1993 рік

A linear polyethylene (LPE) has been blended with a series of random ethylene-octene copolymers of differing octene content. Melts of blends containing the lowest octene contents (2, 3, 5 and 8 mol%) showed liquid-liquid phase separation at some temperatures and for some compositions. The phase-separated regions were in the shape of closed loops and asymmetrically placed at low LPE content. This behaviour has been found previously for LPE/branched PE blends. However, unexpectedly, the phase-separated loops became smaller as the octene content of the copolymer increased. Blends of LPE with a 12 tool% octene copolymer showed extensive separation and rather different morphologies

Детальніше...  

Segmented copolymers were synthesized from poly(tetramethylene oxide) with hydroxy end-groups or aliphatic diols and a short-chain diester diamide with a uniform length. The diester diamide (N,N'-bis(p-carbomethoxybenzoyl)butanediamine) (Tm=257°C) used is made from butanediamine and an excess of dimethyl terephthalate. The polymers are prepared in the melt with Ti(OCH3H7) 4 as catalyst, for 30 min at 160-170°C under atmospheric pressure and 60 min at 250-260°C under a high vacuum. The polymers were studied by solution viscometry, differential scanning calorimetry and dynamic mechanical thermal analysis. The melting and glass transition temperatures decreased with increasing soft-block length. The crystalline order of the uniform unit is high and not very dependent on the soft-block length. The rate of crystallization is very fast. The moduli of these polymers are hardly dependent on temperature in the region between Tg and T m.

Детальніше...  

The intrinsic viscosities [~7] of some poly(methyl acrylate) fractions at 35°C have been measured in a mixture of carbon tetrachloride and methanol (CC14 + CH3OH) at different liquid compositions. The [r/I-composition plot shows a maximum for each fraction at composition ~bcn~oH (volume fraction of methanol) = 0.33. Values of the Huggins constant, determined from the slope of a plot of rlsp/C versus C, exhibit a minimum at the same composition in the Huggins constant-composition plot for almost all fractions. Huggins constant values indicate association of poly(methyl acrylate) chains in the poorer cosolvent mixtures and the association increases as the solvent becomes poorer. The molecular association decreases with increase in molecular weight. The unperturbed dimension (K0), determined from a Burchard, Stockmeyer, Fixman plot and also from other methods, varies with solvent composition and exhibits a maximum at ~bcx~on = 0.33. The molecular extension parameter cq decreases with decrease in molecular weight. Its variation with cosolvent composition is rather different : ct, shows a minimum at ~cn3on = 0.33. A possible reason for this is discussed.

Детальніше...  

It has been shown that blends of homopolymers with lightly branched copolymers exhibit liquid-liquid phase separation. The region of phase separation is asymmetrically placed towards the copolymer-rich side of the phase diagram, and the width of the region of phase separation decreases as the branch content of the copolymer increases. A simple model which can qualitatively explain the observed behaviour is presented. The basic principle is that there is an asymmetric extra term in the free energy of mixing

Детальніше...  

A low-molecular-weight poly(e-caprolactone) triol (M n = 540) was reacted with an excess of methacryloyl chloride to give a 3-arm methacrylate-endcapped polyester. The loss of the hydroxyl endgroups, which are capable of hydrogen bonding, lowered the viscosity of the polymer, thus enabling the formation of networks without solvent processing. The prepolymer was free radically homopolymerized, and copolymerized with methyl methacrylate, styrene, and 2-methylene-l,3-dioxepane to give a series of twelve biodegradable networks. Extraction studies indicated substantial network formation for all of the networks except those in which 2-methylene-1,3-dioxepane was used as the reactive diluent. A series of three low-molecular-weight poly(t>,L-lactide) triols (M,< 10000) was synthesized by the trimethylolpropane-initiated ring-opening polymerization of D,L-lactide. Number-average molecular weights of the triols were estimated to be 2300, 5100, and 8700, by using gel permeation chromatography (g.p.c.), calibrated with polystyrene standards. The triols were reacted with excess methacryloyl chloride to produce a series of low-molecular-weight 3-arm methacrylate-endcapped polyesters. These prepolymers were free radically homopolymerized, and copolymerized with methyl methacrylate and styrene to give a series of twenty-seven biodegradable networks. Extraction studies indicated substantial network formation for all of these systems. The Tg values of each of the three homopolymer networks were higher than the corresponding Tg values of either of their respective copolymer networks, thus illustrating substantial network formation in the absence of reactive diluents. The ultimate strengths and tensile modulii of the homopolymer networks synthesized from the higher-molecular-weight prepolymers (M,=5100 and 8700) were higher than those measured for corresponding copolymer networks.

Детальніше...  

Viscosity measurements of a 4,4'-diphenylmethane diisocyanate based cationomer in a low-polarity solvent, methyl ethyl ketone (MEK), and a high-polarity solvent, N,N'-dimethylformamide (DMF), and in water/MEK and water/DMF mixtures were performed. For the un-ionized sample in pure MEK and DMF, the reduced viscosities of both solutions follow the Huggins relation. For ionized samples in pure MEK and DMF, aggregation of the ionized hard segments still exists in the MEK solution but can be almost negligible in the DMF solution in the high polymer concentration range, whereas chain expansion occurs in the low polymer concentration range. For ionized samples in water/solvent mixtures, at a mixing ratio (by weight) of 0.12, the reduced viscosity indicates an aggregation behaviour in MEK/water and a polyelectrolyte behaviour in DMF/water. At a mixing ratio (by weight) between 0.24 and 4.44, the reduced viscosity indicates a polyelectrolyte behaviour. The polymer particles change from a clear elastic gel (at a water/MEK mixing ratio less than 1.0) to microspheres (at a water/MEK mixing ratio higher than 1.0). For emulsions of the ionized samples, the reduced viscosity exhibits polyelectrolyte behaviour.

Детальніше...  

statistical thermodynamics theory of polydisperse polymer blends based on a lattice model description of a fluid is formulated. Characterization of a binary polydisperse polymer mixture requires a knowledge of the pure polymer system and the interaction energy. It is assumed that the intrinsic and interactive properties of polymer (for example, T*, P*, p*, and e*) are independent of molecular size. Thermodynamic properties of ternary and higher order mixtures are completely defined in terms of the pure fluid polymer parameters and the binary interaction energies. Thermodynamic stability criteria for the phase transitions of a binary mixture are shown. The binodal and spinodal of general binary systems and of special binary systems are discussed.

Детальніше...  

A simple, high yield synthesis of 2,5-diaminoterephthalamide (DATA) from 2,5-dicarbomethoxy-l,4- cyclohexanedione (succinoyl succinate) in two steps was developed: amination with ammonium acetate followed by aromatization in the same pot; the enamino ester was ammonolysed in a second step with excess NH 3. Direct polycondensation plus cyclization of DATA with terephthalic acid in strong acid gave much better results than polycondensation of DATA with terephthaloyl dichloride in N-methyl pyrrolidone/CaC12 followed by cyclization in dehydrating strong acid. The polymer showed a disappointingly low solubility. The high viscosity and unfavourable viscoelastic behaviour at low concentration hindered satisfactory spinning and only disappointing fibres were collected. Higher concentrations -- that should have furnished nematic solutions with low viscosity and favourable viscoelasticity -- could not be reached in the solvent systems studied

Детальніше...  

Detailed results are presented of dynamic Monte Carlo simulations of the uniform star-branched polymer model confined to a diamond lattice. The model macromolecule consists off= 4 arms, every arm of identical length in the range of 11 to 199 statistical segments. The model incorporates interaction between the nearest neighbour segments and local stiffness (a preference of the trans states over both oauche states). The size and shape of a polymer chain was studied for various solvent conditions and various degrees of stiffness. The appropriate scaling laws are described. The ® conditions were also determined. Two different types of collapse transitions were found for the flexible chains and for stiff chains, similarly to the ease of linear chains.

Детальніше...  

We apply the tube model to a specific problem in polymer melt dynamics -- the rheology of star polymers as an additive to a monodisperse linear matrix. We find that the tube dilation picture of constraint release may be applied to the relaxation of the star fraction. There are four qualitatively different cases depending on the relative concentrations and relaxation times of the two fractions. Terminal relaxation times and relaxation spectra are calculated for each case. A comparison with experimental data is made in the case of dilute stars in a matrix of linear chains. This supports the theoretical prediction of a modified Rouse relaxation such that G(t)~ t-3/2.

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