The preparation of hyperbranched polymers pursued a technique mentioned by Gao [18]. with the diagram of the optimal two-step reaction in Fig. 1. In the current research, a modification was developed to enhance the synthesis's reliability. First, at room temperature, Michael addition of DA to TETA yields intermediates 1 or 2. Although amidation reaction is unavoidable between (DA: TETA), at lower temperatures, Michael addition tends to react faster. Gradually increasing the temperature causes intermediates 1 or 2 to form an amine terminated hyper branched polymer, as shown in Table (1). To isolate the methanol, the reaction took place in a rotating evaporator under vacuum and at high temperature, amidation products, and solvent as quickly as possible.
When aiming to limit the molecular weight distribution, diethyl ether purification can effectively eliminate any remaining monomers or low molecular weight products. The reaction scheme is as Scheme (1). FTIR is an effective instrument for analysing how prepared hyperbranched polymers behave.
As shown in Figs. (1–2), the FTIR spectra of the prepared samples have two reaction modes, with The disappearance of the peak at 1730 cm− 1 was attributed to C = O of DA. Meanwhile, -CONH has peaks at 1650 cm− 1 and 1558 cm− 1, which were previously assigned to -CONH ]18] These two patterns demonstrated how intermediates 1 and 2 came together over time to create the final A or E samples. Methyl acrylate might be reacted with a substance having a hydroxyl group and one main amino or two secondary amino groups to produce a methoxycarbonyl-terminated hyperbranched polymer. The feed ratios clearly affect the polymerization process. In this study, E sample was synthesised using a method described by Gao and Yan [18], Table 1 shows the ratio of mole feed of dodecyl acrylate to TETA monomer. The FTIR spectrum of the E sample revealed a broad band for NH groups at 3200–3600 cm− 1, a strong band for CH alkanes at 3000 − 2850 cm− 1, a C-N band at 1350 − 1000 cm− 1, an O = C-N band of amide at 1648 cm− 1 and a C-O band at 1250 − 1000 cm− 1
The presence of the ester group O = C-O-R band at 1732 cm-1 revealed that the ester terminated of the synthesised E sample had formed. Moreover Figs. (3–7) show 1HNMR chart Protons of 5 hyper branched polymers. Peaks of samples A to E have almost the same spectra. that shows, CH-NR protons at (1.3 − 1.5 ppm), NH2-O-C = O protons at (3.3–3.5 ppm) and R-NH protons at (2.3–2.6 ppm), the peak at about 2.5 ppm is certified to the remaining hydrogen protons of the solvent (DMSO). All the above peaks approve the construction of hyper branched polymers.
Dynamic Light Scattering (DLS) is another method commonly used to investigate the structure of macromolecules [22]. In this work, the particle size distribution of synthesised samples with various terminations was measured using the DLS. Figure (8) and Table (2).
To protonate the terminal primary amine group, The samples were dissolved in 2% diluted distilled water, high dilution methanol, and 0.01% HCl. The data revealed that increasing the molecular weights and the number of branches increases particle size. This result could be attributed to the disruption of ordering molecules caused by increasing the branched moiety. It is clear from the data of particle size that, the particle size increase in order of A˃B˃C˃D˃E this means that, the size of prepared polymers increase by increasing terminal amine chains (TETA) .This may be attributed that, as the terminated ended chains increase the regular structure (ordering structure) may be formed with large surface area and small particle size [22] .
Differential scanning calorimetry (DSC) was applied to investigate the thermal behavior and classify the polymers into amorphous polymers and semi-crystalline by using cooling run and heating run which identify the glass transition temperature (Tg), melting temperature (Tm), and crystallisation temperature (Tc), and enthalpies, making DSC a useful tool for creating phase diagrams for various chemical systems. In this work Fig. (9). show DSC Analysis of prepared hyper branched polymer (A) it is endothermic peaks are observed, (Tm) is 223°C and the enthalpy − 49.08 J/g. also Fig. (10). show DSC Analysis of prepared hyper branched polymer (C) it is endothermic peaks are observed, (Tm) is 216°C and the enthalpy − 170.27 J/g. the different between the structure of A and C give increase in enthalpy due to increase the dodecyl acrylate ratio but Fig. (11). show DSC Analysis of prepared hyper branched polymer (E) it is endothermic peaks are observed, (Tm) is 151.43°C and the enthalpy − 43.79 J/g. the more negative the enthalpy of formation is for a substance, the greater its thermal stability so from the above result the more stable one is hyper branched polymer (C). All the prepared hyper branched polymer are (crystalline like structures this confirm that the prepared hyberpranchedpolymers are ordinary shape seems like dendrimers ).
Evaluation of Prepared hyperbranched polymers as Lube Oil Viscosity Index improver
The dispersion phase behavior of hyperbranched polymer molecules is critical to how polymeric Viscosity index enhancer’s function (base oil). The efficiency of the soluble hyperbranched polymers as base oil viscosity index enhancers was assessed in accordance with ASTM D2270 (SAE 30). between 40 and 100°C, for example, the kinematic viscosity of the oil that has not been doped and the oil that includes various amounts of the tested additives was measured then calculated the viscosity index as shown in the Table (3) and Fig. (9) To examine the impact of the additive concentration, various additive concentrations ranging from 0 to 30 x10− 3 ppm of the synthesized additives were employed. The VI rises when the prepared additives' concentration in the solution is increased. The lubricating oil viscosity reduces as the temperature rises, while the hyperbranched polymer molecule expands as a result of the rise in solvation power, and the micelle size rises. This drop in lubricating oil viscosity is balanced by the expansion of micelles, which reduces the fluctuations in viscosity with mixture temperature. As the concentration of the polymer increases, the overall volume of hyperbranched polymer micelles in the oil solution increases.
The viscosity index of a high concentration polymer will thus be greater than that of a low concentration polymer. On the other hand, the VI rises also when the percentage of triethylenetetramine as shown in prepared hyperbranched polymers(A,D and E) although VI decrease by increase the percentage of dodecyl acrylate s shown in prepared hyperbranched polymers (A,B and C) and the most efficiency one as VII is (E) VI = 212 which is higher than previous work [2, 4, 21, 26–28] because it has different functional group as mention before.
The rheological behavior for all the prepared hyperbranched polymers is the same for example (E) at concentration 30 x10− 3 ppm the most efficiency one as VII which show in Fig. (13). The fluid has a Newtonian rheological behavior, which means that it meets the requirements with Newton's law of viscosity. Shear rate has no effect on viscosity.[28–32]
