Electrochemical copolymerization of m-toluidine and o-phenylenediamine

Electroactive copolymers of m-toluidine (MT) and o-phenylenediamine (OPD) were prepared electrochemically in aqueous sulfuric acid by potential cycling and characterized with cyclic voltametry, in situ conductivity measurements and FT-IR spectroscopy. The voltammograms of the copolymers exhibit different behavior for different concentrations of OPD in the comonomer feed. At optimum conditions the resulting poly(OPD-co-MT) shows an extended useful potential range of the redox activity as compared to the corresponding homopolymers. The effect of scan rate and pH on the electrochemical activity was studied. The copolymer was electrochemically active even at pH 8.0. The stability of the copolymer film was also tested. The copolymer has a potential region of maximum conductivity different from that of PMT and POPD. The conductivity of the copolymer is between the conductivity of the homopolymers. The vibrational bands at 3122/3450 and 2922/875 cm⁻¹ in the FT-IR spectra of the copolymer indicate the presence of both OPD and MT units, respectively, in the copolymer backbone.     

In situ UV-vis spectroelectrochemistry of poly(o-phenylenediamine-co-m-toluidine)

Results of in situ UV-vis spectroelectrochemical studies of the electropolymerization of o-phenylenediamine (OPD), m-toluidine (MT) and the copolymerization of OPD with MT are reported. Electropolymerization was performed in aqueous acidic medium at a constant potential of E_SCE = 1.0 V at an indium doped tin oxide (ITO) coated glass electrode. The course of homopolymerization was followed for MT and OPD solutions with various monomer concentrations. The spectral characteristics of the mixed solutions were studied at a constant concentration of MT and various concentrations of OPD in the comonomer feed. An absorption band at λ = 497 nm was assigned to the head-to-tail mixed dimer/oligomer resulting from the cross reaction between OPD and MT cation radicals. UV-vis spectra recorded during copolymerization show dependence of the growth of the band at λ = 497 nm on OPD concentration in the feed. At lower OPD feed concentration it appears as the major band in the corresponding spectra. The UV-vis spectra recorded for the copolymer films suggest the incorporation of both monomer units in the copolymer. The FT-IR spectra of the copolymers show the presence of phenazine type structures in the copolymer backbone.     

Mobilities of charge carriers in poly(o-methylaniline) and poly(o-methoxyaniline)

Mobilities of charge carriers in poly(o-methylaniline) (PMA) and poly(o-methoxyaniline) (PMOA) films are electrochemically determined over a range of oxidation stages of the polymer films. In the low oxidation region, mobilities of both the polymers are comparable to that of polyaniline (PANI). In the high oxidation region, however, mobility values systematically decrease in the order of PANI > PMA > PMOA, showing that the bulky groups present at the ortho position play a more important role in the high oxidation region. The low mobilities of charge carriers in the high oxidation region explain why PMA and PMOA are less conducting than PANI.     

Corrosion protection aspects of electrochemically synthesized poly(o-anisidine-co-o-toluidine) coatings on copper

The poly(o-anisidine-co-o-toluidine) coatings were synthesized on copper substrates by electrochemical copolymerization of o-anisidine with o-toluidine using sodium salicylate as supporting electrolyte. These coatings were characterized by cyclic voltammetry, UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and scanning electron microscopy (SEM). The formation of the copolymer with the mixture of monomers in the aqueous sodium salicylate solution was ascertained by a critical comparison of the results obtained with the polymerization of the individual monomers, o-anisidine and o-toluidine, respectively. The corrosion protection aspects of poly(o-anisidine-co-o-toluidine) coatings to copper was investigated in aqueous 3% NaCl solution by potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The results of the potentiodynamic polarization measurements and EIS studies showed that the poly(o-anisidine-co-o-toluidine) coatings provided the effective corrosion protection to copper than that of respective homopolymers. The corrosion rate is observed to depend on the feed ratio of o-toluidine used for the synthesis of the copolymer coatings.     

Potentiodynamic deposition of poly (o-anisidine-co-metanilic acid) on mild steel and its application as corrosion inhibitor

For the first time, poly (o-anisidine-co-metanilic acid) (PASM) was deposited on mild steel substrate by electrochemical polymerization of o-anisidine and metanilic acid monomers in aqueous solution of 0.1 M H₂SO₄. The electrochemical polymerization of o-anisidine takes place in the presence of metanilic acid monomer and uniform, strongly adherent coating was obtained on the substrate. The electroactivity of copolymer was studied by cyclic voltammetry and AC impedance techniques. There is an increasing anodic current due to oxidation of metanilic acid monomer at the surface of the electrode when the applied potential is cycled from −0.2 V to 0.8 V. These deposits were characterized by Fourier transform infrared (FTIR) spectroscopy, UV-vis and TG/DTA techniques. The effect of various concentrations of PASM copolymer solution in acid rain corrosive media has been studied through potentiodynamic polarization, AC impedance and I-E curve methods. The soluble form of polymeric solution provided better anti-corrosive behavior in artificial acid rain solution.     

Spectroelectrochemistry of two-layered composites of polyaniline and poly(o-aminophenol)

Electropolymerization of aniline on poly(o-aminophenol)(POAP)-coated gold and indium-doped tin oxide (ITO)-coated glass electrodes yields polyaniline(PANI)/POAP two-layer composite films, exhibiting reversible redox functions in aqueous acidic solution. The PANI deposition on the POAP-coated electrodes was monitored by cyclic voltammetry (CV) and in situ UV-vis spectroelectrochemistry. CV results show that PANI/POAP composite films exhibit better stability as compared to PANI films during potential cycling in aqueous acidic solutions. Characteristic UV-vis and Raman features of the composite films have been identified and their dependencies on the electrode potential are discussed. They were significantly different from the corresponding spectral characteristics of PANI and POAP films alone.     

Spectroelectrochemistry of aniline-o-aminophenol copolymers

Electroactive copolymers of aniline and o-aminophenol (OAP) with varying concentration ratios prepared by potential cycling in acidic aqueous solutions of the monomers on indium-doped tin oxide (ITO) coated glass and gold electrodes were studied with in situ UV-vis and Raman spectroscopy. Characteristic UV-vis and Raman features have been identified and their dependencies on the electrode potential are discussed. Spectroelectrochemical results reveal the formation of polyaniline-based copolymers at low concentration of OAP in the feed but incorporation of more OAP units into the copolymer with higher concentration of OAP in the comonomer feed. Spectroelectrochemical features are significantly different from those of both homopolymers.     

Morphology and properties of nanocomposites formed from ethylene/methacrylic acid copolymers and organoclays

Nanocomposites were prepared by melt mixing ethylene/methacrylic acid copolymers and organoclays, which were compared to equivalent composites prepared from low-density polyethylene (LDPE) and a sodium ionomer of poly(ethylene-co-methacrylic acid). The effects of matrix modification and organoclay structure on the morphology and properties of these nanocomposites were evaluated using stress-strain analysis, wide-angle X-ray scattering (WAXS), and transmission electron microscopy coupled with particle analysis. With all four polymers, the use of a two-tailed organoclay, M₂(HT)₂, led to the formation of more exfoliated nanocomposites than a one-tailed organoclay, M₃(HT)₁. Nanocomposites prepared from ethylene/methacrylic acid copolymers revealed better exfoliation compared to similar composites prepared from LDPE. It seems that the presence of relatively small quantities (1.3-3.1 mol%) of the polar methacrylic acid monomer aids in improving the organoclay exfoliation efficiency of these polymers. Nanocomposites prepared from the sodium ionomer of poly(ethylene-co-methacrylic acid) exhibited the highest levels of organoclay exfoliation compared to all other polymers examined in this study. However, from the observations made in this study, it was not possible to determine conclusively the relative interaction of carboxyl acid groups versus the salt form with the organoclay and, thus, their influence on exfoliation; additional studies will be needed to reach a conclusion on this important point.     

Shear induced crystallization of poly(m-xylylene adipamide) with and without nucleating additives

The shear induced crystallization of the poly(m-xylylene adipamide) (MXD6) which is a semi-aromatic polyamide, was studied for a virgin (PA1) and a nucleated (PA2) grades using a shearing hot stage coupled with a microscope. Half crystallization times were measured according to the crystallization conditions (crystallization temperature, shear rate and shearing time). The effect of shear on the crystallization kinetics was shown by a strong decrease of the crystallization times for both materials. PA2 sensitivity to shear was much lower than that of PA1. This was attributed to the presence of nucleating agents which increased the primary nucleation density in the unsheared quiescent melt, leading to a higher necessary shear rate to overcome the quiescent nucleation. Kinetic models were proposed to predict the crystallization process as a function of the crystallization conditions. They were based on both Avrami and Hoffman-Lauritzen theories and modified to take into account the effect of shear. In the model the nucleation rate of the crystalline entities was related to the shear rate by a power function. Besides, crystalline morphology and orientation were studied by wide and small angle X-ray scattering to confirm the orientation effect of the shear in the crystalline part of the material.     

Synthesis and characterization of graft copolymers with poly(epichlorohydrin-co-ethylene oxide) as backbone by combination of ring-opening polymerization with living anionic polymerization

Series of graft copolymers with [Poly(epichlorohydrin-co-ethylene oxide)] [Poly(ECH-co-EO)] as backbone and polystyrene (PS), poly(isoprene) (PI) or their block copolymers as side chains were successfully synthesized by combination of ring-opening polymerization (ROP) with living anionic polymerization. The Poly(ECH-co-EO) with high molecular weight (M_n = 3.3 × 10⁴ g/mol) and low polydispersity index (PDI = 1.34) was firstly synthesized by ring-ROP using ethylene glycol potassium as initiator and triisobutylaluminium (i-Bu₃Al) as activator. Subsequently, by “grafting onto” strategy, the graft copolymers Poly(ECH-co-EO)-g-PI, Poly(ECH-co-EO)-g-PS and Poly(ECH-co-EO)-g-(PI-b-PS) were obtained using the coupling reaction between living PI⁻Li⁺, PS⁻Li⁺ or PS-b-PI⁻Li⁺ species capped with or without 1,1-diphenylethylene (DPE) agent and chloromethyl groups on poly(ECH-co-EO). By model experiment, the addition of DPE agent was confirmed to have an important effect on the grafting efficiency at room temperature. Finally, the target graft copolymers and intermediates were characterized by SEC, ¹H NMR, MALLS and FTIR in detail, and thermal behaviours of the graft copolymers were also investigated by DSC measurement.     

Synthesis and properties of ABA-type triblock copolymers of poly(glycolide-co-caprolactone) (A) and poly(ethylene glycol) (B)

Poly(glycolide-co-caprolactone) (A)-poly(ethylene glycol) (B) ABA-type triblock copolymers (PGCE) were synthesized by bulk ring opening polymerization, using the hydroxyl endgroups of poly(ethylene glycol) (PEG) as initiator and stannous octoate as catalyst. The resulting copolymers were characterized by various analytical techniques. Gel permeation chromatographic analysis indicated that the polymerization product was free of residual monomers, PEG and oligomers. ¹H NMR and differential scanning calorimeter results demonstrated that the copolymers had a structure of poly(glycolide-co-caprolactone) (PGC) chains chemically attached to PEG segments. All the PGCE copolymers showed improved hydrophilicity in comparison with the corresponding PGC copolymers with the same molar ratio of glycolidyl and caproyl units. The microspheres of PGCE copolymer exhibited rough surfaces quite different from the smooth surface of PGC microspheres. This phenomenon was attentively ascribed to the highly swollen ability of PGCE copolymers and the freeze-drying process in the microspheres fabrication.     

Poly[(styrene-co-p-methylstyrene)-b-isobutylene-b-(styrene-co-p-methylstyrene)] triblock copolymers. 1. Synthesis and characterization

The synthesis of poly(isobutylene) (PIB)-based triblock copolymers having copolymer end blocks containing styrene and p-methylstyrene (pMSt) repeat units was investigated in an attempt to minimize chain-coupling reactions that occur at the 4-position on styrene repeat units during end block polymerization. Model end block copolymerizations using varying feed ratios of styrene and pMSt were conducted, and it was determined by ¹H NMR analysis that the addition of pMSt to the living chain end was favored slightly at low conversion. However, DSC revealed a single T_g that increased with increasing pMSt content verifying the absence of blockiness in the microstructure. Poly[(styrene-co-pMSt)-b-isobutylene-b-(styrene-co-pMSt)] triblock copolymers were synthesized using varying feed ratios of styrene and pMSt. The rate of end block propagation increased with increasing pMSt in the feed, and the end block copolymerizations initiated by PIB displayed longer reaction times and more curvature in their first order plots than did the model end block copolymerizations initiated by TMPCl. This effect was attributed to lower ionization equilibrium constant and higher degree of termination caused by the more non-polar local reaction medium provided by the PIB center blocks in block copolymerization. GPC analysis of the final BCPs revealed a decrease in a high molecular weight peak representing the chain-coupled product as the concentration of pMSt in the feed was increased.     

Inhibition of steel corrosion by electrosynthesized poly(o-anisidine)-dodecylbenzenesulfonate coatings

Poly(o-anisidine)-dodecylbenzenesulfonate (POA-DBSA) coatings were synthesized on stainless steel from aqueous solution containing o-anisidine and dodecylbenzene sulfonic acid by using cyclic voltammetry. These coatings were characterized by Fourier transform infrared spectroscopy (FTIR), UV-vis absorption spectroscopy, scanning electron microscopy (SEM) and cyclic voltammetry (CV). Corrosion tests of these coatings were carried out in aqueous 3% NaCl solution by using open circuit potential (OCP) measurements, potentiodynamic polarization technique, cyclic potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS). The results reveal that POA-DBSA acts as a corrosion protective coating on steel and reduces the corrosion rate (CR) of steel almost by a factor of 14.5.     

Electropolymerization of m-aminophenol on mild steel and its corrosion protection effect

Poly-m-aminophenol (PMAP) films were synthesized using cyclic voltammetric (CV), chronoamperometric (CA) and chronopotentiometric (CP) methods in basic hydro-alcoholic medium on mild steel (MS). The structure and properties of these films were characterized by FTIR, UV–vis and scanning electron microscopy (SEM). SEM microphotographs reveal that the surface of MS was coated with PMAP films using CV, CP and CA methods. Some pinholes were seen in the SEM microphotograph of PMAP films prepared using CP method. The anti-corrosion behavior of PMAP films synthesized by CV, CA and CP has been investigated in 3.5% NaCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy. The results show that PMAP films synthesized by CV and CA methods are much more effective in reducing the corrosion of MS than PMAP films synthesized by CP method. Corrosion performance of these films arises from the barrier effect for the diffusion of O₂.     

Synthesis of exfoliated poly(styrene-co-acrylonitrile) copolymer/silicate nanocomposite by emulsion polymerization; monomer composition effect on morphology

Two types of SAN/silicate nanocomposites were prepared to set up the relationship between the composition of monomers and the resultant morphology of the composites using a pristine sodium montmorillonite (Na-MMT). SAN I series were synthesized with acrylonitrile in initial stage and a mixture of styrene and acrylonitrile in increment stage. SAN II series were prepared with the mixture of styrene and acrylonitrile throughout polymerization. SAN I series showed exfoliated states but SAN II series exhibited intercalated states because SAN I series consisted of hydrophilic AN initially. The chemical affinity between monomer and silicate had a strong influence on the morphology of SAN/silicate nanocomposites. The exfoliated SAN I series had enhanced moduli and glass transition temperatures, T_g, compared to the intercalated SAN II series and pure SAN.     

Characterization of ultrathin electroactive films synthesized via the self-limiting electropolymerization of o-methoxyaniline

The electropolymerization of o-methoxyaniline under self-limiting deposition conditions yields ultrathin (<20 nm) coatings of an insoluble, low-molecular-weight polymer on planar indium-tin-oxide electrode substrates. The self-limiting nature of the electropolymerization is achieved by using citrate-buffered aqueous electrolytes (pH 4.7) in which the developing polymer that deposits at the electrified interface is neither conductive nor permeable to monomer. Although non-conductive as electrodeposited, the resulting poly(o-methoxyaniline) coating becomes electroactive when transferred to acidic aqueous electrolytes. The morphology and chemical structure of the poly(o-methoxyaniline) coatings are characterized by surface-sensitive methods including atomic force microscopy, specular-reflectance infrared spectroscopy, X-ray photoelectron spectroscopy, and electrochemistry. Fundamental understanding of the structure/property relationships derived from these investigations on planar substrates will ultimately be applied to three-dimensional electrode nanoarchitectures that incorporate such electroactive coatings for enhanced charge-storage functionality.     

The effect of flexible chain length on thermal and mechanical properties of poly(m-methylene 2,6-naphthalate)s

The effect of flexible chain length on the thermal and mechanical properties such as melting temperature, glass transition temperature, dynamic mechanical relaxation behavior, and uniaxial tensile deformation for melt-quenched poly(m-methylene 2,6-naphthalate) (PmN) films was investigated using differential scanning calorimeter (DSC), dynamic mechanical thermal analyzer, and universal tensile machine. It was found from DSC thermograms that PmNs with even number of methylene group have higher melting temperatures and faster crystallization rates than PmNs with odd number of methylene group, showing an odd-even fluctuation. The plots of versus temperature show that all PmN samples have three relaxation processes (β, β^∗, and α) regardless of the number of methylene group in their backbone. It was found that both β^∗- and α-relaxations are cooperative processes and that the activation energies of both relaxations as well as the glass transition temperature associated with the α-relaxation show odd-even fluctuations as a function of the number of methylene group. The initial tensile modulus at the low drawing rate of 0.15 cm/min also shows an odd-even fluctuation. In summary, the macroscopic thermal and mechanical properties of PmN such as melting temperature, glass transition temperature, crystallization rate, activation energies of α- and β^∗-relaxations, and initial modulus measured under a slow drawing rate exhibit odd-even fluctuations as the number of methylene group in PmN increases.     

Double-responsive core-shell-corona micelles from self-assembly of diblock copolymer of poly(t-butyl acrylate-co-acrylic acid)-b-poly(N-isopropylacrylamide)

Self-assembly of poly(t-butyl acrylate-co-acrylic acid)-b-poly(N-isopropylacrylamide) [P(tBA-co-AA)-b-PNIPAM], which was obtained from part hydrolysis of PtBA-b-PNIPAM synthesized by sequential atom transfer radical polymerization (ATRP) was studied. Thermo- and pH-responsive core-shell-corona (CSC) micelles with different structures were formed from (PtBA-co-PAA)-b-PNIPAM in aqueous solution. At pH 5.8 and 25 °C, the block copolymer self-assembled into spherical core-shell micelles with hydrophobic PtBA segments as the core, hydrophilic PAA/PNIPAM segments as the mixed shell. Increasing temperatures, core-shell micelles converted into CSC micelles with PtBA as the core, collapsed PNIPAM as the shell and soluble PAA as the corona. Moreover, decreasing pH at 25 °C, PAA chains collapsed onto the core resulting in CSC micelles with PtBA as the core, PAA as the shell and PNIPAM as the corona.     

Synthesis and characterization of bionanocomposites of poly(lactic acid) and TiO2 nanowires by in situ polymerization

Bionanocomposites from biopolymers and inorganic nanoparticles are of great interest for packaging materials due to their enhanced physical, thermal, mechanical, and processing characteristics. In this study, poly(lactic acid) (PLA) nanocomposites with covalent bonding between TiO₂ nanowire surface and PLA chains were synthesized through in situ melt polycondensation. Molecular weight, structure, morphology, and thermal properties were characterized. Fourier transform infrared spectroscopy confirmed that PLA chains were covalently grafted onto TiO₂ nanowire surface. Transmission electron microscopy images also revealed clearly a third phase presence on the nanowires after the grafting process. Those grafted PLA chains exhibited significantly increased glass transition temperature and thermal stability, compared with pure PLA. The weight-average molecular weight of PLA/2% TiO₂ nanowire bulk nanocomposites increased by 66% compared with that of pure PLA. The electron microscopy results showed that strong interfacial interaction and homogeneous distribution were achieved between inorganic nanowires and organic PLA matrix in the bulk nanocomposites. The PLA matrix in bulk nanocomposites exhibited elevated glass transition temperature and decreased crystallization ability as the TiO₂ nanowire concentrations were increased from 0 to 2%.