JP2004359925A - Proton conductive block copolymer and proton conductive film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proton conductive block copolymer and a proton conductive film for a fuel battery, having water resistance, low water-absorbing properties, reduced methanol permeability, and high proton conductivity. <P>SOLUTION: The block copolymer has a block of general formula (1) and a block of general formula (2). In formulas (1) and (2), at least one of X<SP>1</SP>to X<SP>5</SP>is a protonic acid group and the other are each H or a protonic acid group; A<SP>1</SP>to A<SP>4</SP>are each a direct bonding, -CH<SB>2</SB>-, -C(CH<SB>3</SB>)<SB>2</SB>-, -C(CF<SB>3</SB>)<SB>2</SB>-, -O-, -SO<SB>2</SB>-, or -CO-; g, h, i, j, k, and l are each 0 or 1; the hydrogen atom on the aromatic ring is hydrogen, or -C<SB>m</SB>H<SB>2m+1</SB>wherein m is an integer of 1 to 10, -Cl, -F, -CF<SB>3</SB>, or -CN. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

［式（１）および（２）中、Ｘ^１〜Ｘ^５の少なくとも１つがプロトン酸基であり、他はそれぞれ独立してＨまたはプロトン酸基であり、Ａ^１〜Ａ^４はそれぞれ独立して直接結合，−ＣＨ_２−，−Ｃ（ＣＨ_３）_２−，−Ｃ（ＣＦ_３）_２−，−Ｏ−，−ＳＯ_２−または−ＣＯ−であり、ｇ，ｈ，ｉ，ｊ，ｋ，ｌはそれぞれ独立して０または１を示し、芳香環の水素原子は、水素原子、または−Ｃ_ｍＨ_２ｍ＋１（ｍは１〜１０の整数），−Ｃｌ，−Ｆ，−ＣＦ_３または−ＣＮである。］
【００１７】
ここで、本発明におけるプロトン酸基とは、具体的には、下記式（４）〜（６）で示されるスルホン酸基、カルボン酸基、ホスホン酸基などが挙げられる。中でも下記式（４）で示されるスルホン酸基が好ましく、下記式（４）においてｎ＝０、Ｙ＝Ｈで示されるスルホン酸基が特に好ましい。
−Ｃ_ｎＨ_２ｎ−ＳＯ_３Ｙ（ｎは０〜１０の整数、ＹはＨ，ＮａまたはＫ）…（４）
−Ｃ_ｎＨ_２ｎ−ＣＯＯＹ（ｎは０〜１０の整数、ＹはＨ，ＮａまたはＫ）…（５）
−Ｃ_ｎＨ_２ｎ−ＰＯ_３Ｙ_２（ｎは０〜１０の整数、ＹはＨ，ＮａまたはＫ）…（６）
【００１８】
本発明のプロトン伝導性ブロック共重合体は、一般式（１）で表される繰り返し構造単位を有するプロトン伝導を担うブロックと、一般式（２）で表される繰り返し構造単位からなる耐水性に優れ且つ吸水膨張の小さいブロックとからなる。本発明のプロトン伝導性ブロック共重合体は、それぞれのブロックが適度にミクロ相分離すると考えられ、その相間が同一分子で結合されているので、プロトン伝導を担うブロックによる水へ溶解あるいは吸水膨張が、耐水性に優れ且つ吸水膨張の小さいブロックにより抑制されると考えられる。その結果、プロトン伝導性ブロック共重合体はプロトン酸基の含有量が高く、高プロトン伝導性を有しながら、耐水性及び低吸水性に優れ、水とともに伝搬するメタノールの透過量も低く抑えることができると推定される。また、相間が同一分子で結合されていることによるため、温度や湿度の変化による膨張収縮の差が抑制され、膜に成形した場合にクラックの発生が抑えられる。
【００１９】
なお、一般式（１）で表される繰り返し構造単位を有するプロトン伝導性ブロックと一般式（２）で表される繰り返し構造単位からなる耐水性に優れ吸水膨張の小さいブロックとの混合物は、２つのブロックの極性が極端に異なるためミクロ相分離構造を形成しがたく、相間が分子鎖で結合されていないためプロトン伝導性ブロックの水への溶解性や吸水膨張を抑制できず、膜に成形した場合に温度や湿度の変化による２つの相の膨張収縮度合の差により相界面にクラックが入る等の問題があり好ましくない。
【００２０】
また、一般式（１）および（２）で表わされる繰り返し構造単位を有するランダム共重合体は、上記２つの構造単位がミクロ相分離せず単一相となると考えられるので、プロトン伝導を担う一般式（１）で表わされる繰り返し構造単位の割合が多くなると水への溶解性や吸水膨張が助長され、高プロトン伝導性と、耐水性及び低吸水性とを両立できない。
【００２１】
本発明に係るプロトン伝導性ブロック共重合体のイオン交換基当量は３００〜２０００ｇ／ｍｏｌであることが好ましく、５００〜１０００ｇ／ｍｏｌであることが特に好ましい。
【００２２】
ここで、イオン交換基当量とは、プロトン酸基１モル当たりの樹脂重量で定義され、樹脂単位重量当たりのプロトン酸基のモル数の逆数を意味する。すなわち、一般式（１）で表わされる繰り返し構造単位を有するブロックの割合は、イオン交換基当量が小さいほど高く、イオン交換基当量が大きいほど低いことを示す。イオン交換基当量が小さすぎる場合には、一般式（２）で表わされる繰り返し構造単位からなるブロックの割合が少なすぎるため、該プロトン伝導性ブロック共重合体の耐水性、低吸水性が不十分となるおそれがある。イオン交換基当量が大きすぎる場合には、一般式（１）で表わされる繰り返し構造単位を有するブロックの割合が少なすぎるため、十分なプロトン伝導性を得ることができないおそれがある。
【００２３】
本発明のプロトン伝導性ブロック共重合体の吸水率は５〜２０ｗｔ％であることが好ましい。ここで、吸水率は、乾燥したプロトン伝導性ブロック共重合体の、２３℃２４時間純水浸漬前後の重量増加率から求めることができる。本発明のプロトン伝導性ブロック共重合体は、同等のイオン交換基当量を有するランダム共重合体に比べ吸水膨張が小さく、吸水率が低い点で優れる。
【００２４】
本発明の一般式（１）で表わされる繰り返し構造単位を有するブロックは、還元粘度（濃度０．５ｇ／ｄｌ、３５℃で測定）が好ましくは０．０５〜１．２ｄｌ／ｇ、より好ましくは０．１〜０．９ｄｌ／ｇ、さらに好ましくは０．１〜０．６ｄｌ／ｇであるオリゴマーにより得られることが好ましい。該オリゴマーの分子量が小さすぎる（還元粘度が小さすぎる）場合には、得られるプロトン伝導性ブロック共重合体の２つのブロックがミクロ相分離しないため好ましくない。一方、該オリゴマーの分子量が大きすぎる（還元粘度が大きすぎる）場合には２つのブロックが微細に相分離しがたく、一部の分子鎖が一般式（１）で表される繰り返し構造単位を有するブロックのみから形成され、それが水に溶出するなどの問題があり好ましくない。
【００２５】
前記オリゴマーは、一般式（１）で表される繰り返し構造単位を有していれば、他の繰り返し構造単位を有していても良い。この場合、前記オリゴマーを構成する全繰り返し構造単位のうち一般式（１）で表される繰り返し構造単位の占める割合は、１００〜３０モル％であることが好ましく、１００〜５０モル％であることが特に好ましい。
【００２６】
一般式（１）で表わされる繰り返し構造単位を有するブロックの割合が少ない場合には、プロトン伝導性が低くなり好ましくない。なお、他の繰り返し構造単位の好ましい例としては、一般式（２）で表される繰り返し構造単位が例示される。一般式（２）で表される繰り返し単位を共重合させて一般式（１）で表される繰り返し構造単位を有するブロックのイオン交換基当量を変えることにより、プロトン伝導性ブロック共重合体のプロトン伝導度、メタノール透過性、耐メタノール性等の特性を制御することができる。
【００２７】
本発明に係る一般式（２）で表わされる繰り返し構造単位からなるブロックは、前記式（１）で表わされる繰り返し構造単位を有するブロックの水への溶解や吸水膨張を抑制するため、吸水性が低く且つ加水分解を受けにくい構造単位からなる。ここで、一般式（２）で表わされる繰り返し構造単位からなるブロックは、一般式（２）で表わされる２種類以上の繰り返し構造単位からなっていても良い。該ブロックにエステル結合、カーボネート結合、アミド結合、イミド結合やプロトン酸基を含むと、加水分解や吸水による膨張を受けやすくなり、ブロック共重合体の水への溶解性、吸水性が高くなるため好ましくない。しかしプロトン伝導性ブロック共重合体の製膜等の加工性をより容易にするために、スルホン酸基を有する一般式（１）で表される繰り返し単位をブロックに、全繰り返し構造単位に対してプロトン酸基として、例えばスルホン酸基を０．１〜２０モル％含んでいても良い。
【００２８】
本発明のプロトン伝導性ブロック共重合体は、芳香族ポリエーテル構造により構成され、熱水、酸、アルカリ、アルコールなどの加水分解を受けやすい連結基や耐熱性、耐ラジカル性が低い基を有さないため、燃料電池に用いた際に劣化や変性を起こすことがほとんどない。プロトン伝導性ブロック共重合体が、エステル結合、カーボネート結合、アミド結合、イミド結合や、耐熱性が低くラジカルの攻撃を受けやすいα水素を持つアルキレン結合、脂肪族エーテル結合などを有すると、熱水、酸、アルカリ、アルコールなどの加水分解を受けやすい燃料電池内で劣化するため好ましくない。
【００２９】
本発明のプロトン伝導性ブロック共重合体は、一般式（１）で表される繰り返し構造単位が下記一般式（３）で表される繰り返し構造単位であることが特に好ましい。該プロトン伝導性ブロック共重合体のプロトン酸基は、電子吸引基である−ＳＯ_２−または−ＣＯ−に直接結合した芳香環に結合しており、他の芳香環に結合したプロトン酸基に比べ結合力が強く、分解、解離を受けにくいため特に好ましい。なお、既存の芳香族ポリエーテルを発煙硫酸などでスルホン化した場合には、電子吸引基である−ＳＯ_２−または−ＣＯ−が直接結合していない芳香環にスルホン酸基が導入されることが知られている。
【化３】

［式（３）中、Ｘ^１およびＸ^２はプロトン酸基、Ａ^１は−ＳＯ_２−または−ＣＯ−、Ａ^２は直接結合，−ＣＨ_２−，−Ｃ（ＣＨ_３）_２−，−Ｃ（ＣＦ_３）_２−，−Ｏ−，−ＳＯ_２−または−ＣＯ−であり、ｈ，ｉそれぞれ独立して０または１を示し、芳香環の水素原子は、水素原子または、−Ｃ_ｍＨ_２ｍ＋１（ｍは１〜１０の整数），−Ｃｌ，−Ｆ，−ＣＦ_３または−ＣＮである。］
【００３０】
本発明のプロトン伝導性ブロック共重合体の分子量に特に制限はないが、還元粘度（濃度０．５ｇ／ｄｌ、３５℃で測定）にして０．５〜２．０ｄｌ／ｇの範囲が好ましく、０．７〜１．５ｄｌ／ｇの範囲が特に好ましい。分子量が低すぎるとブロック共重合体の強度が低く、得られる膜が乾燥・吸湿時の収縮・膨張により割れる場合がある。また、分子量が高すぎるとブロック共重合体の溶剤への溶解が不十分となり、製膜等に支障を生じる場合がある。
【００３１】
本発明のプロトン伝導性ブロック共重合体の製造方法に特に制限はないが、例えば、以下の公知の方法で合成することができる。
（Ａ）プロトン酸基を有するモノマーと、プロトン酸基を有しないモノマーまたは有するモノマーとを縮重合して、一般式（１）で表される繰り返し構造単位からなるブロックを有するオリゴマーとする。そのオリゴマーと、一般式（２）で表される構造単位からなるブロックを有するのモノマーまたはそのオリゴマーとを縮重合させてプロトン伝導性ブロック共重合体を得る方法。
（Ｂ）プロトン酸を有しないモノマーを縮重合して、一般式（２）で表される繰り返し構造単位を有するブロックからなるオリゴマーとする。そのオリゴマーと、一般式（１）で表される構造単位を有するブロックを有するモノマーまたはそのオリゴマーとを縮重合させてプロトン伝導性ブロック共重合体を得る方法。
（Ｃ）プロトン酸基を有しないモノマーを縮重合して前駆体オリゴマーとし、次にスルホン化等の方法で前駆体オリゴマーにプロトン酸基を導入して、一般式（１）で表される繰り返し構造単位を有するブロックからなるオリゴマーとする。そのオリゴマーと、プロトン酸基有しないモノマーまたはそのオリゴマーとを縮重合させてプロトン伝導性ブロック共重合体を得る方法。
（Ｄ）プロトン酸基が導入され易い構造単位からなるブロックと、プロトン酸基が導入され難い一般式（２）で表される繰り返し構造単位からなるブロックとを有する前駆体ブロック共重合体を合成する。この前駆体ブロック共重合体中の、プロトン酸基が導入され易い構造単位からなるブロックにのみスルホン化等の方法でプロトン酸基を導入して一般式（１）で表される繰り返し構造単位からなるブロックとし、プロトン伝導性ブロック共重合体を得る方法。
【００３２】
本発明のプロトン伝導性ブロック共重合体の製造方法は、上記（Ａ）の方法がプロトン伝導性ブロック共重合体のイオン交換基当量の制御が容易であるので好ましい。特にプロトン酸基を有するモノマーを重縮合して一般式（１）で表される繰り返し構造単位を有するオリゴマーとし、このオリゴマーと、プロトン酸基を有しないモノマーまたはオリゴマーとを反応させる方法がプロトン酸基を有するブロックの制御が容易であることより好ましい。
【００３３】
本発明のプロトン伝導性ブロック共重合体の製造方法は、具体的には、プロトン酸基を有する芳香族ジハライド化合物と芳香族ジヒドロキシ化合物を、または、芳香族ジハライド化合物とプロトン酸基を有する芳香族ジヒドロキシ化合物を、あるいは、プロトン酸基を有する芳香族ジハライド化合物とプロトン酸基を有する芳香族ジヒドロキシ化合物を重縮合し、一般式（１）で表わされる繰り返し構造単位を有するプロトン酸基含有オリゴマーを合成する。得られたオリゴマーは、好ましくは３５℃における還元粘度が０．０５〜１．２ｄｌ／ｇであり、オリゴマーの分子量は反応時間、反応温度、芳香族ジハライド化合物と芳香族ジヒドロキシ化合物の仕込み比等の一般的な方法により制御することができる。
【００３４】
前記オリゴマーに、芳香族ジハライド化合物と芳香族ジヒドロキシ化合物を添加して重縮合して一般式（２）で表わされる繰り返し構造単位ブロックを形成させてブロック共重合体とするか、或いは、別途、芳香族ジハライド化合物と芳香族ジヒドロキシ化合物を重縮合して得られた一般式（２）で表わされる繰り返し構造単位からなるオリゴマーを添加して重縮合することによりブロック共重合体を得る。
【００３５】
ここで、本発明に係るプロトン伝導性ブロック共重合体の製造において用いるモノマー類の代表的な具体例を以下に例示する。
芳香族ジハライド化合物としては、例えば、４，４’−ジフルオロベンゾフェノン、３，３’−ジフルオロベンゾフェノン、４，４’−ジクロロベンゾフェノン、３，３’−ジクロロベンゾフェノン、４，４’−ジフルオロジフェニルスルホン、４，４’−ジクロロジフェニルスルホン、１，４−ジフルオロベンゼン、１，３−ジフルオロベンゼン、２，６−ジクロロベンゾニトリル、４，４’−ジフルオロビフェニル、３，３’−ジブロモ−４，４’−ジフルオロビフェニル、４，４’−ジフルオロジフェニルメタン、４，４’−ジクロロジフェニルメタン、４，４’−ジフルオロジフェニルエーテル、２，２−ビス（４−フルオロフェニル）プロパン、２，２−ビス（４−クロロフェニル）プロパン、α，α’−ビス（４−フルオロフェニル）−１，４−ジイソプロピルベンゼン、３，３’−ジメチル−４，４’−ジフルオロベンゾフェノン、３，３’−ジエチル−４，４’−ジフルオロベンゾフェノン、３，３’，５，５’−テトラメチル−４，４’−ジフルオロベンゾフェノン、３，３’−ジメチル−４，４’−ジクロロベンゾフェノン、３，３’，４，４’−テトラメチル−５，５’−ジクロロベンゾフェノン、３，３’−ジメチル−４，４’−ジフルオロジフェニルスルホン、３，３’−ジメチル−４，４’−ジクロロジフェニルスルホン、２，５−ジフルオロトルエン、２，５−ジフルオロエチルベンゼン、２，５−ジフルオロ−ｐ−キシレンなどを挙げられ、単独あるいは２種以上を混合して用いることができる。
【００３６】
芳香族ジヒドロキシ化合物としては、例えば、ハイドロキノン、レゾルシン、カテコール、４，４’−ジヒドロキシビフェニル、４，４’−ジヒドロキシジフェニルスルフィド、４，４’−ジヒドロキシジフェニルメタン、４，４’−ジヒドロキシジフェニルエーテル、４，４’−ジヒドロキシジフェニルスルホン、４，４’−ジヒドロキシベンゾフェノン、２，２−ビス（４−ヒドロキシフェニル）プロパン、１，１，１，３，３，３−ヘキサフルオロ−２，２−ビス（４−ヒドロキシフェニル）プロパン、１，４−ビス（４−ヒドロキシフェニル）ベンゼン、α，α’−ビス（４−ヒドロキシフェニル）−１，４−ジメチルベンゼン、α，α’−ビス（４−ヒドロキシフェニル）−１，４−ジイソプロピルベンゼン、α，α’−ビス（４−ヒドロキシフェニル）−１，３−ジイソプロピルベンゼン、４，４’−ジヒドロキシベンゾフェノン、１，４−ビス（４−ヒドロキシベンゾイル）ベンゼン、３，３−ジフルオロ−４，４’−ジヒドロキビフェニル、２−メチルハイドロキノン、２−エチルハイドロキノン、２−イソプロピルハイドロキノン、２−オクチルハイドロキノン、２，３−ジメチルハイドロキノン、２，３−ジエチルハイドロキノン、２，５−ジメチルハイドロキノン、２，５−ジエチルハイドロキノン、２，５−ジイソプロピルハイドロキノン、２，６−ジメチルハイドロキノン、２，３，５−トリメチルハイドロキノン、２，３，５，６−テトラメチルハイドロキノン、３，３’−ジメチル−４，４’−ジヒドロキシビフェニル、３，３’，５，５’−テトラメチル−４，４’−ジヒドロキシビフェニル、３，３’−ジメチル−４，４’−ジヒドロキシジフェニルメタン、３，３’，５，５’−テトラメチル−４，４’−ジヒドロキシジフェニルメタン、３，３’，５，５’−テトラエチル−４，４’−ジヒドロキシジフェニルメタン、３，３’−ジメチル−４，４’−ジヒドロキシジフェニルエーテル、３，３’，５，５’−テトラメチル−４，４’−ジヒドロキシジフェニルエーテル、３，３’−ジメチル−４，４’−ジヒドロキシジフェニルスルフィド、３，３’，５，５’−テトラメチル−４，４’−ジヒドロキシジフェニルスルフィド、３，３’−ジメチル−４，４’−ジヒドロキシジフェニルスルホン、３，３’，５，５’−テトラメチル−４，４’−ジヒドロキシジフェニルスルホン、２，２−ビス（３−メチル−４−ヒドロキシフェニル）プロパン、２，２−ビス（３−エチル−４−ヒドロキシフェニル）プロパン、２，２−ビス（３，５−ジメチル−４−ヒドロキシフェニル）プロパン、α，α’−ビス（３−メチル−４−ヒドロキシフェニル）−１，４−ジイソプロピルベンゼン、α，α’−ビス（３，５−ジメチル−４−ヒドロキシフェニル）−１，４−ジイソプロピルベンゼン、α，α’−ビス（３−メチル−４−ヒドロキシフェニル）−１，３−ジイソプロピルベンゼン、α，α’−ビス（３，５−ジメチル−４−ヒドロキシフェニル）−１，３−ジイソプロピルベンゼンなどを挙げられ、単独あるいは２種以上を混合して用いることができる。
【００３７】
プロトン酸基を有する芳香族ジハライド化合物としては、前記の芳香族ジハライド化合物のスルホン化物、アルキルスルホン化物のほか、２，５−ジクロロ安息香酸、２，５−ジフルオロ安息香酸、５，５’−カルボニルビス（２−フルオロ安息香酸）、５，５’−スルホニルビス（２−フルオロ安息香酸）、２，５−ジクロロフェニルホスホン酸、５，５’−カルボニルビス（２−フルオロベンゼンホスホン酸）およびそのアルカリ金属塩などを挙げることができる。
プロトン酸基を有する芳香族ジヒドロキシ化合物としては、前記の芳香族ジヒドロキシ化合物のスルホン化物、アルキルスルホン化物のほか、２，５−ジヒドロキシ安息香酸、２，５−ジヒドロキシテレフタル酸、５，５’−メチレンジサリチル酸、５，５’−チオジサリチル酸、２，５−ジヒドロキシフェニルホスホン酸などのリン酸基を有する芳香族ジヒドロキシ化合物およびそのアルカリ金属塩などを挙げることができる。
【００３８】
なお、芳香族ジハライド化合物及び芳香族ジヒドロキシ化合物のスルホン化物、アルキルスルホン化物は、前記芳香族ジハライド化合物及び前記芳香族ジヒドロキシ化合物を、発煙硫酸などの公知のスルホン化剤でスルホン化する等の方法（Ｍａｃｒｏｍｏｌ． Ｃｈｅｍ． Ｐｈｙｓ．， １９９， １４２１ （１９９８））により得ることができる。
【００３９】
本発明のプロトン伝導性ブロック共重合体の形態に特に制限はないが、用途に応じて、粉体、溶剤に溶解あるいは分散したワニス、該ワニスを塗布及び乾燥して得られる膜などの形態とすることができる。なお、該プロトン伝導性ブロック共重合体を溶剤に溶解あるいは分散したワニスとする場合には、その溶剤に特に制限はなく、例えば、水、メタノール、エタノール、１−プロパノール、２−プロパノール、ブタノールなどのアルコール類、トルエン、キシレンなどの炭化水素類、塩化メチル、塩化メチレンなどのハロゲン化炭化水素類、ジクロロエチルエーテル、１，４−ジオキサン、テトラヒドロフランなどのエーテル類、酢酸メチル、酢酸エチルなどの脂肪酸エステル類、アセトン、メチルエチルケトンなどのケトン類のほか、Ｎ，Ｎ−ジメチルホルムアミド、Ｎ，Ｎ−ジメチルアセトアミド、Ｎ−メチル−２−ピロリドン、ジメチルスルホキシド、炭酸ジメチルなどの非プロトン性極性溶剤類などを単独で、あるいは混合して使用できる。
【００４０】
本発明のプロトン伝導性ブロック共重合体は、耐水性、低吸水性、低メタノール透過性と高プロトン伝導性を長期にわたり両立し得るので高分子電解質膜の材料として好適である。これは、一般式（１）で表される繰り返し構造単位を有するプロトン伝導を担うブロックと一般式（２）で表される繰り返し構造単位からなる耐水性に優れ吸水膨張の小さいブロックとが適度にミクロ相分離し、その相間が同一分子で結合されているため、プロトン伝導を担うブロックによる水への溶解性や吸水膨張が抑制され、界面の剥離もないと推定されることによる。また、燃料電池の発電と停止に伴う温度や湿度の変化によるプロトン酸基の脱離や膨張収縮によるクラックの発生が抑制される。
【００４１】
本発明のプロトン伝導性ブロック共重合体は、プロトン伝導膜とすることができる。本発明のプロトン伝導膜は、本発明のプロトン伝導性ブロック共重合体からなり、自立膜のみならず、基材、電極膜や他のプロトン伝導膜等に密着した塗膜も含む。本発明のプロトン伝導膜の厚みに特に制限はないが、自立膜である場合には１０〜２００μｍ、塗膜である場合には１〜１００μｍであることが好ましい。
【００４２】
本発明のプロトン伝導膜は、本発明のプロトン伝導性ブロック共重合体を含んでいればよく、電気導電性を有する導電材、水素の酸化反応、酸素の還元反応を促進する触媒などと複合化されていても良い。
【００４３】
導電材としては、電気伝導性物質であればいずれのものでもよく、各種金属や炭素材料などが上げられる。例えば、アセチレンブラック等のカーボンブラック、活性炭および黒鉛等が挙げられ、これらは単独あるいは混合して、粉末状あるいはシート状で使用される。
【００４４】
触媒としては、水素の酸化反応および酸素の還元反応を促進する金属であれば特に限定されないが、例えば鉛、鉄、マンガン、コバルト、クロム、ガリウム、バナジウム、タングステン、ルテニウム、イリジウム、パラジウム、白金、ロジウムまたはそれらの合金が挙げられる。
【００４５】
本発明のプロトン伝導性ブロック共重合体は、プロトン伝導性結着剤として用いることができる。 本発明のプロトン伝導性結着剤は、本発明のプロトン伝導性ブロック共重合体を含んでなり、粉体、塗膜として、あるいは、溶剤に溶解または懸濁したワニスとして、結着に供することができる。本発明のプロトン伝導性結着剤は、導電材料や触媒などの電極材料と混合して固めて電極とすることもできるし、電解質膜、電極およびセパレーターのそれぞれの間に挟んでつなぎ合わせるために用いることもできる。
【００４６】
本発明のプロトン伝導性結着剤は、本発明のプロトン伝導性ブロック共重合体に他のイオン伝導性高分子材料を組合わせて用いることもできる。このような他のイオン伝導性高分子材料としては、従来公知のプロトン酸基含有フッ素系高分子、あるいは、従来公知のプロトン酸基含有炭化水素系高分子を用いることができる。
この場合、結着剤中のプロトン伝導性ブロック共重合体の組成比は５ｗｔ％以上とすることが好ましく、それにより電極材料や高分子などとの高い接着性を示す。
【００４７】
さらに、本発明のプロトン伝導性ブロック共重合体は、その架橋体であっても良い。また本発明のプロトン伝導膜およびプロトン伝導性結着剤は、前記プロトン伝導性ブロック共重合体を架橋したものからなっても良い。本発明のプロトン伝導性ブロック共重合体は、一般式（１）で表される繰り返し構造単位を有するブロックを架橋させることにより、プロトン酸基を含むブロックの吸水による膨張をさらに抑制することができる、膜や結着剤とした場合にも同様の効果が得られる為好ましい。プロトン伝導性ブロック共重合体の架橋方法としては、プロトン酸基であるスルホン酸同士の脱硫縮合、芳香環とクロロアルキル基のフリーデルクラフト反応、クロロスルホン酸同士をスルホンアミド基を介して結合する架橋などが知られているが、架橋基がカルボニル基および芳香環に直接結合した炭素原子数１〜１０のアルキル基またはメチレン基である架橋は、以下の優位点を有するため好ましい。
１．架橋反応に伴う副生成物（脱離成分）がない。
２．プロトンブロック共重合体を構成する繰り返し単位１単位中にプロトン酸基、カルボニル基、アルキル基またはメチレン基をそれぞれ同時に１以上含有することができ、著しく高い架橋密度を得ることができる。
３．プロトン酸基が架橋反応に寄与しないため、架橋前後でのイオン交換基当量の変化がない。
４．架橋基の導入および架橋反応操作が容易である。
【００４８】
本発明のプロトン伝導性ブロック共重合体がカルボニル基と芳香環に直接結合した炭素原子数１〜１０のアルキル基またはメチレン基からなる架橋基を有する架橋性のプロトン伝導性ブロック共重合体である場合は光、電子線、熱により架橋させることができる。カルボニル基と芳香環に直接結合した炭素原子数１〜１０のアルキル基またはメチレン基の架橋機構について説明する。プロトン伝導性ブロック共重合体中のカルボニル基、および、プロトン伝導性ブロック共重合体中の芳香環に直接結合した炭素原子数１〜１０のアルキル基またはメチレン基は次のような形で架橋反応に関与していると推定される。下記反応式はアルキル基がメチル基の場合について示す。
【化４】

【００４９】
上記反応式に示すように、紫外線照射、電子線照射や加熱処理などによるエネルギー供給により、ベンゾフェノン上にラジカルが発生し、これがメチル基から水素を引き抜く。引き続き、ベンジルラジカルの二量化、ベンジルラジカルとアルコール性炭素ラジカルカップリング反応、アルコール性炭素ラジカルの二量化のような反応が起こることで、プロトン伝導性ブロック共重合体同士の架橋が起こると推定される。本発明にかかる架橋は、得られたプロトン伝導性ブロック共重合体をそのまま架橋しても良いが、プロトン伝導膜またはプロトン伝導性結着剤の形状に加工したものを架橋しても良い。
【００５０】
本発明にかかる架橋のうち、光による架橋を行う場合には、用いる光源としては、特に限定されないが、通常、紫外線、可視の範囲の光を照射できるものを用いる。具体的には、低圧水銀灯、高圧水銀灯、キセノンランプ、メタルハライドランプなどが挙げられる。また、照射線量は光の波長、照射されるプロトン伝導性ブロック共重合体の構造、プロトン伝導性ブロック共重合体の含有量、架橋温度、プロトン伝導膜の膜厚などにより異なるが、通常、５００〜１０００００ｍＪ／ｃｍ^２、好ましくは１０００〜３００００ｍＪ／ｃｍ^２である。本発明にかかる架橋はプロトン伝導膜を製膜したり、プロトン伝導性結着剤により電極材料、高分子膜又はセパレータを接合する際に同時に光照射を行うことで架橋させることもできる。
【００５１】
本発明にかかる架橋のうち、熱による架橋を行う場合には、その熱供給方法は特に限定されないが、通常のオーブンなどにより行うことができる。加熱時の温度または時間は、加熱するプロトン伝導性ブロック共重合体の構造およびプロトン伝導膜膜厚により異なるが、通常、１２０〜３００℃、好ましくは１５０〜２５０℃で、０．１〜１８０分間、好ましくは１〜６０分間である。熱架橋を２００℃以下で行う場合は公知のラジカル発生剤を添加することができる。例えば公知のラジカル発生剤としてはジクミルパーオキシド、ベンゾイルパーオキシド等の過酸化物や２，２’−アゾビスイソブチロニトリル等なのジアゾ化合物が挙げられる。
【００５２】
本発明にかかる熱による架橋は、プロトン伝導膜を製膜したり、プロトン伝導性結着剤により電極材料、高分子膜又はセパレータを接合する際に同時に、その熱により架橋させることもできる。
【００５３】
本発明の燃料電池は、前記プロトン伝導膜またはプロトン伝導性結着剤を用いてなり、好ましくは直接メタノール型燃料電池である。本発明の燃料電池は、膜の溶解、樹脂の溶出やプロトン酸基の脱離、燃料のクロスオーバーによる出力低下が生じにくく、プロトン伝導性の低下やメタノール透過量の増加による発電効率の低下がおこりにくい。そのため、高効率で信頼性に優れる。
【００５４】
【実施例】
以下、本発明を実施例によりさらに詳細に説明するが、本発明はこれにより何ら制限されるものではない。
【００５５】
実施例中の各種試験の試験方法は次に示すとおりである。
（ｉ）還元粘度（ηｉｎｈ）
プロトン伝導性ブロック共重合体またはそのオリゴマー０．５０ｇをジメチルスルホキシド１００ｍｌに加熱溶解したのち、３５℃においてウベローデ粘度計で測定した。
（ｉｉ）イオン交換基当量
プロトン伝導性ブロック共重合体またはプロトン伝導膜を密閉できるガラス容器中に精秤し、そこに過剰量の塩化カルシウム水溶液を添加して一晩攪拌した。系内に発生した塩化水素を０．１Ｎ水酸化ナトリウム標準水溶液にてフェノールフタレイン指示薬を用いて滴定し、計算した。
（ｉｉｉ）吸水率
窒素通風下１２０℃１２時間乾燥したプロトン伝導性ブロック共重合体またはプロトン伝導膜を、２３℃純水に２４時間浸漬し、その重量変化より算出した。（ｉｖ）イオン伝導度（９０℃、膜厚方向）
１Ｍ硫酸で湿潤したサンプルフィルムを、１ｃｍ^２の空孔を有する１００μｍ厚ＰＥＴフィルムの片面に白金電極を貼った測定用セル２個で挟み、空孔を１Ｍ硫酸水で満たした。これを９０℃の恒温槽内に設置してその抵抗値を測定した。サンプルフィルムを挟まなかった場合の抵抗値との差から、サンプルフィルム単体の抵抗値を求め、イオン伝導度（９０℃、膜厚方向）を算出した。なお、イオン伝導度の計算に必要な膜厚は乾燥状態でマイクロメータを用いて測定した。
（ｖ）メタノール透過性
室温にて蒸留水と、１ｍｏｌ／Ｌメタノール水溶液を、直径２３ｍｍφのプロトン伝導膜を介して接し、３時間までの蒸留水側のメタノール濃度変化をガスクロにて測定した。得られたメタノール濃度増加直線の傾きより、膜厚５０μｍでのメタノール透過性を計算した。
（ｖｉ）光架橋
メタルハライドランプを用いて片面７０００ｍＪ／ｃｍ^２の紫外線照射をプロトン伝導性ブロック共重合体からなる膜（フィルム）の両面に行い、光架橋させた。
【００５６】
（実施例１）
窒素導入管、温度計、トルエンで満たした分液器を備えた冷却器、及び撹拌装置を備えたフラスコに、３，３’−カルボニルビス（６−フルオロベンゼンスルホン酸ナトリウム）（以下ＤＳＤＦＢＰと略す）４２．２３ｇ（０．１０ｍｏｌ）、ビス（３−メチル−４ヒドロキシフェニル）メタン２５．６３ｇ（０．１０ｍｏｌ）および無水炭酸カリウム１６．５９ｇ（０．１２ｍｏｌ）を精秤した。これにジメチルスルホキシド２５５．５ｇおよびトルエン３１．９ｇを加え、窒素ガスを通じ撹拌しながら、１４１℃まで２時間かけて昇温した後、８時間反応を行った。反応はトルエン還留下に行い、留出する水は分液器により分液回収した。冷却後、反応物の一部をサンプリングし、ジメチルスルホキシド（以下ＤＭＳＯと略す）で希釈、その上澄みをメタノールに排出してオリゴマーを析出させ、アセトンで洗浄したのち、窒素通風下１５０℃４時間乾燥してオリゴマーを得た。得られたオリゴマーの還元粘度は０．１３ｄｌ／ｇ（ＤＭＳＯ）、ガラス転移温度は２５０℃以上（２５０℃までの測定で未検出）であった。
【００５７】
前記反応物に、４，４’−ジフルオロベンゾフェノン（以下ＤＦＢＰと略す）２１．８２ｇ（０．１０ｍｏｌ）、ビス（３−メチル−４−ヒドロキシフェニル）メタン２５．６３ｇ（０．１０ｍｏｌ）、無水炭酸カリウム１６．５９ｇ（０．１２ｍｏｌ）、ジメチルアセトアミド１７３．８ｇおよびトルエン１５．８ｇを添加し、窒素ガスを通じ撹拌しながら、１５７℃まで２時間かけて昇温した後、８時間反応を行った。
【００５８】
得られた粘稠な反応物をジメチルアセトアミド６００ｇで希釈した後、セライト濾過により副生する塩を除去した。このポリマー溶液を、メタノール１０Ｌに排出し、析出したポリマーを濾集、アセトンで洗浄した後、１５０℃４時間乾燥してプロトン酸基（スルホン酸ナトリウム基）を有するブロック共重合体９９．５ｇ（収率９３％）を得た。得られたブロック共重合体の還元粘度は１．２１ｄｌ／ｇ（ジメチルアセトアミド）、ガラス転移温度は２２０℃であった。
【００５９】
得られたブロック共重合体４ｇをＤＭＳＯ−ジメチルアセトアミド（１／１、ｗｔ／ｗｔ）混合液３６ｇに加熱溶解し、ポリマー濃度１０％の若干濁ったワニスを得た。得られたワニスを、スペーサーを有するブレードを用いてガラス基板上にキャストし、窒素通風下室温から２００℃まで２時間かけて昇温乾燥し、厚さ５０μｍの若干濁ったフィルムを得た。得られたフィルムを２Ｎ硫酸水溶液および純水に１日づつ浸漬してスルホン酸ナトリウム基のプロトン交換を行い、フリーのスルホン酸基を有するフィルムを得た。このフィルムのイオン交換基当量は５１０ｇ／ｍｏｌ、吸水率は１２％、イオン伝導度は０．１４Ｓ／ｃｍ、メタノール透過性は０．４μｍｏｌ／ｃｍ^２・ｍｉｎであった。
【００６０】
（実施例２）
トルエン３１．９ｇの代わりにトルエン３０．０ｇを用いた他は実施例１と同様にして還元粘度は０．３５ｄｌ／ｇ（ＤＭＳＯ）、ガラス転移温度２５０℃以上（２５０℃までの測定で未検出）のオリゴマーを得た。なお、オリゴマー化時の反応温度は１５２℃であった。
【００６１】
トルエン１５．８ｇの代わりにトルエン１７．７ｇを用いた他は、実施例１と同様にして反応物にモノマー類を添加、８時間の反応を行い、還元粘度１．０６ｄｌ／ｇ（ジメチルアセトアミドで測定）、ガラス転移温度２２３℃のブロック共重合体９７．２ｇ（収率９１％）を得た。
【００６２】
得られたブロック共重合体を用い、実施例１と同様にしてフリーのスルホン酸基を有する濁ったフィルムを得た。得られたフィルムのイオン交換基当量は５２０ｇ／ｍｏｌ、吸水率は１８％、イオン伝導度は０．１６Ｓ／ｃｍ、メタノール透過性は０．９μｍｏｌ／ｃｍ^２・ｍｉｎであった。
【００６３】
（比較例１）
窒素導入管、温度計、トルエンで満たした分液器を備えた冷却器、及び撹拌装置を備えたフラスコに、ＤＳＤＦＢＰ４２．２３ｇ（０．１０ｍｏｌ）およびＤＦＢＰ２１．８２ｇ（０．１０ｍｏｌ）、ビス（３−メチル−４−ヒドロキシフェニル）メタン５１．２７ｇ（０．２０ｍｏｌ）および無水炭酸カリウム３３．１７ｇ（０．２４ｍｏｌ）を精秤した。これにＤＭＳＯ４２９．３ｇおよびトルエン４７．７ｇを加え、窒素ガスを通じ撹拌しながら、１７６℃まで２時間かけて昇温した後、１０時間反応を行った。反応はトルエン還流下に行い、留出する水は分液器により分液回収した。
【００６４】
得られた粘稠な反応物をＤＭＳＯ６００ｇで希釈した後、セライト濾過により副生する塩を除去した。このポリマー溶液を、メタノール１０Ｌに排出し、析出したポリマーを濾集、アセトンで洗浄した後、１５０℃４時間乾燥してプロトン酸基（スルホン酸ナトリウム基）を有するランダム共重合体１１２．１ｇ（収率８８％）を得た。得られたランダム共重合体の還元粘度は０．９１ｄｌ／ｇ（ＤＭＳＯ）、ガラス転移温度は２５０℃以上（２５０℃までの測定で未検出）であった。
【００６５】
得られたランダム共重合体を用い、実施例１と同様にしてフリーのスルホン酸基を有する均質で透明なフィルムを得た。このフィルムのイオン交換基当量は５１０ｇ／ｍｏｌ、吸水率は５４％、イオン伝導度は０．２４Ｓ／ｃｍ、メタノール透過性は５．０μｍｏｌ／ｃｍ^２・ｍｉｎであった。
【００６６】
（比較例２）
ＤＳＤＦＢＰ４２．２３ｇ（０．１０ｍｏｌ）、ビス（３−メチル−４−ヒドロキシフェニル）メタン２５．６３ｇ（０．１０ｍｏｌ）、無水炭酸カリウム１６．５９ｇ（０．１２ｍｏｌ）、ＤＭＳＯ２５５．４ｇおよびトルエン２８．４ｇを用いた他は比較例１と同様にして、プロトン酸基（スルホン酸ナトリウム基）を有するホモポリマー５７．０ｇ（収率８９％）を得た。得られたプロトン酸基（スルホン酸ナトリウム基）を有するホモポリマーの還元粘度は０．８３ｄｌ／ｇ（ＤＭＳＯ）、ガラス転移温度は２５０℃以上（２５０℃までの測定で未検出）であった。
【００６７】
別にＤＦＢＰ２１．８２ｇ（０．１０ｍｏｌ）、ビス（３−メチル−４−ヒドロキシフェニル）メタン２５．６３ｇ（０．１０ｍｏｌ）、無水炭酸カリウム１６．５９ｇ（０．１２ｍｏｌ）、ＤＭＳＯ８６．９ｇ、ジメチルアセトアミド８６．９ｇおよびトルエン１９．３ｇを用いた他は比較例１と同様にして、ポリアリールエーテルケトンホモポリマー４０．７ｇ（収率９４％）を得た。なお、反応時の反応温度は１５５℃であった。得られたポリアリールエーテルケトンホモポリマーの還元粘度は０．６５ｄｌ／ｇ（ジメチルアセトアミド）、ガラス転移温度は２１７℃であった。
【００６８】
上記のプロトン酸基（スルホン酸ナトリウム基）を有するホモポリマー５．７ｇをＤＭＳＯ５１．３ｇに加熱溶解し、ポリマー濃度１０％の透明なワニスを得た。別に、上記のポリアリールエーテルケトンホモポリマー４．１ｇをジメチルアセトアミド３６．６ｇに加熱溶解し、ポリマー濃度１０％の透明なワニスを得た。これら２種のワニスを混合し、ポリマー濃度１０％の濁ったワニスを得た。得られたワニスをスペーサーを有するブレードを用いてガラス基板上にキャストし、窒素通風下室温から２００℃まで２時間かけて昇温乾燥し、厚さ４５〜５５μｍの凹凸のあるフィルムを得た。
【００６９】
得られたフィルムを２Ｎ硫酸水溶液および純水に１日づつ浸漬してスルホン酸ナトリウム基のプロトン交換を行い、フリーのスルホン酸基を有するフィルムを得た。このフィルムのイオン交換基当量は５４０ｇ／ｍｏｌ、吸水率は３９％、イオン伝導度は０．２０Ｓ／ｃｍ、メタノール透過性は４．６μｍｏｌ／ｃｍ^２・ｍｉｎであった。
【００７０】
（実施例３）
３，３’−スルホニルビス（６−クロロベンゼンスルホン酸ナトリウム）４９．１３ｇ（０．１０ｍｏｌ）、４，４’−ジヒドロキシビフェニル２０．４８ｇ（０．１１ｍｏｌ）、無水炭酸カリウム１６．５９ｇ（０．１２ｍｏｌ）、ジメチルアセトアミド２４１．８ｇおよびトルエン２６．９ｇを用いた他は実施例１と同様にして還元粘度は０．１７ｄｌ／ｇ（ジメチルアセトアミド）、ガラス転移温度は２５０℃以上（２５０℃までの測定で未検出）のオリゴマーを得た。なお、オリゴマー化時の反応温度は１５２℃であった。
【００７１】
この反応物に添加するものとして、４，４’−ジクロロジフェニルスルホン２８．７２ｇ（０．１０ｍｏｌ）、４，４’−ジヒドロキシビフェニル１６．７６ｇ（０．０９ｍｏｌ）、無水炭酸カリウム１６．５９ｇ（０．１２ｍｏｌ）、ジメチルアセトアミド１６０．２ｇおよびトルエン１７．８ｇを用いた他は実施例１と同様に８時間の反応を行い、還元粘度１．３０ｄｌ／ｇ（ジメチルアセトアミド）、ガラス転移温度２２９℃のブロック共重合体９３．３ｇ（収率９３％）を得た。なお、反応時の温度は１５３℃であった。
【００７２】
得られたブロック共重合体を用い、実施例１と同様にしてフリーのスルホン酸基を有する濁ったフィルムを得た。得られたフィルムのイオン交換基当量は４９５ｇ／ｍｏｌ、吸水率は１８％、イオン伝導度は０．１６Ｓ／ｃｍ、メタノール透過性は１．１μｍｏｌ／ｃｍ^２・ｍｉｎであった。
【００７３】
（実施例４）
窒素導入管、温度計、トルエンで満たした分液器を備えた冷却器、及び撹拌装置を備えたフラスコに、ＤＳＤＦＢＰ１４．７８ｇ（０．０３５ｍｏｌ）、ビス（３，５−ジメチル−４−ヒドロキシフェニル）メタン（以下ＴＭ−ＢＰＦと略す）８．９７ｇ（０．０３５ｍｏｌ）および無水炭酸カリウム６．０５ｇ（０．０４４ｍｏｌ）を精秤した。これにジメチルスルホキシド（以下ＤＭＳＯと略す）９０ｇおよびトルエン３８ｇを加え、窒素ガスを通じ撹拌しながら、１３５℃まで３０分かけて昇温した後、１２時間反応を行った。反応はトルエン還留下に行い、留出する水は分液器により分液回収した。冷却後、反応物の一部をサンプリングし、実施例１と同様にしてオリゴマーの還元粘度を測定したところ０．２５ｄｌ／ｇ（ＤＭＳＯ）であった。
【００７４】
前記反応物に、ＤＦＢＰ１４．１８ｇ（０．０６５ｍｏｌ）、ＴＭ−ＢＰＦ１６．６６ｇ（０．０６５ｍｏｌ）、無水炭酸カリウム１１．２３ｇ（０．０８１ｍｏｌ）、ＤＭＳＯ１１３ｇおよびトルエン４８ｇを添加し、窒素ガスを通じ撹拌しながら、１３５℃まで３０分時間かけて昇温した後、１２時間反応を行い、更にトルエンを留去して１６０℃で６時間反応を行った。
【００７５】
得られた粘稠な反応物をＤＭＳＯ７２ｇおよびＮ−メチル−２−ピロリドン（以下ＮＭＰと略す）１００ｇで希釈した後、セライト濾過により副生塩および未反応炭酸カリウムを除去した。このポリマー溶液を、ロータリーエバポレーターで濃縮後、ホモミキサーを用いてアセトンに排出し、析出したポリマーを濾集、アセトンで洗浄した後、１５０℃４時間乾燥してプロトン酸基（スルホン酸ナトリウム基）を有するブロック共重合体３４．４５ｇ（収率６８％）を得た。得られたブロック共重合体の還元粘度は１．２４ｄｌ／ｇ（ＮＭＰ）、ガラス転移温度は２１０℃であった。
【００７６】
得られたブロック共重合体２．００ｇをＮＭＰ１０．０ｇに加熱溶解し、ポリマー濃度約１７ｗｔ％のワニスを得た。得られたワニスを、スペーサーを有するブレードを用いてガラス基板上にキャストし、窒素通風下室温から２００℃まで４時間かけて昇温後２００℃で４時間保持し、厚さ５０μｍの若干濁ったフィルムを得た。得られたフィルムを（ｖｉ）記載の方法で光架橋した後、実施例１と同様にしてフリーのスルホン酸基を有するフィルムを得た。このフィルムのイオン交換基当量は７１０ｇ／ｍｏｌ、吸水率は１０％、イオン伝導度は０．１２Ｓ／ｃｍ、メタノール透過性は０．３μｍｏｌ／ｃｍ^２・ｍｉｎであった。
【００７７】
（実施例５）
反応時間を１６時間とした他は実施例４と同様にしてＤＳＤＦＢＰとＴＭ−ＢＰＦよりオリゴマーを合成した。ηは０．５８ｄｌ／ｇであった。
【００７８】
ＤＦＢＰの代わりに、４，４’−ジクロロジフェニルスルフォン１８．６７ｇ（０．０６５ｍｏｌ）、ＴＭ−ＢＰＦの代わりに４，４’−ジヒドロキシビフェニル１２．１０ｇ（０．０６５ｍｏｌ）を使用し、他は実施例４と同様にしてブロック共重合体を重合した。収量は４２．９ｇ（収率８９％）、還元粘度は１．３０ｄｌ／ｇ（ＮＭＰ）、ガラス転移温度は２２５℃であった。
【００７９】
実施例４と同様にして得られたブロック共重合体２．０ｇをＮＭＰ８．０ｇとＤＭＳＯ０．５ｇの混合溶剤に加熱溶解し、ポリマー濃度１９％のワニスを得た。得られたワニスを、スペーサーを有するブレードを用いてガラス基板上にキャストし、窒素通風下室温から２００℃まで４時間かけて昇温後２００℃で４時間保持し、厚さ５０μｍの若干濁ったフィルムを得た。得られたフィルムを（ｖｉ）記載の方法で光架橋した後、実施例１と同様にしてフリーのスルホン酸基を有するフィルムを得た。このフィルムのイオン交換基当量は６８０ｇ／ｍｏｌ、吸水率は１３ｗｔ％、イオン伝導度は０．１３Ｓ／ｃｍ、メタノール透過性は０．６μｍｏｌ／ｃｍ^２・ｍｉｎであった。
【００８０】
【発明の効果】
本発明により、耐水性、低吸水性、低メタノール透過性と高プロトン伝導性を有するプロトン酸基含有芳香族ポリエーテルブロック共重合体が提供される。該共重合体から得られる高分子電解質膜は、耐水性、低吸水性、低メタノール透過性と高プロトン伝導性を長期にわたり両立し、燃料電池用、特に直接メタノール型燃料電池用の高分子電解質膜として好適である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a proton conductive block copolymer which is used as a raw material of a proton conductive material used in a fuel cell or the like using hydrogen, alcohol, or the like as a fuel, and a proton conductive membrane comprising the same in a direct methanol fuel cell.
[0002]
[Prior art]
A polymer electrolyte fuel cell is a fuel cell that uses a proton-conducting polymer as the electrolyte, and the fuel, such as hydrogen or methanol, is electrochemically oxidized using oxygen or air to convert the chemical energy of the fuel into electrical energy. It is converted and extracted. The polymer electrolyte fuel cell includes a type using pure hydrogen supplied from a cylinder, a pipe or the like as a fuel, and a type using hydrogen generated from gasoline or methanol by a reformer. In addition, a direct methanol fuel cell (DMFC) that directly generates power using an aqueous methanol solution as a fuel has been developed. Since the DMFC does not require a reformer for generating hydrogen, a simple and compact system can be configured. The DMFC is particularly attracting attention as a power source for portable devices.
[0003]
A polymer electrolyte fuel cell is composed of a polymer electrolyte membrane, and a positive electrode and a negative electrode arranged in contact with both sides of the polymer electrolyte membrane. Fuel hydrogen or methanol is electrochemically oxidized at the negative electrode to generate protons and electrons. The proton moves inside the polymer electrolyte membrane to the positive electrode to which oxygen is supplied. On the other hand, the electrons generated at the negative electrode pass through the load connected to the battery and flow to the positive electrode, where protons and electrons react at the positive electrode to generate water. Therefore, high proton conductivity is required for the electrolyte membrane.
[0004]
As a polymer electrolyte membrane having high proton conductivity, a proton-containing group-containing fluoropolymer membrane is known. However, this proton-acid group-containing fluoropolymer membrane has problems that it is very expensive, hydrofluoric acid gas is generated when incinerated at the time of disposal, and the proton conductivity sharply drops under high temperature and low humidity. I was In addition, since the proton-containing group-containing fluoropolymer membrane has a high methanol permeability, when used as an electrolyte membrane of a DMFC, there is also a problem that a voltage drop and a power generation efficiency drop due to methanol crossover occur. .
[0005]
On the other hand, the development of a non-fluorinated polymer electrolyte membrane using a hydrocarbon polymer having a protonic acid group is also in progress. It is known that a hydrocarbon polymer containing a protonic acid group can be produced at low cost, there is no generation of halogen-based gas at the time of incineration, and there is little decrease in proton conductivity under high temperature and low humidity. However, for example, in the case of sulfonated polystyrene, the tertiary carbon of the main chain structure is easily attacked by radicals, and hydrogen in the α-position is easily released in the battery. It has been known.
[0006]
For this reason, a large number of aromatic hydrocarbon-based proton acid group-containing polymers having no aliphatic chain in the main chain have been developed (for example, see Non-Patent Document 1). In particular, it has been reported that a membrane made of sulfonated polyetheretherketone has excellent heat resistance and chemical durability and can be used for a long time as a polymer electrolyte (for example, see Non-Patent Document 2). ).
[0007]
In order to increase the proton conductivity of these proton acid group-containing aromatic hydrocarbon polymer membranes, it is necessary to increase the amount of proton acid groups introduced, that is, to reduce the ion exchange group equivalent. However, it is known that increasing the amount of proton acid groups introduced increases the hydrophilicity at the same time and increases the water absorption or becomes water-soluble (for example, see Patent Document 1). Since a fuel cell produces water as a by-product of the reaction between fuel and oxygen, a water-soluble resin cannot be used as a polymer electrolyte membrane for a fuel cell. In addition, even if it does not become water-soluble, if the water absorption is high, problems such as swelling of the membrane, a decrease in strength, and permeation of methanol from the negative electrode to the positive electrode through the absorbed water occur.
[0008]
Therefore, a method of improving water resistance and reducing water absorption by introducing a crosslinked structure into a polymer electrolyte membrane has been developed. For example, a proton acid group-containing crosslinked resin membrane obtained by sulfonating a polyphenylene oxide film crosslinked by a Friedel-Crafts reaction using fuming sulfuric acid has been reported (for example, see Patent Document 2). Further, desulfurization condensation between sulfonic acids in a crosslinked resin film containing a proton acid group using a Friedel-Crafts reaction between an aromatic ring and a chloroalkyl group (for example, see Patent Document 3) or a sulfonated polyetheretherketone film. Thus, a proton acid group-containing crosslinked resin membrane in which a sulfonate bond is formed (for example, see Patent Document 4) has been reported.
Further, a method of thermally decomposing a part of chlorosulfonic acid of a membrane made of chlorosulfonated polydiphenylmethane to form a cross-linking bond by a sulfonate bond, and then hydrolyzing the remaining chlorosulfonic acid to form a sulfonic acid (for example, And a cross-linking method by a sulfonamide bond using a chlorosulfonated polyetheretherketone and a diamine (see, for example, Patent Document 6).
[0009]
However, these methods require a treatment for crosslinking during or after film formation.Sulfuric acid, hydrochloric acid, and a crosslinking mechanism involving elimination of chlorine, etc. There have been problems such as different crosslink densities, difficulty in increasing the thickness of the film, formation of voids in the film, and corrosion of the production equipment by the desorbed acid gas.
[0010]
On the other hand, as a method that does not involve a chemical crosslinking reaction, a water-soluble, sulfonated resin having water absorbency and a water-soluble, basic polymer having no water absorbency are mixed to form a salt, thereby increasing water resistance. A method for improving the water absorption and reducing the water absorption is disclosed (for example, see Patent Document 7). However, salt formation is an equilibrium reaction. For example, since the dissociation and recombination are repeated by a protonic acid moving in the membrane during power generation, there is a problem that the sulfonated resin is gradually eluted.
[0011]
Further, a method has been disclosed in which a proton conductive polymer is filled in pores of a porous membrane to suppress physical expansion due to moisture absorption and reduce water absorption (for example, see Patent Document 8). However, these methods are prone to separation at the interface due to differences in the coefficient of thermal expansion and the coefficient of hygroscopic expansion between the proton conductive polymer and the porous membrane, resulting in a decrease in proton conductivity due to interface resistance and permeation of methanol from the interface. Therefore, it was difficult to obtain a highly reliable fuel cell.
[0012]
From the above, there has been a demand for a polymer electrolyte membrane that can achieve both water resistance, low water absorption, low methanol permeability, and high proton conductivity for a long time without requiring a crosslinking reaction or salt formation. Alternatively, there has been a demand for a polymer electrolyte membrane having no inconvenience such as voids in the membrane even when a crosslinking reaction occurs.
[0013]
[Patent Document 1]
JP-A-10-45913
[Patent Document 2]
JP-A-52-91788
[Patent Document 3]
JP-A-02-248434
[Patent Document 4]
JP 2000-501223 A
[Patent Document 5]
JP-A-52-99882
[Patent Document 6]
International Patent Publication No. WO 99/61141
[Patent Document 7]
WO 00/66254 specification
[Patent Document 8]
JP-A-2002-358979
[Non-patent document 1]
Macromol. Chem. Phys. , 199, 1421-1426 (1998).
[Non-patent document 2]
Tadashi Honma, Proceedings of the 3rd Separations Science and Technology Workshop, “Basics and Applications of Polymer Membrane Fuel Cells,” p. 17 (1999)
[0014]
[Problems to be solved by the invention]
An object of the present invention is to provide a proton conductive copolymer for a fuel cell, particularly for a direct methanol fuel cell, and to achieve both water resistance, low water absorption, low methanol permeability and high proton conductivity using the same for a long time. An object of the present invention is to provide a polymer electrolyte membrane.
[Means for Solving the Problems]
[0015]
That is, the present invention relates to a proton acid group-containing aromatic polyether block copolymer having a block structure composed of a specific repeating structural unit or a crosslinked product thereof, and further relates to a polymer electrolyte membrane and a proton conductive binder comprising the same. .
BEST MODE FOR CARRYING OUT THE INVENTION
[0016]
The proton conductive block copolymer of the present invention is characterized by having a block having a repeating structural unit represented by the following general formula (1) and a block including a repeating structural unit represented by the following general formula (2). Is a proton conductive block copolymer.
Embedded image

[In formulas (1) and (2), X ¹ ~ X ⁵ At least one is a protonic acid group and the others are each independently H or a protonic acid group; ¹ ~ A ⁴ Are each independently a direct bond, -CH ₂ -, -C (CH ₃ ) ₂ −, −C (CF ₃ ) ₂ -, -O-, -SO ₂ -Or -CO-, g, h, i, j, k, and l each independently represent 0 or 1, and the hydrogen atom of the aromatic ring is a hydrogen atom or -C _m H _{2m + 1} (M is an integer of 1 to 10), -Cl, -F, -CF ₃ Or -CN. ]
[0017]
Here, specific examples of the proton acid group in the present invention include sulfonic acid groups, carboxylic acid groups, and phosphonic acid groups represented by the following formulas (4) to (6). Among them, a sulfonic acid group represented by the following formula (4) is preferable, and a sulfonic acid group represented by n = 0 and Y = H in the following formula (4) is particularly preferable.
-C _n H _2n -SO ₃ Y (n is an integer of 0 to 10, Y is H, Na or K) (4)
-C _n H _2n -COOY (n is an integer of 0 to 10, Y is H, Na or K) (5)
-C _n H _2n -PO ₃ Y ₂ (N is an integer of 0 to 10, Y is H, Na or K) (6)
[0018]
The proton conductive block copolymer of the present invention has a water resistance comprising a block having proton repeating units having a repeating structural unit represented by the general formula (1) and a repeating structural unit represented by the general formula (2). It is made of a block that is excellent and has a small water absorption expansion. In the proton-conductive block copolymer of the present invention, it is considered that each block is moderately microphase-separated, and since the phases are bonded by the same molecule, dissolution in water or swelling due to proton-conducting blocks is prevented. It is considered to be suppressed by a block having excellent water resistance and small water absorption expansion. As a result, the proton-conductive block copolymer has a high content of proton acid groups, has high proton conductivity, is excellent in water resistance and low water absorption, and suppresses the permeation amount of methanol propagating with water. It is estimated that can be. Further, since the phases are bonded by the same molecule, a difference in expansion and contraction due to a change in temperature or humidity is suppressed, and the occurrence of cracks when formed into a film is suppressed.
[0019]
In addition, a mixture of a proton conductive block having a repeating structural unit represented by the general formula (1) and a block composed of the repeating structural unit represented by the general formula (2) and having excellent water resistance and small water absorption is 2 The polarities of the two blocks are extremely different, making it difficult to form a microphase-separated structure.Because the phases are not linked by molecular chains, the solubility of the proton conductive block in water and the expansion of water absorption cannot be suppressed, and it is formed into a membrane. In this case, there is a problem that cracks are formed in the phase interface due to a difference in expansion / shrinkage degree of the two phases due to a change in temperature or humidity, which is not preferable.
[0020]
Further, the random copolymer having the repeating structural units represented by the general formulas (1) and (2) is considered to be a single phase without the microphase separation of the above two structural units, and therefore, is generally responsible for proton conduction. When the proportion of the repeating structural unit represented by the formula (1) is increased, solubility in water and expansion of water absorption are promoted, and high proton conductivity, water resistance and low water absorption cannot be achieved at the same time.
[0021]
The proton exchange block copolymer according to the present invention preferably has an ion exchange group equivalent of 300 to 2000 g / mol, particularly preferably 500 to 1000 g / mol.
[0022]
Here, the ion exchange group equivalent is defined as the weight of resin per mole of protonic acid group, and means the reciprocal of the number of moles of protonic acid group per unit weight of resin. That is, the ratio of the block having the repeating structural unit represented by the general formula (1) is higher as the ion exchange group equivalent is smaller, and is lower as the ion exchange group equivalent is larger. If the ion exchange group equivalent is too small, the proportion of the block composed of the repeating structural unit represented by the general formula (2) is too small, so that the water resistance and low water absorption of the proton conductive block copolymer are insufficient. May be caused. When the ion exchange group equivalent is too large, the proportion of the block having the repeating structural unit represented by the general formula (1) is too small, so that sufficient proton conductivity may not be obtained.
[0023]
The water absorption of the proton conductive block copolymer of the present invention is preferably 5 to 20% by weight. Here, the water absorption can be determined from the rate of weight increase of the dried proton conductive block copolymer before and after immersion in pure water at 23 ° C. for 24 hours. The proton-conductive block copolymer of the present invention is excellent in that the water-absorption expansion is small and the water-absorption rate is low as compared with a random copolymer having the same ion exchange group equivalent.
[0024]
The block having a repeating structural unit represented by the general formula (1) of the present invention preferably has a reduced viscosity (concentration: 0.5 g / dl, measured at 35 ° C.) of 0.05 to 1.2 dl / g, more preferably It is preferably obtained by an oligomer having a concentration of 0.1 to 0.9 dl / g, more preferably 0.1 to 0.6 dl / g. If the molecular weight of the oligomer is too small (reduced viscosity is too small), it is not preferable because two blocks of the obtained proton conductive block copolymer do not undergo microphase separation. On the other hand, when the molecular weight of the oligomer is too large (reduced viscosity is too large), the two blocks are hardly finely phase-separated, and some of the molecular chains have a repeating structural unit represented by the general formula (1). It is not preferable because it is formed only from a block having the compound and has a problem that it is eluted in water.
[0025]
The oligomer may have another repeating structural unit as long as it has a repeating structural unit represented by the general formula (1). In this case, the proportion of the repeating structural unit represented by the general formula (1) in all the repeating structural units constituting the oligomer is preferably 100 to 30 mol%, and more preferably 100 to 50 mol%. Is particularly preferred.
[0026]
When the proportion of the block having the repeating structural unit represented by the general formula (1) is small, the proton conductivity is undesirably low. In addition, as a preferable example of another repeating structural unit, the repeating structural unit represented by General formula (2) is illustrated. By changing the ion exchange group equivalent of the block having the repeating structural unit represented by the general formula (1) by copolymerizing the repeating unit represented by the general formula (2), the proton of the proton-conductive block copolymer is changed. Properties such as conductivity, methanol permeability, and methanol resistance can be controlled.
[0027]
The block composed of the repeating structural unit represented by the general formula (2) according to the present invention suppresses dissolution in water and expansion of water absorption of the block having the repeating structural unit represented by the formula (1). Consists of structural units that are low and are less susceptible to hydrolysis. Here, the block composed of the repeating structural unit represented by the general formula (2) may be composed of two or more types of repeating structural units represented by the general formula (2). When the block contains an ester bond, a carbonate bond, an amide bond, an imide bond or a proton acid group, the block copolymer is susceptible to swelling due to hydrolysis or water absorption, and the solubility of the block copolymer in water and water absorption are increased. Not preferred. However, in order to make processability such as film formation of the proton conductive block copolymer easier, a repeating unit represented by the general formula (1) having a sulfonic acid group is used as a block, and with respect to all repeating structural units. As the protonic acid group, for example, a sulfonic acid group may be contained in an amount of 0.1 to 20 mol%.
[0028]
The proton conductive block copolymer of the present invention is constituted by an aromatic polyether structure, and has a linking group which is susceptible to hydrolysis of hot water, acid, alkali, alcohol and the like, and a group having low heat resistance and radical resistance. Therefore, when used in a fuel cell, deterioration or denaturation hardly occurs. When the proton-conductive block copolymer has an ester bond, a carbonate bond, an amide bond, an imide bond, an alkylene bond having an α-hydrogen which has low heat resistance and is easily attacked by a radical, an aliphatic ether bond, etc. However, it is not preferable because it is deteriorated in a fuel cell which is susceptible to hydrolysis of an acid, alkali, alcohol or the like.
[0029]
In the proton conductive block copolymer of the present invention, the repeating structural unit represented by the general formula (1) is particularly preferably a repeating structural unit represented by the following general formula (3). The proton acid group of the proton conductive block copolymer is an electron-withdrawing group -SO ₂ It is particularly preferable because it is bonded to an aromatic ring directly bonded to-or -CO-, and has a stronger bonding force than a proton acid group bonded to another aromatic ring, and is less susceptible to decomposition and dissociation. When an existing aromatic polyether is sulfonated with fuming sulfuric acid or the like, the electron withdrawing group -SO ₂ It is known that a sulfonic acid group is introduced into an aromatic ring to which-or -CO- is not directly bonded.
Embedded image

[X in the formula (3) ¹ And X ² Is a proton acid group, A ¹ Is -SO ₂ -Or -CO-, A ² Is a direct bond, -CH ₂ -, -C (CH ₃ ) ₂ −, −C (CF ₃ ) ₂ -, -O-, -SO ₂ -Or -CO-, h and i each independently represent 0 or 1, and the hydrogen atom of the aromatic ring is a hydrogen atom or -C _m H _{2m + 1} (M is an integer of 1 to 10), -Cl, -F, -CF ₃ Or -CN. ]
[0030]
The molecular weight of the proton-conductive block copolymer of the present invention is not particularly limited, but is preferably 0.5 to 2.0 dl / g in terms of reduced viscosity (concentration: 0.5 g / dl, measured at 35 ° C). The range of 0.7 to 1.5 dl / g is particularly preferred. If the molecular weight is too low, the strength of the block copolymer is low, and the resulting film may crack due to shrinkage and expansion during drying and moisture absorption. On the other hand, if the molecular weight is too high, the dissolution of the block copolymer in the solvent becomes insufficient, which may cause problems in film formation and the like.
[0031]
The method for producing the proton-conductive block copolymer of the present invention is not particularly limited. For example, it can be synthesized by the following known method.
(A) A monomer having a protonic acid group and a monomer having no protonic acid group or a monomer having a protonic acid group are polycondensed to obtain an oligomer having a block composed of a repeating structural unit represented by the general formula (1). A method of obtaining a proton-conductive block copolymer by condensation-polymerizing the oligomer and a monomer having a block comprising a structural unit represented by the general formula (2) or an oligomer thereof.
(B) An oligomer comprising a block having a repeating structural unit represented by the general formula (2) is obtained by condensation polymerization of a monomer having no protonic acid. A method of obtaining a proton-conductive block copolymer by condensation polymerization of the oligomer and a monomer having a block having a structural unit represented by the general formula (1) or an oligomer thereof.
(C) A monomer having no protonic acid group is polycondensed to form a precursor oligomer, and then a protonic acid group is introduced into the precursor oligomer by a method such as sulfonation to repeat the process represented by the general formula (1). The oligomer is composed of a block having a structural unit. A method of obtaining a proton-conductive block copolymer by condensation polymerization of the oligomer and a monomer having no proton acid group or the oligomer.
(D) A precursor block copolymer having a block composed of a structural unit into which a protonic acid group is easily introduced and a block composed of a repeating structural unit represented by the general formula (2) into which a protonic acid group is not easily introduced is synthesized. I do. In the precursor block copolymer, a proton acid group is introduced by a method such as sulfonation only into a block composed of a structural unit into which a proton acid group is easily introduced, and a repeating structural unit represented by the general formula (1) is obtained. A method of obtaining a proton-conductive block copolymer as a block.
[0032]
The method for producing a proton-conductive block copolymer of the present invention is preferably the above-mentioned method (A) because the ion-exchange group equivalent of the proton-conductive block copolymer can be easily controlled. In particular, a method in which a monomer having a protonic acid group is polycondensed to form an oligomer having a repeating structural unit represented by the general formula (1), and this oligomer is reacted with a monomer or an oligomer having no protonic acid group is known as a protonic acid. It is more preferable that the control of the block having a group is easy.
[0033]
The method for producing a proton-conductive block copolymer of the present invention is, specifically, an aromatic dihalide compound having a protonic acid group and an aromatic dihydroxy compound, or an aromatic dihalide compound and an aromatic compound having a protonic acid group. Polycondensation of a dihydroxy compound or an aromatic dihalide compound having a proton acid group with an aromatic dihydroxy compound having a proton acid group to synthesize a proton acid group-containing oligomer having a repeating structural unit represented by the general formula (1) I do. The resulting oligomer preferably has a reduced viscosity at 35 ° C. of 0.05 to 1.2 dl / g, and the molecular weight of the oligomer depends on the reaction time, reaction temperature, charge ratio of the aromatic dihalide compound and the aromatic dihydroxy compound, and the like. It can be controlled by a general method.
[0034]
An aromatic dihalide compound and an aromatic dihydroxy compound are added to the oligomer and polycondensed to form a repeating structural unit block represented by the general formula (2) to form a block copolymer. A block copolymer is obtained by adding an oligomer comprising a repeating structural unit represented by the general formula (2) obtained by polycondensing an aromatic dihalide compound and an aromatic dihydroxy compound, and performing polycondensation.
[0035]
Here, typical specific examples of the monomers used in the production of the proton conductive block copolymer according to the present invention will be illustrated below.
Examples of the aromatic dihalide compound include 4,4'-difluorobenzophenone, 3,3'-difluorobenzophenone, 4,4'-dichlorobenzophenone, 3,3'-dichlorobenzophenone, 4,4'-difluorodiphenyl sulfone, 4,4'-dichlorodiphenylsulfone, 1,4-difluorobenzene, 1,3-difluorobenzene, 2,6-dichlorobenzonitrile, 4,4'-difluorobiphenyl, 3,3'-dibromo-4,4 ' -Difluorobiphenyl, 4,4'-difluorodiphenylmethane, 4,4'-dichlorodiphenylmethane, 4,4'-difluorodiphenylether, 2,2-bis (4-fluorophenyl) propane, 2,2-bis (4-chlorophenyl ) Propane, α, α'-bis (4-fluorophenyl) -1,4-di Sopropylbenzene, 3,3′-dimethyl-4,4′-difluorobenzophenone, 3,3′-diethyl-4,4′-difluorobenzophenone, 3,3 ′, 5,5′-tetramethyl-4,4 '-Difluorobenzophenone, 3,3'-dimethyl-4,4'-dichlorobenzophenone, 3,3', 4,4'-tetramethyl-5,5'-dichlorobenzophenone, 3,3'-dimethyl-4, 4'-difluorodiphenylsulfone, 3,3'-dimethyl-4,4'-dichlorodiphenylsulfone, 2,5-difluorotoluene, 2,5-difluoroethylbenzene, 2,5-difluoro-p-xylene and the like. , Or a mixture of two or more.
[0036]
Examples of the aromatic dihydroxy compound include hydroquinone, resorcin, catechol, 4,4′-dihydroxybiphenyl, 4,4′-dihydroxydiphenyl sulfide, 4,4′-dihydroxydiphenylmethane, 4,4′-dihydroxydiphenyl ether, 4'-dihydroxydiphenylsulfone, 4,4'-dihydroxybenzophenone, 2,2-bis (4-hydroxyphenyl) propane, 1,1,1,3,3,3-hexafluoro-2,2-bis (4 -Hydroxyphenyl) propane, 1,4-bis (4-hydroxyphenyl) benzene, α, α′-bis (4-hydroxyphenyl) -1,4-dimethylbenzene, α, α′-bis (4-hydroxyphenyl ) -1,4-Diisopropylbenzene, α, α′-bis (4-hydroxy L) -1,3-diisopropylbenzene, 4,4′-dihydroxybenzophenone, 1,4-bis (4-hydroxybenzoyl) benzene, 3,3-difluoro-4,4′-dihydroquibiphenyl, 2-methylhydroquinone , 2-ethylhydroquinone, 2-isopropylhydroquinone, 2-octylhydroquinone, 2,3-dimethylhydroquinone, 2,3-diethylhydroquinone, 2,5-dimethylhydroquinone, 2,5-diethylhydroquinone, 2,5-diisopropylhydroquinone , 2,6-dimethylhydroquinone, 2,3,5-trimethylhydroquinone, 2,3,5,6-tetramethylhydroquinone, 3,3'-dimethyl-4,4'-dihydroxybiphenyl, 3,3 ', 5 , 5'-Tetramethyl-4,4'-dihydrido Xybiphenyl, 3,3'-dimethyl-4,4'-dihydroxydiphenylmethane, 3,3 ', 5,5'-tetramethyl-4,4'-dihydroxydiphenylmethane, 3,3', 5,5'-tetraethyl -4,4'-dihydroxydiphenylmethane, 3,3'-dimethyl-4,4'-dihydroxydiphenylether, 3,3 ', 5,5'-tetramethyl-4,4'-dihydroxydiphenylether, 3,3'- Dimethyl-4,4'-dihydroxydiphenyl sulfide, 3,3 ', 5,5'-tetramethyl-4,4'-dihydroxydiphenyl sulfide, 3,3'-dimethyl-4,4'-dihydroxydiphenyl sulfone, 3 , 3 ', 5,5'-Tetramethyl-4,4'-dihydroxydiphenylsulfone, 2,2-bis (3-methyl-4-hydroxyphenyl) pro Pan, 2,2-bis (3-ethyl-4-hydroxyphenyl) propane, 2,2-bis (3,5-dimethyl-4-hydroxyphenyl) propane, α, α′-bis (3-methyl-4 -Hydroxyphenyl) -1,4-diisopropylbenzene, α, α′-bis (3,5-dimethyl-4-hydroxyphenyl) -1,4-diisopropylbenzene, α, α′-bis (3-methyl-4 -Hydroxyphenyl) -1,3-diisopropylbenzene, α, α′-bis (3,5-dimethyl-4-hydroxyphenyl) -1,3-diisopropylbenzene, etc., alone or as a mixture of two or more. Can be used.
[0037]
Examples of the aromatic dihalide compound having a protonic acid group include, in addition to the sulfonated and alkyl sulfonated aromatic dihalide compounds, 2,5-dichlorobenzoic acid, 2,5-difluorobenzoic acid, and 5,5′-carbonyl. Bis (2-fluorobenzoic acid), 5,5'-sulfonylbis (2-fluorobenzoic acid), 2,5-dichlorophenylphosphonic acid, 5,5'-carbonylbis (2-fluorobenzenephosphonic acid) and alkalis thereof Metal salts and the like can be mentioned.
Examples of the aromatic dihydroxy compound having a protonic acid group include, in addition to the sulfonated and alkyl sulfonated compounds of the aromatic dihydroxy compound, 2,5-dihydroxybenzoic acid, 2,5-dihydroxyterephthalic acid, and 5,5′-methylene Aromatic dihydroxy compounds having a phosphate group such as disalicylic acid, 5,5′-thiodisalicylic acid, and 2,5-dihydroxyphenylphosphonic acid, and alkali metal salts thereof can be mentioned.
[0038]
Incidentally, the sulfonated product and the alkyl sulfonated product of the aromatic dihalide compound and the aromatic dihydroxy compound can be obtained by a method such as sulfonating the aromatic dihalide compound and the aromatic dihydroxy compound with a known sulfonating agent such as fuming sulfuric acid. Macromol. Chem. Phys., 199, 1421 (1998)).
[0039]
The form of the proton-conductive block copolymer of the present invention is not particularly limited, but depending on the application, powder, a varnish dissolved or dispersed in a solvent, and a form such as a film obtained by applying and drying the varnish. can do. When a varnish is prepared by dissolving or dispersing the proton-conductive block copolymer in a solvent, the solvent is not particularly limited, and examples thereof include water, methanol, ethanol, 1-propanol, 2-propanol, and butanol. Alcohols, hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as methyl chloride and methylene chloride, ethers such as dichloroethyl ether, 1,4-dioxane and tetrahydrofuran, and fatty acids such as methyl acetate and ethyl acetate In addition to esters, acetone, ketones such as methyl ethyl ketone, aprotic polar solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethyl carbonate, etc. Can be used alone or mixed That.
[0040]
The proton-conductive block copolymer of the present invention is suitable as a material for a polymer electrolyte membrane because it can achieve both water resistance, low water absorption, low methanol permeability and high proton conductivity for a long period of time. This is because a block having proton repeating properties having a repeating structural unit represented by the general formula (1) and a block composed of a repeating structural unit represented by the general formula (2) and having excellent water resistance and small water absorption expansion are appropriately formed. Because microphase separation is performed and the phases are bonded by the same molecule, solubility in water and expansion due to water absorption by the block responsible for proton conduction are suppressed, and it is estimated that there is no separation of the interface. In addition, the generation of cracks due to desorption and expansion and contraction of proton acid groups due to changes in temperature and humidity due to power generation and shutdown of the fuel cell is suppressed.
[0041]
The proton conductive block copolymer of the present invention can be used as a proton conductive membrane. The proton conductive membrane of the present invention is made of the proton conductive block copolymer of the present invention, and includes not only a free-standing membrane but also a coating film adhered to a substrate, an electrode membrane, another proton conductive membrane, or the like. Although the thickness of the proton conducting membrane of the present invention is not particularly limited, it is preferably 10 to 200 μm for a self-supporting membrane and 1 to 100 μm for a coating.
[0042]
The proton conductive membrane of the present invention only needs to contain the proton conductive block copolymer of the present invention, and is composited with a conductive material having electric conductivity, a catalyst that promotes an oxidation reaction of hydrogen, a reduction reaction of oxygen, and the like. It may be.
[0043]
As the conductive material, any material may be used as long as it is an electrically conductive material, such as various metals and carbon materials. For example, carbon black such as acetylene black, activated carbon, graphite and the like can be mentioned, and these can be used alone or as a mixture in powder or sheet form.
[0044]
The catalyst is not particularly limited as long as it is a metal that promotes the oxidation reaction of hydrogen and the reduction reaction of oxygen.For example, lead, iron, manganese, cobalt, chromium, gallium, vanadium, tungsten, ruthenium, iridium, palladium, platinum, Rhodium or alloys thereof.
[0045]
The proton conductive block copolymer of the present invention can be used as a proton conductive binder. The proton conductive binder of the present invention comprises the proton conductive block copolymer of the present invention, and is subjected to binding as a powder, a coating film, or as a varnish dissolved or suspended in a solvent. Can be. The proton conductive binder of the present invention can be mixed with an electrode material such as a conductive material or a catalyst and solidified to form an electrode, or an electrolyte membrane, an electrode and a separator in order to connect them. It can also be used.
[0046]
The proton conductive binder of the present invention can also be used by combining the proton conductive block copolymer of the present invention with another ion conductive polymer material. As such another ion conductive polymer material, a conventionally known proton-acid group-containing fluoropolymer or a conventionally known proton-acid group-containing hydrocarbon polymer can be used.
In this case, the composition ratio of the proton conductive block copolymer in the binder is preferably set to 5 wt% or more, thereby exhibiting high adhesion to an electrode material, a polymer, or the like.
[0047]
Further, the proton conductive block copolymer of the present invention may be a crosslinked product thereof. Further, the proton conductive membrane and the proton conductive binder of the present invention may be formed by cross-linking the proton conductive block copolymer. The proton conductive block copolymer of the present invention can further suppress the expansion of the block containing a proton acid group due to water absorption by crosslinking a block having a repeating structural unit represented by the general formula (1). It is also preferable to use a film or a binder because similar effects can be obtained. The crosslinking method of the proton conductive block copolymer includes desulfurization condensation between sulfonic acids, which are protonic acid groups, Friedel-Crafts reaction between aromatic rings and chloroalkyl groups, and bonding of chlorosulfonic acids to each other via sulfonamide groups. Although cross-linking is known, cross-linking in which the cross-linking group is an alkyl group having 1 to 10 carbon atoms or a methylene group directly bonded to a carbonyl group and an aromatic ring has the following advantages and is therefore preferable.
1. There are no by-products (elimination components) associated with the crosslinking reaction.
2. One unit of the repeating unit constituting the proton block copolymer can contain one or more protonic acid groups, carbonyl groups, alkyl groups or methylene groups at the same time, and a remarkably high crosslinking density can be obtained.
3. Since the protonic acid groups do not contribute to the crosslinking reaction, there is no change in ion exchange group equivalent before and after crosslinking.
4. It is easy to introduce a crosslinking group and perform a crosslinking reaction operation.
[0048]
The proton-conductive block copolymer of the present invention is a cross-linkable proton-conductive block copolymer having a cross-linking group comprising an alkyl group having 1 to 10 carbon atoms or a methylene group directly bonded to a carbonyl group and an aromatic ring. In this case, crosslinking can be performed by light, electron beam, or heat. The cross-linking mechanism of an alkyl group having 1 to 10 carbon atoms or a methylene group directly bonded to a carbonyl group and an aromatic ring will be described. The carbonyl group in the proton-conductive block copolymer and the alkyl group or methylene group having 1 to 10 carbon atoms directly bonded to the aromatic ring in the proton-conductive block copolymer are cross-linked in the following manner. It is presumed to be involved in The following reaction formula shows the case where the alkyl group is a methyl group.
Embedded image

[0049]
As shown in the above reaction formula, radicals are generated on benzophenone by energy supply by ultraviolet irradiation, electron beam irradiation, heat treatment, and the like, and hydrogen is extracted from a methyl group. Subsequently, it is presumed that cross-linking between proton-conductive block copolymers occurs due to reactions such as dimerization of benzyl radical, coupling reaction of benzyl radical with alcoholic carbon radical, and dimerization of alcoholic carbon radical. You. In the crosslinking according to the present invention, the obtained proton-conductive block copolymer may be cross-linked as it is, or may be cross-linked into a proton-conductive membrane or a proton-conductive binder that has been processed into a shape.
[0050]
In the case of performing cross-linking by light among the cross-links according to the present invention, the light source to be used is not particularly limited, but usually a light source capable of irradiating ultraviolet light or visible light is used. Specific examples include a low-pressure mercury lamp, a high-pressure mercury lamp, a xenon lamp, and a metal halide lamp. The irradiation dose varies depending on the wavelength of light, the structure of the irradiated proton-conductive block copolymer, the content of the proton-conductive block copolymer, the crosslinking temperature, the thickness of the proton-conductive membrane, and the like. ~ 100000mJ / cm ² , Preferably 1000 to 30000 mJ / cm ² It is. The cross-linking according to the present invention can also be performed by forming a proton-conductive membrane or simultaneously irradiating light when the electrode material, the polymer membrane, or the separator is joined with the proton-conductive binder.
[0051]
In the case of performing cross-linking by heat in the cross-linking according to the present invention, the heat supply method is not particularly limited, but it can be performed by a usual oven or the like. The heating temperature or time varies depending on the structure of the proton-conductive block copolymer to be heated and the thickness of the proton-conductive membrane, but is usually from 120 to 300 ° C, preferably from 150 to 250 ° C, for from 0.1 to 180 minutes. , Preferably for 1 to 60 minutes. When performing thermal crosslinking at a temperature of 200 ° C. or lower, a known radical generator can be added. For example, known radical generators include peroxides such as dicumyl peroxide and benzoyl peroxide and diazo compounds such as 2,2'-azobisisobutyronitrile.
[0052]
The cross-linking by heat according to the present invention can also be carried out by the heat at the same time as forming a proton conductive membrane or joining an electrode material, a polymer membrane, or a separator with a proton conductive binder.
[0053]
The fuel cell of the present invention uses the proton conductive membrane or the proton conductive binder, and is preferably a direct methanol fuel cell. In the fuel cell of the present invention, the dissolution of the membrane, the elution of the resin and the elimination of the proton acid group, the output decrease due to the fuel crossover hardly occurs, and the decrease in the proton conductivity and the decrease in the power generation efficiency due to the increase in the amount of methanol permeation are reduced. Less likely to happen. Therefore, it is highly efficient and excellent in reliability.
[0054]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.
[0055]
Test methods for various tests in the examples are as follows.
(I) Reduced viscosity (ηinh)
After heating and dissolving 0.50 g of the proton-conductive block copolymer or its oligomer in 100 ml of dimethyl sulfoxide, it was measured at 35 ° C. with an Ubbelohde viscometer.
(Ii) ion exchange group equivalent
The proton-conducting block copolymer or the proton-conducting membrane was precisely weighed in a glass container capable of closing, and an excess amount of an aqueous calcium chloride solution was added thereto, followed by stirring overnight. Hydrogen chloride generated in the system was titrated with a standard aqueous solution of 0.1 N sodium hydroxide using a phenolphthalein indicator and calculated.
(Iii) Water absorption
The proton-conductive block copolymer or the proton-conductive membrane dried at 120 ° C. for 12 hours under nitrogen ventilation was immersed in pure water at 23 ° C. for 24 hours, and the weight change was calculated. (Iv) Ionic conductivity (90 ° C., thickness direction)
1cm sulfuric acid wet sample film 1cm ² Was sandwiched between two measurement cells each having a platinum electrode adhered to one surface of a 100 μm-thick PET film having pores, and the pores were filled with 1M aqueous sulfuric acid. This was placed in a 90 ° C. thermostat and its resistance was measured. The resistance value of the sample film alone was determined from the difference from the resistance value when the sample film was not sandwiched, and the ionic conductivity (90 ° C., thickness direction) was calculated. The film thickness required for calculating the ion conductivity was measured using a micrometer in a dry state.
(V) methanol permeability
At room temperature, distilled water and a 1 mol / L methanol aqueous solution were brought into contact with each other via a proton conductive membrane having a diameter of 23 mmφ, and the change in methanol concentration on the distilled water side for up to 3 hours was measured by gas chromatography. The methanol permeability at a film thickness of 50 μm was calculated from the slope of the obtained methanol concentration increasing line.
(Vi) Photocrosslinking
7000mJ / cm on one side using a metal halide lamp ² UV irradiation was performed on both surfaces of a membrane (film) made of a proton-conductive block copolymer to cause photocrosslinking.
[0056]
(Example 1)
A flask equipped with a nitrogen inlet tube, a thermometer, a condenser equipped with a separator filled with toluene, and a stirring device was charged with 3,3′-carbonylbis (sodium 6-fluorobenzenesulfonate) (hereinafter abbreviated as DSDFBP). ) 42.23 g (0.10 mol), 25.63 g (0.10 mol) bis (3-methyl-4hydroxyphenyl) methane and 16.59 g (0.12 mol) of anhydrous potassium carbonate were precisely weighed. 255.5 g of dimethyl sulfoxide and 31.9 g of toluene were added thereto, and the mixture was heated to 141 ° C. over 2 hours while stirring with nitrogen gas, and then reacted for 8 hours. The reaction was performed under toluene distillation, and the distilled water was separated and collected by a separator. After cooling, a part of the reaction product was sampled, diluted with dimethyl sulfoxide (hereinafter abbreviated as DMSO), the supernatant was discharged into methanol to precipitate an oligomer, washed with acetone, and dried at 150 ° C. for 4 hours under a nitrogen stream. Thus, an oligomer was obtained. The reduced viscosity of the obtained oligomer was 0.13 dl / g (DMSO), and the glass transition temperature was 250 ° C. or higher (not detected by measurement up to 250 ° C.).
[0057]
To the reaction product, 21.82 g (0.10 mol) of 4,4′-difluorobenzophenone (hereinafter abbreviated as DFBP), 25.63 g (0.10 mol) of bis (3-methyl-4-hydroxyphenyl) methane, and anhydrous carbonic acid After adding 16.59 g (0.12 mol) of potassium, 173.8 g of dimethylacetamide, and 15.8 g of toluene, the mixture was heated to 157 ° C. over 2 hours while stirring with nitrogen gas, and then reacted for 8 hours.
[0058]
After the obtained viscous reaction product was diluted with dimethylacetamide (600 g), salts produced as by-products were removed by celite filtration. The polymer solution was discharged into 10 L of methanol, and the precipitated polymer was collected by filtration, washed with acetone, dried at 150 ° C. for 4 hours, and subjected to 99.5 g of a block copolymer having a protonic acid group (sodium sulfonate group) ( Yield 93%). The reduced viscosity of the obtained block copolymer was 1.21 dl / g (dimethylacetamide), and the glass transition temperature was 220 ° C.
[0059]
4 g of the obtained block copolymer was heated and dissolved in 36 g of a mixed solution of DMSO-dimethylacetamide (1/1, wt / wt) to obtain a slightly cloudy varnish having a polymer concentration of 10%. The obtained varnish was cast on a glass substrate using a blade having a spacer, and was heated and dried from room temperature to 200 ° C. for 2 hours under nitrogen ventilation to obtain a slightly cloudy film having a thickness of 50 μm. The obtained film was immersed in a 2N aqueous solution of sulfuric acid and pure water every day to perform proton exchange of sodium sulfonate groups to obtain a film having free sulfonic acid groups. This film has an ion exchange group equivalent of 510 g / mol, a water absorption of 12%, an ionic conductivity of 0.14 S / cm, and a methanol permeability of 0.4 μmol / cm. ² Min.
[0060]
(Example 2)
Except that 30.0 g of toluene was used instead of 31.9 g of toluene, the reduced viscosity was 0.35 dl / g (DMSO), and the glass transition temperature was 250 ° C. or higher (not detected up to 250 ° C.). ) Was obtained. The reaction temperature during the oligomerization was 152 ° C.
[0061]
Except that 17.7 g of toluene was used instead of 15.8 g of toluene, monomers were added to the reaction product in the same manner as in Example 1, and a reaction was carried out for 8 hours to obtain a reduced viscosity of 1.06 dl / g (dimethylacetamide). Measurement), 97.2 g (91% yield) of a block copolymer having a glass transition temperature of 223 ° C.
[0062]
Using the obtained block copolymer, a cloudy film having free sulfonic acid groups was obtained in the same manner as in Example 1. The obtained film has an ion exchange group equivalent of 520 g / mol, a water absorption of 18%, an ionic conductivity of 0.16 S / cm, and a methanol permeability of 0.9 μmol / cm. ² Min.
[0063]
(Comparative Example 1)
In a flask equipped with a nitrogen inlet tube, a thermometer, a condenser equipped with a separator filled with toluene, and a stirring device, 42.23 g (0.10 mol) of DSDFBP, 21.82 g (0.10 mol) of DFBP, and bis (3 -Methyl-4-hydroxyphenyl) methane 51.27 g (0.20 mol) and 33.17 g (0.24 mol) of anhydrous potassium carbonate were precisely weighed. 429.3 g of DMSO and 47.7 g of toluene were added thereto, and the mixture was heated to 176 ° C. over 2 hours while stirring with nitrogen gas, and then reacted for 10 hours. The reaction was carried out under reflux of toluene, and the distilled water was separated and collected by a separator.
[0064]
After the obtained viscous reaction product was diluted with 600 g of DMSO, salts produced as by-products were removed by filtration through Celite. This polymer solution was discharged into 10 L of methanol, and the precipitated polymer was collected by filtration, washed with acetone, dried at 150 ° C. for 4 hours, and dried to obtain 112.1 g of a random copolymer having a protonic acid group (sodium sulfonate group) ( (88% yield). The reduced viscosity of the obtained random copolymer was 0.91 dl / g (DMSO), and the glass transition temperature was 250 ° C. or higher (not detected by measurement up to 250 ° C.).
[0065]
Using the obtained random copolymer, a homogeneous and transparent film having free sulfonic acid groups was obtained in the same manner as in Example 1. This film has an ion exchange group equivalent of 510 g / mol, a water absorption of 54%, an ionic conductivity of 0.24 S / cm, and a methanol permeability of 5.0 μmol / cm. ² Min.
[0066]
(Comparative Example 2)
DSDFBP 42.23 g (0.10 mol), bis (3-methyl-4-hydroxyphenyl) methane 25.63 g (0.10 mol), anhydrous potassium carbonate 16.59 g (0.12 mol), DMSO 255.4 g and toluene 28.4 g Was carried out in the same manner as in Comparative Example 1 except that 57.0 g (89% yield) of a homopolymer having a protonic acid group (sodium sulfonate group) was obtained. The reduced viscosity of the obtained homopolymer having a protonic acid group (sodium sulfonate group) was 0.83 dl / g (DMSO), and the glass transition temperature was 250 ° C. or higher (not detected by measurement up to 250 ° C.).
[0067]
Separately, DFBP 21.82 g (0.10 mol), bis (3-methyl-4-hydroxyphenyl) methane 25.63 g (0.10 mol), anhydrous potassium carbonate 16.59 g (0.12 mol), DMSO 86.9 g, dimethylacetamide 86 In the same manner as in Comparative Example 1 except that 9.9 g and 19.3 g of toluene were used, 40.7 g (yield 94%) of a polyaryletherketone homopolymer was obtained. The reaction temperature during the reaction was 155 ° C. The reduced viscosity of the obtained polyaryletherketone homopolymer was 0.65 dl / g (dimethylacetamide), and the glass transition temperature was 217 ° C.
[0068]
5.7 g of the above-mentioned homopolymer having a protonic acid group (sodium sulfonate group) was dissolved by heating in 51.3 g of DMSO to obtain a transparent varnish having a polymer concentration of 10%. Separately, 4.1 g of the above polyaryletherketone homopolymer was dissolved by heating in 36.6 g of dimethylacetamide to obtain a transparent varnish having a polymer concentration of 10%. These two varnishes were mixed to obtain a cloudy varnish having a polymer concentration of 10%. The obtained varnish was cast on a glass substrate using a blade having a spacer, and heated and dried from room temperature to 200 ° C. for 2 hours under nitrogen ventilation to obtain a 45-55 μm-thick uneven film.
[0069]
The obtained film was immersed in a 2N aqueous solution of sulfuric acid and pure water every day to perform proton exchange of sodium sulfonate groups, thereby obtaining a film having free sulfonic acid groups. The ion exchange group equivalent of this film is 540 g / mol, the water absorption is 39%, the ion conductivity is 0.20 S / cm, and the methanol permeability is 4.6 μmol / cm. ² Min.
[0070]
(Example 3)
49.13 g (0.10 mol) of 3,3′-sulfonylbis (sodium 6-chlorobenzenesulfonate), 20.48 g (0.11 mol) of 4,4′-dihydroxybiphenyl, 16.59 g (0.12 mol) of anhydrous potassium carbonate ), 241.8 g of dimethylacetamide and 26.9 g of toluene, except that the reduced viscosity was 0.17 dl / g (dimethylacetamide) and the glass transition temperature was 250 ° C. or more (measured up to 250 ° C.). (Not detected). The reaction temperature during the oligomerization was 152 ° C.
[0071]
As additions to this reaction product, 28.72 g (0.10 mol) of 4,4'-dichlorodiphenylsulfone, 16.76 g (0.09 mol) of 4,4'-dihydroxybiphenyl, and 16.59 g (0. .12 mol), a reaction was carried out for 8 hours in the same manner as in Example 1 except that 160.2 g of dimethylacetamide and 17.8 g of toluene were used, and a reduced viscosity of 1.30 dl / g (dimethylacetamide) and a glass transition temperature of 229 ° C. 93.3 g (93% yield) of a block copolymer was obtained. The temperature during the reaction was 153 ° C.
[0072]
Using the obtained block copolymer, a cloudy film having free sulfonic acid groups was obtained in the same manner as in Example 1. The obtained film has an ion exchange group equivalent of 495 g / mol, a water absorption of 18%, an ionic conductivity of 0.16 S / cm, and a methanol permeability of 1.1 μmol / cm. ² Min.
[0073]
(Example 4)
14.78 g (0.035 mol) of DSDFBP, bis (3,5-dimethyl-4-hydroxyphenyl) were placed in a flask equipped with a nitrogen inlet tube, a thermometer, a condenser provided with a separator filled with toluene, and a stirring device. 8.) 8.97 g (0.035 mol) of methane (hereinafter abbreviated as TM-BPF) and 6.05 g (0.044 mol) of anhydrous potassium carbonate were precisely weighed. 90 g of dimethyl sulfoxide (hereinafter abbreviated as DMSO) and 38 g of toluene were added thereto, and the mixture was heated to 135 ° C. over 30 minutes while stirring with nitrogen gas, and then reacted for 12 hours. The reaction was performed under toluene distillation, and the distilled water was separated and collected by a separator. After cooling, a part of the reaction product was sampled, and the reduced viscosity of the oligomer was measured in the same manner as in Example 1. The result was 0.25 dl / g (DMSO).
[0074]
To the reaction product, 14.18 g (0.065 mol) of DFBP, 16.66 g (0.065 mol) of TM-BPF, 11.23 g (0.081 mol) of anhydrous potassium carbonate, 113 g of DMSO, and 48 g of toluene were added, and the mixture was stirred with nitrogen gas. While the temperature was raised to 135 ° C. over 30 minutes, the reaction was carried out for 12 hours. Further, toluene was distilled off, and the reaction was carried out at 160 ° C. for 6 hours.
[0075]
After the obtained viscous reaction product was diluted with 72 g of DMSO and 100 g of N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP), by-product salts and unreacted potassium carbonate were removed by filtration through celite. After concentrating this polymer solution with a rotary evaporator, the polymer solution was discharged into acetone using a homomixer, and the precipitated polymer was collected by filtration, washed with acetone, dried at 150 ° C. for 4 hours, and subjected to protonic acid groups (sodium sulfonate groups). 34.45 g (68% yield) of a block copolymer having the following formula: was obtained. The reduced viscosity of the obtained block copolymer was 1.24 dl / g (NMP), and the glass transition temperature was 210 ° C.
[0076]
2.00 g of the obtained block copolymer was heated and dissolved in 10.0 g of NMP to obtain a varnish having a polymer concentration of about 17 wt%. The obtained varnish was cast on a glass substrate using a blade having a spacer, heated from room temperature to 200 ° C. over 4 hours under nitrogen ventilation, and kept at 200 ° C. for 4 hours, and became slightly turbid with a thickness of 50 μm. A film was obtained. After photocrosslinking the obtained film by the method described in (vi), a film having free sulfonic acid groups was obtained in the same manner as in Example 1. This film has an ion exchange group equivalent of 710 g / mol, a water absorption of 10%, an ionic conductivity of 0.12 S / cm, and a methanol permeability of 0.3 μmol / cm. ² Min.
[0077]
(Example 5)
An oligomer was synthesized from DSDFBP and TM-BPF in the same manner as in Example 4 except that the reaction time was changed to 16 hours. η was 0.58 dl / g.
[0078]
18.67 g (0.065 mol) of 4,4'-dichlorodiphenylsulfone was used in place of DFBP, and 12.10 g (0.065 mol) of 4,4'-dihydroxybiphenyl was used in place of TM-BPF. The block copolymer was polymerized in the same manner as in Example 4. The yield was 42.9 g (89% yield), the reduced viscosity was 1.30 dl / g (NMP), and the glass transition temperature was 225 ° C.
[0079]
2.0 g of the block copolymer obtained in the same manner as in Example 4 was heated and dissolved in a mixed solvent of 8.0 g of NMP and 0.5 g of DMSO to obtain a varnish having a polymer concentration of 19%. The obtained varnish was cast on a glass substrate using a blade having a spacer, heated from room temperature to 200 ° C. over 4 hours under nitrogen ventilation, and kept at 200 ° C. for 4 hours, and became slightly muddy with a thickness of 50 μm. A film was obtained. After photocrosslinking the obtained film by the method described in (vi), a film having free sulfonic acid groups was obtained in the same manner as in Example 1. This film has an ion exchange group equivalent of 680 g / mol, a water absorption of 13 wt%, an ionic conductivity of 0.13 S / cm, and a methanol permeability of 0.6 μmol / cm. ² Min.
[0080]
【The invention's effect】
According to the present invention, a proton acid group-containing aromatic polyether block copolymer having water resistance, low water absorption, low methanol permeability, and high proton conductivity is provided. The polymer electrolyte membrane obtained from the copolymer has water resistance, low water absorption, low methanol permeability and high proton conductivity for a long period of time, and is used for fuel cells, especially for direct methanol fuel cells. It is suitable as a film.

Claims (13)

A proton conductive block copolymer comprising a block having a repeating structural unit represented by the following general formula (1) and a block including a repeating structural unit represented by the following general formula (2).

[In the formulas (1) and (2), at least one of X ^{1 to} X ⁵ is a proton acid group, the others are each independently H or a proton acid group, and A ^{1 to} A ⁴ are each independently A direct bond, —CH ₂ —, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, —O—, —SO ₂ — or —CO—, g, h, i, j, k , l represents 0 or 1 each independently, a hydrogen atom of the aromatic ring is a hydrogen atom or _-C m _{H 2m +} 1 (m is an integer of from 1 to 10),, - Cl, -F, -CF ₃ or - CN. ] It has a block having a repeating structural unit represented by the general formula (1), and has a reduced viscosity (concentration: 0.5 g / dl, measured at 35 ° C.) of 0.05 to 1.2 dl / g. The proton conductive block copolymer according to claim 1, which is obtained by an oligomer. In the general formula (1), at least one of A ¹ and A ² is —CO—, and at least one of hydrogen atoms of the aromatic ring is —C _m H _{2m + 1} (m is an integer of 1 to 10). 3. The proton conductive block copolymer according to 1 or 2. In the general formula (1), X ¹ and X ² are protonic acid groups, X ^{3 to} X ⁵ are H, A ¹ is —SO ₂ — or —CO—, A ² is a direct bond, —CH ₂ —, —C _{(CH 3) 2 -, -} C (CF 3) 2 -, - O -, - SO 2 - or a -CO-, claim g is 1, h and i is 0 or 1 each independently 3. The proton conductive block copolymer according to 1 or 2. In general formula (1), A ¹ is —CO—, and at least one hydrogen atom of the aromatic ring that is not directly bonded to A ¹ is —C _m H _{2m + 1} (m is an integer of 1 to 10). The proton conductive block copolymer according to claim 4, wherein General formula (1), ^{A 1} is -CO-, ^{A 2} is -CH ₂ - proton conducting block copolymer according to claim 4, characterized in that a. The proton conductive block copolymer according to any one of claims 1 to 6, wherein the proton exchange block copolymer has an ion exchange group equivalent of 300 to 2000 g / mol and a water absorption of 5 to 20 wt%. Block copolymer. Protonic acid _{group, -C n H 2n -SO 3 Y} (n is an integer of 0, Y is H, Na or K.) In any one of claims 1 to 7, characterized in that the The proton conductive block copolymer according to the above. The proton-conductive block copolymer according to any one of claims 1 to 8, wherein the proton-conductive block copolymer is crosslinkable with light, heat, or an electron beam. A crosslinked product of a proton conductive block copolymer obtained by crosslinking the proton conductive block copolymer according to any one of claims 1 to 9. A proton conductive membrane for a direct methanol fuel cell comprising the proton conductive block copolymer according to any one of claims 1 to 10 or a crosslinked product thereof. A proton conductive binder for a fuel cell, comprising the proton conductive block copolymer according to claim 1. A direct methanol fuel cell comprising the proton conductive membrane according to claim 11 or the proton conductive binder according to claim 12.