Coil Chain Research Articles

Glass transition of expanded polystyrene coils

Monodisperse polystyrene (PS), with molecular weight of 1.8 × 10 6, was dissolved and refluxed in cyclohexane, keeping the polymer concentration below the critical value for chain shrinkage. After rapidly freezing the solution by injecting it directly into liquid nitrogen, the solvent was sublimed so that expanded chain coils with few entanglements could be obtained. The glass transition temperature, T g, for this material was found to be 45°C lower than that of the ordinary PS, even after annealing up to 180°C. Comparison of the infra-red spectra showed some conformational differences between the rapidly frozen and the ordinary PS. Dilute polymer solution was rotated in a flask while it was immersed in a cold ethanol bath, so that the solution was frozen relatively slowly. After the solvent was sublimed, the resulting PS showed a lower T g in its first d.s.c. scan, but exhibited the same T g as ordinary PS after annealing.

Conformational features of carrabiose polymers: I. Configurational statistics of κ-carrageenan

Potential energy functions evaluating both repulsive-attractive van der Waals non-bonding interactions and electrostatic interactions have been used to evaluate the conformational energies of the repeating units of the kappa-carrageenan polymers. Structural parameters have been obtained by minimization MNDO procedures (MOPAC). Energy maps have been calculated for the (1-3) alpha-D-galactose-4-sulphate (GS) and the (1-4)-3,6-anhydro-alpha-D-galactose (A) residues, taking into account the conformational freedom of the sulphate group. The configurational statistics of the random coiled kappa-carrageenan chain have been explored, disclosing a highly flexible character, which can mainly be ascribed to the random occurrence of two different conformers of the GS-A dimeric unit.

Secondary relaxation, brittle–ductile transition temperature, and chain structure

AbstractWe show that the subglass secondary relaxation temperature at which a polymer changes from brittle (crazing) to ductile (yielding) behavior is a function of the characteristic ratio C∞ (which is a measure of the intrinsic flexibility and rigidity of a coiled chain). At 1 Hz frequency, the correlation is given by {Tβ}/{Tα} = Tb/Tg = 0.135 + 0.082C∞, where {Tβ} is the secondary relaxation temperature, which corresponds to Tb the brittle—ductile transition temperature, and {Tα} is the primary relaxation temperature, which corresponds to the glass transition temperature Tg at the given frequency. The ratio {Tβ}/{Tα} or Tb/Tg can be predicted from chemical structure alone.

Characterization of hydroxypropylcellulose–indomethacin grafts as a function of molecular weight

AbstractThe physical characterization of hydroxypropylcellulose–indomethacin grafts (HPC–IND) is described. Using size‐exclusion chromatography (SEC) and serial differential refractive index (dRI) and ultraviolet spectrophotometric (UV) detection methods, it was possible to characterize the chemical substitution of the HPC–IND graft. Using the acid chloride of IND as the reactive intermediate, the HPC–IND graft was synthesized. The amount of IND grafted onto the polymer as a function of the HPC molecular weight (MW) was then quantitatively estimated. It was found that the substitution of IND onto the HPC was not uniform, representing chemical heterogeneity of the first kind. Increasingly higher substitution (of IND to HPC) was observed as the MW decreased (<250,000 Daltons) for the HPC backbone. Lower, more uniform substitution was observed for the higher molecular weight regions of the HPC (>250,000 Daltons). Possible contributing factors affecting the observed nonuniform substitution include (1) the chain coiling of the HPC in solution, thus limiting the availability of the pendant hydroxyl groups, (2) nonuniform substitution of the hydroxypropyl moiety onto the cellulose backbone, and (3) steric effects resulting from the incorporation of the bulky aromatic drug molecule onto the backbone HPC.

Structural study of a wholly aromatic polyamide with a rigid pendent group by scanning tunneling microscopy

The scanning tunneling microscope was used to study nonconducting wholly aromatic polyamide chains deposited onto highly oriented pyrolytic graphite (HOPG) substrates. Images, taken in air, were analyzed to address questions concerning the attachment sites of rigid pendent groups to the polymeric molecular backbone as well as to answer general, larger morphological questions relating to such issues as possible helical coiling of chains, monomeric or dimeric, and multichain aggregation. Films were prepared from solutions of the polyamide dissolved in dimethylacetamide and differing in salt content to change the degree of association between chains and, therefore, the tendency of chains to form large bundles. Evidence was found for coiling of multimolecular chains and a tendency to form large ordered multimacromolecular assemblies.

Structures of two crystal forms of poly(ethylene oxide)-sodium thiocyanate complex with molar ratios of 3:1 and 1:1

The poly(ethylene oxide) (PEO)-sodium thiocyanate system was found to exhibit polymorphism: there exist at least three crystal modifications. Among them, the crystal structures of two kinds of PEO-NaSCN complex with molar ratios (EO:NaSCN) of 3:1 (form I) and 1:1 (form II), respectively, were determined by X-ray diffraction. Crystal data are as follows: form I, monoclinic P2 1 a , a = 16.83, b = 10.64, c( chain axis)=7.19 A ̊ ° 1 A ̊ =10 −1 nm , γ=125.5° ( c-unique), N=12 EO units (2 chains) and 4 NaSCN ions; form II, monoclinic P2 1 c , a=7.55, b=12.10, c( chain axis)=5.83 A ̊ , β=97.5° ( b-unique), N=4 EO units (2 chains) and 4 NaSCN ions. Form I has a crystal structure resembling that of the PEO-NaI complex. The polymer chains have a twofold helical structure of (-t 2gt 2gt - g ̄ -) 2 conformation, the chain repeat comprising six EO units. The helical polymer chain coils around an array of Na ions and each Na ion is coordinated by four polymer O atoms and two N of the SCN ions (the coordination number is six). In form II, which exists only under high tension, the polymer chains have a glide structure of (-tg 2t g ̄ 2-) conformation, the chain repeat comprising two EO units. Since the PEO chain in form II takes a rather stretched conformation, the Na ions are not wrapped by the polymer chain. The coordination number is again six, but each Na ion is coordinated by two polymer O atoms, two N and two S of the SCN ions. Form II is transformed into form I when the tension is released.

Symposium on Matrix Proteins as Templates for Mineralization. Satellite symposium of the 66th general session of the International Association for Dental Research and the 12th annual meeting of the Canadian Association for Dental Research. Proceedings.

The production of type I collagen by fibroblasts, odontoblasts, and osteoblasts is reviewed on the basis of results obtained by electron microscopy, 3H-proline radioautography, and immunostaining for type I procollagen. In the three cell types, the precursors of type I collagen are processed along the rough endoplasmic reticulum (rER)-Golgi-secretory granule pathway in the same manner as secretory proteins, but the available evidence suggests a few special features: 1) From the rER site of synthesis, the initial collagen precursors, known as pro-alpha chains, are transported to the Golgi apparatus within tubular structures, referred to as intermediate tubules, rather than within vesicles. 2) The pro-alpha chains coil into a triple helix within spherical distensions present along the saccules on the cis side of Golgi stacks. 3) The resulting procollagens are fairly rigid and form bundles that cause spherical distensions to lengthen into cylindrical ones, whereas by an unknown mechanism these distensions become part of the saccules on the trans-side of Golgi stacks. 4) The procollagen-containing cylindrical distensions are released from trans-saccules to become secretory granules, and some procollagen material finds its way into lysosomes. 5) The secretory granules release their procollagen content by exocytosis at the cell surface. 6) The released procollagen is transformed into collagen before or, more probably, after associating with the surface of a collagen fibril.

Influence of secondary structure of polyglycine on some conformational properties.

Values of four conformational properties, namely unperturbed dimension [r2]0, dipole moment [mu 2], mean squared optical anisotropy [gamma 2], and molar Kerr constant [mK], have been calculated for polyglycine chains allowing several combinations of the secondary structure with the aim of studying the dependence of these magnitudes on the secondary structure of the chain. Two different approaches to the secondary structure have been used. In the first, chains with all their units in a given conformation (random coil, alpha-helix or beta-sheet) are interrupted at several positions by one unit in a different conformation. In the second, chains with varying composition of two conformations alpha-helix/beta-sheet and beta-sheet/random coil were allowed and the results obtained compared with previous work for alpha-helix/random coil chains.

The conformations of macromolecules in interacting plane layers of grafted chains

Taking into account the main contributions to the free energy of the system, the interaction of 2 layers grafted to the plane of polymer chains has been studied by the scaling method. The chain length N, the area of grafting of a chain σ < R 2 (R ∼ N v, v = 3 5 and 1 2 for good and θ solvents, the distance the planes, H </ 2 h 0 is the quilibrium chain height in the monolayer. For the given system in all regimes of the ( τ− c) diagram, the decreasing separation between the planes H was shown to result in a more economic state, in which penetration of the chains from the different planes into a “foreign” layer did not occur, but chain coiling resulted. The data obtained are compared with some on the structure of bi-layer membranes and the supercrystalline structure of block copolymers.

Assignment and conformation of neurotensin in aqueous solution by 1H NMR.

A complete assignment of exchangeable and unexchangeable proton resonances of neurotensin 1-13 in aqueous solution has been carried out with the help of its 1-8 and 8-13 fragments. To detect formation of a secondary structure, the effects of peptide fragmentation, temperature decrease, pH changes and addition of denaturing agents on the neurotensin 1H NMR spectrum were investigated. The small changes observed in all cases support the conclusion that neurotensin exists mainly as a flexible random coiled polypeptidic chain in aqueous solution in agreement with previous CD studies.

A molecular model for structural changes during shear yielding and crazing in amorphous polymers

Based on macroscopic and microscopic observations, a model is proposed concerning molecular conformation and chemical structure changes occurring during mechanical deformation of amorphous polymers below their Tg. It is assumed that a bulk polymer, with high molecular mass, consists of interpenetrating, coiled chain molecules. The intrinsic flexibility and the thickness of chain molecules depend on their chemical nature. Stresses are transferred from one chain to others by physical entanglements.

Rheology Enhancement by Molecular Association Complexes

Abstract Associations between polyethylene oxide polymer (PEO) chains and species containing sulfate groups can be used to increase the viscosity and elasticity of polymer solutions. The condensation of sodium dodecyl sulfate (SDS) micelles onto the PEO chain is shown to lead first to chain coil collapse and then to network or gel structure formation as SDS concentration is increased. Stronger interactions are produced between PEO and either Congo-red dye (a large organic molecule with two widely spaced sulfate groups) or polystyrene sulfonate (PSS). In these cases the association complexes lead to minor changes in the solution viscosity but large changes in the primary normal stress and storage modulus G′ at low frequencies. The structures formed by association are disrupted by flow but rapidly re-form. Association complexes are an attractive way of obtaining high-viscosity fluids that would be resistant to permanent shear degradation.

Crystallization of low and high molecular materials

For a better understanding of the crystallization of high molecular materials the paper starts with detailed statements as to the crystallization of low molecular materials. In this way it can be shown that there exist more properties in common than supposed before. This fact becomes evident from the thermodynamical point of view if the polymer is formally considered as a 2-components-system. In this system the stable rotational isomers, viz., the trans- and the gauche-form, are the components. In that case the crystallization process of linear polyethylene (HDPE) can be regarded as a crystallization of the trans-form in a trans-gauche mixture. In the paper the critical nuclei, which build up at the beginning of the crystallization and which have so-called equilibrium shapes, as well as the complete crystals, which have so-called growth shapes influenced by the kinetics of formation, are discussed. Special attention is paid to the lamellar growth because it often occurs in polymers. It is shown that the lamellar growth can be attributed to an activated sorption of foreign substances. In many polymers the role of the foreign substance is played by the gauche-form (autogenous activated sorption). By means of electron micrographs and calorimetric measurements of HDPE samples with a bimodal distribution of the lamellar thicknesses it could be proved that the melting range of polymers is due to a distribution of the lamellar thicknesses and apparently not to a changing conformational partΔs Lk of the melting entropy as supposed by other authors [1]. Values from the literature for the conformational entropyΔs Lk of different polymers confirm in a good approximation thatΔs Lk can be compared to a mean entropy of mixing $$\overline {\Delta s_{Mi} } $$ of the 2-components-model for polymers. This result makes evident that Flory's model for a polymer melt of interpenetrating chain coils can indeed be replaced, in a good approximation, by an ideal mixture of independent trans and gauche units in the sense of the 2-components-model. There follows in conclusion thatΔs Lk is a function of the gauche-trans ratio.

Comment on the concentration and temperature dependences of the translational diffusion coefficient of flexible‐coil macromolecules in solution: Poly(2‐vinyl pyridine) in tetrahydrofuran

AbstractConcentration‐dependence coefficients kDϕ of the mutual diffusion coefficient of poly(2‐vinyl pyridine) in tetrahydrofuran in the temperature range 15–55°C are compared with predictions of recent theories of macromolecular diffusion. In this temperature range a change in local conformation of the polymer occurs. The accompanying changes in chain solvation and coil hydrodynamics result in a sizable decrease in the hydrodynamic interaction parameter X defined by Akcasu. The formulation of theory appropriate for comparison with frame‐indifferent experimental diffusivities is discussed. We find that current theories predict qualitatively, but not quantitatively, the change in temperature dependence of kDϕ that occurs at the conformational transition. The discrepancies closely parallel those reported in recent independent comparisons of theoretical kDϕ versus experimental data for flexible‐coil molecules. No theory can adequately predict kDϕ over a wide range of X.

Two-dimensional random coil chains on hexagonal lattices

In this article a method of formulating random coil chains that can be used as models of amorphous polymers is described. The method is based on an algorithm that finds self avoiding random (SAR) chains on finite lattices. The lattice constant is chosen to be wide enough to avoid the substituents of the polymer interfering with one another. As an example, the construction of the two dimensional random coil packing structure of polyethylene is discussed. In a following paper three-dimensional models will be treated. The mean squared end-to-end distance of chains, generated with this new method, is linear in the number of lattice points.

A theory crack healing in polymers

A theory of crack healing in polymers is presented in terms of the stages of crack healing, namely, (a) surface rearrangement, (b) surface approach, (c) wetting, (d) diffusion, and (e) randomization. The recovery ratio R of mechanical properties with time was determined as a convolution product, R = Rh (t)*φ(t), where Rh (t) is an intrinsic healing function, and φ(t) is a wetting distribution function for the crack interface or plane in the material. The reptation model of a chain in a tube was used to describe self-diffusion of interpenetrating random coil chains which formed a basis for Rh (t). Applications of the theory are described, including crack healing in amorphous polymers and melt processing of polymer resins by injection or compression molding. Relations are developed for fracture stress σ, strain ε, and energy E as a function of time t, temperature T, pressure P, and molecular weight M. Results include (i) during healing or processing at t&amp;lt;t∞, σ,ε∼t1/4, E∼t1/2; (ii) at constant t&amp;lt;t∞, σ,ε∼M−1/4, E∼M−1/2; (iii) in the fully interpenetrated healed state at t = t∞, σ,ε∼M1/2, E∼M; (iv) the time to achieve complete healing, t∞ ∼M3, ∼exp P, ∼exp 1/T. Chain fracture, creep, and stress relaxation are also discussed. New concepts for strength predictions are introduced.

Morphology of spore-bearing structures in Streptomyces ipomoea.

Sporulating colonies of Streptomyces ipomoea were observed using light and scanning electron microscopy. In addition to the open loops and spiral chains of spores characteristic of S. ipomoea, globose structures resembling sporangia of the genus Streptosporangium were found. The "sporangia" had a smooth surface, were 5-6 micrometers in diameter, and consisted of an unbranched coiled hypha within an enveloping sheath. As the sporangia matured, septa formed in the internal sporogenous hypha forming coiled chains of spores morphologically similar to those formed on the typical spore chains. The sporangia germinated on agar, without releasing the nonmotile spores, by formation of several germ tubes at several locations on the sporangia.

ChemInform Abstract: VIBRATIONAL RELAXATION IN JET‐COOLED PARA‐ALKYLANILINES

Absorption and fluorescence spectra have been obtained for the 1B2(ππ*)←1A1 transition of a series of para‐alkylanilines cooled in a supersonic free jet. The series consists of all p‐n‐alkylanilines through n‐butyl‐ as well as p‐isopropylaniline and aniline itself. For those members of the series having an alkyl chain length of three or greater, two distinct molecular conformations are found to be populated in the jet with roughly equal likelihood. Spectra of both the extended chain conformation [p‐n‐(t)‐alkylanilines] and the coiled chain conformation [p‐n‐(g)‐alkylanilines] show that two optically active aniline vibrations are largely unaffected by changes in the length and nature of the n‐alkyl chain. One of these vibrations (the inversion motion of the –NH2 group) would be expected to be particularly weakly coupled to the torsions and bends of p‐alkyl chain. Nonetheless, fluorescence spectra obtained when this vibration is excited in the 1B2 state show that intramolecular vibrational relaxation occurs...

Vibrational relaxation in jet-cooled p a r a-alkylanilines

Absorption and fluorescence spectra have been obtained for the 1B2(ππ*)←1A1 transition of a series of para-alkylanilines cooled in a supersonic free jet. The series consists of all p-n-alkylanilines through n-butyl- as well as p-isopropylaniline and aniline itself. For those members of the series having an alkyl chain length of three or greater, two distinct molecular conformations are found to be populated in the jet with roughly equal likelihood. Spectra of both the extended chain conformation [p-n-(t)-alkylanilines] and the coiled chain conformation [p-n-(g)-alkylanilines] show that two optically active aniline vibrations are largely unaffected by changes in the length and nature of the n-alkyl chain. One of these vibrations (the inversion motion of the –NH2 group) would be expected to be particularly weakly coupled to the torsions and bends of p-alkyl chain. Nonetheless, fluorescence spectra obtained when this vibration is excited in the 1B2 state show that intramolecular vibrational relaxation occurs into the chain modes within a nanosecond.

Scanning Electron Microscopy Studies of Fractured Natural Rubber Surfaces

Abstract A tensile ruptured gum specimen shows formation of crystalline regions at an angle of 45° to the flow lines, whereas a tensile ruptured filled specimen shows formation of depression. A tear fractured gum specimen shows again the formation of crystallites at an angle of 45° to the flow lines. Tear fractured filled specimens show the enhancement of crystallinity throughout the matrix, but the surface is rough. Flex fractured gum specimen show a large number of cracks on the surface while the filled vulcanizate shows formation of balls presumably due to coiling of polymer chains on the filler surface. An abraded gum surface shows dimple structure, while a filled vulcanizate indicates coarse ribbed structure. Addition of lignin, in general, reduces the crystallinity of tensile and tear fractured samples and increases the fibrosity of flex cracked and abraded samples.