Thermal characterization of polyethylene glycols applied in the pharmaceutical technology using differential scanning calorimetry and hot stage microscopy

Abstract

In the present study, the effect of the molecular weight and thermal treatments on commercial polyethylene glycols (PEG) samples used in the pharmaceutical processing technology, has been analyzed using DSC and HSM. The molecular weight of these polymers range from 1500 to 200000. Thermal investigations on the melting behavior of original PEG samples (as received from the manufacturer) showed only one single melting DSC endotherm effect before 373 K. This fact was associated to the presence of only one type of polymeric chain. Using standard conditions, PEG samples were solidified from the melt at 373 K, either by flash cooling (.using liquid nitrogen and an ice bath) and by slow cooling, soaked and by slow cooling at room temperature. They were further studied by DSC. It was found that after cooling, PEG with molecular weight 1500 and 15000 showed DSC thermograms with a single endothermic peak. However, thermograms for PEG 4000 and 6000 produced a splitted melting endotherm. This fact was attributed to the presence of two types of chains, that are the folded and extended chains.Ageing time influences also the shape of the DSC endothermal effects. It was concluded that the endotherms obtained after heating these PEG indicate that the thermal history determine the structure (extended or folded chain type forms) and the degree of erystallinity, as evidenced by changes in heat of fusion values, melting points and structures after crystallization. The relationships between melting enthalpies and melting points, as deduced from DSC diagrams, with molecular weight of the polymers are also presented.

Effect of the Added Polyethylene Glycol Molecular Weight and Calcination Heating Rate on the Morphology of TiO₂ Films Formed by Sol-Gel

“…This was in agreement with the report that the heat of formation of extended chain PEG crystals was higher than that of folded chain crystals. 16) In addition, the exothermic heat of combustion tended to be higher with higher heating rates as well as the decomposition rate.…”

“…In contrast, PEG of M W < 4,000 g·mol −1 only formed extended chain crystals. 16) Hence, the weight loss at 230-335 C in the 6kPEG samples is ascribed to the decomposition of semi-crystalline (extended chain crystal) PEG. Figure 3(c) shows the TGA and DTG results of the 35kPEG samples, which contained of four stages of weight loss at 50-210, 200-225, 251-275 and 325-400 C. Dehydration and the decomposition of Ti-AcAc accounted for the rst (50-210 C) and fourth (325-400 C) stage, respectively, while the weight loss at 200-225 C and 251-275 C were probably related to the decomposition of the folded and extended PEG chain crystals, respectively, given that folded chain crystals are less thermodynamically stable than extended chain crystals.…”

“…The rst and third step was the dehydration and Ti-AcAc decomposition, respectively, while the second stage is likely to be the decomposition of PEG molecules because this step was not found in the noPEG samples, while PEG (M W = 6,000 g·mol −1 ) has been reported to decompose at 268-351 C. 9) In addition, PEG tended to arrange into semi-crystalline molecules (extended and folded chain crystals) with increasing molecular weight. 16,17) Indeed, M W ≥ 4,000 g·mol −1 PEG can simultaneously form both extended and folded chain crystals, where the volume fraction of folded chain crystals increases with increasing molecular weight. In contrast, PEG of M W < 4,000 g·mol −1 only formed extended chain crystals.…”

“…Figure 3(c) shows the TGA and DTG results of the 35kPEG samples, which contained of four stages of weight loss at 50-210, 200-225, 251-275 and 325-400 C. Dehydration and the decomposition of Ti-AcAc accounted for the rst (50-210 C) and fourth (325-400 C) stage, respectively, while the weight loss at 200-225 C and 251-275 C were probably related to the decomposition of the folded and extended PEG chain crystals, respectively, given that folded chain crystals are less thermodynamically stable than extended chain crystals. 16) The maximum decomposition rates characterized by the DTG peaks (Gaussian tting) were different among the different heating rates and the decomposition steps are shown in Table 1. The temperature of the maximum decomposition rate increased in all samples with increasing heating rates, in agreement with Kissinger s equation, 18) where the energy and temperature of combustion of a polymer increase with the heating rate.…”

Poly(ethyleneglycol) 500 Dimethylether as Novel Solvent for Injectable In Situ Forming Depots

“…Controlled release systems comprising PLGA that are currently on the market are all stored at reduced temperature (2-8°C). PEGs show (semi)crystalline structures depending on the storage conditions (7). We therefore investigated the thermal behavior of the three solvents and the polymer solutions in both PEGs and NMP using differential scanning calorimetry (DSC).…”