Three lightly branched commercial polyethylene copolymers, produced using the metallocene catalyst process, were blended together in binary pairs. Two of the materials were ethylene–butene copolymers of differing butene content, the third was an ethylene–hexene copolymer with the same branch content as the more lightly branched ethylene–butene material. Note that the components of one system differ in both branch type and branch content; those of another, in branch content but not branch type; and those of the third in branch type only. Morphology maps were produced for all three systems. Where the two components had the same branch content, only one crystal type was seen on quenching melts of all compositions from all temperatures. Where the branch contents varied, two crystal types were seen when blends of some compositions were quenched from some temperatures, and the morphology maps resembled those found when copolymers produced by traditional methods are blended—or when a linear polyethylene is blended with a lightly branched copolymer. These findings confirm the view that it is the branch content of the copolymers that effects the morphology most strongly, the branch type is of secondary importance.
In highly oriented polymers, stress can stabilize fibres against melting by favouring the low entropy fibrillar state against the high entropy melt. In this work we have investigated the thermal stability of gel-spun ultra-high modulus polyethylene subjected to tensile stress. The Daresbury X-ray synchrotron radiation source and optical microscopy have been utilized to follow dynamically the transformation, melting and recrystallization of fibres, under optimum conditions of controlled stress. The orthorhombic phase is stable up to 164°C, after which the crystals transform into a hexagonal phase which can be stable up to temperatures as high as 179°C. Whilst this is the greatest thermal stability reported for the orthorhombic phase, the question of the ultimate stability is still unanswered and is presently limited by the effectiveness of the stress transfer to the fibrils.
Random copolyesters were obtained by the reactions of 1,4-benzenedimethanol, trans-1,4-cyclohexane-dimethanol or 1,4-bicyclo[2.2.2]octanedimethanol and 1,4-dihydroxybicyclo[2.2.2]octane with bicyclo [2.2.2]octane-1,4-dicarbonyl chloride or trans-1,4-cyclohexanedicarbonyl chloride. A number of these copolyesters formed brightly coloured birefringent melts.
We report the change in interfacial Brownian dynamics upon adsorption of a polymer chain to an immobile substrate. Using C-13 nuclear magnetic resonance spin-lattice relaxation measurements, we have found that the presence of polymer loops and tails slows Brownian motion within a region approximately 7 angstrom from the surface by roughly 25%. We have also found that these interfacial dynamics are insensitive to molecular weight.
This paper provides experimental data which have been used to estimate the thermal diffusivity of a polyurethane in nitrogen gas at 0.1 and 40 MPa in the temperature range 20-60-degrees-C. The thermal diffusivity increases from 5 x 10(-8) to 2.5 x 10(-7) m2 s-1 on the application of the pneumatic pressure. It is concluded that the main reason for this increase is due to an increase in the thermal diffusivity of the system when it imbibes a significant quantity of gas. At ambient pressure the phonon damping length of the elastomer is about 2 nm and we have concluded that this length is essentially unaffected by the high pressure gas environment. At high gas concentrations the mean free path of the particle-particle collisions in gas-polymer solutions reduces. If this distance becomes significantly less than the phonon damping length of the polymer we speculate that the thermal conductivity will then be enhanced by an efficient gas-particle momentum exchange process. Such processes are ineffective at the low gas concentrations which exist at ambient pressure.
Direct C-13 n.m.r. evidence for chain transfer to polymer in emulsion polymerization of n-butyl acrylate is reported. This reveals that the reaction proceeds by abstraction of tertiary C-H bonds in n-butyl acrylate repeat units and, under the usual condition of high instantaneous conversion, leads to polymers with high extents of branching (10-20 branches per 1000 backbone carbon atoms). Changes in molar mass distribution during emulsion polymerization correlate with observations on the extent of chain transfer to polymer.
An aromatic polyazomethine (PAM) was prepared by two routes from a novel bisdecyloxyterephthaldehyde monomer and 1,4-phenylenediamine. The extended chains prepared were comparable in molecular weight to previously prepared polyazomethines based on solution viscosity values; however, the PAM polymers exhibited total solubility in protonating acidic media only.
Mechanical damping measurements of small amplitude are superimposed on polycarbonate strained in the non-linear viscoelastic range. The experiments are carried out on specimens aged at room temperature for various lengths of time after quenching from above T(g). A simple rheological model is used to described the stress and time dependence of the viscosity. It is derived that the increase of viscosity at the first stage of deformation may result from the non-linearity of the stress-strain relationship, without any change of the parameter linked to the structural state, whereas the influence of preliminary ageing that manifests itself by an increase of the viscosity under stress is consistent with free volume relaxation.
The dilute solution behaviour of secondary amine telechelic polybutadiene neutralized with organic acids is reported. In non-polar medium, an increase in viscosities of the solutions (compared to non-neutralized polymer) was found, due to polymer chain-end associations resulting from ammonium-carboxylate ion pair formation. The extent of the association was dependent on the nature of the neutralizing agent and the dielectric constant of the solvent. The addition of low amounts of polar cosolvent did not have any appreciable effect on the viscosity of the solution.
The thermochromic transition in poly(3-pentylthiophene), prepared by chemical polymerization, has been characterized. A high density of head-head defects in the polymer main chain limits the conjugation length. The thermochromic transitions occur at much lower temperatures than observed in Grignard-synthesized poly(3-alkylthiophenes). We show that the molecular and electronic models of thermochromism can account for these observations.
The liquid chromatographic behaviour of sulphonated urea-melamine-formaldehyde resins was investigated in aqueous eluents using various stationary phases. It was demonstrated that electrostatic interactions, including ion exclusion and association phenomena, can be successfully eliminated when aqueous sodium sulphate solution or ion-pair reagents were used as the mobile phase. Molar masses were determined using a calibration based on sodium polystyrene sulphonate and the influence of the ratio of the resin components was discussed.
A spherulite-like structure has been found for the casting film of polyethersulphone (PES) blended with a thermotropic liquid crystal polymer. This ordered structure displayed different characteristics from other typical crystalline polymers. The formation and the nature of the PES globules was investigated and discussed.
A series of copoly(imidine esters) was synthesized via polycondensation of aromatic diacid chlorides with a phenol-terminated bis(benzylidenepthalimide). The phenol-terminated monomer was prepared by condensing 3,5-dibenzylidenepyromellitide with p-anisidine followed by treatment with boron tribromide. The diacids used in this work were 2,2-bis(4-chloroformylphenyl)hexafluoropropane and 2,2-bis(4-chloroformylphenyl)propane. The polymers derived from these monomers had inherent viscosities ranging from 0.31 to 0.50 dl g-1 and exhibited good solubility in polar aprotic solvents such as N,N-dimethylacetimide and N-methylpyrolidone. Thermal analyses of these polymers showed thermal stability up to 487-degrees-C by thermal gravimetric analysis and no thermal transitions below 300-degrees-C by differential scanning calorimetry.
Copolyesters were prepared by bulk polycondensation of mixtures of terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4,4'-oxydibenzoic acid and ethylene glycol. Their H-1 nuclear magnetic resonance (n.m.r.) and C-13 n.m.r. spectra were then recorded. C-13 n.m.r. of oxyethylenic groups does not appear sensitive to sequence effects; on the contrary H-1 n.m.r. chemical shifts of oxyethylenic protons depend on their insertion between different couples of acidic residues. The calculated distribution of acidic moieties within the polymers is random.
The synthesis and properties of the first member of a new and novel class of reactive polymers, open chain poly(Reissert compounds), have been investigated.
The disodium salt of glycerol 2-phosphoric acid was acidified with cold concentrated hydrochloric acid. The free glycerol 2-phosphoric acid was then extracted with dimethyl sulphoxide and ethanol. The acidic diol, a solid at room temperature with a boiling point of 230-degrees-C, was very hygroscopic. The phosphate diol was incorporated into the polyurethane using methylene di(4-phenyl isocyanate), and polypropylene glycol as the soft segment, by the step growth solution copolymerization in dimethyl sulphoxide at 90-degrees-C in the presence of a catalyst, di-n-butyltin dilaurate. Nuclear magnetic resonance spectroscopy, infra-red spectroscopy, thermogravimetric analysis, stress/strain analysis and the solubility, with different ionic contents of the ionomer, were investigated. The ionic strength of this ionomer is relatively low because the ionic groups are not in the form of salt, but of the acid, and this is reflected in the properties.
Radical copolymerizations of eight kinds of N-alkylcitraconimides with alpha-methylstyrene in bulk at 40-degrees-C gave alternating copolymer shaving number-average molecular weights in the range of 3400-7100 depending on the N-alkyl substituents.
Etude par osimetrie, pHmetrie, conductimetrie et spectrophotometrie de la formation de complexes formes avec l'ion Cu 2+ par des intercopolymeres entre un copolymere acrylamide/acide acrylique, un copolymere methacrylamide/acide methacrylique, la poly(vinyl pyrrolidone) et la polyethyleneimine en solution aqueuse. Discussion du mode de formation des complexes
The photophysical behaviour of aqueous dispersions of three water-soluble copolymers based upon methacrylic acid (MAA) and 1-vinylnaphthalene (1-VN), containing 1, 13 and 36 mol% 1-VN, has been studied. The singlet state photophysics are complex and dependent upon the degree to which excimer states are accessed. This, in turn, is governed by the copolymer composition and the pH of the medium which controls the conformational characteristics of the macromolecule. The hydrophobic domains which are created within the higher aromatic content copolymers are capable of solubilization of hydrocarbons. These hydrophobic cavities provide a protective environment both for occluded guests and the chromophoric species which form the 'cavity'. Room temperature phosphorescence can be both generated and sustained within the cavity. This unique observation paves the way for the generation of a novel class of media for use in analytical applications in which simultaneous isolation of fluorescence and phosphorescence in aqueous dispersion might be of importance.
