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2011 Volume 29 Issue 3
2011, 29(3): 274-287
doi: 10.1007/s10118-011-1047-5
Abstract:
Gene therapy has emerged as a potential new approach to treat genetic disorders by delivering therapeutic genes to target diseased tissues. However, its clinical use has been impeded by gene delivery systems. The viral vectors are very efficient in delivering and expressing their carried genes, but they have safety issues in clinical use. While nonviral vectors are much safer with very low risks after careful material design, but their gene transcription efficiency is too low to be clinically used. Thus, rational design of nonviral vectors mimicking the viral vectors would be a way to break this bottleneck. This review compares side-by-side how viral/nonviral gene vectors transcend these biological barriers in terms of blood circulation, cellular uptake, endosome escape, nucleus import and gene transcription.
Gene therapy has emerged as a potential new approach to treat genetic disorders by delivering therapeutic genes to target diseased tissues. However, its clinical use has been impeded by gene delivery systems. The viral vectors are very efficient in delivering and expressing their carried genes, but they have safety issues in clinical use. While nonviral vectors are much safer with very low risks after careful material design, but their gene transcription efficiency is too low to be clinically used. Thus, rational design of nonviral vectors mimicking the viral vectors would be a way to break this bottleneck. This review compares side-by-side how viral/nonviral gene vectors transcend these biological barriers in terms of blood circulation, cellular uptake, endosome escape, nucleus import and gene transcription.
2011, 29(3): 288-295
doi: 10.1007/s10118-011-1046-6
Abstract:
P(AA-MA) copolymers composed of acrylic acid and methyl acrylate with different molecular weights and sequence structures were synthesized by combination of ATRP and selective hydrolysis. These copolymers were used as membrane materials to separate benzene/cyclohexane mixture by pervaporation. The effects of molecular weight and sequence structure of the copolymers on the pervaporation performance were investigated in detail. For the random copolymers, the permeate flux decreased rapidly with the increasing of molecular weight. The separation factor was also influenced by the molecular weight, which was changed from no selectivity to cyclohexane selectivity with increasing the molecular weight. Contrarily, the block copolymer membrane showed good benzene selectivity with separation factor of 4.3 and permeate flux of 157 g/(m2h) to 50 wt% benzene/cyclohexane mixture.
P(AA-MA) copolymers composed of acrylic acid and methyl acrylate with different molecular weights and sequence structures were synthesized by combination of ATRP and selective hydrolysis. These copolymers were used as membrane materials to separate benzene/cyclohexane mixture by pervaporation. The effects of molecular weight and sequence structure of the copolymers on the pervaporation performance were investigated in detail. For the random copolymers, the permeate flux decreased rapidly with the increasing of molecular weight. The separation factor was also influenced by the molecular weight, which was changed from no selectivity to cyclohexane selectivity with increasing the molecular weight. Contrarily, the block copolymer membrane showed good benzene selectivity with separation factor of 4.3 and permeate flux of 157 g/(m2h) to 50 wt% benzene/cyclohexane mixture.
2011, 29(3): 300-307
doi: 10.1007/s10118-011-1034-x
Abstract:
Epoxy-terminatedhyperbranched polymers (EHBPs)were prepared by proton transfer polymerization and characterized by FT-IR, 1H-NMR and GPC. The solution and thermal properties of the uncured samples and mechanical properties of cured samples were examined. The thermo-stable products had good solubility in polar solvents, low solution viscosity and Tgs ranging from 15C to 33C depending on their molecular weights. The mechanical properties of cured films were studied and compared with those of a bisphenol-A type epoxy resin. The films of EHBPs had good impact resistance and high gloss values without sacrificing hardness and adhesion.
Epoxy-terminatedhyperbranched polymers (EHBPs)were prepared by proton transfer polymerization and characterized by FT-IR, 1H-NMR and GPC. The solution and thermal properties of the uncured samples and mechanical properties of cured samples were examined. The thermo-stable products had good solubility in polar solvents, low solution viscosity and Tgs ranging from 15C to 33C depending on their molecular weights. The mechanical properties of cured films were studied and compared with those of a bisphenol-A type epoxy resin. The films of EHBPs had good impact resistance and high gloss values without sacrificing hardness and adhesion.
2011, 29(3): 308-317
doi: 10.1007/s10118-011-1031-0
Abstract:
An aryl dicarboxylic acid amide compound TMB-5 is an efficient b-form nucleating agent for isotactic polypropylene (emPP). Because of the solubility of TMB-5, superstructure and morphology of emPP crystals changed with melting conditions. Effects of final heating temperature (Tf) on heterogeneous nucleation of emPP/TMB-5 were investigated. It was discovered that the crystallization temperature increased with decreasing Tf value. The optical microscopic images indicated that when TMB-5 partially dissolved in emPP melt, the remaining (non-dissolved) TMB-5 facilitated the recrystallization of dissolved nucleating agent from the melt, which promoted crystallization. Complete solubility of nucleating agent caused the decreasing efficiency. TMB-5 recrystallized in the form of tiny needles, whose aggregates induced dendritic emPP crystals.
An aryl dicarboxylic acid amide compound TMB-5 is an efficient b-form nucleating agent for isotactic polypropylene (emPP). Because of the solubility of TMB-5, superstructure and morphology of emPP crystals changed with melting conditions. Effects of final heating temperature (Tf) on heterogeneous nucleation of emPP/TMB-5 were investigated. It was discovered that the crystallization temperature increased with decreasing Tf value. The optical microscopic images indicated that when TMB-5 partially dissolved in emPP melt, the remaining (non-dissolved) TMB-5 facilitated the recrystallization of dissolved nucleating agent from the melt, which promoted crystallization. Complete solubility of nucleating agent caused the decreasing efficiency. TMB-5 recrystallized in the form of tiny needles, whose aggregates induced dendritic emPP crystals.
2011, 29(3): 318-324
doi: 10.1007/s10118-011-1038-6
Abstract:
The effect of externally applied mechanical pre-conditioning, i.e. pre-impact treatment, on the fracture resistance was investigated for polypropylene (PP). Impact strength was obtained via notched and/or unnotched samples. It has been shown that the pre-impact treatment is favorable to the improvement of the fracture resistance. The impact strength increases linearly with the applied pre-impact energy. Both optical and SEM results show that there are at least two possible mechanisms for the improvement of the fracture resistance. One is the crack blunting effect which is introduced to notched sample by pre-impact treatment, reducing the sensitivity of PP to the applied notch. The other is the formation of large amount of microvoids induced by pre-impact treatment, which changes the stress distribution and induces intensive plastic deformation of PP at the second impact measurement, leading to the improvement of the fracture resistance.
The effect of externally applied mechanical pre-conditioning, i.e. pre-impact treatment, on the fracture resistance was investigated for polypropylene (PP). Impact strength was obtained via notched and/or unnotched samples. It has been shown that the pre-impact treatment is favorable to the improvement of the fracture resistance. The impact strength increases linearly with the applied pre-impact energy. Both optical and SEM results show that there are at least two possible mechanisms for the improvement of the fracture resistance. One is the crack blunting effect which is introduced to notched sample by pre-impact treatment, reducing the sensitivity of PP to the applied notch. The other is the formation of large amount of microvoids induced by pre-impact treatment, which changes the stress distribution and induces intensive plastic deformation of PP at the second impact measurement, leading to the improvement of the fracture resistance.
2011, 29(3): 325-335
doi: 10.1007/s10118-011-1040-z
Abstract:
We investigated the effects of molecular weight and film thickness on the crystallization and microphase separation in semicrystalline block copolymer polystyrene-block-poly(L-lactic acid) (PS-b-PLLA) thin films, at the early stage of film evolution (when Tg T TODT) by in situ hot stage atomic force microscopy. For PS-b-PLLA 1 copolymer which had lower molecular weight and higher PLLA fraction, diffusion-controlled break-out crystallization started easily. For PS-b-PLLA 2 with higher molecular weight, crystallization in nanometer scales occurs in local area. After melting of the two copolymer films, islands were observed at the film surface: PS-b-PLLA 1 film was in a disordered phase mixed state while PS-b-PLLA 2 film formed phase-separated lamellar structure paralleling to the substrate. Crystallization-melting and van der Waals forces drove the island formation in PS-b-PLLA 1 film. Film thickness affected the crystallization rate. Crystals grew very slowly in much thinner film of PS-b-PLLA 1 and remained almost unchanged at long time annealing. The incompatibility between PS and PLLA blocks drove the film fluctuation which subsequently evolved into spinodal-like morphology.
We investigated the effects of molecular weight and film thickness on the crystallization and microphase separation in semicrystalline block copolymer polystyrene-block-poly(L-lactic acid) (PS-b-PLLA) thin films, at the early stage of film evolution (when Tg T TODT) by in situ hot stage atomic force microscopy. For PS-b-PLLA 1 copolymer which had lower molecular weight and higher PLLA fraction, diffusion-controlled break-out crystallization started easily. For PS-b-PLLA 2 with higher molecular weight, crystallization in nanometer scales occurs in local area. After melting of the two copolymer films, islands were observed at the film surface: PS-b-PLLA 1 film was in a disordered phase mixed state while PS-b-PLLA 2 film formed phase-separated lamellar structure paralleling to the substrate. Crystallization-melting and van der Waals forces drove the island formation in PS-b-PLLA 1 film. Film thickness affected the crystallization rate. Crystals grew very slowly in much thinner film of PS-b-PLLA 1 and remained almost unchanged at long time annealing. The incompatibility between PS and PLLA blocks drove the film fluctuation which subsequently evolved into spinodal-like morphology.
2011, 29(3): 336-341
doi: 10.1007/s10118-011-1033-y
Abstract:
The effects of various reaction conditions on the preparation of polyalkylcyanoacrylate (PACA) nanoparticles are studied. The PACA nanoparticles with different crosslinking degrees and morphology are prepared. Addition of crosslinkers can not only adjust the particle size, but also change the morphology of PACA nanoparticles. Moreover, the loose network structure of the PACA nanoparticles with core/shell-like morphology is investigated by AFM and TEM in detail.
The effects of various reaction conditions on the preparation of polyalkylcyanoacrylate (PACA) nanoparticles are studied. The PACA nanoparticles with different crosslinking degrees and morphology are prepared. Addition of crosslinkers can not only adjust the particle size, but also change the morphology of PACA nanoparticles. Moreover, the loose network structure of the PACA nanoparticles with core/shell-like morphology is investigated by AFM and TEM in detail.
2011, 29(3): 342-351
doi: 10.1007/s10118-011-1036-8
Abstract:
Magnetically responsive hierarchical magnetite/silica/poly(ethyleneglycol dimethacrylate-co-4-vinylpyridine) (Fe3O4/SiO2/P(EGDMA-co-VPy)) tri-layer microspheres were used as stabilizers for gold metallic nanocolloids as a facilely recoverable catalyst with the reduction of 4-nitrophenol to 4-aminophenol as a model reaction. The magnetic microsphere stabilized gold metallic nanocolloids were prepared by in situ reduction of gold chloride trihydrate with borohydride as reductant via the stabilization effect of the pyridyl groups to gold nanoparticles on the surface of the outer shell-layer of the inorganic/polymer tri-layer microspheres.
Magnetically responsive hierarchical magnetite/silica/poly(ethyleneglycol dimethacrylate-co-4-vinylpyridine) (Fe3O4/SiO2/P(EGDMA-co-VPy)) tri-layer microspheres were used as stabilizers for gold metallic nanocolloids as a facilely recoverable catalyst with the reduction of 4-nitrophenol to 4-aminophenol as a model reaction. The magnetic microsphere stabilized gold metallic nanocolloids were prepared by in situ reduction of gold chloride trihydrate with borohydride as reductant via the stabilization effect of the pyridyl groups to gold nanoparticles on the surface of the outer shell-layer of the inorganic/polymer tri-layer microspheres.
2011, 29(3): 352-359
doi: 10.1007/s10118-011-1039-5
Abstract:
A series of cationic surfmers with benzyl groups (QARBCs) with different R groups on the benzene ring were synthesized and characterized by IR, 1H-NMR, 13C-NMR. The aggregation of QARBCs was studied by the steady-state fluorescence technique. It turned out that QARBCs had surface activity and their critical micelle concentration (CMC)values varied in the range of 10-2-10-3 mol/L with slight increase with temperature. The copolymerization of acrylamide (M1) and QARBCs (M2) was studied below and above CMC, their reactivity ratios were determined by the Finemann-Ross method. It was found that below CMC,copolymerization took place in a homogeneous system and reactivity ratios of acrylamide and QARBCs were less than 1; while above CMC, reactivity ratios of QARBCs were greater than 1. The copolymerization mechanism of QARBC was observed to be similar to that of micellar polymerization. QARBCs tended to homopolymerization, which gave rise to micro-blocky sequences in the polymer backbone. The Qcritical associating concentrations (CAC) were estimated. The results showed that samples of poly(AM-co-QARBC) prepared above CMC had stronger hydrophobic association in aqueous solution than those prepared belowCMC.and e values of QARBCs were calculated according to the Alfrey-Price equation by using r1 (AM) and r2 (QARBC). Samples of poly(AM-co-QARBC) were prepared above and below CMC and their hydrophobic associations were studied by the steady-state fluorescence spectra and 2D NOESY spectra, and their
A series of cationic surfmers with benzyl groups (QARBCs) with different R groups on the benzene ring were synthesized and characterized by IR, 1H-NMR, 13C-NMR. The aggregation of QARBCs was studied by the steady-state fluorescence technique. It turned out that QARBCs had surface activity and their critical micelle concentration (CMC)values varied in the range of 10-2-10-3 mol/L with slight increase with temperature. The copolymerization of acrylamide (M1) and QARBCs (M2) was studied below and above CMC, their reactivity ratios were determined by the Finemann-Ross method. It was found that below CMC,copolymerization took place in a homogeneous system and reactivity ratios of acrylamide and QARBCs were less than 1; while above CMC, reactivity ratios of QARBCs were greater than 1. The copolymerization mechanism of QARBC was observed to be similar to that of micellar polymerization. QARBCs tended to homopolymerization, which gave rise to micro-blocky sequences in the polymer backbone. The Qcritical associating concentrations (CAC) were estimated. The results showed that samples of poly(AM-co-QARBC) prepared above CMC had stronger hydrophobic association in aqueous solution than those prepared belowCMC.and e values of QARBCs were calculated according to the Alfrey-Price equation by using r1 (AM) and r2 (QARBC). Samples of poly(AM-co-QARBC) were prepared above and below CMC and their hydrophobic associations were studied by the steady-state fluorescence spectra and 2D NOESY spectra, and their
2011, 29(3): 360-367
doi: 10.1007/s10118-011-1042-x
Abstract:
The selective cationic polymerization of isobutylene (IB) initiated by a BF3-20C. The effects of CL concentration, BF3 concentration, solvent for preparing BF3-3600) polyisobutylenes (PIBs) with large proportion of exo-double bond end groups were obtained.The exo-double bond content in PIB chain ends increased by increasing CL concentration or by decreasing solvent polarity in initiating system, BF3 concentration and polymerization time. The Mn and MWD of the resulting PIBs were dependent on the concentrations of CL and BF3. Highly reactive PIBs with around 90 mol% of exo-double bonds were successfully synthesized by the selective polymerization of IB from the mixed C4 fraction feed, providing a potentially practical process for its simplicity and low costs.CL complex and polymerization time on the chemical structure of end groups, number-average molecular weight (Mn) and molecular weight distribution (MWD, Mw/Mn) of the resulting polymers were investigated. The experimental results indicate that the BF3CL complex initiating system exhibited an extremely high selectivity toward the cationic polymerization of IB in the mixed C4 fraction feed and low molecular weight (Mn = 900cyclohexanol (CL) complex was carried out from the mixed C4 fraction feed containing the 4C saturated and unsaturated hydrocarbons at
The selective cationic polymerization of isobutylene (IB) initiated by a BF3-20C. The effects of CL concentration, BF3 concentration, solvent for preparing BF3-3600) polyisobutylenes (PIBs) with large proportion of exo-double bond end groups were obtained.The exo-double bond content in PIB chain ends increased by increasing CL concentration or by decreasing solvent polarity in initiating system, BF3 concentration and polymerization time. The Mn and MWD of the resulting PIBs were dependent on the concentrations of CL and BF3. Highly reactive PIBs with around 90 mol% of exo-double bonds were successfully synthesized by the selective polymerization of IB from the mixed C4 fraction feed, providing a potentially practical process for its simplicity and low costs.CL complex and polymerization time on the chemical structure of end groups, number-average molecular weight (Mn) and molecular weight distribution (MWD, Mw/Mn) of the resulting polymers were investigated. The experimental results indicate that the BF3CL complex initiating system exhibited an extremely high selectivity toward the cationic polymerization of IB in the mixed C4 fraction feed and low molecular weight (Mn = 900cyclohexanol (CL) complex was carried out from the mixed C4 fraction feed containing the 4C saturated and unsaturated hydrocarbons at
2011, 29(3): 368-376
doi: 10.1007/s10118-011-1037-7
Abstract:
Graphene oxide was prepared by ultrasonication of completely oxidized graphite and used to improve the flame retardancy of epoxy. The epoxy/graphene oxide nanocomposite was studied in terms of exfoliation/dispersion, thermal stability and flame retardancy. X-ray diffraction and transmission electron microscopy confirmed the exfoliation of the graphene oxide nanosheets in epoxy matrix. Cone calorimeter measurements showed that the time to ignition of the epoxy/graphene oxide nanocomposite was longer than that of neat epoxy. The heat release rate curve of the nanocomposite was broadened compared to that of neat epoxy and the peak heat release rate decreased as well.
Graphene oxide was prepared by ultrasonication of completely oxidized graphite and used to improve the flame retardancy of epoxy. The epoxy/graphene oxide nanocomposite was studied in terms of exfoliation/dispersion, thermal stability and flame retardancy. X-ray diffraction and transmission electron microscopy confirmed the exfoliation of the graphene oxide nanosheets in epoxy matrix. Cone calorimeter measurements showed that the time to ignition of the epoxy/graphene oxide nanocomposite was longer than that of neat epoxy. The heat release rate curve of the nanocomposite was broadened compared to that of neat epoxy and the peak heat release rate decreased as well.
2011, 29(3): 377-389
doi: 10.1007/s10118-011-1035-9
Abstract:
Three types of high-density polyethylene (HDPE) with different molecular weights (high, medium and low) were adopted to evaluate the influence of matrix molecular weight on the structure-property relation of injection-molded HDPE/mica composites through a combination of SEM, 2d-WAXS, DSC, DMA and tensile testing. Various structural factors including orientation, filler dispersion, interfacial interaction between HDPE and mica, etc., which can impact the macroscopic mechanics, were compared in detail among the three HDPE/mica composites. The transcrystallization of HDPE on the mica surface was observed and it exhibited strong matrix molecular weight dependence. Obvious transcrystalline structure was found in the composite with low molecular weight HDPE, whereas it was hard to be detected in the composites with increased HDPE molecular weight. The best reinforcement effect in the composite with low molecular weight HDPE can be understood as mainly due to substantially improved interfacial adhesion between matrix and mica filler, which arises from the transcrystallization mechanism.
Three types of high-density polyethylene (HDPE) with different molecular weights (high, medium and low) were adopted to evaluate the influence of matrix molecular weight on the structure-property relation of injection-molded HDPE/mica composites through a combination of SEM, 2d-WAXS, DSC, DMA and tensile testing. Various structural factors including orientation, filler dispersion, interfacial interaction between HDPE and mica, etc., which can impact the macroscopic mechanics, were compared in detail among the three HDPE/mica composites. The transcrystallization of HDPE on the mica surface was observed and it exhibited strong matrix molecular weight dependence. Obvious transcrystalline structure was found in the composite with low molecular weight HDPE, whereas it was hard to be detected in the composites with increased HDPE molecular weight. The best reinforcement effect in the composite with low molecular weight HDPE can be understood as mainly due to substantially improved interfacial adhesion between matrix and mica filler, which arises from the transcrystallization mechanism.
2011, 29(3): 390-396
doi: 10.1007/s10118-011-1044-8
Abstract:
The poly(2,2-dimethyltrimethylene carbonate) (PDTC) with one hydroxyl and one formate terminal functions was synthesized by in situ generated, tetrahydrosalen stabilized yttrium borohydride complex. The influences of monomer/initiator molar ratio, temperature and reaction time on polymerization of DTC were investigated. Under the condition: [DTC]/[I] = 500, 55C, toluene: 0.5 mL, DTC: 0.6 g, PDTC with Mn = 15600 and PDI = 2.15 was obtained. Through 1H-NMR and 13C-NMR analyses, the structure of PDTC was characterized and a coordination-insertion mechanism was proposed. In addition, the random copolymerization of DTC and caprolactone (CL) initiated by rare-earth borohydride compound was studied. The microstructure of PDTC-co-PCL includes four diads: DTC-CL, CL-CL, DTC-DTC and CL-DTC, which were determined by the specific signals in 1H-NMR spectra. Based on the typical signals of the formate (d= 8.08) and hydroxyl (d= 3.34) end groups of PDTC-co-PCL, a mechanism involving DTC monomer inserts before CL during the initiation process was presumed. Furthermore, the thermal properties of amorphous copolymer were characterized by differential scanning calorimetry (DSC). The results support the random structure of PDTC-co-PCL.
The poly(2,2-dimethyltrimethylene carbonate) (PDTC) with one hydroxyl and one formate terminal functions was synthesized by in situ generated, tetrahydrosalen stabilized yttrium borohydride complex. The influences of monomer/initiator molar ratio, temperature and reaction time on polymerization of DTC were investigated. Under the condition: [DTC]/[I] = 500, 55C, toluene: 0.5 mL, DTC: 0.6 g, PDTC with Mn = 15600 and PDI = 2.15 was obtained. Through 1H-NMR and 13C-NMR analyses, the structure of PDTC was characterized and a coordination-insertion mechanism was proposed. In addition, the random copolymerization of DTC and caprolactone (CL) initiated by rare-earth borohydride compound was studied. The microstructure of PDTC-co-PCL includes four diads: DTC-CL, CL-CL, DTC-DTC and CL-DTC, which were determined by the specific signals in 1H-NMR spectra. Based on the typical signals of the formate (d= 8.08) and hydroxyl (d= 3.34) end groups of PDTC-co-PCL, a mechanism involving DTC monomer inserts before CL during the initiation process was presumed. Furthermore, the thermal properties of amorphous copolymer were characterized by differential scanning calorimetry (DSC). The results support the random structure of PDTC-co-PCL.
2011, 29(3): 296-299
doi: 10.1007/s10118-011-1041-y
Abstract:
The biphenol based discrete ion-pair rare earth complexes, [Ln(EDBP)2(DME)Na(DME)3] [Ln = Er(1), Yb(2), Sm(3)], were prepared and used as catalysts for the ring-opening polymerization (ROP) of 2,2-dimethyltrimethylene carbonate (DTC). Three complexes show moderate activities for the polymerization, and the catalytic activities increase in the following sequence: (Yb Er Sm). The effect of different ratios of [DTC]/[Ln], polymerization temperature and time on the polymerization was investigated. Moreover, PDTC without ether unit developed from possible CO2 elimination was prepared. Biphenol; Ring-opening polymerization; 2,2-Dimethyltrimethylene carbonate
The biphenol based discrete ion-pair rare earth complexes, [Ln(EDBP)2(DME)Na(DME)3] [Ln = Er(1), Yb(2), Sm(3)], were prepared and used as catalysts for the ring-opening polymerization (ROP) of 2,2-dimethyltrimethylene carbonate (DTC). Three complexes show moderate activities for the polymerization, and the catalytic activities increase in the following sequence: (Yb Er Sm). The effect of different ratios of [DTC]/[Ln], polymerization temperature and time on the polymerization was investigated. Moreover, PDTC without ether unit developed from possible CO2 elimination was prepared. Biphenol; Ring-opening polymerization; 2,2-Dimethyltrimethylene carbonate
