Modification of Silica Nanoparticles with Miktoarm Polymer Brushes via ATRP

Silica nanoparticles were successfully modified with miktoarm brushes via atom transfer radical polymerization (ATRP) using three different approaches. In the first approach: “graft onto and from”, a poly(tert-butyl acrylate) (PtBA) macroinitiator was grafted onto the surface of a monomer-modified silica nanoparticle. Then, polystyrene (PSt) brush was grafted from the surface-tethered reactive chain end. In the second approach: “two-step reverse ATRP”, the PtBA and poly(n-butyl acrylate) (PBA) brushes were consecutively grafted from initiator-modified silica particles via ATRP. The polymerization was initiated from the silica surface via a two-step controlled thermal decomposition of surface-tethered diazo initiator moieties. In the third method: “diblock first”, a diblock copolymer of poly(tert-butyl acrylate) and poly(glycidyl methacrylate) (PtBA-b-PGMA) was grafted onto amine-modified silica particles. The diblock copolymer was covalently attached to the silica surface via interaction between surface-tethered amine groups and the short reactive block containing glycidyl groups. Next, the polystyrene brushes were grafted from surface-tethered reactive chain end. The materials prepared by three different approaches were characterized using gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). The PtBA brushes were hydrolyzed under acidic conditions to form poly(acrylic acid) (PAA) brushes. The resulting materials were imaged using atomic force microscopy (AFM) and transmission electron microscopy (TEM).     

Functionalization of MWCNT with P(MMA-co-S) copolymers via ATRP: Influence on localization of MWCNT in SAN/PPE 40/60 blends and on rheological and dielectric properties of the composites

In this work, the localization of functionalized multi-walled carbon nanotubes (MWCNT) with random copolymers of methyl methacrylate and styrene (P(MMA-co-S)) in poly(styrene-co-acrylonitrile)/poly(2, 6-dimethyl-1,4-phenylene ether) blends (SAN/PPE) and its influence on morphological, rheological and dielectric properties of the composites were investigated. P(MMA-co-S) copolymers were grafted onto MWCNT via atom transfer radical polymerization (ATRP). The molecular weight of the copolymers was adjusted by controlling the time of reaction. In SAN/PPE blends, MWCNT grafted with low molecular weight copolymers were predominantly located at the interface of the blend and a few individual tubes were dispersed in the PPE phase. Aggregation of MWCNT was observed nearby the interfacial region because of micellization of grafted copolymers. Aggregation was more pronounced with increasing molecular weight of the grafted P(MMA-co-S) copolymer. In the melt, the composite containing MWCNT with low molecular weight copolymers had higher dynamic moduli than the one with pristine MWCNT. An increasing molecular weight of grafted copolymer led to a softening effect which resulted in a reduction of the moduli of the composite. Although a pronounced enhancement was observed for the composites with pristine MWCNT, only a small increase in electrical conductivity was achieved by adding functionalized MWCNT owing to the poor network formed by functionalized MWCNT in the blends.     

Impact-modified poly(styrene-co-acrylonitrile) blends containing both oxazoline-functionalized poly(ethene-co-1-octene) elastomers and poly(styrene-co-maleic anhydride) as compatibilizer

Blends of a poly(styrene-co-acrylonitrile) (SAN) with poly(ethene-co-1-octene) rubber (EOR) were investigated. An improved toughness–stiffness balance was obtained when adding as a compatibilizer a blend consisting of oxazoline-functionalized EOR, prepared by grafting EOR with oxazoline-functional maleinate, and poly(styrene-co-maleic anhydride) (SMA), which is miscible with SAN. Enhanced interfacial adhesion was evidenced by the improved dispersion of the EOR in the SAN matrix and the reduced glass transition temperature of the dispersed EOR phase. Morphology studies using transmission electron microscopy revealed formation of an interphase between the matrix and the rubber particles. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1685–1695, 1999     

Effect of dehydrochlorination of PVC on miscibility and phase separation of binary and ternary blends of poly(vinyl chloride), poly(ethylene-co-vinyl acetate) and poly(styrene-co-acrylonitrile)

The enhancement of miscibility at the lower critical solution temperature (LCST) of the blends poly(vinyl chloride)/poly(ethylene-co-vinyl acetate) (PVC/EVA), poly(vinyl chloride)/poly(styrene-co-acrylonitrile) (PVC/SAN) and poly(vinyl chloride)/poly(ethylene-co-vinyl acetate)/poly(styrene-co-acrylonitrile) (PVC/EVA/SAN) was observed at the micron level. Such miscibility is attributed to the dehydrochlorination and formation of hydrogen bonds between blend components. However, macrolevel immiscibility of these blends heated to the LCST was observed. Such microdomain compatibility of these blends gives a synergistic character. Brittle-type failure observed for LCST samples testifies to the synergism in treated blends. ©1997 SCI     

Morphology and physical properties of SAN/NBR blends: The effect of AN content and melt viscosity of SAN

To study the effect of dispersed poly(butadiene-co-acrylonitrile) (NBR) rubber size on the physical properties of poly(styrene-co-acrylonitrile) (SAN)/NBR blends, SANs with various melt viscosities and acrylonitrile (AN) contents were examined. The dispersed size of NBR, whose AN content is 30 wt %, was reduced as the melt viscosity of the SAN matrix was increased or as the AN content of the SAN matrix was reduced in the range of 19–32 wt %. As the melt viscosity of the SAN matrix was increased, the damping peak of the NBR phase moved to a higher temperature, and as the AN content of SAN was reduced, the damping peak of the SAN phase moved to a lower temperature. Higher values of impact strength and elongation at break and reduced yield behavior at a low shear rate were observed at a finer dispersion of NBR. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 935–941, 1999     

Synthesis of poly(tetrafluoroethylene)/poly(butadiene) core-shell particles and their graft copolymerization

This article describes how to convert the unreactive surface of poly(tetrafluoroethylene) (PTFE) into poly(styrene-co-acrylonitrile) (SAN). Composite particles with a crosslinked poly(butadiene) (PB) shell covered over a PTFE core were prepared by an emulsifier-free seeded emulsion polymerization of butadiene in the presence of PTFE latex. It was found that the increase in the PB crosslink density resulted in depressing the formation of PB secondary particles. Then, styrene and acrylonitrile were able to graft onto PB shell in high efficiency of 70%. SAN-modified PTFE/PB core-shell particles could eventually be dispersed homogeneously in a SAN matrix. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:185–190, 1998     

Miscibility studies of polymer blends by viscometry methods

The intrinsic viscosities of blends of poly(vinyl chloride)/poly(ethylene-co-vinyl acetate) (PVC/EVA), poly(vinyl chloride)/poly(styrene-co-acrylonitrile) (PVC/SAN), and poly(ethylene-co-vinyl acetate)/poly(styrene-co-acrylonitrile) (EVA/SAN) have been studied in cyclohexanone as a function of blend composition. In order to predict the compatibility of polymer pairs in solution, the interaction parameter term, Δb, obtained from the modified Krigbaum and Wall theory, and the difference in the intrinsic viscosities of the polymer mixtures and the weight average intrinsic viscosities of the two polymer solutions taken separately are used. © 1994 John Wiley & Sons, Inc.     

Nanopatterns of poly(styrene-block-butyl acrylate) block copolymer brushes on the surfaces of exfoliated and intercalated clay layers

We report a study of poly(styrene-block-butyl acrylate) (PSBA) block copolymer brushes on the surfaces of intercalated and exfoliated silicate (clay) layers. The PSBA/clay nanocomposite was synthesized by in situ atom transfer radical polymerization (ATRP) from initiator moieties immobilized within the silicate galleries of the clay particles. Transmission electron microscopy (TEM) analysis showed the existence of both intercalated and exfoliated structures in the nanocomposite. Block copolymer brushes on the surface of exfoliated or intercalated clay layers were found to create nanopatterns after treatment in different solvents. For the block copolymer brushes after treatment in THF, uniform collapsed brush layers are observed. After treatment in acetone, a selective solvent for PBA, wormlike surface aggregates are observed. After treatment in methanol, a precipitant for both of the blocks, micelles as well as wormlike aggregates can be observed. Furthermore, the polymer brushes tend to aggregate together and change their nanopatterns at an elevated temperature.     

Determination of thermodynamic and transport properties of a polystyrene-co-acrylonitrile copolymer by infinite and finite concentration IGC

The capillary column inverse gas chromatography technique was used to determine diffusivity and solubility data for several solutes in a poly(styrene-co-acrylonitrile) random copolymer (SAN). Both infinite dilution and finite concentration experiments were conducted using an IGC-mass spectrometer (IGC-MS) technique that combines the performance of the gas chromatography technique with the resolution of the mass spectrometer detector. Thirteen solutes were studied to obtain thermodynamic and diffusion coefficients at infinite dilution. Finite concentration experiments were conducted with toluene up to 10 wt.% concentration. Pseudo-binary experiments were also conducted in which a trace amount of hexane was injected in a mixture of toluene and SAN.     

Novel blends of alternating propene-carbon monoxide copolymers and styrenic copolymers

Summary Alternating propene-carbon monoxide copolymers (P-CO) were melt-blended with polystyrene, poly(styrene-co-acrylonitrile) (SAN), and with poly(styrene-co-maleic anhydride) (SMA). P-CO forms homogeneously miscible blends with SAN containing 25 wt% AN at the investigated blend compositions. The transparent blends have single, intermediate glass transition temperatures that fit the Fox equation. The elastic properties of P-CO at room temperature disappear upon blending with SAN because the T _g is driven above RT. Polystyrene and SMA are not miscible with P-CO and form heterogeneous blends with two glass transitions. This demonstrates that both the polarity of the styrenic copolymer and the nature of the comonomer govern its phase behavior. Received: 14 January 1999/Revised version: 19 April 1999/Accepted: 19 April 1999     

Compatibility enhancement of ABS/PVC blends

The compatibilizing effect of poly(styrene-co-acrylonitrile) (SAN) whose acrylonitrile (AN) content is 25 wt % (SAN 25) in poly(acrylonitrile-co-butadiene-co-styrene) (ABS)/poly(vinyl chloride) (PVC) blend was studied when the AN content of the matrix SAN in ABS was 35 wt % (SAN 35). When some amount of matrix SAN 35 was replaced by SAN 25 in a ABS/PVC (50/50 by weight) blend, the mixed phase of SAN and PVC at the interface was thickened, and about a twofold increase of impact strength was observed. The changes in morphology, dynamic mechanical properties, and rheological properties by the compatibilizing effect of SAN 25 were observed. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 705–709, 1998     

Nanoscale structure of SAN-PEO-SAN triblock copolymers synthesized by atom transfer radical polymerization

Low molecular weight triblock copolymers (TBCs) with poly(styrene-co-acrylonitrile) (SAN) end-blocks and poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO) or polycaprolactone (PCL) mid-blocks were synthesized using atom transfer radical polymerization (ATRP). The influence of molecular weight, composition (mid-block mole fraction), and interaction parameter on the crystallinity and on the formation of an ordered nanoscale phase-separated structure was investigated using thermal analysis, X-ray scattering, and electron microscopy. The TBCs with PEO mole fractions of over 0.5 exhibited PEO crystallinities of around 40% (compared to 72% for the PEO homopolymer) and lamellar nanoscale periodicities of around 176 Å (compared to 143 Å for the PEO homopolymer). The TBCs with PEO, PCL or PPO mole fractions of less than 0.5 exhibited relatively low crystallinities and did not exhibit ordered structures. These results emphasize the importance of the mid-block mole fraction in determining the ability to form an ordered nanoscale structure through mid-block crystallization. The ordered structure disappeared on heating the TBCs above the mid-block melting point, but below the SAN glass transition temperature. The crystallinity was reduced significantly in TBCs that were annealed or cast from a solvent.     

Fe‐mediated ICAR ATRP of styrene and acrylonitrile in polyethylene glycol

In this contribution, random copolymers of p(styrene‐co‐acrylonitrile) via initiators for continuous activator regeneration (ICAR) in atom transfer radical polymerization (ATRP) (ICAR ATRP) of styrene and acrylonitrile (SAN) were synthesized at 90°C in low molecular weight polyethylene glycol (PEG‐400) using CCl₄ as initiator, FeCl₃·6H₂O as catalyst, succinic acid as ligand and thermal radical initiator azobisisobutyronitrile (AIBN) as thermal free radical initiator. In this system, well‐defined copolymer of SAN was achieved. The kinetics results showed that the copolymerization rate obeyed first‐order kinetics model with respect to the monomer concentration, and a linear increase of the molecular weights with the increasing of monomer conversion with narrow molecular weight distribution was observed in the range of 1.1–1.5. The conversion decreased with increasing the amount of FeCl₃·6H₂O and increased with increasing the molar ratio of [St]₀/[AN]₀/[CCl₄]₀ and temperature. AIBN has a profound effect on the polymerization. The activation energy was 55.67 kJ mol^?1. The living character of copolymerization was confirmed by chain extension experiment. The resultant random copolymer was characterized by ¹H‐NMR and GPC. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40135.     

Properties and morphology of nanocomposites based on styrenic polymers. Part I: Styrene-acrylonitrile copolymers

For polymer/organoclay nanocomposites formed by melt processing, interactions between the polymer, montmorillonite surface, and surfactant determine any thermodynamic driving force for dispersion of the clay in the polymer. Interactions between poly(styrene-co-acrylonitrile) (SAN) and a single organoclay were probed by varying the SAN copolymer composition. Sample preparation was accomplished by melt processing on a microcompounder followed by injection molding. The level of mechanical reinforcement was observed to increase with acrylonitrile content. Digital analyses of TEM photomicrographs of core samples suggest an optimum in the aspect ratio of the particles at ∼38 wt% acrylonitrile; montmorillonite particles are much longer and thicker for the PS-based composites indicting poor exfoliation compared to the SAN-based composites. The melt viscosity of the SAN copolymers used in this work increased with AN content; experiments showed that varying melt viscosity independent of AN content can account for some improvement in reinforcement.     

A novel route for the synthesis of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) grafted titania nanoparticles via ATRP

A new method is presented for grafting poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (P(HEMA-co-MMA)) chains from the surface of TiO₂ nanoparticles via atom transfer radical polymerization (ATRP). First, the ATRP initiators were immobilized onto the TiO₂ surface by using 3-aminopropyltriethoxysilane coupling agent and 2-bromoisobutyryl bromide. Then the copolymerization of 2-hydroxyethyl methacrylate with methyl methacrylate was initiated and propagated on the TiO₂ surface by ATRP. The resulting composite nanoparticles were characterized by means of XPS, FT-IR, ¹H NMR, GPC and TGA. The results indicated that the grafting of copolymer chains from the TiO₂ surface was successful. This method opens up new avenues for the preparation of TiO₂-polymer nanocomposites.     

Microwave electromagnetic properties of polyimide/carbonyl iron composites

A facile and effective approach was developed to fabricate dual temperature- and pH-sensitive hollow nanospheres utilizing an atom transfer radical polymerization (ATRP) method. To do this silica nanoparticles were used as primary cores that could be etched by an hydrofluoric (HF) aqueous solution. Due to uncontrolled ATRP of acrylic acid (AA) methyl acrylate (MA) was polymerized via surface-initiated ATRP (SI-ATRP) a and poly(2-hydroxyethyl methacrylate) (PHEMA) block was added via the same approach. To synthesize poly(AA-co-HEMA)-grafted silica nanoparticles polymethyl acrylate (PMA) chains were hydrolyzed to polyacrylic acid (PAA) using an aqueous NaOH solution. PAA segments were partially crosslinked via an esterification reaction of –COOH groups with 1,4-butanediol. Finally, poly(AA-co-HEMA) hollow nanospheres were fabricated by etching silica cores with an HF aqueous solution. The structure of the nanospheres was revealed by transmission electron microscopy (TEM). These hollow nanospheres consisting of poly(AA-co-HEMA) in their structure showed dual pH- and thermo-sensitive properties as measured by dynamic light scattering (DLS). The hydrodynamic diameter was measured as an affected parameter under different pH (3–12) and temperature (25–55 °C) conditions. Results showed that by decreasing pH or by increasing temperature the hydrodynamic diameter decreased and a lower critical solution temperature (LCST) point was observed.     

Rheological properties and interfacial tension of polypropylene-poly(styrene-co-acrylonitrile) blend containing compatibilizer

Rheological and morphological properties of the polypropylene (PP) and poly(styrene-co-acrylonitrile) (SAN) blend containing polypropylene-g-poly(styrene-co-acrylonitrile) (PP-g-SAN) was studied by advanced rheometric expansion system (ARES) and scanning electron microscopy (SEM). Blends of the PP-SAN (20/80) with compatibilizer of the PP-g-SAN, ranging from 0 to 20 wt% (phr) were prepared using a twin screw extruder. In the study of the complex viscosity of the PP-SAN (20/80) blend, the complex viscosity of the blend showed maximum value in the 1.0 phr PP-g-SAN copolymer content, which suggested that the compatibilizing effect of the PP-g-SAN copolymer was achieved. From the morphological studies, the PP-SAN (20/80) blend showed droplet dispersion type morphology, and the PP droplet size showed minimum value (0.44 μm) in the 1.0 phr PP-g-SAN copolymer content. The interfacial tension of the PP-SAN (20/80) blend was determined from the morphological studies and form relaxation time using the Palierne and the Choi and Schowalter models and showed minimum value in the 1.0 phr PP-g-SAN copolymer content in each models. The results of the interfacial tension was consistent with the results obtained from the rheological and morphological studies of the PP-SAN (20/80) blend. From the results of the morphological, rheological studies and the values of the interfacial tension, it was suggested that the compatibility of the PP-SAN (20/80) blend increased more in the 1.0 phr PP-g-SAN copolymer content.     

Effect of acrylonitrile content of styrene-co-acrylonitrile (SAN) on morphology and electrooptical properties of polymer/liquid crystal composite films

Effects of copolymer composition on morphology and electrooptical properties of polymer/liquid crystal (LC) (40/60 w/w) composite films were studied with styrene-co-acrylonitrile (SAN) of varying acrylonitrile (AN) content (6.3–35 wt %) and a cyanobiphenyl-type liquid crystal (E8). The dimension of the LC domain in the composite film decreased with increase of AN content of SAN up to 30 and increased at 35 wt %. The contact angle of the film with an LC drop showed a similar trend; however, its minimum was obtained at 24% AN. Threshold voltage (V_th) and rise time (τ_R) increased, and decay time (τ_D) decreased with AN content up to 30%, and the tendency is reversed at 35%. The results were interpreted in terms of, possibly, a solubility parameter matching between SAN and LC. © 1993 John Wiley & Sons, Inc.     

Miscibility of copolycarbonate blends with poly(styrene-co-acrylonitrile) copolymer and their interaction energies

The phase behavior of dimethyl polycarbonate-tetramethyl polycarbonate (DMPC-TMPC) blends with poly(styrene-co-acrylonitrile) copolymers (SAN) and the interaction energies of binary pairs involved in blend has been explored. DMPC-TMPC copolycarbonates containing 60 wt% TMPC or more were formed miscible blends with SAN containing limited amounts of AN. The miscibility of copolycarbonate with SAN decreases as the DMPC content increases. The miscible blends showed the LCST-type phase behavior or did not phase separate until thermal degradation. The binary interaction energies involved in the miscible blends were calculated from the phase boundaries using the lattice-fluid theory combined with binary interaction model. The phenyl ring substitution with methyl groups did not lead to interactions that are favorable for miscibility with polyacrylonitrile (PAN). The interaction energies of the polycarbonates blends with SAN copolymers as a function of AN content were obtained. It was revealed that the incline of the number of methyl groups on the phenyl rings of bisphenol-A unit acts favorably for the miscibility with SAN copolymer when SAN contains less than about 30 wt% AN and shifts the most favorable interaction to the low AN content.     

Grafting of pH-sensitive poly (N,N-dimethylaminoethyl methacrylate-co-2-hydroxyethyl methacrylate) onto HNTS via surface-initiated atom transfer radical polymerization for controllable drug release

Copolymer brushes composed of N,N-dimethylaminoethyl methacrylate (DMAEMA) and 2-hydroxyethyl methacrylate (HEMA) were tethered on the surface of HNTs (HNTs) through surface-initiated atom transfer radical polymerization (SI-ATRP). ATRP initiator was anchored to surface and copolymers were synthesized from surface with different compositions of monomers. Successful grafting of copolymer brushes was approved by FTIR, TGA, XPS, FE-SEM, TEM, and N₂ adsorption-desorption.¹H NMR was used to determine the composition of copolymers. pH-sensitive properties of copolymer-grafted nanotubes were investigated by UV-visible absorbance in different pH values. Finally, loading and in vitro drug release from neat and copolymer-grafted HNTs were investigated using diphenhydramine hydrochloride as a model drug. Incorporation of DMAEMA to structure of polymers led to pH sensitivity of grafted-copolymers and controlled release of drug upon varying the pH of release medium. pH-dependent drug release showed that drug release was increased by decreasing pH of release medium and increasing DMAEMA content.