Enhanced antibacterial activity of tetramethylguanidinium-conjugated linear polyethylenimine polymers

In the present study, varying amounts of tetramethylguanidinium moiety have been conjugated to linear polyethylenimine to obtain linear polyethylenimine-tmg (LPTG) polymers. Incorporation of hydrophobic and highly basic moiety in the polymeric backbone resulted in the significant improvement in the antibacterial activity which was confirmed by zone of inhibition and MIC assays. Further, the results of transmission electron microscopy and confocal studies revealed that the projected LPTG polymers possessed higher antibacterial activity than the native polymer. In addition, these modified polyethylenimine (PEI) polymers were capable of reducing auric chloride into stable gold nanoparticles. These polyamine-stabilized gold nanoparticles can be used in various biomedical applications.     

Interaction of richlocain with some linear and crosslinked polymers

The interaction of local anesthetic drug richlocain with linear polyacrylic acid and crosslinked sodium polyacrylate, linear and crosslinked acrylic acid-Schiff base copolymers has been investigated. The compositions of forming polymer-drug complexes were determined. The influence of external factors such as pH, ionic strength, temperature and thermodynamic quality of solvent on the stability of these complexes was studied. The kinetics and activation energy of drug release from the gel matrix has been evaluated.     

Heat capacity of linear high polymers

The molar heat capacity of a 45:55% copolymer of ethylene and tetrafluoroethylene has been measured from 80 to 340 K by the use of an adiabatic calorimeter, to an accuracy of 0.3%. The results are found to be in close agreement with values calculated from the known optical lines of related polymers and the Tarasov model; they are also analysed together with the available data on polyethylene and four other fluoropolymers, showing that the principle of additivity for heat capacities is generally valid to within 2%. The logical relations between these two phenomenological frameworks and their resultant implication on the effective one-dimensional force constant of the carbon backbone are discussed at some length.     

Effects of nuclear radiations on structure and molecular motions in some crystalline stereoregular polymers

Young's modulus and the mechanical damping factor have been determined between ?180 and +280°C. (at a frequency of several kilocycles), in samples of isotactic polypropylene, isotactic polystyrene, and trans-1,4-polybutadiene, subjected to pile irradiation (γ-rays and neutrons) at γ-doses from 90 to 4000 Mrad. In isotactic polypropylene no important structural changes are produced by the irradiation, except for a partial destruction of crystallinity. The samples receiving high radiation doses exhibit a low temperature loss region, which is attributed to the formation of a certain number of branches. Isotactic polystyrene shows very slight modifications of the dynamic mechanical properties at room temperature. At low temperature an increase of intensity of the δ relaxation phenomenon (probably due to oscillations of phenyl rings) with increasing radiation dose is observed. Important structural modifications produced by the radiation, destruction of crystallinity accompanied by crosslinking, which transform the material into a crosslinked rubber, are observed in trans-1,4-polybutadiene. Unlike conventional (sulfur) vulcanization, crosslinking by radiation does not cause a marked shift of the glass transition point. A secondary low-temperature relaxation effect, not existing in the unirradiated material, appears in the mechanical loss curves of the irradiated samples; it is attributed to the formation of ? CH₂? sequences in the main chains through saturation of C?C bonds. The mechanical spectrum of irradiated polybutadiene is very similar to those shown by crosslinked ethylene–butadiene copolymers.     

Water‐soluble polymers. LXXXIII. Correlation of experimentally determined drag reduction efficiency and extensional viscosity of high molecular weight polymers in dilute aqueous solution

The extensional viscosity for aqueous solutions of high molecular weight poly(acrylamide) copolymers and poly(ethylene oxide) homopolymers was measured using a laboratory‐designed screen extensional rheometer. A Bingham model was developed to estimate the average local polymer coil extensional viscosity (η_coil). A strong correlation was found between the measured η_coil values and the polymer extensional viscosity predicted by a bead‐spring model. The dilute aqueous solution drag reduction was measured with a rotating disk instrument under conditions minimizing the effects of shear degradation. Extensional viscosity and drag reduction measurements were performed in deionized water and in 0.514M sodium chloride. The relative drag reduction efficiency values (Δ) in both solvents were found to strongly correlate with measured η_coil values. This is the first report of the accurate prediction of drag reduction behavior for a wide range of polymer types in various solvents from the independently measured molecular parameters η_coil and [η]C. The often‐used relative drag reduction efficiency expressed as the product of [η]C and Δ can now be replaced by the absolute drag reduction efficiency [η]Cη_coil. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1222–1231, 2001     

利用聚乙烯亚胺对SAPO-34分子筛进行改性

以阳离子聚合物聚乙烯亚胺(PEI)为介孔模板剂对SAPO-34分子筛进行改性,考察了一定晶化温度和晶化时间下PEI分子量对SAPO-34分子筛孔结构以及比表面积的影响。结果表明,PEI的引入会导致SAPO-34分子筛结晶度下降;随着PEI分子量增加,表面积略有下降,孔体积基本不变,孔径逐渐增大。对制备的介孔SAPO-34分子筛的MTO反应性能进行测试,结果表明,与未加入PEI的分子筛相比,利用PEI改性的分子筛在MTO中丙烯选择性明显提高,烯烃总选择性上升,并且随着PEI分子量增加,烯烃总选择性也随之提高。     

Mesophase structure of some flexible chain polymers

The mesophase structures of some flexible chain polymers, which do not contain mesogenic groups, but are able to form thermodynamically equilibrium mesomorphic states, were studied by means of the X-ray analysis, the differential scanning calorimetry, and other methods. The mesophase polyethylene in bicomponent polymer blends, mesomorphic ultra-high molecular weight polyphosphazenes, and membrane polyvinylorganosilanes were investigated. The scheme of polymer phase transitions is discussed. Besides conformational disordering, the step-by-step loss of different levels of the positional order (i.e. the multiple-step character of melting) of flexible, semiflexible, and stiff chain polymers is deduced and illustrated by examples from the authors' experience and from the literature.     

Synthesis of linear polymers containing benzoxazine moieties in the main chain with high molecular design versatility via click reaction

Linear polymers with benzoxazine rings in the main chain have been synthesized applying click chemistry approach. These polymers possess molecular weights significantly higher than the benzoxazine polymers which have been chain extended via Mannich reaction. The number average molecular weight is estimated from size exclusion chromatography (SEC) to be between 20,000 and 40,000 Da. The structure of the polymers is confirmed by ¹H and ¹³C nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FTIR). Differential scanning calorimetry (DSC) is used to study crosslinking behavior of the polymers. The nature of the low temperature exotherm DSC peak observed in this work and the previous work of other authors is studied by model reactions. It is due to thermal coupling of the residual propargyl and azide end groups in the absence of active catalyst. In addition, a novel diazide-functional benzoxazine monomer has been prepared, showing a tremendous flexibility for applying click reaction to obtain various polymer architectures. Three types of polymers have been prepared from dipropargyl- and diazide-functional benzoxazine monomers. These polymers have been characterized by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA).     

Synthesis and characterization of high molecular weight water-soluble polymers

The synthesis of high molecular weight acrylic water-soluble polymers in heterophase water-in-oil polymerizations is discussed. A mechanism has been elucidated which includes elementary reactions in the continuous (organic) and dispersed (aqueous) phases, as well as the interfacial layer. The latter allows for the identification of interfacially active species which can concurrently enhance stability and increase the linear molecular weight of the polymer. Suitable species are found to contain multiple radically active functional groups on either the hydrophilic or hydrophobic moieties. A one-point light-scattering method is also developed which improves the accuracy in molecular-weight estimation to /pi5%. compared with /pi10% for the conventional dilution procedure. This is demonstrated for high molecular weight polyacrylamides and is found to reduce the sample measurement time fourfold, to 20 min.     

Size-exclusion chromatography of high molecular weight water-soluble polymers

A preparative-scale, aqueous size-exclusion chromatography system was constructed for fractionation of large molecular weight polymers. Calibration of molecular weight to elution volume was accomplished without polymer standards by using an eluent viscosity detector in series with a refractometer. The system was found to have a hydrodynamic size-separation resolution that ranged from 500 to 3500 Å.     

Light scattering characterisation of polymers II. Analyses of high molecular weight polystyrene

For light scattering analysis of an extremely high molecular weight polymer with large size in solution, use of mixtures of a given polymer with its low molecular weight homologue is described to have great advantages. With such bimodal mixtures as test samples, one can alter the unknown form of the angular variations of scattered lights to a form to be expected and widen the range of the linearity with sin² (ø/2), where ø is the scattering angle. According to the considerations, a sample of linear polystyrene was successfully analysed on a commercial apparatus, Fica 50 to have the weight-average molecular weight of 27 million.     

Influence of molecular weight on dynamic crossover temperature in linear polymers

Dielectric and light scattering spectra of two linear polymers, polyisoprene (PIP) and polystyrene (PS), were analyzed in broad temperature and frequency range above the glass transition temperature, T_g. The crossover temperature, T_C, was estimated using two approaches: (i) derivative analysis of relaxation times proposed by Stickel and (ii) Mode-Coupling Theory approach. Both estimates provide consistent values. T_C varies with molecular weight (MW) in both polymers, while the ratio T_C/T_g changes significantly with MW in PS only. It appears that the segmental relaxation time at T_C has value τ(T_C) ∼ 10⁻⁷ s for both polymers independent of MW and similar to the value reported for many non-polymeric glass-forming systems. No sign of the dynamic crossover has been observed in the chain relaxation around T_C of the segmental dynamics.     

高分子聚合物松弛行为及模型的研究进展

高分子聚合物材料作为一种使用频率高且应用范围广的材料,其松弛行为对于其加工制品的精度具有重要的影响,且高分子化学合成的结果会最终影响高分子聚合物的松弛行为。由此总结了高分子聚合物松弛行为的特点,整理了其力学松弛及模型、松弛时间的研究进展。并由此提出现阶段高分子聚合物的松弛行为研究的局限性,并指出未来的研究方向。     

Reactions of unsaturated fatty alcohols. III. Viscosity and molecular weight studies on some vinyl ether polymers

Summary Molecular weights of the polymers of the vinyl ethers of stearyl, soybean, and linseed fatty alcohols were measured cryoscopically in cyclohexane at three different concentrations. Corrected number-average molecular weights were obtained by extrapolation to zero cocentration. For each family of polymers a series of preparations varying in degree of polymerization were studied with number-average molecular weights ranging from 1,500 to 15,000 or higher. Reduced viscosity measurements at 25°C. were made on benzene solutions of each polymer preparation at three different concentrations. Intrinsic viscosities were obtained by extrapolating to zero concentration. Intrinsic viscosities for the polymers range from 0.05 to 0.20. Logarithmic plots of molecular weightvs. intrinsic viscosity gave linear relationships for stearyl, soybean, and linseed polymers. Values forK′ anda in the equation of Mark and Houwink were obtained from these plots. Presented at fall meeting. American Oil Chemists' Society, September 23–26, 1956, Chicago, Ill.     

Study of molecular packing density in boundary layers of some polymers

Packing density of macromolecules of some amorphous polymers, poly(methyl methacrylate), polystyrene and polydimethylsiloxane, in boundary layers formed at the solid-polymer interface, was studied by a ‘molecular probe’ technique. It was shown that the boundary layers of the above polymers have a complex structure composed of regions with different densities of molecular packing: a surface region of thickness 2 to 4 μm, and a transient and loosely-packed region of thickness of the order of 30 to 60 μm. It was established that both the structure and the thickness of boundary layers for each of the polymers depends both on polymer chain flexibility, and on cohesion energy density of a polymer.     

Effect of molecular weight heterodispersity on linear viscoelastic properties of entangled polymers

Summary The nonlinear, binary blending law of BOGUE has been generalized to include a finite number of entangled species. Good agreement has been observed between the ROUSE theory modified according to this law and linear viscoelastic experiments on cis-1,4-polybutadiene melts and concentrated solutions. The more difficult case of heterogeneity due to simultaneous degradation and crosslinking can only be qualitatively accounted for.We thank the DEUTSCHE FORSCHUNGSGEMEINSCHAFT for generous financial support. CHEMISCHE WERKE HÜLS AG we thank for the polybutadiene samples.     

Effect of molecular oxygen on the n.m.r. relaxation times of some aromatic polymers

Proton spin-lattice (T₁) and spin-spin (T₂) relaxation times are reported for poly(2-vinylpyridine), poly(1-vinylanthracene) and polycarbonate in air, oxygen and in vacuo. The results substantiate earlier findings that oxygen complexes with the aromatic rings giving rise to T₁ minima which are not intrinsic to the polymers. This effect appears to be fairly general for aromatic containing polymers. For those polymers containing low temperature relaxations intrinsic to the polymer, the oxygen paramagnetic effect can complicate the relaxation behaviour and, in some cases, totally mask the intrinsic processes. The transitions in T₁ and T₂, due to the torsional oscillation of the anthracene side group in poly(1-vinylanthracene), is much better defined than the corresponding transitions for previously reported aromatic vinyl polymers. The activation energy for the motion of the side group is comparable to that of polystyrene and poly(N-vinylcarbazole).     

Mechanical degradation of high molecular weight polymers in dilute solution

The mechanical shear degradation of polydisperse polyisobutene and monodisperse polystrene in oils of different viscosities in the concentration range of 0.1% to 1% was studied using a high-shear concentric cylinder viscometer under laminar and uniform well-defined shear field conditions. Molecular weight distributions (MWDs) were measured by gel permeation chromatography (GPC). Degradation of polydisperse polyisobutene solutions narrows the distributions principally through the breaking down of large molecules. Degradation of monodisperse polystyrene broadens the distributions at lower shear stress. At higher shear stresses, the distributions do not broaden as much but are still broader than those of the original polymer. The final M_w/M_n ratios are considerably different from the value of 2 expected for random degradation. Hence, the degradation is likely a nonrandom process. It was found that the extent of degradation has a negative concentration dependence coefficient at relatively high molecular weight and a positive concentration dependence at lower molecular weight. Competing mechanisms of “stretching” and “entanglements” for degradation were postulated to explain the results. The degradation data indicate that the shear stress is the controlling parameter, not the shear rate. The shear degradation is independent of initial molecular weight and viscosity of the solvent.     

Studies of heterocyclic polymers: Part 1. The synthesis and structure of macrocyclic polymers

Pyromellitic tetranitrile and 4,4′-diaminodiphenyl ether have been reacted in solution and in the solid state, and the macrocyclic polymer produced by each method of reaction has been shown to be structurally identical. Other macrocyclic polymers have been prepared by the solid state reactions of a number of aromatic diamines and pyromellitic tetranitrile. The diamines were selected to provide variations in the size of the macrocycle and in the level of strain within the ring. Preliminary studies suggest that these variations have an observable effect upon the ease of macrocyclization, but no marked influence upon the thermal stability of the polymers.     

The structure of amorphous polymers

Over the past ten years the structure of amorphous polymers has been extensively investigated. Publications on this topic were concerned with various aspects of the amorphous structure and were often based on specific molecular models. This review article attempts to discuss the interrelations between the different structural properties which were studied. The topics covered are the short range positional order, the orientational order, the chain conformation, the supermolecular structure and the relation between molecular and macroscopical properties both of the fluid and the glassy state. The basic theory of the fluid state is introduced at the beginning as well as the experimental techniques currently used to characterize the amorphous structure. Experimental results on different amorphous polymers and oligomers are then discussed and the information is pointed out which can be derived from these data. Finally models on the structure of amorphous polymers are considered briefly.