Two-dimensional polymers investigated by scanning near-field optical microscopy: Conformation of single polymer chain in monolayer

The conformation of single polymer chain restricted in a two-dimensional plane was studied by scanning near-field optical microscopy (SNOM). The single dye-labeled chain in a monolayer of poly(isobutyl methacrylate) (PiBMA) with a high molecular weight of ca. 5×10⁶ was directly observed by SNOM as a circular shape with a diameter of 200-300 nm. The observed chain size was considerably smaller than that for a self-avoiding random walk chain generated by computer simulation, indicating that the polymer chain takes a contracted conformation in two dimensions. SNOM imaging was carried out for the labeled PiBMA chain dispersed in the matrix monolayer with 1000-times lower molecular weight. The long chain isolated among shorter chains had an expanded form as large as a random conformation. These results were in good agreement with the scaling theory, providing an unambiguous evidence for the first time with the real image for a single chain conformation by SNOM.     

Affine deformation of single polymer chain in poly(methyl methacrylate) films under uniaxial extension observed by scanning near-field optical microscopy

The conformation of single poly(methyl methacrylate) chain in the uniaxially stretched film was observed by the combination of the fluorescence labeling technique and scanning near-field optical microscopy (SNOM). The dimension of the individual probe chain (M_w = 1.99 × 10⁶) along the extension axis was evaluated from SNOM image. In the high molecular weight matrix (M_w = 1.89 × 10⁶) the average extension ratio at the single chain level coincided with the macroscopic extension ratio. The distribution of the chain conformation was in good agreement with that of the freely jointed chain followed by affine deformation. On the other hand, the probe chain embedded in the low molecular weight matrix (M_w = 1.76 × 10⁵) showed the smaller extension than that expected from the affine deformation. This suggests that the conformation of the probe chain is affected by the relaxation of the short surrounding chains through disentanglement.     

Conformation of single PMMA chain in uniaxially stretched film studied by scanning near-field optical microscopy

The conformation of the single polymer chain in uniaxially stretched poly(methyl methacrylate) (PMMA) films was studied by scanning near-field optical microscopy (SNOM), which enabled us to observe the elongated conformation of each polymer chain embedded in the film. The conformation of the individual PMMA chains was quantitatively evaluated from the fluorescence intensity distribution. Observation of films with different strains showed that the microscopic strain of the single chain was smaller than the macroscopic strain (?) of the film. Especially at the later stage of the deformation (? > 1.5), the PMMA chain was not stretched with the increase in the macroscopic elongation of the film, suggesting the presence of slipping of polymer chain on the course of stretching.     

Synthesis and properties of a new crosslinkable polymer containing benzoxazine moiety in the main chain

Using difunctional phenolic and amine compounds, a new polymer with benzoxazine groups in the main chain has been synthesized through the Mannich reaction of a phenol, formaldehyde, and an amine. ¹H and ¹³C nuclear magnetic resonance spectroscopies, Fourier transform infrared spectroscopy, size exclusion chromatography, and elemental analysis are used to characterize the resulting polymer. Polymer with molecular weight of approximately 10,000 Da is obtained. The resultant polymer has a moderately broad polydispersity index. The thermal properties of the polymer have also been studied by differential scanning calorimetry and thermogravimetric analysis.     

The unwinding of surfactant-induced helical structure of carboxymethyl amylose by single molecule force spectroscopy

We have employed atomic force microscopy (AFM)-based single molecule force spectroscopy (SMFS) to investigate the unwinding process of the surfactant-induced helical structure of carboxymethyl amylose at the single-molecular level. In doing so, the nanomechanical fingerprint for the conformational transition of carboxymethyl amylose at about 270 pN is used as an indicator for identifying the single chain elongation. Upon the addition of NaCl and cetyltrimethylammonium bromide (CTAB), the force-extension curve of carboxymethyl amylose appears as a long flat plateau during the elongation of a single chain followed by the conformational transition. The flat plateau is attributed to the unwinding process of CTAB-induced helical structure of carboxymethyl amylose. By Gaussian fitting, the center value for plateau height histogram is 17 pN, which reflects the force needed to unwind the CTAB-induced helical structure of carboxymethyl amylose. We hope that this line of research provides an example of using characteristic shoulder plateau of α-linked glycan to identify single chain elongation, allowing for direct measurement of the unwinding force of supramolecular structure using SMFS.     

Force spectroscopy of polymers: Studying on intramolecular and intermolecular interactions in single molecular level

Single molecule force spectroscopy (SMFS) is a powerful means in studying the intramolecular and intermolecular interactions in polymer and supramolecular systems, thus opening new horizons for nanomechanic chemistry. This feature article concerns mainly how to employ AFM-based SMFS to obtain some of the important information which is not available by conventional characterizing methods, including single chain mechanics, the interfacial conformation and adhesive energy of polymers, interaction between macromolecules and small molecules, and the direct measurement of intermolecular forces. In addition, some of the recent advances in using the SMFS to bottom-up assembly of functional nanostructure are also discussed.     

Toward understanding the effect of substitutes and solvents on entropic and enthalpic elasticity of single dendronized copolymers

Using single molecule force spectroscopy (SMFS), we have investigated the single chain elasticity of a series of dendronized copolymers, whose original backbone is styryl dendron and maleic anhydride. The amilysis reaction of maleic anhydride introduces amide and carboxyl side groups. Hence, the copolymer bears three type side groups, Fréchet type dendrons, amides and carboxyls. The single chain elasticity of the polymers in tetrahydrofuran (THF) and chloroform (CHCl₃) has been obtained, respectively. There is no hysteresis between the stretching and relaxing force curves of individual polymer chain, indicating that the elongation is carried out at the equilibrium condition. The force curves can be fitted well by the modified freely jointed chain model, which suggests that the elongation of the polymer chain is controlled by the entropic elasticity in the low-force region but dominated by enthalpic elasticity in the high-force region. The polymer with first-generation dendrons shows different elasticities in the two solvents, which should result from the different hydrogen bonds of the dendronized copolymer in two solvents. When the dendron groups are changed to be second and third generations, the single chain elasticity of the polymers is the same in two solvents. Hence, the elasticity of the polymer chain can be different depending on the properties of side groups and solvents.     

Preparing recombinant single chain antibodies

A review of current processing practices in preparation of recombinant single chain antibody fragments is presented. Single chain antibody fragments which are superior to their Fab and IgG counterparts due to their higher affinity for target antigens while imposing minimal antigenicity in recipient hosts, have sparked breakthroughs in immunology and the medical field at large. The rapidly increasing market demand for pure single chain antibodies for research and therapeutic applications, necessitates viable manufacture routes that can produce large amounts of these antibodies efficiently and as cheaply as possible. Medium- to high-producing expression systems reported for recombinant single chain antibody production are reviewed, and their reported or potential success for efficient commercial-viable preparation of pure antibodies discussed. The effects of expression host system choice on product molecular constraints, ease of processing, and flowsheet design and scale-up are compared. It is concluded that there is no unique host system that can consistently yield high expression levels for a wide range of single chain antibodies; instead, product sequence and end application often dictate the optimum choice of expression host. Irrespective of host systems, adequate a priori design and engineering of the molecular construct supported by good biophysical understanding of the single chain fragment molecules, is a crucial pre-requisite for improved product stability and downstream recovery, which will favourably impact final product yield and functionality.     

Dynamic interfacial properties between a flexible‐chain polymer and a thermotropic liquid crystalline polymer investigated by an ellipsoidal drop retraction method

In this study, the dynamic interfacial properties between an isotropic polymer and a thermotropic liquid crystalline polymer (TLCP) were investigated by measuring the time‐dependent interfacial tension between them. As a TLCP drop retracts in a flexible polymer matrix, the evolution of its shape is recorded by microscopy. By fitting the ellipsoidal model of Maffettone and Minale, the model of Marrucci and Santo, and large deformation ellipsoidal models by Jackson–Tucker and Yu–Bousmina, the interfacial tension could then be determined. It was found that the retraction of a TLCP ellipsoidal drop in a flexible polymer cannot be described by these models as accurately as in Newtonian systems. The apparent interfacial tension obtained from these models evolves with time; the evolution is ascribed to the slow relaxation of domain orientation within the TLCP drop. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94:1404–1410, 2004     

Modeling single chain elasticity of single-stranded DNA: A comparison of three models

The dominant models of polymers, i.e., the freely jointed chain (FJC) model, the wormlike chain (WLC) model and the freely rotating chain (FRC) model are modified by integrating the inherent single-molecule elasticity obtained from quantum mechanics (QM) ab-initio calculations. The QM modified models have been utilized to generate fitting curves for single-stranded DNA obtained in organic solvent. The analyses on the deviation between the fitting curve and the experimental force curve demonstrate that the QM-FRC and QM-FJC model are suitable for ssDNA, but not the QM-WLC model. We also find that one repeating unit of ssDNA is corresponding to a Kuhn segment in QM-FJC model or two rotating units in QM-FRC. Having close correlation to the inherent elasticity and real molecular structure of the polymer, QM-FJC and QM-FRC are emerging as structure relevant models.     

The further understanding of chain topology effect on the properties of single polymer in good solvent: Special behaviors of single tadpole chain

Chain topology strongly affects the static and dynamic properties of polymer melts and polymers in dilute solution. For different chain architectures, such as ring and linear polymers, the molecular size and the diffusion behavior are different. To further understand the chain topology effect on the static and dynamic properties of polymers, we focus on the tadpole polymer which consists of a cyclic chain attached with one or more linear tails. It is found that both the number and the length of linear tails play important roles on the properties of the tadpole polymers in dilute solution. For the tadpole polymers with fixed linear tail length and number, with increasing the degree of polymerization of tadpole polymers, a transition from linear-like to ring-like behavior is observed for both the static and dynamic properties. By studying the radii of gyration for different chains, we define a ratio of the number of monomers in linear tails (N_tail) to the total degree of polymerization (N), and found that when the ratio N_tail/N is more than about 0.73, tadpole chains behave as linear chains, while, when N_tail/N is less than about 0.29, they behave as ring chains. This result will be helpful in further understanding of the chain topology dependence on the static and dynamic properties of polymer in dilute solution. Furthermore, the tadpole polymers behave as what Zimm theory expected before they deviate from the linear-like regime, or after they reach the ring-like regime, however, in the intermediate regime, the behavior of tadpole polymer does not show what Zimm model expected.     

环氧聚合型扩链剂对POM/TPU共混体系的相容作用

使用环氧聚合型扩链剂作为POM/TPU共混物的相容剂,研究其对POM/TPU共混物的流变性能、力学性能、结晶性能和耐热性的影响。结果表明,添加环氧聚合型扩链剂后,POM/TPU共混物的熔体流动速率先升高然后降低;冲击强度提高,断裂伸长率大幅提高;结晶度先升高后降低;热变形温度提高。     

Viscoelastic behavior of polymer tape in a wound roll

A viscoelastic computational model is developed that uses experimentally determined viscoelastic material properties as input and can be used to predict the behavior of a tape material in a wound roll as stresses relax over time. Experimental creep test results are used to find best‐fit creep‐compliance parameters to describe two high density data storage tape media. The two tapes used in the analysis are a developmental tape with a poly(ethylenenaphthalate) (PEN) substrate and metal particle (MP) front coat similar to linear tape open (LTO4) (referred to in this work as “Tape C”), and LTO3, a commercially available tape with a PEN substrate and MP front coat. Sets of best‐fit creep‐compliance parameters are determined for both tapes. The differences between the predicted behavior using three‐, five‐, and seven‐parameter Kelvin–Voigt models are evaluated, both for a benchmark case and in a viscoelastic wound roll model. The choice of material model is found to significantly influence the predictions of the wound roll model. The differences between different material models for the same material are on the order of the differences found between the two different materials. A material model with a higher number of creep‐compliance parameters, although more computationally expensive, produces better results, particularly over long spans of time. The relative differences between the three‐, five‐, and seven‐parameter models are shown to be qualitatively consistent for several variations in the computational model setup, allowing predictions to be made based on simple benchmarks. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Room temperature resistance relaxation behavior for carbon black filled conductive polymer composites

Room temperature resistance relaxation was studied with respect to carbon black (CB) volume fraction, the type of polymer matrix, and the environment. It was found that resistance of CB filled poly(methylvinylsiloxane) and polypropylene (PP) conductive composites changed at room temperature with different directions and amplitudes, depending on the filler volume fraction and the environment. The room temperature resistance relaxation was ascribed to the local Joule heat at the tunneling junction or the swelling effect of the solvents. On the other hand, CB filled immiscible PP/Nylon 1212 blends exhibited a stable electrical conduction due to the selective distribution of CB aggregates along the interface between polymer matrices. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Observation of single chain motion in a polymer melt

Molecular motion of single polymer chains has been investigated in a melt sample of polytetrahydrofuran and compared with results for the same polymer in dilute solution. Using a high resolution neutron scattering technique motion over distances up to 30 Å has been observed with an energy resolution of 0.01 μeV (～10⁷s^?1). The motion of the chains in the melt is described by the Rouse model and a friction factor per segment has been extracted from the data. This compares well with values obtained from viscosity and bulk relaxation measurements on similar polymers.     

Correlating miscibility of PVC/PMMA blend with polymer chain orientation

Blends of poly (vinyl chloride) (PVC) and poly (methyl methacrylate) (PMMA) with varying concentrations of the polymers were prepared in a film form by standard solution casting method, using methyl ethyl ketone (MEK) as a common solvent. The miscibility of the blend was studied by dynamic mechanical analysis. The chain orientation behaviors of PVC and PMMA in the stretched blend films were studied by infrared dichroism method. Up to 60 wt % PVC concentration in the blend, PVC showed negative values for orientation function whereas PMMA showed independent positive values for its orientation function. On further increasing PVC concentration in the blend, the orientation function of PVC flipped to positive values, and both PVC and PMMA showed same magnitude and trend in orientation behavior. The chain orientation behavior of individual polymers in the immiscible compositions of the blend was observed to be independent, while there was a high degree of cooperation for chain orientation in the miscible composition. Change in the miscibility of the blend was simultaneously accompanied by conformational changes in PVC. The change in orientation behavior is interpreted in terms of curling of polymer chains in the immiscible phase. The polymer chain curling hypothesis used here is applicable independent of the type of polymers in the blend. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 624–630, 2006     

Fast switching ferroelectric liquid crystal side chain polymer

Two products were isolated at a result of esterification of acrylic acid with 4-[4-(n-hydroxyundecanyloxy)phenyl] benzoic acid (5) One is 4-[4-(n-acryloloxy-undecanyloxy)phenyl] benzoic acid (6), and the other is 4-{4-[n-(3-acryloloxy-propionyloxy)undecanyloxy]phenyl}benzoic acid (7) which containts two molecules of acrylic acid. Compound7 is obtained unexpectedly and still unknown in the literature. Its identification is confirmed by the isolation and characterization of the monomer9. The mesogenic monomers8 and9 which were synthesized from 4-hydroxyphenyl 2(S)-[2(S)-methylbutoxylpropionate (4) and the corresponding acrylates6 and7 exhibit the enentiotropic Sc* and S_A phases. The Sc^* phase temperature range is up to 31 °C. The spontaneous polarization and response time for the monomers8 and9 is 97 and 16 nC/cm² as well as 90 and 64 µs respectively. It us the liquid crystal side chain polymer11, not10, which is switchable in the presence of an electric field. The spontaneous polarization of 36 nC/cm² and the response time of 3.1 ms is obtain from the new polyacrylate.     

Dynamics of irreversible uncoiling of a polymer chain

Using a simple dynamic model, the growth of rigidity and of the mean size of the polymer chain induced by a chemical reaction irreversibly fixing extended conformations of units has been investigated. When the reaction rate is controlled by the rotational diffusion of segments, the change in the mean length of a rigid segment and mean radius of gyration of the chain with time are described by power dependencies. For a macromolecule in a constant viscosity medium, the time needed to complete the reaction (i.e. to transform the coil into an extended rigid rod) is t_comp N³, where N is the initial number of segments in the chain. The cases of a kinetically controlled reaction and a mixed type of reaction have also been considered. The slowing down of the reaction caused by increasing the viscosity of the reaction medium has been evaluated, giving t_comp N⁷.     

Synthesis and solution properties of a new ionic polymer and its behavior in aqueous two-phase polymer systems

The amine salt, N,N-diallyl-N-carboethoxymethylammonium chloride was copolymerized in dimethyl sulfoxide using ammonium persulfate or azo-bis-isobutyronitrile (AIBN) to afford the cationic polyelectrolyte (CPE) having five-membered cyclic structure on the polymeric backbone. The CPE on acidic (HCl) hydrolysis of the pendent ester groups gave the corresponding cationic acid salt (CAS) having the equivalent of chloride salt of N,N-diallylammonio ethanoic acid as monomeric unit. The CAS was converted into an anionic polyelectrolyte (APE) and polybetaine (PB) [having the monomeric unit equivalent of sodium N,N-diallylaminoethanoate and N,N-diallylammonioethanoate] by treatment with two and one equivalent of base, respectively. The solution properties of APE were investigated by potentiometric and viscometric techniques. Basicity constant of the amine functionality in APE is found to be ‘apparent’ and as such follow the modified Henderson-Hasselbalch equation; the protonation of the APE becomes more and more difficult as the degree of protonation (α) of the whole macromolecule increases. The composition and phase diagram of the aqueous two-phase systems of APE and poly(ethyelene glycol) (PEG) has been studied for the first time for this class of ionic polymers. The CAS and PB were found to be virtually insoluble in water.     

Rheology and relaxation processes in a melting thermotropic liquid–crystalline polymer

The relaxation behavior of a thermotropic liquid–crystalline polymer (TLCP), LC‐5000 from Unichika, Japan, was investigated by rheology and optical microscopy. The solid‐nematic transition was shown by DSC and dynamic temperature ramp. The transitions of dynamic modulus with temperature correspond to the end of the melting process. The TLCP is composed of unmelted solid crystals and nematic liquid crystal during the melting process. Macroscopically, it changes from a viscoelastic solid to a viscoelastic liquid in this process, as verified by creep test and dynamic frequency sweep under different temperature. The relaxation spectra of the TLCP under different temperature were calculated from the dynamic modulus. The characteristic relaxation processes determined from the relaxation spectrum are consistent with the observation from polarized optical microscopy. During melting, in particular, the relaxation of deformed polydomains and chain orientation slows down due to the constraining effects of unmelted solid crystals. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3780–3787, 2007