Monomers

For one-part, two-part and anaerobic adhesives, mostly methacrylates are used, while UV-setting adhesives are mainly based on acrylates. UV-setting adhesives are required to cure very rapidly, whereas one-part and two-part systems are often employed as high-performance systems the mechanical properties of which are considered to be more important than the curing rate. The monomers are mainly chosen according to their Tg-value that represents a parameter for the mechanical performance at different temperatures. Appropriate combinations allow the flexibility, strength and durability characteristics to be customized. Some examples of the wide array of monomers available, together with their Tg-values, are listed in Table 5.4.

Acrylate/methacrylate adhesive groups are described in detail in the following sections.

Table 5.4 Glass transition temperatures (Tg) of different monomers [36].

Product Tg (°C)

Polybutadiene dimethacrylate

-75

Tridecyl acrylate

-55

Tridecyl methacrylate

-40

Polyethylene glycol (400) dimethacrylate

-21

Polyethylene glycol (400) diacrylate

+3

2-Phenoxy ethylacrylate

+5

Tetraethylene glycol diacrylate

+23

Glycidyl methacrylate

+41

1,6-Hexane diol diacrylate

+43

Trimethylol propane triacrylate

+62

Triethylene glycol diacrylate

+70

Isobornyl acrylate

+88

Isobornyl methacrylate

+110

74 I 5 Chemistry and Properties of Adhesives and Primers

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