Increase In Degree Of Polymerization Research Articles

Fabrication and characterization of porous calcium polyphosphate scaffolds

Porous calcium polyphosphate (CPP) scaffolds with different polymerization degree and crystalline phases were prepared, and then analyzed by scanning electron microscopy (SEM), Thermmogravimetry (TG) and X-ray diffraction (XRD). Number average polymerization degree was calculated by analyzing the calcining process of raw material Ca(H2PO4)2, as a polycondensation reaction. Amorphous CPP were prepared by the quenching from the melt of Ca(H2PO4)2 after calcining, and CPP with different polymerization degree was prepared by controlling the calcining time. Meanwhile, CPP with the same polymerization degree was prepared to amorphous or different crystalline phases CPP which was made from crystallization of amorphous CPP. In vitro degradation studies using 0.1 M of tris-buffered solution were performed to assess the effect of polymerization degree or crystalline phases on mechanical properties and weight loss of the samples. With the increase of polymerization degree, the weight loss during the degradation decreased, contrarily the strength of CPP increased. The degradation velocity of amorphous CPP, α-CPP, β-CPP and γ-CPP with the same polymerization degree decreased in turn at the same period. The full weight loss period of CPP can be controlled between 17 days and more than 1 year. The results of this study suggest that CPP ceramics have potential applications for bone tissue engineering.

Random isotropic structures and possible glass transitions in diblock copolymer melts

We study the microstructural glass transition in diblock-copolymer melts using a thermodynamic replica approach. Our approach performs an expansion in terms of the natural smallness parameter--the inverse of the scaled degree of polymerization N--which allows us to systematically study the approach to mean-field behavior as the degree of polymerization increases. We find that in the limit of infinite chain length, both the onset of glassiness and the vitrification transition (Kauzmann temperature) collapse to the mean-field spinodal, suggesting that the spinodal can be regarded as the mean-field signature for glass transitions in this class of microphase-separating system. We also study the order-disorder transition (ODT) within the same theoretical framework; in particular, we include the leading-order fluctuation corrections due to the cubic interaction in the coarse-grained Hamiltonian, which has been ignored in previous studies of the ODT in block copolymers. We find that the cubic term stabilizes both the ordered (body-centered-cubic) phase and the glassy state relative to the disordered phase. In melts of symmetric copolymers the glass transition always occurs after the order-disorder transition (below the ODT temperature), but for asymmetric copolymers, it is possible for the glass transition to precede the ordering transition.

Non-isothermal preform infiltration during the vacuum-assisted resin transfer molding (VARTM) process

A control-volume finite-element model is developed to analyze the infiltration of a fiber preform with resin under non-isothermal conditions within a high-permeability resin-distribution medium based vacuum-assisted resin transfer molding (VARTM) process. Due to the exposure to high temperatures during preform infiltration, the resin first undergoes thermal-thinning which decreases its viscosity. Subsequently however, the resin begins to gel and its viscosity increases as the degree of polymerization increases. Therefore, the analysis of preform infiltration with the resin entails the simultaneous solution of a continuity equation, an energy conservation equation and an evolution equation for the degree of polymerization. The model is applied to simulate the infiltration of a rectangular carbon fiber based preform with the NBV-800 epoxy resin and to optimize the VARTM process with respect to minimizing the preform infiltration time. The results obtained suggest that by proper selection of the ramp/hold thermal history of the tool plate, one can reduce the preform infiltration time relative to the room-temperature infiltration time. This infiltration time reduction is the result of the thermal-thinning induced decrease in viscosity of the ungelled resin.

Polymerization and complex formation of phthalocyanine substituted by trioxyethylene in solution

Phthalocyanine substituted by eight trioxyethylenemonomethylethers (EOPc) was prepared, and the solvent effect on the polymerization has been studied at 25.0 °C through absorption and emission spectroscopies. EOPc is soluble in a wide range of solvents from water to nonpolar solvents because of the amphiphilic property of the compound. EOPc predominantly is present as a polymer in polar solvents, such as water. The degree of dissociation to monomer in nonpolar solvent increases by the increase in the E T value (acceptor) of the solvent, and it completely dissociates to monomer in chloroform. The complex formation with alkali metal ions in chloroform was studied by means of H-1 NMR spectroscopy. The structure of the complex, in which the metal ion is pinched by two trioxyethylene groups locating close to the benzene group, was estimated. The degree of polymerization increases by the complex formation in relatively low E T solvents, such as carbon tetrachloride, although the complex is hardly polymerized in chloroform. The structure of the ion pair of the complex with picrate ion was estimated.

A Family 8 Glycoside Hydrolase from Bacillus halodurans C-125 (BH2105) Is a Reducing End Xylose-releasing Exo-oligoxylanase

The gene encoding family 8 glycoside hydrolases from Bacillus halodurans C-125 (BH2105), an alkalophilic bacterium with a known genomic sequence, was expressed in Escherichia coli. The protein was expressed with the intact N-terminal sequence, suggesting that it did not possess a signal peptide and that it was an intracellular enzyme. The recombinant enzyme showed no hydrolytic activity on xylan, whereas it had been annotated as xylanase Y. It hydrolyzed xylooligosaccharide whose degree of polymerization is greater than or equal to 3 in an exo-splitting manner with anomeric inversion, releasing the xylose unit at the reducing end. Judging from its substrate specificity and reaction mechanism, we named the enzyme reducing end xylose-releasing exo-oligoxylanase (Rex). Rex was found to utilize only the beta-anomer of the substrate to form beta-xylose and alpha-xylooligosaccharide. The optimum pH of the enzymatic reaction (6.2-7.3) was found in the neutral range, a range beneficial for intracellular enzymes. The genomic sequence suggests that B. halodurans secretes two endoxylanases and possesses two alpha-arabinofuranosidases, one alpha-glucuronidase, and three beta-xylosidases intracellularly in addition to Rex. The extracellular enzymes supposedly hydrolyze xylan into arabino/glucurono-xylooligosaccharides that are then transported into the cells. Rex may play a role as a key enzyme in intracellular xylan metabolism in B. halodurans by cleaving xylooligosaccharides that were produced by the action of other intracellular enzymes from the arabino/glucurono-xylooligosaccharides.

Glucosylation of α-butyl- and α-octyl- d-glucopyranosides by dextransucrase and alternansucrase from Leuconostoc mesenteroides

For the first time, glucosylation of α-butyl- and α-octylglucopyranoside was achieved using dextransucrase (DS) of various specificities, and alternansucrase (AS) from Leuconostoc mesenteroides. All the glucansucrases (GS) tested used α-butylglucopyranoside as acceptor; in particular, DS produced α- d-glucopyranosyl-(1→6)- O-butyl-α- d-glucopyranoside and α- d-glucopyranosyl-(1→6)-α- d-glucopyranosyl-(1→6)- O-butyl-α- d-glucopyranoside. In contrast, α-octylglucopyranoside was glucosylated only by AS which was shown to be the most efficient catalyst. The conversion rates, obtained with this enzyme at sucrose to acceptor molar ratio of 2:1 reached 81 and 61% for α-butylglucopyranoside and α-octylglucopyranoside, respectively. Analyses obtained from liquid chromatography coupled with mass spectrometry revealed that different series of α-alkylpolyglucopyranosides regioisomers of increasing polymerization degree can be formed depending on the specificity of the catalyst.

Nuclear exopolyphosphatase of Saccharomyces cerevisiae is not encoded by the PPX1 gene encoding the major yeast exopolyphosphatase

Intact nuclei from a parental strain CRY and a PPX1-mutant CRX of Saccharomyces cerevisiae were isolated and found to be essentially free of cytoplasmic, mitochondrial and vacuolar marker enzymes. The protein-to-DNA ratios of the nuclei were 22 and 30 for CRY and CRX nuclei, respectively. An exopolyphosphatase (exopolyPase) with molecular mass of ∼57 kDa and a pyrophosphatase (PPase) of ∼41 kDa were detected in the parental strain CRY. Inactivation of PPX1 encoding a major exopolyPase (PPX1) in S. cerevisiae did not result in considerable changes in the content and properties of nuclear exopolyPase as compared to the parental strain of S. cerevisiae. Consequently, the nuclear exopolyPase was not encoded by PPX1. In the CRX strain, the exopolyPase was stimulated by bivalent metal cations. Co2+, the best activator, stimulated it by ∼2.5-fold. The exopolyPase activity was nearly the same with polyphosphate (polyP) chain lengths ranging from 3 to 208 orthophosphate when measured with Mg2+. With Co 2+, the exopolyPase activity increased along with the increase in polymerization degree of the substrate.

Nuclear exopolyphosphatase of Saccharomyces cerevisiae is not encoded by the PPX1 gene encoding the major yeast exopolyphosphatase.

Intact nuclei from a parental strain CRY and a PPX1-mutant CRX of Saccharomyces cerevisiae were isolated and found to be essentially free of cytoplasmic, mitochondrial and vacuolar marker enzymes. The protein-to-DNA ratios of the nuclei were 22 and 30 for CRY and CRX nuclei, respectively. An exopolyphosphatase (exopolyPase) with molecular mass of approximately 57 kDa and a pyrophosphatase (PPase) of approximately 41 kDa were detected in the parental strain CRY. Inactivation of PPX1 encoding a major exopolyPase (PPX1) in S. cerevisiae did not result in considerable changes in the content and properties of nuclear exopolyPase as compared to the parental strain of S. cerevisiae. Consequently, the nuclear exopolyPase was not encoded by PPX1. In the CRX strain, the exopolyPase was stimulated by bivalent metal cations. Co2+, the best activator, stimulated it by approximately 2.5-fold. The exopolyPase activity was nearly the same with polyphosphate (polyP) chain lengths ranging from 3 to 208 orthophosphate when measured with Mg2+. With Co 2+, the exopolyPase activity increased along with the increase in polymerization degree of the substrate.

Polymer Effect on Molecular Recognition. Enhancement of Molecular-Shape Selectivity for Polycyclic Aromatic Hydrocarbons by Poly(acrylonitrile)

Poly(acrylonitrile) immobilized onto porous silica (Sil-ANn) was prepared to evaluate the effect of polymerization degree of poly(acrylonitrile) on selective interaction with polycyclic aromatic hydrocarbons. The HPLC using the packed column (Sil-ANn) and an aqueous solution as a mobile phase showed higher selectivity for structural isomers of polycyclic aromatic hydrocarbons compared with simply cyanopropylated silica (Sil-CN) and alkylated silica (Sil-C4). It was considered that silica-supported poly(acrylonitrile) recognized molecular aromaticity of π-electron con- taining compounds rather than molecular hydrophobicity. Furthermore, similar results were obtained in the selectivity towards geometrical isomers such as trans- and cis-stilbenes or triphenylene and o-terphenyl and structural isomers such as o-, m-, p-terphenyls. Also the separation factors increased with an increase in polymerization degree of AN n. This paper discusses that polymeric structures enhance the selectivity.

Xylanase–oligosaccharide interactions studied by a competitive enzyme assay

A competitive enzyme assay has been employed to estimate the relative binding of xylo- and cello-oligosaccharides to the active site of the Family 10 xylanase A from Pseudomonas fluorescens sp. cellulosa. The substrate used in the assay was pNPC, the hydrolysis of which can be detected colorimetrically. Consistently with the endo-xylanase nature of this enzyme, the K i(app) for xylo-oligosaccharides decreases with increase in degree of polymerization. Cello-oligosaccharides were poorer inhibitors of pNPC hydrolysis than xylo-oligosaccharides, and the K i(app) did not decrease as dramatically with degree of polymerization. The implications of these results are discussed in the context of other studies on xylanase A and other Family 10 xylanases.

Characterization of the flow properties of sodium carboxymethylcellulose via mechanical and optical techniques

Sodium carboxymethylcellulose (NaCMC) in solution represents a complex rheological system, since it forms aggregates and associations and hence higher-level structures and, depending on the synthesis, is only found in a molecularly dispersed form in exceptional cases. Rheo-mechanical investigations of the viscoelasticity showed that the Cox-Merz rule is not fulfilled. The aim was therefore to examine whether rheo-optics could be employed to provide more detailed conclusions about the parameters that influence the flow behavior of NaCMC than has hitherto been available with mechanical methods. The flow birefringence, Δn′, rises as the degree of polymerization increases, and exhibits the same dependence on molar mass as does the viscosity: Δn′∝Mw3.4. As the degree of polymerization increases while the shear rate remains constant, the polymer segments become more distinctly aligned in the direction of shear. Hence increasing the degree of polymerization also affects the solution structure, i.e. the interaction of the molecules with one another. The stress-optical rule only applies to a limited extent for this system. The stress-optical coefficient, C, is almost independent of the shear rate, but is strongly influenced by the concentration and attains a limiting value of 3 × 10−8 Pa−1. C was determined for a polymer in dilute solution and the curve obtained also enabled transitions in the solution structure to be recognized.

Crossover approach to scaling behavior in dilute polymer solutions: Theory and simulation

We develop a crossover theory for dilute polymer solutions, analogous to crossover theories for critical phenomena in simple fluids. In this theory, a critical degree of polymerization N* is found, which plays a similar role as the Ginzburg number in second-order phase transitions. To test the predictions of this theory, we perform Monte Carlo simulations of polymer chains composed of rigidly bonded hard spheres of various diameters and chain lengths. Various properties of these chains were analyzed, including the end-to-end distance distribution and mean-square radius of gyration. We find that the approach to the asymptotic scaling regime displays two types of crossover behavior, depending on the value of the model parameter ū, which is a measure of the strength of the monomer–monomer excluded volume interaction: (i) ū<1 and (ii) ū>1. In case (i), the system exhibits crossover from a Gaussian chain to the Kuhnian chain, as the degree of polymerization increases. In case (ii), the system exhibits crossover from the rigid rod to a Kuhnian chain. Our crossover theory is found to work well for polymers with ū>1 only near the asymptotic scaling regime. However, for ū<1, the theory works well in all regimes.

Solvent effects on microwave dielectric relaxation in poly(ethylene glycols)

This paper reports the results of a systematic study of microwave dielectric relaxation times of poly(ethylene glycols), average molecular weight 200–9000, in dilute solutions of benzene at 9·83GHz. These results are compared with the values of relaxation times obtained earlier in carbon tetrachloride solutions. This shows that the average relaxation times τ0 and the relaxation time corresponding to segmental reorientation τ1 are influenced by the solvent environment. The variation in chain flexibility in these polymers with the increase in degree of polymerization and formation of intra- and inter-molecular hydrogen bonding in benzene and carbon tetrachloride solutions is discussed with the help of relaxation data. The relaxation time τ2 corresponding to group rotations has been determined. It is found that the τ2 value is independent of solvent environment and degree of polymerization, and may be attributed to the rotation of chain −OH end-groups around the C−O bonds in dynamic equilibrium, with the formation of a five-membered ring due to intra-molecular hydrogen bonding at the end of the chain. © 1998 SCI.

Solvent effects on microwave dielectric relaxation in poly(ethylene glycols)

This paper reports the results of a systematic study of microwave dielectric relaxation times of poly(ethylene glycols), average molecular weight 200–9000, in dilute solutions of benzene at 9·83GHz. These results are compared with the values of relaxation times obtained earlier in carbon tetrachloride solutions. This shows that the average relaxation times τ0 and the relaxation time corresponding to segmental reorientation τ1 are influenced by the solvent environment. The variation in chain flexibility in these polymers with the increase in degree of polymerization and formation of intra- and inter-molecular hydrogen bonding in benzene and carbon tetrachloride solutions is discussed with the help of relaxation data. The relaxation time τ2 corresponding to group rotations has been determined. It is found that the τ2 value is independent of solvent environment and degree of polymerization, and may be attributed to the rotation of chain −OH end-groups around the C−O bonds in dynamic equilibrium, with the formation of a five-membered ring due to intra-molecular hydrogen bonding at the end of the chain. © 1998 SCI.

X-ray diffraction and optical studies of fractionalized regioregular poly(3-hexylthiophene)

We report results of structural and photoabsorption studies of regioregular polyhexylthiophene fractions of different backbone length. Polymer of longer chains have better planarity and higher degree of crystallinity. The vibrational structure in the optical spectrum is more clearly visible. Increase of conjugation length and decrease of the optical gap with increasing polymerization degree have been observed. Moreover, the evolution of the photoabsorption spectra as a function of external pressure is presented. The spectra red shift with increasing pressure. The largest shifts have been observed for sample of the longest chains. The results are interpreted in terms of the large interchain coupling induced by pressure.

Action of Poly(β-D-mannuronate)lyase fromTurbo cornutuson Oligomeric Substrates

A kinetic analysis of splitting oligomeric substrates by poly(β-D-mannuronate)lyases (alginate lyases I, SP1 and SP2) from a marine mollusk was done. Monomer and oligomers of mannuronate and guluronate were prepared by hydrolyzing poly β-1,4-D-mannuronate and poly α-1,4-L-guluronate from alginate with H2SO4, respectively, and thereafter by gel filtration on a Bio-Gel P-2 column. Alginate lyases I apparently did not act on the trimer of mannuronate but did on the tetramer or those longer than that, indicating the increased kcad/Km with increasing polymerization degree. The kinetic analyses suggest that the size of the subsite structure of the enzymes is most likely to be able to bind the linear pentamer of mannuronate units.

Capillary flow properties of PVC melts (abstract)

The effects of degree of polymerization and temperature on flow properties of PVC melts have been studied by using a Koka Flow Tester. Each flow curve is expressed by two straight lines of different slopes which meet at a breaking point. The critical shear rate γ̇wc’ at the breaking point increases as the degree of polymerization decreases or the temperature increases. The critical shear stress τc at γ̇wc’ increases as the degree of polymerization decreases, being almost independent of the temperature. The end correction coefficient ν shows a minimum or begins to increase around γ̇wc’. The coefficient ν increases as the degree of polymerization increases or the temperature decreases. The extrudate is smooth on the surface at low shear rates, shows a small wavy roughness (shark skin) at shear rates just below γ̇wc’, becomes fairly smooth again beyond γ̇wc’, and then shows intensive irregular roughness (melt fracture) at higher shear rates. The die swell becomes notable as degree of polymerization decreases or the temperature increases. The die swell takes a maximum at a shear rate just below γ̇wc’, where a shark skin appears on the extrudate. Differing from usual thermoplastic resin melts, PVC melts show a negative correlation between the die swell ratio and the end correction coefficient. This seems to be due to the following reason: PVC melts have high viscosities and have long relaxation times for strain recovery, and thus the extrudates solidify without being fully relaxed. This tendency of solidification without relaxation is more noticeable as the degree of polymerization increases or the temperature decreases.

Dielectric relaxation in poly(ethylene glycols) at 9.83 GHz

AbstractDielectric relaxation studies of poly(ethylene glycols), average molecular weight 200–9000, have been carried out in carbon tetrachloride solutions at microwave frequency, i.e. 9.83 GHz. Average relaxation times τ0 and relaxation times corresponding to segmental motion τ1, and group rotations τ2 have been calculated. The variations of relaxation times with increase in degree of polymerization and temperature have been determined. With the increase in the degree of polymerization the flexibility increases and hence the coiling of the chain increases. At a certain temperature there is a decrease in the relaxation time corresponding to segmental motion, suggestive of some switch‐over mechanism in higher polymers. The relaxation time corresponding to group rotations is independent of temperature and degree of polymerization.

Purification and properties of the endo-1,4-β-glucanase III from Ruminococcus albus

Endoglucanase III (EGIII) was purified from Ruminococcus albus culture supernatant. An enzyme having a molecular weight of 53,000 was stabilized by mercaptoethanol and inhibited by sulfhydryl group-blocking reagents, and exhibited its highest CMC-degrading activity of pH 5.7 and 55°C. The enzyme hydrolyzed cellobiose (G2) and cellotriose (G3) only negligibly, but significantly hydrolyzed cellotetraose (G4), cellopentaose (G5) and cellohexaose (G6). The major hydrolysis reactions conducted by the enzyme were G4→2G2, G5→G2+G3, G6→G2+G4 and G6→2G3. The Vmax values of these reactions increased remarkably while the Km values decreased significantly with an increase in degree of polymerization of the substrate.

Anionic Polymerization of Vinylsilanes III. Polymerization Behavior of Trimethylvinylsilane

Polymerization behavior of trimethylvinylsilane by sec-butyllithium was investigated in the presence or absence of N,N,N′,N′-tetramethylethylenediamine (TMEDA). In the absence of TMEDA, the elimination reaction of lithium hydride which was observed apparently at 40°C was suppressed at −10°C. In the presence of TMEDA, the chain transfer reaction to the monomer occurred even at −10°C. Initial monomer concentration was found to affect the propagation rate considerably. In the absence of TMEDA at −10°C, the apparent propagation rate constant was high at high initial monomer concentration. In the presence of TMEDA, the reverse relation was observed. The former was interpreted by the association state of the active centers and the latter by the combination of two types of propagation reaction. For the isomerization reaction, low monomer concentration and high temperature were advantageous. The content of isomerized units in the polymer increased with an increase in degree of polymerization.