Effect of hygrothermal aging history on sorption process,swelling, and glass transition temperature in a particle‐filled epoxy‐based adhesive

The effects of hygrothermal aging history and initial water content on sorption behavior and the physical properties of a commercial particle‐filled epoxy‐based adhesive were studied by the analysis of the water reabsorption process. ATR‐FTIR analysis was performed to characterize the hydrogen bond interactions among the water and either resin or fillers. Swelling behavior and the depression of the glass transition temperature (T_g) under different hygrothermal aging histories were related to the water in the apparent free volume of the adhesive. The results show that the water diffusion of the adhesive is a non‐Fickian process. It is also observed that swelling (which is reversible and consistent with hydrogen bond formation) and the rate of diffusion are not only dependent on the hygrothermal temperature but also the hygrothermal history. In addition, the swelling observed on the reabsorption process does not alter the apparent free volume of this adhesive system, and T_g depression is independent of the final equilibrium water content of the system. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1581–1591, 2002; DOI 10.1002/app.10447     

Characterization and CO2 sorption properties of poly[methacryloxypropylheptacyclopentyl‐T8‐silsesquioxane‐ co‐3‐methacryloxypropyltris(trimethylsiloxy)silane]

Poly[methacryloxypropylheptacyclopentyl‐T8‐silsesquioxane (MAPOSS)‐co‐3‐methacryloxypropyltris(trimethylsiloxy)silane (SiMA)] was synthesized through free radical polymerization. The physical and carbon dioxide (CO₂) sorption properties of the copolymer membranes were investigated in terms of the MAPOSS content. As the MAPOSS content increases, the membrane density increased, suggesting a decrease in the fractional free volume. In addition, the thermal stability was improved with increasing the MAPOSS content. These are because of the polyhedraloligomericilsesquioxane (POSS) units that restrict the high mobility of poly(SiMA) segments. The glass transition temperature, T_g of the copolymers was single T_g based on the differential scanning calorimetry, suggesting that the copolymers were random and not phase separation. Based on the CO₂ sorption measurement, the POSS units play a role in reducing Henry's dissolution by suppressing the mobility of the poly(SiMA) component, while POSS units increase the nonequilibrium excess free volume, which contributes to the Langmuir dissolution. Based on these results, the introduction of MAPOSS unit is one of the effective ways to improved the thermal stability and CO₂ sorption property due to the enhancement of the polymer rigidity. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of swelling agent on the molecular weight of poly(2,6‐dimethyl‐1,4‐phenylene oxide) synthesized in an aqueous medium

The effects of the species and content of a swelling agent on the molecular weight of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) synthesized in an aqueous medium were studied. It was found that the molecular weight of PPO increases after introducing a certain amount of the swelling agent during the oxidative polymerization of 2,6‐dimethylphenol (DMP). T_g of the PPO/swelling agent mixture decreases with the increase of the swelling agent content, and the relation between T_g of the PPO/swelling agent mixture and the swelling agent content obeys Fox equation. After the introduction of the swelling agent during the oxidative polymerization of DMP, the molecular weight of PPO is correlated with T_g of the PPO/swelling agent mixture and it was revealed that T_g plays an important role in the molecular weight of PPO synthesized in the aqueous medium. The same molecular weight of PPO can be obtained only if T_g of the PPO/swelling agent mixture is the same, no matter what kind of swelling agent is introduced during the oxidative polymerization of DMP. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Functionalization of lignin: Synthesis of lignophenol‐graft‐poly(2‐ethyl‐2‐oxazoline) and its application to polymer blends with commodity polymers

Lignophenol (LP)‐graft‐poly(2‐ethyl‐2‐oxazoline) (POZO) was prepared to reuse lignin, an industrial waste material, and to produce novel LP‐based polymer blends with poly(vinyl chloride) (PVC), poly(bisphenol A carbonate) (PC), polyvinylpyrrolidone (PVP), and polystyrene (PSt) as commodity polymers. The resulting graft polymer was soluble in various types of organic solvents such as chloroform, THF, acetone, and methanol, unlike LP. The miscibility of LP‐graft‐POZO with commodity polymers was measured by differential scanning calorimetry (DSC) to determine the glass transition temperatures (T_g). In the cases of the blends of LP‐graft‐POZO with PVC, PC, and PVP, the T_g values decreased during the second scan. Moreover, in the cases of the blends with PVC and PVP, the T_g values were not detected during the third scan. Therefore, it was inferred that LP‐graft‐POZO was miscible with PVC, PC, and PVP while forming single phases; in particular, the blends of LP‐graft‐POZO with PVC and PVP exhibited a secondary miscibility because the T_g values were not detected. Furthermore, the blend of LP‐graft‐POZO with PC exhibited better thermostability than LP and LP‐graft‐POZO. These results indicated that LP blended with POZO could be used as a polymer additive and as an adhesive to combine different polymers, organic–inorganic polymers, etc. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Glass‐transition temperature of poly(vinylidene fluoride)‐poly(methyl acrylate) blends: Influence of aging and chain structure

The glass‐transition temperature (T_g) of the poly(vinylidene fluoride) (PVF₂)‐poly(methyl acrylate) (PMA) blends increase with aging time. The T_g versus log(time) plots are straight lines whose slope values depend on the head to head (H–H) defect content of PVF₂ samples and on the composition of the blends. The values of polymer–polymer interaction parameters (χ) increase with an increase in the H–H defect of PVF₂ for a fixed composition of the blend. Consequently, the T_g of the blend decreases with an increase in the H–H defect of the PVF₂ sample. However, after aging for longer times this decrease of the T_g with H–H defects is lower than those of the unaged blends. The possible reasons are discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1541–1548, 2001     

Effects of water on the long‐term properties of Bis‐GMA and silylated‐(Bis‐GMA) polymers

Bis‐GMA (2,2‐bis‐[4‐(2‐hydroxy‐3‐methacryloxypropoxy)phenyl]propane) is a viscous hygroscopic monomer which is used with triethyleneglycol‐dimethacrylate (TEGDMA) for dental restorations. Bis‐GMA was silylated with dimethyl‐isopropyl‐siloxane and further polymerized in order to increase water resistance and viscosity. The viscosity of the silylated monomer, Sil·Bis‐GMA, was 50 times lower than that of the parent monomer. After 1 month in water, poly(Bis‐GMA/TEGDMA) absorbed 2.6% water and the silylated polymer, poly(Sil·Bis‐GMA), only 0.56%. During this process water extracted residual monomer from each polymer. The behavior of water sorption and desorption as a function of time in poly(Sil·Bis‐GMA) was completely different from that shown by poly(Bis‐GMA/TEGDMA). The difference is discussed in terms of diffusion coefficients. Initially, water advancing contact angles (θ_ADV) were 75° and 95°, respectively. After 1 month in water both polymers showed a reduction of about 20° in θ_ADV. In poly(Bis‐GMA/TEGDMA), the reduction in θ_ADV obey to water absorption and bulk plasticization; it showed a reduction of 15°C in glass transition temperature, T_g. In contrast, the reduction in θ_ADV in poly (Sil·Bis‐GMA) obeyed to water adsorption and reorientation of the molecules at the surface in contact with the water phase; it only showed a change of 2°C in T_g. Contact angle hysteresis provided further evidence about plasticization. According to our results poly(Sil·Bis‐GMA) is more stable in water than poly(Bis‐GMA/TEGDMA). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Pervaporation membranes from natural rubber latex grafted with poly(2‐hydroxyethyl methacrylate) (NR‐g‐PHEMA) for the separation of water–acetone mixtures

NR‐graft‐PHEMA latexes were synthesized by the use of graft emulsion polymerization. By increasing the HEMA monomer concentration, we found that the grafting percentage (GP) also increased. In addition, GP increased significantly at low initiator concentrations before it leveled off at moderate concentrations, and a slight decrease was observed at high initiator concentrations. NR‐g‐PHEMA latexes were prepared as pervaporation membranes for the separation of water–acetone mixtures. From the equilibrium swelling, the nonideal behavior of membrane swelling in water–acetone mixtures was found such that there appeared the maximum swelling degree at a certain concentration of liquid mixtures. Moreover, the water concentration at maximum swelling shifted to high water concentration with increasing amount of graft‐PHEMA. The sorption study suggested the preferential sorption of water on the membranes. Also, the sorption isotherms implied that there was a coupling between water and acetone molecules. Pervaporation separation of water–acetone mixtures was studied with NR‐g‐PHEMA membranes. As the feed water concentration increased, the partial water fluxes increased in contrast to the partial fluxes of acetone. From the permeation ratio, θ_w, the strong coupling of acetone on the water transport was observed, particularly for the membrane with high graft‐PHEMA under acetone‐rich conditions. As the feed temperature increased, the total permeation across the membranes was enhanced. The partial fluxes of water and acetone as a function of temperature followed the Arrhenius relationship by which the activation energies for permeation were estimated as 3.53 kJ/mol for water and 21.95 kJ/mol for acetone. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Diffusion of mineral oil in styrene‐butadiene polymer films

Mineral oil diffusion in styrene‐butadiene polymer films was investigated with a simple gravimetric sorption method. Over the selected range of temperatures and film thicknesses for which sorption tests were performed, the diffusion process is described in terms of Fick's third law. Polymer dissolution was found to compete with the diffusion process especially at high temperature. Possible interference due to dissolution on data generated using a gravimetric method, resulted in an estimation of apparent activation energy using diffusion coefficient set calculated with Crank's half‐time relationship. The mineral oil diffusion activation energy was found to be relatively high compared with those of hydrocarbons diffusing in natural and synthesized rubbers or crosslinked polybutadiene as reported in the literature. The influence of polymer T_g, crosslinking density, and polarity on mineral oil ability to penetrate polymer film was evaluated in terms of percent weight increase over time. Maximum absorption after 60‐min sorption time linearly correlates with mineral oil absorption rate for polymers prepared with different structures. This linear relationship suggests that diffusion of solvent in styrene‐butadiene polymers reveals the macroscopic composition and structural polymer modification rather than local changes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Glass‐transition‐temperature depression in chemically crosslinked low‐density polyethylene and high‐density polyethylene and their blends with ethylene vinyl acetate copolymer

A reduction in the glass‐transition temperature (T_g) was found for polyolefins chemically crosslinked by peroxide. This tendency, which was observed for low‐density and high‐density polyethylenes, was also validated for their blends with Ethylene Vinyl Acetate copolymer. It is proposed that the constrained crystallization process, as a result of a restriction imposed on the chain packing by the chemical crosslinks, results in an increasing net free volume in the amorphous phase and hence reduces T_g. The T_g depression becomes greater with increasing crosslink density, whereas at the same time, the degree of crystallinity and consequently the density of the system decreases with an increase in the peroxide content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1654–1660, 2007     

Polystyrene composites of single‐walled carbon nanotubes‐graft‐polystyrene

Single‐walled carbon nanotubes (SWCNTs) dispersed in N‐methylpyrrolidone (NMP) were functionalized by addition of polystyryl radicals from 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐ended polystyrene (SWCNT‐g‐PS). The amount of polystyrene grafted to the nanotubes was in the range 20‐25 wt% irrespective of polystyrene number‐average molecular weight ranging from 2270 to 49 500 g mol^?1. In Raman spectra the ratios of D‐band to G‐band intensity were similar for all of the polystyrene‐grafted samples and for the starting SWCNTs. Numerous near‐infrared electronic transitions of the SWCNTs were retained after polymer grafting. Transmission electron microscopy images showed bundles of SWCNT‐g‐PS of various diameters with some of the polystyrene clumped on the bundle surfaces. Composites of SWCNT‐g‐PS in a commercial‐grade polystyrene were prepared by precipitation of mixtures of the components from NMP into water, i.e. the coagulation method of preparation. Electrical conductivities of the composites were about 10^?15 S cm^?1 and showed no percolation threshold with increasing SWCNT content. The glass transition temperature (T_g) of the composites increased at low filler loadings and remained constant with further nanotube addition irrespective of the length and number of grafted polystyrene chains. The change of heat capacity (ΔC_p) at T_g decreased with increasing amount of SWCNT‐g‐PS of 2850 g mol^?1, but ΔC_p changed very little with the amount of SWCNT‐g‐PS of higher molecular weight. The expected monotonic decrease in ΔC_p coupled with the plateau behavior of T_g suggests there is a limit to the amount that T_g of the matrix polymer can increase with increasing amount of nanotube filler. Copyright © 2012 Society of Chemical Industry     

Silicone membranes to inhibit water uptake into thermoset polyurethane shape‐memory polymer conductive composites

Electroactive shape memory polymer (SMP) composites capable of shape actuation via resistive heating are of interest for various biomedical applications. However, water uptake into SMPs will produce a depression of the glass transition temperature (T_g) resulting in shape recovery in vivo. While water actuated shape recovery may be useful, it is foreseen to be undesirable during early periods of surgical placement into the body. Silicone membranes have been previously reported to prevent release of conductive filler from an electroactive polymer composite in vivo. In this study, a silicone membrane was used to inhibit water uptake into a thermoset SMP composite containing conductive filler. Thermoset polyurethane SMPs were loaded with either 5 wt % carbon black or 5 wt % carbon nanotubes, and subsequently coated with either an Al₂O₃‐ or silica‐filled silicone membrane. It was observed that the silicone membranes, particularly the silica‐filled membrane, reduced the rate of water absorption (37°C) and subsequent T_g depression versus uncoated composites. In turn, this led to a reduction in the rate of recovery of the permanent shape when exposed to water at 37°C. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41226.     

Sorption and transport of water vapor in nylon 6,6 film

The sorption and transport of water in nylon 6,6 films as functions of the relative humidity (RH) and temperature were studied. Moisture‐sorption isotherms determined gravimetrically at 25, 35, and 45°C were described accurately by the GAB equation. Water‐vapor transmission rates were enhanced above ≈ 60–70% RH, primarily due to the transition of the polymer from glassy to rubbery states. The glass transition temperatures (T_g's) of nylon 6,6 were measured at various moisture contents using differential scanning calorimetry. The results showed that the sorbed water acted as an effective plasticizer in depressing the T_g of the polyamide. Fourier transform infrared spectroscopy (FTIR) was utilized to characterize the interaction of water and the nylon. Evidence from FTIR suggested that the interaction of water with nylon 6,6 took place at the amide groups. Based on the frequency shift of the peak maxima, moisture sorption appeared to reduce the average hydrogen‐bond strength of the N H groups. However, an increase was seen for the CO groups. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 197–206, 1999     

Polymer blends of stereoregular poly(methyl methacrylate) and poly(styrene‐co‐p‐hydroxystyrene)

Isotactic, atactic, and syndiotactic poly(methyl methacrylates) (PMMAs) (designated as iPMMA, aPMMA, and sPMMA) were mixed with poly(styrene‐co‐p‐hydroxystyrene) (abbreviated as PHS) containing 15 mol % of hydroxystyrene separately in 2‐butanone to make three polymer blend systems. Differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were used to study the miscibility of these blends. The three polymer blends were found to be miscible, because all the prepared films were transparent and there was a single glass transition temperature (T_g) for each composition of the polymers. T_g elevation (above the additivity rule) is observed in all the three PMMA/PHS blends mainly because of hydrogen bonding. If less effective hydrogen bonding based on the FTIR evidence is assumed to infer less exothermic mixing, sPMMA may not be miscible with PHS over a broader range of conditions as iPMMA and aPMMA. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 431–440, 1999     

Synthesis and characterization of pH‐ and temperature‐sensitive silk sericin/poly(N‐isopropylacrylamide) interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) composed of silk sericin (SS) and poly(N‐isopropylacrylamide) (PNIPAAm) were prepared simultaneously. The properties of the resultant IPN hydrogels were characterized by differential scanning calorimetry and SEM as well as their swelling behavior at various temperatures and pH values. The single glass transition temperature (T_g) presented in the IPN thermograms indicated that SS and PNIPAAm form a miscible pair. The swollen morphology of the IPNs observed by SEM demonstrated that water channels (pores present in SEM micrographs) were distributed homogeneously through out the network membranes. The swelling ratio of the IPNs depended significantly on the composition, temperature and pH of the buffer solutions. The dynamic transport of water into the IPN membrane was analyzed based on the Fickian equation. Copyright © 2006 Society of Chemical Industry     

Prediction of solvent‐diffusion coefficient in polymer by a modified free‐volume theory

Several versions of free‐volume theory have been proposed to correlate or predict the solvent diffusion coefficient of a polymer/solvent system. The quantity of free volume is usually determined by the Williams–Landel–Ferry (WLF) equation from viscosity data of the pure component in these theories. Free volume has been extensively discussed in different equation‐of‐state models for a polymer. Among these models, the Simha–Somcynsky (SS) hole model is the best one to describe the crystalline polymer, because it describes it very approximately close to the real structure of a crystalline polymer. In this article, we calculated the fractions of the hole free volume for several different polymers at the glass transition temperature and found that they are very close to a constant 0.025 by the SS equation of state. It is quite consistent with the value that is determined from the WLF equation. Therefore, the free volume of a crystalline polymer below the glass transition temperature (T_g) is available from the SS equation. When above the T_g, it is assumed that the volume added in thermal expansion is the only contribution of the hole free volume. Thus, a new predictive free‐volume theory was proposed. The free volume of a polymer in the new predictive equation can be estimated by the SS equation of state and the thermal expansion coefficient of a polymer instead of by the viscosity of a polymer. The new predictive theory is applied to calculate the solvent self‐diffusion coefficient and the solvent mutual‐diffusion coefficient at different temperatures and over most of the concentration range. The results show that the predicted values are in good agreement with the experimental data in most cases. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 428–436, 2000     

Hydroxyethyl chitosan‐g‐poly(acrylic acid‐co‐sodium acrylate) superabsorbent polymers

A novel hydroxyethyl chitosan‐g‐poly(acrylic acid‐co‐Sodium Acrylate) (HECTS‐g‐(PAA‐co‐PSA)) superabsorbent polymer was prepared through graft copolymerization of acrylic acid and sodium acrylate onto the chain of hydroxyethyl chitosan. The structure of the polymer was characterized by FTIR. By studying the water absorption of the polymer synthesized under different conditions, the optimal conditions for synthesizing the polymer with the highest swelling ratio was defined. This superabsorbent polymer was further treated by the solvent precipitation method and by the freeze‐drying method. We found that the water absorption rate of the treated polymer was greatly increased and the microstructure of the treated polymer was changed from small pores to loose macro pores. The swelling processes of the polymers before and after modification fit first‐order dynamic processes. The amount of the residual acrylic acid was greatly decreased after treatments. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Properties of crosslinked polyurethanes synthesized from 4,4′‐diphenylmethane diisocyanate and polyester polyol

Polyurethanes were synthesized using the high functional 4,4′‐diphenylmethane diisocyanate (MDI), polyester polyol, and 1,4‐butane diol. The synthesized polyurethanes were analyzed using differential scanning calorimeter (DSC), dynamic mechanical thermal analysis (DMTA), Fourier transform infrared (FTIR) spectrometer, and swelling measurement using N,N′‐dimethylformamide. From the result of thermal analysis by DSC and DMTA, single T_gs were observed in the polyurethane samples at all the formulated compositions. From this result, it is suggested that the polyurethanes synthesized in this study have crosslinked structure rather than the phase‐separated segmented structure because of the high functionality (f = 2.9) of the MDI. By annealing the polyurethane samples using DSC, the T_gs were increased by 4.7∼16.0°C at the various annealing temperatures. From the results of FTIR and swelling measurement of polyurethanes, it is suggested that the increase of T_g of the polyurethanes by annealing is not due to increase of the hydrogen bond strength but mainly due to the increase of the crosslink density. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 624–630, 2000     

Diffusivities of dichloromethane in poly(lactide‐co‐glycolide)

Diffusion of dichloromethane in poly(lactide‐co‐glycolide) (PLGA), the rate‐limiting step in the later stages of drying of microparticles formed in common encapsulation processes, was studied by the step‐change sorption technique in a dynamic vapor sorption apparatus. Methods were developed to create films of polymer with the appropriate thicknesses for accurate diffusion determination over a wide range of solvent composition. Mutual diffusivities were measured at 5, 25, and 35°C from 10 to 70 wt % solvent. Values range from 2 × 10^?10 m²/s at high solvent compositions to as low as 1 × 10^?13 m²/s at solvent compositions just above the glass transition of the mixture. Equilibrium sorption isotherms were measured in the same apparatus and agreed favorably with Flory‐Huggins theory using a value of χ = 0.31. The glass transition temperatures of the system were measured over the range of 0–11 wt % solvent content by modulated differential scanning calorimetry. The composition dependence was fit to the Fox equation, which estimated values of the pure polymer and the solvent T_g to be 39.3 and ?131°C, respectively. These values, along with the diffusivity data, were used to deduce the free‐volume parameters specific to PLGA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Glass‐transition temperature based on dynamic mechanical thermal analysis techniques as an indicator of the adhesive performance of vinyl ester resin

Vinyl ester resins are being used extensively as matrices in fiber‐reinforced polymer composite materials, but their use as a structural adhesive has been limited. Initial studies investigating the durability of a vinyl ester as a wood adhesive showed unsatisfactory performance in comparison with other adhesives. In this work, the glass‐transition temperatures (T_g's) of a vinyl ester and a E‐glass/vinyl ester composite material, fabricated by the Composites Pressure Resin Infusion System, were determined with dynamic mechanical thermal analysis. The results indicated that the resin cured under ambient conditions had a much lower T_g (～60°C) than the postcured material (～107°C). This suggested undercuring, that is, incomplete crosslinking, of the resin when it was cured at room temperature. E‐glass/vinyl ester samples, however, showed virtually no difference in T_g between room‐temperature‐cured and postcured samples. The exact reasons for this are not currently known but are thought to be both mechanical and chemical in nature. On the basis of the findings presented in this article, it can be concluded that if this vinyl ester resin is to be used as a structural adhesive, postcuring or formulation to ensure a high degree of crosslinking under ambient conditions is necessary. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2221–2229, 2005     

Preparation and properties of emulsifier‐/solvent‐free polyurethane‐acrylic hybrid emulsions for binder materials: Effect of the glycidyl methacrylate/acrylonitrile content

To obtain binder materials, emulsions of emulsifier‐/solvent‐free waterborne polyurethane‐acrylic hybrids with a fixed acrylic monomer content (30 wt %) were prepared in this study. This study focused on the effect of glycidyl methacrylate (GMA)/acrylonitrile (AN) wt % on the shelf stability, mean particle size and viscosity of hybrid emulsion samples, water swelling %/dynamic mechanical thermal properties/mechanical properties of hybrid film samples, and the failure mode and adhesive strength of binder materials prepared in this study. Characterization of the chemical structures of prepolymers, hybrid materials (binder materials), and atmospheric pressure plasma‐treated polyethylene (PE) has been performed by means of Fourier transformed infrared spectroscopy to determine the presence/disappearance/peak intensity change of functional groups. Various properties such as mean particle size, viscosity, T_g, water swelling %, hardness and mechanical properties, and failure mode and adhesive strength for leather/leather, control PE/leather, and plasma‐treated PE/leather were found to be significantly dependent on the weight ratio of GMA/AN. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44497.