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International Journal of Polymer Science
Volume 2013 (2013), Article ID 528468, 8 pages
Preparation and Characterization of Some Hyperbranched Polyesteramides/Montmorillonite Nanocomposites
Polymers and Pigments Department, National Research Center, Dokki, Giza, Egypt
Received 3 February 2013; Revised 29 April 2013; Accepted 20 May 2013
Academic Editor: Yan Bao
Copyright © 2013 Amal Amin and Moshera Samy. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Different polyesteramides hyperbranched polymers (HPEA1-6)/montomorillonite clay (MMT) nanocomposites were prepared with three different loading contents of clay (4, 10, and 15 wt%). The obtained nanocomposites were characterized via XRD, thermal analyses, and TEM. Generally, intercalation behavior was observed. The hyperbranched polyesteramides (HPEA1-6) were originally prepared by the bulky reaction between maleic anhydride (MAn), succinic anhydride (ScAn), and phthalic anhydride (PhAn) with either diethanolamine (DEA) or diisopropanolamine (DiPA). The resulting hyperbranched polyesteramides (HPEA1-6) were characterized by GPC, IR, 1H-NMR, TGA, and DSC.
Recently, polymer/clay nanocomposites have been considered as rising area of research from both scientific and industrial perspectives where they result from the interaction between the organic polymer phase and the inorganic clay phase. Therefore, polymer/clay nanocomposites combine both the properties of inorganic phase such as rigidity, high stability, and the properties of organic phase such as flexibility, dielectric, ductility, and processability [1–4]. Layered silicates such as montmorillonite are the most versatile member of the nanofillers used in manufacturing polymer/clay nanocomposites. The nanoparticles improve the polymer performance over conventional fillers with a smaller loading content . The advantages of nanocomposites include enhanced mechanical properties such as elastic modulus  and tensile strength [7, 8].
Additional enhancements are expected in coefficient of linear thermal expansion, heat distortion temperature, flammability resistance, ablation performance, gas barrier properties, and others [9–12]. Generally, polymer/clay nanocomposites have been widely used in many fields, such as automobile and tire industries, construction fields, food packaging, electrical fields, antimicrobial agents, and other potential applications [13–17]. Several polymers are involved in producing such nanocomposites as vinyl polymers [18, 19], condensation polymers [20, 21], polyolefins [22, 23], and others [24, 25]. Hyperbranched polymers have been lately used in such nanocomposites due to their brilliant physical and chemical properties to obtain nanocomposites with excellent properties that can be invested in different applications [26, 27]. Hyperbranched polymers belong to the dendritic polymers; however, they are prepared via several easy preparative methods in one-pot reaction which is considered as merit over the dendrimers themselves especially in the industry where dendrimers are labor-intensive materials. Hyperbranched polymers with numerous different functional groups can be obtained due to the easy-end groups’ modification, for example, esters, carboxylic acids, and tertiary amines . The hyperbranched polyesteramides represent important category of the functional and widely applicable hyperbranched polymers which were firstly developed in an industrial viable route by van Bentherm and others . Thereby, the produced hyperbranched polymers had improved flow and air-drying properties for use in combination with alkyd resins. Those products were tested for plastics-additives applications . Generally, hyperbranched polyesteramides (HBPAs) were synthesized by the bulk polycondensation of a trifunctional dialkanolamine (DAA) as bB2 monomer, where b and B2 represent the secondary amine and the two alcohol functional groups, respectively, and a difunctional cyclic anhydride (CAn), as an Aa monomer, where Aa represents the anhydride functional group . The hyperbranched polyesteramides—because of the special shape and the large number of end groups of highly branched structures—have several applications in coatings, surface modifiers, biomedical applications, and others [32, 33]. Consequently, in the current publication, members of hyperbranched polyesteramides were chosen to be involved in forming some nanocomposites with montomorillonite clay to be used in the future in our research group in several applications specifically in the biomedical ones.
Maleic anhydride (MAn) (98%), succinic anhydride (ScAn) (98%), and diisopropanolamine (DiPA) (98%) were provided by Fluka, Germany. Phthalic anhydride (99.98%) was purchased from Arab lab, Dubai, UAE. Diethanolamine (DEA) (99%) was from analytical Rasayan, India. Montmorillonite (MMT) clay was provided by Southern clay products, TA, USA.
Gel permeation chromatography (GPC) was used to determine number-average molecular weight () and polydispersity of the polymers by using Agilent-1100 GPC technologies with refractive index detector where polystyrene (PS) and N, -dimethyl formamide (DMF) were used as standard and eluent, respectively. Infrared spectra (IR) were recorded via Pye-Unicum SP-1100 in the range of 400–4000 cm−1 using KBr pellets.
Nuclear magnetic resonance (1HNMR) was measured via Jeol JNM-EX 270 MHZ using tetramethylsilane (TMS) as internal standard and DMSO-d6 as the deuterated solvent.
Thermogravimetric analysis (TGA) was performed on TGA Q 5000 TA instrument, in the range from 40 to 750°C with heating rate 10 K/min under nitrogen. Differential scanning calorimetry (DSC) was conducted to determine the glass transition temperatures () by using differential scanning calorimeter Q 1000 TA from −80°C to 150°C with scanning rate of 20 K/minutes under nitrogen. The morphology of the nanocomposites was investigated via transmission electron microscopy (TEM) JEOL-JEM-1230 at 100 KV by drop casting the suspended sample onto carbon-coated copper grids, followed by evaporation of the solvent in air.
The hyperbranched polyesteramides (HPEA1–6) were prepared by introducing (0.115 mol) of DiPA or DEA into three-necked flask equipped with a mechanical stirrer, thermometer, and a vacuum pump and placed at thermostated oil bath. Then, 0.10 mol of anhydride was added to the flask. The reaction mixture was gradually heated to 70°C, with continuous stirring, and then more slowly to 170°C. Vacuum was applied during heating to remove the condensates. The formed hyperbranched polymer was washed with acetone, filtered, and dried at 50°C for 24 hours.
2.4. Preparation of Polymer/Clay Nanocomposites
For synthesis of polymer/clay nanocomposites, 0.45, 0.3, and 0.12 gm of untreated MMT corresponding to three percent of clay (e.g., 15, 10, and 4 wt%, resp.) were used individually with the equivalent amounts of mol of HPEA1–6. The used amount of MMT was dispersed in 60 mL distilled H2O for 24 h at 60°C. The hyperbranched polymer was dissolved separately in 40 mL distilled H2O for 3 h at the same temperature. Then, the hyperbranched polymer solution was added to the dispersed clay with stirring for 24 h at 60°C. The formed precipitate was filtered and dried. The resulting nanocomposites were characterized by XRD, TGA, DSC, and TEM.
3. Results & Discussion
Polymer/clay nanocomposites are good example on organic/inorganic hybrids gathering the advantages of both sides which are widely invested in numerous applications [13–17]. Hyperbranched polymers represent relatively new polymeric member in this category of composite materials [26, 27]. Accordingly, herein, hyperbranched polyesteramides (HPEA1–6, Figure 1) were subjected to form nanocomposites with clay to be progressively applied in current work at our laboratories that will be published later.
3.1. Characterization of the Hyperbranched Polymers HPEA1–6
HPEA1–6 polymers were prepared via one-pot reaction between anhydrides (Aa) and dialkanolamines (bB2) [28, 33]. Three different anhydrides were used such as maleic anhydride, succinic anhydride, and phthalic anhydride. Diethanolamine (DEA) and diisopropanolamine (DiPA) were involved in such condensation preparative reactions. HPEA1,3,5 resulted from the reaction of maleic, succinic and phthalic anhydrides, respectively, with diethanolamine (DEA). HPEA2,4,6 resulted from similar reaction of the same anhydrides with diisopropanolamine (DiPA). The prepared parent hyperbranched polymers (HPEA1–6) were characterized via GPC, IR, and 1HNMR to confirm their structures [34–36]. Accordingly, GPC of HPEA1–6 recorded and values for each hyperbranched polymer. and PDI values were found to be 2000 g/mol & 3.53 for HPEA1, 3500 g/mol & 2.54 for HPEA2, 1400 g/mol & 1.43 for HPEA3, 1800 g/mol & 1.56 for HEA4, 2100 g/mol & 1.27 for HPEA5, and 2400 g/mol & 1.64 for HPEA6. Further evidence on formation of the former HPEA1–6 was provided via IR where IR spectra of HPEA1–6 showed several supportive bands for the structures. Thereby, IR of HPEA1 and HPEA2 (KBr, ν cm−1): 3432–3421 (O–H), 1643–1641 (ν C=O in amide groups), 1734–1731 (ν C=O for α-unsaturated carbonyl of ester groups), two bands at 2978–2940 and 2934–2876 (C–H stretching), bands at 1494–1487 & 1451–1450 (CH2 bending), 1377 (CH3 bending), 943–856 and 1066–1050 (=CH bending). The bands at 1129–1125, 1184–1175, and 1276–1269 were ascribed to C–O and C–N stretching. IR of HPEA3 and HPEA4 (KBr, ν cm−1): 3441–3396 (ν O–H), 1624–1622 (ν C=O in amide groups), 1727–1724 (ν C=O in ester groups), 2979–2953 (C–H stretching), 1416 (CH2 bending), 1260–1234 (C–O stretching), and 1074–1064 (C–N stretching). IR of HPEA5 and HPEA6 (KBr, ν cm−1): 3401–3392 (ν O–H), 1623–1612 (ν C=O in amide groups), 1721-1720 (ν C=O in ester groups), 2976–2955 (C–H stretching), 1430–1432 (CH2 bending), 1377 (CH3 bending), 1276–1269 (C–O stretching), and 1065–1064 (C–N stretching). Lastly, 1HNMR of the previously prepared hyperbranched polymers (HPEA1–6) was carried out to confirm the polymer structures. 1H-NMR for HPEA1 (DMSO-d6), the chemical shifts (δ, ppm): 2.9–3.29 (O=CN–CH2), 3.39–4.19 (O=CO–CH2), 5.78–6.31 (CH=), and 6.4 (OH). 1H-NMR for HPEA2 (DMSO-d6), δ (ppm): 1.03–1.11 (CH3), 2.6–3.32 (CH2), 3.88–4.47 (CH), 5.1 (OH), and 6.02–6.8 (CH=).
1H-NMR for HPEA3 (DMSO-d6), δ (ppm): 3.59–4.08 (CH2–N–C=O), (CH2–O–C=O) and (–CH2OH), 4.2 (OH). 1H-NMR for HPEA4 (DMSO-d6), δ (ppm): 0.95–1.14 (CH3), 2.26–2.37 (CH2CON), 2.6–2.9 (CH2COO), 3.26–3.57 (–CH2NCO), 3.6 (CH) and 5.01 (OH). 1H-NMR for HPEA5 (DMSO-d6), δ (ppm): 2.97–3.38 (O=CN–CH2), 3.62–3.90 (O=CO–CH2), 4.48 (OH), 7.15–8.17 (ph). 1H-NMR for HPEA6 (DMSO-d6), δ (ppm): 0.78–1.31 (CH3), 2.73–3.02 (CH2), 3.56 (CH), 5.12–5.43 (OH) and 7.24–8.16 (ph).
3.2. Hyperbranched Polymers/MMT Nanocomposites
HPEA1–6 formed nanocomposites with untreated MMT depending on the high degree of functionality of the parent hyperbranched polymers. Such kind of functional polymers needs no further modification of clay. Three percent of clay (4%, 10%, and 15%) was tested in forming such hyperbranched polymers/clay nanocomposites to determine the proper percent for further applications for the expected nanocomposites. The samples M1–3, M4–6, M7–9, M10–12, M13–15, and M16–18 were referred to HPEA1, HPEA2, HPEA3, HPEA4, HPEA5, and HPEA6, respectively (Table 1). The resulting nanocomposites were characterized by XRD where the presence of hyperbranched polymers generally widened the d-spacing inside the internal gallery of clay as seen in Table 1 and (Figures 2, 3, and 4) causing intercalation morphology of the expected nanocomposites. However, the best situation of inclusion of polymers through the clay platelets was observed with respect to M1, M4, M7, M10, M13, and M16 in case of lower clay loading contents (4%) where the highest d-spacing values were recorded at low intensity values more than that in case of the other samples with percent (10% or 15%). Thereby, the d-spacing increased from 1.226 nm for pristine MMT (33) to 1.935, 2.143, 1.384, 1.856, and 1.865 nm for HPEA1-5 samples at 4% clay contents. Also, exfoliation behavior was recorded in case of HPEA6 at the same percent of clay. That behavior was attributed to the high degree of functionalities and hence bulkiness of these polymers which led to the relative destruction of the clay ordering.
The hyperbranched polymers/MMT nanocomposites formed at 4% clay (i.e., M1, M4, M7, M10, M13, and M16) were further analyzed and characterized via TGA and DSC. For complete comparison, thermal behavior of the parent hyperbranched polymers (HPEA1–6) was also studied via TGA and DSC. TG thermograms of M1, M4, M7, M10, M13, and M16 samples are indicated with respect to their parent hyperbranched polymers as in Figures 5–7 [34–36].
Firstly, with respect to M1, M4, and their pristine hyperbranched HPEA1,2 polymers (Figure 5), it was observed that only 21.35% and 17.4% weight loss was recorded for M1 and M4 nanocomposites up to 440°C. However, 10% and 5% weight loss was recorded for HPEA1 and HPEA2, respectively up to 190°C, and then sharp decomposition of both samples began at 290°C. On the other hand, although M7 and M10 nanocomposites lost 20.45 and 14.87% of their weights approaching 440°C, and HPEA3 and HPEA4 lost 11.5% and 7.4% of their samples weights up to 165°C, then the loss approaching 18% for HPEA3 (Figure 6). TG curves of HPEA3 and HPEA4 descended for complete decomposition of samples at 300°C and 310°C, respectively.
The weight loss with respect to M13 and M16 nanocomposites reached 18% and 10% of the samples’ initial weights approaching the same temperature range (440°C). Slight weight loss was detected for HPEA5 and HPEA6 till 180°C (i.e., 6% HPEA5 and 3% HPEA6) (Figure 7). Both samples began their final degradation at 280–340°C.
From the previous results, the diethanolamine-based hyperbranched polymers and their nanocomposites demonstrated less thermal stability than that of the diisopropanolamine-based ones. That was strongly ascribed to the larger number of carboxyl groups in the first DEA-based hyperbranched polymers more than that in the second DIPA-based ones which probably reacted with alcohol groups to from easily evaporated water molecules.
DSC measurements indicated obvious changes in (°C) values of M1, M4, M7, M10, M13, and M16 nanocomposites with respect to their pristine hyperbranched polymers HPEA1-6, where the values transformed from −24, 30, −32, −14, −19, and 42°C for HPEA1,2,3,4,5,6 parents hyperbranched polymers to 81, 187.7, 63.6, 75, 74.7, and 188°C for M1, M4, M7, M10, M13, and M16 nanocomposites. Therefore, compared to the parent hyperbranched polymers, the nanocomposites demonstrated higher thermal stability referring to the influence of clay.
The morphology of the resulting nanocomposites was studied via TEM (Figure 8). Irregular ordering of clay platelets including areas of destructed ones revealing intercalation to semiexfoliation structure. However, in case of M16, complete regions of destructed clay platelets appeared led to exfoliation behavior.
Polyesteramide-hyperbranched polymers successfully formed nanocomposites with untreated montomorillonite clay (MMT) relying on their high number of polar end groups. Three percent of clay were used such as (4, 10, 15 wt%). However, the low loading content of clay (4%) presented obvious higher displacement of the clay layers than other percents and caused intercalated nanocomposites with the hyperbranched polymers in most cases. Phthalic anhydride-based hyperbranched polymers with DIPA showed exfoliated morphology for its nanocomposite at 4% clay. Also, referring to the thermal studies (TGA and DSC data), it was elucidated that the nanocomposites based on the hyperbranched polymers derived from the reaction of the anhydrides and DEA (M1, M7, and M13) were less thermally stable than that resulted from DIPA-based ones (M4, M10, and M16). Generally, hyperbranched polyesteramides/MMT nanocomposites displayed higher thermal stability than the original hyperbranched polymers. TEM confirmed the intercalated morphology in almost all cases.
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