Plasticizers polar aliphatic

The second group consists of plasticizers having polar groups attached to aliphatic chains and is called the polar aliphatic group. Examples are aliphatic alcohols and acid or alkyl esters of phosphoric acid (such as trioctyl phosphate). Their polar groups interact with polar sites on polymer molecules, but since their aliphatic part is rather bulky and flexible other polar sites on the polymer chain maybe screened by plasticizer molecules. This reduces the extent of intermolecular interactions between neighboring polymer chains, as shown in Figure 1.44b. 

Polar aliphatic plasticizers mis less well with polymers than do polar aromatics and, consequently, may exude (bloom) from the plasticized polymer more easily. Their polymer miscibility temperature is higher than that for the first group. These plasticizers are called oil-type plasticizers, and their kerosene extraction index is high. Their plasticization action is, however, more pronounced than that of polar aromatic plasticizers at the same molar concentration. Moreover, since the aliphatic portions of the molecules retain their flexibility over a large temperature range, these plasticizers give a better elasticity to finished products at low temperature, as compared to polar aromatic plasticizers, and allow the production of better cold-resistant materials. In PVC they also cause less coloration under heat exposure. 

FIGURE 1.44 Action of (a) a polar aromatic plasticizer and (b) a polar aliphatic plasticizer on PVC chains. 

Polarity. The increase in the polarity of the plasticizer (e.g. existence of polar groups, substitution of aryl groups by alkyl ones) reduces softening efficiency, worsens low-temperature properties of the plasticized polymers, improves solvation, and reduces extractability by aliphatic solvents. 

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-... 

It was also found that better plasticization occurs if the polar group is on an aliphatic molecule (because of its greater mobility) rather than on an aromatic molecule. 

Plasticizers include the esters of a few aliphatic and aromatic mono and dicarboxylic acids, aliphatic and aromatic phosphorus acid esters, ethers, alcohols, ketones, amines, amides, and non-polar and chlorinated hydrocarbons. These additives are used in various mixtures. For their separation and qualitative detection, thin-layer chromatography (TLC) is preferred. Usually Kieselgur plates, 0.25 mm thick, activated at 110°C for 30 min, in the saturated vapor are used. Methylene chloride and mixtures of diisopropyl ether/petether at temperatures between 40 to 60°C have been successfully used as the mobile phase. Refer to Table 1. 

A more polar comonomer, eg, an AN comonomer, increases the water-vapor transmission more than VC when other factors are constant. For the same reason, AN copolymers are more resistant to penetrants of low cohesive energy density. All VDC copolymers, however, are very impermeable to aliphatic hydrocarbons. Comonomers that lower T and increase the free volume in the amorphous phase increase permeability more than the polar comonomers higher acrylates are an example. Plasticizers increase permeability for similar reasons. 

Apart from the Cl, some low-molecular components of inhibited plastics can be a source of contamination. For example, materials plasticized by a toxic phosphate of phthalate can present a danger to the environment [13]. An alternative to these PI can be mineral oils, polar PI of the esters of aliphatic dicarboxylic acids and alcohols, amogst others. These esters represent perfect PI of a number of thermoplastics, can dissolve Cl and are, besides, contact inhibitors and water-repellent agents for metal surfaces [22] (e.g. dibutyl se-bacates). 

Superior resistance to oils Nitrile rubber has the highest resistance of any of the generally used elastomers to grease, oil, plasticizers, and most organic solvents, both aliphatic and aromatic. There is limited resistance to some polar solvents, and polymers are generally soluble in ketones. 

Hydrocarbons such as dibenzyl toluene and products with an aliphatic-aromatic structure are used as extenders for immersion and rotation molding pastes. Polyamide flexibilizing with the help of plasticizers with comparable polar structures (e.g., Cetamoll in the sulfamide group), has receded into the background ever since the development of PA copolymers with elastomeric qualities that are for the most part resistant to low temperatures. 

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