Sorption and transport of water in nylon-6 films

Sorption and transport properties of water through films of Nylon-6 were obtained at 5, 23, and 40°C. Commercially available films were used and a Cahn electrobalance was employed for measuring the water uptake by the polymer samples. Values of the water sorption isotherms are accurately described by the Langmuir/Flory-Huggins dual-mode sorption model. At water activity values below 0.15, the volume fraction of water described by the Langmuir portion of the model was greater than the Flory-Huggins population. Solubility and diffusion coefficients of water, as well as the diffusion activation energy and enthalpy of dissolution of water for Nylon-6, were determined from the sorption experiments. Values obtained support the hypothesis of a bimodal water sorption mode, and the formation of water clusters. © 1994 John Wiley & Sons, Inc.     

Chelating ion-exchangers containing n-substituted hydroxylamine functional groups: Part 6. Sorption and separation of gold and silver by a polyhydroxamic acid

The sorption and desorption characteristics of gold and silver on a polyhydroxamic acid chelating resin are described. Gold is quantitatively sorbed from 0.5 M nitric acid or neutral solutions, and readily eluted with 0.5% ($\text{w}\text{v}$) potassium cyanide solution. Silver is removed from 0.05 M nitric acid or neutral solutions, and can be eluted with the cyanide solution or with 0.5 M nitric acid. Gold can be quantitatively separated from copper, iron and silver; gold and silver are sorbed from dilute cyanide solutions. Tests with river water and other eluting systems are reported.     

Sorption of boric acid by polymers containing dihydroxypropylamine fragments

Products of polymer-analogous transformations of chitosan, aminopolystyrene, and polyallylamine containing dihydroxypropylamine fragments were used as sorbents of boric acid. A dependence of their sorption properties on the structure of the main polymeric chain and its functionalization degree was found.     

Molecular recognition of sialic acid end groups by phenylboronates

A multinuclear NMR study of the interaction between phenylboronic acid (PBA) and sialic acid (Neu5 Ac) has been performed. The latter compound is known to be overexpressed on the cell surface of tumor cells. The results of this investigation suggest that the binding of PBA to sialic acid is pH dependent. 17O NMR experiments with glycolic acid as the model compound prove that an interaction at the alpha-hydroxycarboxylate occurs at pH < 9, while a study with threonic and erythronic acids shows that the PBA group interacts selectively with the vicinal diol functions at higher pH. Similarly, Neu5 Ac binds PBA through its alpha-hydroxycarboxylate at low pH (< 9) and through its glycerol side chain at higher pH values. The conditional stability constant of the phenylboronate ester at pH 7.4 is 11.4. On cell surfaces, sialic acid is connected to the neighboring sugar unit through the 2-hydroxy group. To mimic this the 2-alpha-O-methyl derivative of Neu5 Ac was included in this study. The erythro configuration of the hydroxy substituents prevents stable-complex formation at positions C7 and C8 and, consequently, the strongest interaction is observed at positions C8 and C9, leading to a five-membered 2-boron-1,3-dioxalate. In addition, a relatively small amount of the C7-C9 six-membered complex was observed. Molecular modeling studies confirm that the C8-C9 boronate complex has the lowest energy.     

Radiation-induced grafting of acrylic acid to nylon-6 in solution

The mutal irradiation technique has been employed to graft acrylic acid to nylon-6 in solution. Homogeneity of reactants and products was achieved by the use of the mixed solvent, o-chlorophenol-methanol (55·6/44·4 vol). The process resembled the heterogeneous grafting to nylon film rather than the homopolymerization of acrylic acid in solution. Some evidence is presented for a micellar growth of the graft copolymer.     

Characterization of end groups in nylon 6 by MALDI-TOF mass spectrometry

Four samples of Ny6, each terminated by different end groups, i.e., diamino terminated, monoamino terminated (monocapped), dicarboxyl terminated, and amino-carboxyl terminated, were synthesized and analyzed by MALDI-TOF Mass Spectrometry, in order to accurately characterize their structure by direct identification of mass resolved chains. A self-calibrating method for the MALDI-TOF mass spectra of polymeric samples was used in order to distinguish the end groups existing in the four samples of Ny6. The MALDI-TOF spectra showed the presence of protonated, sodiated, and potassiated ions that were assigned to Ny6 chains containing the expecteted end groups. Furthermore, the MALDI-TOF spectra made possible the simultaneous detection of the cyclic oligomers of Ny6 present in these samples, thus achieving the full structural characterization of the molecular species present in these polyamides. © 1996 John Wiley & Sons, Inc.     

Organo-sulfonic acid catalyzed degradation kinetics and thermodynamic studies of nylon-6 by hydrothermal method

Nylon-6 as an engineering polymer and its starting monomer are both costly. Chemical reutilization offers some economic and environmental benefits. Depolymerization of nylon-6 was carried out by the conventional technique of hydrothermal method using various organo-sulfonic acids such as Methane sulfonic acid (MSA), para-toluene sulfonic acid (p-TSA), benzene sulfonic acid (BSA), and tetra-butyl ammonium bromide (TBAB) as a phase transfer catalyst. Various parameters such as temperature, time, normality of acids, and phase transfer catalyst concentration were varied to optimize its parameters, and characterization techniques such as amine value titrations and Fourier transform infrared spectroscopy were used for quantitative measurements. Solid-state ¹³C NMR was done for structure confirmation. A chemical kinetics interpretation shows degradation mechanism follows first-order kinetics under various catalysts. MSA has the highest reaction rate of 8.49 × 10^?2 h^?1 at 90°C; it decreases to 7.72 × 10^?2 h^?1 at 100°C. At the same time, aromatic Sulfonic acids such as p-TSA and BSA have a higher reaction rate of 8.995 × 10^?2 h^?1 and 5.582 × 10^?2 h^?1, respectively. The activation energy was lowered as the acidity of organo-sulfonic acids increased as benzene sulfonic acid has the lowest E_a. Followed by p-TSA, and MSA has the highest E_a. Free energy shows a similar kind of value. A simple theoretical model was used to calculate the activation energy. Thermodynamic parameters such as heat of enthalpy and entropy of reaction were evaluated using the Eryig–Polanyi equation. The combined catalytic effect of organo-sulfonic acids and phase-transfer catalyst provides a better environment-friendly method for depolymerizing nylon-6.     

Rheology of carbosilane dendrimers with various types of end groups

The rheological properties of high-generation carbosilane dendrimers carrying different kinds of terminal groups are studied. It is shown that the nonlinear viscoelastic behavior of dendrimers and the high-temperature relaxation transition in dendrimers are interrelated and result from the reversible breakdown of the supramolecular structure formed by the system of contacts of exterior shells of dendrimers. The strength of the supramolecular structure is dependent on the specific interaction of terminal groups of dendrimers and their mobility. The dendrimers under study demonstrate the dualism of macromolecule-particle properties: They behave as both polymer melts and colloidal systems.     

Water-absorption capacity of cross-linked copolymers of acrylic acid and acrylamide,containing various ionic groups

Radical copolymerization of acrylic acid with acrylamide in the presence of sodium 1,3-diallyl isocyanurate cross-linking agent was studied.     

Two dimensional self-assembly of bis-acylureas having various functional end groups

We present the synthesis and morphology study of thirteen bis-acylurea molecules with various functional end groups. The bis-acylureas have two acylurea groups, -NH-CO-NH-CO-, divided by a pentamethylene spacer, -(CH(2))(5)-, and two symmetric functional end groups, such as, aliphatic, benzyl, mono- and bi-thiophenyl, sulfur-containing, and propargyl (HC[triple bond]CCH(2)-) moieties. The bis-acylureas were synthesized by the coupling reactions of ureas with pimeloyl chloride or pimelic acid. Upon cooling from hot isotropic solutions, the bis-acylureas spontaneously form supermolecules. In the cases of aliphatic, benzyl, mono- and bi-thiophenyl functional groups, two dimensional supramolecular structures with molecularly flat surfaces were formed. Single crystal X-ray diffraction results demonstrate that each bis-acylurea molecule forms biaxial hydrogen bonds with four adjacent molecules forming a grid-like crystalline structure. Among the bis-acylureas with sulfur-containing end groups, those with sulfide (-S-) and disulfide (-SS-) moieties self-organize into two dimensional superstructures, while those with thiol (-SH) and bulky protecting group (-S-trityl) precipitate with irregular shapes. The bis-acylurea with propargyl end groups form superstructures of low order possibly due to the steric effect between the rigid moieties. However, the derivatives prepared by click reactions have lamellar molecular packing similar to those of bis-acylureas forming multilayered nanosheet structures.     

Polymorphism of nylon-6 in nylon-6/nanoclay/functionalized polyolefin blends

The crystallization behavior of Nylon-6 and the interaction in Nylon-6/nanoclay/functionalized polyolefin blends were investigated by X-ray diffraction and Fourier transform infrared spectroscopy. For samples without any thermal history, the interaction between Nylon-6 and nanoclay or the interaction between Nylon-6 and functionalized polyolefin favors the formation of γ form crystal. In contrast, the presence of both nanoclay and functionalized polyolefin together in Nylon-6 was found to have an antagonistic effect on each other's ability to promote the formation of γ form crystal. This was attributed to the complex interactions between the constituents. The crystallization behavior of Nylon-6 in Nylon-6/nanoclay/functionalized polyolefin blends is clearly affected by the cointeraction of these effects. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1494–1502, 2007     

Thermal stability of 6FDA-(co-)polyimides containing carboxylic acid groups

Different (co-)polyimides with and without carboxylic acid groups have been synthesized, characterized and thin films have been prepared. Aging as well as degradation effects at temperatures up to 380 °C have been investigated in order to determine whether high temperature applications are possible. Thus this work was focused on aromatic fluorinated polyimides and copolyimides derived from 6FDA (4,4′-hexafluoroisopropylidene diphthalic anhydride), 4MPD (2,3,5,6-tetramethyl-1,4-phenylene diamine) and DABA (3,5-diamino benzoic acid), since 6FDA-(co-)polyimides are well known for high stability and superior processability. Aging processes have been analyzed using infrared spectroscopy, density measurements and thermogravimetric analysis. It has been found that up to 380 °C the synthesized materials show minor weight losses and aging effects but remain mechanically stable. On the one hand some properties like colour and solubility changed but on the other hand gas separation characteristics could be improved. In all cases structure and mechanical stability persisted after heat treatment. The analytical results lead to the conclusion that the synthesized materials can be used as high performance polymers in various applications, i.e. hydrogen fuel cell and aerospace applications.     

Synthesis of tridepsipeptides containing imino acid groups

Summary The synthesis of sarcosylglycolylglycine and L-prolylglycolylglycine was carried out.     

Copolymerization of acrylic acid to nylon-6 by trapped radicals—I. Vapour phase grafting

Film of nylon-6 has been γ-irradiated in vacuo to various doses D. Grafting has been effected by subsequent exposure in vacuo to vapour at 50° of composition 9.1 wt% acrylic acid and 90.9 wt% water. Determinations have been made of total vapour uptake as well as the individual swellings due to monomer and water. For D ? ca. 2 Mrad, the initial rate of grafting R_g increased with D in accord with R_g ∝ D^β with β = 0.45 ± 0.05, thus suggesting bimolecular chain termination. However, for D ? ca. 2 Mrad, there is no further increase in R_g. This is attributed in part to the fact that the radical yield is proportional to dose only for D ? ca. 2.5 Mrad. Diffusion controlled grafting has been predicted elsewhere to be characterized by β = 0.67. Grafting proceeds from the surface and the initial stages are concluded to be essentially free from diffusion control, since (a) β ≠ 0.67, (b) the rate of uptake of monomer vapour >R_g and (c) a large change in film thickness yields only a very small change in R_g.     

Solvent-induced crystallization of nylon-6I

The ability of various hydrogen bond-forming solvents to induce crystallinity in nylon-6I was studied using DSC, FTIR spectroscopy, and x-ray diffraction. Comparison was made with predictions using the solubility parameter, which is related to possibilities of interaction formation. General predicted tendencies agreed with experimental results, in agreement with proposed influence of solvent-polymer interactions in the solvent-induced crystallization process. FTIR investigation of polymers treated with methanol and methanol-d shows that polymer segments forming hydrogen bonds with solvent molecules crystallize preferentially. It is therefore concluded that hydrogen bond exchanges with the solvent favor chain rearrangements leading to crystallization. © 1995 John Wiley & Sons, Inc.     

Graft copolymerization of acrylic acid to nylon-6 by mutual irradiation—V: Influence of temperature

Film of nylon-6, immersed in an aqueous solution of acrylic acid containing cupric chloride, has been subjected to γ-irradiation in vacuo at different temperatures. From the initial rates, negative overall activation energies E_o(G) and E_o(H) were derived for grafting and for the attendant homopolymerization. The value of E_o(H) is consistent with a process, which is known to involve termination exclusively by cupric ions. However, no satisfactory explanation can be proposed for the value of E_o(G).