Polymer-related chemicals

Examples of reaction and application of cationic initiators

Polymerization Utilizing Acid

Cationic polymerization (chain polymerization)

[Ring-opening polymerization of epoxide and oxetane]

Mechanism of ring-opening polymerization of epoxides and oxetanes

[Addition polymerization of vinyl ether]

Mechanism of addition polymerization of vinyl ether

Since vinyl ether shows high reactivity, it is possible to initiate polymerization even with CF3SO3H. (In the case of iodonium, there is a large exotherm and a yellowing effect).

Condensation polymerization (Step-growth polymerization)

[Sol-gel method of alkoxylsilane]

Sol-gel Mechanism of Alkoxysilanes

[Condensation polymerization of hydroxymethyl group]

Mechanism of polycondensation of hydroxymethyl groups

Strength and Applications of Typical Acids

Table of Strength and Applications of Typical Acids

※ The colored part shows that the curing reaction is advanced by strong acid.

Difference of epoxy curing performance by the difference of anions

Graph showing the difference in epoxy curing performance

[Composition ratio]
Alicyclic epoxy CEL2021P / WPI-No. = 100 / 2

254nm : 5 mW/cm2
365nm : 100 mW/cm2
405nm : 217 mW/cm2

After leaving samples at the room temperature for 60 seconds, the irradiation time to attain pencil hardness H or more was measured, respectively.

Various Sensitizers are Available for Iodonium

Among the onium salts, iodonium has a higher electron acceptance, and is easier to sensitize (customize) using additives.

Iodonium > Sulfonium > Ammonium

If a sensitizer with long wavelength absorption property is used, iodonium is able to be sensitized with irradiation of UV light ‒ visible light range (near infrared light) and to generate acid. Polycyclic aromatic compounds, heterocyclic compounds, dyes and metallic complexes which do not generate radicals with irradiation of light, are common sensitizers.

Comparison of photosensitivity with iodonium and sulfonium

When epoxy is cationic-polymerized under a light source with a 300 nm (or shorter) wavelength cut-off, and camphorquinone is used as a sensitizer, polymerization advances only in the case with iodonium.

Diagram of cationic polymerization of epoxy using camphorquinone as a sensitizer
Comparison of photosensitivity performance of iodonium and sulfonium in the presence of camphorquinone

J. V. Crivello. M. Sangermano, J. Polym. Sci., Part A, Polym. Chem ., 2001 , 39 , 343-356

Compounds Accelerating Polymerization by Promoting the Decomposition of Iodonium

① 3,4-Dimethoxybenzyl alcohol

② Vinyl ether

③ N-Vinylcarbazole

Antioxidant which Improves the Preservation Stability of Composition.

Since the monomer of cationic polymerization is an ether , it is oxidized in air and forms peroxide. Peroxide is unstable and decomposes radically, while iodonium receives radicals easily and has a high reactivity. Addition of a radical polymerization inhibitor, such as BHT (dibutylhydroxytoluene), is known to improve stability.

2 functional oxetane WPI-166 BHT Storage at 60℃
100 5 Gelates in one day.
100 2 01 Does not gelate in four days.

Nobuaki Koike, “Photo Application Technology/Material Dictionary” P.167 (2006)