Preparation and Characterization of Some Hyperbranched Polyesteramides / Montmorillonite Nanocomposites

Different polyesteramides hyperbranched polymers (HPEA1-6)/montomorillonite clay (MMT) nanocomposites were prepared with three different loading contents of clay (4, 10, and 15wt%).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, H-NMR, TGA, and DSC.


Introduction
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][2][3][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 [5].The advantages of nanocomposites include enhanced mechanical properties such as elastic modulus [6] 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][10][11][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][14][15][16][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 [28].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 [29].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 [30].Generally, hyperbranched polyesteramides (HBPAs) were synthesized by the bulk polycondensation of a trifunctional dialkanolamine (DAA) as bB2 monomer, where b and B2 represent the International Journal of Polymer Science 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 [31].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.

Instrumentation.
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, 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 ( 1 HNMR) was measured via Jeol JNM-EX 270 MHZ using tetramethylsilane (TMS) as internal standard and DMSO-d 6 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.[28,33].The hyperbranched polyesteramides (HPEA 1−6 ) 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.

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 9.35 × 10 −5 mol of HPEA 1−6 .The used amount of MMT was dispersed in 60 mL distilled H 2 O for 24 h at 60 ∘ C. The hyperbranched polymer was dissolved separately in 40 mL distilled H 2 O 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.

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][14][15][16][17]. Hyperbranched polymers represent relatively new polymeric member in this category of composite materials [26,27].Accordingly, herein, hyperbranched polyesteramides (HPEA 1−6 , Figure 1) were subjected to form nanocomposites with clay to be progressively applied in current work at our laboratories that will be published later.
Firstly, with respect to M 1 , M 4 , and their pristine hyperbranched HPEA 1,2 polymers (Figure 5), it was observed that only 21.35% and 17.4% weight loss was recorded for M 1 and M 4 nanocomposites up to 440 ∘ C.However, 10% and 5% weight loss was recorded for HPEA 1 and HPEA 2 , respectively up to 190 ∘ C, and then sharp decomposition of both samples began at 290 ∘ C. On the other hand, although M 7 and M 10 nanocomposites lost 20.45 and 14.87% of their weights approaching 440 ∘ C, and HPEA 3 and HPEA 4 lost 11.5% and 7.4% of their samples weights up to 165 ∘ C, then the loss approaching 18% for HPEA 3 (Figure 6).TG curves of HPEA 3 and HPEA 4 descended for complete decomposition of samples at 300 ∘ C and 310 ∘ C, respectively.The weight loss with respect to M 13 and M 16 nanocomposites reached 18% and 10% of the samples' initial weights approaching the same temperature range (440 ∘ C).Slight weight loss was detected for HPEA 5 and HPEA 6 till 180 ∘ C (i.e., 6% HPEA 5 and 3% HPEA 6 ) (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 DEAbased hyperbranched polymers more than that in the second DIPA-based ones which probably reacted with alcohol groups to from easily evaporated water molecules.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 M 16 , complete regions of destructed clay platelets appeared led to exfoliation behavior.