Inhibitors for Unsaturated Polyester Resins

Inhibitors are chemical compounds, which prevent polymerization process of monomers or other reactive compounds. Suitable compounds to be used in Unsaturated Polyester Resins are Quinones and Phenolic compounds, which are able to liberate weak Hydrogen atoms.

These Hydrogen atoms react with free radicals from peroxide decomposition or with a growing polymer chain and inhibit any further reaction. This inhibition reaction will end, after all inhibitor molecules are consumed.

Inhibitors are therefore not only suitable for enlarging the pot life of activated resins, but also to increase storage life of pre-accelerated resins.

Inhibitors are selected based on their ability to:
• Prevent gelation of the unsaturated polyester during the esterification reaction,
• Prevent gelation during blending of the polyester with the vinyl monomer at elevated temperature,
• Impart good shelf life to the resin,
• Aid in adjusting gel time,
• Exert a minimum effect on subsequent curing of the resin after gelation.

Many commercial polyester resins incorporate a mixture of two or more inhibitors in order to achieve optimum stability without interference with the final cross-linking polymerisation process. If we give information about the inhibitors in Univar Solutions product portfolio;

4-Tert.-Butyl Catechol

It is used as an inhibitor for increasing pot life and gel time of activated or pre-accelerated unsaturated polyester resins at ambient temperatures. Trade name for the technically pure and solid form of this product is ‘PERGASLOW BK-100’. Its performance at ambient temperature in different systems is as follows;

1) lengthens the gel time of a mixture of UP resin / peroxide / accelerator.

Parabenzokinon (PBQ)

SMC-BMC’nin ortam sıcaklığında kap süresini (pot life) artırır.

2) lengthens the pot life of a mixture of UP resin / peroxide.
3) lengthens the pot life of a mixture of UP resin / amine accelerator.
The product is also available in 10% and 1% solutions coded PERGASLOW BK-10 and PERGASLOW BK-1.

2,6-Di-Tert.-Butyl Paracresole

It is used as an inhibitor for increasing gel time of unsaturated polyester resins at ambient temperatures. It does not influence cure time. Trade name for the technically pure and solid form of this product is ‘PERGASLOW PK-100’. Its performance at ambient temperature in different systems is as follows:
1) lengthens the shelf life of SMC and BMC at ambient temperature,
2) lengthens the pot life of a mixture of UP resin / peroxide at ambient temperature.
The product is also available in 40% solution coded PERGASLOW PK-40.

p-Benzoquinone (PBQ)

It is used for lengthening the pot life of SMC and BMC at ambient temperature.

Hydroquinone (HQ)

It is a commonly used inhibitor. It is very effective at protecting the resin during room temperature storage and extending its gel time. It also increases the storage stability and lengthens the pot life of SMC-BMC at ambient temperature.

Toluhydroquinone (THQ)

Similar to Hydroquinone in properties, however, the presence of a methyl group in the ortho position in the toluhydroquinone molecule provides some shielding effect. It also offers better solubility in styrene than HQ. It’s often used as a cook stabilizer for highly reactive unsaturated polyesters. It has a minor effect on cure.

1,4-Naphthoquinone (NQ)

A storage stabilizer in unsaturated polyester resins

Mono-Tert-Butylhydroquinone (MTBHQ)

MTBHQ is an effective storage inhibitor for unsaturated polyesters and is also useful as a cook stabilizer for highly reactive unsaturated polyesters. It offers excellent potency over a wide temperature range and causing only a moderate prolongation on resin cure at elevated temperatures.

It has the greatest solubility of the hydroquinone derivatives. Along with solubility, color is also good, making it suitable for the use in applications that are sensitive to color effects. MTBHQ is also very useful for the resin systems some containing high levels of maleic anhydride when good thermal stability during synthesis is required.

2,5-Di-Tert-Butylhydroquinone (DTBHQ)

It is used to improve the storage stability of unsaturated polyester resins with minimum effect on gel time. Used in combination with other inhibitors.

Hydroquinone Monomethyl Ether (HQMME)

It is a radical polymerisation inhibitor for monomers such as acrylates, methacrylate and styrene. A good stabilizer and antioxidant during synthesis. It has an excellent solubility in organic solvents.

‘You could contact Univar Solutions for your inhibitor inquiries’

Nihan Yaman – Kompozit Satış Müdürü- Türkiye – Composite Sales Manager -Turkey – Univar Solutions

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