Ionic Group Content Research Articles

Modification of PET by Reactive Blending with Sulfonated Esters. II. Isothermal Crystallization Kinetics of PET-Ionomers

The thermal properties of PET-ionomers, obtained by reactive blending between PET and a monofunctional ester containing an ionic group (–SO3Na), were studied using DSC, and results were compared with those of nonionic PET homopolymers. The presence of ionic groups located only at the chain ends induces significant modifications in the thermal behavior: the equilibrium melting temperature increases and the crystallization rate decreases with the ionic group content; moreover, the crystalline level remains high. All of these characteristics are interpreted as due to ionic associations between the sulfonated end groups, both in solid and in molten states, that cause an apparent increment in the molecular weight of ionomers. A confirmation of this simple molecular architecture is found in the growth regime analysis: the fold-surface free-energy values of ionomers do not vary compared to those of nonionic homopolymers, indicating that chain folding is not hindered by the presence of a complex network.

Different dispersion regions during the phase inversion of an ionomeric polymer–water system

Catastrophic phase inversion is induced by changing the phase ratio in a liquid–liquid dispersion and is widely used during the dispersion stage in the production of aqueous polyurethane ionomer (PUI) colloids. In the work reported here, water was added to polyurethane ionomer prepolymer (PUIp) until the water became the continuous phase. Three different dispersion regions have been discovered by changing the ionic group content. Stable emulsions containing small polymer drops were produced in Region I. Stable coarse emulsions containing a mixture of drop structures were produced in Region II, but only temporary dispersions could be produced in Region III. Conductivity measurements could not always be used to detect the phase inversion points effectively because the PUIp was swollen by water. Therefore, torque change measurements have been used in conjunction with the conductivity measurements to detect the phase inversion points for all three dispersion regions. Scanning electron microscopy (SEM) and optical microscopy were used to obtain images of these dispersions in the different regions. A catastrophic phase inversion map is used to represent the changes that occur in the PUIp–W dispersions. This map is plotted using the ionic group content as the ordinate and water content (at the phase inversion points) as the abscissa.

Temperature dependent swelling behavior of ionic poly(N-isopropylacrylamide) gels in PEG solutions

The swelling behavior of poly(N-isopropylacrylamide) (PNIPA) hydrogels in aqueous solution of poly(ethy1ene glycol) (PEG) and the partition parameter of PEG between the gel and the external solution were investigated. The molecular weight of PEG, the ionic group content of the hydrogels and the swelling temperature were taken as the independent variables. Several types of volume phase transitions such as swelling, deswelling and reentrant phase transitions were observed depending on the external parameters. The results were explained in terms of the theory of equilibrium swelling.

Poly(ether-block-sulfonated ester) copolymers. III. Morphology and ionic aggregation in PESE

Sulfonated poly(ether–ester) copolymers (PESE) based on poly(butylene terephthalate-co-butylene 5′-sulfoisophthalate sodium salt) and poly(1,4-oxytetramethylene) were studied. Morphological changes that can occur as a consequence of interactions of the sulfonate groups in PESE were investigated by using differential scattering calorimetry (DSC), wide- and small-angle x-ray scattering, and scanning electron microscope measurements. The x-ray scattering and DSC studies show that the degree of crystallinity decreases with increasing content of ionic groups in the polyester rigid segments. This change is the result of ionic forces caused by incorporation of the ionic units. A morphology of ionic aggregates inside microphase-separated poly(butylene terephthalate) domains is suggested.

Swelling–shrinking hysteresis of poly(N‐isopropylacrylamide) gels in sodium dodecylbenzenesulfonate solutions

AbstractThe swelling and shrinking behaviors of a series of poly(N‐isopropylacrylamide) (PNIPA) hydrogels are studied in aqueous solutions of sodium dodecylbenzenesulfonate (SDBS). Between 0 and 3 mol % 2‐acrylamido‐2‐methylpropanesulfonic acid sodium salt (AMPS) is used as an ionic comonomer in the hydrogel synthesis. It is shown that the collapsed PNIPA gels in water at 52°C start to swell above a critical SDBS concentration in the external solution. This critical concentration decreases as the ionic group content of PNIPA gel increases. A comparison of the swelling and shrinking experiments in SDBS solutions indicates strong hysteresis behavior of PNIPA gels. A more diluted solution is required to make a swollen gel start to reshrink than to cause gel swelling. The results show strong attractive forces between the isopropyl groups of the PNIPA network and the DB groups of SDBS molecules. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1228–1232, 2002

POLY(ETHER-BLOCK-SULFONATED ESTER)COPOLYMERS. I. PHASE STRUCTURE AND PHYSICAL PROPERTIES1*

The physical properties and a microphase-separated structure of multiblockcopolymers based on flexible segments of poly(1,4-oxytetramethylene)(PTMO) and rigid crystalline segments of poly(butylene terephthalate) (PBT) modified by ionic units were studied. Ionic copolymers were characterizedby limiting viscosity number, melt flow index, and tensile property measurements. The mechanical behavior of ionic poly(ether-block-sulfonated ester)(PESE) copolymers can be compared to that of conventional hard-soft thermoplasticelastomers. The phase structure was studied using differential scanningcalorimetry (DSC). Clearly, the DSC results show that the ionic unitsin the polyester segments have no significant influence on the microphaseseparation structure of PESE. A small reduction of the degree of crystallinitywith increasing content of ionic groups in the polyester rigid segments wasobserved. This results from the effect of ionic forces caused by incorporationof ionic units in the polyester segments. *Dedicated to Prof. Francisco J. Balta´ Calleja on the occasion of his 65th birthday.

POLY(ETHER-BLOCK-SULFONATED ESTER) COPOLYMERS. II. MECHANICAL AND DIELECTRIC RELAXATION1*

This work reports mechanical and dielectric relaxation studies of multiblock copolymers based on flexible segments of poly(1,4-oxytetramethylene) (PTMO) and rigid crystalline segments of poly(butylene terephthalate) (PBT) modified by ionic units [poly(ether-block-sulfonated ester), PESE]. The dynamic mechanical thermal analysis (DMTA) results indicate that PESE should behave as unvulcanized rubbers at ambient temperature. The changes in the intensities of dielectric relaxation peaks for the β and γ-processes with respect to concentration of rigid segments and ionic unit content in these segments were found to be associated with corresponding changes in crystalline structure and morphology of the PESE. The mechanical and dielectric results show that the degree of crystallinity decreased with increasing content of ionic groups in the polyester rigid segments. At higher concentrations of rigid segments modified by ionic units, the presence of a relaxation that can be due to the ionic aggregation was observed in the DMTA and dielectric spectra. *Dedicated to Prof. Francisco J. Baltá Calleja on the occasion of his 65th birthday.

Modulating fibroblast cell proliferation with functionalized poly(methyl methacrylate) based copolymers: chemical composition and monomer distribution effect.

Poly(methyl methacrylate)-based terpolymers bearing sulfonate and carboxylate groups have been synthesized by radical copolymerization leading to polymers with random distributions of ionic monomer units. Fibroblast cells were seeded on terpolymers of various molar compositions of ionic groups. Kinetics of the cell proliferation were examined and systematically compared to the nonfunctionalized control polymer, poly(methyl methacrylate). Modulation of cell proliferation was observed on 15% ionic monomer content copolymers of various compositions (R = COO(-)/(COO(-) + SO(3)(-)) and varies from 0 to 1). The inhibition percentage of cell proliferation calculated for each polymer by comparison to the cell proliferation on the control was plotted against R and gave a maximum value for R close to 0.55. Copolymers with ionic group contents higher or lower than 15% exhibit inhibition percentages fitting with those previously observed for the same R values, showing that the hydrophilic properties are not sufficient to explain the modulation effect of this material toward cells. Moreover, for each polymer tested, cells, even if inhibited in growth, were shown to be viable, indicating that the synthesized terpolymers exhibit cytostatic properties excluding any cytotoxic effect. Such polymers may be used for the fabrication of biocompatible intraocular lenses and prevent secondary cataract.

Effect of ions on the dynamic behavior of an electrodriven ionic polymer hydrogel membrane

AbstractThe bending mechanism of an electrodriven ionic polymer hydrogel membrane was investigated in terms of the concentration of ionic groups and the valence of ionic species within the hydrogel membrane. It was elucidated that the distribution of the ionic concentration played an important role in the bending behavior of the membrane. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 76–80, 2001

Cellulose–poly(acrylamide–acrylic acid) interpenetrating polymer network membranes for the pervaporation of water–ethanol mixtures. II. Effect of ionic group contents and cellulose matrix modification

AbstractThe separation properties in the dehydration of a water–ethanol mixture and the swelling behavior of interpenetrating polymer network (IPN) pervaporation membranes based on a cellulose or cellulose–hydroxyethyl cellulose (HEC) matrix and poly(acrylamide and/or acrylic acid) were investigated depending on the ionic acrylate groups content (γ) in synthetic polymer chains (0–100 mol %), the HEC content in the matrix (0–50 wt %), and the temperature (25–60°C). The separation factor (α), permeation rate (P), and separation index (αP) significantly improved with increasing γ values only for the separation of concentrated ethanol solutions (∼86 wt %). For more dilute solutions of ethanol (∼46 wt %), the P and αP values also increased but no considerable increase in α was observed. All types of membranes based on the cellulose matrix were characterized by a drastic decrease in the values of P at [EtOH] ≥90 wt % and, as a result, a decrease in the separation index (kg m−2 h−1) from ∼2000 (for 86 wt % EtOH, 50°C) to ∼240 (for 95 wt % EtOH, 50°C), which correlates with a decrease in the degree of membrane swelling. The modification of the cellulose matrix by introducing HEC into it makes it possible to increase considerably the membrane swelling in concentrated EtOH solutions and, hence, the αP value to ∼760 (95 wt % EtOH, 50°C). All types of IPN membranes exhibit a marked increase in both α and P when the temperature increases from 25 to 60°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1452–1460, 2001

Influence of Synergistic Effects on Ion-Exchange Chromatographic Separation of Proteins

Formation of strong bonds between proteins and polyelectrolyte chains of ion-exchange sorbents gives rise to synergistic effects in multicomponent sorption and chromatographic separation of proteins. A series of heteronetwork-cross-linked polymeric bases with varied content of ionic groups was prepared. Consecutive sorption and cosorption of insulin and α-lactalbumin on these materials were studied.

Swelling of strong polyelectrolyte hydrogels in polymer solutions: effect of ion pair formation on the polymer collapse

A series of strong polyelectrolyte hydrogels based on acrylamide and 2-acrylamido-2-methylpropane sulfonic acid sodium salt or [(Methacrylamido)propyl]trimethyl ammonium chloride were prepared by free-radical crosslinking copolymerization. Their swelling behavior was investigated in a good solvent (water), in polymer melt and in aqueous polymer solutions. Poly(ethylene glycol) of various molecular weights was used as the linear polymer in the swelling experiments. The equilibrium volume swelling ratio q v of the hydrogels in water scales with the network charge density f by the relation q v∝ f 0.66. The volume of the hydrogels in the polymer melt decreases as the number of segments, y, on the polymer increases. It was shown, for the non-ionic hydrogels, that this deswelling occurs due to the mixing entropy of the linear polymer in the external solution, whereas, for the ionic gels, due to trapping of counterions caused by the decreased polarity of the medium. The network–polymer interaction parameter χ 23 was found to vary with y by the relation χ 23=constant/ y. The hydrogels also deswell in aqueous polymer solutions as the polymer concentration increases. This deswelling occurs smoothly or jumpwise, as a first-order phase transition, depending on the ionic group content of the hydrogels. The Flory–Huggins theory correctly predicts the swelling and collapsing behavior of the hydrogels in polymer solutions if the variation of the effective charge density depending on the medium polarity is taken into account.

Acrylamide/2-acrylamido-2-methylpropane sulfonic acid sodium salt-based hydrogels: synthesis and characterization

Relationships between the formation mechanism and the swelling behavior of acrylamide (AAm)/2-acrylamido-2-methylpropane sulfonic acid sodium salt (AMPS)-based hydrogels were studied. The hydrogels were prepared by free-radical crosslinking copolymerization of AAm and AMPS at 40°C in the presence of N, N′-methylenebis(acrylamide) (BAAm) as the crosslinker. Both the crosslinker ratio (mole ratio of crosslinker to monomer) and the initial monomer concentration were fixed at 1/82 and 0.700 M, respectively, while the AMPS content in the monomer mixture was varied from 0 to 100 mol%. It was found that the copolymer composition is equal to the monomer feed composition, indicating that the monomer units distribute randomly along the network chains of the hydrogels. The monomer conversion versus time histories as well as the growth rate of the gel during the polymerization were found to be independent of the amount of AMPS in the initial monomer mixture. It was shown that the reaction system separates into two phases at the gel point and the gel grows in a heterogeneous system. The equilibrium degree of swelling of the final hydrogels increases with increasing AMPS content until a plateau is reached at about 10 mol% AMPS. Between 10 and 30 mol% AMPS, the equilibrium gel swelling in water as well as in aqueous NaCl solutions was independent on the ionic group content of the hydrogels. Further increase in the AMPS content beyond this value increased the gel swelling continuously up to 100 mol%. The polyelectrolyte theories based on the counterion condensation cannot explain the observed swelling behavior of AAm/AMPS hydrogels. The swelling curves of the hydrogels in water and in aqueous NaCl solutions were successfully reproduced with the Flory–Rehner theory of swelling equilibrium including the ideal Donnan equilibria, where the effective charge density was taken as an adjustable parameter. Scaling rules were derived for the ionic group content and the effective excluded volume of the hydrogels.

Evaluation of optimum condition for designing high-performance electro-driven polymer hydrogel systems

This study investigated a parameter that determines an optimum condition of the content of the ionic group and the concentration of outer solution for high-performance electro-driven polymer hydrogel membranes. The optimum condition for quick bending was determined by a simple method that identified the initial conditions based on Donnan equilibrium theory. Since the bending behavior depends on the initial conditions of the ionic group content and the concentration of the outer solution, it can be predicted by the ratio of the ionic concentrations at the membrane–solution interface; the inverse of the Donnan ratio (1/K) at the initial condition. The bending rate of the membranes showed a maximum value at around 1/K = 0.15. The relationship between several interrelated control factors and the bending dynamics of the gel membranes was established by using the initial system parameters alone. 1/K is the effective simple parameter to determine the optimum condition of the content of the ionic group and the concentration of the outer solution for high-performance membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 111–118, 2000

Water-soluble urethane acrylate ionomers: Effect of molecular structure on ultraviolet coating properties

Water-soluble urethane acrylate ionomers containing dimethylolpropionic acid (DMPA) were synthesized, changing the molecular components, and their ultraviolet (UV) coating properties were studied. It was found that the UV coating properties of the urethane acrylate ionomer films were very dependent on the molecular weight of the soft segment, the type of the diisocyanate, and the amount of neutralization. In general observations, the cured films displayed much improved mechanical properties, compared with conventional urethane acrylate film not containing ionic groups. The main reason for the improved film properties seemed to be attributed to the presence of ionic groups in the network. In dynamic mechanical analysis, two distinct glass transition temperatures, corresponding to the ionic hard domains and soft domains, were detected at high content of ionic groups. This suggested that the urethane acrylate network be composed of two phases. Consequently, the ionic hard domains formed by the phase separation from crosslinked network could act as a reinforcing filler, which possibly explains the improved film properties of the urethane acrylate ionomer films. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1853–1860, 2000

Temperature–dependent electrophoretic mobility and hydrodynamic radius measurements of poly(N-isopropylacrylamide) microgel particles: structural insights

Electrophoretic mobility and hydrodynamic radius measurements of poly(N-isopropylacrylamide) [poly(NIPAM)] microgel particles dispersed in water were made as a function of temperature and ionic strength. The data reveal differences between the temperatures at which the particle volume and electrophoretic mobility undergo significant changes. The temperature at which the volume phase transition (VPTT) occurred was 5–6°C lower than the temperature at which pronounced electrophoretic mobility changes occurred. The data appear to be consistent with three stages of collapse for the microgel particles over the temperature range 25–50°C. Ohshima's equations for the electrophoretic mobility of particles covered by an ion-impenetrable surface charge layer were successfully used to fit the data. Electrokinetic equations for hard-sphere systems could not be used for our system. The successful application of the Ohshima theory is evidence that poly(NIPAM) microgel particles prepared by surfactant-free emulsion polymerisation consist of a core–shell structure. It is proposed that the core is relatively highly cross-linked and has a low concentration of ionic groups; whereas, the shell is lightly cross-linked and can be considered as a polyelectrolyte layer. The softness parameter obtained from fitting the Ohshima model to data obtained at 46°C was much higher than expected for a rigid particle and suggests incomplete collapse of the shell at this temperature.

Evaluation of optimum condition for designing high-performance electro-driven polymer hydrogel systems

This study investigated a parameter that determines an optimum condition of the content of the ionic group and the concentration of outer solution for high-performance electro-driven polymer hydrogel membranes. The optimum condition for quick bending was determined by a simple method that identified the initial conditions based on Donnan equilibrium theory. Since the bending behavior depends on the initial conditions of the ionic group content and the concentration of the outer solution, it can be predicted by the ratio of the ionic concentrations at the membrane–solution interface; the inverse of the Donnan ratio (1/K) at the initial condition. The bending rate of the membranes showed a maximum value at around 1/K = 0.15. The relationship between several interrelated control factors and the bending dynamics of the gel membranes was established by using the initial system parameters alone. 1/K is the effective simple parameter to determine the optimum condition of the content of the ionic group and the concentration of the outer solution for high-performance membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 111–118, 2000

Drug release behavior of electrical responsive poly(vinyl alcohol)/poly(acrylic acid) IPN hydrogels under an electric stimulus

The electrically modulated properties of interpenetrating polymer networks (IPN) composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) under electric field were investigated for drug delivery systems. PVA/PAAc IPNs with various compositions were synthesized by a sequential method, that is, ultraviolet polymerization of AAc in the mixture of PVA and aqueous AAc monomer solution, followed by a freeze-thawing process to prepare elastic hydrogels. The amount of loaded drug significantly increased with the content of PAAc containing ionizable groups in IPN. The amount of introduced ionic drug (cefazoline) was greater than that of the nonionic drug (theophylline). Release behaviors of drug molecules from negatively charged PVA/PAAc IPN were switched on and off in a pulsatile pattern depending on the applied electric stimulus. The released amount and the release rate of drug were influenced significantly by the applied voltage, ionic group contents in IPN, ionic properties of drug solute, and the ionic strength of release medium. In addition, the ionic properties of drug molecules dramatically affected release behaviors, thus the release of ionic drug was much more enhanced than that of the nonionic drug. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1752–1761, 1999

Effect of carbon content and cooling rate on properties of high density materials: L.Tremblay, F.Chagnon. (Quebec Metal Powders, Quebec, Canada.)

Polysulfones functionalized with highly phosphonated poly(pentafluorostyrene) side chains of different lengths were synthesized applying controlled polymerization and modification methods. The graft copolymers' thermal properties were evaluated by differential scanning calorimetry and thermal gravimetrical analyses. The proton conductivity of membrane prepared from the graft copolymer with the shortest phosphonated side chains was 134 mS cm−1 at 100 °C under fully immersed conditions. The graft copolymer TEM image shows a nanophase separation of ion-rich segments within the polysulfone matrix. Increasing the ionic groups content in the graft copolymers led to extensive membrane swelling. To improve the dimensional stability the graft copolymers were blended with pyridine-modified polysulfone. The blend membranes were transparent with formation of nano-phase domains as revealed from TEM images. The acid–base blend membranes exhibited a slightly higher thermal stability but lower proton conductivity compared to the membranes formed from pure graft copolymers.

Polyelectrolytes bearing azobenzenes for the functionalization of multilayers

AbstractThin polymeric films are assembled by the alternating adsorption of oppositely charged polyelectrolytes. The polyions are functionalized by azobenzenes, typically carrying donor‐acceptor substituents. The azobenzene chromophores are exploited as versatile analytical tools, to study the assembling process, and to control the film quality. A high concentration of ionic groups does not seem to be advantageous per se for good film growth, but rather the matching of the charge densities of the polyelectrolyte pair used seems to be important. Also, the influence of the strongly interacting, form‐anisotropic character of the azobenzenes on the internal film structure was investigated. Although even high concentrations of azobenzenes and of other mesogens do not induce particular ordering, a few polymer pairs allowed the construction of real multilayer films, exhibiting e.g. Bragg peaks.