Preparation and Isolation of Purely Stereoregular Oligomers without Molecular Weight Distribution and Structural Investigations of the Oligomers

通过甲基丙烯酸甲酯（MMA）的立体定向活聚合制备了高度等规（it-）和高度同规（st-）的低聚物。采用制备型超临界流体色谱法（SFC）将低聚物从10mer到100mer （C_<504>H_<810>O_<200> = 10070）分离为单个同源物。用19 ~ 50mers样品研究了it-和st-低聚物系列玻璃化转变温度对分子量的依赖关系。聚合度大于30的it-低聚物经退火结晶，均匀低聚物的熔点比分子量分布低聚物的熔点更明显。通过x射线分析确定了其晶体结构。当it-50mer和st-50mer混合后，以THF为洗脱液进行GPC时，在100mer对应的洗脱体积处，由于50mer之间的立体配合物，出现了一个尖锐的洗脱峰；在GPC分析的基础上，研究了低聚物混合物的络合化学计量学和络合机理。以RONa为起始，R‘ x为末端，制备了结构为RO[CH(CCl_3)O]_nR’的纯氯醛（CCl_3CHO）低聚物。用GPC或sfc将2 ~ 9聚物分离成单晶，分别以R和R′为t-丁基和乙酰基的it-低聚物通过高效液相色谱（HPLC）分解为光学对映体。x射线分析发现(-)-5mer（[alpa]_D = -23.7）为（R，R，R，R）-异构体，具有右旋4/1螺旋结构。两端携带甲基的it-7mer和it-8mer是中位异构体，也可以完全根据构象手性（单手螺旋）进行光学分辨。

Highly isotactic(it-) and highly syndiotactic(st-) oligomers of methy1 methacrylate (MMA) were prepared by the stereospecific living polymerizations of MMA.The oligomers were separated into the individual homologues from the 10mer to the 100mer (C_<504>H_<810>O_<200> = 10,070) by means of preparative supercritical fluid chromatography (SFC). The molecular weight dependence of the glass transition temperature for the it- and st- oligomer series was investigated using the samples of the 19 - 50mers. The it-oligomers with the degree of polymerization higher than 30 crystallized by annealing, and the melting endotherms of the uniform oligomers were sharper than that of the oligomer having molecular weight distribution. The it-5mer and st-4mer gave single crystals, and the crystal structures were determined by X-ray analysis. When the it-50mer and st-50mer were mixed and subjected to the GPC using THF as eluent, a sharp elution peak due to the stereocomplex between the 50mers was observed at the elution volume corresponding to the 100mer ; on the basis of the GPC analysis of the oligomer mixtures, the complexation stoichiometry and the mechanism of the complexation were studied.Purely it-oligomers of chloral (CCl_3CHO) with a structure RO[CH(CCl_3)O]_nR' were prepared by the oligomerization of chloral initiated with RONa and terminated with R'X.The oligomers from the 2mer to the 9mer were isolated individually as single crystals by GPC or SFC.Each it-oligomer having t-butyl and acetyl groups as R and R', respectively, could be resolved into the optical antipodes by HPLC.The (-)-5mer([alpa]_D = -23.7 ) was found to be the (R,R,R,R,R)-isomer having a right-handed 4/1 helical structure by X-ray analysis. The it-7mer and it-8mer carrying a methyl group at both ends, which are the meso isomers, could also be optically resolved based entirely on conformational chirality (one-handed helix).