The effect of synthesis methods on the mechanical properties of self‐crosslinkable poly(n‐butyl methacrylate‐co‐N‐methylolacrylamide) films

The effects of particle size and parent polymer characteristics on the mechanical properties, gel fraction, and swelling index of self‐crosslinkable poly(n‐butyl methacrylate‐co‐N‐methylolacrylamide) films made by two‐stage emulsion or microemulsion polymerization in the presence of variable amounts of the chain transfer agent, n‐butyl mercaptan, are reported here. In films prepared with latexes made by microemulsion polymerization, the crosslinking degree increased greatly on curing; by contrast, in those made by emulsion polymerization, the crosslinking degree practically did not increase after curing. Stress–strain tests of uncured and cured films indicate that microemulsion‐made films are tougher than the emulsion‐made films. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Anomalous sorption kinetics in the methanol vapor–poly(methyl methacrylate) system

The non‐Fickian sorption kinetics of methanol vapor in poly(methyl methacrylate) films 8 and 51 μm thick at 25°C are presented. The behavior of the system was studied in series of interval and integral absorption runs. The relevant diffusion coefficient and viscous relaxation processes were studied separately by kinetic analysis of the first and second stages of sorption kinetic curves. The sorption isotherm concaved upward at high activities, this being typical of Flory–Huggins behavior, whereas it exhibited a convex‐upward curvature at low methanol vapor activities, this indicating sorption in the excess free volume of the polymer matrix. After excess free‐volume fill‐up, the concentration dependence of the diffusion coefficient was found to be well represented by the free‐volume theory of Vrentas and Duda. Relaxation frequencies calculated from the second stage of two‐stage curves exhibited a weak dependence on the concentration. Integral sorption experiments indicated that the system exhibited nearly case II kinetics at high methanol vapor activities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1184–1195, 2005     

Preparation of superhydrophobic silica‐based films by using polyethylene glycol and tetraethoxysilane

Preparation of superhydrophobic silica‐based films via sol‐gel process by adding polyethylene glycol (PEG4000) in the silica sol precursor solution has been developed. The casting films were prepared by casting the above solution on the glass and adding poor solvent on it or not. Surface roughness of the films was obtained by removing polymer from the films at high temperature. Then, the hydrophobic group on the surfaces was obtained by reaction with hexamethyldisilazane (HMDS). Characteristic properties of the as‐prepared surface of the films were analyzed by contact angle measurement, scanning electron microscopy (SEM), atomic force microscope (AFM), Fourier transform infrared (FT‐IR) spectrophotometer, and X‐ray photoelectron spectrometer (XPS). The results showed that the contact angles of the films were varied with the PEG weight fraction of the films, the solvent for the PEG solution, the reaction temperature and time, and adding poor solvent (n‐hexane) or not. However, the surface roughness has been controlled by adjusting the experimental parameters during the early period. The contact angle of the film that prepared by spraying the poor solvent (n‐hexane) onto each coating layer for four times after casting process was greater than 150°. It was difficult to obtain superhydrophobic surface without adding n‐hexane onto any coating layer in this system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Evaluation of the shrinking‐core model for examining the kinetics of film formation in a reactive latex blend

We prepared reactive latex blends from two copolymer latices comprised of n‐butyl methacrylate (n‐BMA) with acetoacetoxyethyl methacrylate and n‐BMA/dimethylaminoethyl methacrylate to study the kinetics of film formation. We generated thin films by blending equal weights of the two latices. The films were then cured at temperatures ranging from 50 to 90°C. The extent of the crosslinking reaction was calculated from the crosslink density, which was determined from swelling measurements of the films in toluene. The shrinking‐core model, a diffusion/reaction model, which was originally derived for combustion reactions of coal particles, was adopted to calculate the diffusion coefficient (D_e) and reaction rate constants from the extent of the reaction with time data. This model system exhibited a diffusion‐controlled regime above 70°C and a reaction‐controlled regime at temperatures below 70°C. In the reaction‐controlled regime, the shrinking‐core model predicted D_e for the system, which was in agreement with literature values for n‐BMA. In the diffusion‐controlled regime, the model predicted a lower apparent value for D_e but with an activation energy that was close to that obtained for n‐BMA. The model was also used to examine the kinetics of the crosslinking reaction. The kinetic rate constants for the crosslinking reaction were also determined. The activation energy for the crosslinking reaction was 18.8 kcal/mol, which compared reasonably with the activation energy of 22.8 kcal/mol determined for the reaction between the functional monomers as small molecules. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3659–3665, 2006     

Synthesis and characterization of polyacrylamide‐grafted chitosan hydrogel microspheres for the controlled release of indomethacin

Microspheres of polyacrylamide‐grafted‐chitosan crosslinked with glutaraldehyde were prepared and used to encapsulate indomethacin, a nonsteroidal anti‐inflammatory drug. The microspheres were produced by the water/oil emulsion technique and encapsulation of indomethacin was carried out before crosslinking of the matrix. The extent of crosslinking was analyzed by Fourier transform infrared spectroscopy and differential scanning calorimetry. Microspheres were characterized for drug‐entrapment efficiency, particle size, and water transport into the polymeric matrix as well as for drug‐release kinetics. Scanning electron microscopy confirmed the spherical nature and surface morphology of the particles with a mean particle size of 525 μm. Dynamic swelling experiments suggested that, with an increase in crosslinking, the transport mechanism changed from Fickian to non‐Fickian. The release of indomethacin depends upon the crosslinking of the network and also on the amount of drug loading. This was further supported by the calculation of drug‐diffusion coefficients using the initial time approximation. The drug release in all the formulations followed a non‐Fickian trend and the diffusion was relaxation‐controlled. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1525–1536, 2003     

Release of vitamin B12 from poly(N‐vinyl‐2‐pyrrolidone)‐crosslinked polyacrylamide hydrogels: A kinetic study

Hydrogels, composed of poly(N‐vinyl‐2‐pyrrolidone) and crosslinked polyacrylamide, were synthesized and the release of vitamin B₁₂ from these hydrogels was studied as a function of the degree of crosslinking and pH of the external swelling media. The three drug‐loaded hydrogel samples synthesized with different crosslinking ratios of 0.3, 0.7, and 1.2 (in mol %) follow different drug‐release mechanisms, that is, chain relaxation with zero‐order, non‐Fickian and Fickian, or diffusion‐controlled mechanisms. To establish a correlation between their swelling behavior and drug‐release mechanism, the former was studied by the weight‐gain method and, at the same time, the concentration of the drug released was studied colorimetrically. Various swelling parameters such as the swelling exponent n, gel‐characteristic constant k, penetration velocity v, and diffusion coefficient D were evaluated to reflect the quantitative aspect of the swelling behavior of these hydrogels. Finally, the drug‐release behavior of the hydrogels was explained by proposing the swelling‐dependent mechanism. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1706–1714, 2000     

Enzymatically degradable and pH‐sensitive hydrogels for colon‐targeted oral drug delivery. I. Synthesis and characterization

Cylindrical hydrogels, composed of starch and poly(acrylic acid), were synthesized, and their swelling behavior was studied as a function of the pH of the medium. The gels underwent a sharp transition from Fickian swelling behavior (swelling exponent n = 0.30) to non‐Fickian swelling behavior (n = 0.96) as the pH of the swelling medium changed from 2.0 to 7.4. The hydrogels also underwent partial enzymatic degradation in an amylase‐containing medium of pH 7.4 at 37°C. The effects of the enzyme concentration in the swelling media, the amount of starch present in the gel, the initial water content, the degree of crosslinking, and the diameter of cylindrical hydrogels on the degradation behavior were studied. The degradation of the gels followed Michaelis–Menten kinetics, and the value of the Menten constant was 41.62 × 10^?2. The gels exhibited minimum swelling in an acidic pH medium through the formation of a complex hydrogen‐bonded structure and underwent enzymatic degradation in a medium of pH 7.4 (i.e., simulating intestinal fluid) along with chain‐relaxation‐controlled swelling. Therefore, the gels have potential for colon‐targeted drug delivery. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3630–3643, 2004     

Carbon dioxide sorption and diffusion in poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐CO‐3‐hydroxyvalerate)

CO₂ sorption and diffusion in poly(3‐hydroxybutyrate) and three poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) copolymers were investigated gravimetrically at temperatures from 25° to 50°C and pressures up to 1 atm. The sorption behavior proved to be linear for all the copolymers studied. An additional set of measurements performed in a pressure decay apparatus at 35°C showed that the linearity could be extrapolated to pressures up to 25 atm. The sorption results obtained from both techniques were in good agreement. The poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) sorption kinetics were increasingly non‐Fickian at the higher temperatures, thus preventing the calculation of diffusion coefficients above 35°C. Interestingly, this was not the case for poly(3‐hydroxybutyrate), and diffusion coefficients and permeabilities could be calculated at all of the investigated temperatures. The 35°C permeabilities were fairly low, which is attributed to the high degree of crystallinity of this polyester family. Finally, the poly(3‐hydroxybutyrate) barrier properties against CO₂ are successfully compared with those of some selected common thermoplastics. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2391–2399, 1999     

Modeling the solubility of ternary mixtures of ethylene,iso‐pentane,n‐hexane in semicrystalline polyethylene

The coabsorptions of ethylene and iso‐pentane, and ethylene and n‐hexane were measured by the use of a pressure decay method. The solubility data of ethylene‐iso‐pentane and ethylene‐n‐hexane in semicrystalline polyethylene (PE) of crystallinity of 48.6% were obtained at temperatures 70, 80, and 90 °C, and the total pressure 2 MPa, iso‐pentane partial pressure 80–190 KPa, n‐hexane partial pressure 20–90 KPa. The presence of iso‐pentane or n‐hexane in the corresponding ternary system leads to increase the solubility of ethylene, while the solubility of iso‐pentane or n‐hexane remains unchanged with an increase of the ethylene partial pressure, even slightly decreases. Assumed that the presence of iso‐pentane or n‐hexane decreases the crystallinity of the polymer sample, a coabsorption model was built to model the solubility of each gas in the ternary systems. The relative root mean square errors of the coabsorption model for ethylene‐iso‐pentane‐PE system and ethylene‐n‐hexane‐PE system are 5.13% and 4.64%, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3654–3662, 2007     

Removal of textile dyes from single and ternary solutions using poly(acrylamide‐co‐N‐methylacrylamide) grafted katira gum hydrogel

A novel hydrogel poly(acrylamide‐co‐poly‐N‐methylacrylamide) grafted katira gum (KG) was synthesized via free radical copolymerization using a mixture of acrylamide and N‐methylacrylamide in presence of N,N′‐methylene‐bis‐acrylamide as a crosslinking agent. A series of hydrogels (KG‐1 to KG‐6) were prepared by varying amount of acrylamide and N‐methylacryamide. Poly‐acrylamide‐g‐katira gum (PAM‐g‐KG) and poly‐N‐methylacrylamide‐g‐katira gum (PNMA‐g‐KG) hydrogels were also prepared using same crosslinking agent. Swelling characteristics of all the prepared hydrogels in water were evaluated and the hydrogel with best swelling property (KG‐6) was identified. The hydrogel KG‐6 was characterized by FTIR, X‐ray diffractometer, and scanning electron microscopy and was used for the adsorption of textile dyes namely methylene blue (MB), malachite green (MG), and congo red (CR) from single and ternary solutions. Adsorption dynamics, kinetics, isotherm, and thermodynamics of all the prepared hydrogels were studied in the ternary dye solutions. The sorption kinetics data were fitted well to pseudo‐second order and the equilibrium adsorption data were found to follow Freundlich isotherm model. The thermodynamics studies showed that the adsorption process was spontaneous and exothermic in nature. The preferential dye adsorption by the hydrogel was followed in the order MB > MG > CR. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45958.     

Swelling behavior of poly(acrylamide‐co‐N‐vinylimidazole) hydrogels under different environment conditions

A series of random copolymers of acrylamide and N‐vinylimidazole, poly(AAm‐co‐NVI), with various compositions were prepared using redox copolymerization. The influence of environmental conditions such as pH, temperature, and ionic strength on the swelling behavior of the copolymeric hydrogels was investigated. The hydrogels exhibited the highest equilibrium swelling in basic medium at high temperature. Equilibrium swelling decreased with rising ionic strength at pH 5.0. As pH increased, equilibrium swelling of the hydrogels increased at pH 11.0 and I = 0.20 M. Swelling kinetics of the hydrogels was found to be non‐Fickian at 25°C. The process tended to be Fickian at higher pH and temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1783–1788, 2005     

Preparation and application in drug controlled delivery of pH‐sensitive P(CE‐co‐DMAEMA‐co‐MEG) hydrogel

A pH‐sensitive hydrogel [P(CE‐co‐DMAEMA‐co‐MEG)] was synthesized by the free‐radical crosslinking polymerization of N,N‐dimethylaminoethyl methacrylate (DMAEMA), poly(ethylene glycol) methyl ether methacrylate(MPEG‐Mac) and methoxyl poly(ethylene glycol)‐poly(caprolactone)‐methacryloyl methchloride (PCE‐Mac). The effects of pH and monomer content on swelling property, swelling and deswelling kinetics of the hydrogels were examined and hydrogel microstructures were investigated by SEM. Sodium salicylate was chosen as a model drug and the controlled‐release properties of hydrogels were pilot studied. The results indicated that the swelling ratios of the gels in stimulated gastric fluids (SGF, pH = 1.4) were higher than those in stimulated intestinal fluids (SIF, pH = 7.4), and followed a non‐Fickian and a Fickian diffusion mechanism, respectively. In vitro release studies showed that its release rate depends on different swelling of the network as a function of the environmental pH and DMAEMA content. SEM micrographs showed homogenous pore structure of the hydrogel with open pores at pH 1.4. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40737.     

The structure characterization of thermosensitive poly(N‐isopropylacrylamide‐co‐2‐hydroxypropyl methacrylate) hydrogel

The goal of this work was to investigate a possible way of crosslinking polymer chains and the potential formation of intramolecular hydrogen bonds in thermosensitive poly(N‐isopropylacrylamide‐co‐2‐hydroxypropyl methacrylate) (p(NIPAM‐HPMet)) hydrogels obtained by radical polymerization. The chemical structure of the synthesized hydrogels was investigated by Fourier transform infrared (FTIR) spectroscopy and XRD. The FTIR spectrum confirmed the presence of hydrogen bonds formed between the chains in the copolymer. XRD analysis confirmed the amorphous ? crystalline structure of the copolymer. A three‐glass transition and two melting temperatures were detected by DSC. It was found that the addition of HPMet increased the glass transition and melting temperatures of the p(NIPAM‐HPMet) copolymer. The swelling transport mechanism of p(NIPAM‐HPMet) changed from non‐Fickian at 20 °C to case III or zero‐order time‐independent kinetics characterized by a linear mass uptake with time with increasing temperature at 40 °C. © 2013 Society of Chemical Industry     

A comparative study of swelling properties of hydrogels based on poly(acrylamide‐co‐methyl methacrylate) containing physical and chemical crosslinks

Poly (acrylamide‐co‐methyl methacrylate) hydrogels of different ratios were prepared by using chemical and physical crosslinks to study the effect of nature of crosslinks on swelling behavior of hydrogels. The chemically crosslinked gels were prepared by using NN′‐methylene bis acrylamide, while physically crosslinked hydrogels were prepared by precipitation polymerization method, using dioxane as solvent. Detailed swelling kinetics such as swelling ratio, transport exponent n, diffusion coefficient D and the effect of pH on equilibrium swelling studies. The study revealed that the nature of crosslinks alter the swelling characteristics of the hydrogel. In chemically crosslinked hydrogels the water transport is Fickian in nature, while in the case of the physically crosslinked hydrogels the water transport mechanism is anomalous indicating major change in relaxation mechanism due to nature of crosslinks. The results also indicate that with increasing acrylamide content the swelling ratio of the hydrogels were also increased, but the transport exponent n remains nearly constant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 779–786, 2003     

Swelling kinetics of linseed oil‐based polymers

Kinetics of swelling and sorption behavior of copolymers (based on linseed oil, styrene, divinylbenzene, and acrylic acid via cationic and thermal polymerization) is studied in tetrahydrofuran (THF) at different temperatures. The values of n in the transport equation are found to be below 0.4, showing non‐Fickian or pseudo‐Fickian transport in the polymers. The dependence of diffusion coefficient on the composition and temperature has also been studied for the linseed oil‐based polymers. The diffusion coefficient in cationic samples decreases with an increase in the oil contents in the samples. In case of thermal samples, the diffusion coefficient first increases up to 30% oil contents and then decreases. The diffusion coefficient decreases with an increase in temperature for all of the linseed oil polymer samples. The sorption coefficient increases with an increase in the oil contents for all samples. The crosslink density (calculated from the THF swelling) ranges from 20.16 to 92.34 × 10⁶ mol/cm³ for cationic samples and 20.62 to 86.01 × 10⁶ mol/cm³ for thermal samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Molecular transport of n‐alkanes into PU/PBMA interpenetrating polymer network systems

The methylene diisocyanate (MDI) and toluene diisocyanate (TDI) based polyurethane/polybutyl methacrylate (PU/PBMA‐50/50) interpenetrating polymer network (IPN) membranes have been prepared. The molecular migration of n‐alkane penetrants such as hexane, heptane, octane, nonane, and decane through PU/PBMA (50/50) membranes has been studied at 25, 40, and 60°C using a weight gain method. From the sorption results, diffusion (D) and permeation (P) coefficients of n‐alkane penetrants have been calculated. Molecular migration depends on membrane‐solvent interactions, size of the penetrants, temperature, and availability of free volume within the membrane matrix. Attempts have been made to estimate the parameters of an empirical equation and these data suggest that molecular transport follows Fickian mode. From a study of temperature dependence of transport parameters, activation energy for diffusion (E_D) and permeation (E_P) have been estimated from the Arrhenius relation. Furthermore, sorption results have been interpreted in terms of enthalpy (ΔH) and entropy (ΔS) of sorption. The liquid concentration profiles have been computed using Fick's equation with appropriate initial and boundary conditions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 739–746, 2003     

Sorption of organic liquids and vapors by rigid PVC

The effects of activity and solvent strength of a number of organic penetrants upon their sorption kinetics and equilibria in poly(vinyl chloride) have been studied by gravimetric vapor and liquid sorption experiments at 30°C. For each solvent, the relation of equilibrium sorption to activity is well approximated by the Flory–Huggins equation with a characteristic value of the interaction parameter χ. The glass transition temperature T_g is depressed in direct proportion to the volume fraction of solvent absorbed; the composition corresponding to a T_g of 30°C, C_g (30°C), is in the range of 0.22–0.30 volume fraction for several common solvents. The form of the sorption kinetics varies with the ratio of the equilibrium sorption to C_g, and thus depends on the combined effects of χ, solvent activity, and plasticizing action. When the equilibrium sorption is less than about C_g/2, kinetics are Fickian, with the very low diffusivities typical of the glassy state; for sorption values between C_g/2 and C_g, anomalous kinetics are observed; and when the sorption is greater than C_g, transport in thin PVC films follows Case II kinetics. At high sorption levels, increasing film thickness produces a shift of the kinetics toward Fickian form with apparent diffusivity values typical of rubbery polymers.     

Swelling behavior of hydrogels for colon‐site drug delivery

Hydrogels based on n‐alkyl methacrylate esters (n‐AMA), acrylic acid, and acrylamide crosslinked with 4,4′‐di(methacryloylamino)azobenzene were prepared. Swelling behavior of the hydrogels was studied by the immersion of slabs in buffered solutions at pH 2.2–7.4. The diffusion of water into the slabs was discussed on the stress relaxation model of polymer chains. The results obtained are in good agreement with Schott's second‐order diffusion kinetics. The constants A and B of Schott's kinetics equation depend on the balance of hydrophobicity/hydrophilicity, the rigidity/flexibility, and the degree of crosslinking. The factors that exert the greatest influence on the swelling behavior of the gels include the degree of crosslinking, the lengths of the n‐AMA side chains, and pH values. By adjusting these factors, the degree of swelling of the hydrogels in the small intestine can be controlled, and consequently the drugs may avoid being released before arriving in the colon. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2835–2842, 2002; DOI 10.1002/app.10259     

Effect of hydrophobic hexafluoroisopropylidene group on the water sorption behaviors of rigid poly(p‐phenylene pyromellitimide) polyimide thin films

We prepared poly(p‐phenylene pyromellitimide) (PMDA–PDA), poly(p‐phenylene 4,4′‐hexafluoroisopropylidene diphthalimide), and their copolyimides with various compositions to explore the relationship between the water sorption and structure. The water sorption behaviors were gravimetrically investigated as a function of composition and temperature and interpreted with a Fickian diffusion model in films. Overall, the water sorption behaviors were strongly dependent on the changes in morphological structure, which originated from the variations in composition. When the content of the bulky hexafluoroisopropylidene group (6FDA) was increased, the water uptake decreased from 5.80 to 3.18 wt %, whereas the diffusion coefficient increased from 3.6 × 10^?10 to 11.3 × 10^?10 cm²/s. The relatively high water uptake in the PMDA–PDA polyimide film was successfully healed by the incorporation of 6FDA, which may have resulted from the increases in the intermolecular packing order and hydrophobicity. The degree of orientation and crystallinity, which are in‐plane characteristics, were directly correlated to the diffusion coefficient and activation energy in the polyimide film. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3442–3446, 2003     

Diffusion and sorption of benzene vapor through polybutadiene‐, polybutadiene/styrene‐, and polybutadiene/acrylonitrile‐based polyurethanes

A series of polyurethane (PU) films made from toluene diisocyanate (TDI), 1,4‐butanediol (BDO), and hydroxyl‐terminated polybutadiene (HTPB), hydroxyl terminated polybutadiene/styrene (HTBS), or hydroxyl terminated polybutadiene/acrylonitrile (HTBN) was synthesized by solution polymerization. The absorption of benzene vapor was found mainly in the soft phase. The equilibrium adsorption (M_∞) was reduced with increasing hard segment content for all the PUs. The values of M_∞ were in the sequence of HTBN‐PUs > HTBS‐PUs > HTPB‐PUs, which could be explained by the different interaction parameters between soft segments and benzene. The HTBN‐PU film showed the lowest degree of phase segregation and had more hard segments intermixed in the soft phase, restricting the movement of soft segments, and therefore resulted to non‐Fickian behavior, while the HTPB‐PU is antithetical. FTIR and atomic force microscopy were utilized to identify the hydrogen bonding behavior and morphology change of the PU films before and after the absorption of benzene vapor. The tensile strength of the HTBN‐PUs showed a greater decrease than that of HTBS‐PUs and HTPB‐PUs after absorbing benzene vapor. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2984–2991, 2004