Jiasheng Qian

Preparation of pH-sensitive amphiphilic block star polymers, their self-assembling characteristics and release behavior on encapsulated molecules

Poly(ethylene glycol) (PEG), a polymer with excellent biocompatibility, was widely used to form nanoparticles for drug delivery applications. In this paper, based on PEG, a series of pH-sensitive amphiphilic block star polymers of poly(ethylene glycol)-block-poly(ethoxy ethyl glycidyl ether) (PEG-b-PEEGE) with different hydrophobic length were synthesized by living anionic ring-opening polymerization method. The products were characterized using 1H NMR and gel permeation chromatography. These copolymers could self-assemble in aqueous solution to form micellar structure with controlled morphologies. Transmission electron microscopy showed that the nanoparticles are spherical or rodlike with different hydrophilic mass fractions. The pH response of polymeric aggregates from PEG-b-PEEGE was detected by fluorescence probe technique at different pH. A pH-dependent release behavior was observed and pH-responsiveness of PEG-b-PEEGE was affected by the hydrophobic block length. These results demonstrated that star-shaped polymers (PEG-b-PEEGE) are attractive candidates as anticancer drug delivery carriers.

High-efficiency synthesis of dendrimer-like poly(ethylene oxide) via “arm-first” approach

In this study, a dendrimer-like polymer based on poly(ethylene oxide) (PEO) was synthesized through a combination of anionic ring-opening polymerization (AROP) and click reaction via arm-first method. Firstly, the polymeric arm, a linear PEO with one alkynyl group and two bromo groups, was synthesized by AROP of ethylene oxide followed by functionalization with propargyl bromide and esterified with 2-bromopropionic bromide. Second, a star PEO carrying three azide groups was synthesized though AROP of ethylene oxide used 1,1,1-tris(hydrosymethyl) ethane as initiator followed esterificated with 2-bromopropionic acid and azidation. By azide–alkyne click reactions between the azide-terminated PEO star polymer and linear PEO with functionalization alkynyl group, a three generation dendrimer-like PEO, G3-PEO-24Br, was successfully synthesized. The resulting polymers were observed to have precisely controlled molecular weights and compositions with narrow molecular weight distributions.

Solidification behavior of high-density polyethylene (HDPE) during injection molding: Correlation between crystallization kinetics and thermal gradient field

This work mainly investigated the effect of thermal field on the crystallization kinetics of high-density polyethylene (HDPE) during injection molding (IM) process. The thickness X = 0.4 was found to be a crucial location heavily influenced by thermal conduction. The temperature decay tended to be stable, with limited variation of the crystallization rate when X > 0.4. It was observed that the crystallization rate was in good proportion to the cooling rate (). Our experimental finding showed that the consequence of relative crystallinity (χ) was in agreement with that of the secondary temperature difference (STD). This study is practically significant to the further investigation on the relationship among processing-structure-property of polymeric materials.

Y-shaped copolymers of poly(ethylene glycol)-poly(ε-caprolactone) with ketal bond as the branchpoint for drug delivery

In this study, a Y-shaped amphiphilic block copolymer consisting of hydrophilic poly(ethylene glycol) (mPEG) and two poly(ε-caprolactone) (PCL) as the hydrophobic arms with a ketal linker was synthesized (mPEG-Ketal-(PCL)2). The structure of the copolymer with different compositions was characterized by 1H NMR, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The amphiphilic property endows the copolymer with the ability to be self-assembled into micelles for encapsulating anticancer drug doxorubicin (DOX), and the effect of copolymer with different PCL length on drug loading properties were tested. The morphology, size, pH responsiveness, drug release profile and in vitro anticancer activity of the DOX loaded micelles were also studied. In vitro drug release studies showed that over 50% of the DOX was released at pHu202f5.0 in 24u202fh because of hydrolysis of ketal linker in the copolymers. The confocal laser microscopy and flow cytometry experiments showed that the DOX-loaded micelles could be effectively internalized by Hela cells, the ketal bond in the backbone was broken in acid endo/lysosomal compartments and triggered the fast release of DOX. The in vitro antitumor efficacy of the DOX loaded mPEG-Ketal-(PCL)2 micelles was better than that of non-pH sensitive ones. In vivo studies showed that the mPEG-Ketal-(PCL)2 micelles enhanced the DOX blood circulation time and had good tumor-targeting efficiency.

Composite Cationic Exchange Membranes Prepared from Polyvinyl Alcohol (PVA) and Boronic Acid Copolymers for Alkaline Diffusion Dialysis

Boronic acid copolymers with a large number of functional groups were obtained via a free radical polymerization method. The corresponding composite membranes for alkaline diffusion dialysis (DD) were prepared by a crosslinking reaction between polyvinyl alcohol (PVA) and the as-obtained boronic acid copolymers. The composite membranes possessed water uptake (WR) of 122.1–194.4%, ion exchange capacities (IECs) of 0.79–1.17 mmol/g, as well as both good mechanical stability (tensile strength of 40.7–49.9 MPa and elongation at break of 52.1–121.1%) and thermal stability. The as-prepared membranes were stable in 2 M NaOH solution at 65 °C with a swelling degree and mass loss of as-prepared membranes in the range of 305–368% and 9.2–22%, respectively. A NaOH/Na2WO4 mixture was used to investigate the separation properties of as-prepared membranes via the DD process. Results indicated that the dialysis coefficients of OH− (UOH) were in the range of 0.0079–0.0150 m/h, while the separation factors (S) were in the range of 26.6–53.2. The functional groups from boronic acid copolymer and –OH from PVA were demonstrated to promote the ion transport synergistically.

Preparation and Mechanical and Thermal Properties of Chlorinated Polyethylene Reinforced Polypropylene Foam

The foamed polypropylene (PP) with excellent mechanical and thermal insulating properties was reinforced by blending chlorinated polyethylene (CPE), followed by compression molding foaming in cross-link. The effects of CPE on the foaming behavior, thermal and mechanical properties of the foamed PP were studied by the measurements of density, thermal conductivity, Vicat softening temperature, tensile strength, impact strength and SEM. The results showed that the foamed PP got the best properties when the weight ratio of CPE/ PP was 20wt%. The density of the obtained foamed PP was as low as 0.37 g/cm3, the impact strength was 16.5 kJ/m2, the tensile strength was 17.7 MPa, the thermal conductivity was 0.035 W/(m·K), and the Vicat softening temperature was 112 °C.

Synthesis and immobilization of polystyreneb-polyvinyltriethoxysilane micelles

Diblock copolymers polystyrene-block-polyvinyltriethoxysilane (PS-b-PVTES) were synthesized via atom transfer radical polymerization (ATRP), which self-assembled into spherical micelles in solvent of THF-methanol mixtures. The self-assembled micelles were immobilized by cross-linking reaction of VTES in a shell layer of micelles. The chemical structures of block copolymers and morphology of micelles were characterized in detail. It was found that the size of immobilized micelles was strongly affected by the copolymer concentration, composition of mixture solvent, and block ratios.

Melt Crystallization Behavior of Injection-Molded High-Density Polyethylene Based Upon a Solidification Kinetic Analysis

Abstract Rheological characterization and an in-situ temperature measurement were carried out to investigate the solidification behavior and crystallization kinetics of injection-molded (IM) high-density polyethylene (HDPE) samples. The temperature profiles obtained via the enthalpy transformation method (ETM) were also used to disclose the effect of cooling rate on the solidification kinetics during the IM process. A four parameter model (FPM) was developed in the present work, based on a three-parameter model (TPM) we proposed previously, with the FPM shown to have an obviously better fitting effect. It was seen that heat transfer at locations χu2009≤u20090.5 was primarily dominated by a thermal conduction mechanism, which was unlike the situation when χu2009>u20090.5, with χ being the fractional distance from the mold surface to the center. The results of the present study are suggested to be of significance to further research on the correlation between microstructures and properties of IM products.

Electrical Conductivities and Physical and Mechanical Properties of Carbon Fiber (CF) and Carbon Nano-Tube (CNT) Filled Polyolefin Nano-Composites

ABSTRACT Carbon nano-tube (CNT)- and carbon fiber (CF)-filled polyolefin nano-composites were prepared by melt blending. The water absorption, expansion ratio, electrical conductivities, and physical and mechanical properties of the prepared nano-composites were extensively investigated. The experimental results showed that the water absorption increased with the elapsed time from the starting point when the samples were immersed into the water. The linear expansion ratios of the composites were found to increase gradually with time till reaching an equilibrium value. Composites with excellent dielectric properties could be obtained when the filler content was above the percolation threshold. The addition of CNT and CF resulted in no obvious improvement in mechanical properties in the present study, but both Shore hardness and Vicat softening temperature (VST) of the composites increased with increasing filler content. The present work will be of practical importance to the CNT/CF filler composites design, and optimization of processing variables, as well as the further exploration of the “processing-structure-property” relationship of polyolefin materials.

An evaluation of the melt crystallisation behaviour of injection-moulded high-density polyethylene (HDPE) based on a solidification kinetics analysis

ABSTRACT Dynamical rheology, transient temperature measurement, and two-dimensional wide angle X-ray diffraction were performed in this work to investigate the effects of the solidification behaviour and crystallisation kinetics on the gradient structure formation of the injection-moulded high-density polyethylene (HDPE) samples across the thickness. The temperature profiles obtained via enthalpy transformation method were used to elucidate the effect of cooling rates on the solidification kinetics during the injection moulding process. A four-parameter model was proposed for the first time, based on the ‘three-parameter model’ of our previous research, and the former one is shown to have a better fitting effect. Heat transfer at locations χ ≤ 0.5 from the mould surface was found to be primarily dominated by a thermal conduction mechanism, unlike the situation when χ > 0.5. The degree of orientation of the HDPE samples was closely associated with the shear distributions and temperature fields.