Mobility Of Polymer Molecules Research Articles

PREPARATION AND EVALUATION OF LIVER SPECIFIC NON-IONIC POLYMERIC CONTRAST AGENT

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 GdCl_3·6H_2O.The contents of D-lactobionic residues and gadolinium (III) were determined by quantitative ~ 13 C-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~ -1 s~ -1 for PD0-Gd,PD1-Gd and PD3-Gd,respectively) are obviously higher than that of commercial contrast agents (5.95 mmolL~ -1 s~ -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 divided 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.

Processing and properties of SiC/vinyl ester nanocomposites

The feasibility of improving polymer composites was investigated using 30 nm SiCnanoparticles in a vinyl ester resin. Even when the particle loading was less than 4% byweight, the viscosity of the nanoparticle suspension was found to increase much higher thanthat of microparticle suspension. This phenomenon may be the result of associationbetween nanoparticles and polymer molecules, effectively making the nanoparticles larger.The resulting reduction in the mobility of polymer molecules also led to delayed curing.Ultrasonic mixing did not fully disperse the particles. As a result, the compositestrength did not improve although the modulus increased. The use of a dispersant,methacryloxy propyl trimethoxy silane (MPS), improved the dispersion qualityand hence the composite strength. The paper discusses the issues involved withprocessing, characterization and properties of SiC/vinyl ester nanocomposites.Methods of improving the nanocomposite quality are proposed in the paper as well.

A Distortion-Modified Free Volume Theory for Nonlinear Viscoelastic Behavior

Many polymeric materials, including structural adhesives, exhibit anonlinear viscoelastic response. The nonlinear theory of Knauss and Emri(Polym. Engrg. Sci. 27, 1987, 87–100) is based on the Doolittle conceptthat the ‘free volume’ controls the mobility of polymer molecules and,thus, the inherent time scale of the material. It then follows thatfactors such as temperature and moisture, which change the free volume,will influence the time scale. Furthermore, stress-induced dilatationwill also affect the free volume and, hence, the time scale. However,during this investigation, dilatational effects alone were found to beinsufficient for describing the response of near pure shear tests of abisphenol A epoxy with amido amine hardener. Thus, the free volumeapproach presented here has been modified to include distortionaleffects in the inherent time scale of the material. The same was foundto be true for a urethane adhesive. The small strain viscoelastic responses of the two materials havebeen determined from master curves of uniaxial and bulk creep testing atvarious temperatures. The nonlinear free volume model, modified toinclude distortional effects in the reduced time, was incorporated inthe ABAQUS finite element code via a user-defined material subroutine.For the epoxy, validation of the modified theory (a strain-basedformulation of free volume) has been achieved through good agreementbetween the computational and experimental results of butterfly-shapedArcan specimens subjected to loadings ranging from near pure shear toshear with various amounts of superposed tension and compression. Inaddition to predicting the response under a variety of multiaxial stressstates, the modified free volume theory also accurately predicts theformation and growth of shear banding, or regions of highly localizeddeformation, which have been found to occur upon continued loading ofthe epoxy. The urethane did not appear to exhibit any localizeddeformation over the range of temperatures at which it was tested.As a result, a stress-based modified free volume approach was requiredto model its multiaxial and temperature-dependent behavior. Althoughfree volume was the unifying parameter for the two materials, the needfor a stress-based and strain-based formulation of the free volume forthe urethane and epoxy, respectively, could not be reconciled at thistime.

Quantitative Estimation of Free Volume Distribution of Polymers with Photochromic Reactions.

Reactions in polymer solid are different from those in solutions because the mobility of polymer molecules is so restricted that reactivities vary in the local environment and site by site. One of the factors influencing on their reactivity is free volume of the polymer, however free volume has not been quantitatively estimated up to now. In this paper, azobenzene in polymethyl methacrylate was used as photochromic probe. Azobenzenein PMMA were isomerized with photoirradiation and the change in the absorption spectra of azobenzene was observed Quantum yield distribution for the photoreaction was obtained by analyzing the observed curve of isomerization, and the effect of annealing temperature on their quantum yield distribution is also described.

Pulsed NMR studies of translational mobility of polymer molecules in polydialkylphosphate gels

The translational mobility of polypropylenephosphate (PPP) molecules has been studied by the NMR pulsed field gradient technique. The translational diffusion of long chain polymer molecules of polymerization degree ¯m > 20 may be neglected, in NMR measurements, on account of their rigidity. The self-diffusion coefficient of short chain polymer molecules (¯m=8) in PPP gels (¯Ds=3 · 10−8 cm2/s) is about two orders of magnitude lower than that of water molecules in gels.

The Influence of Filler Particles on the Mobility of Polymer Molecules

Abstract A statistical experiment has been conducted to investigate the influence of silica fillers on the mobility of poly(vinyl chloride -co-vinyl acetate) molecules as reflected in glass transition temperatures. Measurement of glass transitions was made graphically from DSC curves. The data showed that the glass transition was affected by the presence of filler. The effect was dependent on the type and level of filler in the polymer. The filler was of either large or small particle size, or had had surface treatment to form trimethylsilyl groups. Significant interaction effects were found between filler types, filler level, and the level of polar vinyl acetate groups in the copolymer.

The influence of filler particles and polymer structure on the mobility of polymer molecules

AbstractThe presence of carbon filler has been shown to cause a change in the glass transition temperature of polymers. For poly(vinyl chloride) and two of its copolymers with 10 and 15% vinyl acetate an increase in Tg was observed when Graphon C Carbon was added. The increase was greater when the proportion of vinyl acetate was greater. Polar vinyl acetate units allow stronger adsorption of polymer onto the carbon. Brittle polymers such as polystyrene and poly(methyl methacrylate) showed scattered Tg's when filled with carbon. The changes were not a function of concentration. It is postulated that the thermal stress of these polymers is increased in the presence of filler.

The self-diffusion of polymers

Abstract The mobility and self-diffusion of polymer molecules in concentrated systems or in the molten bulk state is largely controlled by entanglements between the molecules. These entanglements are a result of the chain-like nature of the molecules and of their extended, coil-like configuration. The conformation and mobility of polymer molecules in dilute solution—which are relatively well understood—are discussed; this leads to a consideration of self-diffusion in the more concentrated states and in the bulk polymer melt, and several special properties of polymers which are controlled and modified by the molecular self-diffusion are examined. Our current theoretical understanding of polymeric self-diffusion in highly entangled systems is outlined, and the ways in which such diffusion may be studied experimentally are briefly described. The final part of the review describes a recent experimental study of self-diffusion in a polymer melt; the results of this study may provide new insight into the motion of entangled, chain-like molecules.

Preparation and structures of the poly(vinyl chloride) porous membranes

Formation of membranes from a binary system, poly(vinyl chloride) and dimethylformamide, was studied. Phase separation during membrane formation was caused by absorption of aqueous vapor from the atmosphere. The membrane structure was closely related to the degree of phase separation. The membrane formation process was divided into three stages, i.e., an early stage, a transitional stage, and a late stage. By leaching the solution at the early stage, where the casting solution was still transparent, a membrane with a finger-like structure was obtained. On the other hand, a network structure was obtained by leaching at the late stage which was dependent on the molecular weight and the concentration of poly(vinyl chloride). The membrane structure was predominantly controlled by the mobility of polymer molecules in the casting solution.