Three-dimensional Molecular Geometry of PEG Hydrogels by an “Expansion-Contraction” Method through Monte Carlo Simulations

Three-dimensional(3-D) coarse-grained Monte Carlo algorithms were used to simulate the conformations of swollen hydrogels formed by copper(I)-catalyzed azide-alkyne cycloaddition(Cu AAC). The simulation consists of three successive steps including diffusion, cross-linking and relaxation. The cross-linking of multifunctional reaction sites is simulated instantly followed by fast crosslinking. In order to explore the validity of this approach pristine poly(ethylene glycol)(PEG) hydrogels with tri- and tetra-functional reaction sites(G3 and G4 respectively) were prepared and characterized. The data from the simulations were found to be in good agreement with experimental results such as PEG lengths between crosslinks, pore volume and pore radius distribution, indicating the validity of the modeling algorithm. The calculated PEG lengths in G3 and G4 networks are close(≈ 4.6 nm). The 3-D visual topological structure of the hydrogel network suggests that the "ideal" hydrogel is far from cubic, diamond or any well defined structures of regular repeating cells.     

Synthesis of α-Hydroxy-ω-Aminotelechelic Polypeptide from α-Amino Acid N-Carboxyanhydrides Catalyzed by Alkali-metal Borohydrides

It is reported that alkali-metal borohydrides(MBH4, M = Li, Na and K) are efficient catalysts for ring opening polymerization(ROP) of α-amino acid N-carboxyanhydrides(NCAs). Polypeptides are prepared in quantitative yields with relatively narrow molecular weight distributions(MWDs = 1.1~1.5) which depend on the reaction temperature. End groups of the produced polypeptide are studied in detail by MALDI-ToF MS, 1H-NMR, 13C-NMR, 1H-1H COSY and 1H-13C HMQC analyses. The results indicate that α-hydroxy-ω-aminotelechelic polypeptides are formed which are suitable for postpolymerization functionalization.     

稀土催化聚ε-癸内酯-聚丙交酯-聚乙二醇热塑性弹性体的合成及自组装

以三(2,6-二叔丁基-4-甲基苯氧基)镧为催化剂,1,4-丁二醇为引发剂,ε-癸内酯(ε-DL)和L-丙交酯(L-LA)为单体进行开环聚合,采用"一锅两步法"合成了3种不同比例的三嵌段聚合物(PLLA-PDL-PLLA).以L-赖氨酸二异氰酸酯(LDI)为扩链剂,将PLLA-PDL-PLLA和生物相容性好的聚乙二醇6000(PEG6000)用LDI进行偶联,制备了两亲性多嵌段聚合物(PLLA-PDL-PLLA-PEG)m.多嵌段聚合物(PLLA-PDL-PLLAPEG)m的断裂伸长率高达1200%,是一种拉伸性能较好的热塑性弹性体.由于PEG6000的亲水性,使两亲性多嵌段聚合物可以自组装形成具有较低临界胶束浓度的胶束,有望应用于生物医药领域.     

Homo-and Copolymerization of ε-Caprolactone and 2,2-Dimethyltrimethylene Carbonate by Rare Earth Initiators

ＩｎｔｒｏｄｕｃｔｉｏｎＡｌｉｐｈａｔｉｃｐｏｌｙｅｓｔｅｒｓａｎｄｐｏｌｙｃａｒｂｏｎａｔｅｓｈａｖｅａｔｔｒａｃｔ ｅｄｇｒｏｗｉｎｇｉｎｔｅｒｅｓｔｆｏｒｔｈｅｉｒｅｘｃｅｌｌｅｎｔｐｒｏｐｅｒｔｉｅｓｏｆｂｉｏｄｅｇｒａｄａｂｉｌｉｔｙ ,ｂｉｏｃｏｍｐａｔｉｂｉｌｉｔｙａｎｄｌｏｗｔｏｘｉｃｉｔｙ .Ｔｈｅｉｒｅｘｐｅｃｔｅｄｕｓｅｓｉｎｃｌｕｄｅｄｒｕｇｄｅｌｉｖｅｒｙｍｅｄｉｕｍ ,ｓｕｒｇｉｃａｌｓｕ ｔｕｒｅｓ ,ｂｏｄｙｉｍｐｌａｎｔｍａｔｅｒｉａｌｓ ,ｃｅｌｌｃｕｌｔｕｒｅｓｕｂｓｔ…     

苯并二噻吩/苯并噻二唑ADA型光电化合物:氟取代的影响

在其组成的共轭基元上进行氟取代是有机光电材料功能修饰的常见策略之一.在前期苯并二噻吩/苯并噻二唑ADA型小分子光电化合物基础上,在两个苯并噻二唑基元上引入不同个数的氟取代基,考察氟修饰位置和个数对其基本性质、场效应晶体管和光伏性能的影响.研究表明,随着氟原子数目的增加,化合物的溶解性能降低,热稳定性提高,最高占有轨道和最低空轨道能级降低,但光谱吸收范围变化不大.有机场效应晶体管器件测试表明,当苯并噻二唑单氟代且位于外侧位点时,化合物的空穴迁移率有所降低;当苯并噻二唑双氟代时,迁移率得到了明显提高,达到0.27cm~2·V~(-1)·s~(-1).光伏器件研究发现,氟原子的引入提高了器件的开路电压,但活性层形貌变差,最终导致短路电流密度和电池效率下降.     

含手性亚胺侧基聚苯乙烯衍生物的设计及其在酸碱诱导下的手光响应性质

以N-(2-羟基-1-萘基)亚甲基-(S)-α-苯基乙胺为模型分子,考察了脱质子前后该手性Schiff碱溶液手光性质的变化,利用DFT计算探讨手光信号反转机理.结果表明,手光反转源于分子内氢键的断裂与形成及伴随的C—C单键旋转所引起的构象转变,且前后2种构象处于拟对映关系.这一发现意味着通过单键旋转操控分子构象转变可作为构建手性开关的一种有效途径.在此基础上设计、合成了苯乙烯型手性功能单体(VNP)及相应的光学活性聚合物.由于邻位基团的协同效应,聚合物的手光性质对酸碱刺激表现出比单体更灵敏的响应性和可重复性.当循环加入H+和OH-时,聚合物溶液的CD信号(382 nm处的Cotton效应)以"ON"-"OFF"方式发生可逆转变,以此为输出信号可无损耗重复至少5次,实现了通过酸碱调控的无损输出的新型聚合物基手性开关.此外,基于该手性开关体系构建了典型的"禁阻"(IHIBIT)分子逻辑门.     

环张力驱动环醚单体开环聚合的DFT验证北大核心CSCD

高分子化学教学中,在向学生讲授环状单体开环聚合驱动力时,单体的环张力是决定其能否进行开环聚合的一个非常重要的热力学因素,但有时并非是根本因素。在部分教材上提及顺式-和反式-8-氧杂双环[4.3.0]壬烷(I)、顺式-和反式-7,9-二氧杂双环[4.3.0]壬烷(II)两对顺反异构体时,都认为它们是由于反式异构体环张力大而易于开环聚合。本文通过密度泛函理论(Density Functional Theory,DFT)方法分别计算了它们发生开环聚合的Gibbs自由能变化,发现前者I单体两个异构体能量非常接近,不存在环张力大小的区别,而反式异构体开环产物在能量上更加稳定,利于开环过程。后者II单体则确实是因为反式环状单体的环张力比顺式异构体高,从而有利于开环聚合。本文希望通过这两个实例的DFT计算,阐明这两种不同的机理,并且向学生们介绍量子化学计算方法。     

ε-己内酯在咪唑型离子液体中开环聚合

报道ε-己内酯在咪唑型离子液体([bmim][Cl])和氧化苯乙烯中的开环聚合.离子液体同时起到了溶剂和催化剂的作用,并且能够回收和循环使用.氧化苯乙烯(SO)是开环聚合起始剂,氢核磁谱分析表明聚己内酯(PCL)端基含有一个SO单元.所得PCL的数均分子量为4.22～6.86kDa,分子量分布小于1.3.该体系无需金属催化剂,减少了有机溶剂的使用.     

三(2,6-二叔丁基-4-甲基-苯氧基)镧催化ε-己内酯低温聚合特征及与环碳酸酯嵌段共聚

摘要用三(2,6-二叔丁基-4-甲基-苯氧基)镧[La(OAr)₃]在-15 ℃引发ε-己内酯(CL)的开环聚合, 发现聚合体系具有活性聚合特征. 在第二步聚合过程中继续补加第二种单体三亚甲基环碳酸酯(TMC)或二甲基三亚甲基环碳酸酯(DTC), 可得到CL与环碳酸酯的嵌段共聚物.