183
extender a one-functional hydroxyl monomer containing double bond in its structure such as HEMA, which is an hydroxy functional acrylate (Chattopadhyay and
Raju 2007).
The acrylate can have one to several double bonds in its structure. The more
double bond, the more crosslink density. Other acrylic monomers such as HEA and
pentaerythritol triacrylate (PETA) are used. HEA has a double bond and PETA has
three double bonds, which leads to increase crosslink density (Kotha et al. 1998).
The prepared urethane with acrylate end group with a photo initiator such as
2,2-dimethoxy-1,2-diphenylethan-1-one, 2-hydroxy-2-methyl-1-phenylpropanone
or benzophenone is applied on the considered substrate. Then, the radiation is
applied by a UV lamp to initiate the radical polymerization and curing the polymer
(Kim et al. 2006). The prepared product shows a hybrid of PU and acrylate properties. No temperature is needed to cure the PU, so this type of polymer is useful for
plastic and wood coatings. One-component WPU is also used as UV curable vehicles. UV curable WPUs can be prepared in almost the same way as WPUs as shown
in this section. In UV curable WPUs, hydroxyl functional acrylate monomer is
added just before adding TEA (Kim et al. 2006; Zhang, Xu et al. 2002).
8.2.5.2 Two-Component Reactive PUs
Two component PUs are the majority of PU production and is the most important
route to PU. One component is an isocyanate terminated polymer with low Mw and
the other component is catalyst, polyol, solvent and other necessary additives. The
curing can be performed at the room or elevated temperatures. All polyols such as
acrylate polyol, polybutadiene polyol, polyester, polyether, etc. can be used in the
two-component urethane formulation. The polyisocyanate/polyol ratio is usually
1.1:1. For regions with high humidity the polyisocyanate/polyol ratio is more than
1.1:1 (Yang et al. 2018).
Two component WPU are also available. The first component is a prepolymer of
hydroxyl or amine terminated which is dispersed in water. This prepolymer is synthesized by method discussed in Sect. 8.2.4.1, only its Mw is less. The second component is a low Mw polyisocyanate which is dispersed in water. Despite solvent-borne
PU have an NCO/OH ratio of about 1.1:1, here the ratio is approx. 2:1 or even more
than that, especially if end group of first component is hydroxyl. This is because
some isocyanate group reacts with water and becomes an amine (Noble 1997;
Melchiors et al. 2000).
8.2.6 Applications and Uses
The application of PUs is divided into four main categories: coatings, elastomers,
foams, and adhesive and sealants. The main application of PUs is in foam production (approx. 80%). PU foams are used for furniture, transportation, mattresses and
8 Reactive and Functional Polyesters and Polyurethanes
extender a one-functional hydroxyl monomer containing double bond in its structure such as HEMA, which is an hydroxy functional acrylate (Chattopadhyay and
Raju 2007).
The acrylate can have one to several double bonds in its structure. The more
double bond, the more crosslink density. Other acrylic monomers such as HEA and
pentaerythritol triacrylate (PETA) are used. HEA has a double bond and PETA has
three double bonds, which leads to increase crosslink density (Kotha et al. 1998).
The prepared urethane with acrylate end group with a photo initiator such as
2,2-dimethoxy-1,2-diphenylethan-1-one, 2-hydroxy-2-methyl-1-phenylpropanone
or benzophenone is applied on the considered substrate. Then, the radiation is
applied by a UV lamp to initiate the radical polymerization and curing the polymer
(Kim et al. 2006). The prepared product shows a hybrid of PU and acrylate properties. No temperature is needed to cure the PU, so this type of polymer is useful for
plastic and wood coatings. One-component WPU is also used as UV curable vehicles. UV curable WPUs can be prepared in almost the same way as WPUs as shown
in this section. In UV curable WPUs, hydroxyl functional acrylate monomer is
added just before adding TEA (Kim et al. 2006; Zhang, Xu et al. 2002).
8.2.5.2 Two-Component Reactive PUs
Two component PUs are the majority of PU production and is the most important
route to PU. One component is an isocyanate terminated polymer with low Mw and
the other component is catalyst, polyol, solvent and other necessary additives. The
curing can be performed at the room or elevated temperatures. All polyols such as
acrylate polyol, polybutadiene polyol, polyester, polyether, etc. can be used in the
two-component urethane formulation. The polyisocyanate/polyol ratio is usually
1.1:1. For regions with high humidity the polyisocyanate/polyol ratio is more than
1.1:1 (Yang et al. 2018).
Two component WPU are also available. The first component is a prepolymer of
hydroxyl or amine terminated which is dispersed in water. This prepolymer is synthesized by method discussed in Sect. 8.2.4.1, only its Mw is less. The second component is a low Mw polyisocyanate which is dispersed in water. Despite solvent-borne
PU have an NCO/OH ratio of about 1.1:1, here the ratio is approx. 2:1 or even more
than that, especially if end group of first component is hydroxyl. This is because
some isocyanate group reacts with water and becomes an amine (Noble 1997;
Melchiors et al. 2000).
8.2.6 Applications and Uses
The application of PUs is divided into four main categories: coatings, elastomers,
foams, and adhesive and sealants. The main application of PUs is in foam production (approx. 80%). PU foams are used for furniture, transportation, mattresses and
8 Reactive and Functional Polyesters and Polyurethanes