最新刊期
卷 ， 期 2 ， 2008
- 摘要：The use of synthetic vascular for cardiovascular and cerebrovascular tissue engineering has made tremendous progress in the past thirty years,but the clinical use of vascular conduits with diameters less than 6 mm remains unsuccessful because of the thrombus formation.Poly(lactic acid) (PLA) was well-suited for applications as tissue engineering materials due to their good biocompatibility and biodegradability.To improve the blood compatibility of polylactide,three polymers based on PLA and poly(malic acid) were synthesized by ring-opening polymerization,namely poly(lactide-co-β-malic acid) (PLMA),poly(lactide-co-RS-hydroxyethyl-b-malolactonate) (PLMAHE) and PLA with pendant carboxyl arms (PCA-PLA).The structure,composition and molecular weight of the copolymers were confirmed by 1H-NMR and GPC.AFM was first used to observe the morphology of the adhered platelets on the polymer films.The platelet adhesion amount on the polymer films was calculated by Hematology Analyzer.The results showed that the copolymers with functional side chains especially with pendant carboxyl arms could obviously reduce the platelet adhesion capacity on the copolymer films compared with PLA.The platelet amount adhered on PLA, PLMA and PLMAHE was 3.2×103,2.5×103 and 1.8×103 after 30 min,respectively,and there was few platelets adhered on the film with pendant carboxyl arms after 1 hour.The thickness of polymer films was determined by AFM,all films of each polymer were about 50 nm thick.From the images of AFM and SEM,it could be seen that only the polymer with hydroxyl groups could activate the platelet.In conclusion,the copolymer with pendant carboxyl was a hopeful material for vessel substitution with good blood compatibility.
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发布时间：2021-03-19 - 摘要：Amphiphilic heteroarm star-shaped polymer was synthesized by the use of polyfunctional chain transfer agent via sequential free radical polymerization in three steps.Firstly,conventional free radical polymerization of methyl methacrylate (MMA) initiated by 2,2′-azobis(isobutyronitrile) (AIBN) was carried out at 70℃ in toluene in the presence of polyfunctional chain transfer agent,pentaerythritol-tetrakis (3-mercaptopropinate) (PETMP),with [MMA]0:[PETMP]0:[AIBN]0 to be 262.5:4:1 and[MMA]0=5 mol/L.After polymerized for 2 h,the monomer conversion reached 43.61%,and HS-PMMA with numberaverage molecular weight to be 4000 determined by gel permeation chromatography (GPC) and polydispersity index 1.37 was obtained.The 1H-NMR spectrum of HS-PMMA confirmed that there were two unreacted thiol groups still existed at the center of PMMA chain.Secondly,the HS-PMMA obtained above was used as macro-chain-transfer agent for free radical polymerization of tert-butyl methacrylate (tBMA).The polymerization of tBMA was carried out at 72℃ in toluene with [tBMA]0:[HS-PMMA]0:[AIBN]0 to be 655:5:1 and [tBMA]0=1.57 mol/L.With the increase of tBMA conversion,the number-average molecular weights of the crude products shifted to higher molecular weight direction.Furthermore,their molecular weight distribution curves were unimodal through out the polymerization process.When tBMA conversion reached 70.00%,its number-average molecular weight increased from 4000 of HS-PMMA to 10600.Its 1H-NMR spectrum showed that the residual thiol groups of the obtained heteroarm polymer decreased from 2.0 of the HS-PMMA to 0.4.That is to say,on average,the heteroarm polymer had two PMMA arms and 1.6 P tBMA arms.Finally,cleavage of the tert-butyl ester groups was achieved by treating the heteroarm star-shaped polymers in 1H-NMR spectrum of hydrolyzed product showed that the tert-butyl protons of the PtBMA disappeared completely,indicating that the PtBMA chains had been successfully transformed into poly(methylacrylic acid) (PMAA) chains.The self-assembly behavior of the amphiphilic heteroarm star-shaped polymer in 1% KOH were investigated.Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to characterize the sizes and size distributions of the aggregates of the hydrolyzed product.TEM showed that the amphiphilic heteroarm star-shaped polymer aggregates took spherical shape and that its diameter was about 50~100 nm.DLS results showed that the average particle diameter was 273.6 nm and the diameter distribution index was 0.114.
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发布时间：2021-03-19
Rapid Communications
- 摘要：Recently a debate about the initial crystallization process which has not been the hotspot for a long time since the theory proposed by Hoffman-Lauritzen (LH) dominated the field arose again.For a long time the Hoffman-Lauritzen model was always confronted by criticism,and some of the points were taken up and led to modifications,but the foundation remained unchanged which deemed that before the nucleation and crystallization the system was uniform.In this article the classical nucleation and growth theory of polymer crystallization was reviewed,and the confusion of the explanations to the polymer crystallization phenomenon was pointed out.LH theory assumes that the growth of lamellae is by the direct attachment of chain sequences from the melt onto smooth lateral sides.Whereas,more and more experimental results show that before the crystallite appears polymer chains go through conformation adjustment and orientation transformation which favor the formation of crystallites, i.e. a preordering structure exists before or at the early stage of polymer crystallization.This is a deviation from the simple process of nucleation and growth at the early stages of melt crystallization which can be gone back to Ostwald’s “rule of stages".Strobl’s multi-step crystallization mechanism based on recent SAXS results was summarized in the paper.The theory assumes for the formation of polymer crystallites,a passage through a transient mesomorphic phase.It is proposed that the initial step is always the creation of a mesomorphic layer which starts with an attachment of chain sequences from the melt onto a growth face of a mesomorphic layer with minimum thickness and spontaneously thickens,up to a critical value,where it solidifies through a cooperative structural transition.The transition produces a granular crystalline layer,which transforms in the last step into homogeneous lamellar crystallites and this granular substructure is observed for many semicrystalline polymers.Crystallization of polymers is controlled by many factors which comprise of the variation of the main structural parameters such as lamellar thickness,long spacing,crystallinity with the crystallization temperature,the structural changes during recrystallization processes and the temperature dependence of growth rates etc. To expatiate upon the transforming process among melting,mesophase and lamellae a thermodynamics scheme was introduced.Many experiments indicate the existence of mesophase,and the thermodynamic framework by Strobl is generally feasible for many situations.Indeed,it is the interference of mesophase which generally dominants polymer crystallization by the selection of the lamellar thickness.Sirota argued that the granular structure of the lamellae was itself a fingerprint of the transient mesophase into which a lamella originally grew,and it was then converted to the higher-density stable form;and the lower interfacial energy of the mesophases is connected with their lower density.Based on Strobl’s suggestion two crystallization modes of mesophase forming polymers have been offered which were partitioned by crystallization rates and only the second case by high rates was deemed to apply to the Ostwald’s rule of stages.In conclusion,it is very important to newly understand the polymer crystallization process for the thermodynamical properties of the mesophase between melting and crystallite.
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发布时间：2021-03-19
Reviews
- 摘要：Contrast agents special for liver are always required to have a relatively longer metabolic time and a stable contrast effect in liver tissue.Therefore,D-lactobionic acid residues,which are generally used as liver-targeted groups,were introduced here.Single N-hydroxysuccinimide active ester of DTPA (SuO-DTPA-Tyr) was synthesized as the ligand of gadolinium (III) ion,forming the basic structure of non-ionic contrast agent.Three α,β poly(L-aspartic acid) derivatives (PD0,PD1 and PD3) with different D-lactobionic acid residue contents were synthesized by conjugation of D-lactobionic acid and single N-hydroxysuccinimide active ester of DTPA with α,β-poly[(2-aminoethyl) L-aspartamide],respectively.Polymeric gadolinium (III) complexes (PD0-Gd,PD1-Gd and PD3-Gd) were prepared by the reaction of α,β-poly(L-aspartic acid) derivatives with GdCl3.6H2O.The contents of D-lactobionic residues and gadolinium (III) were determined by quantitative13C-NMR and ICP,respectively.Properties of these polymeric contrast agents were evaluated here.Cytotoxicity test shows that all the polymer ligands (PC0,PC1 and PC3) have better cell viability rate than that of poly(L-lysine) with corresponding concentrations.The value of cell viability rate rises with the increase of D-lactobionic acid residue content.The reason is the D-lactobionic acid residues mostly shield the positive charge of backbone,which blocks the delivery of carrier to the cells.Compared with the commercial contrast agents,polymer complexes have the same level of cytotoxicity.However,their relaxivities (7.77,8.00 and 9.48 mmolL-1s-1 for PD0-Gd,PD1-Gd and PD3-Gd,respectively) are obviously higher than that of commercial contrast agents (5.95 mmolL-1s-1 for dimeglnmine gadopentetate).That is because the mobility of polymer molecules is lower than that of small molecules,which leads to an increase of relaxivities.Experiments in vivo were carried out on ICR mice,which were divded into 3 groups for 3 different contrast agents (PD0-Gd,PD3-Gd and Dimeglnmine Gadopentetate for commercial used).Mice for each contrast agent were also divided into 5 groups (6 mice each) for testing in different time after injections.As the result shows,polymeric complex with liver targeted groups gives a better result than that of complex without liver targeted groups.All of the polymeric complexes give much better image contrast effects and longer circular time than that of commercial contrast agent in mice livers.During the first 6 h after being injected,polymeric complexes with D-lactobionic residues have much lower metabolism rate than those without D-lactobionic residues and gives the clearest liver image among all those contrast agents,even though the signal is not the strongest one which mostly depends on the relaxivities.Besides that,mice liver with liver-targeted complexes show a stable and clear image statistically.After 6 h,metabolism rate of liver targeted polymer complex increases and has almost same metabolism rate as that of commercial contrast agent.Those results illustrate that the introduction of D-lactobionic acid residues can moderately prolong the metabolic time in liver and stabilize the liver signal enhanced by contrast agents.
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发布时间：2021-03-19 - 摘要：A kind of hydrophobic silica with good dispersibility was prepared first.The silica and epoxy natural rubber (ENR) were blended in Haake internal mixer at high temperature in a powerful shear force filed,and so the grafted silica was made through in-situ grafting reaction between the hydroxyl groups of silica and the epoxy groups of ENR.The grafting processes were performed as follows:first,the silica should be dried about 24 h at 100℃ in an oven to remove the free water molecules that absorbed on the surface of silica.Secondly,the grafting reaction temperature was chosen at 170℃ that confirmed by the test result of a Monsanto MDR2000 moving die rheometer,and the weight proportions between silica and ENR were chosen to be 1:1,2:1 and 3:1 separately in this study.Thirdly,ENR was mixed in HAAKE internal mixer about 1 min,then silica was added to react with the ENR for another 15 min before discharged,and the outputs named ENR-grafted silica were obtained as we wanted.In order to obtain an appropriate grafting condition,the effect of different weight proportions between silica and ENR on the stress-strain curves of natural rubber composites reinforced by the grafted silica was discussed.Through analyses of the reinforcement effect,the appropriate proportion between silica and ENR was chosen to be 3:1.FTIR,TGA and TEM analysis results indicated that ENR was successfully grafted onto the silica surface.FTIR result of the grafted silica showed the new absorptions. The peaks at 2966，2929 and 2862 cm-1 are assigned to C—H stretching vibrations.The absorption band at 1660 cm-1 is characteristic of C＝C stretching.The stretching vibration of epoxy groups that should be at 870 cm-1 was missing,suggesting the epoxy groups were almost used up to react with silanol groups.A new shoulder peak appears at 3640 cm-1,which is ascribed to —OH stretching of C—OH which is the result of the reaction of silanol groups and ENR.TGA curves revealed ENR grafted silica showed a new step between 348～449℃ due to the decomposition of ENR,and the grafting rate reached 21.3%.TEM images indicated the size of silica agglomerates became small obviously after modification because of the grafting layer preventing the silica particles from conglomerating.Then,compared with the silica without grafting,the properties of NR composites filled with grafted silica were investigated.The “Payne effect” results indicated that the grafted ENR molecules reduced the silicasilica interaction by enhancing the rubbersilica interaction,and so the grafted silica had better dispersibility in natural rubber (NR) composites.Mechanical properties test of NR composites proved that the grafted silica could more effectively improve the reinforcement effect due to the strong interface combination between silica and ENR.DMA results showed that the temperature of glassy transition of ENR bound to the silica surface shifted to higher temperatures.Consequently,the composite contained the grafted silica had high strength and high hysteresis at the same time on the normal temperature.So the composites have potential application in the shocking absorber products,the tire of racing cars,and so on.
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发布时间：2021-03-19 - 摘要：The carbocationic polymerization of isobutylene (IB) in a mixture of methylene dichloride (CH2Cl2) and hexane (Hex) was conducted by using H2O as initiator,TiCl4 as co-initiator in the presence of a small amount of oxygencontaining additive,such as methanol(MeOH),isopropanol or ethyl ether.The effects of MeOH concentration,TiCl4 concentration,monomer concentration,solvent polarity and polymerization time on the IB carbocationic polymerization,polyisobutylene (PIB) yield,molecular weight (MW) and molecular weight distribution(MWD,Mw/Mn) and endgroups of PIB chains were investigated.The polymerization products were characterized by gel permeation chromatography (GPC) and 1H-NMR spectroscopy.The carbocationic polymerization of IB in C4 fractions including 2-butane,butane,isobutylene,1-butene and 1,3-butadiene by using H2O/TiCl4/MeOH as initiating system was also investigated.MeOH did play important and effective roles in polymerization initiated by H2O/TiCl4 system.The relative amount of polymers formed via uncontrolled initiation by conventional active species decreased with increasing the concentration of MeOH.MeOH and/or its complexe with TiCl4 interacted with the growing chain end to reduce its cationicity and thus to decrease the propagation rate,decrease MW,suppress the uncontrolled chain transfer and termination reactions, and thus to narrow MWD.The desirable polymerization of IB with relatively slow polymerization rate could be obtained by H2O/TiCl4 initiating system in the presence of MeOH under the appropriate reaction conditions,and PIB products with low molecular weight (Mn=1600～4600) and narrow unimodal molecular weight distribution (Mw/Mn=1.35～2.05) could be obtained.It is found that MeOH also played an extra important role in increasing the content of vinylidene (α-double bonds) in polymer chain ends.The tert-chlorine in PIB chain end obviously decreased with increasing MeOH concentration.The content of α-double bonds increased with decreasing H2O concentration and monomer concentration or prolonging polymerization time.The highly reactive polyisobutylene (HRPIB) with the content of α-double bonds more than 70% could be synthesized by using H2O/TiCl4 initiating system in the presence of MeOH,isopropanol and ether under the appropriate reaction conditions.Furthermore,the preliminary investigation on the IB polymerization in C4 fractions shows that the molecular weight,molecular weight distribution and the content of tert-chlorine end groups of PIB products decreased while the content of α-double bonds at end groups increased with MeOH concentration in the polymerization system.The polymer with Mn of 2000,Mw/Mn of 2.59 and vinylidene isomer content of 38.9% could be obtained.
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发布时间：2021-03-19 - 摘要：Recently the preparation of biodegradable materials using proteins from wheat,soy and corn has been widely studied due to their excellent cohesive,viscoelastic and gas barrier properties.The present work mainly focuses on the influences of starch and moisture contents on the dynamic rhelolgical behavior and uniaxial extensional deformation of glycerol plasticized gluten-starch composites.Wheat gluten,wheat starch and glycerol, compounds with weight ratio of 21:0P9,18:3:9,15:6:9,and 12:9:9,respectively,were prepared by using a three-roll mixer.The compounds were molded into rectangle or dumbbell-shaped samples of 2 mm in thickness and 6 mm in width at room temperature.The dynamic behaviors of the mixtures were investigated using an Advanced Rheometeric Expansion System (ARES) at 0.1% strain and 30℃.The tensile test was performed on a universal testing machine with an extension rate of 20 mm min-1.The results showed that the dynamic storage modulus (G′) of the composite increased with increasing starch fraction.The plasticized gluten forms a crosslinking network at 80℃ due to chemical reaction.The results of temperature scan revealed a “rubber plateau" at temperatures above 100℃.The starch gelatinization was not observed upon heating the composites.It indicates that moisture mainly exists in the glycerol-rich region, and the starch granules act as inert fillers.The dynamic frequency sweep shows that the composites exhibit gel-like behavior at 30℃.A marked “second plateau" appears in the low frequency region,which reveals strong physical interactions between the starch particles and the protein matrix.The interactions between polar groups in starch and protein both lead to the formation of a physical network additional to the chemical crosslinked protein network.The results of uniaxial extensional deformation tests show that the tensile strength and the elongation at break decrease with increasing the starch fraction in samples with 10% moisture.On the other hand,opposite results were observed in the composites containing 20% and 25% moisture,which could be ascribed to the dilution and lubrication between the starch granule and the gluten network by moisture.
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发布时间：2021-03-19 - 摘要：Two kinds of polyphosphazenes,that bear α-D-glucosyl side groups together with methoxyethoxy or ethyl glycinato as cosubstituent groups,have been synthesized and characterized by IR and 1H-NMR analyses.They were examined in order to investigate their possible use as matrix for glucose-sensitive insulin delivery basing on the specific interaction of glucose with lection.Briefly, the polymers were prepared via nucleophilic displacement of the reactive chlorines of polydichlorophosphazene with diisopropylidene D-glucose at first, and subsequently with methoxyethanol (polymer a) or glycine ethyl ester (polymer b) to substitute the residual P-Cl. After filtration and dialysis, the purified polymers were then treated with 90% trifluoroacetic acid to remove isopropylidene groups to get glucosyl groups. The formation of aggregates of glucosyl_substituted polyphosphazenes physically crosslinked by Concanavalin A (Con A) was studied by monitoring the transmittance at 360 nm of dilute polymeric aqueous solutions. Hydrogels were made by mixing concentrated glucosyl-substituted polyphosphazene aqueous solution with Con A aqueous solution.Different polyphosphazenes with various compositions of α-D-glucosyl side group and methoxyethoxy or ethyl glycinato side group combinations were obtained by adjusting the feeding dose of the nucleophiles. And their hydrophilicity differed from each other for the methoxyethoxy group is hydrophilic, and the ethyl glycinato group is hydrophobic, which would affect the formation of hydrogel and the drug release thereof in different way. In the deprotection reaction, the treating time needed to be prolonged to complete the hydrolysis of isopropylidene groups, however, it would cause significant cleavage of polyphosphazene backbones and degradation of cosubstituted ethyl glycinato groups (while almost no effect to methoxyethoxy) in the strong acidic condition. As a result, the deprotection ratio of glucoses was maintained at about 60% in this study to avoid remarkable decrease in molecular weight, and at the same time, the remained diisopropylidene D_glucosyl groups were considered biocompatible and might play a role in balancing polymeric hydrophilicity/hydrophobicity. Con A is one of the most widely used lectins in studying the interaction of specific saccharide with protein, particularly, for nonreducing D-mannosyl and D_glucosyl residues. For both polymers a and b, their dilute solutions rapidly turned turbid when Con A was mixed into, and turbidity increased with increasing the concentration of polymeric solutions and the content of glucosyl side groups in the polymers due to the formation of more and larger aggregates. The aggregates could be dissociated by addition of free glucose, and transmittance of the solution increased. On the other hand, it has been found that the transmittance data of solutions of polymer a mixed with Con A were much larger that those of polymer b, even if they had the similar amount of glucosyl side groups and the same polymeric concentration. One possible reason for this phenomenon was that polymer b could not dissolve well in water due to the presence of hydrophobic ethyl glycinato side groups, and the interaction between Con A and glucosyl groups was hindered. Thus, hydrogels were made from polymer a and Con A by increasing the polymeric concentration above 10 wt%.Higher concentrations of glucosyl-substituted polyphosphazene, more hydrophilic co-substituted side groups and higher amounts of glucosyl side groups would be in favor of hydrogel formation. This hydrogel can be a potential matrix for glusoce_sensitive insulin delivery.
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发布时间：2021-03-19 - 摘要：In recent years,core-shell micro-particles and hollow capsules have aroused great research interests as new useful microstructures for many potential applications.In this work,core-shell spheres and hollow capsules containing azo polyelectrolytes were prepared by electrostatic layer-by-layer self-assembly and core-dissolution after the multiplayer deposition.In the electrostatic layer-by-layer self-assembling process,a side-chain azo polyelectrolytes (PEAPE) as polyanion was alternately adsorbed onto surfaces of polystyrene (PS) colloidal spheres together with a polycation of poly(diallyldimethylammonium chloride) (PDAC).PEAPE is a random copolymer composed of acrylic and azobenzene-containing acrylate units.PEAPE samples with degree of functionalization (DF) of 9.3% and 41.4% were used.Solutions of the polyelectrolytes (PEAPE and PDAC) in water and an aqueous medium of 0.1 mol/L NaCl were alternately added into the diluted suspension of PS latex for electrostatic layer-by-layer adsorption.After 15 min,PS spheres were separated and washed by high-speed centrifuge (ultracentrifuge,Hitachi CR 22G).Then the sediment was dispersed in Milli-Q water again for further experiment.The experiment steps were repeated several times until the required layer number was reached.The resulted core-shell particles were characterized by transmission electron microscopy (TEM,JEM-1200EX) and dynamic light scattering (DLS,Malvern Zetasizer 3000 HS).The layer-by-layer adsorption of PEAPE and PDAC was evidenced by the diameter increase from the TEM images and DLS measurements.The oscillation of Zete-potenctial after each adsorption step,which indicates the over charge compensation,also confirmed the successive self-assembly of azo polyelectrolytes.Changing the ionic strength of PDAC solution (in water or in aqueous medium of 0.1 mol/L NaCl) could obviously shift the Zete-potenctial of the colloids,but had little influence on the diameter increasing of the colloidal spheres.The photoisomerization of the azobenzenes was studied by UVVis spectroscopy.These azobenzene-containing core-shell particles show typical photochromic effect upon UV light irradiation.After adsorbed to colloidal surfaces,the H-aggregation of azobenzene groups decreased in certain degree and resulted in red shifts in UV-Vis spectrum.As a consequence,the azobenzene chromophores exhibited quickly photo-response behavior upon UV irradiation.To obtain hollow capsules with stable shells,a photosensitive cinnamate-containing polyelectrolyte (PAAEH,DF = 27%),synthesized in authors’ lab,was applied to induce covalent crosslinking in the shells of colloidal spheres.In the process,PAAEH was adsorbed onto the core-shell particles of PS/(PDAC/PEAPE)3 through electrostatic self-assembly together with PDAC.In the process,PAAEH was dissolved in Milli-Q water with a concentration of 1 mg/mL and used as polyanions.After two or three layers of PDAC/PAAEH adsorbed,the core-shell colloidal spheres were exposed to UV light (18 mW/cm2) for 30 min.The photosensitive shells were cross-linked upon UV-light radiation.Then PS core of colloidal spheres was removed by dissolving with tetrahydrofuran/H2O (Ｖ:V=1:1).Finally,hollow capsules containing azo chromophores were obtained.Due to their photoresponsive composition, the core-shell particles and hollow capsules may have potential applications in areas such as bio-medicine and photoelectronics.
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发布时间：2021-03-19 - 摘要：Super-hydrophobic surfaces have attracted great research interest dueto their novel performance as self-cleaning,anti-fog,and antioxidation.In this work,a new approach,based on elastomeric templates and UV-curable resins,has been developed to prepare super-hydrophobic surfaces.Poly(dimethylsiloxane) (PDMS,Sylgard 184) was purchased from Dow Corning and used to replicate lotus-leaf surfaces.In the replication step,PDMS blocks were prepared through replica molding against lotus-leaf surfaces.PDMS prepolymer was prepared by mixing the elastomer base and curing agent in a ratio of 10:1.After 20 min,the PDMS prepolymer was poured into molds within fresh lotus-leaf surfaces as masters.Then the prepolymer was cured in 40℃ oven for 4 h.After curing and peeling off,the PDMS blocks with negative lotus-leaf surfaces’ structures were obtained.Microscope observation indicates that the PDMS blocks’ surfaces were featured with hollow cavities of 7~12 microns in diameter.The PDMS blocks could be used as stamps in the following curing step of ultraviolet (UV)-curable prepolymers,which consist of oligomer, cross-linking agent,reactive monomer,and photo-initiator.In the experiment,isobornyl acrylate,siliconized urethane acrylate,benzoin dimethyl ether and dipentaerythritol pentaacrylate were used as monomer,oligomer,photoinitiator and crosslinking agent,respectively.In a typical process,UV-curable prepolymer was prepared by mixing monomer,oligomer,photoinitiator and crosslinking agent in a ratio of 10:68:2:20 Then the prepolymer was put into a 0.085 MPa vacuum oven to remove air bubble.The prepolymer was spread on substrates (silicon wafer or glass slide),pressed by the PDMS stamp with replicated lotusleaf surface.Finally,the UV-curable prepolymer covered with the PDMS stamp was exposed to UV-light (500 μW/cm2).After curing for 15 min,the PDMS stamp was peeled off,and the cured sample was store in 40℃ oven for 5 h before further experiments.Measured by scanning electron microscopy (SEM,Hitachi S-4500),a large amount of papillary microstructures with an average diameter of about 7~10 microns and average height of 10~18 microns could be seen on the surfaces.These papillary microstructures are replicas of the surface patterns of the lotus leaves.The obtained surfaces had water contact angles larger than 150° and small sliding angles,exhibiting fascinating super-hydrophobicity like lotus-leaf surfaces.Obviously,the replicated papillary microstructures played important role in the increase of surface hydrophobicity from about 105° (smooth film surface) to 157°.This result can be explained with the Wenzel theory.Factors influencing the wettability of resulted surfaces,such as content of monomer,cross-linking agent,initiator and light irradiation time,were also studied in detail.Experiments showed that the surface contact angles increase with the content of photoinitiator before 0.7%,and decrease with the content of crosslinking agent when larger than 20%.A monomer content of about 10% and irradiation time longer than 10 min were also preferable for achieving high hydrophobicity.Combining the advantages of soft-lithographic and UV-curing techniques,this approach can be potentially applied in fabrication of large-area super-hydrophobic surfaces.
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发布时间：2021-03-19 - 摘要：Triblock copolymers;poly(2-ethyl-2-oxazoline)-b-poly(ε-caprolactone)-b-poly(L-glutamic acid) (PEOz-b-PCL-b-PLGlu)s with thermo-sensitive PEOz and pH-sensitive PLGlu have been successfully synthesized.Synthetic procedure includes the following steps.(1) PEOz capped with hydroxyl groups was prepared by ring-opening polymerization of 2-ethyl-2-oxazoline using methyl-p-toluenesulfonate as initiator,and following transformation of terminal cationic ions into hydroxyl groups in the presence of KOH.The molecular weights of the resultant polymers increased with increasing the molar ratio of monomer to initiator.(2) The block copolymers,PEOz-b-PCL were synthesized by ring-opening polymerization of ε-caprolactone using PEOz-OH as macroinitiator and Sn(Oct)2 as catalyst.Their structure was confirmed by their 1H-NMR and FT-IR spectra.In comparison with FT-IR spectrum of its precursor PEOz,a new absorption band at υ = 1734 cm-1 was observed,and the characteristic signals of PEOz and PCL could be found in the 1H-NMR spectra,δ= 3.47,2.21~2.56 and 1.14 for PEOz,δ = 4.12、2.35、1.68 and 1.43 for PCL.The relative amount of the two monomer units in the resultant copolymers is determined by their molar ratio in the feed.Their Mn (NMR) agrees well with the theoretical number-average molecular weight, and their molecular weight distribution is relatively narrow.(3) For application of PEOz-b-PCL-OH as macroinitiator in the ring-opening polymerization of N-carboxyl anhydride of γ-benzyl-L-glutamate (BLG-NCA),it is necessary to convert the terminal hydroxyl group into primary amine.This transformation was achieved by condensation reaction of PEOz-b-PCL-OH with Phe-NBOC in the presence of DCC,and successively the protective group BOC was removed to produce amine-terminated copolymer after treated with TFA.Based on the integration ratio of ester methylene protons in PCL to the new signal at δ = 7.38 corresponding to phenyl protons in the terminal phenylalanine group,we can estimated that this reaction efficiency was very high.(4) The triblcok copolymer,PEOz-b-PCL-b-PBLG was obtained by ring-opening polymerization of BLG-NCA derived from benzyl glutamate using PEOz-b-PCL-NH2 as macroinitiator,and the polymerization was carried out in CH3Cl at 30℃ for 72 h.Its FTIR spectrum showed the absorption bands of NH and benzene ring at υ = 3292,697 and 749 cm-1,indicating the occurrence of the block copolymerization.The structure of the resultant triblock copolymer was further verified by its 1H-NMR spectrum,the characteristic signals of PEOz,PCL and PBLG appeared at δ = 3.47 (—NHCH2 in PEOz),4.12 Ｄ(COOCH2Ｆ in PCL) and 5.07 Ｄ(PhCH2Ｆ in PBLG) respectively.Based on their integration ratio,their relative amount in the copolymer can be calculated.(5) The protective benzyl groups in PEOz-b-PCL-b-PBLG was removed and the target triblock copolymer,PEOz-b-PCL-b-PLGlu was obtained after treated with HBr.Complete disappearance of benzyl signals at δ = 5.07 and 7.28 in their 1H-NMR spectra indicates the complete removal of benzyl groups.The molecular weights and molecular weight distributions of the polymers obtained at every synthetic step were measured by GPC,we can see that the GPC curves of PEOz,PEOz-b-PCL and PEOz-b-PCL-b-PLGlu were shifted to high molecular weight position completely,no corresponding precursors were detected and all of them were single and symmetrical,indicating high initiation efficiency of the (macro) initiator.All the molecular weight distributions (Mw/Mn = 1.10~1.33) are relatively narrow.Generally,the molecular weights can be controlled by their feed molar ratios of monomer to (macro) initiators.The thermo and pH sensitivities of the triblock copolymers are under investigation,the results will published in another paper.
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发布时间：2021-03-19 - 摘要：The porous magnetic polymer microspheres containing carboxyl group were prepared by modified suspension polymerization by using stryene (St),divinylbenzene (DVB) and methacrylic acid (MAA) as monomers in the presence of magnetic γ-Fe2O3 which was coated with oleic acid (OA).In this experiment,three modification measures were adopted.First,the surface of the magnetic particles was treated by anionic surfactant OA to improve the hydrophobicity of mciro-size magnetic γ-Fe2O3 Second,the monomer phase containing surface modified magnetic particles and porogens was sonicated for some time to improve the dispersibility of magnetic γ-Fe2O3 in the monomer phase and strengthen absorbence of the monomer and initiator on the γ-Fe2O3 surface.Third,the aqueous phase was added to the monomer phase,and the mixture was sonicated for some time before polymerization to make sure all the magnetic particles can be dispersed in the monomer phase to form stable and uniform droplets which is diffrent from the conventional suspension polymerization with the monomer phase added to the aqueous phase.The pretreatment and polymerization process are as follows:Firstly,10~20 g sample of magnetic particles was added to 200 mL ethanol/water solution (volume ratio=1),and sonicated in a 250 mL beaker for 0.5 h to eliminate impurities on its surface.Then,the purified magnetic powder and 120 g deionized water were mixed together in a 250 mL,three-necked flask equipped with a stirrer,a condenser and a thermometer.As the mixture heated to 85℃,the OA (2/3 (wt/wt) to magnetic particles) was added dropwise within 15 min and the reaction was kept at pH=5.5 for 1 h with vigorous stirring.Afterwards,the resulting materials were isolated by magnetic decantation and washed with deionized water for several times to remove the excess OA.The treated magnetic particles were dried at 50℃ for 12 h.Magnetic porous microspheres were prepared by modified suspension polymerization in a 250 mL fourneck,roundbottomed flask fitted with a mechanical stirrer,a thermometer,a reflux condenser and a nitrogen gas inlet tube.The monomer phase which consisted of 15 mL monomers (St/MAA/DVB＝9/3/3(mL)),0.2 g AIBN as initiator,15 mL diluent system(toluene/n-heptane=2/1 (V/V)) and surface treated magnetic particles was sonicated for 15min.The aqueous phase (AP) was prepared by addition of 0.48 g HEC,0.5 g NaCl and 90 mL deionized water.Then the aqueous phase was added to the organic phase and sonicated for 15 min.Hence,the suspension system was kept at 70℃ for 24 h.The polymer produced beads were filtrated and washed with hot distilled water,ethanol and acetone several times to remove water-soluble impurities,followed by soak in 1 mol/L HCl for 48 h and extraction with solvent in a Soxhlet extractor for 24 h to remove the porogens and organic impurities.The purified beads were washed with methanol and distilled water and then dried under vacuum for 24 h.FTIR,SEM,optical microscopy and TG were used to characterize the chemical composition,morphology,size and magnetic particle distribution and magnetic characteristics of magnetic polymer microsphere.FTIR analysis demonstrated that the hydrophobicity of magnetic γ-Fe2O3 was improved significantly by chemisorption and esterification after the surface modified by oleic acid.The results of FTIR and optical microscopy analysis demonstrated that the desired polymer was bonded to the surface of γ-Fe2O3 particles, and the polymer microspheres contained carboxyl groups.But the magnetic particles were not uniformly incorporated in the magnetic microspheres because of the magnetic agglomerating force.The morphology analysis by SEM and optical microscopy confirmed that the composite magnetic γ-Fe2O3/P(St-DVB-MAA) microsphere had a good sphericity with porous structure and a relatively uniform diameter of about 0.4~0.9 mm.The results of TG analysis indicated the content of magnetite in microspheres was 12.12%.
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发布时间：2021-03-19
Research Article
- 摘要：Amphiphilic block copolymers (PETLA) composed of D,L-lactide,trimethylene carbonate (TMC) and methoxy poly(ethylene glycol) (mPEG) were synthesized with ringopening copolymerization.Initiation of D,L-LA and TMC copolymerization wtih mPEG provided to manipulate the molecular weight of the hydrophobic block. Copolymer characterization with 1H-NMR and gel permeation chromatograph (GPC) illustrated the final copolymer compositions were agreed with the theoretical values in feeding doses. Studies on micellization and drug controlled release behaviors of copolymer PETLA were performed with fluorescence spectroscopy, GPC, dynamic light scattering (DLS), transmission electron microscope (TEM), and ultraviolet spectroscopy (UV). Micelles of MT1 to MT4 were prepared from PETLA1 to PETLA4 respectively. Fluorescence technique with pyrene as hydrophobic probe was used to study the formation of core-shell type micelles. As a result, the critical micelle concentration (CMC) of PETLA was decreased from 5×10-3 g/L (PETLA1) to 2.5 × 10-4 g/L (PETLA4) with the increase of chain length in hydrophobic block while keeping constant corona-forming block. GPC characterization was used to describe the aggregation behavior of copolymers in selective solvent, by which the molecular weight of micelles was determined,and it was increased obviously from MT1 (277500 Dalton) to MT3 (644800 Dalton). Consistent to GPC results, DLS tests indicated the micellar diameters from MT1 to MT3 were increased from 30 nm to 60 nm. This would be related to the following reasons: the length of the hydrophobic block determined the space each chain required in the core, and the block copolymer with high hydrophobic length needed more core space to form larger micelles. TEM photograph illustrated that micelles MT1 had typical core-shell structure and regularly spherical morphology with the diameter of 30~40 nm after negative staining by phosphotungstic acid. Taking 9-nitro-20(s)-camptothecin (9-NC) as model drug, release profiles in vitro shown that the release behavior of 9-NC from micelles was in controlled manner and nearly in zero order after the initial burst release. The release rate decreased from MT1 to MT4, this was because the micelles composed of high hydrophobic composition could form large hydrophobic core and could encapsulate more drags through strong hydrophobic interactions, and the incorporated drug would take relatively long time to overcome the hydrophobic interaction then diffuse across the polymer matrix to the medium. Based on the results given above, micelles with hydrophobic part composed of D,L-lactide and TMC were not only help to control the release behavior of hydrophobic drug, but also help to alleviate local inflammation response which was elicited by acid production biodegraded from poly(D,L-lactide). In conclusion, novel copolymer micelles could open new opportunities for the delivery of poorly soluble anticancer drugs.
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发布时间：2021-03-19 - 摘要：Linear and multi-arm atactic polystyrene with functional groups―OH was synthesized via living free radical polymerization promoted by titanocene complexes in the presence of glycidyl-4-methoxyphenyl ether (I1), 1,4-butanediol diglycidyl ether (I2), 4,4′-methylenebis(N,N-diglycidylaniline) (I4) and poly[(phenylglycidyl ether)-co-formaldehyde] (I5) as initiators, and Sn as reducing agent in this catalyst system. The polymerization mechanism was expatiated. In this article, for the first time, titanocene complexes, for example CpTi(Ⅳ)Cl3 was treated with Sn to form primary free radical CpTi’(Ⅲ)C12 at room temperature, this radical reacted with epoxide(initiator) to give the chain radical which initiated styrene to propagate successfully. The effect of polymerization conditions, such as the structure of the initiator and titanocene complexes, as well as the ratio of initiator to monomers on the performance was investigated. The properties of the obtained polymer were also characterized by GPC. These results showed that the structure of initiator had little influence on the conversion of monomer, the molecular weight and molecular weight distribution of the obtained polymer. Compared with (n-BuCp)2TiCl2 and SiMe2(Ind) 2TiCl2, half-titanocene, CpTICl3 was favorable for the polymerization of styrene via radical mechanism. The monomer conversion was more than 80%, the molecular weight of the polymer was higher than 1.0×105,and the molecular weight distribution was at the range of 1.18 to 1.42. However, when (n-BuCp)2TiCl2 and SiMe2(Ind) 2TiCl2 were used as catalysts, the monomer conversion and the molecular weight of the obtained polymer were lower. But the structure of titanocene complex had less impact on the molecular weight distribution (1.26~1.30). The effect of the ratio of monomer to initiator on the polymerization performance was also studied. A linear dependence of Mn of the obtained polymer on the monomer concentration was observed at the ratio of 250/1, 500/1 and 750/1. Mn of the obtained polymer increased with increasing the ratio of monomer to initiator, and the molecular weight distribution of the obtained polymer kept at the range of 1.0 to 1.40. The obtained polymer was also characterized by 13C-NMR to confirm the atactic structure of the polymer. These results indicated living the free radical mechanism of polymerization.
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发布时间：2021-03-19 - 摘要：An A2+B3 method of preparing hyperbranched azo polymers by azo-coupling reactions was described.The hyperbranched precursor with diazonium salt groups on the periphery was prepared by step-growth polymerization of A2(diazonium salts of 4,4′-diamino diphenyl sulphone)/B3(benzene-1,3,5-tricarboxylic acid tri-2-(N-ethylanilino)ethyl ester)monomers through azo-coupling reaction.Benzene-1,3,5-tricarboxylic acid tri-2-(N-ethylanilino)ethyl ester was prepared by Schotten-Baumann reactions between 1,3,5-benzenetricarbonyl chloride and N-ethyl-N-hydroxyethyl-aniline.Then the hyperbranched precursor with diazonium salt groups on the periphery was further reacted with N,N-diethyl aniline by azo-coupling reaction to obtain the final hyperbranched azo polymer.The azo polymer was characterized by the spectroscopic methods and thermal analysis.The phase transition behavior of the hyperbranched azo polymer was studied by using the differential scanning calorimetry (DSC).The hyperbranched polymer showed a second-order phase transition of typical amorphous substances.The Tg of the hyperbranched azo polymer was about 161℃.As containing the donoracceptor type azo chromophores,the polymer showed typical spectral characteristics of the pseudo-stilbene type azo chromophores.The λ-max value of the hyperbranched azo polymer,corresponding to the π-π transition,was about 465 nm.Spin-coated thin films of the hyperbranched azo polymer were used to carry out the SGR inscription experiments.Two p-polarized Ar+ laser beams (488 nm) with an intensity 80 mW/cm2 were used to produce the interference pattern on the polymer film.After irradiated for 1000 s at room temperature,the surface modulation depth was about 100 nm,and the grating spacing was about 730 nm.The modulation depth depended on the irradiation energy,and the spatial period depended on both the angle between the two interfering beams and the wavelength of the writing beams.Complex patterns could be inscribed when two gratings were recorded orthogonally to each other at the same location.
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发布时间：2021-03-19 - 摘要：Multiwalled carbon nanotubes reinforced nylon 11 (PA11) composites were prepared by in situ polymerization of 11-(amino acid) in the presence of carboxylic acid-functionalized MWNTs (MWNT-COOH).The structure,morphology and mechanical properties were analyzed by X-ray diffraction patterning,FTIR spectroscopy,scanning electron microscopy (SEM),and mechanical tensile tests.The SEM imaging shows that MWNTs are uniformly dispersed in the PA11/MWNTs composites,which benefits to enhance the mechanical properties of the composites.The composites’ tensile modulus is highly superior to that of pure PA11,and it’s incremental quantity increases with the content of MWNTs.Increments of 34.5%,92.9%,and 113.7% were found for the composites containing 1%,5%,and 10% MWNTs,respectively.Moreover,the composites’ storage modulus increases obviously with the content of MWNTs.Thermogravimetric analysis (TGA) shows the composites’ initial thermal degradation temperature is enhanced when adding nanotubes in the polymer substrate.When the content of MWNTs reaches 1%,the composites’ degradation temperature of losing weight 5% or 10% enhances from 404℃ to 414℃,or from 424℃ to 437℃.Differential scanning calorimetry (DSC) shows that the degree of crystallization of the nylon/MWNTs composites decreases as the content of nanotubes increases.
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发布时间：2021-03-19 - 摘要：A gelator (G2) synthesized from 1,2,4,5-benzene tetracarboxylic acid and 4-hydroxy pyridine at molar ratio of 1:4 was characterized by 1H-NMR and FT-IR.Supramolecular hydrogels were formed via cooling the aqueous solutions of G2 under ambient condition.The influence of cooling speed on the structure of the assembling fibers and the macroscopic properties of the gels was investigated via multiple techniques,including scanning electron microscopy (SEM),differential scanning calorimetry (DSC) and rheology measurements.As decreasing the cooling speed,the fiber size becomes larger,and the gel stability becomes lower.Therefore it is possible to control the gel performances via the environmental stimulation.The gel possesses high mechanical properties as indicated by the rheology measurements.The DSC measurement reveals that the freezing water content for the gels becomes lower as increasing the gelator concentration.Compared with G1 synthesized from 1,2,4,5-benzene tetracarboxylic acid and 4hydroxy pyridine at molar ratio of 1:2,G2 gelled water at higher minimum gelator concentration (MGC) and gave the gel with lower gel-to-sol dissociation temperature (Tgel) at the same concentration.Environmental scanning electron microscopy (ESEM) was applied to study the naturally hydrated state of gels directly,it was also noticed that the fibrous networks observed by conventional SEM are similar to those obtained by ESEM,which means that the morphology does not change significantly under drying.The relationship between the assembled structure and properties is helpful for understanding the gel formation mechanism and makes the gels suitable for different applications.
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发布时间：2021-03-19 - 摘要：By radical polymerization initiated with BPO,a novel series of random copolymers of 2,5-bis[(5-decaoxyphenyl)-1,3,4-oxadiazole] styrene (POC10) monomer and vinyl carbazoles (NVKs) are synthesized for first time.The elemental analyses of the copolymers indicated that POC10 and NVK contents in the copolymers were very close to the feed compositions.Molecular weight and its distribution of the copolymers were experimentally elucidated using a gel permeation chromatography.They all have good solubility in common organic solvents,such as chloroform,toluene,and tetrahydrofuran and so on.The structures of the copolymers were characterized by IR and 1H-HNMR. Their weight loss was less than 5% on heating to about 270℃ under nitrogen atmosphere.The DSC graph has only one glass transition,which represents there is no phase-separation in copolymer.The photoluminescence properties were characterized by UV absorption and fluorescence spectrum in detail.The random copolymers exhibited a PC10-segment dominated UV absorption peak at 320 nm and narrow band gap NVK absorption at 228 nm.Under UV excitation,these copolymers emitted bright blue fluorescence at abound 414~447 nm in THF solution and 435~446 nm in thin films form.Their photoluminescences are both in blue light area.Compared with the solution PL,complete PL excitation energy transfer from the NVK segment to the POC10 unit could be achieved by film PL at lower NVK content.With units of carbazole increasing,fluorescence quantum yield of copolymers decreases.
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发布时间：2021-03-19
Research Bulletin
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