Dilute solution properties of carboxymethylchitins in high ionic-strength solvent

The hydrodynamic characteristics in aqueous solution at ionic strength I=0.2  of carboxymethylchitins of different degrees of chemical substitution have been determined. Experimental values varied over the following ranges: the translational diffusion coefficient (at 25.0°C), 1.1<10⁷×D<2.9 cm² s⁻¹; the sedimentation coefficient, 2.4<s<5.0 S; the Gralen coefficient (sedimentation concentration-dependence parameter), 130<k_s<680 mL g⁻¹; the intrinsic viscosity, 130<[η]<550 mL g⁻¹. Combination of s with D using the Svedberg equation yielded ‘sedimentation–diffusion' molecular weights in the range 40 000<M<240 000 g mol⁻¹. The corresponding Mark–Houwink–Kuhn–Sakurada (MHKS) relationships between the molecular weight and s, D and [η] were: [η]=5.58×10⁻³ M^0.94; D=1.87×10⁻⁴ M^−0.60; s=4.10×10⁻¹⁵ M^0.39. The equilibrium rigidity and hydrodynamic diameter of the carboxymethylchitin polymer chain is also investigated on the basis of wormlike coil theory without excluded volume effects. The significance of the Gralen k_s values for these substances is discussed.     

Preparation of high viscosity thermoplastic phenol formaldehyde polymers for application in reactive extrusion

This work deals with the synthesis of high molecular weight, thermoplastic phenol formaldehyde (PF) resins for the application in the synthesis of polypropylene–PF compatibilizers by reactive extrusion. Phenol formaldehyde of high molecular weight is required in reactive extrusion with most polypropylene grades to meet the viscosity ratio (λ) requirement for best mixing. Special lab-grades of PF were therefore developed. The polymers synthesized were highly linear and in the M_w range of 10–30 000 g mole⁻¹.     

Rheological behaviour of blends of narrow molecular weight distribution polystyrenes in the molten state: dynamic viscoelastic properties in the terminal zone

Narrow molecular weight distribution polystyrenes and their blends, with molecular weights exceeding M_c′ have been measured in the molten state by means of a Contraves-Kepes balance rheometer. The vertical and the horizontal shift factors are the same for the fractions and their blends. In the terminal zone, the effect of blending on the complex viscosity η* and its imaginary η″ results in the appearance of two fields representing the respective contributions of both components to the blend. The importance of the coupling between both fields as a function of the weight ratio of both components is discussed. The zero-shear viscosity η₀ is equal to that of a narrow molecular weight distribution polystyrene having the same weight-average molecular weight M_w′ measured at the same temperature.     

Preparation, characterization, solution properties and rheological behaviour of polyacrylamide

In this report a survey is given on structure and properties of polyacrylamide homopolymers (PAAm) in solution. However the review is restricted to all those papers, where a molecular characterization of the polymers has been achieved as a basis to correlate this fundamental information with applicational properties.

Different polymerization methods are summarised in brief, the preparation and solution structure of long chain branched polyacrylamides as well as chemical modification reactions of linear PAAm are also mentioned. A number of experimental characterization methods (GPC, ultracentrifugation, intrinsic viscosity, and light scattering measurements) are described with special emphasis on the difficulties of the different procedures including some proposals for properly designed experimental techniques. The state of solution is discussed in view of experimental data obtained with different solvents. Moreover viscosity constant ø is calculated for aqueous solution and the unperturbed dimensions are estimated. All available data on cross correlations (e.g. [η] - M, S₀ - M, 2>^1/2 - M) are collected with the intention to give a survey of established relations and, comparing the given relationships, to suggest the reliable ones of them.

The phenomenon of long-term viscosity decrease of aqueous PAAm solutions has been investigated and discussed with regard to its molecular origin.

The viscoelastic properties are discussed in dependence on molecular weight, concentration, solvent quality, and shear rate (10⁶ · s⁻¹). Based on these data a simple equation was developed oped for the η₀-c-M relationship, which can be applied to other polymer systems as well. It is further described that the elastic nature (first normal stress difference) may overwhelm the viscous nature (shear stress) at relatively low shear rates. This high elasticity can cause deviation from laminar flow conditions. Moreover, it can be demonstrated — based on instationary measurements as well as the comparison of steady shear flow with dynamic rheology — that energetic interactions (H-bonds) strongly influence the rheological behaviour.     

Estimation of the contribution of tube renewal in the terminal relaxation of linear polybutadiene

A set of low-molecular-weight (low-MW) entangled linear polybutadienes with molecular weights between 1.1 × 10⁴ and 2.5 × 10⁵ have been dilutedly embedded in a high-molecular-weight linear polybutadiene (M_w = 7.6 · 10⁵) matrix. The viscoelastic properties of these blends with 9.1% low-MW polymer have been measured. The loss moduli-frequency master curves, G^″ (Щ), contain contributions from both polymers. The contribution of the low-MW polymer is obtained by subtracting the contribution of the matrix. The maximum in G^″, G^″_m, due to the low-MW polymer occurs at a lower frequency (0.3 to 0.5 log units) than in the homopolymer. This result indicates that the longest relaxation time of the entangled linear polymer embedded in a high-molecular-weight matrix is increased by a factor of 2.0 to 3.0 because tube renewal normally operating in the homopolymer is almost completely absent in the matrix. The longest relaxation time of the polymers in the matrix depends on M^3.3₀. This is only slightly less than the dependence found in linear polymer melts (M^3.3₇). This indicates that reptation and chain-end fluctuation together contribute to the relaxation of linear polymers in permanent networks.     

Homogeneous reverse atom transfer radical polymerization of glycidyl methacrylate and ring-opening reaction of the pendant oxirane ring

The homogeneous reverse atom transfer radical polymerization (reverse ATRP) of glycidyl methacrylate (GMA) was carried out in bulk, using 2,2′-azobisisobutyronitrile (AIBN) as the initiator and N,N-n-butyldithiocarbamate copper (Cu(SC(S)N(C₄H₉)₂)₂) as the catalyst. The polymerization showed typical controlled/‘living’ polymerization behavior, i.e. first-order kinetics, well-controlled molecular weight (M_n) and narrow molecular weight distribution (M_w/M_n). ¹H NMR and IR spectra showed that the pendant epoxy groups in PGMA polymer remained intact throughout the polymerization of GMA. A phosphorated PGMA (PPGMA) polymer was obtained by phosphonation reaction of the pendant epoxy groups in PGMA with diphenylphosphinic chloride (DPPC). Thermal behavior of the PPGMA was studied by TG and DTG. A major DTG peak at 340 °C was observed for the PPGMA.     

Small-angle neutron scattering from branched epoxide resins

Small-angle neutron scattering experiments in the range of q² from 0.01 to 25 nm⁻² have been carried out on branched epoxide resins based on bisphenol-A at the Institute Laue—Langevin (I.L.L) in Grenoble (q=(4π/λ) sin(θ/2)). Measurements were made with six samples in the range of M_W from 1500 to 19 000 and four concentrations between 1.3 and 10% (w/w) in deuterated diglyme. The results are as follows: (i) The mean square radius of gyration follows a relationship S²_z=4.69×10⁻⁴M^1.20_W (nm²). (ii) In all cases fairly large second virial coefficients A₂ are obtained which, however, decrease strongly with molecular weight. Above M_W=2500, the virial coefficient follows the relationship A₂=1.6M^−0.85_W (mol cm³g⁻²). (ii) The reciprocal particle scattering factor as a function of q² exhibits only a slight upturn and otherwise shows the behaviour of a randomly branched polycondensate. The slight upturn is discussed as being caused by the finite volume of the monomeric unit. Possible reasons for the high exponent in the S²_z versus M_W dependence are briefly discussed.     

Reptation in polymer blends

Forward recoil spectrometry (FRES) was used to measure the tracer diffusion coefficients D*_PS and D*_PXE of deuterated polystyrene (d-PS) and deuterated poly(xylenyl ether) (d-PXE) chains in high molecular weight protonated blends of these polymers. The D*s were shown to be independent of matrix molecular weights and to decrease as M⁻², where M is the tracer molecular weight, suggesting that the tracer diffusion of both species occurs by reptation. These D*s were used to determine the monomeric friction coefficients ζ_0,PS and ζ_0,PXE of the individual PS and PXE macromolecules as a function of ф, the volume fraction of PS in the PS:PXE blend. Since ζ_0,PSζ_0,PXE at each ф, the rate at which a PS molecule reptates is much greater than that of a PXE molecule, even though both chains are diffusing in identical surroundings. Part of this difference may be due to the difficulty of backbone bond rotation of the PXE molecule. However, even when measured at a constant temperature increment above the glass transition temperature, ζ_0,PS and ζ_0,PXE were observed to be markedly composition dependent. In addition the ratio ζ_0,PS/ζ_0,PXE varied from a maximum of 4 × 10⁻² near ф=0.85 to a minimum of 5 × 10⁻⁵ for ф=0.0. These results show that intramolecular barriers do not solely determine the ζ₀s of the components in this blend. Clearly, the interactions between the diffusing chains and the matrix chains also influence ζ₀.     

Deformation and toughness of polymeric systems: 3. Influence of crosslink density

In part 1 of this series the phenomenon of a critical ligament thickness (ID_c) below which brittle polymers become ductile was investigated for polystyrene (PS). Using the thermoplastic polystyrene-poly(2,6-dimethyl-1,4-phenylene ether) (PS-PPE) model system, it was demonstrated in part 2 of this series that the absolute value of ID_c as well as the maximum toughness (i.e. maximum strain to break) was dependent on the network density of the polymer used. In this study the toughness and ID_c of crosslinked thermosetting polymers were investigated using epoxides based on the diglycidyl ether of bisphenol A as a model system. The crosslink density (v_c) is varied between values comparable with (v_c = 9 × 10²⁵ chains m⁻³), up to values much higher than (v_c = 235 × 10²⁵ chains m⁻³), the entanglement density in the thermoplastic PS-PPE system. The maximum macroscopic toughness proportional to the strain to break (λ_macr) or given by the slow-speed fracture toughness (G_Ic) and the notched high-speed tensile toughness (G_h) of core-shell rubber-modified epoxides uniquely increases with an increasing molecular weight between crosslinks (M_c). Only by using extreme testing conditions (notched high-speed impact testing), could the ID_c of a limited range of epoxides be determined: 0.21 μm (v_c = 9 × 10²⁵ chains m⁻³) ≤ ID_c ≤ 0.29 μm (v_c = 14 × 10²⁵ chains m⁻³). Both the experimentally determined values of ID_c and the toughness of the epoxides compare well with the values determined for the entangled thermoplastic PS-PPE model system in the same range of network densities, elucidating the principal similarity of the influence of entanglements and crosslinks on the deformation processes. Good agreement was observed between the experimentally determined values of ID_c of the epoxides and the values predicted by the simple model introduced in part 2 of this series.     

Swollen-state polymerization of poly(ethylene terephthalate) in fibre form

The swollen-state polymerization of poly(ethylene terephthalate) in fibre form was performed in hydrogenated terphenyl as the swelling solvent. Ultra-high-molecular-weight poly(ethylene terephthalate) (CHMW-PET) fibre with an intrinsic viscosity of 3–4dl g⁻¹ (M_n = 2–3 × 10⁵) was obtained. The polymerization rate of as-spun PET fibres in the swollen state was greater than that of PET granules in the swollen state. It was clarified that the polymerization rate was related to the chain mobility of the starting materials. The chain mobility was influenced by various conditions, such as changing rigidity of the segments during copolymerization, the chain orientation of the starting fibre before swollen-state polymerization and the temperature of pretreatment with the solvent. Pretreatment with solvent before polymerization was effective in increasing the chain mobility. The relation between chain mobility and polymerization rate was examined by wide-angle X-ray diffraction, density, differential scanning calorimetry, solvent content and viscoelastic measurements. Undrawn UHMW-PET fibres could be drawn 10 times or more by the zone drawing technique in spite of their high crystallinity, and the drawn fibre showed high tensile strength (12 g d⁻¹) and high modulus (240 g d⁻¹).     

RHEOLOGICAL CHARACTERIZATION OF PYROLYTIC WOOD DERIVED OILS: EXISTENCE OF A COMPENSATION EFFECT

Detailed rheological study was made for sixteen pyrolytic wood derived oils provided by different laboratories and obtained from a wide range of liquefaction processes. Molecular characterization of these oils has been performed through gel permeation chromatography (GPC) and intrinsic viscosity [η] measurements.

All pyrolytic wood derived oils exhibit an essentially Newtonian behavior in the range of shear rate examined (10^-1 to 10³s^-1). The variation of viscosity with temperature follows an Arrhenius-type relationship. GPC chromatograms and [ η] measurements have shown the existence of a Mark-Houwink relationship between [ η] and molecular weights of the pyrolytic oils with a Mark-Houwink exponent of the order of 0.58 when tetrahydrofuran (THF) is used as solvent. Therefore the pyrolytic oils despite the diversity of the liquefaction processes all belong to a same family. Moreover, a compensation effect has been found. Because of the Newtonian character of these oils, the compensation effect allows the determination of the temperature dependence of viscosity from only one measurement of viscosity at a given temperature     

Interpenetrating polymer networks of poly(dimethylsiloxane): 1. Preparation and characterization

Model networks of ,ω-dihydroxy-poly(dimethylsiloxane) (PDMS) were prepared by tetrafunctional crosslinking agent tetraethyl orthosilicate (TEOS) and the catalyst stannous 2-ethylhexanoate. Hydroxylterminated chains of PDMS having molecular weights 15 × 10³ and 75 × 10³ g mol⁻¹ were used in the crosslinking reaction. Bimodal networks were obtained from a 50% (w/w) mixture of PDMS chains with M_n = 15 × 10³ and 75 × 10³ g mol⁻¹. A sequential interpenetrating network of these PDMS chains was also prepared. Physical properties of the elastomers were determined by stress-strain tests, swelling and extraction experiments, and differential scanning calorimetry measurements.     

Conformation of isotactic polystyrene (IPS) in the bulk crystallized state as revealed by small-angle neutron scattering

Neutron scattering experiments have been performed on isotactic polystyrene (IPS) samples in the bulk crystallized state (T_{crystallization} = 185°C). The determination of the conformation of tagged chains ranging from 2.5 × 10⁵ to 7 × 10⁵ has been undertaken on two different hydrogenated IPS matrices. A matrix of usual molecular weight (M_w = 4 × 10⁵) leads to results which do not agree with Flory's model. In this case, measurements on radius of gyration R_g show on the one hand an important increase of this parameter (40%) with increasing crystallinity for the highest molecular weight tagged chains and on the other hand a variation with molecular weight like M^0.78. These results are interpreted with a schematic model involving a long crystalline sequence incorporated in the monocrystal along the 110 plane and two amorphous wings. Such an assumption is confirmed by the scattering behaviours in the intermediate range. On the other hand, by using an IPSH matrix of very high molecular weight (M_w = 1.75 × 10⁶), and the same tagged chains previously considered, a very weak variation of R_g with increasing crystallinity is observed. This leads to consider in this case Flory's conformation which is corroborated by data obtained in the intermediate range.     

Upper and lower critical solution temperatures in polyethylene solutions

Upper and lower critical solution temperatures have been determined for solutions of polyethylene in n-butyl acetate and n-amyl acetate over the molecular weight range of M_η = 1·36 × 10⁴ to 17·5 × 10⁴. Polyethylene solution in n-butyl acetate displays a smaller miscibility region than that of the polyethylene/n-amyl acetate system, as indicated by the relative positions of their upper and lower critical solution temperatures. Contributions of the energy and the equation of state terms to the χ1 parameter have been examined by an application of the Patterson-Delmas corresponding state theory to the experimental results of the polyethylene solutions.     

Co-operative diffusion of semi-dilute solutions, concentrated solutions and swollen networks for polystyrene in dibutylphthalate

The diffusion constant of solutions of polystyrenes of molecular weight ranging from 110 000 to 3.6 × 10⁶ in straight-chain-dibutylphthalate has been measured by photon correlation spectroscopy as a function of polymer volume fraction and temperature. In the semi-dilute range the co-operative diffusion constant D_c exhibits a much smaller increase with the polymer volume fraction Φ than theoretically predicted, except at high temperatures (T 100°C) where it follows a Φ^1/2 law characteristic of a marginal solvent. This effect can be described to an enhancement of the friction factor, which is also demonstrated by a decrease in D_c occurring at a volume fraction which increases with temperature. The same effect is observed in swollen networks but it is strongly reduced for swelling equilibrium conditions.     

Introduction of long-chain branches in linear polyethylene by light cross-linking with 1,3-benzenedisulfonyl azide

Metallocene synthesised HDPE with M_w=82,000 and M_n=40,000 was modified with small amounts of 1,3-benzenedisulfonyl azide by reactive extrusion at 200 °C with the purpose to form long-chain branches. At the processing temperature the two azide groups decompose to nitrenes that work as cross-linkers for PE. Cross-linking occurs primarily by insertion of singlet nitrenes into CH bonds. Size exclusion chromatography revealed that the modification resulted in the formation of a long-chain branched (LCB) high molecular weight fraction. The LCB was detectable with SEC for concentrations above 100 ppm corresponding to approximately 0.03–0.04 branch points pr 10⁴ carbon. No signs of the formation of low molecular species due to chain scission were observed. Dynamical mechanical analysis and shear creep test showed sign of long chain branching at concentrations down to the same limit as SEC (100 ppm). These signs were thermorheological complexity, increased zero shear viscosity, increased shear thinning and increased recovery compliance. The cross-linking efficiency of 1,3-BDSA were estimated to 40–60% from comparison of SEC data with random cross-linking theory and traditional SEC-LCB analyses.     

Additive effects of trialkylaluminum on propene polymerization with (t-BuNSiMe2Flu)TiMe2-based catalysts

Propene polymerization was conducted by [η³:η¹-tert-butyl(dimethylfluorenylsilyl)amido]dimethyltitanium combined with B(C₆F₅)₃ or methylaluminoxane (MAO) as a cocatalyst in the presence or absence of various trialkylaluminums: Me₃Al, Et₃Al, ⁱBu₃Al (triisobutylaluminum) and Oct₃Al (trioctylaluminum). In the case of living polymerization with B(C₆F₅)₃ at −50°C, addition of Oct₃Al and Et₃Al increased the propagation rate. Et₃Al also acted as a chain transfer reagent and selectively gave Al-terminated polymers, while Oct₃Al induced chain transfer reaction only in high concentration. Little polymer was obtained in the presence of Me₃Al or ⁱBu₃Al. When MAO was used as a cocatalyst, polymerization did not proceed at −50°C. The MAO system, however, showed high activity at 40°C and selectively gave low molecular weight polymers terminated with Al–C bonds. Contrary to the low temperature polymerization with B(C₆F₅)₃ at −50°C, the polymer yield was enhanced by the addition of Me₃Al and ⁱBu₃Al, while the molecular weight was reduced by Me₃Al and enlarged by ⁱBu₃Al. On the other hand, Et₃Al and Oct₃Al significantly decreased both the polymer yield and the molecular weight under these conditions. It was found that additive effects of trialkylaluminums were strongly dependent on polymerization temperature as well as on the structure of the alkyl group.     

Isosteric heat of sorption of CO2 in poly(ethylene terephthalate)

Sorption isotherms for carbon dioxide in poly(ethylene terephthalate) have been measured at 35–55°C. The isotherms were measured gravimetrically on a Mettler Thermoanalyzer-1 from vacuum to 1 atmosphere. The sorption data were used to generate sorption isotherms from which the isosteric heat of sorption of CO₂ in PET was determined. At 45°C the isosteric heat of sorption increases from −10 kcal/mole at a concentration of 0.5 cm³ (STP)/cm³ (polymer) to −8 kcal mole⁻¹ at a concentration of 1.5 cm³ (STP)/cm³ (polymer). It has been reported in the literature that the isosteric heat of sorption for this system decreased through a minimum before increasing with increasing concentration. Our measurement of the low-pressure sorption isotherms shows that this is not the case.     

Determination of intrinsic viscosity of polymeric compounds through a single specific viscosity measurement

A modified method based on a combination of the Huggins and Schulz–Blaschke equations is proposed which enables the determination of intrinsic viscosity [η] from the measurement of a single specific viscosity. The method has been verified for different polymer samples having a wide range of [η] values and showed a variation of <±6×10⁻³% from the values obtained by Huggins extrapolation method     

Preparation of three-dimensional ordered macroporous SiCN ceramic using sacrificing template method

Three-dimensional (3D) long range well ordered macroporous SiCN ceramics were prepared by infiltrating sacrificial colloidal silica templates with the low molecular weight preceramic polymer, polysilazane. This was followed by a thermal curing step, pyrolysis at 1250 °C in a N₂ atmosphere, and finally the removal of the templates by etching with dilute HF. The produced macroporous SiCN ceramics showed high BET surface areas (pore volume) in the range 455 m²/g (0.31 cm³/g)–250 m²/g (0.16 cm³/g) with the pore sizes of 98–578 nm, which could be tailored by controlling the sizes of the sacrificial silica spheres in the range 112–650 nm. The sphere-inversed macropores were interconnected by 50 ± 30 nm windows and 3–5 nm mesopores embedded in the porous SiCN ceramic frameworks, which resulted in a trimodal pore size distribution. The surface of the achieved porous SiCN ceramic was then modified by Pt–Ru nanoparticle depositing under mild chemical conditions.