Schiff碱镧配合物的合成及其催化烷基异氰酸酯聚合

POLYMERIZATION OF ALKYL ISOCYANATE CATALYZED BY LANTHANUM SCHIFF BASE COMPLEXES

通过氯化镧与Schiff碱钠盐(NaSalen)的交换反应制备了4种镧的Schiff碱配合物La(HSalen1～4)3,对其中以3,5-二叔丁基水杨醛缩苯胺为配体的配合物La(HSalen2)3进行了X-射线单晶衍射分析,测定其单晶结构为五角双锥构型,七配位的镧金属中心与氮和氧原子相连.将所得的La(HSalen)3配合物作为单组份催化剂用于催化烷基异氰酸酯聚合,发现以水杨醛缩苯胺为配体的配合物La(HSalen1)3的催化活性最高.深入研究了配合物La(HSalen1)3催化的己基异氰酸酯(HIC)的聚合,详细考察了催化剂用量、单体浓度、聚合时间和温度以及聚合溶剂等对单体转化率、产物分子量及分子量分布的影响.研究结果表明,在-40～20℃温度范围内,配合物La(HSalen1)3均可以催化己基异氰酸酯聚合,得到黏均分子量10×104～50×104之间的聚己基异氰酸酯(PHIC),由于存在解聚反应,提高聚合温度和延长聚合反应时间均导致聚合物分子量降低,分布变宽.适宜的聚合条件为:[HIC]=3.43 mol/L,[La]=8.58×10-3 mol/L,-40℃甲苯溶液中聚合12 h,得到的聚合物产率75.5%,Mv=35.4×104,MWD=3.86.

Four Lanthanum Schiff-base complexes were synthesized,and the polymerizations of alkyl isocyanates were studied using these complexes as single component catalysts.Lanthanum Schiff-base complexes La（HSalen1～4）3 have been synthesized by metathesis reaction of anhydrous LaCl3 with Schiff-base sodium salts NaSalen.The complex La（HSalen2）3 with the formula of [3,5-tBu2-2-（O）C6H2CH=NC6H5]3La（THF） was characterized by X-ray diffraction,and the structure around Lanthanum center could be described as a pentagonal bipyramid.The polymerization of alkyl isocyanates was successfully carried out by using these complexes as single component catalysts,and the [OC6H2CH=NC6H5]3La（THF） complex（La（HSalen1）3） shows the highest catalytic activity to the polymerization of isocyanates.The influences of polymerization temperature,polymerization time,the concentration of catalyst and monomer,and the polymerization solvent on the polymerization of hexyl isocyanate（HIC） catalyzed by La（HSalen1）3 were investigated.It was found that under the polymerization conditions examined,PHIC can be prepared under-40℃～20℃ with complex La（HSalen1）3 as catalyst.Due to the depolymerization,higher reaction temperature leads to low polymer yield and molecular weight of PHIC obtained.Confirmed by GPC analysis,prolonging polymerization time is also in favor of depolymerization,the GPC profile of PHIC prepared after 12 h polymerization indicates the exist of dimmers and trimers.PHIC could be prepared with yield of 75.5%,number-average molecular weight（Mn） of 6.00×104and MWD of 3.86 under the following optimum conditions： = 3.43 mol/L,[La（HSalen1）3]= 8.58×10-3mol/L,polymerization at -40℃ for 12 h in toluene.