Jiang Zhaozhong, Azim Himanshu, Gross Richard A, Focarete Maria Letizia, Scandola Mariastella
NSF I/UCRC for Biocatalysis and Bioprocessing of Macromolecules, Department of Chemical and Biological Sciences, Polytechnic University, Six Metrotech Center, Brooklyn, NY 11201, USA.
Biomacromolecules. 2007 Jul;8(7):2262-9. doi: 10.1021/bm070138a. Epub 2007 Jun 6.
Candida antarctica Lipase B (CALB), a metal-free enzyme, was successfully employed as catalyst for ring-opening copolymerization of omega-pentadecalactone (PDL) with p-dioxanone (DO) under mild reaction conditions (<80 degrees C, atmospheric pressure). Poly(PDL-co-DO) with high molecular weight (Mw > 30 000) and a wide range of comonomer contents was synthesized using various PDL/DO feed ratios. During the copolymerization reaction, large ring PDL was found to be more reactive than its smaller counterpart DO, resulting in higher PDL/DO unit ratios in polymer chains than the corresponding PDL/DO monomer ratios in the feed. The copolymers were typically isolated in 50-90 wt % yields as the monomer conversion was limited by the equilibrium between monomers and copolymer. 1H and 13C NMR analysis on poly(PDL-co-DO) formed by CALB showed that the copolymers contain nearly random sequences of PDL and DO units with a slight tendency toward alternating arrangements. Copolymerization with PDL was found to remarkably enhance PDO thermal stability. Differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS) results demonstrate high crystallinity in all copolymers over the whole range of compositions. Depending on copolymer composition, the crystal lattice of either PDO or PPDL hosts units of the other comonomer, a behavior typical of an isodimorphic system. In poly(PDL-co-DO), both melting temperature and melting enthalpy display a minimum at 70 mol % DO, that is, at the pseudoeutectic composition. WAXS diffractograms show one crystal phase (that of either PPDL or PDO) on either side of the pseudoeutectic and coexistence of PPDL and PDO crystals at the pseudoeutectic.
南极假丝酵母脂肪酶B（CALB）是一种无金属酶，在温和的反应条件下（<80℃，常压）成功用作ω-十五内酯（PDL）与对二氧环己酮（DO）开环共聚的催化剂。使用各种PDL/DO进料比合成了具有高分子量（Mw>30000）和广泛共聚单体含量的聚（PDL-co-DO）。在共聚反应过程中，发现大环PDL比其较小的对应物DO更具反应性，导致聚合物链中PDL/DO单元比高于进料中相应的PDL/DO单体比。由于单体与共聚物之间的平衡限制了单体转化率，共聚物通常以50-90 wt%的产率分离出来。对由CALB形成的聚（PDL-co-DO）进行的1H和13C NMR分析表明，共聚物包含几乎无规序列的PDL和DO单元，略有交替排列的趋势。发现与PDL共聚可显著提高PDO的热稳定性。差示扫描量热法（DSC）和广角X射线散射（WAXS）结果表明，在整个组成范围内，所有共聚物都具有高结晶度。根据共聚物组成，PDO或PPDL的晶格容纳另一种共聚单体的单元，这是同形体系的典型行为。在聚（PDL-co-DO）中，熔点和熔化焓在70 mol%DO时均显示最小值，即假低共熔组成时。WAXS衍射图在假低共熔组成的两侧显示一个晶相（PPDL或PDO的晶相），在假低共熔组成时PPDL和PDO晶体共存。
