Properties of Methacrylic Acid–Methyl Acrylate Copolymers of Varied Structure

Physicomechanical and surface properties of films of copolymers of methacrylic acid with methyl acrylate, which have close compositions and molecular masses (M_n ≈ 5.7 × 10⁴) and various chain structures (gradient copolymer and statistical copolymer), were studied. The thermodynamic characteristics of the copolymers were determined; two glass-transition points (29.6 and 141.0°C) were found for the gradient copolymer, and one glass-transition point of 40.1°C, for the copolymer with a statistical distribution of units along the chain. It was found that more mechanically strong films with tensile stress of 2.8 MPa are characteristic of the gradient copolymer. The wetting method was used to determine by using the Hood–Kaelble–Dann–Fowkes approach the surface Gibbs energies of the films and their polar and dispersion components. Atomic-force microscopy was used to find heterogeneities (0.1–0.3 μm) on the surface of a film of a statistical copolymer, whereas the film of a gradient polymer has a homogeneous structure.     

Effect of annealing on self-organized gradient film obtained from poly(3-[tris(trimethylsilyloxy)silyl] propyl methacrylate-co-methyl methacrylate)/poly(methyl methacrylate-co-n-butyl acrylate) blend latexes

The effect of annealing on the self-organized morphology and component gradient distribution of films prepared from bimodal latexes blend containing 1:1 silicon-containing acrylate copolymer/silicon-free acrylate copolymer blend was studied using attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy with X-ray energy-dispersive (SEM-EDX) spectrometry, and atomic force microscopy (AFM). The distribution of silicon through the whole thickness of the film as a function of annealing was investigated using confocal Raman spectroscopy (CRS). AFM results show that poly(methyl methacrylate-co-n-butyl acrylate) latex fuses to form a continuous film at 25?°C. The wettability of the acrylate components and the heterogeneous composition of poly(3-[tris(trimethylsilyloxy)silyl] propyl methacrylate-co-methyl methacrylate) result in a graded block film. ATR-FTIR and SEM-EDX measurements reveal silicon-containing components segregate at the film–air interface upon annealing. CRS further shows that the nonlinear model gradient distribution of silicon is obtained, where the content of silicon component is enhanced and it gradually varies in the bulk. When the annealing temperature increases to 120 and 180?°C, blend latexes films demonstrate varying topography and phase images, indicating phase separation is induced by annealing. Furthermore, CRS implies that the destruction of the gradient structure is attributed to the phase separation of the two blend components.     

Achieving structural control with thin polystyrene-b-polydimethylsiloxane block copolymer films: The complex relationship of interface chemistry,annealing methodology and process conditions

The structure of thin microphase-separated polystyrene-block-polydimethylsiloxane (PS–PDMS) films has been studied using state-of-the-art top-down and cross-sectional electron microscopy. This is the first time that the profile of PS–PDMS films has been measured in situ and these measurements allowed us to image the shape of the PDMS domains within the film as well as examine the wetting behavior of the block copolymer film on a variety of substrates. It was found that for each polymer, substrate chemistry and annealing method combination examined, there was a small range of film thicknesses whereby the films exhibited the optimal characteristics of high levels of ordering without dewetting or multilayering. Specifically, the optimum thickness for films treated by thermal annealing was greater than that for the equivalent solvent annealed film; a change that was correlated with morphology variations related to solvent swelling of the solvent annealed films. The surface chemistry also induced changes in the optimum film thickness. Selective surfaces were shown to control whether a PDMS wetting layer was formed or not, leading to either thicker or thinner wetting optimum film thicknesses; while undulating morphologies were observed for less selective surfaces. Concomitant changes in the periodicity were then hypothesized to occur as a result of confinement effects and the selectivity of the surface.     

Substrate surface energy dependent morphology and dewetting in an ABC triblock copolymer film

A gradient combinatorial approach was used to examine the effect of substrate surface energy on the morphology and stability of films of a poly(isoprene-b-styrene-b-ethylene oxide) triblock copolymer that exhibits an alternating gyroid morphology in the bulk. Atomic force microscopy data across our surface energy (water contact angle) library suggest a transformation to predominantly surface parallel lamellae with an antisymmetric ordering. For substrate water contact angles below 70 degrees the film exhibited autophobic dewetting from an adsorbed half-period triblock copolymer monolayer at longer annealing times. X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure analysis along gradient specimens indicated that the substrate surface energy governed the composition profile of the monolayer, and this variation in chemical expression was key to whether the film was stable or autophobically dewet. These observations demonstrate that enthalpic interactions, in addition to entropic considerations, can play a major role in autophobic dewetting of block copolymer films.     

Chemical synthesis and characterization of aniline and o-anthranilic acid copolymer

The chemical co-polymerization of aniline with o-anthranilic acid (AA) to form copolymer films has been made in aqueous hydrochloric acid medium. The copolymer films were monitored by using the quartz crystal microbalance (QCM) technique. The effect of AA and its concentrations on the film formation was investigated. The results were justified by measuring the UV-Vis absorption spectra for the in situ copolymer films grown onto glass slides immersed into the polymerization media and the in situ UV-Vis absorption spectra for the copolymer in the bulk during the co-polymerization. The conductivity for the copolymer films and powder pellets at different molar ratios of aniline/AA were measured. Also, the IR spectra, X-ray diffraction and the thermal gravimetric analysis for the copolymer powder formed in the bulk in the absence and presence of AA were measured and discussed. It is found that the presence of AA affects the yield, induction period, depletion time and growth rate of the film formation. It also affects the crystallinity, and conductivity as well as the solubility of the polymer. Finally, the dopant weight fraction (w) associated with the copolymer was determined. It is almost half the value determined for the polymer in absence of AA.     

Regulating aspects of biosoluble and insoluble film release systems containing protein proteinase inhibitor

New types of potent aprotinin-containing medicinal polymer films are elaborated for topical applications. The higher the temperature of drying, the lower the steam absorption, the film swelling, and the velocity of aprotinin in vitro release. The presence of antimicrobials having the basic functional groups contributed to compacting the structure of the films and retention of aprotinin in them. The velocity of aprotinin release from the films is regulated by adding different polymers. Inclusion of polyvinylpirrolidone in the film resulted in acceleration and increase of aprotinin release. This was probably because of increasing the film swelling by a factor of 1.7. Additional retention of the inhibitor in films was achieved by inclusion of sodium alginate and cellulose powder capable of binding aprotinin. Soluble bioadhesive films derived from a copolymer of acrylamide,N-vinyl-pirrolidone, ethyl acrylate (M _r 30,000-600,000) and aprotinin were obtained and analyzed. Kinetics of aprotinin release from biosoluble films was studied under various conditions. The duration of aprotinin release was comparable with duration of gradual dissolution of the matrix. Bioavailability of aprotinin from soluble films was linear with time.     

Stimuli-responsive mixed grafted polymer films with gradually changing properties: direct determination of chemical composition

Infrared spectroscopic ellipsometry (IRSE) and visible monochromatic ellipsometry (VISE) approaches were applied to investigate the chemical structure and thickness of ultrathin polymer films. Mixed polystyrene-poly(2-vinylpyridine) and polystyrene-poly(tert-butyl acrylate) polymer grafted films (mixed brushes) with gradually changing composition (1D gradient mixed brush) along the sample were prepared on a temperature gradient stage via two subsequent "grafting to" reactions. The films were characterized by high-precision mapping VISE at a single wavelength (632.8 nm) and IRSE. The set of 1D IRSE spectra of the polymer brush films obtained by mapping the 1D gradient brush were used to estimate the thickness and the local composition of the film and to construct the 1D map of the film in terms of the chemical composition of the brush. The results were compared with the data obtained using monochromatic ellipsometry where the brush composition was estimated from the results of two subsequent measurements followed each grafting step. The measurements of the brush thickness and composition with both methods were found to be in gratifying agreement. The results demonstrate the high potential of IRSE methods for the one-step characterization (by thickness and chemical composition) of ultrathin polymer films of complex composition.     

Crystal phase transformations within propylene/hexene-1 copolymers films as induced by direct current discharge treatment

The effect of a direct current discharge on the films of polypropylene and copolymers of propylene and hexene-1 synthesized with an isospecific catalytic system, rac-Me₂SiInd₂ZrCl₂-polymethylaluminoxane, was investigated. The treatment of isotactic polypropylene films by the discharge did not affect the ratio of crystalline phases in the polymer to a measurable extent. However, for the plasma treated films of copolymers of propylene and hexene-1 (the hexene-1 content of 1-2 mol%), a structural transformation of γ-modification into α-modification has been noticed. The observed phase transition has no apparent relation to any changes in microstructure of the copolymer chain because melting temperature values and the stereoregularity parameters of the samples remained practically unchanged. An experimental investigation of the specific influence exerted by individual components of a direct current discharge on the crystalline structure of copolymers has been undertaken. The exposure to a quantum component of the discharge did not induce any changes in the phase composition of the irradiated samples. The heating of the samples led to a negligible change of their phase composition. It has been determined that the surface of polypropylene and propylene/hexene-1 copolymer films facing the cathode in the course of the direct current discharge treatment had an accumulated negative charge Q > 10 nC/cm² which persisted for a long time afterwards. It has been suggested that the electrical field of a negative discharge may be the main cause of the γ-into α-phase transition in propylene/hexene-1 copolymers under the plasma effect. To verify this assumption, a propylene/hexene-1 copolymer film was charged under electron beam with energy of 4 keV. The electron beam treatment of the film resulted to the negative charge value of 11 nC/cm². The electron beam irradiation has induced the phase transition which was quite similar to the transition observed as the result of plasma treatment. So, it may be concluded that the phase transition from crystal γ-modification to α-modification under the effect of direct current discharge which has been investigated for copolymers of propylene and hexene-1 is induced by electric field of the negative charge accumulated at the surface layers of the films of the copolymers.     

Functionalized Soft Nanoporous Materials through Supramolecular Assembly of End‐Functionalized Polymer Blends

Supramolecular assembly through complementary interaction between molecular subgroups belonging to phase‐separating polymer species offers a great opportunity, not only for constructing nanoscale soft templates reminiscent of conventional block copolymer morphologies, but also for tailoring surface properties by facile removal of one of the structure components by cleaving complementary interactions. Herein we report the fabrication of a novel, organic, nanoporous film through supramolecular assembly of two complementarily, end‐interacting, mono‐end‐functionalized polymers under solvent annealing. The film of end‐functionalized polymer blends under solvent annealing yielded phase‐separated nanodomains that resemble nanoscopically ordered structures of block copolymers, but that are more advantageous due to easily cleavable and exchangeable links between the phase‐separated domains. The removal of one of the components of the precursor structure formed from the end‐functionalized polymers through cleavage of complementary interactions allowed us to fabricate mono‐ or multilayered nanoporous structures in which the chemically useful end‐functionalities of the remnant polymers are rich on the surface of the pores. The resultant, organic, nanoporous films with tailored surface functionality offer a useful platform for various chemical and biological applications.     

Formation of metastable structures by phase separation triggered by initial composition gradients in thin films

Phase separation kinetics of a binary (A,B) mixture contained in a thin film of thickness D induced by a quench from the one-phase region into the miscibility gap is studied by simulations using a Cahn-Hilliard-Cook model. The initial randomly mixed state (50% A, 50% B) contains a concentration gradient perpendicular to the film, while the surfaces of the film are "neutral" (no preference for either A or B). In thermal equilibrium, a pattern of large A-rich and B-rich domains must result, separated by domain walls oriented perpendicularly to the external surfaces of the thin film. However, it is shown that for many choices of D and the strength of the initial gradient Ψ(g), instead a very long-lived metastable layered structure forms, with two domains separated by a single interface parallel to the external walls. The transient time evolution that leads to this structure is interpreted in terms of a competition between domain growth in the bulk and surface-directed spinodal decomposition caused by the gradient during the initial stages. A surprising and potentially useful finding is that a moderate concentration gradient perpendicular to the film does not favor the layered structure but facilitates the approach toward the true equilibrium with just two domain walls perpendicular to the film. This mechanism may have useful applications in producing layered materials.     

pH sensor based on polyaniline and aniline–anthranilic acid copolymer films using quartz crystal microbalance and electronic absorption spectroscopy

The pH sensitivity based on conducting polyaniline (PANI) and copolymer of aniline and o‐anthranilic acid (AA) films were studied using quartz crystal microbalance (QCM) technique and UV–Vis spectroscopy. The sensor was constructed from these polymer films coated on the electrode of the QCM. The resonant frequency changes as a function of pH in the range of 2–12 were measured. These changes are quantitative indication of the degree of dedoping or redoping of the polymer films upon the subsequent exposure of the electrode to 0.25 M sulfuric acid and different pH solutions. There are two linear regressions between the frequency change and pH with two different and opposite slopes in the regions from 2 to 9 and 9 to 12. The pH sensitivity of the copolymer film was found to be less than using the PANI film. Thin films of PANI and copolymer, which were chemically polymerized in a sulfuric acid solution, were deposited onto the inner walls of the quartz cuvettes. The UV–Vis absorption spectra of these films were measured in different pH solutions. Relations between the maximum absorption and its wavelength versus pH were constructed. The copolymer film shows some advantages over the PANI film. The difference between the PANI and copolymer films as pH sensors using the QCM and electronic absorption extends from the determination of pK_a for both films. Copyright © 2008 John Wiley & Sons, Ltd.     

Chemical heterogeneity in emulsion copolymers of carboxylic monomers

Copolymer latices of butylacrylate (BA) with acrylic and methacrylic acid (AA and MAA) were prepared by batch type emulsion polymerization, and, for comparison, copolymers with identical monomer composition were prepared by batch type solution polymerization.The distribution of the carboxylic monomers in the latex particles and the serum was studied by density gradient and sedimentation experiments with the analytical ultracentrifuge. Dynamic mechanical measurements of films of these copolymers were used to determine the storage and loss moduli as a function of temperature. From these measurements the position and extension of the glass transition range on the temperature scale is obtained. For heterogeneous emulsion copolymers with two glass transition temperatures the distribution of the carboxylic monomer units in the different copolymer phases can be determined. Electron microscopy of ultra thin cross-sections of stained films gave further insight into the film morphology.The combination of the results obtained with the different methods gives rise to the following clues: In the BA/AA latices about 40% (by weight) of the total AA used in the recipe are found in the serum as a water soluble polymer, about 50% are found to increase the glass transition temperatureT _g of the bulk of the BA copolymer and, therefore, are thought to be incorporated into the interior of the latex particles, and the remaining 10% are, conclusively, located on the particle surface.In the BA/MAA latices no water soluble copolymer could be detected in the serum, about 90% of the MAA used is found in the bulk of the copolymer, and about 10% form a second hard phase on the surface of the latex particles.Dynamic mechanical measurements on the copolymer latex films show at least two phases with different glass transition temperatures: the bulk of the copolymer with a relatively low content of (M)AA units and a glass transition range at low temperatures, and a second (M)AA rich phase with a highT _g.The latter phase forms a honeycomb-like structure surrounding the packed latex particles. That results in a three-dimensional network of polymer with a highT _g extending throughout the latex film. In spite of the fact that this phase is built from a small fraction of the total copolymer only, it has a very pronounced influence on the performance behaviour of latex films.Dedicated to Professor Dr. R. Manecke on the occasion of his 70th birthday.     

Polymer‐Coated PtCo Nanoparticles Deposited on Diblock Copolymer Templates: Chemical Selectivity versus Topographical Effects

Metal–polymer hybrid films are prepared by deposition of polymer‐coated PtCo nanoparticles onto block copolymer templates. For templating, a thin film of the lamella‐forming diblock copolymer poly(styrene‐b‐methyl methacrylate) P(S‐b‐MMA) is chemically etched and a topographical surface relief with 3 nm height difference is created. Two types of polymer‐grafted PtCo nanoparticles are compared to explore the impact of chemical selectivity versus the topographical effect of the nanotemplate. A preferable wetting of the polystyrene (PS) domains with poly(styrenesulfonate) (PSS)‐coated PtCo nanoparticles (instead of residing in the space between the domains) is observed. Our investigation reveals that the interaction between PSS‐coated nanoparticles and PS domains dominates over the topographical effects of the polymer surface. In contrast, a non‐selective deposition of poly(N‐vinyl‐2‐pyrrolidone) (PVP)‐coated PtCo nanoparticles and the formation of large metal‐particle aggregates on the film is observed.     

pH-responsive copolymer films by surface-catalyzed growth

We have engineered a new class of pH-responsive polymer films on gold surfaces by first developing a controlled, surface-catalyzed polymerization to prepare a copolymer film consistent with poly(methylene-co-ethyl acetate) and subsequently hydrolyzing the ester side chains to varying extents to yield carboxylic acids (denoted as PM-CO2H). When pH is increased, the acid groups become deprotonated or charged, dramatically increasing their water solubility and greatly altering the film properties. The carboxylic acid content within the copolymer film can be adjusted by changing the monomer concentration ratio used in the polymerization process or the length of time for the hydrolysis. We have designed PM-CO2H films to consist predominately (>95%) of polymethylene (PM) so that the film is hydrophobic in the uncharged state and, thereby, exhibits an extremely large pH-induced response in barrier properties once ionized. The effect of polymer composition on pH response was investigated by electrochemical impedance spectroscopy (EIS), reflectance-absorption infrared spectroscopy (RAIRS), and contact angle measurements. At a 1%-4% molar acid content, the copolymer film exhibits a 5 orders of magnitude change in its resistance to ion transport over 2-3 pH units. The pH at which this response begins can be tailored from pH 5 to pH 10 by decreasing the acid content in the film from 4% to 1%.     

Radiation‐induced fabrication of polymer nanoporous materials from microphase‐separated structure of diblock copolymers as a template

Polymer nanoporous materials with periodic cylindrical holes were fabricated from microphase‐separated structure of diblock copolymers consisting of a radiation‐crosslinking polymer and a radiation‐degrading polymer through simultaneous crosslinking and degradation by γ‐irradiation. A polybutadiene‐block‐poly(methyl methacrylate) (PB‐b‐PMMA) diblock copolymer film that self‐assembles into hexagonally packed poly(methyl methacrylate) cylinders in polybutadiene matrix was irradiated with γ‐rays. Solubility test, IR spectroscopy, and TEM and SEM observations for this copolymer film in comparison with a polystyrene‐block‐poly(methyl methacrylate) diblock copolymer film revealed that poly(methyl methacrylate) domains were removed by γ‐irradiation and succeeding solvent washing to form cylindrical holes within polybutadiene matrix, which was rigidified by radiation crosslinking. Thus, it was demonstrated that nanoporous materials can be prepared by γ‐irradiation, maintaining the original structure of PB‐b‐PMMA diblock copolymer film. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5916–5922, 2007     

From self-assembled monolayers to chemically patterned brushes: Controlling the orientation of block copolymer domains in films by substrate modification

Block copolymer lithography is emerging as one of the leading technologies for patterning nanoscale dense features. In almost all potential applications of this technology, control over the orientation of cylindrical and lamellar domains is required for pattern transfer from the block copolymer film. This review highlights the state-of-art development of brushes to modify the substrates to control the assembly behaviors of block copolymers in films. Selected important contributions to the development of self-assembled monolayers, polymer brushes and mats, and chemically patterned brushes are discussed.     

Polymer Nanostructures by Forced Assembly: Process,Structure, and Properties

The process of micro- and nanolayer coextrusion of polymeric systems with good layer uniformity is described. Coextrusion through a series of layer multiplying die elements has enabled the production of films containing tens to thousands of layers with individual layer thicknesses from the micro- to the nanoscale. Improvements in layer uniformity are discussed through optimization of layer multiplier die design, selection of viscosity matched polymer systems, and incorporation of surface layer capabilities. Design of ‘uneven’ split layer multiplication dies has enabled the coextrusion of layered films with a wide variety of layer thickness distributions having up to a 10× difference in the individual film layer thicknesses. Coextrusion of layered polymer films with individual layer thicknesses down to the nanoscale has resulted in the production of novel systems with improved properties. Nanolayered polymer films were utilized to develop an all-plastic polymer laser, to fabricate gradient refractive index lenses, and to investigate gas barrier enhancement of crystalline polymer nanolayers confined to induce a high aspect ratio, in-plane, single-crystal-like lamellar structure.     

The effect of composition and structure on dielectric characteristics of films based on poly(vinyl alcohol) cyano ether

The composition, bulk structure, and supramolecular structure of poly(vinyl alcohol) cyano ether are studied by the methods of IR and high-resolution NMR spectroscopy and by atomic force microscopy. According to the data on the parameter of blockiness (η = 1.03), this copolymer is characterized by a random structure; the content of residual acetate groups is below the detection level of the applied methods. When the films are formed by screen printing, owing to the high orientation of polymer in the direction perpendicular to the direction of the supporting plane, the dielectric permeability of the films is higher than that of the films prepared by film casting. Films with a thickness of 20–40 μm are prepared, and their dielectric permeability approaches 23.     

Physical Continuity and Vertical Alignment of Block Copolymer Domains by Kinetically Controlled Electrospray Deposition

The fabrication of block copolymer (BCP) thin films is reported with vertically aligned cylindrical domains using continuous electrospray deposition onto bare wafer surfaces. The out‐of‐plane orientation of hexagonally packed styrene cylinders is achieved in the “fast‐wet” deposition regime in which rapid evaporation of the solvent in deposited droplets of polymer solution drives the vertical alignment of the self‐assembled structure. Thermally activated crosslinking of the polybutadiene matrix provides kinetic control of the morphology, freezing the vertical alignment and preventing relaxation of the system to its preferred parallel orientation on the nontreated substrate. Physically continuous vertically oriented domains can be achieved over several micrometers of film thickness. The ability of electrospray deposition to fabricate well‐ordered and aligned BCP films on nontreated substrates, the low amount of material used relative to spin‐coating, and the continuous nature of the deposition may open up new opportunities for BCP thin films.

     

Phase behavior in thin films of cylinder-forming ABA block copolymers: experiments

We experimentally establish a phase diagram of thin films of concentrated solutions of a cylinder forming polystyrene-block-polybutadiene-block-polystyrene triblock copolymer in chloroform. During annealing the film forms islands and holes with energetically favored values of film thickness. The thin film structure depends on the local thickness of the film and the polymer concentration. Typically, at a thickness close to a favored film thickness parallel orientation of cylinders is observed, while perpendicular orientation is formed at an intermediate film thickness. At high polymer concentration the cylindrical microdomains reconstruct to a perforated lamella structure. Deviations from the bulk structure, such as the perforated lamella and a wetting layer are stabilized in films thinner than approximately 1.5 domain spacings.