预聚物分子量对立体复合聚乳酸固相缩聚产物结构和性质的影响

采用乳酸作为引发剂、辛酸亚锡作为催化剂，引发丙交酯开环聚合制得分子量不同的具备缩聚活性的预聚物L-聚乳酸（PLLA）和D-聚乳酸（PDLA），将重均分子量（M_w）相近的预聚物熔融共混后制成前体进行固相缩聚。采用核磁共振（NMR）、凝胶渗透色谱（GPC）、差示扫描量热（DSC）及X射线衍射（XRD）分析了固相缩聚产物的链结构、分子量、热性能及晶体结构。结果表明，固相缩聚产物具有立体嵌段结构。预聚物的分子量大小将影响固相缩聚前体中均相晶体和立体复合晶体的相对含量，进而影响固相缩聚产物的结构。当预聚物PLLA和PDLA的M_w≈5×10⁴时，固相缩聚产物重均分子量的涨幅最大，最终达到1.83×10⁵。因此，采用M_w≈5×10⁴的预聚物进行固相缩聚有利于产物中立体复合晶体结晶度的提高。

Effect of Prepolymer Molecular Weight on Structure and Properties of Products Prepared by Solid State Polycondensation of Stereocomplex Polylactide

Prepolymer L-polylactide and D-polylactide with reactivity for condensation polymerization and different molecular weights were prepared by using lactide as monomer,lactic acid and stannous octoate as initiator and catalyst respectively.A series of stereoblock polylactides were synthesized via solid state polycondensation using precursors obtained by melting blend of L-polylactide (PLLA) and D-polylactide (PDLA) with similar weight-average molecular weights.The chain structure,molecular weight,thermal properties and crystal structure of products acquired were characterized by H-NMR,GPC,DSC and XRD,respectively.The results show that the products have stereoblock structure.The molecular weight of the prepolymers will affect the relative content of homochiral crystal and stereocomplex crystal in the precursor,and thus affect the structure of the solid-phase polycondensation product.When the average molecular weight of PLLA and PDLA are both about 5×10⁴,the molecular weight of the product increases rapidly and reaches 1.83×10⁵,and which is beneficial to the improvement of crystallinity of the stereocomplex crystal in the final product.