水溶性封闭异氰酸酯单体的解封动力学王晓文周正发任凤梅汪瑾马海红徐卫兵*(合肥工业大学化工学院,合肥230009)摘要：采用热失重分析(TGA)法研究了水溶性封闭型异佛尔酮二异氰酸酯(IPDI)的热分解过程,利用傅里叶变换红外光谱法(FTIR)考察了谱图中40与140℃两种温度下的异氰酸酯特征峰.TGA 与FTIR 的结果表明失重阶段即对应封闭异氰酸酯的解封闭反应.用Friedman -Reich -Levi (FRL)和Flynn -Wall -Ozawa (FWO)两种动力学模型研究了解封反应的表观活化能E ,所得平均表观活化能分别为125.0和124.5kJ ·mol -1.采用双等双步法对解封过程进行表观机理函数判断,结果符合Jander 方程,反应机理为三维扩散,结合FWO 方程确定了反应级数n 和指前因子对数ln A 的范围.关键词：动力学;封闭异氰酸酯单体;解封;热稳定性中图分类号：O642;O643Deblocking Kinetics of Water -Solubility Blocked IsophoroneDiisocyanateWANG Xiao -WenZHOU Zheng -Fa REN Feng -Mei WANG JinMA Hai -Hong XU Wei -Bing *(School of Chemical Engineering,Hefei University of Technology,Hefei 230009,P.R.China )Abstract ：The thermal decomposition process of water -solublity blocked isophorone diisocyanate (IPDI)wasstudied using thermal gravimetric analysis (TGA).The characteristic peaks of isocyanante groups at 40and 140℃were observed by Fourier transform infrared spectroscopy (FTIR).Results from TGA and FTIR showed that the degradation stage was a deblocking reaction of the blocked adduct.The Friedman -Reich -Levi (FRL)and Flynn -Wall -Ozawa (FWO)models were employed to investigate the apparent activation energies which were 125.0and 124.5kJ ·mol -1,respectively.Based on the double equal -double step method,the reaction was analyzed by the apparent mechanism of the process of deblocking according to the Jander equation,which indicated that the reactive mechanism was a three -dimensional diffusion.The reaction order (n )and the logarithm of pre -exponential factor (ln A )were also determined using the FWO equation.Key Words ：Dynamics;Blocked isocyanate monomer;Deblocking;Thermal stability[Article]物理化学学报(Wuli Huaxue Xuebao )Acta Phys.-Chim.Sin .,2009,25(11)：2181-2185作为合成聚氨酯的重要原料,异氰酸酯单体中的异氰酸酯基团与亲核试剂具有较高的反应活性,使该体系在室温下非常活泼无法以单组分形式存在[1].作为涂料使用时,因聚氨酯涂料固化前对溶剂、树脂、颜料等原料中的水分或施工现场潮湿空气中的水分非常敏感[2,3],给聚氨酯涂料的应用增加很多困难[4].新型的水溶性封闭异氰酸酯单体将NCO基团封闭起来,使其室温下失去活性,防止水或其他活性物质对它的作用;而当使用时,可在一定温度下释放出NCO 基团,再与含有活泼氢组分发生反November Received:May 27,2009;Revised:July 15,2009;Published on Web:September 1,2009.*Corresponding author.Email:xwb105105@;Tel:+86-551-2901455.The project was supported by the National Natural Science Foundation of China (20776034).国家自然科学基金(20776034)资助项目鬁Editorial office of Acta Physico -Chimica Sinica2181Acta Phys.-Chim.Sin.,2009Vol.25应[5,6],仍保持原有异氰酸酯的特性.封闭异氰酸酯可应用于粘合剂中以增加其稳定性与储存期[7],还可广泛应用于水性聚氨酯、粉末涂料中等[8].因选用亚硫酸氢钠作为封端剂,相比肟类等封端剂,具有较低的解封温度[9,10],是一种较好的封闭物质.为了避免封闭异氰酸酯超过解封温度发生有机物的分解及长期使用过程中产生的粘接等性能失效[11],需要一种有效的方法评估高分子材料的热稳定性.目前,对此种水溶性封闭异氰酸酯单体热分解稳定性的研究较少,本文采用热失重分析(TGA),用不同的动力学模型研究其解封温度及解封动力学[12],计算动力学参数,提出表观机理函数.可以定量地研究此封闭产物的使用范围,确定稳定性,具有重要的意义.1实验1.1实验原料异佛尔酮二异氰酸酯(IPDI),分析纯,德国Bayer 公司生产;亚硫酸氢钠,分析纯,上海国药有限公司出品;醇类溶剂,分析纯,上海国药有限公司出品;电热真空干燥箱,天津实验仪器厂.所得水溶性封闭异氰酸酯单体,真空干燥成固体后研磨备用.合成反应方程式如图1所示.1.2热重分析水溶性封闭IPDI单体的热重分析(TGA)在TG209型热分析仪(德国NETZSCH公司)上进行,升温范围为40-500℃,升温速率分别为5、10、15、20℃·min-1,气氛为氮气,流量为40mL·min-1.水溶性封闭IPDI单体的红外光谱(FTIR)用KBr 压片法在NICOLET8700FT-IR分析仪(美国)上测试所得,升温速率为5℃·min-1.2结果与讨论2.1水溶性封闭型异氰酸酯的TGA分析将水溶性封闭型异氰酸酯在热分析仪上以升温速率为5、10、15和20℃·min-1进行测试,测得的TG曲线如图2所示.从图2水溶性封闭异氰酸酯IPDI的TG曲线可以得到基础动力学数据(表1).从表1中看出,随着升温速率的提高,TG曲线表现为分解温度向高温推移[13].图3为IPDI封闭物质变温红外谱图,从图中可以看出在40℃的红外谱图上未有NCO特征峰(2340cm-1)出现,而在140℃的红外谱图上出现NCO图3封闭IPDI的红外谱图Fig.3FTIR spectra of the blocked IPDI图1封闭型异佛尔酮二异氰酸酯(IPDI)的合成反应Fig.1Synthesis of blocked isophorone diisocyanate(IPDI)T i:initial mass loss temperature;T p:peak temperature 图2水溶性封闭异氰酸酯IPDI的TG曲线Fig.2TG curves of water-soluble blocked isophorone diisocyanateβ:heating rate表1基础动力学数据Table1The basis kinetic dataβ/(℃·min-1)T i/℃T p/℃Mass loss(%) 5122.1134.212.4810129.2139.112.9515132.7142.513.3520135.5147.612.762182No.11王晓文等：水溶性封闭异氰酸酯单体的解封动力学r :linear correlation coefficient特征峰,表明此时IPDI 封闭物质已经达到解封温度[14],封闭的NCO 基团重新释放.除此之外,2360cm -1处有CO 2特征峰的出现,因在高温下解封释放出的NCO 基团会自聚反应得到的脲二酮、异氰脲酸酯、脲基甲酸酯和缩二脲等[15],这些产物随着温度的持续升高会发生部分分解,放出CO 2气体.2.2非等温动力学用Friedman -Reich -Levi(FRL)微分法[16,17]和Flynn -Wall -Ozawa(FWO)积分法[18,19]对所得数据进行线性拟合,求得相应的动力学数据,微分方程与积分方程如下:lnβd αd T !"=ln[Af (α)]-E RT (1)lg β=lgAE#$-2.315-0.4567E RT(2)式中α是转化量,d α/d t 是转化率,T 是绝对温度,A是指前因子,R 为气体常数,E 是表观活化能,β为线性升温速率,f (α)和G (α)分别为微分和积分反应机理函数.对于FRL,ln(βd α/d T )-1/T 线性拟合,可以通过斜率求出表观活化能E ,在机理函数符合的情况下根据截距求出指前因子;对于FWO 方程,由lg β-1/T 作图,同理求得表观活化能E ,截距求得指前因子A .所得线性拟合曲线如图4所示,所得对应的活化能及相关系数如表2所示.结果表明:对于FRL 法,平均表观活化能为125.0kJ ·mol -1,对于FWO 法,平均表观活化能为124.5kJ ·mol -1.因为水溶性封闭型异氰酸酯的解封闭过程所涉及到的所有相关反应都是可逆的,都伴随着副反应的发生;随着温度的升高,解封后重新生成的NCO 基团会发生二聚、三聚及脲基甲酸酯或缩二脲生成的反应等,这些生成的物质反过来又通过不同的动力学历程进行热分解[20],从而导致E 随着转化率的不同出现波动,但总体保持稳定.2.3最概然机理函数的确定Zhang 等[21]在等转化率和变异等转化率的基础上提出了一种新的热分析动力学数据处理方法———双等双步法,该法的优点是活化能与机理函数分别求得.将FWO 方程(式(2))改写为lg G (α)=lg AE%&-2.315-0.4567E RT-lg β(3)将不同TGA 曲线上同一温度处的α值和表3中的15种不同的机理函数G (α)[22]以及不同的升温速率代入方程(3)中,以lg G (α)-lg β进行线性拟合,得到不同温度下直线斜率b ,截距a 和直线的线性相关系数r .若r 较好,b 接近-1,则对应的G (α)就是最概然机理函数.对15种机理函数(表3)进行计算,所得斜率b 与相关系数r 如表4所示.根据双等双步法及表4可知,解封阶段符合Jander 方程[23,24],最概然机理为三维扩散,球形对称,三维(3D),减速形α-t 曲线,其机理函数为:f (α)=3/2(1-α)2/3[1-(1-α)1/3]-1,G (α)=[1-(1-α)1/3]2.图4FRL 法(a)和FWO 法(b)所得拟合曲线Fig.4The fitting curves based on the FRL (a)andFWO (b)methodsα:transformation amount表2FRL 法和FWO 法求取活化能(E )Table 2Activation energies (E )based on the FRLand FWO methodsαFRL equationFWO equationE /(kJ ·mol -1)r E /(kJ ·mol -1)r 0.10129.80.9990131.00.99840.20130.60.9999127.60.99950.30137.40.9978125.60.99840.40130.80.9956124.80.99960.50112.00.9976121.40.99500.60106.10.9975116.80.99600.70118.80.9984117.80.99820.80130.10.9994124.80.99920.90129.00.9996130.90.99992183Acta Phys.-Chim.Sin.,2009Vol.252.4动力学参数的判断根据FWO 方程得到相关指前因子,由(4)式所示的Crane 方程式[25]可以求得反应级数n ,所得结果如表5所示.dln βp =-E -2T p (4)当E /nR >>2T p 时,(4)式可简化为dln βd(1/T p )=-E nR(5)以ln β对1/T p 作图,可得一条直线,将E 、T p 代入即可求得反应级数n [26].根据表5可知,计算得到反应级数n 的范围不是整数,说明反应机理复杂,这一情况与可能发生几种自聚反应的复杂情况相符合.3结论采用TGA 法研究了不同升温速率下的水溶性封闭型异氰酸酯的热分解过程,应用Friedman -Reich -Levi(微分法)和Flynn -Wall -Ozawa(积分法)对解封阶段进行分析,得到相应的动力学数据E 、ln A 、r 等,并进一步得到相应的表观机理函数.解封阶段符合Jander 方程,其机理函数为:f (α)=3/2(1-α)2/3[1-(1-α)1/3]-1,G (α)=[1-(1-α)1/3]2,解封阶段的表观活化能总体保持稳定,所以通过此方法计算的活化能较为准确[27].对于FRL 法,平均表观活化能为125.0kJ ·mol -1,对于FWO 法,平均表观活化能为表5FWO 法所得指前因子A 及反应级数n Table 5Pre -exponential factor (A )and reactionorder (n )based on the FWO methodb :linear slope,r :linear correlation coefficient;functions 1-15refer tothose functions listed in Table 3.表3常用热分解动力学机理函数Table 3Classification of kinetic mechanisms of thermal decompositionNo.Function Reaction modelf (α)G (α)1mampel power law n =1/44α3/4α1/42mampel power law n =1/33α2/3α1/33mampel power law n =1/22α1/2α1/24mampel power law phase boundary reaction(one -dimensional),R 1,n =11α5parabola law one -dimensional diffusion 1/(2α)α26Valensi two -dimensional diffusion [-ln(1-α)]-1α+(1-α)ln(1-α)7Jander three -dimensional diffusion3/2(1-α)2/3[1-(1-α)1/3]-1[1-(1-α)1/3]28Avrami -Erofeev random nucleation and later growth,n =1/2,m =22(1-α)[-ln(1-α)]1/2[-ln(1-α)]1/29Avrami -Erofeev random nucleation and later growth,n =1/3,m =33(1-α)[-ln(1-α)]2/3[-ln(1-α)]1/310Avrami -Erofeev random nucleation and later growth,n =1/4,m =44(1-α)[-ln(1-α)]3/4[-ln(1-α)]1/411phase boundary reaction contraction cylinder 2(1-α)1/21-(1-α)1/212phase boundary reaction contraction sphere3(1-α)2/31-(1-α)1/313Jander two -dimensional diffusion,2D,n =1/24(1-α)1/2[1-(1-α)1/2]1/2[1-(1-α)1/2]1/214Jander two -dimensional diffusion,2D,n =2(1-α)1/2[1-(1-α)1/2]-1[1-(1-α)1/2]215Janderthree -dimensional diffusion,3D,n =1/26(1-α)2/3[1-(1-α)1/3]1/2[1-(1-α)1/3]1/2f (α):differential form;G (α):integral form;n ,m :the power index of kinetic mechanism function表4双等双步法计算的相关参数Table 4Relevant parameters based on the doubleequal -double step methodFunctionb r 1-0.08590.95702-0.11450.95703-0.17170.95704-0.34350.95705-0.68700.95706-0.81320.96347-0.97540.97018-0.28760.97519-0.19170.975110-0.14380.975111-0.44790.967212-0.48770.970113-0.22400.967214-0.89590.967215-0.24390.9701αln(A /s -1)n 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