ABC Miktoarm Star Terpolymers Research Articles

Temperature-induced morphological change of ABC 3-miktoarm star terpolymer assemblies in aqueous solution

This work reports temperature-induced morphological change of ABC 3-miktoarm star terpolymer assemblies in aqueous solution. The terpolymer (MPEG)(PCL)(PPE) is composed of hydrophilic monomethoxy poly(ethylene glycol) (MPEG), hydrophobic poly(ɛ-caprolactone) (PCL) and thermosensitive polyphosphoester (PPE) chains, emanating from a central junction point. It is thermosensitive in aqueous solution, forming spherical micelles at lower temperature, which transition to short nano-rod morphology at temperature higher than the cloud point. The temperature induced morphological transition of this biodegradable miktoarm star terpolymer shows that it has potential in stimulus-controlled drug delivery applications.

Hierarchical Smectic Self-Assembly of an ABC Miktoarm Star Terpolymer with a Helical Polypeptide Arm

We demonstrate the first hierarchical smectic self-assembly in miktoarm star terpolymers, using a polymer/polypeptide hybrid (macromolecular chimera) composed of two coil-like arms (polystyrene, PS, and polyisoprene, PI) and a mesogenic α-helical polypeptide arm (poly(ε-tert-butyloxycarbonyl-l-lysine), PBLL). The PBLL α-helices are packed within lamellar nanodomains which leads to an overall smectic alteration of rod- and coil-containing layers typically observed in rod−coil block copolymers. Furthermore, the coil-containing lamellae have an inner structure composed of PS and PI rectangular cylinders, leading to what we call a hierarchical smectic phase. To elucidate the role of polypeptide helices in directing the self-assembly, the ordering is studied both after thermal annealing and after quick drop-casting from chloroform solution. The possibility to combine mesogen packing, tiling patterns, and conformational control of polypeptide blocks makes self-assembled hierarchies of star-shaped macromolecular chimeras appealing for future studies.

Synthesis of amphiphilic and thermoresponsive ABC miktoarm star terpolymer via a combination of consecutive click reactions and atom transfer radical polymerization

AbstractWell‐defined amphiphilic and thermoresponsive ABC miktoarm star terpolymer consisting of poly(ethylene glycol), poly(tert‐butyl methacrylate), and poly(N‐isopropylacrylamide) arms, PEG(‐b‐PtBMA)‐b‐PNIPAM, was synthesized via a combination of consecutive click reactions and atom transfer radical polymerization (ATRP). Click reaction of monoalkynyl‐terminated PEG with a trifunctional core molecule bis(2‐azidoethyl)amine, (N3)2NH, afforded difunctional PEG possessing an azido and a secondary amine moiety at the chain end, PEG‐NHN3. Next, the amidation of PEG‐NHN3 with 2‐chloropropionyl chloride led to PEG‐based ATRP macroinitiator, PEG(N3)Cl. The subsequent ATRP of N‐isopropylacrylamide (NIPAM) using PEG(N3)Cl as the macroinitiator led to PEG(N3)‐b‐PNIPAM bearing an azido moiety at the diblock junction point. Finally, well‐defined ABC miktoarm star terpolymer, PEG(‐b‐PtBMA)‐b‐PNIPAM, was prepared via the click reaction of PEG(N3)‐b‐PNIPAM with monoalkynyl‐terminated PtBMA. In aqueous solution, the obtained ABC miktoarm star terpolymer self‐assembles into micelles consisting of PtBMA cores and hybrid PEG/PNIPAM coronas, which are characterized by dynamic and static laser light scattering, and transmission electron microscopy. On heating above the phase transition temperature of PNIPAM in the hybrid corona, micelles initially formed at lower temperatures undergo further structural rearrangement and fuse into much larger aggregates solely stabilized by PEG coronas. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4001–4013, 2009

Helical Vesicles, Segmented Semivesicles, and Noncircular Bilayer Sheets from Solution-State Self-Assembly of ABC Miktoarm Star Terpolymers

Multicompartment micelles, especially nanostructured vesicles, offer tremendous potential as delivery vehicles of therapeutic agents and nanoreactors. Solution-state self-assembly of miktoarm star terpolymers provides a versatile and powerful route to obtain multicompartment micelles. Here we report simulations of solution-state self-assembly of ABC star terpolymers composed of a solvophilic A arm and two solvophobic B and C arms. A variety of multicompartment micelles are predicted from the simulations. Phase diagrams for typical star terpolymers are constructed. It is discovered that the overall micelle morphology is largely controlled by the volume fraction of the solvophilic A arms, whereas the internal compartmented and/or segregated structures depend on the ratio between the volume fractions of the two solvophobic arms. The polymer-solvent and polymer-polymer interactions can be used to tune the effective volume fraction of the A-arm and, thereby, induce morphological transitions. For terpolymers with equal or nearly equal length of B and C arms, several previously unknown structures, including vesicles with novel lateral structures (helices or stacked donuts), segmented semivesicles, and elliptic or triangular bilayer sheets, are discovered. When the lengths of B and C arms are not equal, novel micelles such as multicompartment disks and onions are observed.

Synthesis and Aggregation Behavior of Multi‐Responsive Double Hydrophilic ABC Miktoarm Star Terpolymer

We report the first example of the synthesis and the "schizophrenic" micellization behavior of a multi-responsive double hydrophilic ABC miktoarm star terpolymer. A well-defined miktoarm star terpolymer consisting of poly(ethylene glycol), poly(2-(diethylamino)ethyl methacrylate), and poly(N-isopropylacrylamide) arms, PEG(-b-PDEA)-b-PNIPAM, was synthesized via the combination of atom transfer radical polymerization (ATRP) and click reaction. Containing pH-responsive PDEA and thermo-responsive PNIPAM arms, this novel type of miktoarm star terpolymer molecularly dissolves in aqueous solution at acidic pH and room temperature, but supramolecularly self-assembles into PDEA-core micelles at alkaline pH and room temperature, and PNIPAM-core micelles at acidic pH and elevated temperatures. Most importantly, both types of micellar aggregates possess well-solvated hybrid coronas.

One‐pot synthesis of ABC miktoarm star terpolymers by coupling ATRP, ROP, and click chemistry techniques

AbstractWe report on the one‐pot synthesis of well‐defined ABC miktoarm star terpolymers consisting of poly(2‐(dimethylamino)ethyl methacrylate), poly(ε‐caprolactone), and polystyrene or poly(ethylene oxide) arms, PS(‐b‐PCL)‐b‐PDMA and PEO (‐b‐PCL)‐b‐PDMA, taking advantage of the compatibility and mutual tolerability of reaction conditions (catalysts and monomers) employed for atom transfer radical polymerization (ATRP), ring‐opening polymerization (ROP), and click reactions. At first, a novel trifunctional core molecule bearing alkynyl, hydroxyl group, and bromine moieties, alkynyl(OH)Br, was synthesized via the esterification reaction of 5‐ethyl‐5‐hydroxymethyl‐2,2‐dimethyl‐1,3‐dioxane with 4‐oxo‐4‐(prop‐2‐ynyloxy)butanoic acid, followed by deprotection and monoesterification of alkynyl(OH)2 with 2‐bromoisobutyryl bromide. In the presence of trifunctional core molecule, alkynyl(OH)Br, and CuBr/PMDETA/Sn(Oct)2 catalytic mixtures, target ABC miktoarm star terpolymers, PS(‐b‐PCL)‐b‐PDMA and PEO(‐b‐PCL)‐b‐PDMA, were successfully synthesized in a one‐pot manner by simultaneously conducting the ATRP of 2‐(dimethylamino)ethyl methacrylate (DMA), ROP of ε‐caprolactone (ε‐CL), and the click reaction with azido‐terminated PS (PS‐N3) or azido‐terminated PEO (PEO‐N3). Considering the excellent tolerability of ATRP to a variety of monomers and the fast expansion of click chemistry in the design and synthesis of polymeric and biorelated materials, it is quite anticipated that the one‐pot concept can be applied to the preparation of well‐defined polymeric materials with more complex chain architectures. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3066–3077, 2009

PH-Responsive Supramolecular Self-Assembly of Well-Defined Zwitterionic ABC Miktoarm Star Terpolymers

We report the first example of the synthesis and pH-responsive supramolecular self-assembly of double hydrophilic ABC miktoarm star terpolymers. Well-defined ABC miktoarm star terpolymers consisting of poly(ethylene glycol), poly(tert-butyl methacrylate), and poly(2-(diethylamino)ethyl methacrylate) arms [PEG(-b-PtBMA)-b-PDEA] were synthesized via the combination of consecutive click reactions and atom transfer radical polymerization (ATRP), starting from a trifunctional core molecule, 1-azido-3-chloro-2-propanol (ACP). The click reaction of monoalkynyl-terminated PEG with an excess of ACP afforded difunctional PEG bearing a chlorine and a secondary hydroxyl moiety at the chain end, PEG113(-Cl)-OH (1). After azidation with NaN3, PEG-based macroinitiator PEG113(-N3)-Br (3) was prepared by the esterification of PEG113(-N3)-OH (2) with 2-bromoisobutyryl bromide and then employed in the ATRP of tert-butyl methacrylate (tBMA). The obtained PEG(-N3)-b-PtBMA copolymers (4) possessed an azido moiety at the diblock junction point. The preparation of PEG(-b-PtBMA)-b-PDEA miktoarm star terpolymers was then achieved via the click reaction of 4 with an excess of monoalkynyl-terminated PDEA. The obtained miktoarm star terpolymers were successfully converted into PEG(-b-PMAA)-b-PDEA, where PMAA is poly(methacrylic acid). In aqueous solution, PEG(-b-PMAA)-b-PDEA zwitterionic ABC miktoarm star terpolymers can self-assemble into three types of micellar aggregates by simply adjusting solution pH at room temperature. Above pH 8, PDEA-core micelles stabilized by PEG/ionized PMAA hybrid coronas were formed due to the insolubility of PDEA block. In the range of pH 5-7, micelles possessing polyion complex cores formed as a result of charge compensation between partially ionized PMAA and partially protonated PDEA sequences. At pH<4, hydrogen bonding interactions between fully protonated PMAA and PEG led to the formation of another type of micellar aggregates possessing hydrogen-bonded complex cores stabilized by protonated PDEA coronas. The fully reversible pH-responsive formation of three types of aggregates were characterized by 1H NMR, dynamic and static laser light scattering (LLS), and transmission electron microscopy (TEM).

Micelles possessing mixed cores and thermoresponsive shells fabricated from well‐defined amphiphilic ABC miktoarm star terpolymers

AbstractAmphiphilic ABC miktoarm star terpolymers consisting of polystyrene, poly(ε‐caprolactone), and poly(N‐isopropylacrylamide) arms, PS(‐b‐PNIPAM)‐b‐PCL, were synthesized via a combination of atom transfer radical polymerization, ring‐opening polymerization (ROP), and click chemistry. Difunctional PS bearing an alkynyl and a primary hydroxyl moiety at the chain end, PS‐alknyl‐OH, was prepared by reacting azido‐terminated PS with an excess of 3,5‐bis(propargyloxy)benzyl alcohol (BPBA) under click conditions. The subsequent ROP of ε‐caprolactone using PS‐alknyl‐OH macroinitiator afforded PS(‐alkynyl)‐b‐PCL copolymer bearing an alkynyl moiety at the diblock junction point. Target PS(‐b‐PNIPAM)‐b‐PCL amphiphilic ABC miktoarm star terpolymers were then prepared via click reaction between PS(‐alkynyl)‐b‐PCL and an excess of azido‐terminated PNIPAM (PNIPAM‐N3). The removal of excess PNIPAM‐N3 was accomplished by “clicking” onto alkynyl‐functionalized Wang resin. All the intermediate and final products were characterized by gel permeation chromatography, 1H NMR, and FTIR. In aqueous solution, the obtained amphiphilic ABC miktoarm star terpolymer self‐assembles into micelles possessing mixed PS/PCL cores and thermoresponsive shells, which were further characterized by dynamic laser light scattering and transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1636–1650, 2009

Self-Assembly and pH-Responsiveness of ABC Miktoarm Star Terpolymers

This work deals with the self-assembly in water of ABC miktoarm star terpolymers consisting of hydrophobic poly(-caprolactone), hydrophilic poly(ethylene oxide) (PEO), and pH-sensitive poly(2-vinylpyridine) (P2VP). A variety of experimental techniques were used, including dynamic light scattering, transmission electron microscopy, and zeta potential. Special attention was paid to the pH dependency of the supramolecular self-assemblies. A key observation is the capability of the miktoarm terpolymers to form micelles stable over the whole range of pH, although a transition was observed from neutral to highly positively charged nanoobjects upon decreasing pH.

Synthesis and Characterization of an ABC Miktoarm Star Terpolymer of Cyclohexadiene, Styrene, and 2-Vinylpyridine

The three arms of the novel ABC mixed-arm star terpolymerdescribed herein were chosen purposefully to create, uponexposure to a silica or mica surface, a conformationallyasymmetric binary brush having a P2VP “anchor” block withboth PS and high 1,4-PCHD “buoys”. The chemical dissimilarityof the arms and the short-term longevity of poly(cyclohexadi-enyl) macroanions combine to pose a difficult synthetic chal-lenge. For example, the cyclohexadiene block needs to besynthesized in nonpolar media without the presence of P2VPas polar components complicate both control of the PCHD anionstability and the resultant microstructure of the PCHD polymerobtained. In contrast, polymerization of 2-vinylpyridine is mostsuccessfully achieved in tetrahydrofuran (THF) at low temper-atures, so switching of polymerization media during thesynthesis was required.The target polymer was sought through the use of a1,1-diphenylethylene (DPE)-based strategy as shown in Scheme1. Employing anionic polymerization techniques previouslydetailed,

Synthesis of Amphiphilic ABC 3-Miktoarm Star Terpolymer by Combination of Ring-Opening Polymerization and “Click” Chemistry

Novel biodegradable amphiphilic ABC 3-miktoarm star terpolymers composed of poly(e-caprolactone) (PCL), monomethoxy poly(ethylene glycol) (MPEG), and polyphosphoester (PPE) were synthesized by a combination of ring-opening polymerization and “click” chemistry. MPEG was first end-capped by epoxide ring, which was opened by sodium azide in the presence of ammonium chloride to give modified MPEG bearing reactive azide and hydroxyl groups (MPEG(−OH,−N3)). “Click” chemistry was then applied to conjugate α-propargyl-ω-acetyl-poly(e-caprolactone) and MPEG(−OH,−N3), resulting in a diblock copolymer of MPEG and PCL with reactive hydroxyl groups at the junction point (MPEG(−OH)-b-PCL), which further initiated ring-opening polymerization of 2-ethoxy-2-oxo-1,3,2-dioxaphospholane (EEP) under the catalytic action of stannous octoate to obtain the desired well-defined (MPEG)(PCL)(PEEP) 3-miktoarm star terpolymers. Such terpolymers and their intermediates were characterized by 1H NMR, FT-IR, and gel permeation chromatogr...

Multicompartment Micelles from Polyester-Containing ABC Miktoarm Star Terpolymers

Well-defined μ-[poly(ethylethylene)][poly(ethylene oxide)][poly(γ-methyl-e-caprolactone)] (μ-EOC) miktoarm star terpolymers were prepared by a combination of two successive living anionic polymerizations and one controlled ring-opening polymerization (ROP). A mid-hydroxyl-functionalized poly(ethylethylene)-block-poly(ethylene oxide) (PEE−PEO) diblock copolymer served as a macroinitiator for the aluminum-mediated ROP of γ-methyl-e-caprolactone (MCL), leading to a family of μ-EOC triblock copolymers having monomodal molecular weight distributions and controlled PMCL weight fractions. Micelle structures formed in water from μ-EOC containing various lengths of PMCL were examined by cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering. Increasing the fraction of hydrophobic PMCL resulted in a transition from spherical to wormlike to approximately spherical micelles. Although the multicompartment cores of the μ-EOC micelles could not be directly resolved by cryo-TEM, small-angle X-...

Microstructures from a Mixture of ABC 3-Miktoarm Star Terpolymers and Homopolymers in Two-Dimensional Space

Using a 2D real-space self-consistent field theory, we studied the microstructures of the mixture of ABC 3-miktoarm star terpolymer and linear homopolymers. First, we found that the microstructures depend on both the chain length and volume fraction of the linear homopolymer. Second, despite different linear homopolymer lengths, all the mixtures finally converge to the core/shell pattern after the sum of blocks and homopolymer comprises the majority. Third, some novel microstructures that are not found in the pure ABC 3-miktoarm star terpolymer are produced. These calculations are supposed to be helpful for the design of novel microstructures involving star terpolymers that blend with homopolymer.

Morphologies of Multicompartment Micelles Formed by ABC Miktoarm Star Terpolymers

Several new multicompartment micellar structures have been identified by cryogenic transmission electron microscopy (cryoTEM) from the aqueous self-assembly of mu-[poly(ethylethylene)][poly(ethylene oxide)][poly(perfluoropropylene oxide)] (mu-EOF) miktoarm star terpolymers. This work extends our previous studies, in which it was found that, upon decreasing the length of the hydrophilic block (O), the resulting micelles evolved from "hamburger" micelles to segmented worms and ultimately to nanostructured bilayers and vesicles. In the terpolymers examined here segmented ribbons and bilayers were found at an intermediate composition between segmented worms and nanostructured bilayers, provided that the fluoropolymer (F) was the minority component in the micelle core. On the other hand, when the F block exceeded the chain length of the hydrocarbon block (E), the superhydrophobic F block imposed a "double frustration" on the self-assembly of the mu-EOF(2-9-5) terpolymer; while F prefers to minimize its interfacial contact with the O corona, it must occupy the majority of the micellar core. Therefore, a richer variety of multicompartment micelles, including well-defined segmented worms, raspberry-like micelles, and multicompartmentalized worms, were formed from one terpolymer, as revealed by cryoTEM. Despite the complexity and variety of the observed aggregate morphologies, a small number of common structural elements can be invoked to interpret the observed micelles and to relate a given structure to the terpolymer composition.

Synthesis of Novel Amphiphilic and pH-Sensitive ABC Miktoarm Star Terpolymers

Novel amphiphilic ABC miktoarm star terpolymers were synthesized that consist of hydrophilic poly(ethylene oxide) (PEO), hydrophobic poly(ε-caprolactone) (PCL), and pH-sensitive poly(2-vinylpyridine) (P2VP), thus a water-soluble block upon protonation. In the first step, poly(ethylene oxide monomethyl ether) (MPEO) was capped by one ω-epoxy end group by reaction of the original hydroxy end group with epichlorohydrin. MPEO-b-P2VP diblock copolymers were prepared by nucleophilic addition of living P2VP-Li+ chains onto the epoxy group of MPEO's. Finally, the hydroxy group formed at the junction of the MPEO and P2VP blocks was used to initiate the ring-opening polymerization of ε-caprolactone in the presence of tin octoate. The ABC star-shaped triblocks were characterized by 1H NMR spectroscopy and size exclusion chromatography.

A Monte Carlo simulation for the micellization of ABC 3-miktoarm star terpolymers in a selective solvent

We have used Monte Carlo simulation to study the micellization of ABC 3-miktoarm star terpolymers in a selective solvent (good to A segment, bad to B and C segments). The simulation results reveal that the self-assembled morphology is determined by the block length, molecular architecture, terpolymer concentration and insolubility of insoluble block in the solvent. In dilute solution, symmetric terpolymers ( N B = N C = 30) tend to aggregate into a novel wormlike pearl-necklace structure linked by an alternating arrangement of B and C spheres, whereas the asymmetric terpolymers ( N B = 10, N C = 50) are likely to aggregate into spherical or cylindrical micelles (formed by C blocks) connected with some small B spheres, when the concentration of terpolymer is relatively low (chain number is 100). However, when the concentration of terpolymer is relatively high (chain number is 250), the symmetric terpolymers tend to aggregate into a netlike structure linked by an alternation of B and C spheres, whereas the asymmetric terpolymers are likely to aggregate into wormlike micelles (formed by C blocks) connected with some of small spheres (formed by B blocks). Moreover, when the insolubility of insoluble block in the solvent is weak, the insoluble blocks aggregate into some incompact micelles. However, if we increase the insolubility of insoluble block, the resulting micelles will become more compact at first, and thereafter almost remain unchanged with further increasing the insolubility of insoluble blocks.

Preparation of ABC miktoarm star terpolymer containing poly(ethylene glycol), polystyrene, and poly(tert‐butylacrylate) arms by combining diels–alder reaction, atom transfer radical, and stable free radical polymerization routes

AbstractThe ABC type miktoarm star terpolymer was prepared utilizing “core‐in” and “core‐out” methods via combination of Diels–Alder reaction (DA), stable free radical polymerization (SFRP), and atom transfer radical polymerization (ATRP). First, in DA reaction, poly(ethylene glycol)‐maleimide (PEG‐maleimide) precursor was reacted with succinic acid anthracen‐9‐ylmethyl ester 3‐(2‐bromo‐2‐methyl‐propionyloxy)‐2‐methyl‐2‐[2‐phenyl‐2‐(2,2,6,6‐tetramethyl‐piperidin‐1‐yloxy)‐ethoxy‐carbonyl]‐propyl ester, 8, to give DA adduct, 9, which has appropriate functional groups for SFRP and ATRP. Second, a previously obtained 9 was used as a macroinitiator for SFRP of styrene at 125 °C. As a third step, this PEG‐polystyrene (PEG‐PSt) precursor with a bromine functionality in the core was employed as a macroinitiator for ATRP of tert‐butylacrylate (tBA) in the presence of Cu(I)Br and pentamethyldiethylenetriamine at 80 °C to give ABC type miktoarm star terpolymer (PEG‐PSt‐PtBA) with controlled molecular weight and low polydispersity (Mw/Mn &lt; 1.27). The obtained polymers were characterized by gel permeation chromatography and 1H NMR. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 499–509, 2006

Ordered microstructures by assembly of ABC 3-miktoarm star terpolymers and linear homopolymers

Ordered microstructures assembled from the mixture of the ABC 3-miktoarm star terpolymers and the linear homopolymers have been investigated by using dynamic density functional theory. The simulations reveal that completely different ordered microphase pattern is found with addition of a few percent homopolymers that is identical in component to one of the arms on the ABC 3-miktoarm star terpolymer. For example, the original density pattern of ABC 3-miktoarm star terpolymers with parameters of N(A)=N(B)=N(C)=10 and chi(AB)=0.90, chi(BC)=chi(CA)=0.45 is in a perfectly ordered knitting feature. However, with gradual addition of the linear polymer same as block C on ABC 3-miktoarm star terpolymer into the system, the density patterns evolve with the volume fraction of the linear polymer from the ordered knitting patterns into the hexagonal patterns. Furthermore, with addition of linear polymers same as block A, lamellar microstructure has finally resulted. The simulation points out a way for designing and manufacturing nanomaterials with totally different microstructures.

Synthesis of ABC 3-Miktoarm Star Terpolymers from a Trifunctional Initiator by Combining Ring-Opening Polymerization, Atom Transfer Radical Polymerization, and Nitroxide-Mediated Radical Polymerization

We report a new method to synthesize ABC 3-miktoarm star terpolymers by combining three different controlled/“living” polymerization techniques: ring-opening polymerization (ROP), atom transfer radical polymerization (ATRP), and nitroxide-mediated radical polymerization (NMRP). A trifunctional initiator bearing a hydroxy group, an ATRP initiator, and a NMRP initiator was designed and synthesized. The structure was confirmed by 1H NMR, 13C NMR, and mass spectroscopy. ABC star terpolymers were then prepared from the trifunctional initiator by sequential ROP of e-caprolactone, ATRP of methyl methacrylate, and NMRP of styrene. GPC and kinetic analysis indicated that the polymerizations were controlled. The 3-miktoarm star structure was further confirmed by cleavage of a star terpolymer.

Localizations of junction points of ABC 3-miktoarm star terpolymers

Microdomain structures of ABC 3-miktoarm star terpolymers in three-dimensional space were investigated by dynamic density functional theory (DDFT). Analysis of DDFT demonstrates that the junction points are restricted to lie on the periodically spaced parallel lines formed by the mutual intersections of different domains at the strong segregation between distinct blocks. With the improvement of compatibility of one component with the two other components, the localization of junction points is changed to the tendency of distribution over intermaterial dividing surface between the domains.