JP2004083460A - Method for preventing polymerization of (meth)acrylic ester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preventing the polymerization of a (meth)acrylic ester exhibiting excellent polymerization-preventing effects. <P>SOLUTION: The method for preventing the polymerization of a (meth)acrylic ester containing an acid and/or water comprises reducing the amount of the acid and/or water contained in the (meth)acrylic ester and causing an N-oxyl compound to co-exist. The amount of the acid is reduced, for example, by adding a base to the (meth)acrylic ester, and the amount of water is reduced, for example, by performing azeotrpoic dehydration using a solvent forming an azeotropic composition with water. <P>COPYRIGHT: (C)2004,JPO

Description

（式中、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^４は炭素数１〜８のアルキル基であって直鎖状でも分岐状でもよい。さらにＲ^１とＲ^２および／またはＲ^３とＲ^４は互いに環を形成していてもよい。Ｒ^５はＨ、ＯＨ、ＯＲ、ＯＣＯＲ、ＮＨＣＯＲまたはＯ−［（ＥＯ）_ｎ＋（ＰＯ）_ｍ］−Ｈ、Ｒ^６はＨ、またはＲ^５とＲ^６は一緒になって＝Ｏを表す。Ｒは水素原子または炭素数１〜１８のアルキル基、アルケニル基またはアリール基であり、アルキル基は直鎖状でも分岐状でもよく、アリール基は水素原子がアルキル基で置換されたものでもよい。ＥＯはエチレンオキシ基を、ＰＯはプロピレンオキシ基を示し、ｎおよびｍは同一または異なる０〜１０の整数であってｎおよびｍが同時に０になることはない。）
【０００９】
【発明の実施の形態】
本発明で重合防止の対象である（メタ）アクリル酸エステルとしては、例えば、（メタ）アクリル酸メチル、（メタ）アクリル酸エチル、（メタ）アクリル酸プロピル、（メタ）アクリル酸ターシャリーブチル、（メタ）アクリル酸ノルマルブチル、（メタ）アクリル酸イソブチル、（メタ）アクリル酸２−エチルヘキシル、（メタ）アクリル酸ラウリル、（メタ）アクリル酸トリデシル、（メタ）アクリル酸ステアリル等のアルキルエステル類、（メタ）アクリル酸シクロヘキシル、（メタ）アクリル酸イソボルニル、（メタ）アクリル酸テトラヒドロフルフリル等の脂環式アルキルエステル類、（メタ）アクリル酸ベンジル等の芳香族基含有エステル類、（メタ）アクリル酸グリシジル等の複素環基含有エステル類、（メタ）アクリル酸アリル等の不飽和アルキルエステル類、（メタ）アクリル酸ヒドロキシエチル、（メタ）アクリル酸ヒドロキシプロピル等のヒドロキシアルキルエステル類、（メタ）アクリル酸２−メトキシエチル、（メタ）アクリル酸２−エトキシエチル等のアルコキシアルキルエステル類、ジ（メタ）アクリル酸エチレングリコール、ジ（メタ）アクリル酸トリエチレングリコール、ジ（メタ）アクリル酸１，３−ブチレングリコール、ジ（メタ）アクリル酸１，６−ヘキサンジオール、ジ（メタ）アクリル酸ポリブチレングリコール、トリ（メタ）アクリル酸トリメチロールプロパン等の多価アルコールのエステル類、フタル酸２−（メタ）アクリロイルオキシエチル、ヘキサヒドロフタル酸２−（メタ）アクリロイルオキシエチル等のカルボン酸含有アルコールのエステル類、（メタ）アクリル酸ジメチルアミノエチル、（メタ）アクリル酸ジメチルアミノエチルメチルクロライド塩、（メタ）アクリル酸ジメチルアミノエチルベンジルクロライド塩、（メタ）アクリル酸ジエチルアミノエチル等のジアルキルアミノアルキルエステルおよびその塩類、（メタ）アクリル酸トリフルオロエチル、（メタ）アクリル酸ヘプタデカフルオロデシル等のフルオロアルキルエステル類等が挙げられる。
【００１０】
なお、慣用されるように、（メタ）アクリル酸とはメタクリル酸およびアクリル酸の総称であり、（メタ）アクリロイルとはメタクリロイルおよびアクリロイルの総称である。
【００１１】
本発明においては、（メタ）アクリル酸エステルに含まれる酸および／または水分を低減させることが必要である。ここで酸とはブレンステッド酸を意味する。このような酸としては、例えば、塩酸、硫酸、硝酸等の鉱酸、メタクリル酸、アクリル酸、メタンスルホン酸、ｐ−トルエンスルホン酸等の有機酸、強酸性イオン交換樹脂、ゼオライト等の固体酸が挙げられる。
【００１２】
酸は目的の（メタ）アクリル酸エステルを合成するための触媒として用いられることがある。この場合の酸は反応終了時に中和または固液分離などの方法で分離されるが、この分離操作が十分でないと、得られる（メタ）アクリル酸エステルに酸が含まれる。また、（メタ）アクリル酸は、メタクリル酸エステル自身の加水分解やエステル化反応の原料の残留等によって含まれる場合がある。（メタ）アクリル酸エステルに含まれる酸の量は特に限定されないが通常１００ｐｐｍ以上である。
【００１３】
一方、水分は（メタ）アクリル酸エステル合成の原料に含まれていた水分の残存、エステル化反応で（メタ）アクリル酸エステルを合成したときに副生した水の残存、（メタ）アクリル酸エステル取扱い時の吸湿等によって（メタ）アクリル酸エステルに含まれることがある。（メタ）アクリル酸エステルに含まれる水分量は特に限定されないが通常２００ｐｐｍ以上である。
【００１４】
酸を低減させる方法は特に限定されないが、塩基を（メタ）アクリル酸エステルに添加して酸を中和する方法が好ましい。この方法で使用できる塩基としては、例えば、アルカリ土類金属酸化物、アルカリ土類金属水酸化物、アルカリ金属酸化物、アルカリ金属水酸化物、塩基性イオン交換樹脂等が挙げられ、なかでも、酸化カルシウム、水酸化カルシウム、酸化マグネシウム、水酸化マグネシウム、水酸化リチウムが好ましい。添加する塩基の量は、酸１モルに対して、通常０．１〜１００モルであり、好ましくは１〜１０モルである。酸を低減した後の酸の量は特に限定されないが、５０ｐｐｍ以下が好ましく、３０ｐｐｍ以下がより好ましい。
【００１５】
一方、水分を低減させる方法は特に限定されないが、例えば、水と共沸組成を形成する溶媒を用いて共沸脱水することにより水分を低減させる方法、乾燥剤を添加して水を吸着除去する方法等が挙げられる。なかでも共沸脱水する方法が好ましい。水分を低減することにより（メタ）アクリル酸エステルの加水分解による（メタ）アクリル酸の増加を抑えることができる。水分を低減した後の水分量は特に限定されないが、１００ｐｐｍ以下が好ましく、５０ｐｐｍ以下がより好ましい。
【００１６】
さらに本発明では、（メタ）アクリル酸エステルに含まれる酸および／または水分の低減に加えて、Ｎ−オキシル化合物を共存させる必要がある。
【００１７】
Ｎ−オキシル化合物とは、窒素原子に酸素ラジカルが結合したニトロキシルラジカル構造を含む化合物であり、なかでも前記式（１）で表されるＮ−オキシル化合物が好ましい。式（１）において、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^４は炭素数１〜８のアルキル基であって直鎖状でも分岐状でもよい。さらにＲ^１とＲ^２および／またはＲ^３とＲ^４は互いに環を形成していてもよい。なかでもＲ^１、Ｒ^２、Ｒ^３、Ｒ^４はいずれもメチル基が好ましい。Ｒ^５はＨ、ＯＨ、ＯＲ、ＯＣＯＲ、ＮＨＣＯＲまたはＯ−［（ＥＯ）_ｎ＋（ＰＯ）_ｍ］−Ｈ、Ｒ^６はＨ、またはＲ^５とＲ^６は一緒になって＝Ｏを表す。Ｒは水素原子または炭素数１〜１８のアルキル基、アルケニル基またはアリール基であり、アルキル基は直鎖状でも分岐状でもよく、アリール基は水素原子がアルキル基で置換されたものでもよい。ＥＯはエチレンオキシ基を、ＰＯはプロピレンオキシ基を示し、ｎおよびｍは同一または異なる０〜１０の整数であってｎおよびｍが同時に０になることはない。なかでもＲ^５はＯＨ、ＯＣＯＰｈ、ＮＨＣＯＣＨ_３が好ましく、Ｒ^６は水素が好ましい。
【００１８】
式（１）で表されるＮ−オキシル化合物としては、具体的には、２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−ヒドロキシ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−アセチルオキシ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−アクリロイルオキシ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−メタクリロイルオキシ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−ベンゾイルオキシ−２，２，６，６−テトラメチル−ピペリジン−Ｎ−オキシル、４−メトキシ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−エトキシ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−フェノキシ−２，２，６，６−ピペリジン−Ｎ−オキシル、４−ベンジルオキシ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−アセチルアミノ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−アクリロイルアミノ−２，２，６，６ーテトラメチルピペリジン−Ｎ−オキシル、４−メタクリロイルアミノ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−ベンゾイルアミノ−２，２，６，６−テトラメチルピペリジン−Ｎーオキシル、４−シンナモイルアミノ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−クロトニルアミノ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−プロピオニルアミノ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−ブチリルアミノ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、２，２，６，６−テトラメチル−４−ピペリドン−Ｎ−オキシル、４−［Ｈ−（ＥＯ）_２−Ｏ］−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−［Ｈ−（ＥＯ）_４−Ｏ］−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−［Ｈ−（ＥＯ）_６−Ｏ］−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−［Ｈ−（ＥＯ）_８−Ｏ］−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−［Ｈ−（ＥＯ）_１０−Ｏ］−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−［Ｈ−［（ＥＯ）_２＋（ＰＯ）_４］−Ｏ］−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−［Ｈ−［（ＥＯ）_４＋（ＰＯ）_３］−Ｏ］−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−［Ｈ−［（ＥＯ）_６＋（ＰＯ）_３］−Ｏ］−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−［Ｈ−（ＰＯ）_１０−Ｏ］−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−［Ｈ−（ＰＯ）_６−Ｏ］−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−［Ｈ−［（ＥＯ）_５＋（ＰＯ）_１０］−Ｏ］−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４，４’−（フタロイルジオキシ）ビス（２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル）等が挙げられる。
表１および表２に前記式（１）で表されるＮ−オキシル化合物の代表例を示した。
【００１９】
【表１】

【００２０】
【表２】

【００２１】
（メタ）アクリル酸エステルに共存させるＮ−オキシル化合物の種類は１種類でも２種類以上であってもよい。また（メタ）アクリル酸エステルにはＮ−オキシル化合物以外の重合防止剤が含まれていてもよい。
【００２２】
（メタ）アクリル酸エステルに共存させるＮ−オキシル化合物の濃度は、（メタ）アクリル酸エステルの質量に対して、通常０．０１〜５０００ｐｐｍである。Ｎ−オキシル化合物の濃度は（メタ）アクリル酸エステルに含まれる酸のモル濃度以上が好ましく、酸のモル濃度の１〜１００倍にすることがより好ましい。
【００２３】
Ｎ−オキシル化合物と併用できる重合防止剤としては、例えば、ハイドロキノン、ハイドロキノンモノメチルエーテル等のハイドロキノン系重合防止剤、ジフェニルアミン、ｐ−フェニレンジアミン誘導体等のアミン系重合防止剤、２，２，６，６−テトラメチルピペリジン等のヒンダードアミン化合物、フェノチアジンなどが挙げられる。
【００２４】
【実施例】
以下、本発明を実施例および比較例を挙げて説明する。使用したＮ−オキシル化合物は表１または表２に示した化合物番号で表示した。重合開始時間は、アンプル内の（メタ）アクリル酸エステルの固化または粘度上昇を目視により確認する方法で測定した。
【００２５】
［実施例１］
メタクリル酸１００ｐｐｍを含むメタクリル酸シクロヘキシル１００ｇに酸化カルシウムを０．０５ｇ添加してメタクリル酸の濃度を１０ｐｐｍ（１．２×１０^−７ｍｏｌ／ｇ）まで低減し、重合防止剤としてＮ−オキシル化合物８を２００ｐｐｍ（９．４×１０^−７ｍｏｌ／ｇ）添加した。このメタクリル酸シクロヘキシル５ｍｌを内容量２０ｍｌのアンプルに入れ、気相部を空気の状態のまま封管した。このアンプルを１２０℃に加熱した油浴中に浸漬し、重合開始時間を測定したところ、３００時間後に重合が観測された。
【００２６】
［実施例２〜４］
表３に示すＮ−オキシル化合物（重合防止剤）および各濃度の重合防止剤を用いた以外は実施例１と同様にして重合開始時間を測定した。その結果は表３のとおりであった。
【００２７】
［比較例１］
メタクリル酸シクロヘキシル中のメタクリル酸を低減しなかったこと以外は実施例１と同様にして重合開始時間を測定したところ、２０５時間後に重合が観測された。
【００２８】
［比較例２〜４］
表３に示すＮ−オキシル化合物および各濃度の重合防止剤を用いた以外は比較例１と同様にして重合開始時間を測定した。その結果は表３のとおりであった。
【００２９】
［実施例５］
９８％硫酸１００ｐｐｍを含むメタクリル酸シクロヘキシル１００ｇに酸化カルシウムを０．０５ｇ添加して硫酸の濃度を１ｐｐｍ＞（０．１×１０^−７ｍｏｌ／ｇ＞）に低減し、重合防止剤としてＮ−オキシル化合物８を２００ｐｐｍ（９．４×１０^−７ｍｏｌ／ｇ）添加した。このメタクリル酸シクロヘキシル５ｍｌを内容量２０ｍｌのアンプルに入れ、気相部を空気の状態のまま封管した。このアンプルを１２０℃に加熱した油浴中に浸漬し、重合開始時間を測定したところ、３１３時間後に重合が観測された。
【００３０】
［比較例５］
メタクリル酸シクロヘキシル中の硫酸を低減しなかったこと以外は実施例５と同様にして重合開始時間を測定したところ、２時間後に重合が観測された。
【００３１】
［実施例６］
メタクリル酸メチル１０ｍｌと強酸性イオン交換樹脂（三菱化学（株）社製、ＲＣＰ１６０Ｍ）３ｍｌの混合物から全ての強酸性イオン交換樹脂を濾別したメタクリル酸メチル１０ｍｌ（メタクリル酸１ｐｐｍ以下）に重合防止剤としてＮ−オキシル化合物８を２００ｐｐｍ添加した。このメタクリル酸メチル１０ｍｌを内容量２０ｍｌのアンプルに入れ、気相部を空気の状態のまま封管した。８０℃に加熱した油浴中に浸漬し、重合開始時間を測定したところ、１０８０時間以上重合が観測されなかった。
【００３２】
［比較例６］
強酸性イオン交換樹脂を濾別しなかったこと以外は実施例６と同様にして重合開始時間を測定したところ、２１時間で重合が観測された。
【００３３】
［実施例７］
重合防止剤としてＮ−オキシル化合物６を３００ｐｐｍ用いた以外は実施例６と同様にして重合開始時間を測定したところ、１０８０時間以上重合が観測されなかった。
【００３４】
［比較例７］
強酸性イオン交換樹脂を濾別しなかったこと以外は実施例７と同様にして重合開始時間を測定したところ、２１時間で重合が観測された。
【００３５】
［実施例８］
メタクリル酸１００ｐｐｍを含むメタクリル酸２−エチルヘキシル１００ｇに酸化マグネシウムを０．０５ｇ添加してメタクリル酸の濃度を１０ｐｐｍ（１．２×１０^−７ｍｏｌ／ｇ）まで低減し、重合防止剤としてＮ−オキシル化合物８を２００ｐｐｍ（９．４×１０^−７ｍｏｌ／ｇ）添加した。このメタクリル酸２−エチルヘキシル５ｍｌを内容量２０ｍｌのアンプルに入れ、気相部を空気の状態のまま封管した。このアンプルを１２０℃に加熱した油浴中に浸漬し、重合開始時間を測定したところ、３４７時間後に重合が観測された。
【００３６】
［比較例８］
メタクリル酸２−エチルヘキシル中のメタクリル酸を低減しなかったこと以外は実施例８と同様にして重合開始時間を測定したところ、２５１時間後に重合が観測された。
【００３７】
［実施例９］
メタクリル酸１００ｐｐｍを含むメタクリル酸ラウリルに水酸化カルシウムを０．０５ｇ添加してメタクリル酸の濃度を８ｐｐｍ（０．９×１０^−７ｍｏｌ／ｇ）まで低減し、重合防止剤としてＮ−オキシル化合物８を２００ｐｐｍ（９．４×１０^−７ｍｏｌ／ｇ）添加した。このメタクリル酸ラウリル５ｍｌを内容量２０ｍｌのアンプルに入れ、気相部を空気の状態のまま封管した。このアンプルを１２０℃に加熱した油浴中に浸漬し、重合開始時間を測定したところ、５５２時間後に重合が観測された。
【００３８】
［比較例９］
メタクリル酸ラウリル中のメタクリル酸を低減しなかったこと以外は実施例９と同様にして重合開始時間を測定したところ、２１６時間後に重合が観測された。
【００３９】
【表３】

【００４０】
［実施例１０］
水０．１％を含むメタクリル酸シクロヘキシル１００ｇに共沸溶媒としてｎ−ヘキサン３０ｇを添加し、ディーンスターク型脱水装置を用いて減圧下５０℃で３０分脱水操作を行い水分濃度を７５ｐｐｍまで低減し、重合防止剤としてＮ−オキシル化合物８を２００ｐｐｍ添加した。このメタクリル酸シクロヘキシル５ｍｌを内容量２０ｍｌのアンプルに入れ、気相部を空気の状態のまま封管した。このアンプルを１２０℃に加熱した油浴中に浸漬し、重合開始時間を測定したところ、２８８時間後に重合が観測された。
【００４１】
［比較例１０］
メタクリル酸シクロヘキシル中の水分を低減しなかったこと以外は実施例１０と同様にして重合開始時間を測定したところ、１７５時間後に重合が観測された。
【００４２】
【発明の効果】
本発明によれば、（メタ）アクリル酸エステルに含まれる酸および／または水分を低減させ、かつＮ−オキシル化合物を共存させることによって、（メタ）アクリル酸エステルの重合をより良く防止することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for preventing polymerization of a (meth) acrylate, and more particularly to a method for preventing polymerization of a (meth) acrylate containing an acid and / or water.
[0002]
[Prior art]
(Meth) acrylic acid esters are extremely easily polymerized, and are easily polymerized by factors such as heat and light during the manufacturing process, storage, and transportation. Therefore, various polymerization inhibitors are usually used. Among them, N-oxyl compounds are known as excellent polymerization inhibitors.
[0003]
As a method for preventing polymerization of (meth) acrylic acid ester using an N-oxyl compound as a polymerization inhibitor, for example, 2,2,5,5-tetramethyl-3-oxopyrrolidine-1-oxyl, 2,2,2 A method using an N-oxyl compound such as 6,6-tetramethyl-4-acetoxypiperidine-1-oxyl (JP-B-58-46496), 2,2,6,6-tetramethylpiperidine-1-oxyl , A method of using a combination of hydroquinones and phenothiazine (JP-A-6-345681), a manganese salt compound, an N-oxyl compound such as 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, A method in which a copper salt compound, a 2,2,6,6-tetramethylpiperidine compound, and another compound of a nitroso compound are used in combination (Japanese Patent Laid-Open No. 8650), a method in which a 2,2,6,6-tetramethylpiperidine-1-oxyl is used in combination with a phosphorus compound (JP-A-9-316026), and 2,2,6,6-tetramethylpiperidine- A method in which a 1-oxyl and a cobalt compound are used in combination (Japanese Patent Application Laid-Open No. H10-175912) is exemplified.
[0004]
[Problems to be solved by the invention]
However, in many cases, polymerization cannot be sufficiently prevented by conventional methods, and a polymerization prevention method capable of more stably handling (meth) acrylic acid esters has been demanded.
[0005]
An object of the present invention is to provide a method for preventing polymerization of a (meth) acrylic ester having an excellent polymerization preventing effect.
[0006]
[Means for Solving the Problems]
The present inventors have conducted intensive studies and found that if the (meth) acrylic acid ester contains an acid and / or moisture, the effect of preventing the polymerization of the N-oxyl compound cannot be sufficiently exhibited.
[0007]
The present invention relates to a method for preventing polymerization of a (meth) acrylic ester containing an acid and / or water, wherein the acid and / or water contained in the (meth) acrylic ester is reduced and an N-oxyl compound coexists. A method for preventing polymerization of (meth) acrylate. As a method of reducing the acid in advance, a method of adding a base to the (meth) acrylic acid ester is preferable. Further, as a method for previously reducing the water content, a method for reducing the water content by azeotropic dehydration using a solvent that forms an azeotropic composition with water is preferable. Further, as the N-oxyl compound, an N-oxyl compound represented by the formula (1) is preferable.
[0008]
Embedded image

(Wherein R ¹ , R ² , R ³ , and R ⁴ are alkyl groups having 1 to 8 carbon atoms and may be linear or branched. Further, R ¹ and R ² and / or R ³ and R ^{4 May} form a ring with each other R ⁵ is H, OH, OR, OCOR, NHCOR or O-[(EO) _n + (PO) _m ] -H, R ⁶ is H, or R ⁵ and R ⁶ together represent ＯO. R is a hydrogen atom or an alkyl, alkenyl or aryl group having 1 to 18 carbon atoms, the alkyl group may be linear or branched, and the aryl group is a hydrogen atom. May be substituted with an alkyl group. EO represents an ethyleneoxy group, PO represents a propyleneoxy group, n and m are the same or different integers from 0 to 10, and n and m are simultaneously 0. Is not.)
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Examples of the (meth) acrylate which is a target of polymerization prevention in the present invention include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, tertiary butyl (meth) acrylate, Alkyl esters such as normal butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, and stearyl (meth) acrylate; Alicyclic alkyl esters such as cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, and tetrahydrofurfuryl (meth) acrylate; esters containing aromatic groups such as benzyl (meth) acrylate; (meth) acrylic Esters containing heterocyclic group such as glycidyl acid, (meth) acrylic acid Unsaturated alkyl esters such as ril; hydroxyalkyl esters such as hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate; 2-methoxyethyl (meth) acrylate; 2-ethoxyethyl (meth) acrylate Etc., ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, 1,6-hexane di (meth) acrylate Esters of polyhydric alcohols such as diol, polybutylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 2- (meth) acryloyloxyethyl phthalate, 2- (meth) hexahydrophthalate Contains carboxylic acid such as acryloyloxyethyl Dialkylaminoalkyl such as alcohol esters, dimethylaminoethyl (meth) acrylate, dimethylaminoethyl methyl chloride (meth) acrylate, dimethylaminoethyl benzyl chloride (meth) acrylate, and diethylaminoethyl (meth) acrylate Examples thereof include esters and salts thereof, and fluoroalkyl esters such as trifluoroethyl (meth) acrylate and heptadecafluorodecyl (meth) acrylate.
[0010]
As is commonly used, (meth) acrylic acid is a general term for methacrylic acid and acrylic acid, and (meth) acryloyl is a general term for methacryloyl and acryloyl.
[0011]
In the present invention, it is necessary to reduce the acid and / or moisture contained in the (meth) acrylate. Here, the acid means a Bronsted acid. Examples of such acids include mineral acids such as hydrochloric acid, sulfuric acid and nitric acid, organic acids such as methacrylic acid, acrylic acid, methanesulfonic acid and p-toluenesulfonic acid, solid acids such as strongly acidic ion exchange resins and zeolites. Is mentioned.
[0012]
An acid is sometimes used as a catalyst for synthesizing a target (meth) acrylate. In this case, the acid is separated at the end of the reaction by a method such as neutralization or solid-liquid separation. If this separation operation is not sufficient, the resulting (meth) acrylic acid ester contains the acid. In addition, (meth) acrylic acid may be included due to hydrolysis of the methacrylic acid ester itself or residual raw materials for the esterification reaction. The amount of the acid contained in the (meth) acrylate is not particularly limited, but is usually 100 ppm or more.
[0013]
On the other hand, water is the residual water contained in the raw materials for the synthesis of (meth) acrylate, the residual water by-produced when (meth) acrylate is synthesized by the esterification reaction, and (meth) acrylate. It may be contained in (meth) acrylate due to moisture absorption during handling. The amount of water contained in the (meth) acrylate is not particularly limited, but is usually 200 ppm or more.
[0014]
The method for reducing the acid is not particularly limited, but a method in which a base is added to the (meth) acrylate to neutralize the acid is preferable. Examples of the base that can be used in this method include, for example, alkaline earth metal oxides, alkaline earth metal hydroxides, alkali metal oxides, alkali metal hydroxides, basic ion exchange resins, and the like. Calcium oxide, calcium hydroxide, magnesium oxide, magnesium hydroxide and lithium hydroxide are preferred. The amount of the base to be added is generally 0.1 to 100 mol, preferably 1 to 10 mol, per 1 mol of the acid. The amount of the acid after reducing the acid is not particularly limited, but is preferably 50 ppm or less, more preferably 30 ppm or less.
[0015]
On the other hand, the method of reducing water is not particularly limited, for example, a method of reducing water by azeotropic dehydration using a solvent that forms an azeotropic composition with water, a method of adding a desiccant and adsorbing and removing water. Method and the like. Of these, a method of azeotropic dehydration is preferred. By reducing the water content, an increase in (meth) acrylic acid due to hydrolysis of (meth) acrylic acid ester can be suppressed. Although the amount of water after reducing the water is not particularly limited, it is preferably 100 ppm or less, more preferably 50 ppm or less.
[0016]
Further, in the present invention, it is necessary to coexist an N-oxyl compound in addition to reducing the acid and / or moisture contained in the (meth) acrylate.
[0017]
The N-oxyl compound is a compound having a nitroxyl radical structure in which an oxygen radical is bonded to a nitrogen atom, and among them, the N-oxyl compound represented by the formula (1) is preferable. In the formula (1), R ¹ , R ² , R ³ , and R ⁴ are an alkyl group having 1 to 8 carbon atoms and may be linear or branched. Further, R ¹ and R ² and / or R ³ and R ⁴ may form a ring with each other. Among them, R ¹ , R ² , R ³ and R ⁴ are all preferably methyl groups. R ⁵ is H, OH, OR, OCOR, NHCOR or _O - represents the _{[(EO) n + (PO} ) m] -H, R 6 is H, or ^{R 5} and ^{R 6} together = O. R is a hydrogen atom or an alkyl group, an alkenyl group or an aryl group having 1 to 18 carbon atoms, the alkyl group may be linear or branched, and the aryl group may be a hydrogen atom substituted with an alkyl group. EO represents an ethyleneoxy group, PO represents a propyleneoxy group, n and m are the same or different integers from 0 to 10, and n and m are not simultaneously 0. Among them, R ⁵ is preferably OH, OCOPh, and NHCOCH ₃ , and R ⁶ is preferably hydrogen.
[0018]
Specific examples of the N-oxyl compound represented by the formula (1) include 2,2,6,6-tetramethylpiperidine-N-oxyl and 4-hydroxy-2,2,6,6-tetramethyl Piperidine-N-oxyl, 4-acetyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-acryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl, Methacryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-benzoyloxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-methoxy-2,2,6 , 6-Tetramethylpiperidine-N-oxyl, 4-ethoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-phenoxy-2,2,6,6-piperi 4-N-oxyl, 4-benzyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-acetylamino-2,2,6,6-tetramethylpiperidine-N-oxyl, Acryloylamino-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-methacryloylamino-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-benzoylamino-2,2,6 , 6-Tetramethylpiperidine-N-oxyl, 4-cinnamoylamino-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-crotonylamino-2,2,6,6-tetramethylpiperidine- N-oxyl, 4-propionylamino-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-butyrylamino-2,2,6, - tetramethylpiperidine -N- oxyl, 2,2,6,6-tetramethyl-4-piperidone -N- _{oxyl, 4- [H- (EO) 2} -O] -2,2,6,6- tetra Methylpiperidine-N-oxyl, 4- [H- (EO) _4- O] -2,2,6,6-tetramethylpiperidine-N-oxyl, 4- [H- (EO) _6- O] -2 , 2,6,6-tetramethylpiperidine-N-oxyl, 4- [H- (EO) _8- O] -2,2,6,6-tetramethylpiperidine-N-oxyl, 4- [H- ( _EO) 10 -O] -2,2,6,6- tetramethylpiperidine -N- _{oxyl, 4- [H - [(EO} ) 2 + (PO) 4] -O] -2,2,6,6 - tetramethylpiperidine -N- _{oxyl, 4- [H - [(EO} ) 4 + (PO) 3] -O] - 2,2,6,6-tetramethylpiperidine -N- _{oxyl, 4- [H - [(EO} ) 6 + (PO) 3] -O] -2,2,6,6- tetramethylpiperidine -N- Oxyl, 4- [H- (PO) _10- O] -2,2,6,6-tetramethylpiperidine-N-oxyl, 4- [H- (PO) _6- O] -2,2,6, 6-tetramethylpiperidine--N- _{oxyl, 4- [H - [(EO} ) 5 + (PO) 10] -O] -2,2,6,6- tetramethylpiperidine -N- oxyl, 4,4 ' -(Phthaloyldioxy) bis (2,2,6,6-tetramethylpiperidine-N-oxyl) and the like.
Tables 1 and 2 show typical examples of the N-oxyl compound represented by the formula (1).
[0019]
[Table 1]

[0020]
[Table 2]

[0021]
The type of the N-oxyl compound coexisting in the (meth) acrylate may be one or more. The (meth) acrylic acid ester may contain a polymerization inhibitor other than the N-oxyl compound.
[0022]
The concentration of the N-oxyl compound coexisting in the (meth) acrylate is usually 0.01 to 5000 ppm based on the mass of the (meth) acrylate. The concentration of the N-oxyl compound is preferably equal to or higher than the molar concentration of the acid contained in the (meth) acrylic acid ester, and more preferably 1 to 100 times the molar concentration of the acid.
[0023]
Examples of the polymerization inhibitor that can be used in combination with the N-oxyl compound include hydroquinone-based polymerization inhibitors such as hydroquinone and hydroquinone monomethyl ether; amine-based polymerization inhibitors such as diphenylamine and p-phenylenediamine derivatives; and 2,2,6,6. -Hindered amine compounds such as tetramethylpiperidine, phenothiazine and the like.
[0024]
【Example】
Hereinafter, the present invention will be described with reference to Examples and Comparative Examples. The N-oxyl compounds used were indicated by the compound numbers shown in Table 1 or Table 2. The polymerization initiation time was measured by a method for visually confirming the solidification or viscosity increase of the (meth) acrylate in the ampoule.
[0025]
[Example 1]
0.05 g of calcium oxide was added to 100 g of cyclohexyl methacrylate containing 100 ppm of methacrylic acid to reduce the concentration of methacrylic acid to 10 ppm (1.2 × 10 ⁻⁷ mol / g), and N-oxyl compound 8 was used as a polymerization inhibitor. Was added at 200 ppm (9.4 × 10 ⁻⁷ mol / g). 5 ml of this cyclohexyl methacrylate was placed in an ampoule having an internal volume of 20 ml, and the gas phase was sealed in an air state. The ampoule was immersed in an oil bath heated to 120 ° C., and the polymerization initiation time was measured. As a result, polymerization was observed after 300 hours.
[0026]
[Examples 2 to 4]
The polymerization start time was measured in the same manner as in Example 1 except that the N-oxyl compound (polymerization inhibitor) shown in Table 3 and the polymerization inhibitor at each concentration were used. Table 3 shows the results.
[0027]
[Comparative Example 1]
The polymerization initiation time was measured in the same manner as in Example 1 except that methacrylic acid in cyclohexyl methacrylate was not reduced. As a result, polymerization was observed after 205 hours.
[0028]
[Comparative Examples 2 to 4]
The polymerization start time was measured in the same manner as in Comparative Example 1 except that the N-oxyl compound shown in Table 3 and the polymerization inhibitor at each concentration were used. Table 3 shows the results.
[0029]
[Example 5]
0.05 g of calcium oxide was added to 100 g of cyclohexyl methacrylate containing 100 ppm of 98% sulfuric acid to reduce the concentration of sulfuric acid to 1 ppm> (0.1 × 10 ⁻⁷ mol / g>), and N-oxyl was used as a polymerization inhibitor. Compound 8 was added at 200 ppm (9.4 × 10 ⁻⁷ mol / g). 5 ml of this cyclohexyl methacrylate was placed in an ampoule having an internal volume of 20 ml, and the gas phase was sealed in an air state. This ampoule was immersed in an oil bath heated to 120 ° C., and the polymerization initiation time was measured. As a result, polymerization was observed after 313 hours.
[0030]
[Comparative Example 5]
When the polymerization start time was measured in the same manner as in Example 5 except that sulfuric acid in cyclohexyl methacrylate was not reduced, polymerization was observed after 2 hours.
[0031]
[Example 6]
From a mixture of 10 ml of methyl methacrylate and 3 ml of a strongly acidic ion exchange resin (RCP160M, manufactured by Mitsubishi Chemical Corporation), 10 ml of methyl methacrylate (1 ppm or less of methacrylic acid) obtained by filtering off all strongly acidic ion exchange resins was used as a polymerization inhibitor. 200 ppm of N-oxyl compound 8 was added. 10 ml of this methyl methacrylate was placed in an ampoule having a content of 20 ml, and the gas phase was sealed in an air state. It was immersed in an oil bath heated to 80 ° C. and the polymerization initiation time was measured. No polymerization was observed for 1080 hours or more.
[0032]
[Comparative Example 6]
When the polymerization initiation time was measured in the same manner as in Example 6 except that the strongly acidic ion exchange resin was not filtered off, polymerization was observed in 21 hours.
[0033]
[Example 7]
When the polymerization initiation time was measured in the same manner as in Example 6 except that 300 ppm of the N-oxyl compound 6 was used as the polymerization inhibitor, no polymerization was observed for 1080 hours or more.
[0034]
[Comparative Example 7]
When the polymerization initiation time was measured in the same manner as in Example 7 except that the strongly acidic ion exchange resin was not filtered off, polymerization was observed in 21 hours.
[0035]
Example 8
0.05 g of magnesium oxide was added to 100 g of 2-ethylhexyl methacrylate containing 100 ppm of methacrylic acid to reduce the concentration of methacrylic acid to 10 ppm (1.2 × 10 ⁻⁷ mol / g), and N-oxyl was used as a polymerization inhibitor. Compound 8 was added at 200 ppm (9.4 × 10 ⁻⁷ mol / g). 5 ml of this 2-ethylhexyl methacrylate was put into an ampoule having a content of 20 ml, and the gas phase was sealed in an air state. The ampoule was immersed in an oil bath heated to 120 ° C., and the polymerization initiation time was measured. As a result, polymerization was observed after 347 hours.
[0036]
[Comparative Example 8]
When the polymerization initiation time was measured in the same manner as in Example 8 except that methacrylic acid in 2-ethylhexyl methacrylate was not reduced, polymerization was observed after 251 hours.
[0037]
[Example 9]
0.05 g of calcium hydroxide was added to lauryl methacrylate containing 100 ppm of methacrylic acid to reduce the concentration of methacrylic acid to 8 ppm (0.9 × 10 ⁻⁷ mol / g), and the N-oxyl compound 8 was used as a polymerization inhibitor. Was added at 200 ppm (9.4 × 10 ⁻⁷ mol / g). 5 ml of this lauryl methacrylate was placed in an ampoule having an internal volume of 20 ml, and the gas phase was sealed in an air state. The ampoule was immersed in an oil bath heated to 120 ° C., and the polymerization initiation time was measured. As a result, polymerization was observed after 552 hours.
[0038]
[Comparative Example 9]
When the polymerization initiation time was measured in the same manner as in Example 9 except that methacrylic acid in lauryl methacrylate was not reduced, polymerization was observed after 216 hours.
[0039]
[Table 3]

[0040]
[Example 10]
30 g of n-hexane was added as an azeotropic solvent to 100 g of cyclohexyl methacrylate containing 0.1% of water, and the mixture was subjected to a dehydration operation at 50 ° C. for 30 minutes under reduced pressure using a Dean-Stark dehydrator to reduce the water concentration to 75 ppm. 200 ppm of N-oxyl compound 8 was added as a polymerization inhibitor. 5 ml of this cyclohexyl methacrylate was placed in an ampoule having an internal volume of 20 ml, and the gas phase was sealed in an air state. The ampoule was immersed in an oil bath heated to 120 ° C., and the polymerization initiation time was measured. As a result, polymerization was observed after 288 hours.
[0041]
[Comparative Example 10]
When the polymerization start time was measured in the same manner as in Example 10 except that the water content in cyclohexyl methacrylate was not reduced, polymerization was observed after 175 hours.
[0042]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the polymerization of a (meth) acrylate can be prevented better by reducing the acid and / or moisture contained in a (meth) acrylate and coexisting with an N-oxyl compound. it can.

Claims (4)

A method for preventing polymerization of a (meth) acrylic acid ester containing an acid and / or water, wherein the acid and / or water contained in the (meth) acrylic acid ester is reduced and an N-oxyl compound coexists. A method for preventing polymerization of (meth) acrylate. The method for preventing polymerization of (meth) acrylate according to claim 1, wherein the acid is reduced by adding a base to the (meth) acrylate. The method for preventing polymerization of a (meth) acrylate according to claim 1 or 2, wherein water is reduced by azeotropic dehydration using a solvent that forms an azeotropic composition with water. The method for preventing polymerization of a (meth) acrylate according to any one of claims 1 to 3, wherein the N-oxyl compound is an N-oxyl compound represented by the formula (1).

(Wherein R ¹ , R ² , R ³ , and R ⁴ are alkyl groups having 1 to 8 carbon atoms and may be linear or branched. Further, R ¹ and R ² and / or R ³ and R ^{4 May} form a ring with each other R ⁵ is H, OH, OR, OCOR, NHCOR or O-[(EO) _n + (PO) _m ] -H, R ⁶ is H, or R ⁵ and R ⁶ together represent ＯO. R is a hydrogen atom or an alkyl, alkenyl or aryl group having 1 to 18 carbon atoms, the alkyl group may be linear or branched, and the aryl group is a hydrogen atom. May be substituted with an alkyl group. EO represents an ethyleneoxy group, PO represents a propyleneoxy group, n and m are the same or different integers from 0 to 10, and n and m are simultaneously 0. Is not.)