The present invention improves the long-term storage stability of a polymerizable composition including an organoborane and a polymerizable monomer. A polymerizable composition includes (A) an organoborane, (B) an acidic group-free polymerizable monomer, and (C) a stabilizer for the organoborane (A), the composition being such that when the composition, after being allowed to stand at 45° C. for 48 hours, is analyzed with an E-type viscometer at a temperature of 25° C. and a rotational speed of 50 rpm, the ratio of the viscosity after the standing to the viscosity before the standing (viscosity after standing/viscosity before standing) is less than 100.

A composition includes a polymerizable liquid crystal compound (A), a photopolymerization initiator (B), and a crosslinking agent (C), and satisfies:

|λ.sub.a1−λ.sub.b1|≤20 nm   (i), and

λ.sub.c1≤250 nm   (ii),

where λ.sub.a1 represents a wavelength of an absorption local maximum that is the longest one of wavelengths of absorption local maxima in a light absorption spectrum of from 200 nm to 500 nm of the polymerizable liquid crystal compound (A), λ.sub.b1 represents a wavelength of an absorption local maximum that is the longest one of wavelengths of absorption local maxima in a light absorption spectrum of from 200 nm to 500 nm of the photopolymerization initiator (B), and λ.sub.c1 represents a wavelength of at least one absorption local maximum in a light absorption spectrum of from 200 nm to 500 nm of the crosslinking agent (C)).

A composition includes a polymerizable liquid crystal compound (A), a photopolymerization initiator (B), and a crosslinking agent (C), and satisfies:

|λ.sub.a1−λ.sub.b1|≤20 nm   (i), and

λ.sub.c1≤250 nm   (ii),

where λ.sub.a1 represents a wavelength of an absorption local maximum that is the longest one of wavelengths of absorption local maxima in a light absorption spectrum of from 200 nm to 500 nm of the polymerizable liquid crystal compound (A), λ.sub.b1 represents a wavelength of an absorption local maximum that is the longest one of wavelengths of absorption local maxima in a light absorption spectrum of from 200 nm to 500 nm of the photopolymerization initiator (B), and λ.sub.c1 represents a wavelength of at least one absorption local maximum in a light absorption spectrum of from 200 nm to 500 nm of the crosslinking agent (C)).

A synergistic polymerization inhibitor composition, the composition having a copper salt, and a manganese salt; a copper salt or a manganese salt, and a cationic polymer; or a phenothiazine and a manganese salt. A method for inhibiting polymerization of unsaturated polymerizable monomers, the method providing adding a synergistic polymerization inhibitor composition to an methacrylic acid manufacturing system or component thereof, the composition having a copper salt, and a manganese salt; a copper salt or a manganese salt, and a cationic polymer; or a phenothiazine and a manganese salt.

A synergistic polymerization inhibitor composition, the composition having a copper salt, and a manganese salt; a copper salt or a manganese salt, and a cationic polymer; or a phenothiazine and a manganese salt. A method for inhibiting polymerization of unsaturated polymerizable monomers, the method providing adding a synergistic polymerization inhibitor composition to an methacrylic acid manufacturing system or component thereof, the composition having a copper salt, and a manganese salt; a copper salt or a manganese salt, and a cationic polymer; or a phenothiazine and a manganese salt.

Described are methods and compositions for inhibiting polymerization of a monomer (e.g., styrene) composition using a hydroxylated quinone antipolymerant. The hydroxylated quinone antipolymerant can be used with little or no nitroxyl group containing antipolymerant yet still provide excellent antipolymerant activity in a monomer-containing composition.

Described are methods and compositions for inhibiting polymerization of a monomer (e.g., styrene) composition using a hydroxylated quinone antipolymerant. The hydroxylated quinone antipolymerant can be used with little or no nitroxyl group containing antipolymerant yet still provide excellent antipolymerant activity in a monomer-containing composition.

There is provided an active energy ray-curable composition having excellent storage stability. The active energy ray-curable composition includes: active energy ray-curable compound (A) having an unsaturated ethylenic double bond; thiol compound (B) having two or more mercapto groups in one molecule; reaction inhibitor (C) configured to inhibit a reaction between the unsaturated ethylenic double bond and the mercapto groups; radical polymerization inhibitor (D); and water (E), wherein the content of water (E) is 0.05 ppm by mass or more and less than 1% by mass. When the total content of active energy ray-curable compound (A) and thiol compound (B) is 100 parts by mass, the content of reaction inhibitor (C) is 0.005 parts by mass or more and 10 parts by mass or less, and the content of radical polymerization inhibitor (D) is 0.005 parts by mass or more and 5 parts by mass or less.

There is provided an active energy ray-curable composition having excellent storage stability. The active energy ray-curable composition includes: active energy ray-curable compound (A) having an unsaturated ethylenic double bond; thiol compound (B) having two or more mercapto groups in one molecule; reaction inhibitor (C) configured to inhibit a reaction between the unsaturated ethylenic double bond and the mercapto groups; radical polymerization inhibitor (D); and water (E), wherein the content of water (E) is 0.05 ppm by mass or more and less than 1% by mass. When the total content of active energy ray-curable compound (A) and thiol compound (B) is 100 parts by mass, the content of reaction inhibitor (C) is 0.005 parts by mass or more and 10 parts by mass or less, and the content of radical polymerization inhibitor (D) is 0.005 parts by mass or more and 5 parts by mass or less.

A conventional polymerization inhibitor is for example an agent to scavenge radicals generated during storage of a radical polymerizable compound and used to stably handle the radical polymerizable compound, but is unnecessary when the radical polymerizable compound is to be subjected to radical polymerization reaction, and is preferably removed at the time of the radical polymerization reaction. The object of the present invention is to obviate inconvenience of removing the polymerization inhibitor at the time of radical polymerization.

The radical polymerization control agent contained in a radical polymerizable composition of the present invention functions as a radical polymerization inhibitor for example stored in a dark place, but loses its radical polymerization inhibiting effect when polymerization is initiated while being irradiated with light at a certain specific wavelength at the time of polymerization. Thus, radical polymerization of the radical polymerizable compound is easily initiated without increasing the amount of a radical polymerization initiator. That is, the radical polymerization control agent of the present invention is a radical polymerization control agent which is a corn pound having an effect to inhibit radical polymerization of a radical polymerizable compound and which loses the radical polymerization inhibiting effect under irradiation with light rays containing light within a wavelength range of from 300 nm to 500 nm.