Effects of resin hydrophilicity on water sorption and changes in modulus of elasticity

As acidic monomers of self-etching adhesives are incorporated into dental adhesives at high concentrations, the adhesive becomes more hydrophilic. Water sorption by polymers causes plasticization and lowers mechanical properties. The purpose of this study was to compare the water sorption and modulus of elasticity (E) of five experimental neat resins (EX) of increasing hydrophilicity, as ranked by their Hoy's solubility parameters and five commercial resins. METHODS: After measuring the initial modulus of all resin disks by biaxial flexure, half the specimens were stored in hexadecane and the rest were stored in water. Repeated measurements of stiffness were made for 3 days. Water sorption and solubility measurements were made in a parallel experiment. RESULTS: None of the specimens stored in oil showed any significant decrease in modulus. All resins stored in water exhibited a time-dependent decrease in modulus that was proportional to their degree of water sorption. Water sorption of EX was proportional to Hoy's solubility parameter for polar forces (delta(p)) with increasing polarity resulting in higher sorption. The least hydrophilic resin absorbed 0.55 wt% water and showed a 15% decrease in modulus after 3 days. The most hydrophilic experimental resin absorbed 12.8 wt% water and showed a 73% modulus decrease during the same period. The commercial resins absorbed between 5% and 12% water that was associated with a 19-42% reduction in modulus over 3 days.     

Solvent and water retention in dental adhesive blends after evaporation

This study examined the extent of organic solvent and water retention in comonomer blends with different hydrophilicity (Hoy's solubility parameter for hydrogen bonding, delta(h)) after solvent evaporation, and the extent of tracer penetration in polymerised films prepared from these resins. For each comonomer blend, adhesive/solvent mixtures were prepared by addition of (1) 50 wt% acetone, (2) 50 wt% ethanol, (3) 30 wt% acetone and 20 wt% water and (4) 30 wt% ethanol and 20 wt% water. The mixtures were placed in glass wells and evaporated for 30-60s for acetone-based resins, and 60-120 s for ethanol-based resins. The weight of the comonomer mixtures was measured before and after solvent evaporation. Resin films were prepared for transmission electron microscopy (TEM) after immersion in ammonical silver nitrate. The percentages of solvent and water retained in the comonomer mixtures, and between the acetone and ethanol groups were measured gravimetrically and were statistically compared. In comonomer-organic solvent mixtures, the percentage of solvent retained in acetone and ethanol-based mixtures increased significantly with hydrophilicity of the comonomer blends (P < 0.05). In resin-organic solvent-water mixtures, significantly more solvent and water were retained in the ethanol-based mixtures (P < 0.0001), when compared to acetone-based mixtures after 60s of air-drying. TEM revealed residual water being trapped as droplets in resin films containing acetone and water. Water-filled channels were seen along the film periphery of all groups and throughout the entire resin films containing ethanol and water. The addition of water to comonomer-ethanol mixtures results in increased retention of both ethanol and water because both solvents can hydrogen bond to the monomers.     

Evaluation of the effect of water-uptake on the impedance of dental resins

Electrical impedance spectroscopy (EIS) offers a quantitative method of measuring the stability of resin films in aqueous solution over time. PURPOSE: The purpose of this study was to measure the EIS of five experimental dental adhesive films (ca. 17 microm thick) of increasing hydrophilicity (ranked by their Hoy's solubility parameters), and how much these values change over 3 weeks in aqueous buffer. METHODS: The resin films were placed in a U-shaped chamber and a pair of Ag-AgCl electrodes was used for EIS. The EIS results were confirmed by immersing the films in 50% AgNO3 for 24 h to trace the distribution of any water absorption into the resins by TEM observations. RESULTS: The resistance (Rr) of the resins 1-4 films increased most during the first day, and varied from 1x10(11) ohm for resin 1, to 40Omega for resin 5 at day 1. The day 1 Rr values of resins 1-4 were inversely proportional to their Hoy's solubility parameter for hydrogen bonding forces. Electrical impedance values of resins 1-3 and 5 varied widely but were relatively constant over time, while those of resin 4 decreased more than 99% from day 1 to 21 (p<0.05). Capacitance (Cr) of films of resins 1-4 all increased over the first day and then were relatively unchanged over the 20 days (except for resin 4 that continued to increase) and were between 0.01 and 1 nF. Silver uptake by TEM revealed the development of water-filled branching structures that formed in resins 4 and 5 over time.     

Solvent-induced dimensional changes in EDTA-demineralized dentin matrix

The purpose of this study was to test the null hypothesis that the re-expansion of dried matrix and the shrinkage of moist, demineralized dentin is not influenced by polar solvents. Dentin disks were prepared from midcoronal dentin of extracted human third molars. After complete demineralization in 0.5M of EDTA (pH 7), the specimens were placed in the well of a device that measures changes in matrix height in real time. Dry, collapsed matrices were created by blowing dry N(2) on the specimens until they shrank to a stable plateau. Polar solvents [water, methanol, ethanol, n-propanol, n-butanol, formamide, ethylene glycol, hydroxyethyl methacrylate (HEMA), or mixtures of water-HEMA] as model primers then were added and the degree of re-expansion measured. These same solvents also were applied to moist, expanded matrices and the solvent-induced shrinkages measured. Regression analysis was used to test the correlations between matrix height and Hansen's dispersive, polar, hydrogen bonding, and total solubility parameters (delta(d), delta(p), delta(h), delta(t)). The results indicate that water-free polar solvents of low hydrogen bonding (H-bond) ability (e.g., neat HEMA) do not re-expand dried matrices and that they shrink moist matrices. When HEMA was mixed with progressively higher water concentrations, the model water-HEMA primers expanded the dried matrix in proportion to their water concentrations and they produced less shrinkage of moist matrices. Solvents with higher H-bonding capacities (methanol, ethanol, ethylene glycol, formamide, and water) re-expanded the dried matrix in proportion to their solubility parameters for H-bonding (delta(h)). They also induced small transient shrinkages of moist matrices, which slowly re-expanded. The results require rejection of the null hypothesis.     

Water-sorption kinetics of dental polymeric resin under tensile stressing conditions.

Water sorption tests were conducted on unfilled poly(methyl methacrylate) samples in distilled water at 5, 37, and 60 degrees C under three different tensile stress ratios (sigma appl/sigma ys = 0%, 5%, and 10%). Each sample was placed in a modified Hoffman open-side tubing clamp and subjected to four-point bending at pre-determined stress level for 1 day, 3 days, 1 week, 2 weeks, and 4 weeks. Water sorption was measured by weight change calculations, without accounting for any weight loss due to solubility of uncured monomer. A generalized diffusion equation can be used to express both stress-free and stress conditions; D = D0exp[-E (sigma)/kT]. It was found that the activation energy for water sorption diffusion was linearly related to applied stress ratios; i.e., E = 1.15 sigma appl/sigma ys + 10.76 (kJ/mol), with the correlation coefficient r = 0.97. Since the proportional pre-exponential constant, D0, is independent of temperature, it is speculated that the loading percentage of reinforcing filler elements in composite resin materials can be related to this constant.     

Sorption and solubility testing of orthodontic bonding cements in different solutions

To evaluate and compare the solubility and sorption of orthodontic bonding cements after immersion in different solutions, five different cements were used: a fluoride-containing resin composite, a light-cured glass ionomer cement, a light-cured resin composite, a paste-paste chemically cured resin composite, and a liquid-paste chemically cured resin composite. Five different solutions were employed: distilled water, artificial saliva, an alcohol-free mouthrinse solution (Orthokin), a 5% alcohol mouthrinse solution (Perioaid), and a 75% ethanol/water solution. Five disc specimens (15 mm x 0.85 mm) were used for each experimental condition. Materials were handled following manufacturers' instructions and were ground wet with silicon carbide paper. Solubility and sorption of the materials were calculated by means of weighing the samples before and after immersion and desiccation. Data were analyzed by two-way ANOVA and Student-Newman-Keuls test (p < 0.05). The light-cured glass ionomer cement showed the lowest solubility and the highest sorption values. When using alcohol-containing solutions as storage media, solubility of the paste-paste chemically cured resin composite increased, and sorption values for the tested chemically cured resin composites were also increased. The use of alcohol-free mouthrinses does not affect sorption and solubility of orthodontic cements. The chemically cured (paste-paste) composite resin cement, requiring a mixing procedure, was the most affected by immersion in alcohol-containing solutions.     

Effect of resin hydrophilicity and water storage on resin strength

This study evaluated the change in the ultimate tensile strength (UTS) of five polymerised resin blends of increasing hydrophilicity, after ageing in distilled water or silicon oil. Resin blocks were prepared from each resin blend by dispensing the uncured resin into a flexible, embedding mould, containing multiple cavities. The resins were polymerised in the moulds under nitrogen at 551.6 kPa and light-activated at 125 degrees C for 10 min. After dry ageing for 24 h at 37 degrees C, the middle third of each resin specimen was trimmed into an 'I' shape. Fifteen control specimens were randomly selected from each resin blend for baseline UTS evaluation. The UTS of the experimental specimens were determined after 1, 3, 6 and 12 months of ageing in water or oil. The UTS of each group of resins at different storage periods in water or oil were analysed using the Friedman multiple ANOVA on ranks and Dunn's multiple comparison tests at 95% confidence level. Significant reduction (p < 0.01) in UTS was observed in Groups II-V resins after 12-month storage in water, while the most hydrophobic Group I resin showed no significant change (p > 0.05) in the same period. The percentage reduction in UTS increased with the hydrophilicity of the resin blends. Long-term water storage of hydrophilic resin blends such as those employed in dentine adhesives, resulted in a marked reduction in their mechanical strength that may compromise the durability of resin-dentine bonds.     

Net expansion of dried demineralized dentin matrix produced by monomer/alcohol saturation and solvent evaporation

The purpose of this work was to determine if nonaqueous methacrylate monomer/alcohol mixtures could expand dried collapsed demineralized dentin matrix. Thin disks (ca. 200 microm) of human dentin were demineralized and placed in wells beneath contact probes of linear variable differential transformers. The probes were placed on water-saturated expanded matrices to record the shrinkage associated with drying. Monomer mixtures containing hydroxyethyl methacrylate, 2,2-bis[4-(2-hydroxy-3 methacryloyloxy)propoxyphenyl] propane, or triethyleneglycol dimethacrylate were mixed with methanol or ethanol at alcohol/monomer mass fraction % of 90/10, 70/30, 50/50, or 30/70. They were randomly applied to the dried matrices to determine the rate and magnitude of expansion; then shrinkage was recorded during evaporation of the alcohols. The results indicated that matrix expansion was positively correlated with the Hoy's solubility parameters for hydrogen bonding forces (delta(h)) of the monomer/solvent mixtures (p < 0.001). Expansions were more rapid with methanol-containing than with ethanol-containing monomer mixtures. For the test solutions, triethyleneglycol dimethacrylate-containing mixtures produced the slowest rate of matrix expansion and hydroxyethyl methacrylate-containing mixtures the most rapid expansion. When the solvents were evaporated, the matrix shrank in proportion to the solvent content and the delta(h) of the monomer-solvent mixtures. The results indicate that expansion of dried, collapsed dentin matrices requires that the delta(h) of the mixtures be larger than 17 (J/cm(3))(1/2). The greater the delta(h) of the monomer solutions, the greater the rate and extent of expansion.     

NIR-spectroscopic investigation of water sorption characteristics of dental resins and composites.

A near infrared (NIR) method using the 5200 cm(-1) absorption of water has been employed to examine water absorbed in photopolymerized dental resins and composites in the form of 0.01-cm- to 0.15-cm-thick specimens. The concentration, c [mol L(-1)], of absorbed water in specimens of thickness t [cm] was calculated by means of Beer's law, A = e ct. A is the NIR absorbance and e is the absorptivity of absorbed water. e depends on the environment of the water molecule and it is necessary to estimate e for water in each material. Water sorption was determined gravimetrically and correlated to the absorbance in the NIR spectrum. Once the relationship between e and water content was known for a material, water sorption was determined rapidly on very thin specimens for faster equilibration. Where dissolution of the specimen occurred, the solubility behavior of the specimen was evaluated from a comparison of NIR and gravimetric measurements. The NIR absorptivity, e, of water absorbed in a polymeric medium was found to be inversely related to the degree of hydrophilicity and hydrogen bonding capability of the polymer. The presence of water clusters in a polyethylene oxide methacrylate polymer was inferred from convex-up curvature in the plot of e vs. water content.     

Application of hydrophobic resin adhesives to acid-etched dentin with an alternative wet bonding technique

Hydrophilic dentin adhesives are prone to water sorption that adversely affects the durability of resin-dentin bonds. This study examined the feasibility of bonding to dentin with hydrophobic resins via the adaptation of electron microscopy tissue processing techniques. Hydrophobic primers were prepared by diluting 2,2-bis[4(2-hydroxy-3-methacryloyloxy-propyloxy)-phenyl] pro- pane/triethyleneglycol dimethacrylate resins with known ethanol concentrations. They were applied to acid-etched moist dentin using an ethanol wet bonding technique that involved: (1) stepwise replacement of water with a series of increasing ethanol concentrations to prevent the demineralized collagen matrix from collapsing; (2) stepwise replacement of the ethanol with different concentrations of hydrophobic primers and subsequently with neat hydrophobic resin. Using the ethanol wet bonding technique, the experimental primer versions with 40, 50, and 75% resin exhibited tensile strengths which were not significantly different from commercially available hydrophilic three-step adhesives that were bonded with water wet bonding technique. The concept of ethanol wet bonding may be explained in terms of solubility parameter theory. This technique is sensitive to water contamination, as depicted by the lower tensile strength results from partial dehydration protocols. The technique has to be further improved by incorporating elements of dentin permeability reduction to avoid water from dentinal tubules contaminating water-free resin blends during bonding.     

Isoprene-styrene copolymer elastomer and tetrahydrofurfuryl methacrylate mixtures for soft prosthetic applications

Novel elastomer/methacrylate systems have been developed for potential soft prosthetic applications. Mixtures of varying compositions of an isoprene-styrene copolymer elastomer and tetrahydrofurfuryl methacrylate (SIS/THFMA) formed one-gel systems and were heat cured with a peroxide initiator. The blends were characterised in terms of sorption in deionised water and simulated body fluids (SBF), tensile properties and viscoelastic parameters of storage modulus and tan delta, as well as glass transition temperatures using dynamic mechanical analysis (DMA). DMA data gave two distinct peaks in tan delta, a lower temperature transition due to the isoprene phase in SIS and one at high temperature thought to be a combination of THFMA and the styrene phase in SIS. The tensile data showed a clear phase inversion within the mid range compositions changing from plastic to elastomeric behaviour. The sorption studies in deionised water showed a two stage uptake with an initial Fickian region that was linear to t 1/2 followed by a droplet growth/clustering system. The slope of the linear region was dependent on the composition ratio. The extent of overall uptake was osmotically dependent as all materials equilibrated at a much lower uptake in SBF. The diffusion coefficients were found to be concentration dependent.     

Molecular Dynamics in Poly(N‐vinylpyrrolidone)‐Poly(ethylene glycol) Blends Investigated by the Pulsed‐Field Gradient NMR Method: Effects of Aging,Hydration and PEG Chain Length

The self‐diffusion in PVP‐PEG blends has been studied as a function of PEG molecular weight, water content and temperature. The blend corresponding to a stoichiometric PVP‐PEG complex with 36 wt.‐% PEG400 results from hydrogen bonding of the PEG terminal hydroxyl groups to the carbonyls of the PVP repeating units. Changes in diffusion parameters during the time of storage of the samples up to 1.5–2 months after preparation have been established. The attainment of an equilibrium value is characterized by a redistribution of the PEG molecules bonded to the comparatively long PVP chains, resulting in the formation of a supramolecular network. The spin echo attenuation, S_inc(q, t_d), has been found to depend on the temperature, PEG chain length and water content. Water acts as a mediator in the complex formation, accelerating the PVP‐PEG complexation. The PVP blend with PEG200 retains about 21 wt.‐% of water after evacuation at 378 K. This amount of water is believed to be incorporated into the network. The longer the PEG chain length, i.e. the larger the flexibility of the chain, and the lower the OH group concentration in the blend, the smaller the number of PEG molecules bound to PVP. This has been established by comparing diffusion parameters of PVP blends containing PEG400 and PEG600, respectively.     

Diffusion coefficient of water through dental composite resin

Water sorption of polymer filling materials affects dimensional stability, mechanical properties and bonding strength with tooth structures. To clarify the effect of the degradation on service life and micro-leakage, the diffusion coefficient of water through the resin should be identified. Distributions of time-dependent water concentrations in the resin were computed. Water sorption of composite resin discs with different thicknesses was measured and compared with the solution of Fick's second law. The diffusion coefficient of water through the resin discs was computed to be D=3.9-5.0 x 10(-13)m(2)/s from the measurements of specimens with different thicknesses. Results of water sorption measurements for the discs with different thicknesses were in good agreement with the theoretical results. The relationship among the thickness of the disc, the diffusion coefficient and the water sorption ratio was shown clearly. The testing method for water sorption by International Standard ISO 4049 for resin-based filling materials was discussed.     

三种义齿软衬材料吸水性和溶解性的实验研究

我们对自凝水凝胶、自凝型丙烯酸酯和SDG－A硅橡胶三种义齿软衬材料进行吸水性和溶解性的实验探讨。采用的方法是将各材料制成直径50mm,厚1mm,表面平整光滑的园子,干燥24h后称重（m1）。再分别浸在人工唾液和蒸馏水溶液中保持7d和28d,称湿重（m2）,继续干燥后称重（m3）,最后计算材料的吸水值、吸水率和溶解率,统计学分析处理。结果显示：在人工唾液中7d和28d的吸水率,水凝胶为28.62%和24.96%,自凝型丙烯酸酯为1.89%和1.65%,SDG－A硅橡胶为0.25%和0.29%;溶解率分别为0.56%和0.51%,0.74%和0.83%,以及0.10%和0.12%。在蒸馏水中7d和28d的吸水率,水凝胶为30.15％和27.85％,自凝型丙烯酸酯为3.64％和6.17％,SDG－A硅橡胶为0.83％和0.98％;溶解率分别为0.79%和1.16%,0.86％和1.01％,以及0.10％和0.14％。结论是三种义齿软衬材料的吸水率大小依次为水凝胶＞丙烯酸酯＞硅橡胶。丙烯酸树脂由于含有一定量的增塑剂,其溶解率高于其他两种材料;浸泡溶液中增加离子成份可能对材料的吸水性能和溶解性能都有不同程度的影响;水凝胶材料的高吸水性能对临床实际意义还有等进一步研究。     

Physicochemical properties and in vitro biocompatibility of PEO/PTMO multiblock copolymer/segmented polyurethane blends

A multiblock copolymer composed of poly(ethylene oxide) (PEO) and poly(tetramethylene oxide) (PTMO) and which forms a physical hydrogel was blended with Pellethane, a commercial segmented polyurethane (SPU) developed for various biomedical devices, to provide a PEO-rich surface with improved stability. The effect of the copolymer blending was evaluated with respect to surface hydrophilicity, long-term stability, mechanical properties, in vitro protein adsorption, and platelet adhesion. A small amount of the copolymer additive (5 wt%) significantly improved surface hydrophilicity, which was then gradually enhanced by increasing the amount of the copolymer in the blends. The blend films exhibited minimal extraction of the copolymer additive when exposed to a buffer solution for 2 months at 37 degrees C, resulting in less than 1 wt% weight loss of the films even with 30 wt% content of the copolymer in the blends. Although a certain degree of alteration in the mechanical properties was observed by increasing the copolymer content, the mechanical properties were well maintained for up to 10 wt% addition of the copolymer, when compared with the bare SPU. Protein adsorption was significantly reduced with a small amount of copolymer additive as low as 5 wt%. Fibrinogen, an adhesive protein for further cellular adhesion and activation, was effectively repelled by increasing the amount of copolymer additive. The platelet adhesion test revealed that the blend film surface reduced platelet adhesion and the degree of inhibition was proportional to the content of the additive, up to 30 wt%. The high molecular weight (Mw = 66,000) and compatible chemical structure of the copolymer with SPU made the surfaces PEO-rich and stable in an aqueous environment, resulting in an enhancement of the resistance to protein adsorption and platelet adhesion without a significant deterioration in physical properties.     

New chitin-based polymer hybrids, 3. Miscibility of chitin-graft-poly(2-ethyl-2-oxazoline) with poly(vinyl alcohol)

The miscibility of blends of poly(vinyl alcohol) (PVA) with chitin-graft-poly(2-ethyl-2-oxazoline) ( 1 ) and poly(2-ethyl-2-oxazoline) homopolymer (PEtOZO) was investigated. Calorimetric results showed a single glass transition temperature (T_g) in the entire range of compositions for both blend systems, which indicated that PVA is miscible with both the graft copolymer 1 and PEtOZO. The T_g of PVA is also shifted to lower temperature upon blending with the graft copolymer 1 . IR analysis revealed the existence of specific interactions via hydrogen bonding between the hydroxyl groups in PVA and the carbonyl groups in the poly(2-ethyl-2-oxazoline) side chain of graft copolymer 1 . The results show that the interaction of graft copolymer 1 with PVA is increased by introduction of longer poly(2-ethyl-2-oxazoline) side chains. Thermal decomposition (TG) measurements supported the compatibility of PVA with graft copolymer 1 and with PEtOZO, and showed that the thermal stability of PVA is improved upon blending with 1 or PEtOZO.     

Recent advances in the theory and mechanism of adhesive resin bonding to dentin: a critical review

Dentin bonding issues involving adhesive resins have attracted considerable research interest in recent years. An important advance due to the ongoing research is the concept of hybridization of the tissue with primer/adhesive systems. Hybridization involves permeation of primer monomer into the tissue substrate. Although the mechanism of adhesive permeation and interaction with tissue may be complex, significant advances have been made. In systems where etching precedes priming and bonding steps, the Hoy's solubility parameter compatibility of the primer formulation with that of demineralized dentin matrix may determine adhesive permeability. Monomer permeation brings the primer atoms in closer contact with the substrate atoms, leading to adhesive interactions through van der Waals, hydrogen bonding, and electrostatic interactions. In self-etch primer systems, stronger electrostatic interaction between primer monomers and hydroxyapatite has been used to explain the adhesion process. These interactions have been computer-modeled and analyzed. Such interactions and subsequent polymerization of the monomer promote improved bond strength and efficient margin sealing. Incomplete permeation of monomer into the full depth of demineralized region may, however, leave exposed collagen fibrils and cause nanoleakage of water into these regions through a 20-100 nm sized marginal gap, leading to subsequent hydrolytic degradation of these collagen fibrils and the hybrid layer. Microleakage is also a problem in some single step formulations. In this review, we analyze these current theoretical and mechanism-related issues of interest in adhesive resin bonding to dentin, and outline the continuing problems that need to be overcome in the future.     

Miscibility and specific interactions in blends of poly(vinyl acetate-co-vinyl alcohol) with poly(ethyloxazoline)

Miscibility of poly(ethyloxazoline) (PEOX) with poly(vinyl acetate) (PVAC), poly(vinyl alcohol) (PVAL) and poly(vinyl acetate-co-vinyl alcohol) (ACAL copolymers) has been investigated over a wide composition range. In some blends, due to the small difference between the glass transition temperatures of the components, the enthalpic relaxation method was used as miscibility criterion. Differential scanning calorimetry (DSC) results indicate that PEOX is immiscible with PVAC and PVAL but is miscible with ACAL copolymers in a certain range of compositions. The ACAL/PEOX phase diagram for different copolymer compositions has been determined. The variation of the glass transition temperature with blend composition for miscible systems was found to follow the Kwei equation. Infrared spectroscopy studies of blends reveal the existence of specific interactions via hydrogen bonding between hydroxyl groups in vinyl alcohol units and the carbonyl group in the tertiary amide, which appear to be decisive for miscibility.     

Water absorption of poly(methyl methacrylate) containing 4-methacryloxyethyl trimellitic anhydride

The amount of water absorption of poly(methyl methacrylate) (PMMA) containing 0, 1, 3 and 5 wt% of an adhesive monomer, 4-methacryloxyethyl trimellitic anhydride (4-META), was measured at 7 degrees C, 37 degrees C and 60 degrees C. After the water uptake reached equilibrium in specimens, they were desorbed to obtain a constant value and the absorption process was repeated. Mass changes in the second desorption were recorded for the storage temperatures of 37 degrees C and 60 degrees C. Multiple regression analyses were conducted on three independent variables, 4-META concentration, storage temperature and absorption-desorption cycle. A statistically significant relationship was found between the maximum water uptake and 4-META concentration, while there was no relationship between the maximum water uptake and diffusion coefficient obtained using the Fick's law. The negative relationship in the latter did not support the free space theory. The significant and positive relationship between the maximum water uptake and 4-META concentration demonstrates that water molecules diffuse through the formation of a hydrogen bond at polar sites. The maximum water uptake was not influenced by temperature, while the diffusion coefficient increased with the rise in temperature. The activation energy was 41-47 and 50-53 kJ/mol in the first and second absorption tests, respectively.     

The Study of Miscibility and Hydrogen Bonding in Blends of Phenolics with Poly(ε‐caprolactone)

Blends of phenolics with poly(ε‐caprolactone) (PCL) were prepared by solution casting from the tetrahydrofuran (THF) solution. Differential scanning calorimetry (DSC) and Fourier‐Transform infrared spectroscopy (FTIR) were used to examine the miscibility behavior and hydrogen bonding of the blend. This phenolics/PCL blend system is fully miscible based on single glass transition temperature due to the formation of inter hydrogen bonding between hydroxyl of phenolic and carbonyl of PCL. In addition, a negative polymer‐polymer interaction energy density “B” was obtained based on the melting depression of PCL using the Nishi‐Wang equation. Furthermore, FTIR was used to study the hydrogen‐bonding interaction between the phenolic hydroxyl group and the PCL carbonyl group at various temperatures and compositions. Moreover, the inter‐association equilibrium constant and its related enthalpy of phenolic/PCL blends were determined and used to predict the miscibility window, free energy and fraction of the hydrogen bonding according to the Painter‐Coleman association model (PCAM).