Pederson Erik N, McChalicher Christopher W J, Srienc Friedrich
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Biomacromolecules. 2006 Jun;7(6):1904-11. doi: 10.1021/bm0510101.
Polyhydroxyalkanoates (PHA) containing block copolymers were synthesized in Cupriavidus necator using periodic substrate addition. Poly(3-hydroxybutyrate) (PHB) segments were formed during fructose utilization. Pulse feeds of pentanoic acid resulted in the synthesis of 3-hydroxyvalerate monomers, forming poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) random copolymer. PHA synthesis was controlled using analysis of oxygen uptake and carbon evolution rates from the bioreactor off-gas. A combination of characterization techniques applied to the polymer batches strongly suggests the presence of block copolymers: (i) Thermodynamically stable polymer samples obtained by fractionation and analyzed by differential scanning calorimetry (DSC) and nuclear magnetic resonance spectroscopy (NMR) indicate that some fractions, representing approximately 30% of the total polymer sample, exhibit melting characteristics and nearest-neighbor statistics indicative of block copolymers, (ii) preliminary rheology experiments indicate additional mesophase transitions only found in block copolymer materials, (iii) dynamic mechanical analysis shows extension of the rubbery plateaus in block copolymer samples, and (iv) uniaxial extension tests result in differences in mechanical properties (modulus and elongation at failure) expected of similarly prepared block copolymer and single polymer type materials.
采用周期性添加底物的方法，在食酸铜绿假单胞菌中合成了含聚羟基链烷酸酯（PHA）的嵌段共聚物。在利用果糖的过程中形成了聚（3-羟基丁酸酯）（PHB）链段。戊酸的脉冲进料导致3-羟基戊酸单体的合成，形成聚（3-羟基丁酸酯-co-3-羟基戊酸酯）（PHBV）无规共聚物。利用对生物反应器尾气中氧气吸收和碳释放速率的分析来控制PHA的合成。应用于聚合物批次的多种表征技术强烈表明存在嵌段共聚物：（i）通过分级分离获得并经差示扫描量热法（DSC）和核磁共振光谱（NMR）分析的热力学稳定聚合物样品表明，一些占总聚合物样品约30%的级分表现出表明嵌段共聚物的熔融特性和近邻统计特征，（ii）初步流变学实验表明仅在嵌段共聚物材料中发现的额外中间相转变，（iii）动态力学分析显示嵌段共聚物样品中橡胶态平台的延伸，以及（iv）单轴拉伸试验导致类似制备的嵌段共聚物和单一聚合物类型材料预期的力学性能（模量和断裂伸长率）存在差异。
