic reaction of mPEG-N3(-OH) with 2-bromoisobutyryl bromide. Propargyl-terminated polycaprolactones, Prop-PCLs, were synthesized by ROP of different contents of CL using propargyl alcohol as initiator and Sn(Oct)2 as catalyst. In the presence of mPEG-N3(-Br) and mixture of Cu(0)/PMDETA/tBA, target ABC miktoarm star terpolymers mPEG-b-PtBA-b-PCL were successfully synthesized in a one-pot manner by simultaneously conducting the SET-LRP of t-butyl acrylate (tBA) and the click reaction with bromine- and azido-group of mPEG-N3(-Br), respectively. PH-sensitive terpolymers, mPEG-b-PAA-b-PCL, were prepared by selective acidolysis of tBA groups. The terpolymers were characterized by FT-IR, 1H NMR and GPC, and their pH sensitivity and self-assembly behavior were investigated by DLS and TEM techniques. Naproxen (Nap) as a model drug was incorporated in the micelles and drug release was evaluated as a function of pH. In addition, the cytotoxicity and degradation of the prepared terpolymers were also investigated.

Crystallization-Driven Solution Self-Assembly of μ-ABC Miktoarm Star Terpolymers with Core-Forming Polyferrocenylsilane Blocks

A comparative study of the solution self-assembly behavior of two polystyrene-arm-polyisoprene-arm-polyferrocenylsilane (μ-SIF) miktoarm star terpolymers of similar composition has been conducted: one with a short, atactic, noncrystallizable poly(ferrocenylethylmethylsilane) (PFEMS) block (μ-SIFa) and one with a short, crystallizable poly(ferrocenyldimethylsilane) (PFDMS) block (μ-SIFc). Both solvent composition and the amorphous/crystallizable nature of the polyferrocenylsilane (PFS) block exhibited a profound influence on the morphologies of the micelles obtained. In hexane, the formation of uniform spherical micelles with an amorphous, phase-mixed PS/PFS core was observed for both μ-SIFa and μ-SIFc. The introduction of cyclohexane (a theta-solvent for PS at 34.5 °C) to give a 1:1 cyclohexane/hexane (v/v) solvent composition resulted in the formation of distorted spherical micelles with a core composed of phase-separated PS and PFS, for both μ-SIFa and μ-SIFc. Interestingly, the distorted spherical micelles formed from crystallizable μ-SIFc evolved with time into elongated fiber-like structures with a phase-separated PS and PFDMS core, while the noncrystallizable counterpart, μ-SIFa, remained as distorted spheres. It was found that in ethyl acetate, a good solvent for PI and PS, μ-SIFa remained unimeric in solution, whereas μ-SIFc formed cylindrical micelles composed of a crystalline PFDMS core and a phase-separated, patchy, PS and PI corona. Finally, seeded growth of μ-SIFc from short, cylindrical PFDMS-b-PDMS seeds (PDMS = polydimethylsiloxane) was demonstrated, yielding B–A–B block comicelles where outer segments derived from μ-SIFc blocks bore a strong resemblance to that ultimately formed under conditions of homogeneous nucleation.

Functional mikto-arm star terpolymers by an association-and-reaction strategy

Two functional mikto-arm star terpolymers μ-(PB)(PSm)(PC) were prepared, where PB, PC, and PSm denote poly(tert-butyl acrylate), poly[2-(cinnamoyloxy)ethyl methacrylate], and poly(solketal methacrylate), respectively. To prepare the samples, two PB-b-PCOOH-b-PSm triblock copolymers containing a carboxyl-bearing PCOOH block of 5 units and a PNH2-b-PC diblock copolymer incorporating an amino-bearing PNH2 block of 5 units were first prepared. The PCOOH and PNH2 blocks were then associated in solution, bringing together a triblock copolymer chain and a diblock copolymer chain. Functional μ-(PB)(PSm)(PC) copolymers were obtained from amidation of the associated PCOOH and PNH2 blocks. The effect of varying the reactant concentration on the yield and selectivity of μ-(PB)(PSm)(PC) synthesis was examined. Further, we developed fractional precipitation protocols for purifying the crude reacted mixtures to yield essentially pure μ-(PB)(PSm)(PC) samples.

Synthesis and Self-assembly Behaviors of the ABC Miktoarm Star Terpolymer

The ABC miktoarm star terpolymer MPEG-PTHF (-PDMA) was synthesized by the combination of click chemistry, atom transfer radical polymerization (ATRP) and cationic ring opening polymerization (CROP). A block copolymer of poly(ethylene glycol) (PEG) and poly(N,N-dimethylaminoethyl methacrylate) (PDMA) which bears an azido at diblock junction (MPEG-N3 (-PDMA)) was first prepared by atom transfer radical polymerization. Then, an alkynyl-terminated narrow distributed polytetrahydrofuran (PTHF-Alk) was synthesized as another building block via cationic ring opening polymerization. The well-defined ABC miktoarm star shaped terpolymer was afforded by clicking MPEG-N, (-PDMA) onto the chain end of PTHF-Alk. The structure of the star terpolymer was characterized by the FTIR,NMR and SEC/MALLS. The self-assembly behavior of the polymer were investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). This star shaped terpolymer consists of a hydrophobic PTHF chain, a hydrophiphilic PEG chain and another stimuli-responsive PDMA chain. It can self-assemble into micelles with different sizes and morphologies at various pH values, such as 5. 0,7. 4 and 9. 5. The micellar size also exhibits temperature-dependence at pH 7. 4 and 9. 5. The variation of size and morphology of the micelles with the solution pH and temperature is ascribed to the pH- and thermo-responsive properties of the PDMA block.

ABC-type miktoarm star terpolymers accessed by H-bonding driven supramolecular self-assembly

A supramolecular ABC-type miktoarm star polymer was prepared using a Hamilton wedge (HW) mid-chain functionalized polyethylene glycol-b-polystyrene (PEG-HW-PS) block copolymer and an α-cyanuric acid (CA) chain-end functional linear homopolymer poly-(n-butylacrylate) (CA-PnBA). The PEG-HW-PS element prepared via a combination of atom transfer radical polymerization (ATRP) and copper-catalyzed azide alkyne cycloaddition (CuAAC) (Mn=13,700gmol−1, PDI=1.04). The CA-PnBA strand was synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization (Mn=11,300gmol−1, PDI=1.06). The quantitative formation of a well-defined supramolecular ABC-type miktoarm star polymer was unambiguously proven via proton nuclear magnetic resonance (1H NMR) spectroscopy, diffusion ordered NMR spectroscopy (DOSY) and dynamic light scattering (DLS) analyses.

Thin Film Knitting Pattern Morphology from a Miktoarm Star Terpolymer

Thin film knitting pattern from a miktoarm star terpolymer is demonstrated. Such structures have been predicted but not observed in bulk or thin film form. The knitting pattern exhibits well organized periodic structures consisting of undulating lamellae and alternating cylinders, with well-defined defects that result in sharp 90° bends and T junctions.

Kinetics of Laterally Nanostructured Vesicle Formation by Self-Assembly of Miktoarm Star Terpolymers in Aqueous Solution

Dissipative particle dynamics (DPD) simulation was used to study the self-assembly of laterally nanostructured vesicles in aqueous solution from μ-[poly(ethylethylene)]-[poly(ethylene oxide)][poly(perfluoropropylene oxide)] (μ-EOF) star terpolymers. The simulated results show that the laterally nanostructured vesicle forms when the length of the hydrophilic O blocks are relatively short. In the lateral nanostructure, the hexagonally packed domains formed by the hydrophobic F blocks are immersed in a two-dimensional hydrophobic E block matrix. The formation conditions and microstructure of the vesicles in our simulation agree with the reported experimental results from the literature. The complicated formation pathway of laterally nanostructured vesicles follows three stages: (1) combination of spherical and short cylindrical raspberry-like micelles into an intermediate polygonal sheet; (2) the intermediate polygonal sheet grows to form a larger polygonal sheet with a tail; (3) the large polygonal sheet with a tail eventually folds and forms a vesicle.

Self-assembly behavior of [formula omitted] [formula omitted]-miktoarm star terpolymers

The self-assembly of miktoarm star terpolymers provides a powerful route to obtain complex microstructures. Here we use self-consistent field theory to investigate the melt morphologies self-assembled from A(BC)3 4-miktoarm star terpolymers composed of a homopolymer arm A and three copolymer arms BC. A variety of ordered microstructures are predicted by controlling the volume fractions of different components and the Flory–Huggins interaction parameters. At the same time a series of order–order and order–disorder transitions are observed. The results may be helpful for the design of novel microstructures.

Square and Rectangular Symmetry Tiles from Bulk and Thin Film 3‐Miktoarm Star Terpolymers

The directed self assembly of a 3-miktoarm star terpolymer (polyisoprene-arm-polystyrene-arm-polyferrocenylethylmethylsilane (3μ-ISF)) into a (4.8²) square symmetry Archimedean tiling pattern is described. Bulk samples of 3μ-ISF generate equilibrium columnar (4.8²) tile patterns (symmetry p 4 mm) on annealing, which is preceded by a metastable c 2 mm centered rectangular structure. In contrast, in thin films of 3μ-ISF blended with PS homopolymer, the c 2 mm phase is stable with columns oriented out of plane when the film thickness is below 50 nm. However, the 3μ-ISF/homopolymer blend rapidly forms a p 4 mm symmetry when the film thickness is ∼80 nm, with grain sizes of several μm and excellent order. Defects in the p 4 mm structure are described.

Hierarchical self-assembly of miktoarm star polymers containing a polycationic segment: A general concept

We recently introduced a concept for the counterion-mediated hierarchical self-assembly of an amphiphilic ABC miktoarm star terpolymer in aqueous media into micrometer-sized compartmentalized particles with a highly periodic lamellar fine structure (“woodlice”). Herein, we extend this concept to different miktoarm star polymer systems containing a polycationic segment. The presence of a poly(N-methyl-2-vinylpyridinium) (P2VPq) block and its interaction with iodide/triiodide counterions is crucial. In analogy to linear diblock copolymer systems the hydrophilic/hydrophobic balance of polybutadiene-arm-poly(N-methyl-2-vinylpyridinium iodide)-arm-polystyrene miktoarm star terpolymers determines the morphology of the primary building blocks (spherical micelles and cylindrical micelles/vesicles) and the obtained superstructures (stacked lamellar structures and multilamellar vesicles) during this hierarchical process. When an ABA' miktoarm star copolymer (polystyrene-arm-poly(N-methyl-2-vinylpyridinium iodide)-arm-polystyrene) without a dynamic core-forming block was investigated, a different mechanism into “woodlouse” structured aggregates via aggregation and deformation of intermediate vesicles was found. The individual steps of the different self-assembly processes were investigated by transmission electron microscopy and additionally supported by dynamic light scattering, differential scanning calorimetry, and small-angle X-ray scattering.

Counterion-Mediated Hierarchical Self-Assembly of an ABC Miktoarm Star Terpolymer

Directed self-assembly processes of polymeric systems represent a powerful approach for the generation of structural hierarchy in analogy to biological systems. Herein, we utilize triiodide as a strongly polarizable counterion to induce hierarchical self-assembly of an ABC miktoarm star terpolymer comprising a polybutadiene (PB), a poly(tert-butyl methacrylate) (PtBMA), and a poly(N-methyl-2-vinylpyridinium) (P2VPq) segment. Hereby, the miktoarm architecture in conjunction with an increasing ratio of triiodide versus iodide counterions allows for a stepwise assembly of spherical micelles as initial building blocks into cylindrical structures and superstructures thereof. Finally, micrometer-sized multicompartment particles with a periodic lamellar fine structure are observed, for which we introduce the term "woodlouse". The counterion-mediated decrease in hydrophilicity of the corona-forming P2VPq block is the underlying trigger to induce this hierarchical structure formation. All individual steps and the corresponding intermediates toward these well-defined superstructures were intensively studied by scattering and electron microscopic techniques, including transmission electron microtomography.

Ordered Nanoscale Archimedean Tilings of a Templated 3-Miktoarm Star Terpolymer

The directed self-assembly of 3-miktoarm star terpolymer chains (polyisoprene-arm-polystyrene-arm-polyferrocenylethylmethylsilane (3 μ-ISF)) into 2D Archimedean tilings is described. A morphological change from (4.8(2)) to (6(3)) tiling is reported in the 3 μ-ISF thin film blended with PS homopolymer when a greater swelling of PI is achieved during the solvent annealing process. Highly oriented (4.8(2)) tilings were produced by templating the self-assembled three colored structures in blended thin films. The use of (4.8(2)) and (6(3)) tilings as nanolithographic masks to transfer square and triangular hole arrays into the substrate is also demonstrated.

Novel amphiphilic and photo-responsive ABC 3-miktoarm star terpolymers: synthesis, self-assembly and photo-responsive behavior

Novel amphiphilic and photo-responsive ABC 3-miktoarm star terpolymers consisting of hydrophilic poly(ethylene glycol) monomethyl ether (MPEG), hydrophobic polystyrene (PS) and azobenzene-containing poly[6-(4-methoxy-azobenzene-4′-oxy) hexylmethacrylate] (PMMAZO) were synthesized by a combination of atom transfer radical polymerization (ATRP) and click chemistry. MPEG was first end-capped by an epoxide ring, which was opened by sodium azide for the preparation of the modified MPEG bearing reactive azide group and hydroxyl group (MPEG–(OH)(N3)). Click chemistry was then performed to conjugate α-alkynyl-ω-diethylamino-PS and MPEG–(OH)(N3) for the preparation of a block copolymer with reactive hydroxyl group at the junction point (MPEG(–OH)–b–PS), which was further esterified with 2-bromoisobutyryl bromide to prepare the macroinitiator with reactive bromo group at the central point (MPEG(–Br)–b–PS). Finally, an azobenzene-containing PMMAZO arm was introduced into the diblock copolymer by ATRP of 6-(4-methoxy-azobenzene-4′-oxy) hexylmethacrylate monomer (MMAZO) initiated with macroinitiator MPEG(–Br)–b–PS for the preparation of ABC 3-miktoarm star terpolymer (MPEG)(PS)(PMMAZO). The self-assembled morphologies of the star terpolymers in selective solvents changed from bowl-shaped structures to multibowl-shaped structures with the lengthening of the hydrophobic chains (PS or PMMAZO). Photo-responsive investigation showed that the different aggregation states had a great effect on the photo-induced isomerization behaviors. These results may provide guidelines for the design of effective photoresponsive anisotropic materials.

A Modular Route for the Synthesis of ABC Miktoarm Star Terpolymers via a New Alkyne-Substituted Diphenylethylene Derivative

We introduce a modular route for the synthesis of well-defined ABC miktoarm star terpolymers. To this aim, the synthesis of a 1,1-diphenylethylene derivative bearing a protected alkyne function (1-[(4-(tert-butyldimethylsilyl)ethynyl)phenyl]-1-phenylethylene) was developed. This compound was for the first time employed in sequential anionic polymerization to readily prepare alkyne mid-functionalized diblock copolymers with polybutadiene as first and a poly(alkyl methacrylate) (poly(tert-butyl methacrylate), poly(N,N-dimethylaminoethyl methacrylate)) as second block. For the third arm controlled radical polymerization methods (polystyrene, poly(tert-butyl methacrylate), poly(N,N-dimethylaminoethyl methacrylate)) and anionic ring-opening polymerization (poly(ethylene oxide)) were used to separately prepare homopolymers with an azido function. Afterward, azide–alkyne Huisgen cycloaddition was successfully employed to synthesize a library of ABC miktoarm star terpolymers with different molecular weights and chemical compositions via modular combination of the functionalized diblock copolymers and homopolymers. The resulting new ABC miktoarm star terpolymers showed narrow, monomodal molecular weight distributions with dispersities typically below 1.10, as determined by size exclusion chromatography.

Striped networks and other hierarchical structures inAmBmCn(2m+n)-miktoarm star terpolymer melts

Using dissipative particle dynamics simulations we give numerical evidence of the formation of "striped" (or AB alternating) diamond and gyroid network structures and other hierarchical morphologies in A(m)B(m)C(n) (2m+n)-miktoarm star terpolymers where the main variable is the ratio x=n/m with m,n being the number of equal length polymer arms of A and B and C, respectively. The formed networks are purely a result of the star topology, as clearly shown by direct comparison with parallel ABC miktoarm star terpolymer simulations with matching overall composition. Progressively changing x, the system adopts the following phase sequence: three-colored lamellae, C spheres embedded in AB lamellae, C spheres decorating AB lamellae, three-colored [6.6.6] tiling, AB striped diamond network, AB striped gyroid network, AB striped hexagonally arranged cylinders, and finally AB striped globular aggregates. The striped gyroid is particularly interesting as it constitutes an inherently chiral structure made from achiral building blocks.

Kaleidoscopic tilings, networks and hierarchical structures in blends of 3-miktoarm star terpolymers

Dissipative particle dynamics simulations are used to explore blends of 3-miktoarm star terpolymers. The investigated system is a 50/50 blend of ABC and ABD stars, which is investigated as a function of composition and at different symmetric segregation levels. The study shows that in analogy to pure ABC star melts cylindrical tiling patters form, but now in four-coloured variants. Also, a large part of the phase diagram is dominated by multi-coloured network structures showing hierarchical features. Most prominently, a novel alternating gyroid network structure with a hyperbolic lamellar interface is predicted to form. Here, the two gyroidal nets are composed of respectively C and D components, with the minority A and B components forming the lamellar-like curved structure on the dividing interface between the two nets.