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Thomas P. Russell - One of the best experts on this subject based on the ideXlab platform.

  • Nano- to Macro-Sized Heterogeneities Using Cleavable Diblock Copolymers
    Macromolecules, 2004
    Co-Authors: James T. Goldbach, Kristopher A. Lavery, Jacques Penelle, Thomas P. Russell
    Abstract:

    Polystyrene-block-poly(methyl methacrylate) copolymers containing [4π + 4π] anthracene photodimer at the junction point between the blocks (PS-AA-PMMA) can be cleaved to the parent Homopolymer blocks upon heating above 130 °C or by UV irradiation at 280 nm. PS-AA-PMMA was characterized and then used in thin films to create micro- to macroscale poly(methyl methacrylate) (PMMA) domains in a polystyrene (PS) matrix. Microphase-separated morphologies in thin films were initially achieved by annealing spin-coated films in supercritical carbon dioxide at 80 °C. Subsequent heating and/or UV irradiation was used to cleave the copolymer junction point, affecting an in situ conversion of the diblock copolymer to its parent Homopolymers. The evolution of phase separation, from microdomains of PMMA in a matrix of PS to macrophase-separated structures, was investigated by SFM. Subsequent washing with selective solvents removed Homopolymer, producing raised nanostructures or nanoporous templates.

  • Phase Behavior of Mixtures of Block Copolymer and Homopolymers in Thin Films and Bulk
    Macromolecules, 2003
    Co-Authors: Unyong Jeong, Du Yeol Ryu, Dong Han Kho, Dong Hyun Lee, Jin Kon Kim, Thomas P. Russell
    Abstract:

    Mixtures of polystyrene-block-poly(methyl methacrylate) (PS−PMMA) having PMMA cylindrical microdomains with Homopolymers of PMMA and poly(ethylene oxide) (PEO) were used to study the effect of the interaction between Homopolymers confined to the cylindrical microdomains and the PS matrix on the microdomain spacing of the mixtures. The microdomains in all thin films are oriented perpendicular to the film surface. It was found that the miscibility between PMMA Homopolymer and PMMA block in thin film was enhanced compared with that in bulk at a given molecular weight of PMMA Homopolymer. Also, the PMMA Homopolymer chains in thin films were more localized to the center of PMMA microdomains than in the bulk, which results in a larger increase of the lattice spacing (D) in the former. D increased rapidly at low volume fractions of PMMA Homopolymer, but it approached a saturated value as the content of PMMA increased. The increase of D with increasing molecular weight of PMMA Homopolymer was saturated at a certa...

  • Homopolymer distributions in ordered block copolymers
    Macromolecules, 1992
    Co-Authors: Anne M. Mayes, Thomas P. Russell, Sushil K. Satija, Charles F. Majkrzak
    Abstract:

    Mixtures of polystyrene (PS) or poly(methyl methacrylate) (PMMA) Homopolymers with symmetric P(S-b-MMA) diblock copolymerswere investigated by neutron reflectivity. In a thin-film geometry, these mixtures form alternating lamellar microdomains oriented parallel to the substrate surface. When the molecular weight of the Homopolymer is comparable to the block molecular weight, the Homopolymer is confined to the corresponding copolymer domain, with a distribution which peaksd at the center of the domain. The results are shown to be in excellent agreement with mean-field predictions. With decreasing molecular weight, the Homopolymer is more uniformly distributed within the domain

Tadashi Sobue - One of the best experts on this subject based on the ideXlab platform.

Andrew B. Lowe - One of the best experts on this subject based on the ideXlab platform.

  • the nucleophilic phosphine catalyzed thiol ene click reaction and convergent star synthesis with raft prepared Homopolymers
    Polymer, 2009
    Co-Authors: Justin W. Chan, Charles E. Hoyle, Andrew B. Lowe
    Abstract:

    Abstract The synthesis of 3-arm star polymers from reversible addition–fragmentation chain transfer (RAFT)-prepared precursor Homopolymers in combination with thiol–ene click chemistry is described. Homopolymers of n -butyl acrylate and N , N -diethylacrylamide were prepared with 1-cyano-1-methylethyl dithiobenzoate and 2,2′-azobis(2-methylpropionitrile) yielding materials with polydispersity indices (M w /M n ) ≤ 1.18 and controlled molecular weights as determined by a combination of NMR spectroscopy, size exclusion chromatography (SEC), and matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Subsequent one-pot reaction of Homopolymer, hexylamine (HexAM), dimethylphenylphosphine (DMPP), and trimethylolpropane triacrylate (TMPTA) results in cleavage of the thiocarbonylthiol end-group (by HexAM) of the Homopolymer yielding a macromolecular thiol that undergoes DMPP-initiated thiol-Michael addition to TMPTA yielding 3-arm star polymers. The presence of DMPP is demonstrated to serve an important second role in effectively suppressing the presence of any polymeric disulfide as determined by SEC. Such phosphine-mediated thiol–ene reactions are shown to be extremely rapid, as verified by a combination of FTIR and NMR spectroscopies, with complete consumption of the C C bonds occurring in a matter of min. MALDI-TOF MS and SEC were used to verify the formation of 3-arm stars. A broadening in the molecular weight distribution (M w /M n  ∼ 1.35) was observed by SEC that was attributed to the presence of residual Homopolymer and possibly 2-arm stars formed from trimethylolpropane diacrylate impurity. Interestingly, the MALDI analysis also indicated the presence of 1- and 2-arm species most likely formed from the fragmentation of the parent 3-arm star during analysis. Finally, a control experiment verified that the consumption of C C bonds does not occur via a radical pathway.

  • Sequential thiol‐ene/thiol‐ene and thiol‐ene/thiol‐yne reactions as a route to well‐defined mono and bis end‐functionalized poly(N‐isopropylacrylamide)
    Journal of Polymer Science Part A, 2009
    Co-Authors: Justin W. Chan, Charles E. Hoyle, Andrew B. Lowe
    Abstract:

    Sequential thiol-ene/thiol-ene and thiol-ene/thiol-yne reactions have been used as a facile and quantitative method for modifying end-groups on an N-isopropylacrylamide (NIPAm) Homopolymer. A well-defined precursor of polyNIPAm (PNIPAm) was prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization in DMF at 70 °C using the 1-cyano-1-methylethyl dithiobenzoate/2,2′-azobis(2-methylpropionitrile) chain transfer agent/initiator combination yielding a Homopolymer with an absolute molecular weight of 5880 and polydispersity index of 1.18. The dithiobenzoate end-groups were modified in a one-pot process via primary amine cleavage followed by phosphine-mediated nucleophilic thiol-ene click reactions with either allyl methacrylate or propargyl acrylate yielding ene and yne terminal PNIPAm Homopolymers quantitatively. The ene and yne groups were then modified, quantitatively as determined by 1H NMR spectroscopy, via radical thiol-ene and radical thiol-yne reactions with three representative commercially available thiols yielding the mono and bis end functional NIPAm Homopolymers. This is the first time such sequential thiol-ene/thiol-ene and thiol-ene/thiol-yne reactions have been used in polymer synthesis/end-group modification. The lower critical solution temperatures (LCST) were then determined for all PNIPAm Homopolymers using a combination of optical measurements and dynamic light scattering. It is shown that the LCST varies depending on the chemical nature of the end-groups with measured values lying in the range 26–35 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3544–3557, 2009

Hideto Tsuji - One of the best experts on this subject based on the ideXlab platform.

Juan J. De Pablo - One of the best experts on this subject based on the ideXlab platform.

  • Monte-Carlo simulation of ternary blends of block copolymers and Homopolymers
    The Journal of chemical physics, 2011
    Co-Authors: Darin Q. Pike, Marcus Müller, Juan J. De Pablo
    Abstract:

    We perform a theoretically informed coarse grain Monte-Carlo simulation in the nPT-ensemble and the Gibbs ensemble on symmetric ternary mixtures of AB-diblock copolymers with the corresponding Homopolymers. We study the lamellar period by varying the length and amount of Homopolymers. The Homopolymer distribution within the lamellar morphology is determined as is the maximum amount of Homopolymer within the lamellae. Gibbs ensemble simulations are used to locate the three-phase coexistence between two Homopolymer-rich phases and a lamellar phase.

  • Behavior of single nanoparticle/Homopolymer chain in ordered structures of diblock copolymers
    The Journal of Chemical Physics, 2003
    Co-Authors: Qiang Wang, Paul F. Nealey, Juan J. De Pablo
    Abstract:

    We have performed Monte Carlo simulations to study the behavior of a single nanoparticle and a single Homopolymer chain in ordered structures of diblock copolymers. Our results show that the microphase-separated copolymers can be used to position nanoparticles or Homopolymers according to their interactions with the two blocks. This is consistent with recent experimental observations. We also observe that, while short neutral Homopolymers segregate at the A–B interfaces, longer neutral Homopolymers exhibit an apparent preference for the cylinders over the matrix, mainly due to geometrical considerations associated with the curvature of A–B interfaces.