Showing papers in "Polymer Bulletin in 1997"

Synthesis of chitosan derivatives with quaternary ammonium salt and their antibacterial activity

Abstract: N-alkyl chitosan derivatives were prepared by introducing alkyl groups into the amine groups of chitosan via Schiff’s base intermediates. Quaternization of the N-alkyl chitosan derivatives were carried out using methyl iodide to produce water soluble cationic polyelectrolytes, novel chitosan derivatives with quaternary ammonium salt. Their antibacterial activities against S. aureus were explored by the viable cell counting method in acetate buffer(pH 6.0). The antibacterial activities of the chitosan derivatives with quaternary ammonium salt increased with increase in the chain length of the alkyl substituent, and this increased activity could be ascribed to the contribution of the increased hydrophobic properties of the derivatives.

Successive self-nucleation/annealing (SSA): A novel technique to study molecular segregation during crystallization

Abstract: A new procedure to fractionate ethylene/α-olefin copolymers using DSC is presented. This procedure allows melt/melt and melt/solid segregation to occur during thermal cycles that promote self-nucleation, crystallization and annealing processes (Successive Self-Nucleation/ Annealing, SSA). The SSA has been compared with the Step-Crystallization (SC) method proposed earlier in the literature to qualitatively characterize chain branching distribution in a faster and easier way than Temperature Rising Elution Fractionation (TREF). In general, SSA produces better fractionation than SC and the DSC derived chain branching distribution by SSA can be qualitatively comparable to that obtained by TREF. The SSA technique could have important applications for the characterization of polymers that crystallize over a broad temperature range.

Improved infrared spectroscopic method for the analysis of degree of N -deacetylation of chitosan

Abstract: Various infrared spectroscopic techniques for the analysis of degree of N-deacetylation of chitosan were evaluated for accuracy. A new method was proposed which involved development of a calibration curve using the absorbance intensities of the chitosan infrared spectrum at 1655 and 3450 cm−1. The degree of N-deacetylation of various chitosan samples was then determined by using the absorption ratios [A1655/A3450] in the equation of the calibration curve. This method yielded results which were superior to those of any of the previously reported infrared spectroscopic methods tested herein.

Spin coating as a method for polymer molecular weight determination

Abstract: The spin coating process was investigated using solutions of polystyrene dissolved in toluene. The residual film thickness depends not only on the spinning velocity and concentration, but also on molecular weight. Specific scaling exponents were determined. The molecular weight dependence was investigated in detail to reveal the type of molecular weight average. This enables a fast determination of the molecular weight by use of spin coating. The use of model molecular weight distributions yields a relation to number Mn and weight Mw average molecular weight.

New biomedical polyurethane ureas with high tear strengths

Abstract: Biodegradable polyurethanes ureas (PUU) were synthesized by a two step polymerization. First a poly (e-caprolactone) prepolymer was terminated with three different diisocyanates: lysinediisocyanate (LDI), 1,6-hexanediisocyanate (HDI) and 1,4-butanediisocyanate (BDI). Second the prepolymers were chain extended with 1,4-butanediamine. The degradation products of these polymers are non-toxic. The mechanical properties of the PUU are compared with those of three PU’s. Compared to these PU’s, the HDI and BDI based PUU showed a very high resistance to tearing.

High-content polystyrene latex by microemulsion polymerization

Abstract: The semicontinuous addition of styrene to a low solid-content (6 wt%) polystyrene latex obtained by polymerization of a three-component microemulsion, allows the production of a high solid-content latex (ca. 40 wt%) containing small particles ( 106 g/mol). The method can be extended to latex made from microemulsions containing other water-insoluble monomers.

Synthesis of polystyrene/silica gel polymer hybrids by in-situ polymerization method

Abstract: Homogeneous polystyrene and silica gel polymer hybrids were prepared by in-situ radical polymerization method. Styrene monomer was introduced into a sol-gel reaction mixture of tetramethoxysilane (TMOS) and the polymerization was initiated by Azobisisobutyronitrile (AIBN), while sol-gel reaction of TMOS proceeded to form a silica gel. The homogeneity of the hybrids was found to be dependent on the amount of the acid catalyst. The homogeneity was confirmed quantitatively by measuring porosity of charred hybrids with nitrogen porosimetry method. It was found that polystyrene was dispersed at a nano-meter level in the silica gel matrix.

Homo-, co- and terpolymerization of 1,5-hexadiene using a methylalumoxane activated mono-Cp-amido-complex

Abstract: Homo- and copolymerizations of 1,5-hexadiene with ethene and styrene using halfsandwich metallocene catalyst Me2Si(Me4Cp)(N-tert-butyl)TiCl2 / MAO (Cp=cyclopentadienyl, Me=methyl, MAO=methylalumoxane) were investigated. According to 13C-NMR spectroscopic microstructure analysis, cyclopolymerization of 1,5-hexadiene afforded randomly distributed cis- and trans-cyclopentane rings in the homo- and copolymer backbone. 1,5-hexadiene incorporation reached 52 mol-%. The ratio of vinyl side chains to cyclopentane rings was controlled by 1,5-hexadiene concentration, where low 1,5-hexadiene concentration promoted cyclopolymerization. Copolymer glass transition temperatures increased with increasing content of cyclic units in the backbone. Styrene was used successfully as termonomer in ethene/1,5-hexadiene polymerization, resulting in a semicrystalline terpolymer with cyclic and styrenic units in the polymer backbone.

Relationships between molecular and plane-stress essential work of fracture parameters in amorphous copolyesters

Abstract: The plane-stress fracture toughness of amorphous copolyester (aCOP) sheets of different intrinsic viscosity (IV) was determined by the essential work of fracture (EWF) concept using tensile-loaded deeply double-edge notched (DDEN-T) specimens. It was found that the specific essential work of fracture (we) is a composite parameter: its constituents are relied on yielding (we,y) and necking (we)/ respectively. The we values, and especially we,y did not change as a function of IV. This finding along with the fact that the mean entanglement length of the aCOP series was constant, suggest that we,y (which is related to the critical plane-strain toughness value) is likely dependent on the entanglement network. This assumption was reasoned by the observation that the plastic zone was completely recovered after annealing the specimen beyond the glass transition temperature (Tg). Recall that the shape recovery in case of cold-drawing (i.e. deformation below Tg) is controlled by the initial entanglement network structure in amorphous polymers.

Asymmetric polymerization of N -substituted maleimides with organolithium — bisoxazolines complex

Abstract: Asymmetric anionic polymerizations of achiral N- substituted maleimide (RMI) (N− cyclohexyl (CHMI), N-phenyl (PhMI), N-tert- butyl (TBMI)) by n-butyllithium (n-BuLi) or fluorenyllithium (FILi) complexes of chiral bisoxazoline derivatives in toluene gave optically active polymers ([α] 435 25 −2.9° to −8.2°). The polymers prerared with initiator of n-BuLi-2,2′-bis(4,4′-isopropyl-l,3-oxazoline) showed negative specific rotations (poly(RMI), [α] 435 25 − 5.8° to −8.2°) which were greater than those ([α] 435 25 −2.9° to −5.9°) with other chiral 2,2′-bis(4,4′-alkyl-l,3-oxazoline) (alkyl group = iso-butyl and benzyl).

Linear and nonlinear rheological responses in aqueous systems of hydrophobically modified chitosan and its unmodified analogue

Abstract: Oscillatory shear and viscosity measurements have been carried out on semidilute acid aqueous systems of unmodified chitosan (UM-chitosan) and of hydrophobically modified chitosan (HM-chitosan) with three different degrees of C12-aldehyde substitution. These systems form physical gels at higher concentrations. The gel point, determined by the observation of a frequency independent loss tangent, was found to be shifted toward lower concentrations with increasing hydrophobicity. At the gel point, a power law frequency dependence of the dynamic moduli (G′∼G″∼ωn) was observed, with n values of 0.36 and 0.46 for the UM-chitosan and the hydrophobically modified chitosans, respectively. These values are interpreted in the framework of a fractal model. The gel strength parameter S increased with decreasing hydrophobicity. The UM-chitosan and HM-chitosan systems exhibited a non-Newtonian shear thinning behavior. This effect is promoted by increasing polymer concentration and hydrophobicity. Both the linear and nonlinear rheological properties elucidate the intricate interplay between hydrophobic associations and entanglement effects.

An alternating copolymer for a blue light-emitting diode

Abstract: An alternating copolymer composed of 9,9′-dihexylfluorene and N-2-ethylhexyl carbazole was synthesized to use as an emissive polymer in a light-emitting diode(LED). The copolymer is soluble in organic solvents and spin-cast to make a fine film. An LED fabricated by sandwiching the alternating copolymer between indium-tin oxide and aluminum emits a white color with the full width at half maximum of 150 nm. The electroluminescence spectrum becomes simplified to have an emission peak at 460 nm for fine blue color when the copolymer is blended with poly(vinylcarbazole) with a ratio of 1 to 4 before the use as an emissive layer. The forward bias turn-on voltage for the LED is 13, and quantum efficiency is 0.002%.

Surface activity of water soluble amphiphilic chitin derivatives

Abstract: Chitin was derivatized to extend its applications in the field of water soluble systems. It was first carboxymethylated and then alkylated. Two technics were used for that purpose: ionic surfactants playing the role of counterions form an electrostatic complex, and covalent derivatization. The difference between covalent alkylation and dynamic association (SPEC) is discussed in relation with the length of the alkyl chain and the density of alkylation.

Synthesis and bulk properties of poly(tetrahydrofuran)-poly(2-methyl-2-oxazoline) ABA triblock copolymers

Abstract: A series of linear triblock-copolymers of the ABA type in which the central B-block is poly(tetrahydrofuran) (polyTHF) and the A-segments are poly(2-methyl-2-oxazoline) (polyMeOX) were synthesized by a one-pot sequential monomer addition copolymerization, utilizing the living nature of the cationic ring-opening polymerization of both monomers.

Influence of ageing on the cold crystallization of glassy poly(ethyleneterephthalate)

Abstract: The thermal crystallization from the glassy state of different samples of Poly(ethyleneterephthalate) (PET) was investigated with different techniques, such as infrared and x-ray analysis and polarized optical microscopy. The different samples of PET were obtained by ageing the glassy PET films at room temperature and at 60°C; the behaviour of these films was compared with that of the fresh sample, put at the crystallization temperature as soon as prepared. The temperature of crystallization was 120°C. All the techniques, investigated to follow the crystallization phenomenon, show that the fresh sample crystallizes with longer times than the others. This result was correlated with the initial structural organization of the glassy amorphous films.

On-line HPLC 1H NMR coupling for the analysis of fatty alcohol ethoxylates

Abstract: The characterisation of fatty alcohol ethoxylate based surfactants by on-line LC-NMR coupling is described. Different surfactant mixtures were separated by a mixed exclusion-adsorption method of liquid chromatography and simultaneously characterised by 1H-NMR spectroscopy. Information about the degree of oligomerisation of the ethylene oxide chain and the chemical structure of the endgroups can be obtained in a one-step experiment.

Effect of reaction parameters on the polymerization of methyl methacrylate with nickel acetylacetonate/methylaluminoane

Abstract: Polymerizations of methyl methacrylate (MMA) employing nickel acetylacetonate [Ni(acac)2] as catalyst combined with methylaluminoxane (MAO) as cocatalyst were investigated. The main purpose of this work is concerned with the study of reaction parameters MMA polymerization. Temperature of polymerization, Al/Ni mole ratio, type of solvent, catalyst concentration and time dependence were examined. The influence of Lewis bases on the polymerization was also studied. The binary system Ni(acac)2/MAO was the only one able to polymerize MMA at the conditions employed in this work. The cocatalytic activity of MAO was compared to those of common alkylaluminium compounds. The polymers were characterized by gel-permeation chromatography (GPC) and 13C-NMR techniques.

Effect of surfactant concentration, pH, and shear rate on the rheological properties of aqueous systems of a hydrophobically modifed chitosan and its unmodified analogue

Abstract: Oscillatory shear, shear relaxation and viscosity experiments have been carried out on semidilute solutions of chitosan and on a hydrophobically modified analogue (HM-chitosan) in 1 % acetic acid. This was done in the presence of various amounts of cetyltrimethylammonium bromide (CTAB) and at different pH values. All the rheological measurements on the HM-chitosan solutions revealed significant polymersurfactant interaction and pH effects. The observed rheological effects were least pronounced at pH≈4, while a strong viscoelastic response was found at pH values of 1 and 5 in HM-chitosan solutions of low surfactant concentration. At these conditions, significant shear-thinning effects were observed. In semidilute solutions of unmodified chitosan, the influence of pH, surfactant concentration and shear rate on the rheological properties was moderate or insignificant.

Responsibility of electric resistance of polyethyleneimine-grafted carbon black against alcohol vapor and humidity

Abstract: Crystalline polyethyleneimine (PEI(C)) was successfully grafted onto carbon black surface by direct condensation of imino groups of PEI with carboxyl groups on the surface using N,N′-dicyclohexylcarbodiimide as a condensing agent. The electric resistance of a composite prepared from PEI(C) and PEI(C)-grafted carbon black drastically increased to 103–104 times of initial resistance in methanol, ethanol, and water vapor. But the change of electric resistance of the composite hardly observed in hexane and toluene vapor. These results suggest the possibility of detection of a slight change of crystalline structure of PEI by the absorption of solvent as a large increase of electric resistance of the composite.

Synthesis of novel organoboron polymers by hydroboration polymerization of bisallene compounds

Abstract: This paper describes synthesis of novel organoboron polymers by hydroboration polymerization of bisallene compounds. The polymers were prepared by polyaddition between thexylborane and bisallenes. The polymers obtained have allylborane units in their main chains and can be expected as a novel type of reactive polymers. The polymer was subjected to a chain transformation reaction and the corresponding polyalcohol was obtained. Hydroboration polymerization of bisallene with mesitylborane was also carried out. It was found that the polymer prepared from mesitylborane showed higher stability than that prepared from thexylborane.

Supramolecular association of acid terminated polydimethylsiloxanes 1. Synthesis and characterization

Abstract: Benzoic acid terminated polydimethylsiloxanes (PDMS) have been synthesized by hydrosilylation of allyloxybenzylbenzoate with SiH terminated precursors followed by deprotection. These oligomers have been characterized by 1H, 13C and 29Si NMR, by FTIR and by SEC in tetrahydrofurane. Because of the flexibility and low polarity of the siloxane backbone, they are ideally suited to study the effect of hydrogen bonding on macromolecular properties.

Synthesis and thermal properties of fullerene-containing polymethacrylates

Abstract: Three poly(methyl methacrylate-co-2-bromoethyl methacrylate) samples were prepared. The bromine groups in the copolymers were converted to azide groups followed by reaction with fullerene (C60) to afford fullerene-containing polymethacrylates. The glass transition temperatures (Tgs) and heat capacity changes (ΔCp) at Tg of these polymers were measured by differential scanning calorimetry. With increasing fullerene content in the polymethacrylate, the Tg value increases while the ΔCp value decreases. The incorporation of fullerene improves the thermal stability of the polymethacrylate as shown by thermogravimetric analysis.

The synthesis of dendrimers bearing alkyl chains and their behavior at air-water interface

Abstract: A new kind of amphiphilic polyether dendrimer bearing eight alkyl chains at the periphery were synthesized step by step using the convergent method. Their structures were confirmed by FT-IR spectra, 1H NMR spectra and mass spectra etc. The π-A isotherms, hysteresis and molecular area-time curves at air water interface were reported. These results showed that they could form stable monolayers at water surface.

Synthesis and characterization of vinyl silane modified imidazole copolymer as a novel corrosion inhibitor

Abstract: For a novel corrosion inhibitor for copper, the free radical copolymerization of vinyl imidazole(VI) and vinyl trimethoxy silane(VTS) was carried out in benzene at 68 °C using azobisisobutyronitrile(AIBN) as an initiator. The reactivity ratios of the two monomers were determined from instantaneous composition diagram: r VI =3.22 and r VTS =0. Thermal stability of poly(VI-co-VTS) depended on VTS mole fraction in the feed rather than the molecular weight of the copolymer, due to the disiloxane bond linkages formed during heating.

Effects of cyclization and pendant vinyl group reactivity on the swelling behavior of polyacrylamide gels

Abstract: A series of polyacrylamide (PAAm) gels were prepared by free-radical crosslinking copolymerization of acrylamide and N,N′-methylenebis(acrylamide) (BAAm) in water at various crosslinker (BAAm) and chain transfer agent (isopropyl alcohol, IPA) concentrations. It was shown that only 5 % of the crosslinker used in the feed forms effective crosslinks in the final hydrogels. At BAAm contents as high as 3 mole %, the equilibrium swelling ratio of the gels in water is independent of the crosslinker content in the feed. This is due to the prevailing multiple crosslinking reactions during the gel formation process. At a fixed crosslinker content, the onset of gelation is shifted towards higher conversions and reaction times as the amount of IPA increases. Addition of IPA in the monomer mixture also increases the equilibrium swelling ratio of PAAm gels. It was shown that the gel crosslinking density increases on rising IPA concentration in the feed due to the increasing rate of intermolecular crosslinking reactions.

Polymerization of vinyl acetate in ternary microemulsions stabilized with hexadecyltrimethylammonium bromide

Abstract: The polymerization of vinyl acetate (VA) in three component o/w microemulsions stabilized with the cationic surfactant, CT AB, is presented. Initiation is achieved thermally with a water soluble initiator (V-50). Stable latex containing small particles (ca. 35 nm) with molecular weights (Mw) of around 4 × 105 are obtained. Analysis of the molecular weight distribution suggests that chain transfer to monomer (and not to polymer, which is the typical termination mechanism in emulsion polymerization, specially at high conversions) is the dominant mechanism of termination.

Synthesis of triblock and random copolymers of 4-acetoxystyrene and styrene by living atom transfer radical polymerization

Abstract: Triblock copolymers containing polystyrene (PSt) and poly(4-acetoxystyrene) (PAcOSt) segments have been prepared by atom transfer radical polymerization (ATRP). In the first step one of the two monomers was polymerized in bulk using the initiating system α,α′-dibromo-p-xylene/CuBr/2,2′-bipyridine (1/1/3). Subsequently the resulting telechelic polymers with active bromo end group structures were used as macroinitiators for the polymerization of the second monomer under ATRP conditions. This process gave PAcOSt-PSt-PAcOSt and PSt-PAcOSt-PSt triblock copolymers with predetermined molecular weights and narrow molecular weight distributions. Polymerization of a mixture of equal molar amounts of the two monomers yielded a random copolymer with narrow molecular weight distribution.

Spatially resolved and integral NMR investigation of the aging process of carbon black filled natural rubber

Abstract: A complex aging regime takes place in the course of thermal aging of natural rubber. Depending on the kind and the content of the free crosslinker, the aging temperature, the duration of the aging period and the reactivity of the atmosphere (air or nitrogen) a different aging process can be observed also by NMR. The methods used are the common spin-echo-NMR (1H) and parameterselective NMR-imaging (1H). The decay of the echo-magnetization was evaluated on the basis of a modified single chain model (based on the tube model of de Gennes). The thermal aging course of a filled (carbon black) sample at 100°C shows a characteristic behaviour, beginning with a strong decrease of T2 followed by a weak increase through aging times of 10 to about 50 hours. At longer aging times the solid-like behaviour rises again.

Compatibilization of low-density polyethylene/polystyrene blends by segmented EB(PS-block-EB)(n) block copolymers

Abstract: Hydrogenatedsegmented poly[butadiene-block-(styrene-block-butadiene)n] block copolymers, which were developed by use of a polymeric iniferter technique, were tested on their compatibilizing effectiveness for (10/90) LDPE/PS blends. They were found to be effective compatibilizers for this mixture, already giving a pronounced improvement in both tensile strength and strain of the blend at block copolymer concentrations of one percent. A concentration of five weight percent of segmented block copolymer provided a tenfold improvement in blend toughness. The effectiveness of the segmented block copolymers was found be dependent on the block copolymer composition. Block copolymer compositionsof close to 50:50 EB:PS gave the best results.

Comparative study on the lamellar crystal structure of high and low density polyethylenes

Abstract: A comparative study was undertaken on well characterized HDPE and LDPE samples in order to obtain a better understanding of the morphology of the crystalline phase. Thickness of the lamellae was determined by WAXS. The melting points were calculated by empirical and Gibbs-Thomson equations, considering either folded or extended chains, and compared to DSC data. The results confirm that in HDPE the chains are folded, the segment between folds containing about 100 carbon atoms, while in LDPE, the chains are extended, with segments of about 73 carbon atoms in the crystalline core, linked to the paracrystalline layer and amorphous zones, which contain long folds and chain ends, as proposed in the 3-phase model by Vile et al.