Miktoarm Star Terpolymers Research Articles

Dendrimer‐like miktoarm star terpolymers: A3‐(B‐C)3 via click reaction strategy

AbstractTwo samples of dendrimer‐like miktoarm star terpolymers: (poly(tert‐butyl acrylate))3‐(polystyrene‐poly(ε‐caprolactone))3 (PtBA)3‐(PS‐PCL)3, and (PS)3‐(PtBA‐poly(ethylene glycol)3 were prepared using efficient Cu catalyzed Huisgen cycloaddition (click reaction). As a first step, azido‐terminated 3‐arm star polymers PtBA and PS as core (A) were synthesized by atom transfer radical polymerization (ATRP) of tBA and St, respectively, followed by the conversion of bromide end group to azide. Secondly, PS‐PCL and PtBA‐PEG block copolymers with alkyne group at the junction as peripheral arms (B‐C) were obtained via multiple living polymerization mechanisms such as nitroxide mediated radical polymerization (NMP) of St, ring opening polymerization (ROP) of ε‐CL, ATRP of tBA. Thus obtained core and peripheral arms were linked via click reaction to give target (A)3‐(B‐C)3 dendrimer‐like miktoarm star terpolymers. (PtBA)3‐(PS‐PCL)3 and (PS)3‐(PEG‐PtBA)3 have been characterized by GPC, DSC, AFM, and SAXS measurements. (PtBA)3‐(PS‐PCL)3 did not show any self‐organization with annealing due to the miscibility of the peripheral arm segments. In contrast, the micro‐phase separation of the peripheral arm segments in (PS)3‐(PtBA‐PEG)3 resulted in self‐organized phase‐separated morphology with a long period of ∼ 13 nm. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5916–5928, 2008

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.

Control of Structure in Multicompartment Micelles by Blending μ-ABC Star Terpolymers with AB Diblock Copolymers

A unique multicompartment micelle, herein referred to as a “hamburger” micelle, was formed from a binary mixture of spherical micelles, formed from polyethylethylene-b-poly(ethylene oxide) (EO) diblock copolymers, and segmented wormlike micelles, formed from μ-(polyethylethylene)(poly(ethylene oxide))(polyperfluoropropylene oxide) (μ-EOF) mikto-arm star terpolymers. Cryogenic transmission electron microscopy (cryoTEM) and dynamic light scattering (DLS) were used to characterize the evolution of micelle structure and size distribution as a function of annealing time, over the course of several months. Considering the extremely low critical micelle concentration of these amphiphilic copolymers, we propose that the micelle evolution was due to a collision/fusion/fission process. The long segmented wormlike micelles first fused with EO spherical micelles, followed by fission to progressively shorter micelles, which finally evolved into more stable hamburger micelles. Three elementary “reactions” were used to describe these structural transitions. Multiple fusions of spherical micelles into already formed hamburger micelles sometimes resulted in the formation of asymmetric hamburger micelles and also induced a micelle shape change from prolatelike to more oblatelike ellipsoids. A binary blend of μ-EOF miko-arm star terpolymer with EO diblock in the bulk prior to micellization did not generate new intermediate micelle structures, presumably because of phase separation between μ-EOF and EO during the film-casting process.

Simultaneous, Segregated Storage of Two Agents in a Multicompartment Micelle

The simultaneous, segregated storage of two different chromophores in a multicompartment micelle, which is formed from self-assembly of (polyethylethylene)(polyethylene oxide)(polyperfluoropropylene oxide) mikto-arm star terpolymers in water, was investigated by spectrophotometry. The multicompartment micelles, with segregated micellar cores composed of fluorocarbon and hydrocarbon compartments, can simultaneously absorb two chemically different molecules. These two molecules were confined into their preferred compartments with high selectivity.

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 < 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

Blends of a 3-Miktoarm Star Terpolymer (3μ-ISD) of Isoprene (I), Styrene (S), and Dimethylsiloxane (D) with PS and PDMS. Effect on Microdomain Morphology and Grain Size

The morphologies of a 3-miktoarm star terpolymer of isoprene (I), styrene (S), and dimethylsiloxane (D), 3μ-ISD, and its blends with PDMS and PS homopolymers, having a lower molecular weight than the corresponding blocks of the star, were studied. Combined EF-TEM and 3D electron tomography clearly revealed that three kinds of cylindrical structures, composed of three different blocks, joined to fill the space and that these cylinders were curved collectively into an arc. The grain size of this star terpolymer was extremely small compared with that of other known linear block copolymers. By blending the neat 3μ-ISD with a small quantity of PDMS homopolymer (5 wt %), the morphology remained the same, but the grain size increased dramatically. It seems that the PDMS homopolymer inserts into the PDMS phase of the star terpolymer and straightens the bent cylinders, thereby increasing long-range order. However, the extra PDMS accumulates in line defects, which if controlled could be beneficial as waveguides in photonic crystals. Blending with PS leads to smaller grain sizes and unstable hexagonal symmetry, which disappears upon the addition of extra PS. Therefore, tetragonal symmetry is inherent in the neat star.

Formation of superlattices in blends of 3-miktoarm star terpolymers with diblock copolymers

Abstract In this contribution we report on the morphological structures formed in blends of microphase-separated 3-miktoarm star terpolymers of polystyrene-armpolybutadiene- arm-poly(2-vinylpyridine) (SBV*) and polystyrene-block-polybutadiene (SB), polystyrene-block-poly(2-vinylpyridine) (SV), poly(2-vinylpyridine)- block-poly(cyclohexyl methacrylate) (VC) diblock copolymers. The morphologies are characterized by transmission electron microscopy. Blends with similar morphologies as known from linear triblock terpolymers are found, like core-shell structures based on cylinders or gyroids. Other blends show very distorted morphologies, or morphologies similar to the ones found for pure 3-miktoarm star terpolymers. While attractive interactions between blocks of the two species enhance the formation of common superlattices, blends with too large diblock copolymers tend to macrophase-separate.

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.

Synthesis and morphology of model 3-miktoarm star terpolymers of styrene, isoprene and 2-vinyl pyridine

The combination of anionic polymerization and controlled chlorosilane chemistry made possible for the first time the synthesis of model 3-miktoarm star terpolymers of styrene (PS), isoprene (PI) and 2-vinylpyridine (P2VP) (3μ-SIV). The morphology of a nearly symmetric 3μ-SIV star terpolymer, was also studied. From the preliminary results, it seems that the PI and P2VP phases form hexagonally packed adjoined cylinders, whereas the PS phase occupies the remaining space forming non-regular curved hexagons, hexagonally packed as well. The star junction points reside on periodically spaced, parallel lines defined by the intersection of the three microdomain interfaces. Non of the phases form the matrix. The star molecular architecture gives the molecule the ability to “choose” which arms directly interact in the microphase segregate state, in order to minimize the most highly unfavorable contact between the PI and P2VP arms.

Novel 2-Dimensionally Periodic Non-Constant Mean Curvature Morphologies of 3-Miktoarm Star Terpolymers of Styrene, Isoprene, and Methyl Methacrylate

The morphology of a family of four 3-miktoarm star terpolymers of polystyrene (PS), polyisoprene (PI), and polymethyl methacrylate (PMMA) was studied. For three of the samples, the molecular weight of the PMMA block was systematically varied while that of the PS and PI blocks were held fixed. In the fourth sample, the PS and PMMA blocks were approximately of the same molecular weight and the PI was the majority component. In all terpolymers, the system displayed a three-phase, two-dimensionally periodic microstructure of an inner PI column with a surrounding PS annulus in a matrix of PMMA. For the two samples with the longer PMMA blocks (218 and 186 kg/mol), the PI−PS and PS−PMMA interfaces were cylindrical, whereas a unique nonconstant mean curvature (non-CMC) concentric diamond prism shape of the PI and PS microdomains occurred for the sample with the lowest molecular weight PMMA block (144 Kg/mol) as well as the polymer with the longer PI block. In these star terpolymers there are three chemically diff...

Microphase separation in block CO‐ and terpolymers of novel macromolecular architectures

AbstractThe synthesis of model miktoarm stars of the A2B, A3B, (AB)2(BA)2 and ABC (A:polyisoprene, B: polystyrene C: poly (methyl methacrylate)) was achieved by using anionic polymerization techniques and controlled chlorosilane chemistry. The microphase separation was studied by TEM, SAXS and image simulation. In the case of A2B and A3B miktoarm star copolymers, the morphology results are in agreement with the newly and after the experimental results developed theory of Milner. One of the symmetric in composition inverse block copolymers ((AB)2(BA)2) shows the OBDD morphology due to the special spatial arrangements of the arms. The first morphological results of ABC miktoarm star terpolymer show interesting future.

Synthesis of Model 3-Miktoarm Star Terpolymers of Styrene, Isoprene, and Methyl Methacrylate

Synthesis of Model 3-Miktoarm Star Terpolymers of Styrene, Isoprene, and Methyl Methacrylate

Microphase Separation in Model 3-Miktoarm Star Co- and Terpolymers. 2. Dynamics

Dielectric spectroscopy has been employed to study the local and global dynamics of polyisoprene in the asymmetric star (polystyrene)(polyisoprene)2 (SI2) and in the 3-miktoarm star terpolymer (polystyrene)(polyisoprene)(polybutadiene) (SIB). All measurements refer to the ordered phase where PS cylinders are embedded on the I and I/B matrix, respectively. Effectively, we are studying the local and global dynamics of tethered PI chains in two environments: one made by I-chains (SI2) and another by the I/B-chains (SIB). At low temperatures, the PI local segmental dynamics in SI2 and SIB are different, reflecting the modification of the local friction by introducing the faster PB chains in the latter. At higher temperatures, however, this effect diminishes due to the demixing of I and B. To explore the thermodynamic and mobility effects on the global dynamics, we have studied, respectively, a ternary blend composed of PI, PB, and PS and binary blends of SIB and SI2 with short PB chains. The PI global dynamics in SI2 and SIB resemble the dynamics of PI stars with additional entanglement effects in the latter.

Microphase Separation in Model 3-MiktoarmStar Copolymers (Simple Graft and Terpolymers). 1. Statics and Kinetics

The static and kinetic aspects of the order-disorder transition (ODT) in newly synthesized model 3-miktoarm star copolymer (simple graft) of SI2 type, (polystyrene)(polyisoprene) 2 , and a 3-miktoarm star terpolymer of SIB type, (polystyrene)(polyisoprene)(polybutadiene), have been studied using SAXS and rheology. The morphology and the order-disorder transition temperature (T ODT ) have been identified from the two-dimensional SAXS patterns with shear-oriented samples. Hexagonally ordered cylindrical microdomains aligned along the direction of shear and with T ODT =379 K have been formed for both samples studied. The SAXS profiles at temperatures well above the T ODT have been fitted to the mean-field theory (MFT) for graft copolymers. Near the ODT deviations from the theory have been observed and the SAXS data provide unambiguous evidence for the existence of fluctuations. The T ODT obtained from rheology is in excellent agreement with the one from SAXS. Discontinuities in the SAXS peak intensity and in the storage modulus near the T ODT are more pronounced in these systems as compared to linear diblocks. The ordering kinetics have been studied with rheology and complementary with SAXS. The width of the kinetically accessible metastable region is enlarged as compared to linear diblocks. For shallow quenches the ordering proceeds by heterogeneous nucleation and growth of three-dimensional grains with cylindrical microstructure. Our kinetic studies probe the metastable states near but below the T ODT