Large Degree Of Polymerization Research Articles

Investigation of the Effect of Molecular Weight, Density, and Initiator Structure Size on the Repulsive Force between a PNIPAM Polymer Brush and Protein

This paper focuses on the effect of degree of polymerization (N), density ( σ ), and pattern size ( x ) on the interaction force between a periodically patterned Poly(N-isopropylacrylamide) (PNIPAM) brush and protein. The hydrophobic interaction, the Van der Waals attractive force, and the steric repulsive force were expressed in terms of N , σ , and x . The osmotic constant (k1) and the entropic constant (k2) were determined from the fit of the steric repulsive force to an experimentally obtained force distance curve. The osmotic constant was 0.105, and the entropic constant was 0.255. Using these constants, the steric repulsive force was plotted as a function of the separation distance(s) between the substrate and the protein. The forces were determined at a separation distance equal to 0.3 nm, where L0 is the equilibrium thickness of the PNIPAM brush. At this separation distance, the value of the steric repulsive force was much higher than the value of the sum of the hydrophobic interaction and the Van der Waals attractive force for large degree of polymerization ( N > 100 ) and density ( σ > 0.2 chains/nm2). However, the repulsive force was comparable to the sum of the hydrophobic interaction and the Van der Waals attractive force for a small degree of polymerization ( N < 100 ) and density ( σ = 0.2 ). Furthermore, the steric repulsive force was plotted as a function of pattern size x . The plot indicated that the steric repulsive force becomes nearly zero for all degrees of polymerization and density when the value of the initiator structure size was less than 200 nm. In addition to the steric repulsive force, the lateral extension of the chains in the periodically patterned PNIPAM brush was calculated by scaling low and compared with the experimental data taken from previously published literatures. The polymer brush structure was modelled as if the immediate bare substrate is so wide that even a stretched polymer segment cannot reach to the next polymer brush structure. In such models, the value of the lateral extension was equal to the thickness of the homogenous brush. It was independent of the pattern size. However, when the polymer brush structure was modelled as if there is another polymer brush structure at a distance half of the size of the period, the lateral extension was found to be dependent on the size of the initiator structure size due to chain bridging. This was witnessed by the patterning of polymer brushes using the interferometric patterning of PNIPAM brushes and an atomic force microscopy imaging of the polymer brush structures both in air and in water. The polymer brush structure resolution in water was much lower than the resolution in air, which indicates the lateral extension of the polymer chains in water. For such kind of periodic polymer brush structures, the gap between them was calculated, and it was found dependent on the degree of polymerization, density, and initiator structure size.

Micellar aggregation and thermogelation of amphiphilic random copolymers in water hierarchically dependent on chain length

Micellar aggregates and thermoresponsive gelation of amphiphilic random copolymers in water were examined in detail, focused on effects of the degree of polymerization (DP) on the behavior. For this purpose, we designed random copolymers carrying hydrophilic poly(ethylene glycol) and hydrophobic dodecyl groups, where the DP was varied from 63 to 358. The content of the hydrophobic monomer was set to 60 mol% to facilitate thermogelation. All the copolymers formed multichain aggregates in water, while the size distribution depended on DP. Since copolymers with larger DP had less composition distribution, the copolymers with 145 or more of DP formed size-controlled aggregates in water. Their concentrated solutions, above the overlap concentration of the aggregates, gelled entirely upon heating, followed by syneresis. In contrast, the short copolymer with 63 of DP formed aggregates with multimodal size distribution, and the concentrated solution underwent macroscopic phase separation upon heating, followed by gelation of the polymer-rich lower layer. As confirmed by small-angle neutron scattering, the copolymer suitable for thermogelation originally formed aggregates consisting of multiple micelle subunits in the aqueous dilute solution, and the thermogelation of the concentrated solution was driven by the physical packing of the micelle subunits upon heating. Thus, we revealed that the DP hierarchically affected not only the self-assembly of the copolymers into size-controlled micellar aggregates in water but also the thermogelation of the concentrated solutions via intermicellar association.

Effect of Various Factors for the Electrochemical Adsorption of Polydopamine on TiO<sub>2</sub> Film

To fabricate polydopamine-sensitized solar cells with improved solar power conversion efficiency, the effects of pH, buffer, adsorption time and electrode potential for the electrochemical oxidation and polymerization of dopamine on TiO2 film were investigated. The optimum pH was around 7. It was found that the use of a buffer, especially 2-(N-morpholino)ethanesulfonic acid, significantly deteriorated the electrochemical adsorption of polydopamine, and the highest solar power conversion efficiency was obtained without buffer. With increasing adsorption time, the amount of adsorbed polydopamine increased but the solar power conversion efficiency decreased, suggesting the increased resistivity of polydopamine with a larger degree of polymerization. It was suggested that the reversal of electrode potential from positive to negative would be essential for the electrochemical adsorption of polydopamine.

Kinetic modeling of phosphorylase-catalyzed iterative \u03b2-1,4-glycosylation for degree of polymerization-controlled synthesis of soluble cello-oligosaccharides

BackgroundCellodextrin phosphorylase (CdP; EC 2.4.1.49) catalyzes the iterative β-1,4-glycosylation of cellobiose using α-d-glucose 1-phosphate as the donor substrate. Cello-oligosaccharides (COS) with a degree of polymerization (DP) of up to 6 are soluble while those of larger DP self-assemble into solid cellulose material. The soluble COS have attracted considerable attention for their use as dietary fibers that offer a selective prebiotic function. An efficient synthesis of soluble COS requires good control over the DP of the products formed. A mathematical model of the iterative enzymatic glycosylation would be important to facilitate target-oriented process development.ResultsA detailed time-course analysis of the formation of COS products from cellobiose (25 mM, 50 mM) and α-d-glucose 1-phosphate (10–100 mM) was performed using the CdP from Clostridium cellulosi. A mechanism-based, Michaelis–Menten type mathematical model was developed to describe the kinetics of the iterative enzymatic glycosylation of cellobiose. The mechanistic model was combined with an empirical description of the DP-dependent self-assembly of the COS into insoluble cellulose. The hybrid model thus obtained was used for kinetic parameter determination from time-course fits performed with constraints derived from initial rate data. The fitted hybrid model provided excellent description of the experimental dynamics of the COS in the DP range 3–6 and also accounted for the insoluble product formation. The hybrid model was suitable to disentangle the complex relationship between the process conditions used (i.e., substrate concentration, donor/acceptor ratio, reaction time) and the reaction output obtained (i.e., yield and composition of soluble COS). Model application to a window-of-operation analysis for the synthesis of soluble COS was demonstrated on the example of a COS mixture enriched in DP 4.ConclusionsThe hybrid model of CdP-catalyzed iterative glycosylation is an important engineering tool to study and optimize the biocatalytic synthesis of soluble COS. The kinetic modeling approach used here can be of a general interest to be applied to other iteratively catalyzed enzymatic reactions of synthetic importance.

Influences of PVA modification on performance of microencapsulated reversible thermochromic phase change materials for energy storage application

The aim of the paper was to enhance the mechanical properties and anti-permeability performance of microcapsules through shell modification to keep complete and stable structure during the manufacturing process. The effect of PVA adding dosage, modified methods and types of PVA on the performance of microcapsules was discussed in detail. When the PVA/MF ratio (0.04–0.25) was appropriate, the supercooling degree of microcapsules was reduced and thermal stability was improved to some extent. Furthermore, the modified method of adding PVA-1788 into microcapsules after curing probably formed the second protective encapsulation for RTPCMs, which contributed to obtaining MicroRTPCMs-2 with excellent mechanical properties and anti-permeability performance. Compared among the effects of various types of PVA modification on the performance of MicroRTPCMs, PVA with larger polymerization degree and higher alcoholysis degree can form modified resin with larger crosslinking degree, which was beneficial to generating more stable composite shell structure. Therefore, MicroRTPCMs1-2699 presented more outstanding mechanical properties and anti-permeability performance, satisfactory cycle stability and long-term reliability, as well as reversible thermochromic coloration and leakage-prevention performance. In the end, the main characteristic of RTPCMs was to in-situ observe the heat absorption, energy storage and heat release process of PCM cores, which would be great significance for the practical application of MicroRTPCMs in the fields of thermoregulated fibers, thermal energy storage textiles, heat energy transfers and energy-saving building materials.

Effect of Colombian raw materials on the Prins condensation reaction over Sn/MCM-41

Colombian sodium silicate was used as silicon source in the synthesis of MCM-41 with several surfactant: SiO2 molar ratios (MR = 0.12, 0.30, 0.50 and 0.70). Sn was incorporated on MCM-41 by incipient impregnation and by wetness impregnation using a rotaevaporador. The materials were characterized by AAS, XRD, N2 adsorption-desorption isotherms, TEM, adsorption of pyridine, NH3-TPD, UV–vis-DRS and XPS. Materials with Na2SiO3 (MR = 0.70) showed crystalline, textural and structural properties very similar to MCM-41 synthesized with tetraethyl orthosilicate (TEOS). The highest total acidity of materials synthesized with Na2SiO3 compared with materials synthesized with TEOS could be owing to the use of sulfuric acid in the synthesis or the presence of more silanol groups in the solid surface. TOF values obtained in nopol production over materials synthesized with TEOS and Na2SiO3 (MR = 0.70), using wetness impregnation with rotoevaporation, were 420 and 476 h−1, respectively. Low cost paraformaldehyde with larger polymerization degree than Sigma-Aldrich source of formaldehyde was characterized by XRF, XRD, FTIR, TGA and DSC. Polymerization degree seems to affect TOF for nopol production; lower TOF values were obtained with paraformaldehyde with larger polymerization degree. Depolymerization occurs by two parallel reactions: Avrami-Erofeyev (A4) and contracting area (R2) models, with activation energies of 19.8 and 77.5 kJ mol−1, respectively. Sn-MCM-41 synthesized with Na2SiO3 can be used four times without considerable loss of catalytic activity; furthermore, no Sn leaching was detected.

Effect of lyophilization on the bacterial cellulose produced by different Komagataeibacter strains to adsorb epicatechin

Bacterial cellulose (BC) has been widely used as a model system to investigate the interaction of polyphenols with the polysaccharides of cell walls. In this study, the water absorption ability and the adsorption ability of epicatechin of the never-dried and freeze-dried BC produced by a high-yield Komagataeibacter hansenii strain ATCC 53582 was compared with two normal-yield strains. The structural characteristics of BC were investigated via microscopy observation and mechanical/rheological tests. The 1-butyl-3-methylimidazolium acetate/dimethyl sulfoxide ([BMIM]Ac/DMSO) co-solvent was used to dissolve BC to calculate the degree of polymerization (DP). Results showed that compared with the other two strain, the BC synthesised by ATCC 53582 had a higher cellulose concentration (1.2 wt%) but lower epicatechin adsorption (29 μg/mg under 4 mM, pH 7). Its fibril network collapsed and led to a reduced recovery ratio (86 %) in the compression-relaxation test, which may be due to large DP (2856).

The growth mechanism of sulfuric acid clusters: Implication for the formation of cloud condensation nuclei

The investigation on the growth mechanism of sulfuric acid clusters is helpful for the understanding about the formation of cloud condensation nuclei. The sulfuric acid may aggregate in linear, bent, or orbicular modes with two types of hydrogen bonds, viz. OH…OH and OH…O=S. The length of the linear mode polymers increases linearly along with the degree of polymerization (DP). The bent conformation distorts into the linear configuration when the DP is over 6. The diameter of the central ring generated by OH…OH hydrogen bonds in orbicular conformation increases distinctly from 3.441Å in tetramer to 7.543Å in nonamer. The IR spectra exhibit distinct variations along with both the DP and the coupling modes. As can be employed to infer the detailed geometrical structures of sulfuric acid polymers. The linear structure is more stable as compared to the bent and the orbicular conformations. The variation of the Gibbs free energy indicates that the sulfuric acid can aggregate with a larger DP in linear mode. The temperature effect on the stability of the sulfuric acid polymer is more significant as compared with that of the pressure. The complex with high DP tends to be more stable at higher temperature, while the complex with low DP prefers low temperature. The findings are helpful for further study on atmospheric aerosol growth and the formation of cloud nucleation.

Hyperbranched Polymers Formed Through Irreversible Step Polymerization of AB2‐Type Monomer with Substitution Effect in a Continuous Flow Stirred‐Tank Reactor (CSTR)

A new Monte Carlo simulation method is proposed for the step polymerization of AB2‐type monomer conducted in a continuous flow stirred‐tank reactor (CSTR). The effect of the second B group reactivity, represented by the reactivity ratio r is investigated. The degree of branching (DB) at large degree of polymerization (P) limit, DBP→∞ does not change with the mean residence time . The value of DBP→∞ becomes larger by increasing r and is larger than the corresponding batch polymerization. The weight fraction distribution at high molecular weight tail follows a power law , and a simple formula to predict the power exponent α is proposed. The relationship between the radius of gyration 〈s2〉0 and P does not change with , and large polymers obtained in a CSTR are much more compact than those formed in batch polymerization. CSTR is advantageous to synthesize compact HB polymers, especially with a smaller r‐value.

Hyperbranched Polymers Formed through Irreversible Step Polymerization of AB2‐Type Monomer in a Continuous Flow Stirred‐Tank Reactor (CSTR)

Hyperbranched polymers formed through step polymerization of AB2‐type monomer with equal reactivity for both B groups in a continuous flow stirred‐tank reactor (CSTR) are investigated theoretically. The weight fraction distribution at high molecular weight tail follows a power law, W(P) ∝ P −1/ξ for ξ ≤ 0.5 with , where is the mean residence time. The degree of branching (DB) at the large degree of polymerization (P) limit is DB P→∞ = 0.6 irrespective of the ξ‐value, which is larger than the case for the corresponding batch polymerization that gives DB P→∞ = 0.5. The relationship between the radius of gyration 〈s 2〉0 and P shows that the hyperbranched polymers formed in a CSTR are very compact, and the 〈s 2〉0‐values for large polymers are even smaller than the smallest possible case for a batch reactor with DB P→∞ = 1. For large polymers, the power law 〈s 2〉0∝P 1/3 holds, which is 〈s 2〉0∝P 1/2 for batch polymerization. image

Oligo-polyethene glycol (PEG)-modified 14-deoxy-11,12-didehydroandrographolide derivatives: synthesis, solubility and anti-bacterial activity

A class of 14-deoxy-11,12-didehydroandrographolide (DA) derivatives with oligo-polyethylene glycol (PEG) substituents has been synthesized. It is found that small degree of polymerization of PEG favors the synthesis of dual-PEGylated DA derivatives, whereas large degree of polymerization is good for the preparation of mono-PEGylated DA derivatives. As compared to the prototype compound DA, the PEGylated DA derivatives show enhanced water solubility which is beneficial to drug's bioavailability. Preliminary study finds that the PEGylated DA derivatives exhibit better anti-bacterial activity than that of DA.

Universality in Branching Frequencies and Molecular Dimensions during Hyperbranched Polymer Formation: Step Polymerization of AB2 Type Monomer with Equal Reactivity

Hyperbranched polymer formation during step polymerization of AB2 type monomer with equal reactivity of two B's is investigated theoretically, focusing the attention to the degree of branching (DB) and the mean square radius of gyration for the unperturbed chains, . It is found that the DB‐value at large degree of polymerization (P) limit, = 0.5 is unchanged during the whole course of polymerization. The average value of having the same P is invariant throughout the polymerization. The universal curve between and P agrees perfectly with that for the self‐condensing vinyl polymerization (SCVP), another method to synthesize hyperbranched polymers, when the reactivity ratio for SCVP, rSCVP, is 2.589 that gives = 0.5. The power law, is found for large values of P. image

Universality in Branching Frequencies and Molecular Dimensions during Hyperbranched Polymer Formation: 2. Step Polymerization of AB2 Type Monomer with Different Reactivity for the Second B Group

Hyperbranched polymer formation during step polymerization of AB2 type monomer with different reactivity for the second B group is investigated to find the following universal characteristics that are invariant during the whole course of polymerization: (1) The degree of branching (DB) at large degree of polymerization (P) limit, , and (2) the mean square radius of gyration for the unperturbed chains having the same P. The value of and the universal curve for change with the reactivity ratio of two B groups; however, the universal power law holds for large polymers, irrespective of the magnitude of reactivity ratio. The exponent, 0.5, is the same as that for the random branched polymers. Similarities and differences in comparison with random branched polymer formation are discussed. image

Chemoenzymatic Synthesis of Oligo(L-cysteine) for Use as a Thermostable Bio-Based Material.

Oligomerization of thiol-unprotected L-cysteine ethyl ester (Cys-OEt) catalyzed by proteinase K in aqueous solution has been used to synthesize oligo(L-cysteine) (OligoCys) with a well-defined chemical structure and relatively large degree of polymerization (DP) up to 16-17 (average 8.8). By using a high concentration of Cys-OEt, 78.0% free thiol content was achieved. The thermal properties of OligoCys are stable, with no glass transition until 200 °C, and the decomposition temperature could be increased by oxidation. Chemoenzymatically synthesized OligoCys has great potential for use as a thermostable bio-based material with resistance to oxidation.

Effect of carboxymethyl cellulose on the drying dynamics and thermal cracking performance of iron ore green pellets

Carboxymethyl cellulose (CMC) is an efficient organic binder in iron ore pelletization. However, the addition of CMC will reduce the anti-thermal cracking performance of the green pellets prepared. The objective of this article is to investigate the effect of CMC property on the drying dynamics and thermal cracking performance of green pellets. The results show that as the degree of polymerization (DP) and degree of substitution (DS) of CMC increase, drying rate declines and apparent activation energy of second drying stage goes up. When more CMC or CMC with larger DP and DS is added, the green pellets possess better mechanical strength but worse anti-thermal cracking performance. Although CMC decomposes during drying at 300–350°C, which may destroy the reticulate structure of organic chains, thermal cracking is attributed to high resistance of water/vapor diffusion caused by compact structure of the pellets rather than CMC decomposition.

In vitro fermentation of galacto-oligosaccharides and its specific size-fractions using non-treated and amoxicillin-treated human inoculum

In order to elaborate on the impact of amoxicillin treatment on the in vitro fermentation of specific structures of galacto-oligosaccharides (GOS), GOS was fractionated based on its degree of polymerization (DP) and the fermentation of individual DPs was studied. Different DP fractions of GOS and different isomeric structure within a DP fraction were preferentially degraded depending on the treatment applied to the microbiota. For the non-treated microbiota, the small DP fractions (dimers and trimers) were preferentially degraded as compared to the large DP fractions (tetramers till hexamers). β-D-Gal-(1→4/6)-D-Glc and β-D-Gal-(1→4)-β-D-Gal- (1→4)-D-Glc were the isomeric structures preferentially degraded within the DP2 and DP3 fraction, respectively. The fermentation of each size-fraction induced the production of various short chain fatty acids and the growth of several species of bifidobacteria. For amoxicillin-treated microbiota, the large size-fractions of GOS were preferentially degraded as compared to the small fractions. β-D-Gal-(1→4)-D-Gal and β-D-Gal-(1→4)-β-D- Gal-(1→3)-D-Glc were the isomeric structures preferentially degraded within the DP2 and DP3 fraction, respectively. Butyrate was only produced upon the fermentation of the large size-fractions. The differences in metabolic pattern of GOS depending on the treatment applied correlated with the changes in the microbiota composition, especially the growth of bifidobacteria. These results suggest that GOS, especially its large size-fractions, support the recovery of bifidobacteria and butyrate-producing bacteria after a treatment of the microbiota with amoxicillin. © 2014 Elsevier Ltd. All rights reserved.

Characterization of hydrolyzed Fe(III) species produced in Fenton’s reaction

In this paper, the applicability of the ferron assay for the characterization of hydrolyzed Fe(III) produced in the Fenton’s reaction system was investigated, and then the hydrolysis process of Fe(III) under typical Fenton’s reaction conditions was compared with that in a normal ferric sulphate solution system, by applying the ferron assay method and the modified hydrolyticity, B*, a parameter that takes into account all the possibilities of base generation and reduction. It was found that the residual Fe(II) and H2O2 under normal Fenton’s reaction conditions had little influence on the Fe(III)–ferron colorimetric reaction. Experimental results showed that the hydrolysis process of Fe(III) in the Fenton system was quite different from that in the ferric salt solution system. Under the same hydrolyticity, the hydrolysis rate of Fe(III) in the Fenton system was faster and more complicated than that in the ferric sulphate system, and the Fe(III) species produced in the Fenton system had a larger polymerization degree. With the increase in H2O2/Fe, Fea and Feb (the monomers and small polymeric Fe(III) species) increased gradually while Fec (the colloidal part) decreased, indicating that the increase in H2O2 had restrained the hydrolysis of Fe(III). This conclusion was also supported by the comparison of effective particulate diameters in the two systems. The fact that larger particles were produced with a shorter time in the Fenton system provided direct proof for the observation of the differences in the hydrolysis of Fe(III) in the two systems. The results of this study are useful for the possible utilization of the hydrolyzed Fe(III) produced in the Fenton’s system for the removal of organic pollutants.

Synthesis of hybrid mesoporous spheres using the chitosan as template

Abstract Hybrid mesoporous spheres of Al and Si oxides were synthesized for the mixture of organic material (chitosan) with inorganic material (aluminum and silicon hydroxide). It was observed that chitosan with larger polymerization degree, resulted in a larger mechanical resistance of the spheres. The oxides were characterized by the following: Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), differential scanning calorimetry (DSC), as well as, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and adsorption isotherms of N2 (BET). Highly uniform oxide sphere diameters were obtained (average of 1.0 mm). The results of the adsorption isotherms indicated that the material is mesoporous. The surface area of the materials ranged between 620 and 245 m2/g, and the pore volume varied between 0.82 and 0.28 cm3/g, depending on the molar ratio of the organic and inorganic materials.

Colloidal Stability Dependence on Polymer Adsorption through Disjoining Pressure Isotherms

The disjoining pressure of polymers confined by colloidal walls was computed using dissipative particle dynamics simulations at constant chemical potential, volume, and temperature. The polymers are able to adsorb on the surfaces according to two models. In the so-called surface-modifying polymers, all monomers composing the chains have the same affinity for the substrate, whereas for the end-grafted polymer only the monomer at one of the ends of the polymer molecule adsorbs on the colloidal surface, resembling the behavior of dispersing agents. We find that these adsorption models yield markedly different disjoining pressure isotherms, which in turn predict different stability conditions for the colloidal dispersion. Our results show that for end-grafted polymers, a larger degree of polymerization at the same monomer concentration leads to better stability than for the surface-modifying ones. But also the unbound monomers of the surface-modifying type dominate over both kinds of polymers at large surface distances. The origin of these differences when the chemical nature of monomers is the same, and molecular weight and polymer concentration are used to characterize colloidal stability, is found to be mainly entropic.

Evidence for anomalously large degree of polymerization in Mg2SiO4 glass and melt

Ab-initio molecular dynamics simulation of forsterite (Mg2SiO4) melt at 2273 K shows the presence of nearly 40% of the Si atoms as (Si2O7)6- dimers. This result is directly corroborated by the 29Si nuclear magnetic resonance spectrum of bulk Mg2SiO4 glass, prepared by container-less levitation techniques. The presence of a large excess of bridging O atoms associated with the (Si2O7)6- dimers in forsterite glass and melt is in sharp contrast with their complete absence in crystalline forsterite. Such structural differences between the crystal and the melt can have important implications in understanding the dynamics of crystallization and segregation in a primordial magma ocean and the continuing chemical differentiation of the Earth.