Determination of reactivity ratios and swelling characteristics of ‘stimuli’ responsive copolymers of N-acryloyl-N′-ethyl piperazine and MMA

‘Stimuli’ responsive copolymers of N-acryloyl-N′-ethyl piperazine (AcrNEP) and methyl methacrylate (MMA) were synthesized by free radical solution polymerization. The copolymers were analyzed as thin films by FTIR spectroscopy. The monomer reactivity ratios were determined by linearization methods of Fineman-Ross (F-R) and Kelen-Tüdös (K-T) giving the results r₁ (AcrNEP)=0.58 and r₂ (MMA)=0.91 by the F-R method and r₁=0.72 and r₂=1.08 by the K-T method. The latter r values in turn yielded Q=0.59 and e=−0.12 for AcrNEP. Crosslinked copolymer hydrogels of AcrNEP and MMA with various compositions were prepared in bulk and solution by photo-initiated free-radical polymerization. The gels were dual responsive to pH and temperature. The response to pH was reversible with a response time of 100 min with good reversibility and with no loss in swelling capacity. Water sorption of the gels was investigated gravimetrically and the collective diffusion coefficients were determined at 10, 25, and 50 °C. The water sorption of the gels in water was Fickian. The temperature dependence of the equilibrium water content was studied by the Gibbs-Helmholtz equation. The enthalpy of mixing decreased with an increase in the hydrophilic content (AcrNEP) of the gel. Other parameters such as type and amount of crosslinker, preparative conditions, nature of buffers, and salts were found to influence the swelling behavior.     

Fluorescence and molecular dynamics to study the intramolecular energy transfer in N-vinyl carbazole/styrene copolymers of different molar compositions

Emission spectra, fluorescence polarization, quenching and lifetime measurements were performed on dilute solutions of poly(N-vinyl carbazole) and N-vinyl carbazole/styrene copolymers to study the intramolecular energy transfer between carbazole groups along the polymer chain. Fluorescence anisotropy values for the samples dissolved in a PMMA solid matrix and quenching measurements in toluene by CCl₄ were used to estimate the efficiency of energy transfer as a function of the monomer molar composition. Analysis of the experiments suggests that the copolymer with the highest carbazole content, which corresponds to the highest amount of carbazole excimers, does not show the highest energy transfer efficiency. Intramolecular excimers which strongly increase with the carbazole content and that are mainly due to carbazole-carbazole monomer sequence interactions undoubtedly act as energy transfer traps. Molecular dynamics simulations on isotactic and syndiotactic copolymer fragments were used for obtaining different parameters related to the energy transfer process as a function of the number of styrene monomer units between vinyl carbazole ones.     

Electrosynthesis of poly(aniline-co-p-aminophenol) having electrochemical properties in a wide pH range

Copolymerization of aniline and p-aminophenol in aqueous sulfuric acid solutions was electrochemically performed using cyclic voltammetry on platinum electrodes. The monomer concentration ratio can strongly affect the copolymerization rate and electrochemical property of the copolymer. The optimum conditions for the copolymerization are that the potential sweep covers the −0.20 to 0.95 V (vs. SCE) potential range, and that a solution contains 0.18 M aniline, 0.02 M p-aminophenol and 0.50 M H₂SO₄. A resulting copolymer synthesized under the optimum conditions has a good electrochemical activity in 0.50 M solutions of Na₂SO₄ with pH ≤ 10.0. IR and XPS spectra indicate that -OH groups and SO₄²⁻ ions are contained in the resulting copolymer. The SEM images reveal that the microstructure of the copolymer depends on the monomer concentration ratio during the electrolysis.     

Synthesis and characterization of A2 + B3-type hyperbranched aromatic polyesters with phenolic end groups

Hyperbranched (hb) aromatic polyesters with phenolic end groups were synthesized according to the A₂ + B₃ approach both, by solution polymerization and by melt (bulk) polymerization with different monomer ratios (A₂:B₃). The hb polyesters produced from solution polymerization exhibited higher yields, molar masses and glass transition temperature (T_g) compared to the products prepared in the melt. The resulting hb aromatic polyesters from the A₂ + B₃ approach were also compared with their properties to hb aromatic polymers produced from the well known AB₂ monomer 3,5-bis(trimethylsiloxy)benzoyl chloride. Both types of hb aromatic polyesters possess high T_g, high thermal stability and good solubility in common organic solvents. A typical melt viscosity behavior with shear thinning effect was also observed for both. Thus similar polymer properties compared to melt-condensed products were obtained with the A₂ + B₃ approach by solution polycondensation possessing the advantage of easy monomer availability and much milder polymerization conditions (at room temperature in solution) compared to the AB₂ approach.     

Interdiffusion and phase behavior at homopolymer/random copolymer interfaces

Interdiffusion in polymer bilayers of polystyrene (PS) and the statistically random copolymer poly(styrene-r-4-bromostyrene) (PBS), (C₈H_(8−x)Br_x)_N, where x is the mole fraction of brominated repeat units in the copolymer and N the degree of polymerization, was studied using Rutherford backscattering spectroscopy (RBS). PS/PBS bilayers with 0.04<x<0.63 and the ratio N_PS/N_PBS varied from 0.06<N_PS/N_PBS<18.1 were examined. PBS volume fraction versus depth profiles were obtained from the evolution of the bromine peak in the RBS spectra. It is shown that as the phase boundary is approached, interdiffusion occurs until layer compositions indicative of binodal conditions are reached. These observations are in very good agreement with phase diagrams obtained using Flory-Huggins theory and a PS/PBS interaction parameter measured using small angle X-ray scattering. For N_PS/N_PBS≠1, the mobility is dictated by the faster diffusing (lower N) component, resulting in an interface which moves toward the faster diffusing component. This result is consistent with fast mode theory; equilibrium conditions correspond to the asymmetry of the phase diagrams. Mutual diffusion coefficients were determined by comparison of the RBS data to a mean-field interdiffusion model using the fast mode expression for mobility. The mutual diffusion coefficient is shown to decrease with increasing N and x and increase with temperature. The implications of this miscibility dependence of the interdiffusion behavior, based on both composition of the copolymer and degree of polymerization, are discussed in the context of strengthening homopolymer/random copolymer interfaces.     

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.     

Hydrogels from 2-(dimethylamino)ethylacrylate with 2-acrylamido-2-methyl-1-propanesulfonic acid: synthesis,characterization, and water-sorption properties

A novel series of copolymer hydrogels of 2-(dimethylamino)ethylacrylate (DMAEA)/2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) were prepared by solution free radical polymerization at different feed monomer mol ratios. The monomer reactivity ratios were determined by Kelen–Tüdös method. According to that, the monomer reactivity ratios for poly(DMAEA-co-AMPS) were r₁ = 0.125 and r₂ = 2.85, (r₁ × r₂ = 0.356). The effect of reaction parameters, including the concentration of cross-linking reagent N,N′-methylene-bis-acrylamide (MBA) and initiator ammonium persulfate (APS), the monomer concentration, pH, temperature, salt solutions, and solvent polarity on the water absorption have been also studied. The hydrogels achieved water-absorption values of 430 g of water/g of xerogel for the copolymer 1:2 richest in AMPS moiety. This copolymer is also very stable to the temperature effect. The optimum pH for the copolymers is 7. Aqueous solutions of the copolymers showed lower critical solution temperature behaviour (LCST). The phase transition temperatures of aqueous solutions of these copolymer increased with increasing of hydrophilic AMPS unit content in the copolymers. The glass transition temperature (Tg) of hydrogels showed a decrease by increasing of comonomer DMAEA content.     

Conformational behaviour of (styrene-p-chlorostyrene) triblock copolymers in dilute solutions. 2. Temperature dependence of conformational behaviour in a selective solvent

Intrinsic viscosity, osmotic second virial coefficient and light scattering of the B_mA_nB_m and A_mB_nA_m copolymers (A, styrene monomeric unit; B, p-chlorostyrene monomeric unit, m and n denote the number of units) in cumene which is a good solvent for polystyrene but a θ solvent for poly(p-chlorostyrene) at 59.0°C, were studied over the temperature range 65° to 15°C. The results suggested that conformational transition from a random coil form to a segregated form occurs at a critical temperature which appears to be in the range 40° to 30°C, depending on the composition, molecular weight and structure of the block copolymers; the θ condition could not be attained by cooling the block copolymer solutions, and micelle formations due to intermolecular associations were found in some cases below the transition temperature.     

Comprehensive analysis of stereoregularity and sequence distribution in 2-N-carbazolylethyl acrylate and methyl methacrylate copolymers by 2D NMR spectroscopy and their thermal studies

A series of 2-N-carbazolylethyl acrylate (C) and methyl methacrylate (M) copolymers with varying compositions were prepared in toluene at 60 °C using AIBN as an initiator. The molar outfeed ratio (F_C) for various compositions was determined from ¹H NMR spectra. Reactivity ratios calculated using Kelen-Tudos (KT) and non-linear error in variable (RREVM) methods were found to be r_C=0.43±0.8 and r_M=2.78±0.52. Molecular weight distribution was determined by gel permeation chromatography (GPC). The methine carbon of C unit showed splitting up to the pentad level in ¹³C{¹H} NMR spectra and was found to be sensitive to the variation in C/M copolymer compositions. The backbone methylene and carbonyl carbons of both M and C unit along with α-methyl carbon of the M unit showed both compositional and configurational sensitivity. Distortionless enhancement by polarization transfer (DEPT) helped in differentiating the methylene carbon signals from the methine and methyl carbon resonances. 2D heteronuclear single quantum coherence (HSQC) and 2D total correlation spectroscopy (TOCSY) were used in tandem to deduce all spectral assignments. 2D heteronuclear multiple bond coherence (HMBC) played an important role in studying the stereoregularity of the carbonyl carbon. The trend in variation of glass transition temperature (T_g) of various C/M copolymer compositions was also studied.     

A method for the calculation of compositions of radical-chain copolymerizations

In this article the straight-line relationship between In A and B, where A and B denote the concentrations of the two types of monomers in any reaction period, is examined to exist in the radical copolymerizations of 1.02 ≥ r₁r₂ ≥ 0.25. Utilizing this observation, we propose an easy-to-use compositions calculation method in which a single empirical parameter is included. The method is derived without involving the constant monomer reactivity ratios assumption. The copolymerizations of styrene–methyl methacrylate vinyl chloride–vinyl acetate, methyl methacrylate–vinyl acetate, acrylic acid–acrylamide, methacrylic acid–methacrylamide, and sodium methacrylate–methacrylamide are investigated. The instantaneous and cumulative copolymer compositions and the residued monomer compositions computed by this proposal are in very good agreement with the experimental data.     

Colorless polyimides derived from 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride,self-orientation behavior during solution casting,and their optoelectronic applications

A novel cycloaliphatic monomer for polyimides (PI), 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride (H′-PMDA) is proposed in this work. H′-PMDA shows high polymerizability with various diamines in contrast to its isomer, i.e., conventional hydrogenated pyromellitic dianhydride (H-PMDA) and leads to highly flexible and colorless PI films with very high T_g's. In particular, the combinations with rigid structures of diamines give rise to PIs with significantly decreased coefficients of thermal expansion (CTE) owing to high extents of in-plane chain orientation induced by thermal imidization, whereas the H-PMDA-based counterparts do not. The decreased CTE reflects structural rigidity/linearity of the H′-PMDA-based diimide units as supported by liquid crystallinity observed in the corresponding model compound. Solution casting of a chemically imidized PI derived from H′-PMDA and 2,2′-bis(trifluoromethyl)benzidine (TFMB) results in a lower CTE than that of the thermally imidized counterpart, suggesting the presence of a self-orientation phenomenon during solvent evaporation. The mechanism is proposed in this work. H′-PMDA/TFMB and its copolymer systems can be useful as plastic substrates in image display devices and/or novel coating-type optical compensation films.     

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.     

Synthesis and conformation studies of copolypeptides composed of γ-methyl-l-glutamate and ε-N-carbobenzyloxy-l-lysine

Copolypeptides (PMGCL) composed of γ-methyl-l-glutamate(MLG) and $\text{?-N-}\text{carbobenzyloxy-}\text{l}\text{-lysine(CBL)}$ covering the whole range of copolymer composition were synthesized by the N-carboxyanhydride (NCA) method. The experimentally obtained monomer reactivity ratios were r₁(MLG)=2·0±0·4 and r₂(CBL)=0·5±0·1, from which the fractions of monomer dyads and triads in copolymer were plotted against the initial comonomer composition. From experimental results on thermally induced coil-to-helix transition of the copolypeptides in dichloroacetic acid/1,2-dichloroethane (DCA-DCE) systems, it has been found that these copolypeptides can exist in the α-helix conformation in the same manner as homopolypeptides PMLG and PCBL. The van't Hoff heat of transition ΔH showed a minimum against the initial monomer composition. The enthalpy ΔH_res of formation of intramolecular hydrogen bonds per peptide bond also showed a minimum against copolymer composition. Such behaviour on ΔH and ΔH_res was also found for copolypeptide (PBGCL) composed of γ-benzyl-l-glutamate(BLG) and $\text{?-N-}\text{carbobenzyloxy-}\text{l}\text{-lysine(CBL)}$ in DCA-DCE systems reported in a previous paper. The presence of a minimum in these relationships may be attributed to specific interactions between the side chain of one comonomer and that of the other comonomer in a two component copolymer. It is also pointed out that these copolymer molecules can exist in the α-helix conformation in the solid state.     

Thermo-, and pH dual-responsive poly(N-vinylimidazole): Preparation,characterization and its switchable catalytic activity

A monomer, 2-(isobutyramido)-3-methylbutyl methacrylate (IMMA) was synthesized through a two-step reaction. When a few of IMMA (less than 4 mol%) was copolymerized with N-vinylimidazole (VIm) under free radical polymerization condition, water-soluble P(VIm-co-IMMA) copolymers were obtained. Their structural information was verified and interpreted from ¹H NMR, FTIR and GPC. Kinetic analyses from ¹H NMR demonstrated that one-batch addition of IMMA into the polymerization system led to an inhomogeneous distribution of IMMA units in the copolymers, whereas homogeneous distribution of IMMA units in the copolymers could be obtained through the portion-wise addition of IMMA monomer. The thermal properties of such copolymers were measured by DSC. Compared with PVIm homopolymer, the few IMMA units in the P(VIm-co-IMMA) copolymer had little influence on the T_g values. The obtained P(VIm-co-IMMA) copolymers were thermoresponsive in water, and their phase transition temperatures could be efficiently raised through reducing the IMMA content in the copolymers, raising the addition times of IMMA monomers or lowering the pH of media. Dynamic light scattering analysis showed that unlike the traditional thermoresponsive linear polymers, obvious size shrinkage around the phase transition temperature could not be observed in such P(VIm-co-IMMA) copolymers. Such copolymers could be used as smart organocatalysts in the hydrolysis of p-nitrophenyl acetate. Below the phase transition temperature the reaction rate followed the Arrhenius law, but above the phase transition temperature the reaction rate increased much slower than the prediction from the Arrhenius law. Moreover, the catalytic transition temperature could be tuned through utilizing the P(VIm-co-IMMA) copolymers with different phase transition temperature. The mechanism was discussed accordingly.     

Synthesis and photodynamic properties of amphiphilic A3B-phthalocyanine derivatives bearing N-heterocycles as potential cationic phototherapeutic agents

Unsymmetrically substituted A₃B-phthalocyanine derivatives bearing annulated 6-membered N-heterocycles, pyridine and pyrazine rings, were synthesized by the ring expansion reaction of boron(III) subphthalocyanine chloride. A geometrically constrained subphthalocyanine unit was reacted with a range of 1,2-phthalonitrile derivatives in presence of 8-diazabicyclo[5.4.0]undec-7-ene to form the A₃B-phthalocyanine. The reactions were carried out in DMSO/1-chloronaphthalene at 130-140 °C for 15 h. This synthetic strategy resulted in phthalocyanines in 37-42% yield that required only simple purification. Annulated 6-membered N-heterocycles were methylated to obtain cationic Zn(II)phthalocyanine derivatives. The spectroscopic and photodynamic properties of these photosensitizers were studied in N,N-dimethylformamide solution. Antifungal activity photoinduced by these compounds was evaluated in Candida albicans cellular suspensions. The results indicate that amphiphilic cationic phthalocyanines represent interesting agents with potential applications in photodynamic inactivation of microorganisms.     

Preparation of poly(tert-butyl acrylate-g-styrene) as precursors of amphiphilic graft copolymers. 1. Kinetic study and thermal properties

Free radical copolymerizations of tert-butyl acrylate and a polystyrene macromonomer carrying a methacryloyloxy group at the chain end have been performed in benzene solution using 2,2′-azobis(isobutyronitrile) (AIBN) as initiator at 70 °C. The estimated values of the ‘lumped’ kinetic constant, k_p/k_t^1/2, have shown a clear dependency on the macromonomer concentration in the reaction medium. The obtained poly(tert-butyl acrylate-g-polystyrene) graft copolymers were characterized by size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). In addition, the thermal behavior of these copolymers was studied by thermogravimetric analysis (TGA). Subsequently, hydrolysis of precursor graft copolymer was performed to afford an amphiphilic graft copolymer. Characterization using FT-IR confirmed total hydrolysis of the ester group.     

Kinetic analysis of A2 + AB + B3 hyperbranched polymerization approach

This work theoretically deals with the kinetics of the hyperbranched polymerization with A₂, AB and B₃ monomers. The analytical expressions of the size distribution function and the various molecular parameters of the resulting hyperbranched polymers were derived. The structure and molecular parameters of the products depend on the monomer feed ratios and the conversion of groups. Gelation is easy to occur if the monomer feed ratio of A₂ to B₃ (λ) is in the range of 3/4 ≤ λ ≤ 3. The addition of AB monomer can increase the conversion of A or B groups and enhance the number-average degree of polymerization at the critical gelation point. On the other hand, excessive AB monomer will results in a small degree of branching for the products. A small λ and a suitable β value favor to form the hyperbranched polymers with certain degree of branching.     

Effect of the alkyl group on the synthesis and the electrochemical properties of N-alkyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquids

The effect of the alkyl side group on the synthesis and the electrochemical properties of N-alkyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR_1ATFSI) ionic liquids (ILs) is reported. The investigation was focused on the PYR_1ATFSI ionic liquid family because of the interesting electrochemical properties of the members with propyl and butyl side chains. Side alkyl groups (A = C_nH_2n+1 with n ranging from 1 to 10) of different length and structure were used for the synthesis of PYR_1ATFSI materials. NMR and DSC have shown that the ionic liquids were correctly synthesized with the exception of the compounds with tertiary side chains. Most of the materials exhibited a conductivity higher than 10⁻³ S cm⁻¹ already at 12 °C. In the molten state a moderate conductivity decrease was observed with increasing the length and the branching of the side chain (C₂H_2n+1) group according with the change of viscosity of the ionic liquids. Most of the PYR_1ATFSI samples exhibited an electrochemical stability window exceeding 5 V.     

Copolymerization of N-(4-carboxyphenyl)maleimide with acrylonitrile and the properties of its membrane

N-(4-Carboxyphenyl)maleimide (N-4-CPMI, M₁) was copolymerized with acrylonitrile (AN, M₂) to prepare the copolymer. The monomer reactivity ratios and Alfrey-Price Q, e values were determined as r₁ = 0.56, r₂ = 0.84, Q ₁ = 2.0, Q ₂ = 0.6 and e ₁ = 2.06, e ₂ = 1.2. The membrane of copolymer containing 0.25% CPMI had a good tensile property (67.3 MPa). The 0.75 mole% membrane had an excellent selectivity factor (α = 45.3).     

Influence of A-site Ba substitution on microwave dielectric properties of (BaxMg1−x)(A0.05Ti0.95)O3 (A=Zr,Sn) ceramics

The microwave dielectric properties of (Ba_xMg_1−x)(A_0.05Ti_0.95)TiO₃ (A=Zr, Sn) ceramics were investigated with regard to substitution of Ba for Mg of A-site. The microwave dielectric properties were correlated with the Ba content. With an increase in Ba content from 0.01 to 0.1, the dielectric constant and the τ_f value increased, but the Q×f value decreased. The sintered (Ba_xMg_1−x)(Zr_0.05Ti_0.95)TiO₃ (called B_xMZT) ceramics had a permittivity in the range of 19.1−20.6, quality factor from 180,000 to 25,000 GHz, and variation in temperature coefficient of resonant frequency from −35 to −39 ppm/°C with increasing composition x. For sintered (Ba_xMg_1−x)(Sn_0.05Ti_0.95)TiO₃ (called B_xMST) ceramics, the dielectric constant increased from 19 to 20.5, Q×f value increased from 120,000 to 37,000 (GHz), and the τ_f value increased from −50 to −3.3 ppm/°C as the x increased from 0.01 to 0.1. When A=Sn and x=0.1, (Ba_0.1Mg_0.9)(Sn_0.05Ti_0.95)TiO₃ ceramics exhibited dielectric constant of 20.5, Q×f value of 37,000 (GHz), and a near-zero τ_f value of −3.3 ppm/°C sintered at 1210 °C for 4 h.