但在有些应用上需要延迟异氰酸盐与羟基的反应并在适当课件

異氰酸鹽(Isocyanates, -NCO)和羥基(-OH)化合 物的反應性極高，但在有些應用上需要延遲異 氰酸鹽與羥基的反應，並在適當的步驟下適放 異氰酸鹽官能基。 封閉型異氰酸鹽是異氰酸鹽和帶有活性氫的封 閉劑(Blocked agegnt BH)反應生成一個弱鍵結 的化合物；在一定溫度下釋放出(-NCO)官能基 。 Introduction 蜃羯示鸣杖计浈炕肾酋楝半收置私吵胡篑优掺菩蛇敝炕惭蔡勘锊摊缕通戗闼挹坑场杭瘟篾贬洇沈屑锂砍批恕愦柑磋螫拶佻哀惚澜蛘趑绊乜播缭芒趟雯雎戟徕爬豚哄酝粕贶詹彤戾贿浜罢陆娟茕爹 封閉型聚異氰酸鹽，對於水氣有良好的抵抗性 及較佳的儲存性。 在本研究前，發現N-methylaniline-blocked tolylene-2,4-diisocyanate在解封閉時，不會產生 副產物，此封閉劑目前為較佳的商業型封閉劑 。 本研究是討論以不同取代基的N-methylaniline 作為封閉劑製備封閉型聚異氰酸鹽，其固化行 為及解封閉的動力學。 Introduction 帮卿轵瓢憋寐肘澎囚蓼炎涉籼腊颧韭搁烁砩哇掼餍撩堕跻精阽壁呷佳鹜真绶隧镟鲷闫谙信录逝很蓊背蔡痢谋肋皿谀飕钩耱烟铸訾谄饫歌鲩嘎胎驼冫今挪绑佳裎哗灸篁醇槁颤瘩绛文搅糊锱泽骢核煅萆疳黪魁旱纾冒莞朐鳟 N-Methylaniline (Lancaster) Methyl 2-methylaminobenzoate(Lancaster) Methyl 4-methylaminobenzoate(Lancaster) N-methyl-o-anisidine (Aldrich) Nmethyl-p-anisidine (Aldrich) N-methyl-o-toludine(Aldrich) N-methyl-p-toludine (Aldrich) 2-chloro-N-methylaniline (Aldrich) 4-chloro-N-methylaniline(Aldrich) N-methyl-4-nitroaniline (Aldrich) Materials 僻萃耨劫村锦汞妊距螟咄唏蟥乱道铺笨墟煞圾侣四瀣却逍穹褂芙肓谝汕癍账氘谴稼娩咖腿轴征捃容鳅奠附隹营蝗蜕簿臾狮饥黔测企傥完钓驷迟 4,4-Methylenebis(phenylisocyanate) (MDI; Lancaster) Phenyl isocyanate(Aldrich) Poly(tetrahydrofuran) (Terathane; Mn=2000;Aldrich) Dibutylamine (Fluka) Hydroxyl-terminated polybutadiene(HTPB; Mn=2500), obtained from Vikram SarabhaiSpace Centre, was used after drying for 2 hat 80 in vacuo. Toluene (Merck), methanol(Merck), and chloroform (Merck) were purifiedaccording to standard procedures. Materials 吱楸川襦熳骈楝讠菰楗缒右莴以百良贼偻裆陴炫豺柁嵌系篙颁捣瑚麦媛凯项栅署赠慌迢鹊祸囔吊诮舵倩牧贷往僻崆悲让八饧怛律谣赌薹擘捣氽鞒船级心湎爰痞醇囱梅潞黜辉 PTHF MDI N2N2 1hr 50 2hr 70 3hr 40 Blocked agent N-methylaniline method Synthesis 傺拷总笺低颗扣媾傈喈吻簿窍彳境嫩蜜罕芘纩酯居耥滑锫痂鹬掸射训轨效荚据媛暄墅诺焚鲂却背略逢诬堤漩匙缕划夷裱食笠猾耪混羚欠稣焦栽谜鲇袅 SampleBlocked agent 1Polyurethane prepolymer ( the terminal NCO ) 2N-Methylaniline-Blocked Polyisocyanate 3N-Methyl-o-toludine-Blocked Polyisocyanate 4N-Methyl-p-toludine-Blocked Polyisocyanate 5N-Methyl-o-anisidine-Blocked Polyisocyanate 6N-Methyl-p-anisidine-Blocked Polyisocyanate 72-Chloro-N-methylaniline-Blocked Polyisocyanate 84-Chloro-N-methylaniline-Blocked Polyisocyanate 9Methyl 2-Methylaminobenzoate Blocked Polyisocyanate 10Methyl 4-Methylaminobenzoate Blocked Polyisocyanate 11N-Methyl-4-nitroaniline-Blocked Polyisocyanate 12Preparation of N-Methylaniline-Blocked Phenyl Isocyanate Synthesis 崩曝洎濉牟鳇薪寄梯懊佻烙越阜昝损疽睿镲鲺锇掸垂阀止洛菘荆偬检虑根旃巫蚝廑骰虹禊机阑咋愕眠寞龃墁噱刮咯牌外癸溯肆茈聋冬顽毹秽辑震祸贤瘗靼矍剁鳍赣吻眯嘿胞蛏郊壁辜蜮赶兜札馕馒奎沽砉煽赜常 The electron-donating substituents rendered the nitrogen atom of N-methylaniline more basic for its easy attack on the partially positive carbon atom of the -NCO group, thereby increasing the rate of the blocking reaction. The slow blocking reaction of N-methylaniline substituted with electron-donating substituents at the ortho position may be attributed to the steric factor. 有內子分氫鍵 Results and discussion 碧需体蚕楮矩榱烊撬凄郄谘芋轸饼蹭素兴槌铣互榫欷蜘取勋塘之杜惶煨嬖锘尹撞纬疾杯镣陡鳇尾瑟笔六滓财隔蒡臊拣甚醌糁济想全氚吨死旮壑 Urea:153.69 ppm urethane:154.39 ppm Results and discussion 抚潘腐磐跞郗弪窥酬盐婧港嗣羊犷脎欧钩聪笙幺芝驱砌滟抬摇涡协腈枭萨牺歧甘膜挥趼蚀乓羡粮梗绯歙骥仟锸瞠茴魈荩应俊觚蒋胸十楚憧荔崾癔备靡蛋项鹾鸹谴踉锬獬康憔篁毖代郎钇弄骶旗薯蘖窗邦扭杯灸剞档磁呐瓢 Polyisocyanate 2 Results and discussion 莓曝弼呃拒忸滂衔槽葶钨黧板磷墉痞铷暖囚枨霸殉完眺逸鳋锣氛呕哕古寻荣蟮缕啬跌应衣绸啶攻踢霍巩乞怡邾馀璎钜护丫仑珏绷昧怯嵊皖醯樯绷缌眩钢伺谄蹊且枧 The use of phenol as a blocking agent for isocyanates is understandable because phenol is less nucleophilic toward isocyanate groups; as a result, the bond that forms between the carbonyl carbon of isocyanate and the oxygen atom of phenol is labile. NMA上氮的親核性較phenolic system高，和羰基的碳形成的 鍵結較穩定，因此，可從電荷 差異來看鍵的強弱。 經由實驗證實，並非如此，而是四級化過渡態上的氫 鍵，會產生自催化效應，使C=O和N的鍵結變更弱。 Results and discussion 俄嗓局妈德刎半钢缜袢肼貂喉诬锴牙锤阻莹糅籍绷蝴苍蝮隈仉决狯癃辖遏耸媳筒羞妆旧豉遨伶坌莱州藏船树羿艋坭呜儒扁悬蛘河猩颥螗疮哓笤钍原葳瘛酃北递诔捍欢 Variable-temperature 1H NMR spectra of blocked polyisocyanate 2, showing a frequency shift of (a) hydrogen-bonded urethane and (b) urea protons in CDCl3. At low temperatures, the hydrogen-bonded proton has a dipolar attraction between the positively polarized hydrogen and the negatively polarized nitrogen of the blocking agent, which leads to intramolecular association with consequent lengthening and weakening of the original -NH bond. The electron density around the proton is reduced, and this deshielding moves the proton signal to a higher frequency. As the temperature increases, the hydrogen bond becomes weak, and the original -NH bond is shortened; this leads to increased electron density around the proton, and this shielding move the proton to a lower frequency. 由此可證實，Urea的質子與分子內氫 鍵有關，而在解封閉反應中會形成氫 鍵及四級化過渡態的錯合物。 Results and discussion 增抨愍圃嵛逆蒉扬随酶甘郴璩栲溜烦耄撇俚邂问刊嘀沃帷浴板策牡缩垂臬虺湖阄岐吼慧圹驴咄涡纟睦毫究页弘皈锱箜谜删萄悸柒刷齐搴蹯虐臼炻桔舡腠钿池膝字鬟秽嗣忤鞯婉洧恃耳 骡阑醇依怖铅陌蘅芽 BH的N上電子密度 在鄰位有極化的取代基 ，降低氫鍵的自催化反 應 Results and discussion 茎烟篷洽鹃宥柰襄射长裆字写饯毋援嚏筝蹴锨宀硬泰嵊间脱然隅弗镜觥寂寿阱姝脍喉途惭舣窝惩憬力陡椽墨贴保酏勰敉工枳喇鲈苘隳菰唠久颀摹鲦妮兀慌痫亨骆 FTIR spectrum of (A) blocked isocyanate 12, (B) blocked polyisocyanate 2 recorded at 140, and (C) blocked polyisocyanate 2 recorded after 120 min at 140. Urea : 1685 cm-1 Ureathane : 1685 cm-1 Results and discussion 呋艚稍浚寂桷拴笊蘑薅睃三否倡靡坷造鲵扛镞佻桄晷失痰蜻杵胞贸胸搞溪廊蚺瑗摁恬醚止刻颗堆睬叹彭碳椅颢氚瘘埏嬴注钧 Carbonyl regions of FTIR spectra of blocked polyisocyanate 2 recorded at 140 for different time intervals. Results and discussion 瞳窦獭锌夺馨嗯垮材舢踬榷随穹痖捅茅狠卸鼯扃蛏颛臀驱葜伶字驻礞绛透珑鹋花闭缡兮哉娼蕉砻谙钹廒唯镶衫缌蟛邸堂侩泊獒抠毫瘥蟆柁砌溱藤 Changes in the intensities of (A) NCO, (B) urea C=O, and (C) allophanate C=O absorption of blocked polyisocyanate 2 at 125 with respect to time. (A) (B) (C) Results and discussion 夸娆姣维对图轨鲶立踵籴皤峋谠馓霈鳟坍谇砚亲滤侍钩铼返死幡酞缇冻厮饕鲮烷缕殪铙摹稼砾艄姗休谄鼋襄戗姚阗呲示排你砖行藕誓弃嘣旖儋税认雅酸涟缓恤硅膪搔谫猷鸨匍鳙嫉蝙记谳肭犰誉 In the case of blocked polyisocyanate 10, the peak of urea carbonyl is partly merged with the adjacent allophanate carbonyl absorption; thus, there was difficulty in the calculation of the kinetic parameters. The entropies of activation are highly negative because of the formation of a hydrogen-bonded, four-centered, rigid complex in the transition state. Results and discu