Jiang Zhaozhong
Biomedical Engineering Department, Yale University, 55 Prospect Street, New Haven, Connecticut 06511, USA.
Biomacromolecules. 2008 Nov;9(11):3246-51. doi: 10.1021/bm800814m. Epub 2008 Oct 22.
Candida antarctica lipase (CALB) has been successfully used as catalyst for copolymerization of dialkyl diester with diol and lactone to form aliphatic polyesters. The polymerization reactions were performed using a two stage process: first stage oligomerization under low vacuum followed by second stage polymerization under high vacuum. Use of the two-stage process is required to obtain products with high molecular weights at high yields for the following reasons: (i) the first stage reaction ensures that the monomer loss via evaporation is minimized to maintain 1:1 diester to diol stoichiometric ratio, and the monomers are converted to nonvolatile oligomers; (ii) use of high vacuum during the second stage accelerates equilibrium transesterification reactions to transform the oligomers to high molecular weight polymers. Thus, terpolymers of omega-pentadecalactone (PDL), diethyl succinate (DES), and 1,4-butanediol (BD) with a M w of whole product (nonfractionated) up to 77000 and M w/ M n between 1.7 and 4.0 were synthesized in high yields (e.g., 95% isolated yield). A desirable reaction temperature for the copolymerizations was found to be around 95 degrees C. At 1:1:1 PDL/DES/BD monomer molar ratio, the resultant terpolymers contained equal moles of PDL, succinate, and butylene repeat units in the polymer chains. (1)H and (13)C NMR analyses were used to determine the polyester microstructures. The synthesized PDL-DES-BD terpolymers possessed near random structures with all possible combinations of PDL, succinate, and butylene units via ester linkages in the polymer backbone. Furthermore, thermal stability and crystallinity of a pure PDL-DES-BD terpolymer with 1:1:1 PDL to succinate to butylene unit ratio and M w of 85400 were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The copolyester was found to be a semicrystalline material with a T g of -34 degrees C and a T m of 64 degrees C, which degrades in a single weight loss step centered at T max = 408 degrees C.
南极假丝酵母脂肪酶（CALB）已成功用作二烷基二酯与二醇和内酯共聚以形成脂肪族聚酯的催化剂。聚合反应采用两步法进行：第一阶段在低真空下进行低聚反应，随后第二阶段在高真空下进行聚合反应。采用两步法是为了以高收率获得高分子量产物，原因如下：（i）第一阶段反应确保通过蒸发造成的单体损失最小化，以维持二酯与二醇1:1的化学计量比，并且单体转化为不挥发的低聚物；（ii）在第二阶段使用高真空加速平衡酯交换反应，将低聚物转化为高分子量聚合物。因此，成功合成了ω-十五内酯（PDL）、琥珀酸二乙酯（DES）和1,4-丁二醇（BD）的三元共聚物，整个产物（未分级）的Mw高达77000，Mw/Mn在1.7至4.0之间，收率很高（例如，分离收率为95%）。发现共聚反应的理想反应温度约为95℃。在1:1:1的PDL/DES/BD单体摩尔比下，所得三元共聚物在聚合物链中含有等摩尔的PDL、琥珀酸酯和丁烯重复单元。通过（1）H和（13）C NMR分析确定聚酯的微观结构。合成的PDL-DES-BD三元共聚物具有接近无规的结构，聚合物主链中通过酯键连接的PDL、琥珀酸酯和丁烯单元存在所有可能的组合。此外，通过热重分析（TGA）和差示扫描量热法（DSC）研究了PDL与琥珀酸酯与丁烯单元比例为1:1:1且Mw为85400的纯PDL-DES-BD三元共聚物的热稳定性和结晶度。发现该共聚酯是一种半结晶材料，玻璃化转变温度（Tg）为-34℃，熔点（Tm）为64℃，在以Tmax = 408℃为中心的单一失重步骤中降解。
