As shown in Figure 2.1, polyester polyol production is only about 25% of the total polyol production; however, given the scale of the industry and the importance and ubiquity of polyester polyols, the impression from the pie chart could be misleading. Indeed, the world capacity for polyester polyols in 2012 was about 2300 thousand metric tons and actual consumption at about 1900 thousand metric tons (~4.2 billion pounds!). The annual growth rate of polyester polyol consumption is about 4%, similar to polyether polyols, and approximately mirrors the growth of the world and local economies. Within polyurethane production, polyester polyols are a key feedstock in coatings, adhesives, elastomer, and rigid foam formulations. Depending on the application, an aromatic or an aliphatic diacid will be employed to deliver the desired suite of properties. As will be discussed in detail, aromatic polyesters are usually deployed for the purpose of enhancing flame retardance , increased T, and reduced gas permeability and so are widely used in polyurethane insulation foams. Aliphatic polyesters used in urethane formulations enhance tensile strength, abrasion resistance, UV resistance, and low temperature flexibility (low r) and find primary use in coatings and elastomers. Although the synthetic procedures for preparation of aromatic and polyester polyols are similar, the properties and applications are diverse enough to warrant their separate treatment.
Figure 2.21 breaks out the approximate differential consumption of aromatic and aliphatic polyester polyol consumption. The usage of aromatic versus polyester polyols is not uniform across geographies. Aromatic polyols are used to a much greater extent in the United States due to consumer expectations for superior flame
FIGURE 2.22 Polymerization of polyesters via estenfication reaction between a dialcohol and a diacid, transesterification between a diester and a dialcohol and ring opening polymerization between an acid anhydride and a dialcohol.
retardance, structural integrity, and thermal insulation properties found in polyurethane and polyisocyanurate insulation panels . The relative usage of aliphatic polyester polyols is much higher in China due to the relatively high manufacturing for coatings, elastomers, artificial leather, etc. .