Methyl Methacrylate Block Copolymers Research Articles

Free-Radical Polymerization in Ionic Liquids: The Case for a Protected Radical

The free-radical polymerization of methyl methacrylate (MMA) in ionic liquids at low monomer concentration is reported with emphasis on elucidating the “magic” rate and molecular weight enhancement that are often observed. We show that traditional methods of molecular weight capping using dodecylmercaptan as chain transfer agent significantly reduces the molecular weight of the polymer, but to a much lesser extent than analogous reactions in xylene. Similarly, the adverse effect of elevated temperatures upon reactions of this type is much less significant for polymerizations conducted in ionic liquids than those in organic solvents. Indeed, almost quantitative yield can be obtained for polymerization at temperatures up to 120 °C in ionic liquid, while almost no polymer is observed in an organic solvent case due to rapid initiator burnout. These factors lead to the proposal that a “protected” radical mechanism is in operation; however, elucidation of the exact nature of this protection remains elusive. As an extension of this hypothesis, block copolymers of methyl methacrylate, grown from styrene, have been prepared and characterized by NMR, GPC-MALLS, GPEC, and DSC. The absence of poly(methyl methacrylate) homopolymer in the final product suggests that the monomer is only initiated from protected polystyrene macroradicals in the ionic liquid. This process cannot be reproduced in organic solvents, unless additional control agents are present. Furthermore, we report much higher molecular weights of A−B block copolymers than those previously reported in the literature. © 2008 American Chemical Society

Direct synthesis of amphiphilic block copolymers, consisting of poly(methyl methacrylate) and poly(sodium styrene sulfonate) blocks through atom transfer radical polymerization

Amphiphilic block copolymers of methyl methacrylate (MMA) and sodium styrene sulfonate (SSNa) were successfully synthesized via direct atom transfer radical polymerization (ATRP) of SSNa. First, poly(sodium styrene sulfonate) (PSSNa) or poly(methyl methacrylate) (PMMA) macroinitiators were prepared using proper ATRP systems for each case. In some cases, functional initiators, which allow further reactions, were used. The macroinitiators were characterized and further used to synthesize PSSNa/PMMA block copolymers, by using proper solvent combinations, such as N, N-dimethylformamide/water or methanol/water at appropriate volume ratios, in order to ensure solubility of the synthesized amphiphilic copolymers. The molecular weight of the copolymers was determined by gel permeation chromatography, using water as eluent. By using a combination of analytical techniques like 1H NMR, FTIR and thermogravimetry, the chemical structure and the actual copolymer composition were determined. Since, the block copolymers were soluble in water, forming hydrophilic/hydrophobic domains in aqueous solution, their micellization behavior was further studied by pyrene fluorescence probing.

Synthesis of poly(vinyl acetate) block copolymers by successive RAFT and ATRP with a bromoxanthate iniferter

Poly(vinyl acetate)-b-polystyrene, poly(vinyl acetate)-b-poly(methyl acrylate) and poly(vinyl acetate)-b-poly(methyl methacrylate) block copolymers with low polydispersity (M(w)/M(n) < 1.25) were prepared by successive reversible addition-fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) employing a bromoxanthate iniferter (initiator-transfer agent-terminator).

Programmed Thermodynamic Formation and Structure Analysis of Star-like Nanogels with Core Cross-linked by Thermally Exchangeable Dynamic Covalent Bonds

Programmed thermodynamic formation of star-like nanogels from designed diblock copolymers with thermally exchangeable dynamic covalent bonds in their side chains and structure analysis of the nanogels were performed. Linear diblock copolymers that consist of poly(methyl methacrylate) block and random copolymer block of methyl methacrylate (MMA) and methacrylic esters with alkoxyamine moiety were prepared by atom transfer radical polymerization (ATRP). By heating the diblock copolymers in anisole, a cross-linking reaction occurred as a result of the radical crossover reaction of alkoxyamine moieties to afford star-like nanogels. Kinetic studies have revealed that the cross-linking behavior reaches equilibrium at a given reaction time, with characteristic reaction behaviors for thermodynamic reactions being observed. The equilibrium structures of the star-like nanogels were controlled by the initial concentrations of diblock copolymers as well as their compositions and molecular weights. Furthermore, by heating the star-like nanogels with excess alkoxyamine, linear polymers were successfully regenerated. The molecular weights and sizes of the nanogels were evaluated by gel permeation chromatography-multiangle laser light scattering (GPC-MALLS) and small-angle X-ray scattering (SAXS) measurements, respectively, and the morphologies of the nanogels were directly observed by scanning force microscopy (SFM).

Block Copolymerization of Methyl Methacrylate from Fluorine-contained Polyimide Macroinitiator by Atom-transfer Radical Polymerization

Abstract The linear fluorine-contained polyimide macroinitiator capped with the chloromethylphenyl group at both polymer ends was synthesized and reacted with methyl methacrylate (MMA) to form an ABA-type triblock copolymer (MMA-b-PI-b-MMA) by atom-transfer radical polymerization (ATRP). The poly(methyl methacrylate) (PMMA) homopolymer was decomposed completely at ca. 400 °C, whereas the polyimide macroinitiator was thermally stable up to ca. 500 °C The MMA component in MMA-b-PI-b-MMA was selectively decomposed up to ca. 400 °C, while the polyimide component remained.

Thermally Driven Assembly of Nanoparticles in Polymer Matrices

Thermally responsive bulk polymer films utilizing reversible Diels−Alder chemistry have been developed. Gold nanoparticles (AuNPs) were passivated with thiol-terminated poly(styrene)-b-poly(ethylene glycol) (PS-b-PEG) copolymer ligand, where the PS and PEG blocks are joined via a Diels−Alder (DA) linkage. The ligand-functionalized nanoparticles were dispersed within a microphase-separated PS-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer. Nanoparticle location was dictated by the compatibility of the external shell with the block copolymer matrix. As cast, the PEG shell compatibilized the nanoparticles with the PMMA domains. Subsequent thermal treatment caused the Diels−Alder linkages between the polymer blocks to dissociate, leaving the AuNPs functionalized by PS ligands. Immiscibility within the PMMA matrix caused AuNP migration to the PS domains. Migration of the Au nanoparticles was determined using morphological characterization via small-angle X-ray scattering (SAXS) and cross-sectional transmission electron microscopy (TEM).

Synthesis of Laterally Linked Poly(tetrahydrofuran)−Poly(methyl methacrylate) Block Copolymers via Use of a “Jekyll and Hyde” Comonomer

Glycidyl methacrylate (GMA) is an example of a heterobifunctional monomer, a so-called “Jekyll and Hyde” monomer, in that one functional group can be polymerized via conventional free radical polymerization and the other via cationic ring-opening polymerization. Laterally linked diblock copolymers differ from conventional linear diblock copolymers in that the blocks are not linked via their termini but at a point some way along each chain. This architecture has therefore some of the characteristics of a graft copolymer. Free radical copolymerization of a low level of GMA with methyl methacrylate (MMA) yields MMA/GMA copolymers with a few pendent epoxide groups. Likewise cationic ring-opening copolymerization of low levels of GMA with tetrahydrofuran (THF) yields THF/GMA copolymers with a few pendent methacrylate groups. Subsequent cationic polymerization of the first copolymer type with THF, and subsequent free radical polymerization of the second copolymer type with MMA, yields laterally linked block cop...

Micellization of PS‐PMMA Diblock Copolymers in an Ionic Liquid

AbstractThree polystyrene‐block‐poly(methyl methacrylate) (PS‐PMMA) block copolymers with varying molecular content have been shown to form micelles when dissolved in the ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIM PF6). The micellar structure was studied via cryogenic transmission electron microscopy and dynamic light scattering, and a morphological transition from spherical to cylindrical micelles was observed upon reduction of the PMMA volume fraction. The possibility of frozen micellar morphology was considered, due to the solution preparation method and high glass transition temperature (Tg) of the PS blocks that form the micellar cores. By comparison of the behavior of a 100 kDa PMMA homopolymer dissolved in both BMIM PF6 and a known good solvent, acetone, it was determined that BMIM PF6 behaves as a good solvent for PMMA. It was also observed that extended exposure to the electron beam during cryogenic transmission electron microscopy could damage the copolymer micelles and result in a reversal of contrast.magnified image

Alignment of Cylindrical Microdomains on a Grating Substrate by Binary Blends of Polystyrene-Poly(methyl methacrylate)

We have investigated the effect of blending on the orientation of cylindrical domains in binary mixture of asymmetric polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) block copolymers. Thin films of PMMA-cylinder-forming block copolymer were prepared on flat substrate with silicon oxide surface. Atomic force microscope observation reveals that the PMMA cylinders orient perpendicular to the substrate by tuning the film thickness. Further, the grating substrate was used to guide the alignment of the perpendicular cylinders. As a result, an array of highly ordered, hexagonally-packed PMMA cylinders in PS matrix with domain spacing of less than 30nm has been produced.

Chemical composition effects on the fracture of polystyrene‐block‐poly(methyl methacrylate)block copolymers

AbstractThe crazing and fracture behaviors of glassy–glassy block copolymers were investigated for polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) diblock copolymers that had similar overall molecular weights but different poly(methyl methacrylate) (PMMA) molar fractions. A liquid chromatography technique was applied to separate as‐synthesized PS‐b‐PMMA [(1) weight‐average molecular weight (Mw) = 94,000 g/mol and PMMA molar fraction = 0.35 and (2) Mw = 65,000 g/mol and PMMA molar fraction = 0.28] into three fractions with different chemical compositions. With a copper‐grid technique, the fracture behaviors of 0.5‐μm‐thick PS‐b‐PMMA films were studied as a function of the applied strain. For the higher Mw PS‐b‐PMMA samples, the median strains at crazing and fibril breakdown increased with an increase in the PMMA molar fraction from 0.24 to 0.46, corresponding to an increase in the chain entanglements in the PMMA domains. In contrast, for the lower Mw samples, the two values were not significantly changed even when the PMMA molar fraction was varied from 0.16 to 0.35. Mw of the minor component in PS‐b‐PMMA played a critical role in controlling the fracture behaviors of the block copolymers. Specifically, Mw/Me of the minor component (where Me is the molecular weight between entanglements) had to be roughly larger than 2 for the block copolymers to sustain sufficient strains before fracture. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3612–3620, 2006

Hydrodynamics and light scattering in solutions of a hyperbranched perfluorinated polyphenylenegermane-poly(methyl methacrylate) block copolymer

The dilute solutions of the hyperbranched perfluorinated polyphenylenegermane-PMAA block copolymer have been studied by dynamic and static light scattering and viscometry. It has been demonstrated that macromolecules of the block copolymer aggregate in all the solvents under study (methyl ethyl ketone, dioxane, and ethyl acetate) and form elongated micelles.

Octadecyl acrylate based block and random copolymers prepared by ATRP as comb-like stabilizers for colloidal micro-particle one-step synthesis in organic solvents

Three random and three block copolymers of methyl methacrylate (MMA) and octadecyl acrylate (ODA) were synthesised by atom transfer radical polymerisation. These copolymers were assessed for their application as stabilizers in the one-step non-aqueous dispersion polymerisation of MMA in a non-polar solvent mixture of hexane and dodecane. In all cases stable spherical micro-particle colloidal dispersions were formed with particle diameters in the range of 400–2730nm. Uniform monodisperse particles with standard deviations in size distributions of less than 5% were obtained in two cases demonstrating the utility of ODA:MMA copolymers as replacement preformed stabilizers in the one-step synthesis of MMA micro-spheres.

Partially fluorinated proton exchange membranes based on PVDF–SEBS blends compatibilized with methylmethacrylate block copolymers

This paper reports on a new route to prepare functional polymer blends for fuel cell's proton exchange membrane applications. Polyvinylidene fluoride (PVDF) and styrene-ethylene/butylene-styrene (SEBS) thermoplastic elastomer were melt blended and extruded into films. Interface modification using poly(methylmethacrylate-butylacrylate-methylmethacrylate) block copolymer (MAM), and two grades of poly(styrene-butadiene-methylmethacrylate) block copolymer was used to optimize the blends performance. The films made out of these blends were grafted with sulfonic acid moieties to obtain ionic conductivity leading to semi-fluorinated proton exchange membranes. The effect of varying the nature and concentration of the compatibilizer on the morphology and properties of a 50/50 wt.% PVDF/SEBS blends was investigated. SEM analysis showed that the addition of the block copolymers to the blends affected the morphology significantly and in the best case, that as low as 1 wt.% block copolymer was sufficient to dramatically reduces the segregation scale and improves mechanical properties. The samples were characterized in terms of morphology, microstructure and thermo-mechanical properties and in terms of conductivity, ion exchange capacity (IEC) and water uptake to establish the blends morphology–property relationships. Compatibilized blend membranes showed conductivities up to 3 × 10 −2 S cm −1 at 100% relative humidity, and an IEC = 1.69 meq g −1. Water swelling decreased for compatibilized blend membranes.

Inverted to Normal Phase Transition in Solution-Cast Polystyrene−Poly(methyl methacrylate) Block Copolymer Thin Films

We have investigated the inverted phase formation and the transition from inverted to normal phase for a cylinder-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer in solution-cast films with thickness about 300 nm during the process of the solution concentrating by slow solvent evaporation. The cast solvent is 1,1,2,2-tetrachloroethane (Tetra-CE), a good solvent for both blocks but having preferential affinity for the minority PMMA block. During such solution concentrating process, the phase behavior was examined by freeze-drying the samples at different evaporation time, corresponding to at different block copolymer concentrations, φ. As φ increases from ∼0.1% (v/v), the phase structure evolved from the disordered sphere phase (DS), consisting of random arranged spheres with the majority PS block as a core and the minority PMMA block as a corona, to ordered inverted phases including inverted spheres (IS), inverted cylinders (IC), and inverted hexagonally perforated lamellae (IHPL) with the minority PMMA block comprising the continuum phase, and then to the lamellar (LAM) phase with alternate layers of the two blocks, and finally to the normal cylinder (NC) phase with the majority PS block comprising the continuum phase. The solvent nature and the copolymer solution concentration are shown to be mainly responsible for the inverted phase formation and the phase transition process.

Development of Block Co-Polymers as Self-Assembling Templates for Magnetic Media and Spin-Valves

ABSTRACTPoly(styrene)-Poly(methylmethacrylate) block co-polymers (PS-b-PMMA) of appropriate block length and PS to PMMA ratio self-assemble into a 2-D hexagonal phase in which the PS majority phase is continuous and surrounds cylinders of the minority, PMMA phase. By UV irradiation and washing with acetic acid it is possible to remove the minority phase to leave empty channels. It is also possible to rearrange the PMMA phase with acetic acid to leave somewhat smaller pores. For most substrates the interactions between the polymer and the substrate surface are such that one block is preferentially adsorbed to the substrate resulting in alignment of the PMMA domains parallel to the substrate surface. It is possible to orient the polymer perpendicular to the surface by first adding a thin film of a random PS-PMMA co-polymer before applying the PS-b-PMMA block co-polymer. However thin films of the random PS-PMMA do not give good surface coatings, and thicker films are generally too thick for the pores in the PS-b-PMMA block co-polymer to be propagated to the substrate surface. For a few substrates, thin PS-b-PMMA films naturally adopt a perpendicular orientation after annealing, washing with acetic acid produces arrays of pores of diameter as small as 3 nm. For a number of other substrates the interaction between the polymer blocks and the surface is such that upon annealing the polymer rearranges to form micron sized domains which are not polymer coated, surrounded a areas which have a thicker polymer coating. We have observed this behavior with both carbon coated substrates and with ITO glass substrates. In both cases the areas of polymer are perpendicularly oriented, and upon washing with acetic acid give rise to pores that extend completely through the polymer film. In some cases films on ITO glass are continuous even after annealing. After washing with acetic acid it was possible to electrodeposit nickel into the pores to give nickel nano-pillars of 18 nm diameter.

Development of Block Co-Polymers as Self-Assembling Templates for Patterned Media

ABSTRACTBlock copolymers that self-organize are of interest as templates for patterned media, as they potentially provide a low cost fabrication route. Poly(styrene)-Poly(methylmethacrylate) block co-polymers (PS-b-PMMA) of appropriate block length and PS to PMMA ratio self-assemble into a 2-D hexagonal phase in which the PS majority phase is continuous and surrounds cylinders of the minority, PMMA phase. For application of this phase to patterned media it is necessary that the cylinders of the minority phase be oriented perpendicular to the substrate surface. This can be achieved by a number of methods, including appropriate choice of substrate and use of a random co-polymer underlayer. Appropriate substrates include H-terminated silicon, some carbon coatings and some ITO glasses. Use of an acetic acid wash causes the minority PMMA component can be induced to be rearranged, giving rise to pores perpendicular to the substrate. Electrodeposition of a metal into the pores produces a hardmask which can be used with ion-milling to transfer the block co-polymer pattern onto a magnetic thin film.

Synthesis of polyisoprene–poly(methyl methacrylate) block copolymers via a two‐electron‐transfer mechanism

AbstractSupramolecular complexes of alkali metals were used as catalysts in the polymerization of isoprene via a two‐electron‐transfer mechanism. The obtained polyisoprene, having a living end group, was subsequently used to initiate methyl methacrylate polymerization in tetrahydrofuran. Polyisoprene–poly(methyl methacrylate) block copolymers were obtained, and their structure was established with 1H NMR, gel permeation chromatography, differential scanning calorimetry, and experiments of selective extraction. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1086–1092, 2006

Development of high-temperature separation techniques for the chemical composition analysis of ethylene - methyl methacrylate block copolymers

AbstractEthylene - methyl methacrylate block copolymers are semicrystalline polymers that dissolve in organic solvents only at high temperatures. Accordingly, microstructure analysis by solution methods must be conducted at temperatures above 130°C. For the analysis of block copolymers of different compositions several analytical techniques were used, including high-temperature size-exclusion chromatography (SEC), hyphenated SEC-FTIR, and CRYSTAF (crystallisation analysis fractionation). While SEC with refractive index detection indicated a certain multimodality of the samples, SEC coupled with FTIR revealed that the samples were chemically inhomogeneous and may contain homo- and copolymer fractions. The presence of polyethylene and poly(methyl methacrylate) homopolymers in the copolymer samples was confirmed by CRYSTAF analysis, when the total concentration as well as the carbonyl group distribution were monitored separately. Chromatographic separation of the different sample components was achieved when liquid chromatography at critical conditions (LC-CC) was used. For the first time, true high-temperature LC-CC methods were developed operating at a column temperature of 140°C. As the stationary phase, silica gel was used. Suitable mobile phases were binary mixtures of 1,2,4-trichlorobenzene or 1,2- dichlorobenzene with cyclohexanone. Using LC-CC, the samples were separated into the copolymer and the homopolymer fractions.

Fluorescently tagged star polymers by living radical polymerisation for mucoadhesion and bioadhesion

The synthesis of 3-, 5- and 8-arm dimethylaminoethyl methacrylate star polymers are reported, final M n (PDI) = 12.2 K (1.09), 18.9K (1.10) and 38.4 K (1.11), respectively. The synthesis of 3-arm methyl methacrylate and dimethylaminoethyl methacrylate block co-polymer stars is also described. Living polymerisation occurred in all cases providing well defined stars with predictable molecular weights and narrow polydispersity. A fluorescent tag, 2-(8-methacryloyloy-3,6-dioxaoctyl)thioxantheno[2,1,9-dej]isoquinoline-1,3-dione, derived from a commercially available pigment, was incorporated into the star polymers. The fluorescence spectra of the polymers prepared were recorded over a range of pH and the peak emission frequency and intensity have been reported, λ ex = 462 nm. All of the multi-arm polymers exhibit fluorescence across a broad pH range with maximum emission at pH 4. A 3-arm star polymer has been demonstrated to show good bioadhesion in rat tissue. A reduced adhesion in epithelial tissues not covered by a viscoelastic mucus gel indicates an increased tendency for mucoadhesion over bioadhesion.

Kinetic study on reversible addition–fragmentation chain transfer (RAFT) process for block and random copolymerizations of styrene and methyl methacrylate

The degenerative (exchange) chain transfer constant C ex was determined for the dithioacetate-mediated living radical block and random copolymerizations of styrene (St) and methyl methacrylate (MMA) at 40 °C. The addition of the polystyrene (PSt) radical to a polymer–dithioacetate adduct (P–X) to form the intermediate radical (PSt–(X )–P) was (about twice) faster than that of the poly(methyl methacrylate) (PMMA) radical to form the intermediate radical PMMA–(X )–P. The fragmentation (release) of the PMMA radical from the PSt–(X )–PMMA intermediate formed at the initiating stage of block copolymerization was much (about 100 times) faster than the release of the PSt radical, explaining why the block copolymerization of MMA from a PSt–dithiocarbonate adduct is not so satisfactory as that of St from a PMMA–dithiocarbonate adduct. In the random copolymerization, there was implicit penultimate unit effect on the exchange chain transfer process, which appeared in the addition process but not in the fragmentation process.