THE OBSERVATION OF INTERNAL MOTION OF LINEAR POLYSTYRENE CHAINS IN CYCLOHEXANE AROUND 0 TEMPERATURE

A high molecular weight (M_w=1.85×10~7) polystyrene (PS) with narrow distribution was prepared by high vacuum anionic polymerization in tetrahydrofuran.By use of dynamic light scattering,the dynamics of PS chains in cyclohexane was studied around theθtemperature.For the first time,we have observed the internal motion of polymer chains in solutions below theθtemperature by using dynamic light scattering at smaller angles (even qR_g<1).     

NONCONVENTIONAL EMULSION POLYMERIZATION OF ACRYLONITRILE CATALYZED BY in situ METAL COMPLEXw

 Nano-sized polyacrylonitrile (PAN) particles were prepared under the catalytic effect of in situ developed CoCl₂/EDTA complex with ammonium persulfate as the initiator in the absence of any added emulsifier. The emulsion polymerization was studied at varying concentrations of the initiator, monomer, complex and solvent over a temperature range of 30-70^oC. The overall activation energy (Ea, 49.79 kJ/mol), energy of dissociation of initiator (Ed, 82.68 kJ/mol), number of micelles (0.163 x 1018) and the viscosity average molecular weight of the polymer were computed. The distribution of particle sizes was determined by transmission electron microscopy (TEM). It was found that the oil-in-water polymerization was stabilized by the presence of the CoCl₂/EDTA in situ complex reducing the particle size into the nano order. The average diameters of PAN nano particles, obtained by TEM, were in the range of 50–150 nm at the maximum conversion. The experimental particle size was mainly dependent on the concentration of the complex and temperature.     

A SLOW RELAXATION MODE OF POLYMER CHAINS IN A SEMIDILUTE SOLUTION

Dust-free semidilute and concentrated polystyrene(PS)solutions in different solvents were prepared by slow evaporation and in situ anionic polymerization,which removes the effects of troublesome artifacts such as dust contamination and concentration gradient.The dynamics was reexamined by a combination of static and dynamic laser light scattering.In benzene and toluene(good solvents for PS),only one fast diffusive mode of polymer chains can be observed when the concentration(c)is up to 20%,which is attri...     

DIFFUSION OF LONG CHAINS THROUGH A POROUS THIN GEL NETWORK

Using a core(142 nm)made of linear polystyrene(PS)chains as a seed,we further polymerized a thin layer of cross-linked PS shell(7 nm)on it in water to form a core-shell particle.Such a particle swells in toluene,which enables linear PS chains inside the core to gradually diffuse out through the porous shell.Using a combination of static and dynamic laser light scattering,we examined the chain diffusion process by following the change of the scattering intensity(i.e.the average molar mass of the particles).For the first time,we have revealed that the diffusion exhibits three stages.In the first stage,the chain diffusion through the shell is even faster than their translational diffusion in a dilute solution.The three stages respectively correspond to the change of the solution in the core from concentrated to semidilute and then from semidilute to dilute.     

MONTE CARLO STUDY ON THE CRITICAL ADSORPTION POINT OF BOND-FLUCTUATED POLYMER CHAINS TETHERED ON ADSORBING SURFACES

 The behavior of three-dimensional bond fluctuation model chains tethered on an adsorbing flat surface was simulated by the Monte Carlo method. The dependence of the number of surface contacts M on the interaction strength e and the chain length N was investigated by a finite-size scaling law M = N[a₀ + a₁N^1/v_k + O((N ^1/v_k)²)] for e near the critical adsorption point e_c, i.e., k ≡(e-e_c)/e_c closes to 0. The critical adsorption point was estimated to be e_c = 0.93, and the exponents &#61542; = 0.49 and 1/v= 0.57.     

A COMPARATIVE STUDY OF CHAIN DYNAMICS OF DI-AND TRI-BLOCK COPOLYMERS IN SEMIDILUTE SOLUTION IN A NON-SELECTIVE SOLVENT

The chain dynamics of a pair of diblock poly(styrene-b-butadiene) (PS210-b-PB960) and triblock poly(styrene-b-butadiene-b-styrene) (PS200-b-PB1815-b-PS200) copolymers in both dilute and semidilute toluene solutions has been comparatively studied by dynamic laser light scattering. As expected, the mutual diffusion of individual chain changes into a fast cooperative diffusion of the chain segments (“blobs“) between two neighboring entanglement points for both the copolymers as the solution changes from dilute to semidilute. Further increases of the concentration lead to a second slow relaxation mode. For the triblock chains, there exists an additional middle relaxation between the fast and the slow modes.with 0.33 ＜α＜ 0.44, much smaller than 0.75 predicted or 0.72 observed for linear homopolymer chains in good solvent. It implies that the solvent quality of toluene for PB might not be as good as that for PS. Due to such a difference in solubility, it is reasonable to speculate that the PB and PS blocks are transiently segregated in semidilute solution. The relaxation of these transient PB and PS richer domains leads to the observed slow relaxation. Such a speculation is supported by the appearance of an additional slow relaxation mode in the study of polyisoprene-b-polystyrene-b-polyisoprene in semidilute solution in cyclohexane, a non-selective solvent, in which we alternated the solubility difference by a variation of the solution temperature.     

2-AMINOMETHYLPYRIDINE NICKEL(II) COMPLEXES — SYNTHESIS，MOLECULAR STRUCTURE AND CATALYSIS OF ETHYLENE POLYMERIZATION

 A series of new nickel(II) complexes with 2-aminomethylpyridine ligands, (2-PyCH₂NHAr)₂NiBr₂(Ar = 2,6-dimethylphenyl 2a; 2,6-diisopropylphenyl 2b, 2,6-difluorophenyl 2c), have been synthesized and used as catalyst precursors for ethylene polymerization in the presence of methylaluminoxane (MAO)．The catalysts containing ortho-alkyl-substituents afford high molecular weight branched polyethylenes as well as a certain amount of oligomers. Enhancing the steric bulk of the alkyl substituent of the catalyst resulted in higher ratio of solid polymer to oligomer and higher molecular weight of the polymer. Catalyst 2c containing ortho-fluoro-substituents exhibited the highest catalytic activity, but only oligomers in which C₁₂H₂₄ had the maximum content were obtained by the catalyst. The molecular weight, molecular weight distribution, and microstructure of the resulted polymer were characterized by gel permeation chromatography and ¹³C-NMR spectrogram.     

THE ADSORPTION OF LINEAR POLY(N-ISOPROPYLACRYLAMIDE)CHAINS ON SURFACTANT-FREE POLYSTYRENE NANOPARTICLES

The adsorption of linear poly(N-isopropylacrylamide) (PNIPAM) chains on surfactant-freepolystyrene (PS) nanoparticles was used as a model system to study the hydrophobic adsorption of polymeron the surface, because the hydrophobility of PNIPAM can be continuously varied by a small temperaturechange. The adsorption was investigated by a combination of static and dynamic laser light scattering (LLS)measurements, In static LLS, the absolute excess scattered light intensity led to the amount of PNIPAMadsorbed on the surface. In dynamic LLS, the hydrodynamic thickness of the adsorbed PNIPAM layer wasaccurately measured. For a given particle concentration, the adsorption increases as thc PNIPAMconcentration and the incubation temperature increase. The average density of the adsorbed PNIPAM layer isreciprocally proportional to the number of the PNIPAM chains on the surface, revealing a simple scaling ofthe chain density distribution. The adsorption follows the Langmuir's isotherm. The enthalpy changeestimated from the adsorption at 25℃and 30℃is slightly positive, indicating that the adsorption involvesthe coil-to-globule transition of the chains on the surface.     

SYNTHESIS AND pH-SENSITIVE SELF-ASSEMBLY OF DENDRITIC POLY(AMIDOAMINE)-b-POLY(L-GLUTAMATE)BIOHYBRIDS

 Dendritic poly(amidoamine)-b-poly(L-glutamate) (PAMAM-b-PLG) biohybrids were synthesized by the ring-opening polymerization of γ-benzyl-L-glutamate N-carboxyanhydride monomer, followed by the deprotection of benzyl groups on poly(benzyl-L-glutamate), and were characterized by ¹H-NMR, FT-IR and gel permeation chromatography. The self-assembly behavior of the PAMAM-b-PLG biohybrid was investigated by means of UV-Vis, dynamic light scattering (DLS), transmission electronic microscopy (TEM) and ¹H-NMR. UV-Vis analysis demonstrated that the critical aggregation concentration of PAMAM-b-PLG was dependent on the pH value of aqueous solutios. DLS results further evidenced that the PAMAM-b-PLG biohybrid exhibited a pH-sensitive self-assembly behavior, and the average size of the self-assembled nanoparticles decreased gradually with the increasing pH value of the PAMAM-b-PLG solution. The self-assembled nanoparticles gave a nearly spherical morphology, and the pH-induced self-assembly had no obvious effect on the morphology of nanoparticles.     

ORIENTED TEXTURE OF MESOMORPHIC SOLUTIONS OF CYANOETHYL CELLULOSE/DIMETHYL ACETAMIDE

Textures of the oriented mesomorphic solutions of cyanoethyl celluloss/dimethyl acetamide were studied by polarized light microscopy, small angle light scattering and depolarized light transmission. If the mesomorphic solutions were sheared, they could form the band-like texture. Molecular chains in the solutions highly oriented almost along the shear direction. But the orientation directions of the molecular chains in the bands neighbouring each other were slightly different.     

PREPARATION AND MAGNETIC PROPERTIES OF POLY(SCHIFF BASE) COMPLEXES CONTAINING PHENANTHROLINE UNITS

 Two poly(Schiff base)s (PDBT and PDPE) were synthesized by polycondensation of 1,10-phenanthroline-5,6-dione (PD) with 2,2′-diamino-4,4′-bithiazole (DABT) and 4,4′-diaminodiphenyl ether (DAPE), respectively. The structures of the polymers were determined by FTIR and element analysis. The metal (Fe²⁺, Ni²⁺) complexes were prepared from the polymers with FeSO₄ or NiSO₄, and the metal contents of the complexes were measured by complexometric titration. The magnetic behaviors of the complexes were examined as a function of magnetic field strength at 4 K and as a function of temperature (4-300 K) at a magnetic field strength of 2.4 ×106 A/m. The results show that the relative saturation magnetization of the PDBT complexes is higher than that of the corresponding PDPE complexes, and PDBT-Ni²⁺ and PDPE-Ni²⁺ are soft ferromagnets, while PDBT-Fe²⁺ and PDPE-Fe²⁺ exhibit the features of antiferromagnet.     

FORMATION OF MESOGLOBULES BY POLY(N,N-DIETHYLACRYLAMIDE) CHAINS IN DILUTE SOLUTIONS

The association of poly(N,N-diethylacrylamide)(PDEA) chains has been investigated by a combination of static and dynamic laser light scattering(LLS).Unlike poly(N-isopropylacrylamide)(PNIPAM),PDEA chains can not form the C=O…H-N hydrogen bonds.Our results demonstrate that a limited number of PDEA chains collapse and associate into metastable globules in dilute solutions.The heating rate has great effect on the mesoglobule size.The formation of such mesoglobules is attributed to the competition between in...     

STUDIES ON THE MORPHOLOGY OF THERMOTROPIC POLYESTER DURING TRANSITIONS BETWEEN ISOTROPIC AND ANISOTROPIC MELTS

The morphology of a thermotropic aromatic polyester during the transitions between isotropic and anisotropic melts was studied by means of polarizing microscopy and small angle light scattering techniques. Both transition processes were found to be composed of the initiation of a new phase at local places of the old phase matrix and the growth of the new phase domains. A change of Hv scattering patterns was observed in the transition temperature ranges and was explained as the result of heterogeneity of the mesophase system, but not the change in ordering of a homogeneous mesophase.     

THE ASSOCIATION OF LIVING POLYSTYRYLLITHIUM IN BENZENE

The effects of the chain length,active end group and concentration on the association of living polystyryllithium (PS~-Li~+)chains in benzene were examined by a combination of static and dynamic laser light scattering in a cuvette equipped with a high-vacuum stopcock.The results show that long PS~-Li~+ chains(M_w>1×10~4)usually form dimers in the solution. In contrast,shorter PS~-Li~+ chains exhibit two relaxation modes,where the fast mode is related to the translational diffusion of the living chain dim...     

ORDERED STRUCTURAL EVOLUTION AND RELAXATION BEHAVIORS OF A SERIES MICROPHASE SEPARATED “HAIRY-ROD” POLYIMIDES WITH MULTIPLE ALKYL SIDE CHAINS

A series of “hairy-rod” polyimides, BBPA(n), with multiple alkyl side chains was prepared from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-biphenyldiamine substituted in the 2,2′-positions with benzoate, which was substituted in the 3,4,5-positions with ether side chains of varying lengths. The number of the methylene units, n, in these alkyl side chains were in even numbers ranging from 8 to 18. Combining techniques of one-dimensional (1D) and 2D wide angle x-ray diffraction, 1D small angle X-ray scattering, differential scanning calorimetry experiments, it was found that this series of “hairy-rod” polyimides possess a micro-phase separation between the backbones and side chains. This led to the formation of ordered structures in two different length scales, of which both are hexagonal packing: one is attributed to the alkyl side chains on the sub-nanometer scale, and another is for the whole polymer chains on the nanometer scale. The development of the hexagonal structure on the sub-nanometer scale was critically dependent upon the lengths of the alkylside chains. Three relaxation processes were captured by dynamic mechanical analysis, i.e., segmental motion of the backbones, α the melting of the side chain crystals, β1, which exits only for the materials with longer side chains(n=18,16); and the subglass relaxation of side chains, β2- The peak relaxation temperature of the α process decreased with increasing the length of side chains, while the one of the β2 process increased. The activation energy of the α relaxation was relatively independent on the length of side chain, whereas, β2 process showed the increasing of activation energy with increasing the length of side chains.     

Formulation ofα-linolenic acid microemulsion free of co-surfactant

<正>A novel class ofα-linolenic acid-in-water microemulsion free of co-surfactant was investigated as potential food delivery systems.Rough demarcation within the transparent region was deduced from the results of conductivity and polarizing optical microscopy.The microemulsion mean hydrodynamic diameter and characterization were determined by dynamic light scattering and negative-staining TEM.The location of ALA molecules in the microemulsion formulations was determined by ~1H NMR spectroscopy.     

CRYSTALLIZATION KINETICS OF SYNDIOTACTIC POLYPROPYLENE STUDIED BY TIME-DEPENDENT LIGHT ATTENUATION

Crystallization kinetics of syndiotactic polypropylene(sPP)was observed by light attenuation measurements. The initial stages of temperature dependent sPP crystallization fall in the range of Rayleigh scattering and Rayleigh-Debye- Gans scattering.Initial time and growth time of crystallization were obtained,and the trend of crystallization temperature dependent linear attenuation coefficient on the radius and the index of the refraction of the spherulite were evaluated.     

Highly sensitive determination of trace potassium ion in serum using the resonance light scattering technique with sodium tetraphenylboron

A resonance light scattering technique has been developed in order to determine potassium ion in serum. Potassium ion was found to bind the tetraphenylboronate anion [(C₆H₅)₄B]⁻ in acetate buffer (pH 8.0) in the presence of sodium dodecyl benzene sulfonate as a stabilizer, forming the B(C₆H₅)₄-K aggregate which produces intense resonance scattering light. Effects of factors such as acidity, ionic strength and interferents on the RLS of B(C₆H₅)₄-K were investigated. The solution pH close to neutral facilitates the production of RLS, and few biologically relevant species interfere in the determination of potassium ion. The resonance scattering light intensity at the maximum peak of 567 nm was linear to the concentration of potassium ion in the range of 0.2–2.0 μg mL⁻¹ with a detection limit of 20.0 ng mL⁻¹. The method was applied to determine trace amounts of potassium ion in serum and showed high sensitivity and accuracy compared with the clinically used ion-selective electrode method.     

ADDITIVE-INDUCED ENHANCEMENT OF OPTICAL CLARITY OF POLYACRYLAMIDE HYDROGEL

The aqueous polymerization of acrylamide and crosslinking with N,N-methylenebisacrylamide afforded hydrogelsdisplaying high levels of light scattering (poor optical clarity). Enhancement of the optical clarity within a polyacrylamide(PAm) hydrogel was accomplished through the implementation of "refractive index matching". Water-soluble additives wereutilised to better match the refractive index inhomogeneities throughout a given hydrogel. This resulted in lower lightscattering within the system and hence improved clarity. Amino acids, sugars, polymers, and other water-soluble additivessuch as glycerol were investigated by this methodology. Most additives investigaed displayed potential for effectivelyreducing the light scattering within a PAm hydrogel as a function of increased additive concentration. On increasing therefractive index of the water medium, the overall refractive index of a PAm hydrogel was also observed to increase. Thisprovided a quantitative means of determining the effectiveness of a given additive for improving the optical clarity within ahydrogel.     

DYNAMIC LIGHT SCATTERING STUDY ON TRANSLATION DIFFUSION OF 8-ARM STAR POLYSTYRENE IN GOOD AND THETA SOLVENTS

The technique of dynamic light scattering has been used to investigate the translation diffusion behavior of 8-arm star polystyrene (SPS)in a good solvent, tetrahydrofuran (THF) or benzene (BZ) and a theta solvent, cyclohexane (CH), by homodyne photon correlation spectroscopy .The intensityintensity autocorrelation function was analyzed by the method of cumulant. The translation diffusion coefficients have been obtained as a function of temperature and concentration. Under theta condition ,the non-concentration dependence of diffusion coefficient showed the unperturbed Gaussian state o the SPS molecular chain. The different hydrodynamic radii estimated from Stokes- Einstein equation reflected the stretch extent of the arm chain for regular star polymer. The data of diffusion activation energy of SPS in THF, BZ and CH were also obtained respectively.