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Temperature gradient interaction chromatography (TGIC) is applied to the characterization of polyisoprene (PI) and polystyrene (PS) using normal-phase (NP) stationary phase--bare silica or diol bonded silica. Tetrahydrofuran-isooctane mixtures are used as a mobile phase. PI and linear and star shaped PS samples are successfully fractionated in terms of the molecular mass with a high resolution comparable to that of reversed-phase (RP) HPLC. Temperature dependence of the retention shows that the enthalpy of adsorption of PS to the stationary phase is exothermic. In addition, some characteristic features of the NP-TGIC system relative to those of RP-TGIC are presented, which include a high sensitivity on the polar end group and the simultaneous size-exclusion chromatographic and TGIC characterization of PS and PI mixtures.

Layer structure and thermal stability of alternating Langmuir–Blodgett (LB) films of cadmium arachidate (CdA 2 ) and poly( tert -butyl methacrylate) (PtBMA) was investigated by X-ray reflection and in-plane diffraction study. The LB films were deposited on hydrophobically pre-treated silicon wafer surface and the polymer layers are inserted between CdA 2 bilayers. Layer spacing of the alternating LB film increases linearly by 9.8 A per PtBMA layer, which is consistent with the single layer spacing of homo-PtBMA LB film. Lateral lattice structure of CdA 2 in alternating LB films maintains its hexagonal packing structure as found in CdA 2 monolayers while the multilayer CdA 2 LB film is known to change its structure from hexagonal to orthorhombic lattice. Therefore, the polymer layers inserted between CdA 2 bilayers in the alternating LB films effectively prevent the CdA 2 film not only from the growth of defect but also from the formation of three-dimensional crystallites of CdA 2 . In addition, the hexagonal packing structure of CdA 2 bilayer was maintained up to 90°C while the molecular area increases slightly.

We investigated the hydrogen bonding of a small molecule to polymer chains by forced Rayleigh scattering, equilibrium binding, and computer simulation. Diffusion of 4-(4‘-(dimethylamino)phenylazo)benzoic acid (p-MR) was reported previously to be far more retarded in a toluene solution of poly(methyl methacrylate) (PMMA) or poly(vinyl acetate) (PVAc) than in a polystyrene solution due to the hydrogen bonding of the carboxylic hydrogen in p-MR with the carbonyl groups in PMMA or PVAc. In this study, we found that PVAc solution exhibits a more effective retardation of the p-MR diffusion than the PMMA solution despite their similar molecular structures. The difference in the p-MR diffusivity in PVAc and PMMA solutions could be attributed to the difference in binding efficiency of the probe dye onto the two polymers. In addition, the computer simulation calculation of the surface area of the carbonyl group of the polymer chains accessible for a small molecule to hydrogen bond showed a difference between the tw...

Various zinc dicarboxylate catalysts were synthesized by the reaction of zinc oxide with eleven different glutaric acid derivatives, and their coordination characteristics were investigated by infrared spectroscopy. The electronic nature and steric hinderance of substituents influenced the coordination of the carboxylate and the zinc metal ion. The coordination characteristics were classified into three categories: (i) compounds exhibiting bridging bidentate coordinating bonding modes, such as syn-anti and syn-syn bridging; (ii) compounds with only unidentate coordination; and (iii) compounds with mixed coordinations of unidentate and bridging bidentate. All the zinc carboxylate catalysts produced poly(propylene carbonate)s (PPCs) by the copolymerization of carbon dioxide and propylene oxide. The first category of catalysts produced relatively higher yields than the other categories. Zinc glutarate without any substituent, which is a catalyst in the first category, produced PPC with the highest yield and the highest molecular weight. The catalytic activity of zinc glutarate was suppressed by incorporation of substituents. The suppression of the catalytic activity might be due to the variation in the Lewis acidity of the zinc site as well as changes in the morphological structure caused by the substituents. Methylaluminoxane was also evaluated as a catalyst for the copolymerization, but it produced copolymers containing a large amount of ether linkages.

A set of polystyrenes of varying molecular weights was synthesized by anionic polymerization under identical conditions, and their molecular weight distributions were critically examined. Polymerization of styrene was initiated with 2-butyllithium in cyclohexane at 45 °C. During the polymerization, seven aliquots of the reaction mixture were taken out at various reaction times using a cannula and terminated. The polymerization time varying molecular weights and molecular weight distributions of the polystyrenes were analyzed by temperature gradient interaction chromatography (TGIC) as well as size exclusion chromatography. The molecular weight distribution of the polystyrene approaches the Poisson distribution in the late stages of the polymerization, in accordance with the early prediction of Flory. We also confirmed that the molecular weight distribution of polystyrenes determined by TGIC is close to the true value.

Several poly(amic diisopropyl ester-alt-imide)s have been synthesized, which are a new type of polyimide precursors. The precursors consist of amic ester and imide units alternatively on the backbone, so that they are hydrolytically stable as well as low shrinkable through thermal imidization. These precursors have an easy processability because of their good solubility in common solvents that are widely used as good solvents for most polyimide precursors. The precursors and their alternating copolyimides in films have exhibited structural orders that are estimated to have a dimension of 15–42 A (along the chain axis) and 8–16 A (along the lateral direction), depending upon the polymer backbone chemistry. However, all the precursors and resultant copolyimides were laterally packed in an irregular way. Their crystallinities were apparently low. These results might be attributed mainly to the bend or kinked units on the polymer backbone. In addition, properties of the precursors and their polyimides in films: optical and dielectric properties, glass transition, thermal imidization characteristics, thermal stability, thermal expansion and residual stress, were investigated in detail. Overall, the precursor polymers, as well as the resultant alternating copolyimides were characterized to have relatively good properties suitable for applications in the fabrication of microelectronic devices.

Forced Rayleigh scattering (FRS) studies have been carried out on methyl yellow/alcohol solutions at two different probe wavelengths (633 and 543 nm). The signal shapes observed at the two wavelengths are quite different: using ethanol and 2-propanol as solvents, we observe at 633 nm a decay–grow–decay (DGD) shape similar to profiles frequently reported in the literature, while at 543 nm we observe a DGD shape in which the signal at the local minimum does not reach the baseline. In principle, the nonzero minimum can be accounted for by a difference (due to amplitude/phase-grating mixtures) in the phase shifts of light scattered from the photoproduct and ground-state molecules. To test this hypothesis, we first show in a straightforward manner that the signal can be approximated as the product of a polynomial and an exponential decay, which allows for data reduction of profiles with zero or nonzero phase-shift differences. Using this approach, the diffusion coefficients measured using the two probe wavelengths are found to be the same to within an uncertainty of 2%–3%. The results provide strong evidence that the difference in signal shapes is caused by amplitude/phase-grating mixtures within the methyl yellow/alcohol system, and imply that diffusion coefficients can be measured without difficulty for other FRS systems characterized by such mixtures.

Temperature gradient interaction chromatography (TGIC) analysis of polyisoprene (PI) is reported. PI can be fractionated in terms of molecular weight with high resolution by TGIC using a C18 bondedd silica column as the stationary phase and a mixture of CH 2 Cl 2 /CH 3 CN (80/20. v/v as the mobile phase. The temperature was increased during the elution from 5°C to 34°C to optimize the fractionation of high molecular weight PI. The relatively poor resolation in the low molecular weight range was improved by changing the eluent composition. For example, all the oligomeric species from the unimer to the 29mer of a low molecular weight PI (average mol. wt.: 900) were fully resolved with the mixed eluent of CH 2 Cl 2 / CH 3 CN (50/50, v/v) and a linear temperature program from 6°C to 40°C. In addition, simultaneons site exclusion chromatography and TGIC fractionation of PI/polystyrene, PI/poly(methylmethacrylate) mixtures are also reported.

Thermodynamic principles and some applications of the temperature gradient interaction chromatography (TGIC) recently developed for the characterization of synthetic polymers are described. TGIC is a form of high performance liquid chromatography (HPLC) that varies column temperature in a programmed manner to control the retention of polymeric species during isocratic elution. The retention of polymers strongly depends on their molecular weights, and the polymers are well separated by TGIC in terms of their molecular weights. TGIC is superior to size exclusion chromatography (SEC) in resolution and sample loading capacity, and has higher sensitivity to molecular weight in the analysis of nonlinear polymers. TGIC has an advantage over solvent gradient HPLC because it permits the use of refractive index sensitive detection method such as differential refractometry and light scattering due to the isocratic elution. In addition, temperature provides finer and more reproducible retention control than the solvent composition, which is important in determining the molecular weight distribution by secondary calibration methods. With TGIC analysis, we found that the molecular weight distribution of anionically polymerized polymers is much narrower than has been generally accepted from SEC analysis. We also found the TGIC separation conditions for polystyrene, polyisoprene, poly(methyl methacrylate), poly(vinyl chloride), and poly(vinyl acetate) over wide molecular weight range. Because of its sensitivity to the molecular weight alone, TGIC was successfully applied to the characterization of star shaped polystyrene, and the detailed linking kinetics between living polystyrene anions and a chlorosilane linking agent was investigated.

Using the disymmetric N,N‘-bis(trimethylsilyl)aminobenzylamine (H2MABA; 1) ligand, the new group 4 metal complexes (MABA)TiCl2 (2), (MABA)TiMe2 (3), (MABA)Ti(CH2Ph)2 (4), (MABA)ZrCl2 (5), and (MABA)2Zr (6) were prepared. X-ray crystal structures of 2, 4, and 6 were determined. The crystal structure of 2 suggests that an agostic interaction between the titanium metal center and benzylic protons exists in the solid state. However, the agostic interaction is not sustained in solution, as indicated by NMR spectroscopy. Complexes 2 and 5, activated by MMAO, and 4, activated by B(C6F5)3, have moderate catalytic activities for the polymerization of α-olefins.

The catalytic activities of tetraphenylporphinatoaluminum chloride (TP-PAlCl) and its propylene oxide adduct (TPPAl(PO) 2 Cl) were investigated in detail together with a quarternary salt Et 4 NBr for the copolymerization of carbon dioxide and propylene oxide. In addition, for the components and starting raw materials of the catalyst systems, catalytic activities were examined for the copolymerization. The TPPAlCl catalyst delivered oligomers containing ether linkages to a large extent, regardless of its PO adduction. And cyclic propylene carbonate, as byproduct, was formed in a very small portion. Using the TPPAlCl coupled with Et 4 NBr as a catalyst system, the formation of ether linkages was reduced significantly in the copolymerization; however, the obtained oligomer still contained ether linkages of 25.0 mol % in the backbone. On the other hand, the formation of cyclic carbonate was increased to 22.4 mol % relative to the oligomer product. The results indicate that the salt, which was coupled with the TPPAlCl catalyst, plays a key role in reducing the formation of ether linkage in the oligomer and, however, in enhancing the formation of cyclic carbonate. Similar results were obtained for the copolymerization catalyzed by the TPPAl(PO) 2 Cl/ Et 4 NBr system. That is, the formation of ether linkages was not restricted further by the PO adduction of the TPPAlCl component in the catalyst system. Only oligomers with a relatively high molecular weight were produced. This indicates that the PO adduction of the TPPAlCl component contributes highly to the initiation and propagation step in the oligomerization, consequently leading to a relatively high molecular weight oligomer. In contrast, the Et 4 NBr, as well as the Et 2 AlCl, produced only cyclic carbonate in a very low yield. Furthermore, tetraphenylporphine exhibited no catalytic activity, regardless of using together with Et 4 NBr, On the other hand, the Et 2 AlCl coupled with Et 4 NBr provided a low molecular weight oligomer having ether linkages of 92.3 mol % in addition to the cyclic carbonate.

Various physical proper-ties, such as the sol-gel transition, micellization, anddegradation, need to be considered to optimize thefunctional characteristics of the block copolymer sys-tems, and they are mainly determined by the molecularstructure of the block copolymers. In particular, thebalance of hydrophilic and hydrophobic components iscrucial.

A nonmonotonic, decay−growth−decay type forced Rayleigh scattering (FRS) decay profile was observed in the study of methyl red (o-MR) diffusion in polymer solutions in which the carboxylic hydrogen of o-MR can form a hydrogen bond with polymer chain segments (Lee and Lodge, J. Phys. Chem. 1987, 91, 5546; Lee et al. Macromolecules 1992, 25, 6977). The diffusivities of ground state o-MR (trans form) and of its photoexcited isomer (cis form) are different enough to show the nonmonotoic decay profile, but the origin of the behavior has not been fully understood. In order to elucidate this observation, the dependence of the decay profile shape on polymer concentration as well as on tempreature was investigated by FRS. From the results, we propose that the internal hydrogen-bonding strength between the carboxylic hydrogen and the azo nitrogen in o-MR changes upon photoisomerization from the trans to cis form, which results in the different diffusivities of the two isomers in hydrogen-bonding media. This proposi...

The layer structure of alternating Langmuir−Blodgett (LB) films of cadmium arachidate (CdAA2) and poly(tert-butyl methacrylate) (PtBMA) was investigated by an X-ray reflection and in-plane diffraction study. The LB films were deposited on a silicon wafer surface pretreated hydrophobically by transferring a behenic acid monolayer, and two or four PtBMA layers are inserted between each CdAA2 bilayer. While CdAA2 homo-LB films are known to show gradual deterioration of the transfer ratio as the number of accumulated layers increases, the alternating LB films maintain the transfer ratio near unity up to 32 layers. The layer spacing of the alternating LB films determined from the position of the Bragg diffraction peaks increases linearly by 9.9 A per PtBMA layer. The lateral lattice structure of CdAA2 in alternating LB films maintains its hexagonal packing structure, as found in CdAA2 monolayers, while the multilayer CdAA2 LB film is known to change its structure from hexagonal to orthorhombic lattice. The spa...

Poly(dichlorophosphazene) of a low molecular weight was prepared by the thermal polymerization of hexachlorocyclotriphosphazene in the presence of aluminum chloride (10 wt %). The chloro groups were replaced by 4-methylphenoxy groups to give [NP(OC6H4-p-CH3)]n. The methyl groups of the polymer were brominated with N-bromosuccinimide and benzoyl peroxide, resulting in [NP(OC6H4-p-CH3)x(OC6H4-p-CH2Br)y]n. The brominated unit content was 5% – 20%. These polymers were employed in initiating polymerization of 2-methyl-2-oxazoline. The weight average molecular weight of the 5% grafted polymer measured by GPC in chloroform was 11,000. Their micelle formation in water was investigated by fluorescence spectroscopy and surface tension measurement.

The linking reaction kinetics of a chlorosilane-linked polystyrene six-arm star was investigated by temperature gradient interaction chromatography using a light scattering detector. The precursor arm material (Mw = 83 000) was made by anionic polymerization and end capped with isoprene, and 1,2-bis(trichlorosilyl)ethane was used as the linking agent. All the reaction intermediates, from unlinked arm to six-arm star, were successfully resolved from the aliquots taken from the reactor at various linking reaction times. From the time-varying relative abundance of the star molecules with different numbers of arms, linking reaction rate constants were determined. It was found that the linking reaction rate becomes progressively slower as the number of attached arms increases. We were able to extract the quantitative ratio of the linking rate constants, k5/k4 = 0.097 and k6/k5 = 0.30, where ki stands for the rate constant of the reaction incorporating the ith arm to an (i − 1)-arm star to form an i arm star. T...

We report the characterization of polystyrene by temperature-gradient interaction chromatography (TGIC) with on-line light-scattering (LS) detection. Since a binary mixture eluent, CH2Cl2/CH3CN (57/43, v/v), was employed in TGIC, a systematic deviation in apparent molecular weight due to preferential sorption was observed. After an appropriate correction, however, correct molecular weights could be obtained. Second virial coefficients obtained from light-scattering measurement showed that the TGIC separation condition is very close to the ϑ condition. With the TGIC/LS setup, analysis of an unfractionated six-arm star polystyrene was carried out. The resolution of TGIC was high enough to resolve all the polymer molecules having one to six arms. Comparison of LS detection results with the results obtained by calibration with linear PS standards reveals that elution in TGIC is far more sensitive to molecular weight alone. Thus it provides an excellent route to separating polymer molecules of similar hydrodyn...

The molecular weight distribution of anionically polymerized poly(methyl methacrylate) (PMMA) was investigated by temperature gradient interaction chromatography (TGIC). PMMA was well separated under an isocratic elution condition in which C4-bonded silica and acetonitrile were employed as the stationary and mobile phases, respectively. Column temperature was varied from 10 to 60 °C, while six PMMA standard samples (molecular weight range: 8 500−1 327 000) of narrow molecular weight distribution were eluted. Despite the temperature change during elution, the absolute molecular weight of each sample could be determined by light scattering detection. The molecular weight distribution of PMMA standards was not as narrow as that of polystyrene standards. Further fractionation of anionically polymerized PMMA can be achieved by exploiting the high resolution of TGIC.

A new method, temperature gradient interaction chromatography(TGIC) is employed for the characterization of macromolecules. Fine and reproducible control of interaction between polymer chains and the alkyl chain bonded silica packing material can be achieved by varying the temperature of the column. This method provides a far superior resolution to the conventional size exclusion chromatography. In addition, this method has a high sample loading capacity to be effective for preparative purpose. Furthermore, this method can be used to characterize binary polymer mixtures, where one component ofa polymer mixture is separated by the size exclusion mechanism and the other is by the interaction mechanism simultaneously from single isocratic elution.

We show for the first time that entangled polymeric liquids containing long-chain branching can exhibit strain hardening upon startup shear. As the significant long-chain branching impedes chain disentanglement, Gaussian coils between entanglements can deform to reach the finite extensibility limit where the intrachain retraction force exceeds the value expected from the usual conformational entropy loss evaluated based on Gaussian chain statistics. The phenomenon is expected to lead to further theoretical understanding.

The diffusivity of 4-[[4‘-(dimethylamino)phenyl]azo]benzoic acid (p-MR) in poly(methyl methacrylate) (PMMA)/toluene solution was found to be much lower than in polystyrene solution due to the hydrogen bonding interaction between the diffusant and the polymer matrix. In order to study the effect of the H-bonding interaction in a quantitative manner, the content of MMA units in the polymer matrix capable of H-bonding with p-MR was varied using mixtures of polystyrene (PS) and PMMA as well as PS/PMMA random and diblock copolymers. In the mixture or diblock copolymer systems, the diffusion behavior of the probe could be well represented by a phenomenological model which assumes the additivity of the diffusional activation barriers due to hydrodynamic interaction and H-bonding interaction. On the other hand, we observed far more effective H-bonding in random copolymers than in mixtures or in block copolymers. The diffusivity of p-MR in a solution of random copolymers with MMA content of 40% or higher was found...

Homogeneous precursor/precursor solutions with various compositions were obtained with appreciably high solid contents in N-methyl-2-pyrrolidone from soluble poly(amic diethyl ester) precursors of rodlike poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) and flexible poly(4,4′-oxydiphenylene biphenyltetracarboximide) (BPDA-ODA), which are hydrolytically more stable as well as more soluble than the corresponding poly(amic acid)s being equilibrated with the constituent monomers. Both optical microscopic and light scattering measurements showed that the dried precursor blend films and resultant polyimide composite films were optically transparent, regardless of compositions and process conditions. The composite films showed a single Tg behavior. However, for the composite of 30 wt % BPDA-PDA dispersed in the matrix of 70 wt % BPDA-ODA, a smectic crystalline-like aggregation of the BPDA-PDA component was detected on wide-angle x-ray diffraction patterns, indicative of microscopic phase separation between the two components. This phase separation was not detected on the optical microscopy, light scattering, and dynamic mechanical thermal analysis because of their resolution limits: Optical microscopy has a resolution of submicrometers, whereas dynamic mechanical thermal analysis and light scattering have a resolution of ca. 50 A. Therefore, it is speculated that in the composite films BPDA-PDA and BPDA-ODA polyimide molecules have demixed on the scale of a few nanometers. The mean long periodicity, which was estimated from the small-angle x-ray scattering pattern, varied from 134 to 170 A as the content of BPDA-ODA component increased. In addition, mechanical properties of the composite films were characterized. ©1995 John Wiley & Sons, Inc.

We demonstrated that both components of binary polymer mixtures of polystyrene and poly(methyl methacrylate) can be characterized simultaneously by size exclusion chromatography equipped with multiple detectors. In this analysis scheme, the individual peaks of the two components are separated from the overlapped chromatogram by simultaneously solving the response signal intensities from two concentration detectors, i.e. a refractive-index detector and an ultra-violet/visible absorption detector. Then the absolute molecular-weight distribution of each component is obtained from the response of a light-scattering detector in conjunction with universal calibration. This method can be applied to binary mixture systems the two components of which have a distinguishable difference in refractive index as well as in absorptivity.

We present a rigorous investigation on elution behaviors of ultrasonically shortened multiwalled carbon nanotubes in size-exclusion chromatography. The size separation of five carbon nanotube samples that underwent ultrasonic shortening for varying lengths of time revealed the existence of three kinds of carbon species: large nanotubes, small nanotubes, and amorphous carbon species. Separation of the three different carbon species was confirmed by SEM analyses on the fractionated eluates and also by light scattering/UV absorbance double detection. The chromatographic peak intensity ratio between the large and small nanotubes suggested an increased amount of small carbon nanotubes upon longer mechanical treatment time. The effect of the concentration of carbon nanotube dispersion on elution behavior was examined, and the elution volume of the shortened nanotubes was found to decrease upon dilution while that of the large nanotubes showed the opposite tendency. Unusual elution behaviors of the multiwalled carbon nanotubes were also observed by altering the flow rate, and these behaviors could be explained by the longer equilibration time taken for large nanotubes to access the pores of the packing materials and a possible morphology change of small carbon nanotubes.

This work describes the determination of the band broadening function (BBF) in a size exclusion chromatograph fitted with 2 mixed-gel columns, a light scattering (LS) detector, and a differential refractometer (DR). The raw data were the chromatograms of 4 narrow polystyrene standards. First, the interdetector volume shift was indirectly estimated from its upper and lower limiting values. Then, for each of the standards, their ‘‘local’’ BBFs were estimated by application of an existing theoretical method. Each local BBF is an assumed elution-volume invariant in the narrow ranges of the analyzed standards and is represented by an exponentially-modified Gaussian of standard deviation rBB and exponential decay sBB. Finally, a ‘‘global’’ BBF (valid for the complete fractionation range) was interpolated from the local BBF parameters. For increasing elution volumes, the global BBF exhibits an increasing rBB and a decreasing sBB. In addition, the asymmetry factor [sBB=rBB] and the global variance [r2 BB þ s2 BB] both decrease with elution volume. Fil: Yossen, Mariana Matilde. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico Para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico Para la Industria Química; Argentina Fil: Vega, Jorge Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Chang, Taihyun. Pohang University of Science and Technology; Corea del Sur Fil: Meira, Gregorio Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

A novel polymer, poly(2-(N -carbazolyl)ethyl methacrylate) end-capped with fullerene (PCzMA-C(60) ), has been synthesized via living anionic polymerization. Electrically programmable flash memory devices were easily fabricated with this polymer by using solution coating and metal deposition. This polymer was found in these devices to exhibit bipolar and unipolar switching behaviors with a high ON/OFF current ratio, a long retention time, high reliability, and low power consumption. The excellent properties and easy processability of this polymer open up the possibility of the mass production of high performance nonvolatile memory devices at low cost.

The ring-opening polymerization of L-lactide with stannous octoate was investigated in the presence of pentaerythritol. By this way it was possible to prepare higher molecular weight star-shaped poly(L-lactide)s compared with the linear ones obtained by stannous octoate only. The weight-average molecular weights of linear and star poly(L-lactide)s were measured by light scattering analysis from hexafluoro-2-propanol solution, and the respective Mark-Houwink equations were derived. The second virial coefficient and the intrinsic viscosity of the star polymers were lower than those of the linear ones, which confirms the star-shaped architecture.

A recently proposed mechanism for complex signal profiles of forced Rayleigh scattering (Park et al. J. Phys. Chem. 1991, 95, 7121) is tested with a system of globular protein-surfactant complexes. The mechanism starts with a hypothesis of double grating of pure phase complementarity which is shown to produce extreme departures, such as decay-growth-decay type, from single exponential decay. A new analysis scheme for such a complex signal type is proposed, and it has been validated here experimentally with the dynamic light scattering results in conjunction with the FRS measurements

The mechanism of defect formation upon thermal treatment of the fatty acid salt LB film was investigated by FTIR (Fourier transform infrared) spectroscopy and X-ray reflectivity. It was observed from FTIR spectra of alternating LB film of normal and deuterated lead stearate that the major mechanism of deterioration of the film with thermal treatment was the ablation of the top layer.

While nature is capable of producing uniform macromolecules as found in complex biosystems, man-made polymers are hardly homogeneous. They exhibit inherent distributions at least in molecular weight, and often come with multivariate distributions in chemical composition, functionality microstructure, chain architecture, and so on. Size-exclusion chromatography (SEC) has been the most widely employed chromatographic technique for the characterization of molecular weight and its distribution of synthetic polymers since its inception about half a century ago. Compared to conventional molecular weight characterization methods, SEC is an excellent method with regard to precision, analysis speed, required amount of samples, etc. Nonetheless, SEC separates the polymer molecules in terms of their chain size, which is not only a function of molecular weight but also depends on other molecular characteristics such as composition, branching, and microstructure. Therefore, SEC cannot characterize nonlinear polymers or copolymers effectively. In contrast to SEC, in which the different pore accessibility of the macromolecules is the major separation mechanism, interaction chromatography (IC) fractionates the polymer sample by enthalpic interaction between the polymer solutes and the stationary phase. As a result, IC is sensitive to the chemical nature as well as the molecular weight of the polymers, whereas it is less sensitive to long-chain branching than SEC. By judiciously selecting the IC separation condition, one can characterize specific molecular properties of polymers with much higher resolution than SEC. Furthermore, one can access the chromatographic critical condition (CC) for a given polymer system by adjusting the solute interaction strength with the stationary phase until the exclusion and interaction contributions to the solute retention are exactly compensated. Liquid chromatography at the critical condition (LCCC) can be used as a unique tool for the characterization of polymers. Of late, 2D liquid chromatography (LC) separations by a rational combination of SEC, IC, and LCCC has become more and more popular for the characterization of multivariate polymers. In this article, recent advances in non-SEC analysis methods of a variety of synthetic polymers are reviewed. Keywords: interaction chromatography; chromatographic critical condition; two-dimensional chromatography; polymer characterization

A new model describing the retention in temperature gradient interaction chromatography of polymers is developed. The model predicts that polymers might elute in temperature gradient interaction chromatography in either an increasing or decreasing order or even nearly independent of molar mass, depending on the rate of the temperature increase relative to the flow rate. This is in contrast to solvent gradient elution, where polymers elute either in order of increasing molar mass or molar mass independent. The predictions of the newly developed model were verified with the literature data as well as new experimental data.

A phase diagram was constructed for a polystyrene-block-polyisoprene (PS-b-PI, M(W) = 32 700, f(PI) = 0.670) in thin films on Si wafer as a function of film thickness over the range of 150-2410 nm (7-107L(0) (L(0): domain spacing)). The PS-b-PI exhibits a variety of ordered phases from hexagonally perforated lamellar (HPL) via double gyroid (DG) to hexagonally packed cylinder (HEX) before going to the disordered (DIS) phase upon heating. The morphology of the PS-b-PI in thin film was investigated by grazing incidence small-angle X-ray scattering, transmission electron microscopy, and transmission electron microtomography. In thin film, the phase transition temperature is difficult to be determined unequivocally with in situ heating processes since the phase transition is slow and two phases coexist over a wide temperature range. Therefore, in an effort to find an "equilibrium" phase, we determined the long-term stable phase formed after cooling the film from the DIS phase to a target temperature and annealing for 24 h at the temperature. The temperature windows of stable ordered phases are strongly influenced by the film thickness. As the film thickness decreases, the temperature window of layer-like structures such as HPL and HEX becomes wider, whereas that of the DG stable region decreases. For the films thinner than 160 nm (8L(0)), only the HPL phase was found. In the films exhibiting DG phase, a perforated layer structure at the free surface was found, which gradually converts to the internal DG structure. The relief of interfacial tension by preferential wetting appears to play an important role in controlling the morphology in very thin films.

We describe a novel medium, a captopril/thiophenol (Capt/TP) mixed self-assembled monolayer (SAM) formed on gold, for selectively pre-concentrating serotonin (5-hydroxytryptamine, 5-HT). The 5-HT molecules were shown to be selectively captured via formation of a strong complex, providing anodic stripping currents upon anodic scan or drastic increases in charge-transfer resistances for a redox probe, Fe(CN)(6)(3-/4-) pair, due to their blocking effects. The 5-HT molecules thus collected were subsequently detected by anodic stripping differential pulse voltammetry (ASDPV) or electrochemical impedance spectroscopy (EIS). The detection limit was 1.2 when detected by EIS and 28 nM with ASDPV. 5-HT was shown to be determined in physiological matrices containing ascorbic acid, dopamine, and other commonly encountered neurotransmitters.

The retention behavior of deuterated polystyrene (d-PS) and normal hydrogenous polystyrene (h-PS) was investigated in normal phase (NP) and reversed phase (RP) liquid chromatography (LC). It was found that d-PS was retained slightly longer than h-PS in NPLC (bare silica column and tetrahydrofuran (THF)/n-hexane mixed mobile phase) while in RPLC (C18-bonded silica column and THF/methanol mixed mobile phase) h-PS was retained longer than d-PS. The retention behaviors are interpreted in terms of the thermodynamic variables associated with LC separations. The different retention behavior of deuterated polymers from that of hydrogenous polymers could allow separation of partially deuterated polymers according to the deuterium content, such as for copolymers in LC characterization.

The coil-to-globule transition of the radius of gyration of polystyrene (PS) samples (M w : 3.84×10 6 -8.42×10 6 g/mol) in methylcyclohexane (MCH) has been measured by static light scattering below the Θ-temperature (Θ=69.3°C). In order to analyze our coil-to-globule data as well as already-reported data of polystyrene/cyclohexane (PS/CH) and polystyrene/methyl acetate (PS/MA) systems, (M w /R 0 2 ) 3/2 |τ|/τ c was introduced as a new scaling parameter. The master curve of each overlapped in the plot of α s 3 (M w /R 0 2 ) 3/2 |τ|/τ c . Thus this seems to be a universal parameter in coil to globule transition.

Chain dimensions of the polystyrene-d8 parts of a styrene-d8-2-vinylpyridine block copolymer (DP-33) and a styrene-d8-styrene-h8 block copolymer (DH-44), both with 50:50 compositions, were measured in dilute solutions of pyridine (a common good solvent) benzene (a selective solvent) and methyl ethyl ketone (a poor solvent) by small-angle neutron scattering. The conformation of one block chain within a diblock copolymer is not affected by the existence of another block chain, regardless of the solvent power at least when the composition of the diblock copolymer is 50:50, and the molecular weight is not high.

Water soluble porphyrins were designed and prepared by Williamson ether synthesis reaction between tetrakis(p-bromomethylphenyl)porphyrin and polyethylene glycol (PEG) for photodynamic therapy. The quantum yields for the generation of singlet oxygen of tetra-polyethylene glycol branched porphyrin shows above 80% in D2O. Luminescence of singlet state oxygen was observed from D2O solution under the single-photon excitation at 514 nm. In vitro test, cellular uptake efficiency has been enhanced by simple modification of molecular structure through changing the number of PEG unit without any support such as polymer-encapsulated inorganic nanoparticles.

Uniform nanodonuts: Stable toroidal micelles that have a highly uniform size and shape spontaneously self-assemble from a selective THF/ethanol solvent mixture (see 3D AFM image). The donut-shaped micelles can be used as a template to grow gold nanoparticles, which form along the ring surface.

We investigated the epitaxial phase transition from double gyroid (DG) to hexagonally packed cylinder (HEX) phases of a polystyrene-b-polyisoprene diblock copolymer in a thin film on a Si wafer substrate. The internal structure of the thin film was investigated by grazing incidence small-angle X-ray scattering, transmission electron microscopy, and transmission electron microtomography (TEMT). TEMT allows observation of the 3D-image of coexisting DG and HEX directly. Good domain orientation in the thin film and direct 3D-imaging of TEMT made it possible to observe the coexisting phase of DG and HEX, and a new epitaxial transition path from DG to HEX was found.