Carboxybetaine,sulfobetaine, and cationic block copolymer coatings: A comparison of the surface properties and antibiofouling behavior

Two different zwitterionic block copolymers (BCs) and a cationic BC were synthesized from the same BC precursor, which consisted of a polystyrene (PS) block and a poly[N‐(3‐dimethylamino‐1‐propyl)acrylamide] block. The zwitterionic BCs contained the dimethylammonioacetate (carboxybetaine) and dimethylammoniopropyl sulfonate (sulfobetaine) groups. Thin films cast from these polymers were investigated for surface wettability, surface charge, and protein adsorption. Surface‐energy parameters calculated with advancing contact angle (θ_a) and receding contact angle (θ_r) of different probe liquids showed that it was θ_r and not θ_a that was representative of the polar/ionic groups in the near‐surface regions of the coatings. Electrophoretic mobility was used to characterize the influence of pH on the net surface charge. In aqueous dispersions, the carboxybetaine polymer showed an ampholyte behavior with an isoelectric point of 6, whereas the sulfobetaine polymer was found to be anionic at all pH values between 2 and 10. Protein adsorption on the carboxybetaine BC was relatively independent of the net charges on the protein or the polymer, but the negatively charged sulfobetaine polymer showed a higher adsorption of positively charged protein molecules. Regardless of the net protein charge, both zwitterionic coatings adsorbed less protein compared to the PS and poly(2,3,4,5,6‐pentafluorostyrene) controls. The sulfobetaine and cationic BCs adsorbed higher amounts of oppositely charged protein molecules than like‐charged protein molecules. However, the adsorption of oppositely charged protein was much higher on the cationic surface than on the sulfobetaine surface. The zwitterionic BCs, particularly the carboxybetaine polymer, from this article are expected to function as stable, low‐fouling surface modifiers in different biological environments. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Molecular dynamics study of TiO2/poly(acrylic acid‐co‐methyl methacrylate) and Fe3O4/polystyrene composite latex particles prepared by heterocoagulation

All‐atom molecular dynamics simulations were used to study the morphology of polymer/inorganic composite particles prepared by heterocoagulation. The results were also compared to those of our previous study of the preparation of TiO₂/poly(acrylic acid‐co‐methyl methacrylate) and Fe₃O₄/polystyrene composite particles. In the simulation system, polymer or inorganic particles were simulated by surface‐charge‐modified C₆₀ or Na atoms. Through a combination of analysis of the radial distribution functions of charged atoms and snapshots of the equilibrated structure, three kinds of particle distributions were observed under different conditions. When the polymer and inorganic particles had opposite surface charges and their sizes were very different, the composite morphology showed a core–shell structure with small particles adsorbed onto the surfaces of large particles. Furthermore, when the polymer and inorganic particles had opposite surface charges but comparable sizes, the polymer and inorganic particles aggregated domain by domain. Finally, when the polymer and inorganic particles were endowed with the same surface charge, the distribution of these two types of particles was homogeneous, regardless of their size difference. The simulation results were in agreement with the experimental results. The electrostatic interaction and the size of the particles dominated the final morphology of the composite particles when the heterocoagulation method was used. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Direct synthesis of polymer-grafted inorganic hybrids via reversible chain transfer catalyzed polymerization

In this work, a new simple and robust method for preparation of polymer-grafted inorganic hybrids through “grafting to” reaction is presented. Polymer chains were synthesized by reversible chain transfer catalyzed polymerization (RTCP) are capped with iodine according to the RTCP mechanism. The obtained iodine-capped polymer chains can react irreversibly with the hydroxyl groups available on the surface of inorganic materials through a nucleophilic substitution (SN) reaction. In this method, there is no need to modify the surface of inorganic materials or to functionalize polymer chains prior to the “grafting to” reaction. RTCP produced polystyrenes with different molecular weights, e.g., 4,000, 6,000, and 8,000 g/mol, and silica nanoparticles were employed as the polymer and inorganic materials, respectively. The resulting hybrids were characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, and transmission electron microscopy techniques. According to the results, graft density decreased by increasing the polystyrene molecular weight. Additionally, the rheological studies of prepared polystyrene nanocomposites containing 2 wt % of the produced hybrids confirmed the better dispersion of the modified hybrids in the polystyrene matrix. The glass transition temperature (T _g) of the polystyrene nanocomposites was driven by differential scanning calorimeter technique. Analysis of nanocomposites’ T _g results revealed that increment of the grafted polymer molecular weight of hybrids increased the glass transition temperature of the prepared nanocomposites due to improvement of the dispersion level.     

A facile strategy for the functionalization of poly[cyclotriphosphazene‐co‐(4,4′‐sulfonyldiphenol)] materials

Recently, a new type of phosphazene‐containing material, poly[cyclotriphosphazene‐co‐(4,4′‐sulfonyldiphenol)] (PZS), was successfully prepared. PZS materials including PZS nanotubes, PZS nanofibers and PZS microspheres show excellent thermal stability, biocompatibility and biodegradability. Moreover, PZS‐containing materials such as silver nanowire/PZS, carbon nanotube/PZS and Fe₃O₄/PZS nanotubes have also been prepared. Therefore, we explored a specific method for the functionalization of these PZS and PZS‐containing materials to expand their scope of application. As a model of various PZS and PZS‐containing materials, PZS microspheres (PZSMs) were functionalized via surface‐initiated atom transfer radical polymerization (ATRP). Polymerization of styrene occurred at surface sites covalently derivatized with ATRP initiators to form PZSM–polystyrene. The number‐average molecular weight (M_n) of grafted polymer chains could be well controlled. Furthermore, PZSM–polystyrene was still active for further block copolymerization of methyl methacrylate. Both styrene‐ and acrylate‐type monomers could be directly polymerized or block copolymerized from the surface of PZS and PZS‐containing materials using surface‐initiated ATRP. M_n of grafted polymer chains could be well controlled. This facile strategy could pave the way for a wider range of applications of these materials. Copyright © 2010 Society of Chemical Industry     

Using X-ray tomography,PALS and Raman spectroscopy for characterization of inhibitors in epoxy coatings

Model paint materials were generated by adding a range of inorganic materials into an epoxy. The inorganic materials included inhibitors (Zn₃(PO₄)₂ and SrCrO₄) and a filler (rutile TiO₂).The SrCrO₄ system was characterized using SEM, TEM, PALS and Raman spectroscopy and found to have an even distribution of inhibitor in the polymer matrix. X-ray tomography was performed on the mixed SrCrO₄/TiO₂ and Zn₃(PO₄)₂/TiO₂ systems. A new technique called data constrained modelling was combined with the tomographic technique to produce a 3D distribution of the inorganic phases within the polymer matrix.     

PdCl2 anchorage onto the surface of polystyrene films via oxygen and ammonia plasma treatment

The surface properties of polystyrene as a possible catalytic support for active coordinative species were investigated. To improve the surface properties, discharge treatments in the presence of oxygen and ammonia were carried out. The polymer surface was studied before and after the plasma treatments. Contact angles for the polymer surface were measured in order to determine the surface free energy. Polymer‐bound complex catalysts were prepared by anchoring PdCl₂ on the surface of the polystyrene samples. The chemical compositions were studied by X‐ray Photoelectron Spectroscopy (XPS). Plasma treatments in the presence of oxygen or ammonia caused an increase in the surface free energy of polystyrene, as a consequence of the higher concentration of oxygenated or nitrogenated functional groups, respectively, on the polymer surface. Contact angle measurements are in agreement with the corresponding values obtained by XPS. After treatment with PdCl₂, the amount of palladium anchored to the polymer surface treated with ammonia is greater than in the case of the oxygen plasma treatments; this may be explained on the basis of the higher nucleophilic character of the amine groups. No palladium was detected in the untreated polystyrene surface. © 2000 Society of Chemical Industry     

Postsynthetic surface functionalization,encapsulation, and releasing studies of a novel polymer nanocapsule

Postsynthetic surface functionalizations of the amphiphilic poly(allyamine)‐g‐poly(t‐butylacrylate) nanocapsule of 50–100 nm diameters are reported. The hydrophobic poly(t‐butylacrylate) surface of the polymer nanocapsules were successfully functionalized with poly(acrylate) and poly(ethylene glycol). These new nanocapsules were investigated for their water dispersibility, encapsulation and controlled releasing properties with fluorescein, an anionic fluorescence probe, and 5‐fluorouacil, an anticancer drug as the model compounds. The postsynthetic surface funcitionalization approach of the cross‐linked polymer nanocapsules shows promise for improving the biocompatibility and aqueous dispersibility of the nanocapules without disrupting the encapsulation and releasing properties of the polymer nanocapsules. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and Characterization of PEG-Modified Polystyrene Particles and Isothermal Equilibrium Adsorption of Bovine Serum Albumin on these Particles

A series of monodisperse submicron polystyrene (PS) particles with different surface monomethoxy poly(ethylene glycol) (mPEG) densities were prepared and characterized. The effects of the chemically grafted mPEG chains (MW = 2,000) on the adsorption of bovine serum albumin (BSA) molecules onto these negatively charged particles at pHs 5 and 3 were investigated. The native particles at both pH values showed the largest values of q _max (maximum amount of BSA adsorbed on the particle surface). The surface mPEG chains were very effective in retarding the BSA adsorption and q _max decreased significantly with increasing surface mPEG density. The values of q _max were greater for both the native and mPEG-modified particles at pH 5 compared to those counterparts at pH 3, due to the different adsorption mechanisms. Hydrophobic interaction predominated in the adsorption of BSA molecules on the particles at pH 5, whereas electrostatic interaction had a crucial influence on the BSA adsorption at pH 3. At pH 5, the adsorption behaviors were qualitatively explained by the calculated values of the free energy barrier against the BSA adsorption. A schematic model was also proposed to qualitatively describe the conformations of BSA molecules adsorbed on the particle surfaces.     

Surface enrichment of siloxanes with covalent bound ultraviolet (UV) absorber groups

The ability of siloxanes with UV absorber groups to enrich at the surface of cast polystyrene films was studied. Model compounds were siloxanes of the type Me₃SiO(SiMe₂O) _n (SiMeRO) _m SiMe₃, withR representing a 2-hydroxy-benzophenone-4-oxypropyl group. Surface studies were carried out by contactangle measurements and ESCA (Electron Spectroscopy for Chemical Application) investigations. UV absorbers with a high content of dimethylsiloxane units strongly enrich at the surface of polystyrene, forming a thin surface layer with a high siloxane content. UV absorbers with few or no dimethylsiloxane units pe hydroxybenzophenone group are evenly distributed in the polymer matrix. ESCA sputter depth profiles are also given. Migration studies show that the siloxanes are delivered from the bulk to the surface subsequently after sputtering.Dedicated to Prof. Dr. Dr. h.c. R. Müller on the occasion of his 90th birthday, in recognition of his pioneering contributions to organosilicon chemistry.Siloxanes with Functional Groups, XIV. For communication XIII, see Ref. 1. Long-Term Stabilization of Polymers, VIII. For communication VII, see Ref. 1.     

Controllably crazed polystyrene: Morphology and permeability

The effects of n-heptane and heat treatment on the structural and transport properties of polystyrene films (biaxially oriented and unoriented) were studied to determine whether these treatments improve the film as selective barriers for separation of molecules differing only slightly in size and shape. n-Heptane treatment of biaxially oriented polystyrene produces a sandwich structure composed of expanded, crazed, surface layers surrounding an apparently unaffected central core. The crazed layers contain a continuous network of interconnected channels. The core provides the total resistance to gas permeation, hence, the overall effect of n-heptane treatment is fabrication of a thinner more permeable membrane. By restricting the stress-cracking treatment to one face of the film, it should be possible to make high flux, anisotropic membranes—a type of membrane which is required for successful development of membrane separation processes. n-Heptane treatment of cast, annealed polystyrene results also in a crazed polymer, but the crazing is in the form of spherical voids, and the films, even with a residual uncrazed core, are too weak to be useful as separation membranes. The crazing process in both types of polymer specimens is characteristic of case II non-Fickian diffusion in which the kinetics are apparently controlled by polymer relaxation processes. Sorption of isopentane into cast, annealed polystyrene does not cause visible crazing but the kinetics are again non-Fickian. Desorption of isopentane into n-heptane-treated polystyrene releases the appreciable residual n-heptane in the film which could not be removed by long-term exposure to vacuum. Analysis of D(0) values for isopentane in n-heptane treated films indicates that the polymer surrounding the visible voids in the film is essentially unaltered polystyrene with only a small fraction of the voids being interconnected by open channels.     

Surface modification of silicone rubber by ion beam assisted deposition (IBAD) for improved biocompatibility

We studied the preparation of antimicrobial silicone rubbers of improved interfacial strength, which could be formed with the ion beam assisted deposition (IBAD) technique for coating metallic or inorganic materials (silver (Ag), Copper (Cu), and Hydroxyapatite(HAp)/TiO₂) on the silicone surface. Those coating materials provide high product safety as well as outstanding antimicrobial activity. The deposition methodology is composed of pre‐etching with oxygen gas, vaporizing the coating materials, and post‐treatment with Ar ion. With the evaporation of the coating materials, the Ar beam was focused on the substrate to assist deposition. It was found out that the ion assisting depositions in the IBAD process give a prominent enhancement in adhesion between silicone rubbers and coatings of Ag and Cu. The HAp/TiO₂ coating layer was easily dissolved in aqueous saline solution. All deposited layers display high antimicrobial activities against Staphlococcus aureus (ATCC 6538) and Escherichia coil (ATCC 25,922), showing 99.9% reduction of bacteria, respectively. In a cytotoxicity test, the Ag and HAp/TiO₂ coated silicone shows a decrease of cytotoxicity, while the Cu coating leads to a slight increase of cytotoxicity. The result on the surface modifications of silicone rubber will be employed in further study for applications of medical or rehabilitation devices. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1095–1101, 2005     

Aqueous gel permeation chromatography: The effect of solvent ionic strength

Porous glass packing materials have been used for gel permeation chromatography using an aqueous phosphate buffer. Elution volumes were determined for polystyrene sulfonates, dextrans, and small neutral and charged molecules at three different ionic strengths, viz., 0.01M, 0.1M, and 1.0M phosphate, pH 7.0. The pore diameters of the glasses studied were 75, 240, 700, and 2000 Å. Elution volumes of nonionic species were unaffected by changing the solvent ionic strength. Elution volumes of charged species were markedly affected by the ionic strength of the solvent. This was attributed to a combination of decreased polymer dimensions and decreased ionic exclusion with increasing buffer concentration. The use of low ionic strength solvents may be exploited to tailor the separating range for polyelectrolytes with porous glass packings. This is particularly useful in the low molecular weight range where the lowest pore size available is 75 Å.     

Molecular weights and molecular weight distribution in phase equilibria of the polystyrene-poly(methyl methacrylate)-toluene system

The composite gel permeation chromatography (GPC) chromatogram of a mixture of polystyrene and poly(methyl methacrylate) has been successfully resolved into its component chromatograms by using a newly developed technique. This technique has made possible the calculation of M _w and M _n values of these polymers in the conjugate phases of the ternary systems with toluene as the solvent. Calculated M _w and M _n values of the two polymers indicated that the larger polystyrene molecules tend to stay in the top polystyrene-rich phase while its smaller molecules tend to stay in the bottom phase to interact with the other polymer. The reverse is true with the poly(methyl methacrylate) molecules. This tendency strongly suggests that interactions among the two polymers were accomplished mainly by their smaller molecules.     

Selective patterning of ZnO nanorods on silicon substrates using nanoimprint lithography

In this research, nanoimprint lithography (NIL) was used for patterning crystalline zinc oxide (ZnO) nanorods on the silicon substrate. To fabricate nano-patterned ZnO nanorods, patterning of an n-octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) on SiO₂ substrate was prepared by the polymer mask using NI. The ZnO seed layer was selectively coated only on the hydrophilic SiO₂ surface, not on the hydrophobic OTS SAMs surface. The substrate patterned with the ZnO seed layer was treated with the oxygen plasma to oxidize the silicon surface. It was found that the nucleation and initial growth of the crystalline ZnO were proceeded only on the ZnO seed layer, not on the silicon oxide surface. ZnO photoluminescence spectra showed that ZnO nanorods grown from the seed layer treated with plasma showed lower intensity than those untreated with plasma at 378 nm, but higher intensity at 605 nm. It is indicated that the seed layer treated with plasma produced ZnO nanorods that had a more oxygen vacancy than those grown from seed layer untreated with plasma. Since the oxygen vacancies on ZnO nanorods serve as strong binding sites for absorption of various organic and inorganic molecules. Consequently, a nano-patterning of the crystalline ZnO nanorods grown from the seed layer treated with plasma may give the versatile applications for the electronics devices.     

Temperature- and thickness-dependent elastic moduli of polymer thin films

The mechanical properties of polymer ultrathin films are usually different from those of their counterparts in bulk. Understanding the effect of thickness on the mechanical properties of these films is crucial for their applications. However, it is a great challenge to measure their elastic modulus experimentally with in situ heating. In this study, a thermodynamic model for temperature- (T) and thickness (h)-dependent elastic moduli of polymer thin films E _f(T,h) is developed with verification by the reported experimental data on polystyrene (PS) thin films. For the PS thin films on a passivated substrate, E _f(T,h) decreases with the decreasing film thickness, when h is less than 60 nm at ambient temperature. However, the onset thickness (h*), at which thickness E _f(T,h) deviates from the bulk value, can be modulated by T. h* becomes larger at higher T because of the depression of the quenching depth, which determines the thickness of the surface layer δ.     

Synthesis of block copolymers from PDMS macroinitiators

The synthesis of polystyrene‐b‐polydimethylsiloxane‐b‐polystyrene (PSt‐b‐PDMS‐b‐PSt) copolymers is described. Commercially available difunctional PDMS containing vinylsilyl terminal species was reacted with hydrogen bromide resulting in the PDMS macroinitiators. The terminal alkyl bromide groups were then used as initiators for atom transfer radical polymerization (ATRP) to produce block copolymers. Using this technique, triblock copolymers consisting of a PDMS centre block and polystyrene terminal blocks were synthesized. ATRP of St from those macroinitiators showed linear increases in M_n with conversion, demonstrating the effectiveness of ATRP to synthesize a variety of inorganic/organic polymer hybrids. Copyright © 2004 Society of Chemical Industry     

The incorporation of transition metals into polyhedral oligosilsesquioxane polymers

A new class of polyhedral oligosilsesquioxane (POSS) copolymers has been developed by incorporating into a polymer backbone the POSS disilanol macromer, (c-C₆H₁₁)₈Si₈O₁₁(OH)₂, along with a variety of inorganic comonomers. These new inorganic cluster-based copolymers were synthesized using a condensation polymerization approach, with formation of metal oxygen bonds and climination of HCl (as HNEt₃ Cl) or CH₄ driving the reaction. The polymers thus formed are isolated as amorphous powders but do not display any observable glass transition; they decompose without melting at over 400 C under nitrogen. Especially interesting is the formation of a zirconocene-bridged copolymer which is stable to both air and methanol.     

Head to head polymers IX: The rheological behavior of H-H and H-T atactic polystyrenes

The rheological behavior of a sample of H-H polystyrene of M_n of 41,000 and a M_w/M_n of 2 was compared at 160 and 190°C with a sample of H-T atactic polystyrene of similar molecular weight. The melt viscosity of H-H polymer (unlike the H-T polymer) was non-Newtonian at low stresses and decreased more rapidly with stress. This observation seems to indicate a stiffer polymer chain for the H-H polystyrene. The flow activation energy (E*) of H-H polystyrene was found to be dependent on the dynamic shear stress and decreased with increasing dynamic shear stress. The dynamic shear storage modulus of the H-H polymer has a smaller increase of G′ with ω than that of the H-T polystyrene.     

Characterization and magnetic properties of carbon-coated cobalt nanocapsules synthesized by the chemical vapor-condensation process

Carbon-coated cobalt nanocapsules were synthesized by the chemical vapor-condensation process with cobalt carbonyl (Co₂(CO)₈) used as precursor and carbon monoxide (CO) as carrier gas. The characterization and magnetic properties of carbon-coated cobalt nanocapsules were investigated systematically. The transmission electron microscope (TEM) images showed that the as-prepared nanoparticles consist of a metal core and an amorphous carbon shell. X-ray diffraction and TEM selected area diffraction revealed the presence of f.c.c. Co phase, h.c.p. Co phase, and minority Co₂C, Co₃C phases. The saturation magnetization at room temperature of the nanocapsules is 146.9 Am² kg⁻¹, which is 90% of the bulk ferromagnetic element counterpart. The coercive force at room temperature of the nanocapsules is 0.12 T, while the ratio of remnant to saturation magnetization M_r/M_s is about 0.4. The saturation magnetization and the coercive force increase with increasing the decomposition temperature, mainly due to the increase of the size of the magnetic particles. The decomposition of the cobalt carbonyl (Co₂(CO)₈) and CO gas can decrease efficiently the oxygen content in nanocapsules. The metallic Co nanoparticles completely coated by carbon can resist the dilute acid erosion as well as the oxidation. The thermal stability of the Co nanocapsules is also studied.     

Coating water-swellable polymer latexes by interfacial polymerization

Two techniques of coating water-swellable polymer latexes (hydrogels) with an inorganic or organic layer were developed, based on interfacial polymerization. The hydrogel latexes were prepared by inverse suspension polymerization. The first kind of interfacial polymerization is hydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) or 3-(trimethoxysilyl) propylmethacrylate (TMS-PMA) on the surface of hydrogel latexes. The hydrochloric acid, which is the catalyst for this reaction, was previously loaded into the hydrogel latexes. The HCL-containing hydrogel latexes were then suspended in an organic solution of TEOS or TMS-PMA. The hydrolysis and condensation occur only at the surface of each hydrogel particle and the generated SiO₂ or SiO(PMA) network covers the hydrogel latexes. The second interfacial polymerization is polymerization of methylenedi-p-phenyl diisocyanate (MDI) and triethylene glycol (TEG) on the surface of hydrogel latexes. TEG was deposited on the hydrogel by suspending the hydrogel powder in a tetrahydrofuran (THF) solution of TEG and evaporating the THF. The TEG-deposited hydrogel powder was then suspended in an organic solution containing both MDI and the catalyst dibutyltin dilaurate (DBTL). The MDI and DBTL molecules react with the TEG molecules only at the surface of the hydrogel particles, and the polyurethane P(MDI-TEG) thus formed wraps the particles. Based on these two coating procedures, three kinds of materials were obtained: SiO₂ coated hydrogels, SiO-(PMA) coated hydrogels and P(MDI-TEG) coated hydrogels. Soft polyether brushes were grafted to the SiO-(PAM) coated latexes. The P(MDI-TEG) coated hydrogels were used as reservoirs for β-hydroethyltheophylline (β-HETP), and the release of the latter molecules from the coated hydrogels was investigated. © 1995 John Wiley & Sons, Inc.