Bhayo Adnan Murad, Abdul-Karim Rubina, Musharraf Syed Ghulam, Malik Muhammad Imran
H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences (ICCBS), University of Karachi Karachi 75270 Pakistan
RSC Adv. 2018 Aug 10;8(50):28569-28580. doi: 10.1039/c8ra05000g. eCollection 2018 Aug 7.
Star-shaped polymers exhibit lower hydrodynamic volume, glass transition temperature, critical micelles concentration (CMC), and higher viscosity and drug-loading capacity compared to their linear counterparts. In the present study, amphiphilic biodegradable 4-arm star-shaped block copolymers, based on poly(ethylene oxide) (PEO) as a hydrophilic part and poly(ε-caprolactone) (PCL) as a hydrophobic segment, are synthesized by ring-opening polymerization of ε-caprolactone employing pentaerythritol as an initiator and stannous octoate as a catalyst, followed by the coupling reaction with carboxyl-functionalized monomethoxy poly(ethylene oxide) (MeO-PEO-COOH). The structures of intermediates were deduced through H-NMR and FT-IR spectroscopy. Average chemical composition of the star block copolymer is determined by proton NMR. Information related to molar mass distribution of targeted products and their precursors is obtained by size exclusion chromatography (SEC). However, due to its inherent poor resolution SEC could not reveal whether all the parent homopolymers are coupled to each other or remained unattached to the other segment. In order to comprehensively characterize the synthesized star-block copolymers, liquid chromatography at critical conditions of both blocks is employed. The study allowed for separation of homopolymer precursors from targeted star-block copolymers. The study exposed heterogeneity of star block copolymers that was not possible by conventional techniques.
与线性聚合物相比，星形聚合物具有更低的流体力学体积、玻璃化转变温度、临界胶束浓度（CMC），以及更高的粘度和载药量。在本研究中，以聚环氧乙烷（PEO）为亲水部分、聚己内酯（PCL）为疏水链段的两亲性可生物降解四臂星形嵌段共聚物，通过以季戊四醇为引发剂、辛酸亚锡为催化剂，使己内酯开环聚合，随后与羧基官能化的单甲氧基聚环氧乙烷（MeO-PEO-COOH）进行偶联反应来合成。通过氢核磁共振（H-NMR）和傅里叶变换红外光谱（FT-IR）对中间体的结构进行了推导。星形嵌段共聚物的平均化学组成通过质子核磁共振确定。通过尺寸排阻色谱（SEC）获得了与目标产物及其前体的摩尔质量分布相关的信息。然而，由于其固有的低分辨率，SEC无法揭示所有母体均聚物是否相互偶联或是否仍未与其他链段相连。为了全面表征合成的星形嵌段共聚物，采用了两种链段临界条件下的液相色谱法。该研究实现了从目标星形嵌段共聚物中分离均聚物前体。该研究揭示了星形嵌段共聚物的异质性，这是传统技术无法实现的。
