Ratio Of End Groups Research Articles

Carbonyl-rich porous organic polymers for cobalt adsorption from water

By controlling the ratio of end groups in a series of porous organic polymers, we maximized their cobalt adsorption capacity.

Integrated Approach to Eco-Friendly Thermoplastic Composites Based on Chemically Recycled PET Co-Polymers Reinforced with Treated Banana Fibres.

A major societal issue of disposal and environmental pollution is raised by the enormous and fast-growing production of single-use polyethylene terephthalate (PET) bottles, especially in developing countries. To contribute to the problem solution, an original route to recycle PET in the form of value-added environmentally friendly thermoplastic composites with banana fibres (Musa acuminata) has been developed at the laboratory scale. Banana fibres are a so far undervalued by-product of banana crops with great potential as polymer reinforcement. The melt-processing constraints of commercial PET, including used bottles, being incompatible with the thermal stability limits use of natural fibres; PET has been modified with bio-sourced reactants to produce co-polymers with moderate processing temperatures below 200 °C. First, commercial PET were partially glycolyzed with 1.3-propanediol to produce co-oligomers of about 20 repeating units, which were next chain extended with succinic anhydride and post-treated in a very unusual "soft solid state" process at temperatures in the vicinity of the melting point to generate co-polymers with excellent ductility. The molar mass build-up reaction is dominated by esterification of the chain ends and benefits from the addition of succinic anhydride to rebalance the acid-to-hydroxyl end-group ratio. Infra-red spectroscopy and intrinsic viscosity were extensively used to quantify the concentration of chain ends and the average molar mass of the co-polymers at all stages of the process. The best co-polymers are crystallisable, though at slow kinetics, with a Tg of 48 °C and a melting point strongly dependent upon thermal history. The composites show high stiffness (4.8 GPa at 20% fibres), consistent with the excellent dispersion of the fibres and a very high interfacial cohesion. The strong adhesion can be tentatively explained by covalent bonding involving unreacted succinic anhydride in excess during solid stating. A first approach to quantify the sustainable benefits of this PET recycling route, based on a rational eco-selection method, gives promising results since the composites come close to low-end wood materials in terms of the stiffness/embodied energy balance. Moreover, this approach can easily be extended to many other natural fibres. The present study is limited to a proof of concept at the laboratory scale but is encouraging enough to warrant a follow-up study toward scale-up and application development.

Synthesis of Polycarbonate Diols(PCDLs) via Two-step Process Using CH3COONa as an Effective Catalyst

Polycarbonate diols(PCDLs) with a number average molecular weight(Mn) of 2800 and a narrow polydispersity index(PDI=1.33) were synthesized from dimethyl carbonate(DMC) and 1,4-butanediol(BD) via a two-step process. The influences of the molar ratios of DMC to BD in the feedstock, polycondensation temperature and polycondensation time on the PCDLs preparation were studied. CH3COONa showed the best catalytic performance among the catalysts studied. The highest BD conversion of 73.8% and PCDLs yield of 64.7% were achieved under its optimum reaction conditions. Furthermore, based on the results of 1H NMR, the relationships between the ratio of end groups (—OCH3/—OH) of oligomers, the Mn and chainend constitute of resultant polycarbonates were also investigated. The results indicate that PCDLs can be synthesized when the oligomers mostly bear hydroxyl end groups. In contrast, it was impossible to prepare PCDLs when the oligomers were enriched with methyl carbonate end groups.

Raman spectroscopy studies of phosphorus dendrimers with phenoxy and deuterophenoxy terminal groups

The FT-IR and FT–Raman measurements of 6 generations of phosphorus dendrimers G′ci built from cyclotriphosphazene core with phenoxy and deuterophenoxy terminal groups have been performed. Spectra of dendrimers depends on the ratio of end groups and repeated units. This ratio tends to be r–1 (r – functionality of repeated unit), and becomes constant, when the generation number is above 3. Experimental Raman spectra of generations of dendrimers are very closely similar in accordance with the theory. Structural optimization and normal mode analysis were obtained for G′c1 by the density functional theory (DFT). Calculations have shown that each OC6H4CHNN(CH3) moiety is flat and six repeating units are located above and below the nearly flat cyclotriphosphazene ring. Optimized geometric bond length and angles obtained by DFT show good agreement with the experiment. The phenoxy terminal groups are characterized by the well-defined line at 1008cm−1 in the experimental Raman spectrum of G′c1-H and by line at 968cm−1 in the Raman spectrum of G′c1-D. The medium-intensity line in the Raman spectra of G′c1-H and G′c1-D at 1576cm−1 refer to the repeating units vibrations.

Study for Soluble and Low-Refractive Index Hyperbranched Polymer Consisting of Fluoroadamantane

Soluble hyperbranched polymers consisting of numerous functional groups and end groups were prepared by one pot synthesis of divinyl monomers in a large amount of chain transfer agent (CT). The polymerization conditions for control of molecular weight with suppression of a gelation were investigated at various concentrations of reactants and molar ratio of CT to monomer. Hyperbranched polymers consisting of numerous functional groups and end groups were synthesized and molar ratio of end groups Hyperbranched polymers were evaluated by analysis of TOF MS and NMR. Transparent and low refractive index thin film was easily obtained by polymerization of divinyl fluoroadamantane monomers.

Melt mixed nano composites of PA12 with MWNTs: Influence of MWNT and matrix properties on macrodispersion and electrical properties

Nanocomposites containing four different polyamide 12 (PA12) types and three grades of multiwalled carbon nanotubes (MWNTs) were prepared via small-scale melt processing to study the effect of different MWNTs and the influence of polymer properties on the dispersion of the fillers and the electrical properties of the composites. Under the selected mixing conditions the lowest electrical percolation threshold of 0.7 wt.% was found for Nanocyl™ NC7000 in low viscous PA12. Moreover, big influences of the end group functionality (acid or amine excess) and the melt viscosity of the matrix were found. Composites of PA12 with acid excess showed lower percolation thresholds than those based on amine terminated materials. At constant end group ratio low viscous matrices resulted in lower percolation thresholds than high viscous materials. The best MWNT dispersion was obtained in both high viscous PA12 composites. In these systems the mixing speed was varied indicating an optimum concerning electrical conductivity at 150 rpm as compared to 50 and 250 rpm.

Modeling the continuous melt transesterification of bisphenol-A and diphenyl carbonate in a continuous stirred tank reactor

A model of continuous melt transesterification of bisphenol-A and diphenyl carbonate in a continuous stirred tank reactor is developed using phase equilibria assumption and the method of molecular weight moments. The model equations can be simplified into a polynomial system that has 17 equations and 17 unknowns. Solution of the polynomial system gives out almost every aspects of the continuous transesterification process. Molecular weight and polydispersity index, end group ratio of hydroxyl to phenyl carbonate, contents of molecular species, and lost diphenyl carbonate fractions are studied in different operation parameters.

Mechanical properties of poly(ethylene terephthalate) modified with functionalized polymers

This study examined the effect of blending poly(ethylene terephthalate) (PET) with 5% of a functionalized polymer. The blends were characterized by particle size and size distribution, unnotched tensile behavior, toughness, and notch sensitivity. The improved properties of blends that incorporated a functionalized elastomer were consistent with in situ formation of a graft copolymer by reaction with PET end groups. Triblock copolymers were examined that had styrene end blocks and an ethylene/butylene midblock (SEBS) with grafted maleic anhydride. The present study extended previous investigations that focused on level of grafting to examine the effects of component molecular weight and PET hydroxyl-to-carboxyl end-group ratio. Increasing the molecular weight of the SEBS and decreasing the hydroxyl-to-carboxyl ratio of the PET increased the effectiveness of the SEBS. In addition, a mix of an unfunctionalized SEBS with a functionalized SEBS was more effective than a single SEBS with the same total anhydride content. The same elastomers were the most effective for modifying a lower molecular weight PET (intrinsic viscosity 0.73) and a higher molecular weight PET (intrinsic viscosity 0.95). Some functionalized polypropylenes included in the study did not enhance the properties of PET. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 203–219, 1999

Effect of reactive end groups on the rheology of disk lubricant systems

We systematically investigate the properties of perfluoropolyethers with different weights and chain-end functionalities, which are used as lubricants in hard disk drive systems. The temperature dependence of the viscosity yields an Arrhenius form; the activation energy and hydrodynamic volume are determined for different molecular weights. The activation energy depends on both end group functionality and molecular weight. Also, modified Cole-Cole plots for storage modulus vs. loss modulus reveal the presence of microstructures due to the interaction of polymer chain-end groups in the bulk. The viscosity-molecular weight relationship exhibits a remarkable crossover behaviour at a critical molecular weight (M/sub c/) for ZdolTX (Zdol with C/O end group ratio of 1.7). Fly stiction (tribology) data also exhibit an M/sub c/ and an excellent correlation with viscosity (rheology) is obtained.

Reaction Kinetics and Simulations for Solid-State Polymerization of Poly(ethylene terephthalate)

A comprehensive model for solid-state polymerization of poly(ethylene terephthalate) was developed from analyzing the similarities and the differences between solid-state and melt polymerization. Considering the end groups diffusion limitation and the modification of concentrations of end groups and byproducts in the amorphous phase, a system of mass transfer and balance equations suitable for the solid-state polymerization of PET were obtained, based on simplifying the reaction kinetics of melt polymerization of PET. The degradation and other side reactions neglected in the earlier models for the solid-state polymerization of PET were included in the model. This simulation gave a quantitative prediction in the effect of temperature, particle size, starting molecular weight, and ratio of end groups on the degree of polymerization of products during the solid-state polymerization of poly(ethylene terephthalate). These simulation results were in agreement with experiments.

Determination of molecular weight of nonlinear polymers by NMR spectroscopy: application on a polymer of 2,2-bis(4-cyanatophenyl)propane

The method is based on the backbone to end group ratio measured by 13 C NMR spectroscopy. The number-average molecular weight (M n ) of the poly(cyanate ester) resin prepared from polycyclotrimerization of 2,2-bis(4-cyanatophenyl)propane including the unreacted monomer is represented by the formula M n =834((R'+R+2)/(3R'−R+2)) where R is the backbone to end group ratio and R' is the monomer to end group ratio. Mathematical derivation of this equation is discussed

Carbon‐13 NMR characterization of DGEBPA epoxy resins

AbstractCarbon‐13 nuclear magnetic resonance (NMR) has been used to investigate the structure and character of diglycidyl ether of bisphenol A (DGEBPA) epoxy resins more thoroughly than previously reported in the literature. It is shown that spectra, when run under quantitative conditions, can detect the loss of epoxides at the end groups by reactions such as hydrolysis. The products of acid hydrolysis of a DGEBPA resin are observed and assigned. It is further shown that the possibility of epoxide hydrolysis and impurities or structural irregularities can lead to inaccuracies in epoxy equivalent weight (EEW) calculations using a previously reported methodolgy. A new method is employed which can take into account loss of end group epoxides. Part of this new method consists of a measure of the epoxide to end group ratio (EER) which sheds light on the final possible quality of the cured resin. The EER value is shown to be in many ways more informative than the EEW measure which has the built‐in assumption that there is an epoxide group for each end group.

An analysis of the solid phase behavior of the normal paraffins

A set of best values for the temperatures and enthalpies of fusion and transition for the n-paraffins is presented. From an analysis of these data a general qualitative theory of the phase behavior of the n-paraffins is developed. Four distinct crystal structures—hexagonal, triclinic, monoclinic, and orthorhombic—describe the solid phases of all n-paraffins with more than nine carbon atoms in the chain. The latter two structures become equivalent at longer chain lengths. Odd-even differences are resolved in terms of reasonable differences in end group packing, and the smooth increase in melting and transition temperature with increasing chain length is attributed to a decrease in the ratio of end groups to chain groups. Double transitions are predicted for several pure n-paraffins above n-C34H70. Impurity effects are isolated from the pure n-paraffin properties and discussed. The equation, TM(°K) = 414.3 (n— 1.5)/(n+5.0) is presented as a correct description of the melting temperatures (TM) of all n-paraffins above n-C44H90. Sufficient data to permit an accurate extrapolation of the enthalpies and entropies of fusion to the infinite-chain limit are not available.