Bulk Copolymerization Research Articles

C60 fullerene inclusions in low-molecular-weight polystyrene–poly(dimethylsiloxane) diblock copolymers

Abstract We have synthesized low-molecular-weight diblock copolymers of polystyrene- block -poly(dimethylsiloxane) with total molecular weights 60 added. The C 60 was shown to selectively segregate into the PS phase only although its solubility limit is ∼1 wt%. Although the C 60 aggregates above 1 wt%, the cylindrical morphology observed in the pure copolymer bulk samples persists in the C 60 -copolymer composites even up to 10 wt% C 60 loading. In thin films, the pure copolymer possesses a highly ordered morphology with grains hundreds of microns across. When C 60 is blended with the copolymer the high degree of order rapidly decreases due to increasing numbers of defects observed.

Surface properties of poly(ethylene oxide)‐based segmented block copolymers with monodisperse hard segments

AbstractThe surface properties of segmented block copolymers based on poly(ethylene oxide) (PEO) segments and monodisperse crystallizable tetra‐amide segments were studied. The monodisperse crystallizable segments (T6T6T) were based on terephthalate (T) and hexamethylenediamine (6). Due to the crystallinity of T6T6T being high (∼ 85%), the amount of amorphous T6T6T dissolved in the polyether phase was limited. The length of the PEO segments was varied (between 600 and 4600 g/mol) and effect of extending the PEO segments with terephthalic groups was investigated. Studied was the hydrophilicity of the surface by contact angle measurements and of the bulk copolymers by water absorption measurements The results were compared with data of PEO‐poly(butylene terephthalate) (PEO‐PBT) copolymers. For a given hydrophilicity of the bulk copolymer, the surface hydrophilicity decreased in the order PEO‐PBT, PEO‐T6T6T, and (PEO‐T)‐T6T6T. The use of short monodisperse hard segments resulted in low contact angles, with a lowest observed value of ∼ 29°. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

In Situ Synthesis and Alignment of Au Nanoparticles within Hexagonally Packed Cylindrical Domains of Diblock Copolymers in Bulk

We present a simple method to prepare hexagonally packed metallic nanocylinders based on gold nanoparticles embedded in a copolymeric matrix. The gold nanoparticles are generated selectively within the P4VP-rich cylindrical domains of a polystyrene-b-poly-4-vinylpyridine (PS-b-P4VP) diblock copolymer. In order to achieve this selectivity, a gold precursor (HAuCl4) is coupled to the pyridine blocks of a spherical PS327-b-P4VP27 block copolymer. In consequence, the hybrid block copolymer is able to self-assemble in a hexagonally packed cylinders morphology. The application of mechanical oscillatory shear improved markedly the alignment of these nanocylinders, while simultaneously the gold precursor was reduced in situ into gold nanoparticles. Following rheological characterization in the linear viscoelastic regime, a set of alignment parameters were comprehensively selected and checked with a series of transmission electron microscopy (TEM) micrographs. An optimal temperature of alignment was found after systematic evaluation of samples sheared at different temperatures. The block copolymer exhibited an increase in the domain period as a consequence of chain rearrangements around the newly formed gold nanoparticles. The hexagonally packed morphology was preserved, and under the optimal conditions single grain sizes showed significant improvement to macroscale order in comparison to nonaligned samples. In contrast to current multistep lithographic techniques, the present method constitutes a simple path to produce three-dimensional organic-inorganic conductive nanowires with periodicities at the macroscopic level.

Continuous Concentric Lamellar Block Copolymer Nanofibers with Long Range Order

Fibers with long-range ordered internal structures have applications in various areas such as photonic band gap fibers, optical waveguides, wearable power, sensors, and sustained drug release. Up to now, such fibers have been formed by melt extrusion or drawing from a macroscopic preformed rod and were typically limited to diameters >10 microm with internal features >1 microm (Abouraddy, A. F.; et al. Nat. Mater. 2007, 6, 336). We describe a new class of continuous fibers and fibrous membranes with long-range ordered concentric lamellar structure that have fiber diameters and feature sizes 2-3 orders of magnitude smaller than those made by conventional methods. These fibers are created through confined self-assembly of block copolymers within core-shell electrospun filaments. In contrast to the copolymer in bulk or thin films, the domains of the concentric lamellar structure are shown here to vary quantitatively with (radial) position and to exhibit a novel dislocation that accommodates variations in fiber diameter robustly, permitting for the first time the realization of long-range order in technologically meaningful, continuous fibers with approximately 300 nm diameter and 50 nm radial period.

Application of photo initiation copolymerization during the preparation of polymethacrylimide copolymer foam

AbstractUsing methacrylic acid (MAA), acrylonitrile (AN), and acryl amide (AM) as monomers, a new high‐performance PMI copolymer foam was prepared via radical bulk copolymerization and free heat foaming; afterward, the effects of photo initiation polymerization technology on the foam mechanical and craft performances were further researched. The results showed that photo initiation technology was only fit to be used as the prepolymerization reaction during the preparation of PMI copolymer foam, and it was faster and more easily controlled than thermal initiation prepolymerization. Photo initiation prepolymerization could eliminate not only the foam inner flaws, but also the size nonuniformity of the foam cells effectively. Accordingly, photo initiation prepolymerization is able to make the foam uniform, transparent, stable, and isotropy, and moreover improve the foam tensile strength. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Copolymerization of styrene with acrylonitrile and maleic anhydride

The complex formation constants for styrene (donor)-acrylonitrile (acceptor) and styrene-maleic anhydride (acceptor) systems are found to be 0.19 ± 0.01 and 0.28 ± 0.01 l/mol (1H NMR, CCl4, 298 K); the same values are characteristic for three-component systems of these monomers. The calculated ΔH 0 values (the AM1 method) for styrene-acrylonitrile (C1) and styrene-maleic anhydride (C2) complexes comprise −1.24 and −2.30 kJ/mol. Changes in charges on double bonds of complex-bonded molecules are in the range from 0.001 to 0.006 au. These values are typical of π-π complexes. By analyzing the composition and rate of bulk copolymerization (333 K, 0.03 mol/l AIBN), we have shown that two complexes are involved in chain propagation: r 1 = $$ k_{2C_1 } /k_{2C_2 } $$ = 0.26 ± 0.015 and r 2 = $$ k_{3C_2 } /k_{3C_1 } $$ = 4.17 ± 0.143.

Thermal and mechanical properties of copolymers of methyl methacrylate with N‐aryl itaconimides

AbstractThe article describes the preparation of cast copolymer sheets of methyl methacrylate with varying mole fractions of N‐(p‐methoxyphenyl) itaconimide/N‐(2‐methoxy‐5‐chlorophenyl) itaconimide/N‐(3‐methoxy‐5‐chlorophenyl) itaconimide monomers by bulk copolymerization using azobisisobutyronitrile as an initiator. The effect of incorporation of varying mole fractions of N‐arylsubstituted itaconimides in poly(methyl methacrylate) (PMMA) backbone on the thermal, optical and physicomechanical properties of cast acrylic sheets were evaluated. The glass transition temperature and the thermal stability increased with increasing amounts of itaconimides in the polymer backbone. An increase in tensile strength, flexural strength, and storage modulus was also observed. The impact strength decreased marginally upon incorporation of imides into the polymer backbone. A slight decrease in the transparency and a significant increase (4–50%) in the haze was observed. The chemical resistance of PMMA remains unaffected by copolymerization. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

A Novel Method to Prepare PolyGMA and its Application to Immobilization of β‐Galactosidase

The reactive, macroporous and massive epoxy group containing polyGMA was synthesized simultaneously with methanol aqueous solution and nano‐calcium carbonate as porogen by bulk copolymerization. After the polymer was smashed, particles with diameters in the range of 0.30 to 0.45 mm were taken as the carrier and the scanning electron microscopy (SEM) micrographs were done to characterize its surface structure. Under the optimum conditions, β‐galactosidase was immobilized on the supporter obtained above and the enzyme activity bound per gram drier carrier could attained up to 77.33％, which was much higher than that bound on the carrier prepared by only using methanol aqueous solution as porogen. The conclusion obtained indicated that the ployGMA prepared concurrently with liquid and solid porogen was more suitable to immobilize enzyme because of the much more porous surface structure obtained.

MEASUREMENTS OF MONOMER REACTIVITY RATIOS FOR COPOLYMERIZATION OF STYRENE AND METHYL METHACRYLATE IN CARBON DIOXIDE AT VAPOR-LIQUID EQUILIBRIUM STATE

The monomer reactivity ratios of free radical copolymerization of styrene and methyl methacrylate in carbon dioxide at vapor-liquid equilibrium state (vlCO2) at 65°C and under 7.5–8.5 MPa were measured. The experimental results showed that, in comparison with the data in bulk copolymerization, the monomer reactivity ratio of St in vlCO2 increased acompanied by a somewhat decrease in that of MMA. Further analysis of the sequence distributions of these copolymers by 1H-NMR spectra indicated that there was a significant bootstrap effect in this system. The local monomer concentrations in the proximity of growing free radicals, rather than the true reactivity of monomers or free radicals, were altered by the presence of vlCO2, leading to the change in monomer reactivity ratios.

Study of multiblock polyamide-6/Poly-(isoprene) copolymers by positron annihilation spectroscopy

Abstract Positron annihilation lifetime spectroscopy (PALS) has been used to determine the free volume in multiblock polyamide-6/poly-(isoprene) copolymers (PA-6/PI), synthesized via activated anionic bulk copolymerization. The diisocyanate functionalized telechelic PI, blocked with caprolactam (CL) has been used as a commoner and an activator at the same time. The elastic PI block incorporated into the main chain of PA-6 affects the amorphous and crystal phase of the copolymer leading to changing in degree of crystallinity. The positron annihilation lifetime spectroscopy (PAL) and Doppler broadening of annihilation line (DBAL) technique in a set of pure PA-6 and PA-6/PI copolymers with two different compositions have been applied and evaluation of the size of free-volume holes (pores), localized mainly in the disordered regions of the PA-6/PI copolymer by measuring the o-Ps lifetime (τ3) and o-Ps intensity (I3) has been performed.

Effect of polymethylmethacrylate–montmorillonite nanocomposite on the release of some biologically active 1,2,4‐triazine derivatives

AbstractMethylmethacrylate chloromethylstyrene copolymer–montmorillonite (PMMA–MMT) intercalated nanocomposite was prepared by bulk copolymerization of methylmethacrylate (MMA) and chloromethylstyrene (2 wt%) followed by phosphonium salt formation. The intercalation of polymeric phosphonium salt into montmorillonite was achieved through an ion exchange process between sodium cations in MMT and phosphonium groups attached to the copolymer. Thermogravimetric analysis (TGA) showed improved thermal stability for the intercalated nanocomposite in comparison with the pure PMMA. Biologically active compounds including 4‐amino‐6‐methyl‐3‐thioxo‐3,4‐dihydro‐2H‐[1,2,4]triazin‐ 5‐one (I), 4‐amino‐6‐methyl‐3,4‐dihydro‐2H‐[1,2,4]triazin‐3,5‐dithione (II), 4‐amino‐6‐(4‐methoxystyryl)‐3‐thioxo‐3,4‐dihydro‐2H‐[1,2,4]triazin‐5‐one (III), and 4‐amino‐6‐styryl‐3‐thioxo‐3,4‐dihydro‐2H‐[1,2,4]triazin‐5‐one (IV) have been prepared and reacted with PMMA–MMT intercalates and ion exchanged with sodium montmorillonite (MMT) in the presence of HCl. Infrared spectra (IR) show bands characteristic to amide linkage between triazine derivatives and PMMA. These nanocomposites have been characterized by X‐ray diffraction (XRD) and transmission electron microscope (TEM). The release of biologically active compounds intercalated layered silicates is controllable and these materials have a great potential as a delivery host in the pharmaceutical field. The effect of temperature and presence of saline solution on the release was studied. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Self-Assembly of Star ABC Triblock Copolymer Thin Films: Self-Consistent Field Theory

Microphase separation and morphology of star ABC triblock copolymers confined between two identical parallel walls (symmetric wetting or dewetting) are investigated with self-consistent field theory (SCFT) combined with the "masking" technique to describe the geometric confinement of the films. In particular, we examine the morphology of confined near-symmetric star triblock copolymers under symmetric and asymmetric interactions as a function of the film thickness and the surface field. Under the interplay between the degree of spatial confinement, characterized by the ratio of the film thickness to bulk period, and surface field, the confined star ABC triblock copolymers are found to exhibit a rich phase behavior. In the parameter space we have explored, the thin film morphologies are described by four primary classes including cylinders, perforated lamellae, lamellae, and other complex hybrid structures. Some of them involve novel structures, such as spheres in a continuous matrix and cylinders with alternating helices structure, which are observed to be stable with suitable film thickness and surface field. In particular, complex hybrid network structures in thin films of bulk cylinder-forming star triblock copolymers are found when the natural domain period is not commensurate with the film thickness. Furthermore, a strong surface field is found to be more significant than the spatial confinement on changing the morphology of star triblock copolymers in bulk. These findings provide a guide to designing novel microstructures involving star triblock copolymers via geometric confinement and surface fields.

Surfactant-Free, Controlled/Living Radical Emulsion Polymerization in Batch Conditions Using a Low Molar Mass, Surface-Active Reversible Addition-Fragmentation Chain-Transfer (RAFT) Agent

The purpose of this paper was to study the application of a surface-active trithiocarbonate RAFT agent, the 2-(dodecylthiocarbonothioylthio)-2-methylpropanoic acid, sodium salt (TTCA) in surfactant-free, ab initio, batch emulsion polymerization. Because of the highly water-soluble character of the leaving group favoring exit from the micelles or the particles over reinitiation, the polymerization of styrene was completely inhibited. In contrast, the polymerization of n-butyl methacrylate was fast and led to small, stable particles, demonstrating the good stabilizing efficiency of TTCA. However, the control over molar mass was not effective, as homopolymers with high molar mass were formed. This was related to the inappropriate leaving/initiating group and low chain transfer constant of the RAFT agent in the free-radical polymerization of methacrylic esters and was also observed in bulk. This poor efficiency was overcome by copolymerizing n-butyl methacrylate with a low percentage of styrene or n-butyl acrylate. In this case, the bulk copolymerization led to controlled copolymers with predicted molar mass and narrow molar mass distribution and the chain transfer efficiency was similarly high in surfactant-free emulsion polymerization. The good colloidal characteristics of the latexes with the stabilizing group attached at the chain-end were maintained, leading to autostabilized latexes with small particle diameter, below 150 nm. This work is the first example of the direct and efficient use of a surface-active, low molar mass, RAFT agent in emulsifier-free, batch emulsion polymerization, leading simultaneously to a good control over molar mass and narrow molar mass distribution, together with good colloidal properties.

Reactivity ratios and monomer partitioning in the microemulsion copolymerization of vinyl acetate and butyl acrylate

AbstractThe true monomer reactivity ratios for the vinyl acetate/butyl acrylate system were determined with experimental data from the cumulative copolymer composition at low, intermediate, and high conversions and with the monomer partitioning among the aqueous, microemulsion droplet, and polymer particle phases taken into account. A mixture of sodium dodecyl sulfate and poly(ethylene oxide) (23) dodecyl ether (Brij‐35; 3 : 1 w/w) was used as a stabilizer. Potassium persulfate was used as an initiator. The true values of the monomer reactivity ratios were 0.028 ± 3.2 × 10−3 for vinyl acetate and 6.219 ± 3.1 × 10−1 for butyl acrylate, and these were in agreement with those reported in the literature for bulk copolymerizations but differed from values reported for other compartmentalized copolymerizations. Thus, these results indicate that the monomer partitioning and cumulative copolymer composition throughout the reaction have to be duly accounted for in the determination of monomer reactivity ratios in heterogeneous polymerizations. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Ordering of Cylindrical Domain of Block Copolymers under Moving Temperature Gradient: Effects of Moving Rate

In a previous paper (Macromolecules 2007, 40, 5923), we reported that a zone heating method, which imposes the moving temperature-gradient (∇T) field on ordering process of various melts in general, enabled to control a macroscopic orientation of hexagonally packed cylindrical microdomain structures (hex-cyl) of block copolymer (bcp) bulk. In this report, we have investigated how the variation of the moving rate of ∇T affects the macroscopic orientation by using two kinds of polystyrene-block-polyisoprene bcps having different mobility. We found that the upper limit of the moving rate required to induce the unique texture and orientation of hex-cyl became large with increasing the mobility of the bcps. These results indicate that the moving rate should be smaller than the intrinsic growth rate of the hex-cyl grains in the undercooled disordered melt.

Ordering of Cylindrical Domains of Block Copolymers under Moving Temperature Gradient: Separation of ▽T-Induced Ordering from Surface-Induced Ordering

In a previous paper [Mita et al. Macromolecules 2007, 40, 5923], we reported that the zone heating method applied to the block copolymer bulk forming hexagonally packed cylindrical (hex-cyl) microdomain structure enables to develop unique columnar grains macroscopically extended along the temperature gradient (▽T) axis and that within the grain hex-cyl has a fixed orientation: Both the cylinder axis and the (100) plane of hex-cyl are normal to the ▽T axis, and the rotational angle of the cylinder around the ▽T axis is fixed also. We believe the method involves the ordering under two external fields coupled together: one is a field induced by a glass surface, and the other is a field induced by a moving ▽T. In this paper, we aim to separate effects of the two fields on the ordering of hex-cyl in order to clarify the effects intrinsic in the moving ▽T field. For this purpose, we tilt the glass surface with respect to ▽T direction by an angle of 45°. Small-angle X-ray scattering studies revealed that the mov...

Emulsion and controlled miniemulsion polymerization of the renewable monomer γ‐methyl‐α‐methylene‐γ‐butyrolactone

AbstractThe kinetics of free‐radical emulsion polymerization of γ‐methyl‐α‐methylene‐γ‐butyrolactone (MeMBL), a renewable monomer related to methyl methacrylate, are presented in detail for the first time, and stable polymer latices are prepared. The effects of different reaction parameters on free‐radical emulsion polymerization of MeMBL are presented. Homogeneous nucleation is asserted to be the dominant path for particle formation. Miniemulsion copolymerization of MeMBL and styrene is also reported. In this case, the homogeneous nucleation process appears limited when using an oil soluble initiator. Both the RAFT miniemulsion polymerizations and RAFT bulk polymerizations are well controlled and narrow polydispersity copolymers are produced. Rate retardation is observed in the RAFT miniemulsion polymerizations compared with the free‐radical polymerization and RAFT bulk polymerizations and the possible causes of the retardation are discussed. The reactivity ratios of MeMBL and styrene in RAFT bulk copolymerization are also determined. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5929–5944, 2008

INFLUENCE OF MONOMER COMPOSITION ON THE CHAIN TRANSFER COEFFICIENT IN METHYL METHACRYLATE/BUTYL ACRYLATE RAFT COPOLYMERIZATION

The bulk copolymerization of butyl acrylate (BA) and methyl methacrylate (MMA) in the presence of the RAFT agent with Z=—CH_2C_6H_5 and 2,2′-Azobis(isobutyronitrile)(AIBN) as an initiator was carried out at 60℃.The chain transfer coefficients (C_ tr ) at different monomer compositions were determined by the GPC peak resolution method.In the BA homopolymerization,C_ tr was up to 116 while it was about 0.1 in the MMA homopolymerization.Since C_ tr was too low,the homopolymerization of MMA mediated by the RAFT agent was out of control.In the copolymerization systems,C_ tr showed a nonlinear decrease with the increasing of MMA compositions.When a small fraction of BA was added to an MMA polymerization system,the polymerization became well controlled with PDI around 1.2 at the end of the polymerization.The changing trend of C_ tr with monomer compositions well explained the profiles of the molecular weight and its distribution against conversion with different monomer compositions.

A Mathematical Model of the Bulk Copolymerization of Styrene and Acrylonitrile in the Presence of Polystyrene‐block‐Polybutadiene

AbstractThe bulk copolymerization of styrene and acrylonitrile in the presence of SB using BPO as initiator was investigated. Reactions were carried out at 80 °C with different initial SB concentrations. Global variables, such as conversion and cumulative grafting efficiency of SAN, were determined during the prepolymerization. The isolated non‐grafted SAN was also analyzed to determine its average molar masses and composition. A mathematical model was developed, and theoretical predictions were compared with experimental data. A good agreement between measurements and simulations was obtained from a heterogeneous model when BPO was evenly distributed between phases.magnified image

Contrast Inversion in TEM Studies of Poly(ferrocenylsilane)‐block‐Poly(dimethylsiloxane) Diblock Copolymers

AbstractThis paper describes an unusual contrast inversion phenomenon in TEM imaging of PFS‐b‐PDMS block copolymer bulk samples. It is clearly observed especially in samples that show a lamellar morphology that the contrast inversion is accompanied by a contraction of the PDMS domains and an expansion of the Fe‐rich domains. The location of the iron‐ and silicon‐rich domains was monitored by EDX analysis. We infer that the contrast inversion was caused by electron beam radiation‐induced damage to, and possible cross‐linking of, PDMS chains. A simple way to selectively deposit metal on electron beam patterned polymer film was demonstrated.magnified image