Hygroscopic polar groups

The effectiveness of an internal antistatic agent incorporated in the melt depends primarily on its molecular structure. This determines properties vital to the antistatic effect such as polarity and migration. The aliphatic C)4-C,7 chain in the alkanesulfonates imparts the required migration property to polar plastics, whereas the polar group is responsible for their hygroscopic behav-... 

Due to the presence of the polar groups (CO-NH), nylon attracts water. Hence, water absorption by nylon is relatively high, and higher than by any other thermoplastics, considered in this book. Compared to water absorption (24 h) of HDPE and PP (less than 0.01%), PVC (0.1%) and ABS (0.3%), Nylon 6 absorbs 1.2% water in 24 h (underwater), and 9% water when reached saturation. The lower the degree of crystallinity of nylon, the higher the water absorption. Due to this hygroscopicity, nylons must be dried before melt processing. 

A selection of AN values has already been given in Table 2-5 of Section 2.2.6 cf. also Table 6-6 in Section 6.5.1. The observed solvent-dependent P chemical shifts result mainly from the polarization of the dipolar P=0 group, induced by the interaction with electrophilic solvents A, particularly HBD solvents. The decrease in electron density at the phosphorus atom results in a deshielding proportional to the strength of the probe/solvent interaction. In solutions of protic acids, the P chemical shift of the 0-protonated triethyl hydroxyphosphonium salt is observed. Since Et3PO is very hygroscopic and therefore not very suitable from an experimental point of view, the use of (n-Bu)3PO instead of Et3PO as probe molecule has been recommended [250]. 

Aqueous solubility of solvents is related to polarity and dipole moment. Many solvents are hygroscopic and need drying agents, such as molecular sieves to remove moisture from them. Solubility of solvents in water and vice versa are listed in Table 6. It is observed that the solvents with -OH, -C(0)Me, -COOH, -NH2, and -CN groups have high degree of miscibility with water, whereas hydrocarbons, esters, and chlorinated compounds have a low solubility in water. 

An interesting use of GVS, for amorphous dispersions, is detection and quantification of crystallinity. Due to higher hygroscopicity of hydrophilic polymers and amorphous API of ASD, the exposure of a sample to elevated humidity environment triggers the sorption of water molecules by polar/hydrophilic functional groups at the air-solid interface. The a-relaxation time of amorphous material often correlates with its water sorption potential (Bhardwaj and Suryanarayanan 2013). The gravimetric vapor sorption (GVS)-desorption led to the dissimilar structurally reversal of annealed amorphous trehalose when compared to that obtained by heating beyond Tg (Saxena et al. 2013). The sorbed water molecules Tg = -137°C) increases... 

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