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Pengcheng Yang, Oleksandr O Mykhaylyk, Elizabeth R Jones, Steven P Armes
We report a new nonaqueous polymerization-induced self-assembly (PISA) formulation based on the reversible addition-fragmentation chain transfer (RAFT) dispersion alternating copolymerization of styrene with N-phenylmaleimide using a nonionic poly(N,N-dimethylacrylamide) stabilizer in a 50/50 w/w ethanol/methyl ethyl ketone (MEK) mixture. The MEK cosolvent is significantly less toxic than the 1,4-dioxane cosolvent reported previously [Yang P.; Macromolecules2013, 46, 8545-8556]. The core-forming alternating copolymer block has a relatively high glass transition temperature (Tg), which leads to vesicular morphologies being observed during PISA, as well as the more typical sphere and worm phases...
September 27, 2016: Macromolecules
C K Pandiyarajan, Michael Rubinstein, Jan Genzer
We present a versatile synthetic route leading toward generating surface-attached polyacrylamide gels, in which the cross-link density varies continuously and gradually across the substrate in two orthogonal directions. We employ free radical polymerization to synthesize random copolymers comprising ~5% of photoactive methacrylyloxybenzophenone (MABP), ~5% of thermally active styrene sulfonyl azide (SSAz), and ~90% of N-isopropylacrylamide (NIPAAm) units. The presence of MABP and SSAz in the copolymer facilitates control over the cross-link density of the gel in an orthogonal manner using photoactivated and thermally activated cross-linking chemistries, respectively...
July 26, 2016: Macromolecules
Bernice Akpinar, Lee A Fielding, Victoria J Cunningham, Yin Ning, Oleksandr O Mykhaylyk, Patrick W Fowler, Steven P Armes
A series of model sterically stabilized diblock copolymer nanoparticles has been designed to aid the development of analytical protocols in order to determine two key parameters: the effective particle density and the steric stabilizer layer thickness. The former parameter is essential for high resolution particle size analysis based on analytical (ultra)centrifugation techniques (e.g., disk centrifuge photosedimentometry, DCP), whereas the latter parameter is of fundamental importance in determining the effectiveness of steric stabilization as a colloid stability mechanism...
July 26, 2016: Macromolecules
Victoria J Cunningham, Matthew J Derry, Lee A Fielding, Osama M Musa, Steven P Armes
RAFT solution polymerization of N-(2-(methacryoyloxy)ethyl)pyrrolidone (NMEP) in ethanol at 70 °C was conducted to produce a series of PNMEP homopolymers with mean degrees of polymerization (DP) varying from 31 to 467. Turbidimetry was used to assess their inverse temperature solubility behavior in dilute aqueous solution, with an LCST of approximately 55 °C being observed in the high molecular weight limit. Then a poly(glycerol monomethacylate) (PGMA) macro-CTA with a mean DP of 63 was chain-extended with NMEP using a RAFT aqueous dispersion polymerization formulation at 70 °C...
June 28, 2016: Macromolecules
Andrea S Carlini, Lisa Adamiak, Nathan C Gianneschi
The synthesis of functional polymers encoded with biomolecules has been an extensive area of research for decades. As such, a diverse toolbox of polymerization techniques and bioconjugation methods has been developed. The greatest impact of this work has been in biomedicine and biotechnology, where fully synthetic and naturally derived biomolecules are used cooperatively. Despite significant improvements in biocompatible and functionally diverse polymers, our success in the field is constrained by recognized limitations in polymer architecture control, structural dynamics, and biostabilization...
June 28, 2016: Macromolecules
Jing Sun, Xi Jiang, Aaron Siegmund, Michael D Connolly, Kenneth H Downing, Nitash P Balsara, Ronald N Zuckermann
Polymers that conduct protons in the hydrated state are of crucial importance in a wide variety of clean energy applications such as hydrogen fuel cells and artificial photosynthesis. Phosphonated and sulfonated polymers are known to conduct protons at low water content. In this paper, we report on the synthesis phosphonated peptoid diblock copolymers, poly-N-(2-ethyl)hexylglycine-block-poly-N-phosphonomethylglycine (pNeh-b-pNpm), with volume fractions of pNpm (ϕNpm) values ranging from 0.13 to 0.44 and dispersity (Đ) ≤ 1...
April 26, 2016: Macromolecules
J R Lovett, L P D Ratcliffe, N J Warren, S P Armes, M J Smallridge, R B Cracknell, B R Saunders
A poly(glycerol monomethacrylate) (PGMA) chain transfer agent is chain-extended by reversible addition-fragmentation chain transfer (RAFT) statistical copolymerization of 2-hydroxypropyl methacrylate (HPMA) with glycidyl methacrylate (GlyMA) in concentrated aqueous solution via polymerization-induced self-assembly (PISA). A series of five free-standing worm gels is prepared by fixing the overall degree of polymerization of the core-forming block at 144 while varying its GlyMA content from 0 to 20 mol %. (1)H NMR kinetics indicated that GlyMA is consumed much faster than HPMA, producing a GlyMA-rich sequence close to the PGMA stabilizer block...
April 26, 2016: Macromolecules
Rebecca J Williams, Anaïs Pitto-Barry, Nigel Kirby, Andrew P Dove, Rachel K O'Reilly
The synthesis of cyclic amphiphilic graft copolymers with a hydrophobic polycarbonate backbone and hydrophilic poly(N-acryloylmorpholine) (PNAM) side arms via a combination of ring-opening polymerization (ROP), cyclization via copper-catalyzed azide-alkyne cycloaddition (CuAAC), and reversible addition-fragmentation chain transfer (RAFT) polymerization is reported. The ability of these cyclic graft copolymers to form unimolecular micelles in water is explored using a combination of light scattering, small-angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryoTEM) analyses, where particle size was found to increase with increasing PNAM arm length...
April 12, 2016: Macromolecules
Sarah L Canning, Gregory N Smith, Steven P Armes
Recently, polymerization-induced self-assembly (PISA) has become widely recognized as a robust and efficient route to produce block copolymer nanoparticles of controlled size, morphology, and surface chemistry. Several reviews of this field have been published since 2012, but a substantial number of new papers have been published in the last three years. In this Perspective, we provide a critical appraisal of the various advantages offered by this approach, while also pointing out some of its current drawbacks...
March 22, 2016: Macromolecules
Gary M Leuty, Mesfin Tsige, Gary S Grest, Michael Rubinstein
Molecular dynamics simulations of a coarse-grained bead-spring model have been used to study the effects of molecular crowding on the accumulation of tension in the backbone of bottle-brush polymers tethered to a flat substrate. The number of bottle-brushes per unit surface area, Σ, as well as the lengths of the bottle-brush backbones Nbb (50 ≤ Nbb ≤ 200) and side chains Nsc (50 ≤ Nsc ≤ 200) were varied to determine how the dimensions and degree of crowding of bottle-brushes give rise to bond tension amplification along the backbone, especially near the substrate...
March 8, 2016: Macromolecules
Partha P Datta, Matthew K Kiesewetter
For the first time, the controlled ring-opening polymerization (ROP) of ε-thionocaprolactone (tnCL) is conducted. The organocatalytic ROP of tnCL occurs without carbonyl scrambling, leading to homopoly(ε-thionocaprolactone) (PtnCL). The ROP by base catalysts alone is proposed to proceed via a nucleophilic mechanism, while the addition of an H-bond donating thiourea (TU) is shown to provide excellent reaction control. The increased reaction control provided by the TU occurs in the virtual absence of binding between tnCL and TU, and a mechanistic account for this observation is discussed...
February 9, 2016: Macromolecules
Joseph R Lovett, Nicholas J Warren, Steven P Armes, Mark J Smallridge, Robert B Cracknell
A series of non-ionic poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer vesicles has been prepared by reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of HPMA at 70 °C at low pH using a carboxylic acid-based chain transfer agent. The degree of polymerization (DP) of the PGMA block was fixed at 43, and the DP of the PHPMA block was systematically varied from 175 to 250 in order to target vesicle phase space. Based on our recent work describing the analogous PGMA-PHPMA diblock copolymer worms [Lovett J...
February 9, 2016: Macromolecules
Mathew P Robin, Shani A M Osborne, Zoe Pikramenou, Jeffery E Raymond, Rachel K O'Reilly
Block copolymer micelles have been prepared with a dithiomaleimide (DTM) fluorophore located in either the core or shell. Poly(triethylene glycol acrylate)-b-poly(tert-butyl acrylate) (P(TEGA)-b-P(tBA)) was synthesized by RAFT polymerization, with a DTM-functional acrylate monomer copolymerized into either the core forming P(tBA) block or the shell forming P(TEGA) block. Self-assembly by direct dissolution afforded spherical micelles with R h of ca. 35 nm. Core-labeled micelles (CLMs) displayed bright emission (Φf = 17%) due to good protection of the fluorophore, whereas shell-labeled micelles (SLMs) had lower efficiency emission due to collisional quenching in the solvated corona...
January 26, 2016: Macromolecules
Nassima Bouguerra, Aleš Růžička, Christoph Ulbricht, Christina Enengl, Sandra Enengl, Veronika Pokorná, Drahomír Výprachtický, Elisa Tordin, Razika Aitout, Věra Cimrová, Daniel Ayuk Mbi Egbe
The synthesis and characterization of a set of conjugated polymers, poly(1,4-phenylene-ethynylene)-alt-poly(1,4-phenylene-vinylene)s (PPE-PPVs), with a dissymmetrical configuration (partial or total) of alkoxy side chains is reported. Five new polymers bearing octyloxy and/or octadecyloxy side chains at the phenylene-ethynylene and phenylene-vinylene segments, respectively, were obtained. Two symmetrical substituted polymers were used for comparison. Polymers with weight-average molecular weight, M w, up to 430 000 g/mol and degree of polymerization between 17 and 322 were obtained by a Horner-Wadsworth-Emmons olefination polycondensation reaction of the respective luminophoric dialdehydes and bisphosphonates...
January 26, 2016: Macromolecules
Maltish M Lorenzo, Caitlin G Decker, Muhammet U Kahveci, Samantha J Paluck, Heather D Maynard
Tetrazine end-functionalized telechelic polymers were synthesized by controlled radical polymerization (CRP) and employed to generate T4 Lysozyme homodimers. Mutant T4 Lysozyme (V131C), containing a single surface-exposed cysteine, was modified with a protein-reactive trans-cyclooctene (T4L-TCO). Reversible addition-fragmentation chain transfer (RAFT) polymerization yielded poly(N-isopropylacrylamide) (pNIPAAm) with a number average molecular weight (Mn by (1)H-NMR) of 2.0 kDa and a dispersity (Đ by GPC) of 1...
January 12, 2016: Macromolecules
E R Jones, O O Mykhaylyk, M Semsarilar, M Boerakker, P Wyman, S P Armes
A poly(2-(dimethylamino)ethyl methacrylate) (PDMA) chain transfer agent (CTA) is used for the reversible addition-fragmentation chain transfer (RAFT) alcoholic dispersion polymerization of benzyl methacrylate (BzMA) in ethanol at 70 °C. THF GPC analysis indicated a well-controlled polymerization with molecular weight increasing linearly with conversion. GPC traces also showed high blocking efficiency with no homopolymer contamination apparent and M w/M n values below 1.35 in all cases. (1)H NMR studies confirmed greater than 98% BzMA conversion for a target PBzMA degree of polymerization (DP) of up to 600...
January 12, 2016: Macromolecules
Ren Zhang, Bongjoon Lee, Michael R Bockstaller, Jack F Douglas, Christopher M Stafford, Sanat K Kumar, Dharmaraj Raghavan, Alamgir Karim
The controlled organization of nanoparticle (NP) constituents into superstructures of well-defined shape, composition and connectivity represents a continuing challenge in the development of novel hybrid materials for many technological applications. We show that the phase separation of polymer-tethered nanoparticles immersed in a chemically different polymer matrix provides an effective and scalable method for fabricating defined submicron-sized amorphous NP domains in melt polymer thin films. We investigate this phenomenon with a view towards understanding and controlling the phase separation process through directed nanoparticle assembly...
2016: Macromolecules
Ting Ge, Sergey Panyukov, Michael Rubinstein
A scaling model of self-similar conformations and dynamics of nonconcatenated entangled ring polymers is developed. Topological constraints force these ring polymers into compact conformations with fractal dimension d f = 3 that we call fractal loopy globules (FLGs). This result is based on the conjecture that the overlap parameter of subsections of rings on all length scales is the same and equal to the Kavassalis-Noolandi number O KN ≈ 10-20. The dynamics of entangled rings is self-similar and proceeds as loops of increasing sizes are rearranged progressively at their respective diffusion times...
2016: Macromolecules
Vito Fasano, Maria Moffa, Andrea Camposeo, Luana Persano, Dario Pisignano
Electrospinning in controlled nitrogen atmosphere is developed for the realization of active polymer nanofibers. Fibers electrospun under controlled atmospheric conditions are found to be smoother and more uniform than samples realized by conventional electrospinning processes performed in air. In addition, they exhibit peculiar composition, incorporating a greatly reduced oxygen content during manufacturing, which favors enhanced optical properties and increases emission quantum yield. Active waveguides with optical losses coefficients lowered by 10 times with respect to fibers spun in air are demonstrated through this method...
November 10, 2015: Macromolecules
Pedro A Sánchez, Elena S Pyanzina, Ekaterina V Novak, Joan J Cerdà, Tomas Sintes, Sofia S Kantorovich
The equilibrium structure of supramolecular magnetic filament brushes is analyzed at two different scales. First, we study the density and height distributions for brushes with various grafting densities and chain lengths. We use Langevin dynamics simulations with a bead-spring model that takes into account the cross-links between the surface of the ferromagnetic particles, whose magnetization is characterized by a point dipole. Magnetic filament brushes are shown to be more compact near the substrate than nonmagnetic ones, with a bimodal height distribution for large grafting densities...
October 27, 2015: Macromolecules
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