Miscibility Characterization in Relation to Phase Morphology of Poly

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Miscibility Characterization in Relation to Phase Morphology of Poly(ether sulfone)/ Poly(vinyl pyrrolidone) Blends Containing a Phytochemical Chandrasekaran Neelakandan and Thein Kyu* Department of Polymer Engineering, UniVersity of Akron, Akron, Ohio 44325 ReceiVed: March 6, 2009; ReVised Manuscript ReceiVed: April 30, 2009

Miscibility and morphology of poly(ether sulfone)/poly(vinyl pyrrolidone) (PES/PVP) blends containing a crystalline phytochemical called mangiferin were investigated using differential scanning calorimetry (DSC), Fourier transformed infrared spectroscopy (FTIR), and polarized optical microscopy (POM). The binary blends of PES/PVP were found to be completely miscible. However, FTIR experiments revealed no spectral shift that is attributable to the miscibility of the PES/PVP pair, although the occurrence of hydrogen-bonding interactions can be confirmed in binary blends of both PES/mangiferin and PVP/mangiferin. The addition of mangiferin to the PES/PVP blends resulted in liquid-liquid phase separation as well as liquid-solid phase transition. However, the liquid-liquid phase separation was observed only in a very small ternary composition range of the PES/PVP/mangiferin blends. With further increase of mangiferin concentration, crystallization occurred, leading to phase segregation between the isotropic liquid (PES/PVP) phase and the crystalline mangiferin. A ternary morphology phase diagram of the PES/PVP/mangiferin blends was established based on the evidence from DSC and POM experiments, which exhibited various coexistence regions including isotropic, liquid + liquid, liquid + crystal, and solid crystal regions. Introduction Phytochemicals, plant-derived non-nutritive chemicals having numerous pharmaceutical properties, have gained considerable interest for development of multifunctional biomaterials to facilitate affordable medical treatment.1-4 Some of the compelling advantages of phytochemicals include their natural origin in plants, fruits, and vegetables; abundant availability; easy extraction; minimal levels of toxicity; and inexpensiveness compared to their synthetic counterparts.5 The aforementioned attractive features of these phytochemicals have spurred our motivation to develop a simple but effective strategy for designing multifunctional materials via blending phytochemical with polymers. Among phytochemicals, mangiferin is especially attractive because of its multifunctional properties such as antioxidant, antimicrobial, antiplatelet, antithrombotic, and antiinflammatory, which made it an ideal candidate for alternative medicine and cosmetic applications. Mangiferin is a naturally occurring glucosyl xanthone (2-C-β-D-glucopyranosyl-1,3,6,7tetrahydroxyxanthone) derived from barks, leaves, and fruits of mango tree (Mangifera indica). It is a crystalline substance having a molecular weight of 422 g/mol and a melting temperature of ∼267 °C. The ultimate goal of this work is to develop multifunctional polymeric membranes for hemodialysis applications by incorporating mangiferin into miscible polymer blends. However, it is crucial to understand the role of molecular interactions in the miscibility of the polymer/mangiferin complexes, prior to fabricating phytochemically modified hydrophobic/ hydrophilic polymer composite membranes. In a previous paper,6 we conducted miscibility studies of a binary blend of poly(amide)/poly(vinyl pyrrolidone) (PA/PVP) with and without mangiferin. The binary PA/PVP blends were found to be completely miscible owing to strong hydrogen bonding between the PA and PVP. The binary mixtures of PA/ * To whom correspondence should be addressed. Tel: +1-330-972-6672. Fax: +1-330-258-2339. E-mail: [email protected].

mangiferin and PVP/mangiferin were also miscible at low mangiferin concentrations, but liquid-solid phase transition occurred at higher mangiferin concentrations. One of the important findings was the enhanced glass transition temperature of both PA/mangiferin and PVP/mangiferin blends due to the addition of mangiferin. Furthermore, by virtue of competitive hydrogen -bonding interactions among the constituents, the ternary PA/PVP/mangiferin blend exhibited various coexistence regions such as isotropic, liquid + liquid, liquid + crystal, liquid + liquid + crystal, and solid crystal. One of the recent advances in hemodialysis membranes is the introduction of poly(ether sulfone) (PES) in lieu of poly(amide) (PA) in their blends with PVP.7-10 PES is a highperformance engineering thermoplastic with a high glass transition temperature (230 °C) having superior chemical and thermal resistance. Moreover, PES is highly hemocompatible11 and exhibits profound hydrophobicity.12,13 Consequently, PES found its way to the hemodialysis membrane applications via blending with hydrophilic PVP.14,15 From the hemodialysis perspective, the biggest thrust is the amenability of PES to multiple usages in the hemodialyzers.9 It is intriguing to examine whether or not PES is preferable to PA in blending with PVP and mangiferin in the development of multifunctional hemodialysis membranes. As a sequel to our previous work,6 we shall conduct the miscibility characterization in reference to the phase diagram of the PES/PVP/mangiferin blends. Miscibility behavior of binary blends of PES/PVP, PES/mangiferin, and PVP/ mangiferin was characterized by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Subsequently, a Fourier transform infrared spectroscopy (FTIR) experiment was carried out to probe any occurrence of specific intermolecular interactions such as hydrogen-bonding or dipole-dipole interaction among the blend components. The ternary phase diagram of PES/PVP/mangiferin is discussed in relation to that of the PA/PVP/mangiferin system.

10.1021/jp902057z CCC: $40.75  2009 American Chemical Society Published on Web 06/03/2009

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Experimental Section Materials. In the preparation of polymer/phytochemical blends, the PES/PVP pair was chosen as the polymer matrix and mangiferin as the crystalline phytochemical. PES (Ultrason E 6020P) utilized in the present study is an amorphous polymer having a weight average molecular weight (Mw) of 46 000 with a high glass transition temperature (230 °C); it was generously provided by BASF Corp. (Wyandotte, MI).16 This PES grade was approved by FDA for food-contacting applications and is commonly employed in dialyzer membrane applications.17 PVP (Mw ) 40 000) was bought from Sigma-Aldrich (St. Louis, MO). Dimethyl sulfoxide (DMSO) purchased from Sigma-Aldrich was used without further purification. This PES/PVP blend was shown to be hemocompatible and is known for its multiple usages in hemodialyzer units.9,11 Mangiferin, purchased from Sigma-Aldrich, was HPCL-grade, having 99.9% purity. The multifunctional properties of mangiferin along with its isolation and characterization techniques may be found elsewhere.17-20 Methods. The glass transition temperatures of the PES/PVP blends and the crystal melting temperature of mangiferin were determined by using a differential scanning calorimeter (Model 2920, TA Instruments). Temperature and enthalpy calibration was performed using an indium standard. For DSC experiments, homogeneous solutions of pure components and blends were prepared in DMSO followed by solvent removal under vacuum at 150 °C for 24 h. Approximately 10 mg of the samples were used for each run. During the first DSC cycle, the samples were heated from room temperature to 225 °C to remove any thermal history and subsequently ramped for a second time from ambient temperature to 300 °C. Thermal stability studies of the solvent cast samples were conducted using a thermogravimetric analyzer (TGA) (TA Instruments, Model 2050). In the TGA experiments, the samples were heated at a rate of 10 °C/min from 100 to 500 °C in a nitrogen atmosphere with a flow rate of 120 mL/min. The temperature at which the 5% weight loss occurred was regarded as the degradation temperature. Samples for FTIR analysis were prepared by solution casting on potassium bromide (KBr) disks from a 5 wt % DMSO solution of the neat components and their blends. After drying under vacuum at 150 °C for 24 h, the samples were stored in a desiccator until further use. Infrared spectrum was acquired on a FTIR spectrometer (Thermo Scientific Nicolet 380) at a resolution of 4 cm-1 averaged over 32 scans. In order to minimize the effects of moisture, the samples were initially heated to 150 °C and then equilibrated at 100 °C for data acquisition. The samples for POM experiments were prepared under the same conditions of DSC and FTIR, except that thin films (∼10 µm) were cast on glass substrates. An optical microscope (BX60, Olympus) equipped with a 35 mm digital camera (EOS 400D, Canon) and a hot stage (TMS 93, Linkam) was used for acquiring the POM images. Results and Discussion Thermal Stability and Miscibility Characteristics of PES/ PVP Binary Blends. Figure 1a shows the TGA thermograms labeled by the chemical structures of neat PES and PVP. It is seen that PES is more thermally stable than PVP, which may be attributed to the highly aromatic backbone of PES. The DSC thermograms of PES/PVP blends revealed a single Tg, exhibiting a systematic movement with blend composition (Figure 1b). Moreover, the widths of these glass transition curves of the blends appear comparable to those of pure components, suggesting that the PES/PVP blends are miscible over the entire

Figure 1. (a) TGA thermograms of pure PES and PVP demonstrating the thermal stability of pure components. Insets show the chemical structure of the two polymers. (b) DSC thermograms of binary PES/ PVP illustrating the complete miscibility of the blends. The inset shows the plot of the Tg of blends as a function of weight fraction of PVP.

composition range. A positive departure of the experimental Tg from the trend of the Fox equation21 (inset of Figure 1b) implies possible specific interactions occurring between PES and PVP, which may be contributing to the blend miscibility. In visual examination, the cast films of PES/PVP blends were transparent and colorless to naked eyes. The POM investigation of these PES/PVP blends showed neither phase separated regions nor crystalline textures, in conformity with the findings of the DSC experiments. It should be pointed out that the Tg of PVP is about 177 °C, whereas that of PES is about 230 °C. The Tg of mangiferin, being a small molecule crystalline substance, can hardly be detected by standard characterization tools. Next, FTIR experiments were carried out in order to examine the occurrence of any specific interactions between PES and PVP. To prevent moisture absorption, the FTIR spectra were acquired at 100 °C. Figure 2a depicts the FTIR spectra of various PES/PVP blends in the 1550-1800 cm-1 range. Several characteristic bands of the neat PES can be identified; viz., aromatic CdC band at 1578 and 1485 cm-1, asymmetric and symmetric stretching of OdSdO at 1325 and 1150 cm-1, and 1240 cm-1 (assigned to aromatic ether).22 The characteristic peaks along with the band assignments for the PVP includes 1682 cm-1 (CdO stretching), 1461 cm-1 (CH2 bending), 1428 cm-1 (CH2 deformation), and 1288 cm-1 (C-N stretching).6 As can be seen in Figure 2a, the carbonyl band of PVP and OdSdO band (both asymmetric and symmetric) remained virtually constant with little or no spectral shift when PVP was

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Figure 3. (a) TGA thermograms for PES/mangiferin blends showing the improved thermal stability of mangiferin due to the addition of PES. The horizontal dashed line corresponding to the 5% weight loss is regarded as the degradation temperature. (b) A plot of Tg and Tm of PES/mangiferin blends as a function of mangiferin concentration showing systematic movement of single Tg to lower temperature up to 40% mangiferin concentration and endothermic crystal melting peak at higher mangiferin concentrations. The melting peaks of blends remain virtually stationary owing to a very marginal melting point depression. Figure 2. FTIR spectra recorded for PES/PVP blends at 100 °C (a) in the region of 1550-1800 cm-1 and (b) in the region of 2750-3550 cm-1. Little or no movement of any characteristic band in this region (i.e., 2 cm-1 for ether band, 1 cm-1 for CdO of mangiferin, 1 and 2 cm-1 for symmetric and asymmetric OdSdO bands, respectively) suggests no indication of strong specific interactions between the PES/ PVP pair.

added to PES. In view of the absence of complementary electron donor and acceptor in the chemical structures of both PES and PVP, one can preclude any hydrogen bonding between the two species. In the literature, however, PES and PVP were reported to form a miscible pair due to the interactions involving OdSdO of PES and N-CdO of PVP.14,15 Moreover, the ab initio calculation by Vandermeren et al. revealed that the sulfone groups of PES can be characterized by a net positive charge on the sulfone group.23 On the other hand, PVP is a tertiary amide, which is highly electronegative in nature. The electrostatic dipolar interaction between the sulfone of PES and the tertiary amide group of PVP probably leads to the miscibility of their blends. Figure 2b illustrates the FTIR spectra in the 2700-3300 cm-1 range showing the characteristic bands of 3069 and 3095 cm-1 (C-H asymmetric and symmetric stretching) for PES and

2950 cm-1 (C-H stretching) for PVP, respectively. The lack of any observable spectral shift in the 2700-3300 cm-1 range implies that the above dipolar interaction is presumably not strong enough to cause any noticeable spectral movement. Thermal and Miscibility Characteristics of PES/Mangiferin Binary Blends. Mangiferin is a small crystalline molecule with a sharp crystal melting peak (∼267 °C).6 The solvent-cast PES/ mangiferin sample is tinted yellowish, owing to the inherent color of mangiferin. Figure 3a demonstrates the improvement in thermal stability of PES/mangiferin blends due to the addition of PES. DSC thermograms show the effect of mangiferin addition on the Tg and Tm of its blends with PES (Figure 3b and its inset). All the PES/mangiferin samples exhibited a single Tg. The addition of mangiferin lowered the glass transition temperature of the blends, but only up to a certain composition range (10-40 wt % mangiferin), above which mangiferin crystallizes in its PES blends. The PES/mangiferin blends also exhibited a slight melting point depression at low concentrations of PES (10 wt % PES). The melting peak virtually remained constant with further increase of PES concentration (20-50 wt % PES), implying no further depression. In addition, liquid-

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Figure 4. FTIR spectra of PES/mangiferin blends recorded at 100 °C (a) in the range of 1500-1800 cm-1 demonstrating cross-hydrogen-bond formation as evidenced by the systematic movement of OdSdO to a lower frequency by 4 and 6 cm-1 for symmetric and asymmetric OdSdO bands, respectively, and spectral shift of the aromatic ether band of PES to a lower wavenumber by 6 cm-1 for ether band, and the carbonyl band of mangiferin to a higher wavenumber by 8 cm-1 and (b) in the 2700-3600 cm-1 range demonstrating the low-frequency shift of the broad hydroxyl band of mangiferin (frequency shift not quantified due to the broad nature of the OH band).

liquid phase separation was not discernible in the entire composition range for PES/mangiferin blends. However, there is a limited solubility of mangiferin in PES, especially when mangiferin started to crystallize. According to the literature,24,25 various drug molecules can exert profound plasticizing effect

on polymers, depending upon the rigidity of the drug molecule and its molecular interactions with the polymer counterpart, such as hydrogen bonding. Typical outcomes include the depression of Tm if the drugs were crystalline; otherwise, there is enhanced flexibility of the blends, reflecting the reduction in Tg.

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Figure 4a shows the FTIR spectra of PES/mangiferin blends in the 1500-1800 cm-1 range. It should be emphasized that mangiferin molecules can self-associate among themselves via self-hydrogen-bonding (i.e., intermolecular hydrogen bonding among the same species), while PES, although unable to selfassociate, is capable of interacting with mangiferin (i.e., crosshydrogen-bonding). With the addition of mangiferin, it is seen that the asymmetric, symmetric stretching bands of OdSdO shift 4 and 6 cm-1, respectively, and the aromatic ether of PES shifts to lower frequencies by 6 cm-1 due cross-hydrogenbonding with the hydroxyl groups of mangiferin.26 As a result, some of the self-hydrogen-bonded groups in mangiferin may be released, resulting in a red shift of the carbonyl band of mangiferin of 8 cm-1 at 1658 cm-1. In contrast, the aromatic CdC band does not show any movement because the CdC stretching is not directly involved in any specific interactions. Figure 4b shows the FTIR spectra of PES/mangiferin blends in the 2700-3600 cm-1 range. The broad absorption band of mangiferin at 3355 cm-1 indicates the presence of numerous hydroxyl groups, including those forming self-hydrogen-bonds. When PES is added to mangiferin, the broad peak maximum of the 3355 cm-1 band shows a blue shift of more than 50 cm-1, suggesting the cross-hydrogen-bonding of O-H groups of mangiferin with the OdSdO and aromatic ether of PES. Further, the aromatic stretching peak of PES gradually reduces its intensity due to the dilution effect exerted by the mangiferin concentration. All of the above observations lend support to the conclusion that cross-hydrogen-bonding occurs between PES and mangiferin. The possible interactions in these PES/ mangiferin mixtures include O-H · · · O-H (self), O-H · · · OdC (self), O-H · · · OdSdO (cross), and O-H · · · O-C (cross) hydrogen-bonding interactions. Thermal and Miscibility Characteristics of PVP/Mangiferin Binary Blends. The miscibility characteristics of PVP/ mangiferin were already demonstrated in our previous paper6 and thus only the pertinent highlights of the outcome are presented here. Visually, PVP/mangiferin samples were transparent but tinted slightly yellowish, arising from the inherent color of mangiferin. The thermal stability of mangiferin was improved in the blends due to its cross-hydrogen-bonding with PVP. As shown in Figure 5, the PVP/mangiferin blends exhibited a single glass transition temperature moving to a higher temperature with increasing mangiferin, which is in sharp contrast to the PES/mangiferin blends, where the Tg was found to decline. On the basis of the variation of Tg with mangiferin concentration, the Tg of mangiferin appears to be located in the vicinity of 210-225 °C, which is intermediate between those of PVP and PES. Hence, it is not surprising to discern the trend of the Tg shift occurring in opposite way for the above PVP/ mangiferin and PES/mangiferin systems. The neat mangiferin is highly crystalline and thus its Tg is generally not observable in the DSC experiments. Although a single Tg was observable in the low mangiferin compositions (60 wt %) due to the highly crystalline nature of mangiferin. Another important point is that the blending of PVP with mangiferin shows a significant melting point depression as compared to that of the PES/mangiferin blends, where the melting peaks remain virtually stationary. These DSC observations imply that mangiferin is seemingly more miscible with PVP than with PES. Moreover, the FTIR experiments6 revealed strong hydrogen bonding between PVP and mangiferin, as manifested by the appreciable blue shift of the CdO band.27-29 Hence, it may be inferred that the highly aromatic xanthone backbone of mangiferin

Neelakandan and Kyu

Figure 5. (a) Plots of Tg and Tm of PVP/mangiferin blends as a function of mangiferin composition indicating the enhancement of Tg of the blends with mangiferin concentration and also showing a significant melting point depression. (b) A plot of peak maximum of the carbonyl and hydroxyl peaks of PVP/mangiferin blends as a function of mangiferin composition indicating the low-frequency shift of the carbonyl peak due to cross-hydrogen-bonding between CdO of PVP and O-H of mangiferin.

combined with the strong cross-hydrogen-bonding between PVP and mangiferin might be responsible for the enhancement of the glass transition temperature of these blends. The possible interactions for the PVP/mangiferin blends include hydroxylhydroxyl (self) and hydroxyl-carbonyl (self) of mangiferin and hydroxyl-carbonyl (cross) interactions. Miscibility Characteristics of PES/PVP/Mangiferin Ternary Blends. Even though the binary systems showed varying extents of miscibility for the PES/PVP, PES/mangiferin, and PVP/mangiferin systems, there is no assurance that the same miscibility trend will hold for their ternary case because of the preferential affinity of mangiferin for PVP relative to PES. The 50/50 and 75/25 PES/PVP ternary blends containing mangiferin showed the single phase character in low mangiferin concentrations, especially in the PVP-rich compositions. However, the 75/25 PES/PVP at intermediate mangiferin loading of 40-60 wt % exhibited dual glass transition temperatures, suggestive of liquid-liquid phase separation between PES/mangiferin and PVP/mangiferin phases. At much higher mangiferin concentrations, the DSC thermograms were further complicated by the depressed crystal melting peaks of mangiferin, reflecting the competition between liquid-liquid phase separation and liquid-solid phase transition. To identify various coexistence regions, POM experiments were performed on the ternary PES/PVP/mangiferin blends. In

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Figure 6. Ternary morphology phase diagram in conjunction with POM and DSC data for the PES/PVP/mangiferin blends, showing various coexistence regions (labeled by different shading). Unpolarized and polarized optical microscope images corresponding to left and right images, respectively, representing the typical phase morphology of each region in relation to the ternary phase diagram. In the crystal region, the left image shows the 10/90 PVP/mangiferin blend, whereas the right image shows that of the neat mangiferin crystals (both polarized). Keys for labels are I ) isotropic (unfilled circles), C ) crystal (completely filled squares), (I + C)PVP ) coexistence of isotropic and crystals for PVP-rich compositions (semifilled square), (I + C)PES ) coexistence of isotropic and crystal for PES-rich compositions (semifilled circles) and (L + L) ) liquid + liquid (hourglass-filled circles).

order to better appreciate this complex phase behavior, a ternary morphology phase diagram was mapped out for the PES/PVP/ mangiferin blends on the basis of thermal transitions (i.e., Tg and Tm by DSC) along with the morphological evidence from the POM experiments (Figure 6). Different types of shading were employed to delineate various coexistence regions. The symbols represent the data points obtained from the DSC and POM studies showing isotropic (I) (open symbols), crystal (C) (filled symbols), liquid + liquid (L + L) (hourglass-filled symbols), and isotropic + crystal (I + C) (half-filled symbols) phases. The phase boundary of these coexistence regions was drawn by hand with the guidance of DSC and POM data. At low mangiferin loading, the PES/mangiferin and PVP/mangiferin blends were optically transparent and showed no indication of liquid-liquid phase separation. Moreover, it is noticed that there is a clear preferential interaction for mangiferin with PVP relative to PES. On the other hand, the strength of interactions in PES/PVP blends is the weakest among the three constituent pairs, although this pair is completely miscible. Judging from the DSC and the FTIR results, the strength of molecular interactions among the three binary pairs can be categorized in the following sequence, i.e., PVP/mangiferin > PES/mangiferin > PES/PVP. Hence, it may be inferred that the phase behavior of the present ternary system is dominated by the hydrogenbonding interactions between the PVP/mangiferin and PES/ mangiferin pairs. As manifested by a large single-phase region (nonshaded or white) in Figure 6, the cross-hydrogen-bonding between PVP and mangiferin is much stronger relative to that of PES/mangiferin, especially in the PVP-rich compositions. With increasing mangiferin, the system exhibits a signature of liquid-liquid phase separated morphology, albeit only in the

limited ternary compositions shaded by the horizontal lines (see the left bottom pictures in Figure 6). The morphology of the liquid-liquid phase separated domains resembles a sea-andisland type, i.e., suggestive of nucleation and growth. However, caution should be exercised in this simplistic interpretation because one can distinguish the nucleation and growth versus spinodal decomposition only during the early stages of liquid-liquid phase separation. That is to say, the possibility of late stage ripening of spinodally decomposed structure cannot be ruled out. Further increase in mangiferin concentration resulted in crystallization of mangiferin, showing the large spherulitic structures in the continuum of isotropic liquid, signifying the isotropic + crystal (I+C) coexistence phase (see the central bottom and the right upper pictures). In the PES-rich compositions and lower mangiferin concentrations, the lower solubility of mangiferin with PES has led to a larger (I+C)PES coexistence gap as compared to the (I+C)PVP of the PVP/mangiferin blends. At very high concentrations of mangiferin (>85 wt %), the entire field of the optical microscope view was filled with truncated spherulites of mangiferin crystals (see the right bottom pictures in Figure 6). It appears that the increase in mangiferin concentration has resulted in a higher nucleation density, leading to the development of multiple spherulites, which subsequently impinge on each other. In comparison with a parallel study6 involving PA/PVP/ mangiferin, the PES/PVP/mangiferin system exhibited a large single phase region with relatively very small liquid + liquid and solid + liquid coexistence regions, thereby providing useful guidance to controlling the membrane formation step. That is to say, a wide range of ternary composition is available in order

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to prepare an initially homogeneous casting solution. Moreover, the mangiferin loading can be increased without affecting the isotropic state of the initial casting solution, suggesting that PES/ PVP/mangiferin blends are preferred to PA/PVP/mangiferin in the membrane formation process. Although the ternary phase diagram involving the crystalline phase is seemingly complex, the crystallinity of mangiferin can retain its phytochemical properties longer relative to the isotropic amorphous phase. Thus, the presence of mangiferin crystals may render an added advantage for prolonged time release in drug delivery. Conclusions In summary, we have demonstrated the miscibility behavior of PES/PVP blend with and without mangiferin. The binary PES/PVP blends were found to be completely miscible. However, no evidence of hydrogen-bonding interaction for the PES/PVP blends was observed from the FTIR experiments. A dipolar interaction may be a possibility for the complete miscibility of the PES/PVP blend. The PES/mangiferin and PVP/ mangiferin blends were miscible at low mangiferin loading, but large spherulites developed at higher mangiferin concentrations, signifying the solid-liquid coexistence phase. The FTIR results revealed varying extents of cross-hydrogen-bonding in the binary blends of PES/mangiferin and PVP/mangiferin, which are responsible for the miscibility of these binary pairs. The addition of mangiferin to PES lowered the glass transition temperatures of the blends, whereas it raised the glass transition of PVP/ mangiferin blends. It appears that mangiferin has preferentially stronger hydrogen bonding to PVP relative to PES. The addition of mangiferin to a completely miscible PES/PVP blends led to liquid-liquid and liquid-solid phase separations in a composition-dependent manner, as demonstrated in their ternary morphology phase diagram. It should be emphasized that the PES/ PVP/mangiferin system exhibited a larger isotropic region with smaller liquid + liquid and solid + liquid coexistence gaps as compared to those of the PA/PVP/mangiferin. It is reasonable to conclude that PES/PVP/mangiferin blends are preferred to PA/PVP/mangiferin in the membrane formation process. Moreover, the crystallinity of mangiferin can retain its phytochemical properties longer relative to the isotropic amorphous phase, thereby possibly rendering prolonged time release in drug delivery.

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