Temperature-induced Evolution of Micro-structure and Chain Dynamics in Thermoplastic Polyurethane with Low Hard Segment Content as Studied by In Situ Synchrotron SAXS and Time-Domain NMR Experiments

The microstructural evolution of a thermoplastic polyurethane(TPU) with low hard segment content has been monitored utilizing in situ real-time synchrotron small angle X-ray scattering(SAXS) and time-domain nuclear magnetic resonance(NMR) measurements. The TPU is composed of 23 wt% of [4,4-methylenediphenyl diisocyanate(MDI)]-[1,4-butanediol(BD)] chain segments, which form hard domains, as[polytetrahydrofuran(PTHF)] forming soft domains. The number and distribution of monomer units in hard block...     

MORPHOLOGY EVOLUTION IN PTFE AS A FUNCTION OF MELT TIME AND TEMPERATURE——Ⅰ. HIGH MOLECULAR WEIGHT SINGLE- AND MULTI-MOLECULE FOLDED CHAIN SINGLE CRYSTALS AND BAND STRUCTURES

The effect of sintering dispersed dispersion and nano-emulsion particles of high molecular weight polytetrafluoroethylene (PTFE) on a substrate as a function of “melt” time and temperature is described. Folded chain single crystals parallel to the substrate and as ribbons on-edge (with double striations), as well as bands, are produced for longer sintering times; particle merger and diffusion of individual molecules, crystallizing as folded chain, single (or few) molecule,single crystals when “trapped” on the substrate by cooling occur for shorter sintering times. It is suggested the observed structures develop with sintering time, in a mesomorphic melt. The structure of the nascent particles is also discussed.     

A dual ligand targeted nanoprobe with high MRI sensitivity for diagnosis of breast cancer

Antibody targeted delivery is an effective strategy to improve the diagnostic imaging outcome of nanoscale imaging agents in the focal areas.Dual targeting micelles encapsulating superparamagnetic iron oxide were prepared from the amphiphilic block copolymer poly(ethylene glycol)-poly(ε-caprolactone)(PEG-b-PCL) with different targeting ligands cRGD and scFv-ErbB single chain antibody conjugated to the distal ends of PEG block.The breast cancer animal model was established by subcutaneous injecting the BT474 cells into the BALB/c-nu female nude mice and then employed to assess the potential of the dual ligand targeted magnetic micelles as a novel MRI contrast agent on a 1.5 T clinical MRI scanner.The T2 signal intensity of the tumor in animals receiving the dual ligand targeted magnetic micelles via tail vein decreased more significantly than the single ligand targeted and nontargeted magnetic micelles.These results indicate that the dual ligand targeted magnetic micelles,cRGD/scFv-ErbB-PEG-PCL-SPION,have great potential to act as a new type of effective nanoscale MRI contrast agent for early diagnosis of breast cancer.     

STUDY ON AB-CROSSLINKED POLYMERS Ⅰ. THE SYNTHESIS AND MECHANICAL PROPERTIES OF AB-CROSSLINKED POLYMERS BASED. ON PU/PS

The AB-crosslinked polymers (i.e. ABCP) with polystyrene as chain A and vinyl group blocked prepolymers of polyurethanes (PU) as chain B were synthesized and studied. The results of dynamic mechanical spectrometry (DMS) show that the compatibility between the components A and B can be improved greatly through chemical crosslinking during the formation of ABCPs. This effect is especially pronounced when short chain prepolymers is chosen as one of the components. It is apparent that the degree of crosslinking between the two components plays a major role in determining their compatibility. Copolymerizafion of styrene with maleic anhydride in chain A can improve the compatibility and broaden the damping temperature range. Mechanical properties of the sythesized ABCPs were also studied.     

Synthesis, crystal structure and magnetic property of a three-dimensional cagelike polymer [Co(4,4''''-bpy)(NCS)_2(py)_2]_n

A new organic-inorganic hetero-coordination polymer with three different kinds of ligands [Co(4,4'-bpy)(NCS)2(py)2]n is synthesized in the extremely mild condition. The X-ray diffraction reveals that the title polymer has a highly tactic three-dimensional cagelike supramolecular structure. Although the coordination bond makes it a one-dimension chain, the hydrogen bond plays an important role in the formation of 3-D supramolecular frameworks. The determination of magnetic properties has been carried out, and shows that it behaves weak antiferromagnetic property with J(4,4'-bpy) = -3.8 cm-1.     

Theoretical Interpretation of Conformation Variations of Polydimethylsiloxane Induced by Nanoparticles

There has been controversy as to whether the addition of nanoparticles to a polymer melt causes perturbed chain structure of polymers.In this work,the chain conformations of polydimethylsiloxane (PDMS) with addition of polyhedral oligomeric silsesquioxane (POSS) nanoparticles have been studied using a classical density functional approach.Under the strong interactions of POSS-PDMS,the radius of gyration of PDMS in the nanocomposites can either increase or decline depending on particle loading.After adding nanoparticles with larger size or weaker interactions,both the increasing and the declining amplitudes can be largely suppressed.The results provide a deep understanding of chain conformation in polymer nanocomposites.     

Studies on the magnetic property of μ_3-oxotriiron(Ⅲ) complex [Fe_30(OBz)_6(CH30H)_3](NO_3)(CH_3OH)_2 (HOBz=Benzoic acid)

The magnetic property of u3-oxotriiron(III) complex [Fe3O(OBz)6(CH3OH)3](NO3)-(CH3OH)2 (HOBz=benzoic acid) has been studied. We use isosceles triangle model and molecular field correction to fit the experimental magnetic susceptibility data. It shows that an intramolecular antiferromagnetic exchange interaction occurs with J=-31.27 cm-1, J'=-27.26 cm-1, and a weaker intermolecular antiferromagnetic exchange interaction occurs with zJ'=-3.76 cm-1. We give the d5-d5-d5 energy level diagram of triiron(III) complex as a function of J'/J. From the diagram we can get the total spin ST of the complex as 1/2 in the ground state.     

Effect of Chain Extender on Hydrogen Bond and Microphase Structure of Biodegradable Thermoplastic Polyurethanes

Thermomechanical properties of polyurethanes (PUs) strongly depend on the molecular interactions and microphase structure.In this work,two chain extenders with different ratios,flexile 1,4-butanediol (BDO) and branched trimethylolpropane mono allyl ether (TMPAE),are used to tune the molecular interactions and microphase structures of a series of biodegradable thermoplastic polyurethanes (TPUs).In TPUs,the biodegradable polycaprolactone (PCL,Mn of 2000) is used as soft segment while 1,6-diisocyanatohexane (HDI) and chain extenders are used as hard segment.Fourier transform infrared spectroscopy (FTIR),proton nuclear magnetic resonance spectroscppy (1H-NMR),gel permeation chromatography (GPC),differential scanning calorimetry (DSC),dynamic mechanical analysis (DMA) and mechanical tests were performed to characterize the bulk structure and properties of TPUs.Compared with BDO,the steric bulk of TMPAE is larger.The increment of TMPAE can help to increase the hydrogen bond content,microphase separation,and the elastic modulus ratio (R),which would strongly affect the thermomechanical property of the TPUs.The results of this work verify the importance of the structure of chain extender on the properties of TPUs.It provides valuable information for further understanding the structure-property relationships of these polyurethanes.     

High damping and mechanical properties of hydrogen-bonded polyethylene materials with variable contents of hydroxyls: Effect of hydrogen bonding density

Hydrogen bonding is considered to have significant effect on the interaction between polymeric chains and on the viscoelasticity of the polymeric materials. In this paper, we attempt to discuss the relationship between hydrogen bonding density and damping behavior and mechanical properties of polyethylene-based polymeric materials. For this reason, a series of pendant chain hydrogen bonding polymers(PCHBP) with different hydrogen bonding density(HBD) were prepared by quantitatively changing the content of pendent hydroxyl groups on the main chain of polyethylene. It was found that PCHBP with low HBD showed similar properties to polyethylene, indicating that the property of the materials was dependent mainly on the structure of the main chain. However, PCHBP with high HBD exhibited two tanδ peaks and a platform of loss modulus as well as a high storage modulus(about 400 MPa) at the second tanδ peak temperature, demonstrating that a polymeric material with high strength and damping properties was obtained. More importantly, the maximum of loss modulus showed a linear increase with the HBD, indicating that a higher HBD greatly improved the damping properties of the polymeric materials.     

Synthesis and characterization of non-symmetrical liquid crystals containing a cholesteryl ester moiety

In this paper,a series of chiral non-symmetrical liquid crystals(nBA-chol)consisting of a cholesteryl ester moiety as chiral entity and a biphenyl aromatic core with different terminal alkyl chain has been synthesized and investigated for their liquid crystalline properties.Effects of numbers of methylene units in the terminal alkyl chain on the phase transition temperatures and on the temperature-dependent pitch lengths of the chiral liquid crystals have been studied.The long terminal alkyl chain tends ...     

Virus-like supramolecular assemblies formed by cooperation of base pairing interaction and peptidic association

A peptide nucleic acid(PNA)-peptide conjugated molecule, T′_3(AKAE)_2, was designed to have both a PNA segment for oligonucleotide binding and an ionic self-complementary peptide sequence for self-association. T′_3(AKAE)_2 could co-assemble with oligoadenines(d(A)_x) to form virus-like supramolecular structures whose morphology showed dependence on the chain length and rigidity of the d(A)_x molecules. Smaller nanospheres with diameters of 13.0±2.0 nm were produced in the case of d(A)_6. Wormlike aggregates with lengths of 20–50 nm and diameters of 15.0±2.5 nm were found in the cases of d(A)_(12), d(A)_(18), d(A)_(24) and d(A)_(30). And larger spherical aggregates with diameters of 18±5 nm came into presence in the cases of d(A)_(36) and d(A)_(42). These nanostructures were suggested to be formed under a cooperative effect of base pair recognition and peptidic association. The study provides insights into the programmed assembly of a multi-components system as well as control of the size and shape of the co-assembled structures, which is of great significance in developing gene/drug delivery systems.     

Preparation of a novel magnetic resin for effective removal of both natural organic matter and organic micropollutants

A novel,bifunctional,hypercrosslinked.magnetic resin W2 was prepared using divinylbenzene(DVB) and glycidyl methacrylate(GMA) as comonomers in three steps(i.e.,suspension polymerization, amination and post-crosslinking reactions).To evaluate the adsorption of natural organic matter(NOM) and organic micropollutants(OMPs) on the obtained resin W2,two magnetic resins Wl(the precursor of W2 before post-crosslinking) and WO(the precursor of Wl before amination) were chosen for comparison.The results indicated that W2 would be a promising material for the removal of both NOM and OMPs from aquatic environments.     

A Monte Carlo simulation study of the effect of chain length on the hydrolysis of poly(lactic acid)

Abstract The intrinsic relationship between molecular chain length and the probability of chain reaction during poly(lactic acid)(PLA)hydrolysis was investigated by Monte Carlo simulation.The chain reaction rate was calculated by introducing a power function of different molecular chain lengths.The hydrolysis of both amorphous and extended-chain crystal PLA was selected as the model system.It is found that,the chain reaction probability was proportional to the chain length with a power of 0.4 for amorphous PLA and 0.7 1 for extended-chain crystal PLA,respectively.These results indicate that PLA with longer chain length usually exhibits larger reaction rate than that with shorter length.Comparing the hydrolysis of the two kinds of PLA,the competition between longer and shorter chains in the different condensed structures is different.     

Communication Chain-foldability effect on coaggregation Evidence derived from time-resolved fluorescence spectroscopy

Very recently,we have proposed that all culprit molecules of arteriosclerosis mightpossess a common and measurable inherent property,namely,a coaggregating ten-dency.Extensive kinetic measurements of these tendencies in terms of △CAgC valueshave led to a new and surprising observation,i.e.,the cholesteryl ester with a longsaturated 18-carbon chain(CE-18)actually has a much smaller tendency towardcoaggregation than that of the ester with a“short”8-carbon chain(CE-8).Thisstate of affairs has been coined as the“chain-foldability effect”,i.e.,the 18-carbon     

Three Co(Ⅱ) Coordination Polymers Incorporated with a Bent Connector: Crystal Structures and Magnetic Properties

Based on the bent ligand 1 H-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole(3,4?-Hbpt) with Co(Ⅱ) ions as well as a series of polycarboxylate co-ligands, three new coordination polymers were yielded, namely, {[Co(op)(3,4?-Hbpt)(H_2O)_3]?2 H_2O}n(1), [Co(cyc)(3,4′-Hbpt)(H_2O)]n(2) and [Co(pro)(3,4′-Hbpt)(H_2O)]n(3)(here, op = o-phthalic anion, cyc = 1,1-cyclobutanedicarboxylic anion, pro = propanedioic anion). In cooperation with the auxiliary polycarboxylate co-ligands, a variety of Co(Ⅱ) coordination networks, such as 1-D chain 1 and 2-D layer 2 and 3 have been assembled. The magnetic behaviors of compounds 1～3 were studied. All of them indicated the existence of interesting spin-canting behavior.     

PREPARATION AND MAGNETIC PROPERTIES OF POLYMERIC COMPLEXES CONTAINING 1,10-PHENANTHROLINE

A series of polymeric complexes were prepared from Fe~(2 ),Co~(2 ) or Ni~(2 ) and poly(Schiff base)(DAPcIPA), which was obtained by polycondensation of 5,6-diamino-1,10-phenanthroline(DAP)with isophthalaldehyde(IPA).The structures of the polymer and the polymeric complexes were characterized by IR,~1H-NMR and elemental analysis.The magnetic behavior of these complexes was measured as a function of magnetic field strength(0-3.98×10~6 A/m)at 5 K and as a function of temperature(5-300 K)at a magnetic field strength of 2.39×10~6 A/m.Experimental results show that DAPcIPA-Ni~(2 ),DAPcIPA-Co~(2 ) are soft ferromagnets while DAPcIPA-Fe~(2 ) exhibits features of an antiferromagnet.     

Numerical Simulation of the Distribution Function and Free Energy of a Single Wormlike Polymer Confined between Hard Walls

We focus on the distribution and free energy of a wormlike polymer confined between two parallel hard walls.The variation in the distribution and free energy of the wormlike chain as the spacing between the walls decreases(or as the total contour length of the wormlike chain increases or as the persistence length of the chain increases)is simulated.The main reason for these changes is a degradation of the long wormlike chain into a Gaussian long chain under weak confinement.     

Synthesis of Poly[6-(2,6-bis(1'-methylbenzimidazolyl)pyridin-4-yloxy)hexyl acrylate](PBIP) and Magnetic Property of Its Neodymium Complex(PBIP-Nd~(3+))

Homopolymer(PBIP) containing 2,6-bis(1'-methylbenzimidazolyl)pyridine(Me BIP) ligands in the side chain was synthesized by RAFT polymerization and its kinetics was studied. Polymeric complex PBIP-Nd~(3+) was prepared by chelating PBIP with lanthanide ion Nd~(3+). The homopolymers and PBIP-Nd~(3+) complex were investigated by NMR, FTIR, GPC and TGA. The optical property of PBIP-Nd~(3+) complex was characterized by UV-Vis spectroscopy. The magnetic property of PBIP-Nd~(3+) complex was measured as a function of temperature(5 K to 300 K) and as a function of field(-3.98×10~6 A/m to 3.98×10~6 A/m). These results indicated that PBIP-Nd~(3+) complex is paramagnetic.     

TEMPERATURE DEPENDENCE OF THE FLUORESCENCE SPECTRA OF LADDERLIKE POLYPHENYLSILSESQUIOXANE AND LADDERLIKE 1,4-PHENYLENE-BRIDGED POLYVINYLSILOXANE

Fluorescence spectra of ladderlike polyphenylsilsesquioxane (LPPS) and ladderlike 1,4-phenylene-bridgedpolyvinylsiloxane (LPPVS) have been measured as a function of temperature (4-55℃), in dilute tetrahydrofuran solution.The excimer (I_E) to monomer (I_M) intensity ratio (I_E/I_M) of LPPS dilute solution shows a double linear Arrhenius plot with abreak point ascribable to a transition temperature T_t This behavior has not been found for single chain polyorganosiloxanes.When InI_E of LPPS was plotted against I/T it also gave a double linear plot with one break point, which was found in singlechain polyorganosiloxanes. The different behaviors between LPPS and single chain polyorganosiloxanes may be mainlyattributed to the relatively rigid double-chain macromolecular backbone of LPPS. However, the In(I_E/I_M) of dilute LPPVSsolution versus I/T shows a simple linear variation with a positive slope which confirms our proposition. The differencebetween the fluorescence results of LPPS and those of LPPVS may possibly derive from their structure differences andcooperative motion in backbone chain bonds.     

Morphology evolution of polystyrene-core/poly(N-isopropylacrylamide)-shell microgel synthesized by one-pot polymerization

One-pot polymerization with macroinitiator is supposed to be a robust, facile way to synthesize well-defined coreshell nanoparticles with fixed shell thickness. To testify this, we investigated the temperature-depending morphology evolution of polystyrene(PS) core/poly(N-isopropylacrylamide)(PNIPAM) shell microgel synthesized by one-pot polymerization with PNIPAM-RAFT as macroinitiator in dimethylformamide(DMF) by transmission electron microscopy(TEM), dynamic/static light scattering(DLS/SLS) and small angle neutron scattering(SANS). It is revealed that the microgel has a core-shell structure, i.e., the core is made of pure PS, but the shell is composed of both PNIPAM-RAFT macroinitiator and crosslinked PS. In fact, there are 92.0 wt% D2 O, 6.7 wt% PNIPAM and 1.3 wt% PS in the shell in its aqueous dispersion at 21 °C; therefore, its shell thickness is much larger than the extended chain length of the macroinitiator as revealed by both SANS and DLS observations. Competitive growth of styrene, divinylbenzene and PNIPAM macroinitiator as well as possible chain transfer from amine proton of PNIPAM side chain may lead to the larger shell thickness, compared with the extended chain length of the macroinitiator. Our work can shed light on the real morphology control in one-pot polymerization.