Copolymerization of hexafluoropropylene and tetrafluoroethylene: Effect on chain conformation and crystal structure

A series of new copolymers of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) containing up to 50 mol % of the hexafluoropropylene comonomer have been investigated with respect to chain conformation and crystal structure using wide-angle X-ray diffraction (WAXD). Increasing HFP content leads to significant departures from the highly ordered crystalline structure of the homopolymer PTFE; the helical conformation of the chain relaxes and untwists to accommodate the larger  CF₃ pendant group in the HFP unit. Simultaneously the lateral hexagonal packing of the helices becomes less ordered and the a-dimension of the hexagonal cell increases. The above effects are progressive with increasing HFP content. At 50 mol % HFP incorporation the structure is a disordered crystalline phase. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2811–2819, 1998     

Effect of primary radical termination on chain length and initiator efficiency

In polymerization with primary radical termination, when reaction between primary radicals, which escape from solvent cage, is not negligible, a relation between chain length and polymerization rate is found regardless of tractable approximate procedures. Such a relation is applied to the kinetic data obtained in the polymerizations of methyl methacrylate (MMA) and vinyl acetate (VA) initiated by 2,2′-azobis(2,4-valeronitrile) at 50.0°C. Further, when the primary radical termination is high, an initiator efficiency can not be approximated to a ratio of the primary radicals escaping from the cage to the total primary radicals formed in the cage. In the polymerization of MMA, after the primary radicals escapes from the cage, they immediately react with the monomer. Thus, the reaction between the primary radicals is not significant. However, in the polymerization of VA, the rate of reaction between the primary radical and the monomer might be comparable to the rate of reaction between the primary radicals when the initiator concentration is quite high.     

Synthesis of C-terminal peptide fragments of the heavy chain of hemagglutinin of influenza virus of subtypes H1 and H3

It is proposed to use the chromogenic 2-[4-phenylazo)benzylsulfonyl]ethyl group, which can be eliminated by organic bases in aprotic solvents, for the protection of a C-terminal carboxy group in the synthesis of peptides. The synthesis of a number of 10–16-membered peptides corresponding to C-terminal fragments of the heavy chain of the hemagglutination of influenza virus of subtypes H1 and H3 has been performed with the use of this group.All-Union Scientific-Research Institute of Molecular Biology, Kol'tsovo, Novosibirsk Oblast. Vektor Scientific-Industrial Association, Ministry of the Medical and Biological Industry of the USSR, Novosibirsk. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 732–738, September–October, 1988.     

Effect of chain density and conformation on protein adsorption at PEG-grafted polyurethane surfaces

Polyurethanes were modified using monobenzyloxy polyethylene glycol (BPEG) which possesses a bulky hydrophobic benzyloxy group at one end and a hydroxyl group at the other end as a preconstructed BPEG layer, and poly(ethylene glycol) (PEG) and monomethoxyl poly(ethylene glycol) (MPEG) with various chain lengths as fillers. Our objective was to investigate the effect of PEG graft density and conformation on protein adsorption at PEGlated surface. The graft density was estimated by a chemical titration method. The combination of ATR-FTIR, AFM and titration results provide evidences that the graft density can be increased by backfilling PEG or MPEG to a BPEG layer. However, fibrinogen and albumin adsorption significantly increased on all surfaces after PEG or MPEG backfilling. We conclude that the conformation of hydrophobic benzyloxy end groups of the BPEG layer plays a key role. The benzyloxy end groups of preconstructed PEG chains stretch to the surface after PEG backfilling, which possibly accounts for the observed increase in protein adsorption. The BPEG conformation change after backfilling with PEG or MPEG was also suggested by contact angles. Additionally, protein adsorption was slightly influenced by the length of filler, suggesting a change in surface morphology.     

Effect of the conformation of the alkyl chain on the catalytic miniemulsion copolymerization of ethylene and acrylates

The catalytic copolymerization of ethylene and acrylic monomers is a promising way of incorporating polar functionality into polyolefins and therefore enlarging the range of properties of these materials. This work shows that for the copolymerization of ethylene and C4 acrylates using a sterically encumbered Pd catalyst, the degree of incorporation of the acrylic monomer decreases with the degree of branching of the alkyl chain of the acrylate, the main reason being the difficulty for coordination of bulky acrylates to the catalytic site. This strongly affects the polymerization rate as well as the molecular weight, crystallinity and melting point temperature of the copolymers.     

Effect of chain length and asymmetry on material properties of bilayer membranes

Dissipative particle dynamics is used to extract the material parameters (bending and area stretch moduli) of a bilayer membrane patch. Some experiments indicate that the area stretch modulus of lipid vesicles varies little as the chain length of the lipids composing the bilayer increases. Here we show that making the interactions between the hydrophilic head groups of the model amphiphiles proportional to the hydrophobic tail length reproduces the above result for the area stretch modulus. We also show that the area stretch modulus of bilayers composed of amphiphiles with the same number of tail beads but with asymmetric chains is less than that of bilayers with symmetric chains. The effects on the bilayer density and lateral stress profiles of changes to the amphiphile architecture are also presented.     

Effect of the chain length on the thermal and analytical properties of laterally biforked nematogens

Three laterally substituted liquid crystals were synthesized in order to investigate the effect of a lateral biforked chain on the thermal and analytical properties. The mesogenic molecules have the same core containing four aromatic rings connected by two ester and one diazo linkages, they differ by the length of one chain within the lateral biforked substituent. The phase transition temperatures were obtained by polarized light microscopy and differential scanning calorimetry (DSC). The clearing temperature and the nematic range decrease with increasing length of the lateral biforked chain. The stationary phases derived from these nematogens provide excellent resolution of various classes of compounds, including aromatic hydrocarbons (AH), substituted benzenes, polycyclic aromatic hydrocarbons (PAH), phenols and volatile organic compounds (VOC) present in the essential oils. The selectivities of the stationary phases were found to decrease according to the length of the side chain.     

Effect of length of carbon chain on antioxidation efficiency of o-bisphenols

Conclusions In the oxidation of isotactic polypropylene the highest antioxidant efficiency is shown by an o-bis-phenol, the nuclei of which are linked by a methylene bridge.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2614–2616, November, 1972.     

Effect of chain length on transfection properties of spermine-based gemini surfactants

The synthesis and associated structure-activity relationships for gene transfection of a series of spermine-derived cationic gemini surfactants incorporating diamino acid headgroups and either identical (symmetrical) or different (unsymmetrical) lipophilic tailgroups is described. Transfection activity is found to depend critically upon the structural elements present.     

Effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases

Lyotropic quaternary mixtures of potassium alkanoates (KCx) and sodium alkyl sulphates (NaCxS), where x is the number of carbon atoms in their alkyl chains, were prepared to investigate the effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases. The lyotropic mixtures investigated were formed by the dissolution of KCx (NaCxS) surfactants in the mixture of Rb₂SO₄/1-decanol/water (Na₂SO₄/1-decanol/water), separately. The uniaxial-to-biaxial nematic phase transitions were identified from the temperature dependence of the birefringences of the nematic phases by means of laser conoscopy. The micelle dimensions were obtained from small-angle X-ray scattering measurements. It was observed that the increase in the surfactant alkyl chain length causes the micellar growth in the plane perpendicular to the main amphiphile bilayer. The surfactant alkyl chain length plays a key role on the shape anisotropy of micelles, which triggers the orientational fluctuations that are responsible for the stabilisation of the different lyotropic nematic phases.     

Effect of alkanethiol chain length on gold nanoparticle monolayers at the air-water interface

In this study, we report the effects of the alkyl chain length on alkanethiol-capped gold nanoparticle Langmuir films. Gold nanoparticles (2-3 nm) capped with C(n)H(2n+1)SH (n = 5-12, 14-16, 18) were prepared via a two-phase synthesis. The films were sampled by Langmuir-Schaefer horizontal transfer at various points in the pressure-area isotherm and monitored with transmission electron microscopy. Changes in surface pressure, temperature, and alkyl chain length did not lead to observable differences in the mesoscale film morphology. Pressure-area isotherms at 22 °C, however, revealed that the work of compression and the collapse pressure are directly dependent on alkyl chain lengths of 14 carbons or greater. Variable temperature isotherms suggest that the work of compression is strongly affected by the phase state (i.e., crystalline vs liquid-like) of the gold-thiolate self-assembled monolayer (SAM) capping the nanoparticles.     

Kinetics of polyesterification: Effect of diol chain length

Kinetics of polyesterification of maleic anhydride with polyethylene glycol (PEG) of varying molecular weights have been evaluated. The investigations have been carried out by employing heating cycles comparable to those employed in industrial processes and under nonisothermal conditions. The rate of reaction was found to decrease with increase in the chain length of the polyether. The energy of activation was estimated as 26.91, 40.25, and 47.30 Kcal/mol for PEG of molecular weights 200, 300, and 400, respectively. © 1994 John Wiley & Sons, Inc.     

Effect of chain length and charge density on the construction of polyelectrolyte multilayers on colloidal particles

Two combinations of sodium poly(4-styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) of different chain length and charge density are employed to construct multilayer films. The polyelectrolytes are assembled layer-by-layer on colloidal particles in the absence of salt. We have investigated the formation and electrical characteristics of the films by using electric light scattering technique. The results show that the film thickness is independent of the chain length when fully charged PAH (at pH 4.6) is combined with fully charged PSS. When the films are prepared with less charged PAH (at pH 6.7) and fully charged PSS, lower thickness is found for the film with shorter polymer chains. In all cases, the thickness increment realized on addition of the polymer with lower molar concentration is partially lost on exposure to the solution with higher concentration of the oppositely charged partner. When the film growth is regular (at equal molar concentrations of the fully charged polyelectrolytes), the ratio of PSS to PAH charge, estimated from the electro-optical effect values, exceeds 1. The electro-optical effect is also higher for the films ending with PSS when fully charged PSS is combined with less charged PAH (at pH 6.7). This reveals the key role of the charge in the last-adsorbed layer for the electro-optical behavior of the whole film.     

Effect of n-alkyl chain length on the complexation of phenanthrene and 9-alkyl-phenanthrene with beta-cyclodextrin

The characteristics of host-guest complexation between beta-cyclodextrin (beta-CD) and phenanthrene derivatives (phenanthrene, n-propyl, n-butyl and n-hexyl-phenanthrene) were investigated by fluorescence spectrometry. Linear and non-linear regression methods were used to estimate the formation constants (K1). A 1:1 stoichiometric ratio and an effect of n-alkyl chain length on the formation constant were observed for the binary inclusion complex between guest and beta-CD. The formation constant dramatically increases with the length of n-alkyl, it starts from the value of 140 l mol(-1) for the phenanthrene to reach the value of 580 l mol(-1) for hexyl-phenanthrene. The effect of the temperature on the fluorescence intensity of each complex (guest-host) was also studied; and then the thermodynamic parameters were calculated. The main inclusion site seems to be aromatic moiety for short chain molecules, and it moves toward the alkyl chain part, as the chain becomes longer.     

Effect of polymer size and chain length on depletion interactions between two colloids

A density functional theory based on the weighted density has been developed to investigate the depletion interactions between two colloids immersed in a bath of the binary polymer mixtures, where the colloids are modeled as hard spheres and the polymers as freely jointed tangent hard-sphere chain mixtures. The theoretical calculations for the depletion forces between two colloids induced by the polymer are in good agreement with the computer simulations. The effects of polymer packing fraction, degree of polymerization, polymer/polymer size ratio, colloid/polymer size ratio on the depletion interactions, and colloid-colloid second virial coefficient B2 due to polymer-mediated interactions have been studied. With increasing the polymer packing fraction, the depletion interaction becomes more long ranged and the attractive interaction near the colloid becomes deeper. The effect of degree polymerization shows that the long chain gives a more stable dispersion for colloids rather than the short chain. The strong effective colloid-colloid attraction appears for the large colloid/polymer and polymer/polymer size ratio. The location of maximum repulsion Rmax is found to appear Rmax approximately sigmac+Rg2 for the low polymer packing fraction and this is shifted to smaller separation Rmax approximately sigmac+sigmap2 with increasing the polymer packing fraction, where sigmap2 and Rg2 are the small-particle diameter and the radius of gyration of the polymer with the small-particle diameter, respectively.     

Effect of chain length and substrate temperature on the growth and morphology of n-alkane thin films

Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and microscopy has been used to study the orientational morphology of thin films of the linear alkanes n-C36H74 and n-C60H122, prepared by vacuum deposition onto NaCl (001) surfaces at ambient and elevated substrate temperatures. The orientational morphology, specifically, the nature of domains with lateral and normal orientation, is explored as a function of the chain length and the substrate temperature. It is found that the longer n-C60H122 molecules are laterally oriented on the substrate surface within the investigated substrate temperatures but that the morphology of these thin films varies with substrate temperature. The shorter n-C36H74 molecules are partially laterally oriented at low substrate temperature and are completely normally oriented at high substrate temperature. The relative magnitude of "side-by-side" and "end-to-end" intermolecular interactions leads to the formation of highly ordered alkane structures with a high aspect ratio. The formation of complex, nanoscale orientational morphologies are rationalized by considering kinetic and thermodynamic effects, in particular, the relative enthalpic and entropic contributions to the free energy associated with the different molecular orientations.     

Effect of side‐chain length on the electrospinning of perfluorosulfonic acid ionomers

The effect of the side‐chain length (short side chain and long side chain, SSC and LSC, respectively) of perfluorosulfonic acid (PFSA) ionomers on the properties of nanofibers obtained by electrospinning ionomer dispersions in high dielectric constant liquids has been investigated with a view to obtaining electrospun webs as components of fuel cell membranes. Ranges of experimental conditions for electrospinning LSC and SSC PFSAs have been explored, with a scoping of solvents, carrier polymer and PFSA ionomer concentrations, and carrier polymer molecular weight. Under optimal conditions, the electrospun mats derived from SSC and from LSC PFSA show distinct fiber dimensions that arise from the different chain lengths of the respective ionomers. Enhanced interchain interactions in SSC PFSA with low equivalent weight compared to LSC PFSA result in a considerably lower average fiber diameter and a markedly narrower fiber size distribution. The proton conductivity of nanofiber mats of SSC and LSC PFSA with equivalent weights of 830 and 900 g mol^?1, respectively, are 102 and 58 mS cm^?1 at 80°C and 95% relative humidity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Effect of chain length on thermal conversion of alkoxy-substituted copper phthalocyanine precursors

A series of dialkoxy-substituted copper phthalocyanine (CuPc) precursors (4a-4d) have been prepared by treating phthalonitrile with the corresponding lithium alkoxide under mild conditions. The precursors exhibited high solubilities in common organic solvents, including acetone, toluene, tetrahydrofuran (THF), CH(2)Cl(2), and CHCl(3). Elongation of the alkoxy chains improved the solubilities of the precursors effectively, and accordingly, the butoxy-substituted derivative (4d) showed the highest solubility among 4a-4d. X-ray crystallography clarified that the conjugated skeletons of 4a-4d are all isostructural, and have two alkoxy groups in a syn-conformation fashion, leading to highly bent structures. Thermal conversions of the precursors examined by thermogravimetry (TG) and differential thermal analysis (DTA) demonstrate that 4a was converted into CuPc via two distinct exothermic processes in the 200-250 °C temperature range, while 4d exhibits only one exothermic signal in the DTA. In the field emission scanning electron microscopy (FESEM) images of 4a, the presence of two types of distinct crystal morphology (prismatic and plate-like crystals) can be recognized, implying that the two observed exothermic processes in the DTA can be attributed to the different crystal morphologies of the samples rather than the step-by-step elimination of the alkoxy groups. The thermal formation of CuPc from the precursors has been unambiguously confirmed by X-ray powder diffraction, UV-vis spectroscopy, and elemental analysis. The precursors were converted into CuPc at lower temperature with increasing chain length, presumably because of the increased void volume in the crystals. Thermal conversion performed in the solution phase results in a bright blue-colored solution with prominent absorption bands in the 650-700 nm region, strongly supporting the formation of CuPc.     

Effect of the length of a polymer chain on the rate of donor-acceptor electron transfer

We consider the dependence of the rate of activated and tunnel transfer of an electron between a donor and an acceptor separated by a chain of finite length on the energy and relaxation characteristics of the donor, the chain and the acceptor. It is found that the chain length is important for numbers of units not exceeding 5–7.Institute for Theoretical Physics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 2, pp. 133–139, March–April, 1991. Original article submitted February 19, 1988.