Characteristics of acrylic acid-grafted polyethylene prepared by photografting using mixed solvents consisting of water and organic solvent

Photografting of acrylic acid (AA) on linear-low density polyethylene film (thickness=30 μm) was investigated at 60 °C using mixed solvent consisting of water and organic solvents such as acetone and methanol. Xanthone was used as photoinitiator, which was coated on the film earlier. With longer photoirradiation time, such as 40 and 60 min, the percentage of grafting decreased with increasing the concentration of organic solvent in the mixed solvent, where formation of homopolymer occurred preferentially over the grafting reaction. In the system with photoirradiation of 20 min, on the other hand, a maximum percentage of grafting was observed at a certain concentration of organic solvent, in which formation of grafted polymer rather than homopolymer was emphasized. Photografting using the mixed solvent resulted in AA-grafted film with homogeneous distribution of grafted chains, exhibiting larger pH-responsive character, where the grafted film shrinks in an acidic medium, while it swells in an alkaline region. Polymer catalysts for hydrolysis of p-nitrophenylacetate, which was performed at 40 °C in water/ethanol (1/4, v/v)-mixed solvent at pH=9.0, could be prepared by reacting the AA-grafted film with L-histidine and its catalytic activity was slightly influenced by location of grafted chains.     

pH-responsive protein microcapsules fabricated via glutaraldehyde mediated covalent layer-by-layer assembly

Bovine serum albumin (BSA) hollow microcapsules were fabricated through glutaraldehyde (GA) mediated covalent layer-by-layer assembly. The GA cross-linking of the adsorbed BSA on the colloidal particles enabled their surfaces to be covered by reactive aldehyde groups, which reacted with BSA molecules to result in another covalently linked layer. Repeating of this cycle could then yield particles coated with BSA multilayers. Hollow microcapsules well dispersed in water were obtained after core removal. The good integrity and morphology of the BSA capsules were confirmed and characterized by confocal laser scanning microscopy, scanning electron microscopy and scanning force microscopy. The obtained BSA microcapsules possess reversible pH response, i.e., the capsules are permeable to macromolecules below pH 4 or above pH 10, while impermeable in between. The mechanisms of permeability transition were discussed. Using this property, dextran, with a molecular weight of ~155 kDa, was successfully loaded.     

Melting of stress-crystallized polyethylene

The fusion behavior of lightly cross-linked polyethylene films isothermally crystallized at various temperatures and extensions has been examinedonadifferential scanning calorimeter (DSC). Ameans to hold the specimen at fixed elongation during the melting was devised. At large extensions, a separate higher-temperature endotherm was observed in addition to the major peak, indicating a two-phase nature of the crystal morphology. In addition, crystallization experiments performed on the DSC show the crystallization process to consist of two stages. In contrast to reported results for natural rubber and polychloroprene, the melting temperature for polyethylene was not found to be strongly dependent on crystallization temperature or extension. The reason for the differences between polymers is not presently understood, but they may reflect variations in morphological details.     

MePEG-b-PCL-b-PDMAEMA的可控合成及性能研究

采用可控开环聚合(ROP)和原子转移自由基聚合(ATRP)相结合的方法制备出一系列单甲氧基聚乙二醇-b-聚(ε-己内酯)-b-聚甲基丙烯酸-N,N-二甲氨基乙酯(MePEG-b-PCL-b-PDMAEMA). 采用核磁(¹H NMR)和凝胶渗透色谱(GPC)研究了聚合物的结构并对聚合物的分子量大小和分布进行了表征. 聚合物的热稳定性能、结晶性能和亲水性能分别由热重分析仪(TGA)、X-衍射仪(XRD)和静态水滴接触角测定. 分别采用荧光光谱法和¹H NMR(以D₂O为溶剂)方法研究了聚合物纳米粒子的形成. 激光光散射(DLS)和透射电镜(TEM)研究结果表明聚合物纳米粒子具有球形结构, 粒子大小在40～70 nm之间并且对外界环境具有pH敏感性能. MePEG-b-PCL-b-PDMAEMA纳米粒子在同时包裹带有正电荷药物以及疏水性药物方面具有潜在的应用前景.     

A molecular switch based on acid and base promoted, cation governed binding in a crown ether threaded rotaxane

A rotaxane, containing both oligo ethylene glycol and secondary ammonium cation binding sites for a threaded crown ether, has been prepared. ¹H NMR spectroscopy has been used to show that the crown ether moiety in the rotaxane undergoes acid-base and alkali metal cation dependent switch from binding at the ammonium cation position to cooperative binding to the metal cation at the oligo ethylene glycol site.     

Magnetic Nano-Amorphous-Iron-Oxide-Based Drug Delivery System with Dual Therapeutic Mechanisms

Smart nanoparticles that respond to pathophysiological parameters, such as pH, GSH, and H\begin{document}$ _2 $\end{document}O\begin{document}$ _2 $\end{document}, have been developed with the huge and urgent demand for the high-efficient drug delivery systems (DDS) for cancer therapy. Herein, cubic poly(ethylene glycol) (PEG)-modified mesoporous amorphous iron oxide (AFe) nanoparticles (AFe-PEG) have been successfully prepared as pH-stimulated drug carriers, which can combine doxorubicin (DOX) with a high loading capacity of 948 mg/g, forming a novel multifunctional AFe-PEG/DOX nanoparticulate DDS. In an acidic microenvironment, the AFe-PEG/DOX nanoparticles will not only release DOX efficiently, but also release Fe ions to catalyze the transformation of H\begin{document}$ _2 $\end{document}O\begin{document}$ _2 $\end{document} to \begin{document}$ \cdot $\end{document}OH, acting as fenton reagents. In vitro experimental results proved that the AFe-PEG/DOX nanoparticles can achieve combination of chemotherapeutic (CTT) and chemodynamic therapeutic (CDT) effects on Hela tumor cells. Furthermore, the intrinsic magnetism of AFe-PEG/DOX makes its cellular internalization efficiency be improved under an external magnetic field. Therefore, this work develops a new and promising magnetically targeted delivery and dual CTT/CDT therapeutic nano-medicine platform based on amorphous iron oxide.     

pH响应型P(HEMA/MAA)纳米微凝胶分散液的凝胶化行为和流变性能

制备了在修复受损组织方面有应用潜能的纳米级聚(甲基丙烯酸羟乙酯/甲基丙烯酸) (P(HEMA/MAA))微凝胶; 采用试管倒转法对不同pH值和浓度的P(HEMA/MAA)微凝胶分散液的凝胶化相转变行为进行了研究; 借助椎板流变仪考察了低浓度和高浓度微凝胶分散液的流变性能, 并对pH触发物理凝胶化相转变机理进行了推测. 结果表明: 在生理pH值环境下, 一定浓度的P(HEMA/MAA)微凝胶分散液可以发生凝胶化相转变形成凝胶态, pH=7时, HEMA/MAA进料摩尔比为8/2的微凝胶分散液凝胶化后得到的凝胶力学性能最佳, 最大弹性模量(G')可达7.58×10³ Pa; P(HEMA/MAA)微凝胶颗粒在不同条件下具有不同的溶胀效果, 导致低浓度分散液的表观粘度发生相应的变化, 并由此推测出微凝胶颗粒的溶胀过程由外及内, 分为三个阶段; 高浓度微凝胶分散液发生凝胶化相转变主要是由颗粒间或颗粒与分散介质间形成的空间静电稳定作用和氢键共同作用引起的.     

Synthesis and self-assembly of pH-responsive amphiphilic dendritic star-block terpolymer by the combination of ROP, ATRP and click chemistry

Novel pH-responsive amphiphilic dendritic star-block poly(l-lactide)-b-poly(2-(N, N-diethylamino)ethyl methacrylate)-b-poly(ethylene oxide) (DPLLA-b-PDEAEMA-b-PEO) terpolymers were synthesized by the combination of ring-opening polymerization (ROP), atom transfer radical polymerization (ATRP), and click chemistry. DPLLAOH was synthesized by ROP of l-lactide (LLA) and then reacted with propargyl 3-carboxylic-propanoate to obtain alkynyl-DPLLA. PEO-b-PDEAEMA-Br was prepared by ATRP of DEAEMA and then reacted with NaN₃ to obtain PEO-b-PDEAEMA-N₃. DPLLA-b-PDEAEMA-b-PEO was easily prepared by click chemistry of alkynyl-DPLLA and PEO-b-PDEAEMA-N₃. DPLLA-b-PDEAEMA-b-PEO can assemble into micelles in water with PLLA segments as core and PEO segments as corona. The hydrophilicity/hydrophobicity of PDEAEMA can be adjusted with the alteration of pH values. Therefore, PDEAEMA segments form core or corona of micelles at pH ? 7 or pH < 7. Due to the pH-responsive property of PDEAEMA and unique structure of terpolymer, the size and conformation of the micelles can be changed to some extent by altering the pH values of solutions.     

Microgels containing methacrylic acid: effects of composition on pH-triggered swelling and gelation behaviours

pH-responsive microgels are cross-linked polymer colloids that swell when the pH approaches the pK _a of the particles. In this work, we present a comprehensive investigation of pH-triggered particle swelling and gel formation for a range of microgels containing methacrylic acid (MAA). The microgels investigated have the general composition poly(A/MAA/X), where A and X are the primary co-monomer and cross-linking monomer, respectively. The primary co-monomers were methyl methacrylate (MMA), ethyl acrylate (EA) or butyl methacrylate. The cross-linking monomers were either butanediol diacrylate (BDDA) or ethyleneglycol dimethacrylate (EGDMA). The microgels were studied using scanning electron microscopy, photon correlation spectroscopy (PCS) and dynamic rheology measurements. Gel phase diagrams were also constructed. The particles swelled significantly at pH values greater than approximately 6.0. It was shown that poly(EA/MAA/X) microgels swelled more strongly than poly(MMA/MAA/X) microgels. Furthermore, greater swelling occurred for particles prepared using EGDMA than BDDA. Concentrated dispersions of all the microgels studied exhibited pH-triggered gel formation. It was found that the fluid-to-gel transitions for the majority of the six microgel dispersions investigated could be explained using PCS data. In those cases, gelation was attributed to a colloidal glass transition. Interestingly, the microgels that were considered to have the highest hydrophobic content gelation occurred under conditions where little particle swelling was evident from PCS. The data presented show that gelled poly(EA/MAA/BDDA) and poly(MMA/MAA/EGDMA) microgel dispersions have the strongest elasticities at pH = 7.