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The Temperature Influence upon the Complexation Process between Poly(aspartic acid) and Poly(ethylene glycol) Loredana E. Nita,* Aurica P. Chiriac, Maria Bercea, and Iordana Neamtu “Petru Poni” Institute of Macromolecular Chemistry, Grigore Ghica Voda Alley No. 41 A, 700487, Ias- i Romania ABSTRACT: The temperature influence upon the formation of an interpolymer complex (IPC) based on poly(aspartic acid) (PAS) and poly(ethylene glycol) (PEG), was investigated. The water PAS/PEG mixture was studied in the temperature range between 22 and 37 °C. The registered data were correlated with the blend composition and the molecular weight of PEG. The intervened interchain physical interactions, especially the hydrogen-bonds, were evidenced by FT-IR spectroscopy. The miscibility and polymerpolymer interactions were experimentally estimated from the dynamic viscosity. The determination of the zeta potential and electrical conductivity of the interpolymer complexes during their formation are in good agreement with the rheological and spectral data. The variation of the composition, respectively, the PAS/PEG ratio, and the different molecular weights of PEG were used in order to establish the optimum conditions for the IPC achievement. The information was correlated on the mentioned interval of temperature.
1. INTRODUCTION As it is well-known, polymer blends, as physical mixtures between structurally different polymers that interact through secondary forces with no covalent bonding, constitute a useful approach for preparing materials with tailor-made properties different from those of the constituent polymers. Blending polymers may result in reducing their basic cost, improving their processing, and maximizing their specific properties. The gain in properties of the blend depends on the degree of compatibility or miscibility of the polymers at the molecular level. Related to the degree of molecular mixing, blends were classified as totally miscible (compatible blends), semimiscible (semicompatible), or immiscible (incompatible) blends.1 Progressive elucidation of the specific interactions’ effect on the miscibility in polymer blends has been one of the most noticeable achievements in the study of polymer blends in the last two decades.2 Many experimental results have supported the conclusion that the presence of specific interactions in a blend including hydrogen bonding, ionion pairing, etc., favor the enthalpy for mixing and allow the components to mix completely. Among the examined interactions, hydrogen bonding seems to be the most attractive, since it quite efficiently improved the miscibility without accompanying changes in the properties of the constitutive polymers. The existing methods for improving compatibility or miscibility of the polymer blends can be classified in two categories—physical and chemical. From chemical consideration, the introducing specific interactions into blends is very practically and effective. It is interesting to know how the phase structure, miscibility, and properties of blends vary with simultaneous introduction of both intracomponent crosslinking and intercomponent hydrogen bonding. In the traditional complexation studies, every segment of each component often has a specific interaction group, while, in the studies on miscibility enhancement, only a small amount of interacting sites is introduced. However, the driving force for both complexation and miscibility is the same, namely, intermolecular hydrogen r 2011 American Chemical Society
bonding. The question is whether it is possible to change an ordinary miscible blend in a complex blend only by strengthening intermolecular hydrogen bonds.2 Interpolymer complexation through hydrogen bonds between water-soluble polymers was a subject of interest for many researchers.3,4 Poly(carboxylic acids), mainly poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA), served as the most common proton-donating components. As for the proton-accepting polymers, poly(ethylene oxide) (PEO or PEG) and poly(N-vinyl-2-pyrrolidone) (PVP) were often used. The important results on the formation of complex aggregates and the dependence on the structural parameters have been reviewed.5,6 The thermodynamics of the complexation of a typical polymer pair consisting of protondonating polyacid and proton-accepting poly(ethylene oxide) (PEO) has been studied since the late 1970s.2,7,8 The kinetics and equilibrium of the complexation between PAA and PEO or PVP were studied by Morawetz0 s group,9 and it was shown that the complex formation consisted of an initial diffusion-controlled hydrogen-bonding process with small activation energy and an extensive conformational transition of the two polymer chains which induced additional hydrogen bonds stabilizing the complex. This work also indicates that not only the ability of complexation but also the structure of the complex aggregates can be significantly affected by the molecular weights of the component polymers. Studies concerning the preparation of intermolecular complexes (IPCs) by hydrogen bonding complexation based on the interaction between proton-donating and proton-accepting polymers are still performed.1012 In our previous papers the preparation of an IPC realized by the interpolymer complexation via hydrogen bonding between poly(aspartic acid) (PAS) and Received: December 9, 2010 Accepted: March 16, 2011 Revised: January 28, 2011 Published: March 25, 2011 5369
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Industrial & Engineering Chemistry Research poly(vinyl alcohol) (PAV) was presented.1316 PAS belonging to the family of synthetic polypeptides can be obtained from a polycondensing procedure of the L-aspartic acid, a nonessential amino acid. PAS possesses similar properties to poly(acrylic acid), but it is a biocompatible and biodegradable water-soluble polymer. As a biocompatible compound, with no toxic or mutagenic effect, PAS was used in medicine, cosmetics, and the food industry. It is also considered a sustainable and environmentally friendly chemical product because of its biodegradability which makes it particularly valuable from the viewpoint of environmental acceptability and waste disposal.17 The IPCs based on PAS/PAV were subsequently used for bioactive substances entrapment and also they were doped with silver nanoparticles to achieve an antimicrobial effect. The miscibility and compatibility between the constitutive polymers was evidenced by combining the rheological data with zeta potential analyses, and the homogeneity of the IPCs based on PAS and PEG was demonstrated through the NIR-CI technique combined with dynamic rheology at a constant temperature of 22 °C.18 In the present paper the previous study on IPCs based on PAS/PEG mixtures is extended. The temperature influence during IPC formation was investigated in the temperature range between 2237 °C. The chosen domain of temperature corresponds to the storage temperature of the samples up to human body temperatures, owing to the final purpose, the IPC utilization for biomaterials. The influence of the PEG molecular weight as well as the composition—the ratio between PAS and PEG—of the blends on the IPC formation was investigated. The directions of analysis have in view (1) to confirm the intervening interpolymer interactions based between others on the hydrogen-bonds evidenced by FT-IR spectroscopy and (2) to estimate through the dynamic viscosity the miscibility between PAS and PEG macromolecular chains and also, to find the best conditions to achieve the intermolecular complex related on the PAS/PEG domain of composition, temperature, and PEG molecular weight.
2. MATERIALS AND METHODS 2.1. Materials. Poly(aspartic acid) (PAS) was synthesized through a reaction in two steps. First the precursor poly(succinimide) (PSI) was prepared through the thermal polycondensation of L-aspartic acid (Fluka BioChemika provenience), in dodecane (Fluka Chemika provenience) at 180 °C, for 6 h, using o-phosphoric acid (analytical reagent of 85%, Chemical Co. provenience) as catalyst. In the second step the in situ hydrolysis of PSI at 2024 °C in alkaline medium for 7 h causes the synthesis of sodium poly(aspartate). PAS was characterized from the viewpoint of its molecular weight by gel permeation chromatography (GPC) measurements, made on a Waters liquid chromatograph with water as the eluent and calibration versus polystyrene standards. The determined molecular weight of PAS was about 15 110 Da and the polydispersity index of 1.317. Poly(ethylene glycol)(PEG), Fluka Germany provenience, was used without further purification. PEG of four different molecular weights (Mw), respectively, 2000 Da ([η] = 0.0935 dL/g), 4000 Da ([η] = 0.1211 dL/g), 10 000 Da ([η] = 0.2348 dL/g), and 35 000 Da ([η] = 0.5134 dL/g) (denoted in the present paper as PEG 2000, PEG 4000, PEG 10000 and PEG 35000) in order to cover several orders of weight extent, was taken into study. The molecular weight of PEG samples was also confirmed, on the same Waters liquid chromatograph device, through gel permeation chromatography (GPC) measurements, using water
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as the eluent. Their intrinsic viscosity (η*) was determined in aqueous solution of 1%, at 30 °C; w2 = PEG content in the binary PAS/PEG mixture (w/v %). 2.2. IPC Preparation. Details were presented in a previous work.18 Briefly, the PAS/PEG complex was prepared by direct mixing the stock aqueous solutions of 1% concentration for 60 min in the different experiments. Thus, the total polymer concentration in the mixture was maintained constantly during each experiment. The solution of the polymer mixtures was then poured into Petri dishes and the films were obtained after drying at the room temperature. 2.3. Methods and Equipments of Analysis. 2.3.1. FTIR. Spectra of the polymer structures were registered using a DIGILAB spectrophotometer, Scimitar Series, USA, with a recording resolution of 4 cm1. In the paper just the spectra of the blends with PEG 35000 in composition are illustrated. 2.3.2. Dynamic Rheological Testing. Aqueous solutions of PAS, PEG (1 g/dL), and their mixtures (with different ratio between PAS and PEG) were tested on a Bohlin CVO rheometer equipped with a Peltier device for temperature control. The measurements were performed by using parallel-plate geometry. Both plates are from stainless steel, with a gap of 0.5 mm, the upper plate having the radius of 30 mm. For each determination, 2 mL solutions were poured on the rheometer lower plate. The dynamic shear experiments were realized in the linear viscoelastic range of oscillatory deformation, at a constant frequency (ω) of 0.1 rad/s and shear stress (σ) of 1 Pa for each composition at small amplitude and at different temperatures. The working temperature was selected in the range of 2237 °C, and was maintained constant ((0.1 °C) with the Peltier device. All measurements were done after 60 min from the blend preparation to allow the IPC formation and attaining the thermal equilibrium. 2.3.3. Zeta Potential Estimation. Zeta potential ζ was determined on a Malvern Zetasizer ZS (Malvern Instruments, UK), and the electrophoretic mobility (μ) was calculated with the Smoluchowski relationship: ξ ¼ ημ=ε
and
kR . 1
where η is the viscosity, ε is the dielectric constant, and k and R are the DebyeH€uckel parameter and particle radius. The pH was adjusted at 7 with HCl or NaOH, with the Autotitrator Malvern MPT2 device. The interval of temperature used during experiments was in the range of 2237 °C. The electric conductivity was determined on the same equipment in parallel with zeta potential measurement. Each measurement was made 3 times and the average of the values it is graphically represented.
3. RESULTS AND DISCUSSION 3.1. FTIR Study. A powerful method of detecting specific interactions in polymer blends is Fourier transform infrared (FT-IR) spectroscopy. The changes observed in hydroxyl, carbonyl, and other vibrations provide direct evidence of specific hydrogen-bonding interactions intervened between blend components.3,19 The magnitude of the wavelength shift arising after the polymer complexation provides a measure of the average strength of the intermacromolecular chains interactions. FTIR spectroscopy is also useful for evidencing the hydrogen-bonds intervened in the polymer blends.20 5370
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Figure 1. FTIR spectra: raw (a) and detail (b, c) of the compounds.
The FT-IR spectrum of PAS is characterized by the presence of characteristic bands attributed to the stretching of different group vibrations. Thus, the group frequency around of 15501750 cm1 and 13001420 cm1 corresponds to the carboxylic functional group. Other bands that are associated with the CO and OH functional groups tend to be less evidenced being overlapped with other fingerprint absorptions of the polymeric mixture. PEG exhibits absorptions of a primary alcohol, comprising stretching and bending vibrations restricted to CC stretch, CO stretch, CH stretch (methylene absorptions), and the CH bending. Thus, the peak around of 900 cm1 is due to the COC symmetric stretch absorption; the peak at wavenumber 10001100 cm1 is due to the COC asymmetric stretch; the peak around of 29003000 cm1 is due to the CH2O asymmetric stretch. All of these vibration modes are indications of the specific molecular bonding within the PEG sample. The FT-IR spectra of the blends with the PEG 35000 in composition are illustrated in Figure 1ac (the entire spectra on the 04500 cm1 domain and details in the regions from 1500 to 2000 cm1 and from 2500 to 4000 cm1). Hydroxyl Interaction. Similar bands with those of PEG and PAS are observed in the case of the blends spectra, but the bands
appear at shifted positions confirming the complex formation. Thus, the OH stretching corresponding to 30003500 cml bands (Figure 1c), are particularly sensitive to evidence the hydrogen bonds. The OH stretching vibration corresponding to PAS is observed in the 33303520 cm1 regions exhibiting the stretching vibrations of the intramolecular hydrogen bond (υ OH). Also, the broad and increased bands between 3440 and 3424 cm1 match the hydrogen bonded nature allowed to the PAS presence. Carbonyl Interaction. A broad band in the region of 15501750 cm1 is ascribed to the carbonyl stretching (Figure 1b). Thus, for the present system, two absorption bands, the CdO stretching around of 15501750 cml and the increasing of band intensity from 3200 to 3450 cm1 evidence the hydrogen bonds formed during the complexation process between PAS and PEG. 3.2. Rheological Study. The electrokinetic behavior and the rheological properties are important characteristics for the estimation of the interpolymer complex formation between PAS and PEG. The study of the PAS/PEG blend behavior under different achievement conditions as, for example, ratio between the 5371
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Figure 2. The behavior of the complex viscosity (η*) of the PAS/PEG mixtures as a function of temperature and of the PEG molecular weight: 2000 (a); 4000 (b); 10000 (c); 35000 (d) w2 = PEG content in the binary PAS/PEG mixture (w/v %).
PASPEG partners and the temperature or the molecular weight of the PEG as associate, can give information related to the optimum requirements for the interpolymer PAS/PEG complex preparation. As it is well-known the presence of the proton donor and proton acceptor groups placed along of the macromolecular chains will strongly affect segmentsegment and segmentsolvent interactions, with effect also upon the intermolecular hydrodynamic interactions, closely related on the polymer polymer miscibility and complexation. Thus, the rheological measurements provide information about polymerpolymer interactions as well as the polymersolvent interactions, since polymerpolymer complexation in solution always accompanies contraction or collapse of the component polymer coils, viscometry being useful for the detection of the complexation. Also, the dependence of the viscosity on the interpolymer complex composition has been commonly used for the estimation of the composition of the studied blends. In this context, the study of the rheological behavior of the polymeric pair consisting of proton-donating poly(aspartic acid) and proton-accepting poly(ethylene glycol), illustrated in Figure 2 ad, gives us data concerning the complexation possibilities between the two polymers. PAS contains negative and positive charges at a physiological pH of 7.4 at which measurements were done. Because of this structural characteristic, the electrostatic interactions will play an important role as both attractive and repulsion forces, and therefore, the interpretation
of interactions becomes more difficult. At the same time, such properties lead to discrepancies among the results of electrokinetic behavior and rheological experiments, and make their analysis more interesting. The rheology of polymer blends has been shown to be intimately dependent on the phase morphology and the interactions at the interface.21,22 The viscositycomposition curve usually shows positive deviation from the logarithmic additive rule in the case of intimately mixed polymers and emulsion-type heterogeneous blends with a low interfacial tension and a long relaxation time of the structured morphology. In contrast, melt viscosity shows a negative deviation from the logarithmic additive rule when there is no specific interaction between the phases, thus when no compatibilization agent is added. As it can be seen from the Figure 2, PAS presents a slow increase of its η* with temperature in the range of 2931 °C, which was ascribed to the H-bonds formation between intermolecular chains. The same behavior is registered in case of the blends solutions with PEG 2000 in composition and w2 = 25 or w2 = 50 ratio (Figure 2a). The viscosity decreases for w2 > 50, being nearly the same as the PEG viscosity. The viscosity of the blend solution, with PEG 4000 in composition (Figure 2b), is smaller than those of the PAS solution, the smallest value of the viscosity being registered for w2 = 50 composition, and it is attributed to reduced interactions between components. At the same time, this behavior can be 5372
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Figure 3. The zeta potential evolution of the PAS/PEG IPC as a function of temperature. The PEG molecular weight was (a) PEG 2000; (b) PEG 4000; (c) PEG 10000; (d) PEG 35000.; w2 = PEG content in the binary PAS/PEG mixture (w/v %).
caused by the presence of concentration fluctuations. The hydrogen bonding suppressed concentration fluctuations during PAS/PEG IPC miscible blending, and they are favored when the homopolymers have nearly molecular weights.23 The PEG 10000 blends solutions (Figure 2c) present similarly viscoelastic behavior of the constitutive homopolymers meaning a good miscibility and compatibility between partners. The literature in the field mentions about the parallel superposition of the thermo-rheological behavior of the miscible blends with components having equal entanglement number. The positive deviation indicates the IPC formation (especially when the temperature decreases).24 The PEG 35000 blends (Figure 2d) present similar behavior as depicted for blends with PEG 4000. The breakdown from the superposition of the thermo-rheological behavior is attributed to the different segmental relaxation times of the constituent components with different molecular weights. Concerning the influence of temperature, as it is expected the viscosity decreases with the increasing of the temperature. 3.3. Electrokinetic Study. The thermo-rheological behavior can be comparatively discussed with zeta potential (ZP) evolution as a function of composition and temperature (Figures 3ad). The ZP of the PEG 2000 blend has values close to those of the homopolymers (Figure 3a). Also, the ZP was maintained relatively constant on the entire range of temperature. The behavior of the
ZP evolution for the blends having compositions of PEG 4000 or PEG 35000 (Figure 3b,d) is similar. Differences, such as in the viscosity measurements, can be seen with blends composed with PEG 10000 (Figure 3c). Thus, the zeta potential values of the PAS/PEG 10000 blend are higher than those of the constitutive homopolymers, no matter the composition and temperature used during the experiment. These results point out the stability of the interpolymeric complex with a new supramolecular morphology, practically with functional groups involved in intra-association (self-association) or interassociation (intermolecular interactions). These observations are in agreement with the rheological data presented in Figure 2. As it is well-known, the stability of the dispersion is directly dependent on the particles' interaction during the collision moments. If the attractive van der Waals forces dominate, the particles attract each other during the particle collisions, and the dispersion flocculates. To achieve stable dispersions, the repulsive forces must exceed the attractive forces. The repulsive forces are determined by the absence of the electrostatic interactions between the particles or by the steric hindrance through the adsorbed polymer layer.25 In the case of the blends PAS/PEG, the repulsive forces are higher than attractive forces with beneficial influence upon the colloidal stability of the interpenetrated polymeric complex (IPC), no matter what the composition, PEG molecular weight, or temperature during the experiments. The ZP absolute values, at 37 °C for 5373
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Figure 4. The viscosity (a), zeta potential (b), and conductivity (c) dependence of the PAS/PEG IPC (at a constant composition (w2 = 50)) on the PEG molecular weight.
the PAS/PEG blends, are higher than 30 mV attesting the good stability of the complexes. Figure 4ac illustrates the dependence of the viscosity, the zeta potential values, and the conductivity on the PEG molecular weight, at a constant composition of the blends (w2 = 50). The effect of the PEG molecular weight upon homogeneous blend preparation is obvious. Also, the growth of the temperature determines the decrease of the viscosity (Figure 4a) and of the colloidal stability (Figure 4b). At the same time, from a stability viewpoint, the interpolymer complexes are stable on the entire domain of PEG molecular weight as estimated through the zeta potential values, a statement based on the PZ absolute values of PAS/PEG registered at 37 °C, which are higher than 30 mV (Figure 4b). The mixtures are lowviscosity liquids for all the ratios between PAS and PEG (regardless of the PEG molecular weight) (Figure 4a). Also, the variation of the experimental values from the linear mixing rule attests to the existence of the interactions: positive deviation from the linearity—as in the case of IPC with PEG10000 in
composition—caused by strong intermolecular attractions between the constituent components, and with weak or no specific interactions in the case of the negative deviation. These variations also reflect the turning up interactions occurring during the IPCs formation (Figure 4a). The positive deviation registered for the IPC with PEG 10000 is indicative of the interpolymer complex structure. The negative deviation is attributed to the adhesive forces between polymeric chains during preparation of an interpolymer association with a compact structure based on attractive forces. At the same time the density of the network of H-bonds formed between the terminal OH groups of PEG and the carboxyl in the repeating units of the PAS backbone is a function of PEG chain length. The longer the PEG chain length is, the sparser the H-bond network will be, due to the decrease in both the concentration of OH groups and entropic factor controlling the thermodynamic of PASPEG interaction. Since conductivity is based on the movement of ions, it follows that the concentration of ions in the solution will have a great bearing on the assessment of ions in the solution. Therefore, conductivity is 5374
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Industrial & Engineering Chemistry Research used to indicate and estimate the degree of complexation between polymers in aqueous solution (Figure 4c). The interpolymeric complex has conductivity values in the range of those of the constitutive homopolymers: greater than PEG but lower than PAS. Normally, the conductivity reduces with the growth of PEG content due to decrease of ionizable groups of PAS and increase with temperature.
’ CONCLUSIONS The importance of blending has increased in recent years because it has become a useful approach for preparing materials with tailor-made properties, different from those of the constituent polymers. The electrokinetic and rheological properties of the PAS/PEG blends are important parameters for the estimation of the behavior of blends under different conditions (temperatures and compositions). In the present paper, the influence of the temperature on the IPC formation was investigated in the temperature range of 2237 °C. The observed behavior was discussed as a function of the molecular weight of PEG and the ratio between PAS and PEG during blends preparation. The intra-association (self-association) of the carboxyl groups in PAS and interassociation (intermolecular interactions) between PAS and PEG constituent components influence the frequency dependence of the dynamic moduli in the terminal region of the miscible blend systems investigated. Thus, the local polymerpolymer interactions by FT-IR spectroscopy, confirming hydrogen-bonding interactions, were put into evidence. The miscibility and the polymerpolymer interactions were proved from the dynamic viscosity. Zeta potential and electrical conductivity of the blends were used to obtain the optimum conditions of temperature, PEG molecular weight, and ratio between PAS and PEG, for obtaining intermolecular complexes. The corroborated data evidence the interpolymer complex formation using macromolecular compounds with similar molecular weights or the preparation of an interpolymer association with compact structure based on attractive forces between poly(aspartic acid) and poly(ethylene glycol) in the case of the compounds with different molecular weight. ’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT The authors thank the reviewers for making useful comments and suggestions. This research was supported by CNCSIS Romanian Ministry of Education and Research—Idea Project No. 466/2009. ’ REFERENCES (1) Jayaraju, J.; Basavaraju, K. C.; Keshavayya, J.; Rai, S. K. Viscosity, ultrasonic, and refractometric studies of chitosan/polyethylene glycol blend in solution at 30, 40, and 50 °C. J. Macromol. Sci., Part B 2006, 45, 741. (2) Jiang, M.; Li, M.; Xiang, M.; Zhou, H. Interpolymer complexation and miscibility enhancement by hydrogen bonding. Adv. Polym. Sci. 1999, 146, 122.
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(3) Torrens, F.; Soria, V.; Codonerb, A.; Abad, C.; Campos, A. Compatibility between polystyrene copolymers and polymers in solution via hydrogen bonding. Eur. Polym. J. 2006, 42, 2807. (4) Lai, G.; Du1, Z.; Li, G. The rheological behavior of collagen dispersion/poly(vinyl alcohol) blends. Korea-Aust. Rheol. J. 2007, 19 (2), 81. (5) Tsuchida, E Macromolecular Complexes: Dynamic Interactions and Electronic Processes; VCH Publishers: New York, 1991. (6) Bekturov, E.; Bimendina, L. Complexes of water-soluble polymers. J. Macromol. Sci.Rev. Macromol. Chem. Phys. 1997, C37, 501. (7) Osada, Y. Equilibrium study of polymerpolymer complexation of poly(methacrylic acid) and poly(acrylic acid) with complementary polymers through cooperative hydrogen bonding. J. Polym. Sci. Polym. Chem. Ed. 1979, 17, 3485. (8) Tsuchida, E.; Osaka, Y.; Ohno, H. Formation of interpolymer complexes. J. Macromol. Sci. Phys. B 1980, 17, 683. (9) Bednar, B.; Morawetz, H.; Shafer, A. Kinetics of the cooperative complex formation and dissociation of poly(acrylic acid) and poly(oxyethylene). Macromolecules 1984, 17, 1634. (10) Illiger, S. R.; Fadnis, C.; Demappa, T.; Jayaraju, J.; Keshavayya, J. Miscibility studies of HPMC/PEG blends in water by viscosity, density, refractive index and ultrasonic velocity method. Carbohydr. Polym. 2009, 75, 484. (11) Cabanclas, J. C.; Serrano, B.; Baselga, J. Development of continous morphologies in initially heterogeneous thermosets blended with poly (methyl methacrylate). J. Macromol. 2005, 38, 961. (12) Sionkowska, A.; Skopinska-Wisniewska, J.; Wisniewski, M. Collagensynthetic polymer interactions in solution and in thin films. J. Mol. Liq. 2009, 145, 135. (13) Neamtu, I.; Chiriac, A. P.; Nita, L. E.; Bercea, M.; Stoleriu, A. Investigation of poly(aspartic acid)/vinylic polymer interpolymercomplex. J. Optoel. Adv. Mater. 2007, 9 (4), 981. (14) Neamtu, I.; Chiriac, A. P.; Nita, L. E.; Bercea, M. Poly(aspartic acid) in interpolymer complex with biomedical applications. J. Optoel. Adv. Mater. 2007, 9 (11), 3459. (15) Nita, L. E.; Chiriac, A. P.; Neamtu, I. Study of magnetic field influence upon a binary interpenetrated polymeric complex formation. J. Optoel. Adv. Mater. 2008, 10 (11), 2902. (16) Nita, L. E.; Chiriac, A. P.; Neamtu, I.; Bercea, M. Study of a binary interpenetrated polymeric complex by correlation of in situ viscosity data with zeta potential and electrical conductivity. Colloid. Surface. B 2010, 76, 70. (17) Nakato, T.; Toshitake, M.; Matsubara, K.; Tomida, M.; Kakuchi, T. Relationship between structure and properties of poly(aspartic acid)s. Macromolecules 1998, 31, 2107. (18) Nita, L. E.; Chiriac, A. P.; Neamtu, I.; Bercea, M.; Pintilie, M. An analysis of the complexation between poly(aspartic acid) and poly(ethylene glycol). Colloids Surf., A 2009, 348, 254. (19) Coleman, M. M.; Painter, P. C. Hydrogen bonded polymer blends. Prog. Polym. Sci. 1995, 20, 1. (20) Xinya, Lu; Weiss, R. A. Phase behavior of blends of poly(ethylene glycol) and partially neutralized poly(acrylic acid). Macromolecules 1996, 28, 3022. (21) Utracki, L. A. Melt flow of polymer blends. Polym. Eng. Sci. 1983, 23, 602. (22) Utracki, L. A. Polym. Network Blends 1991, 1, 61. (23) Colby, R. H. Breakdown of timetemperature superposition in miscible polymer blends. Polymer 1989, 30, 1275. (24) Arendt, B. H.; Krishnamoorti, R.; Kornfield, J. A.; Smith, S. D. Component dynamics in miscible blends: equally and unequally entangled polyisoprene/polyvinylethylene. Macromolecules 1997, 30, 1127. (25) Ece, O. I.; Alemdar, A.; Gungor, N.; Hayashi, S. Influences of nonionic poly(ethylene glycol) polymer PEG on electrokinetic and rheological properties of bentonite suspensions. J. Appl. Polym. Sci. 2002, 86, 341.
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