Extended-chain crystals

Summary The morphology of extended chain lamellae and fibrous polytetrafluoroethylene has been analyzed by electron microscopy and compared to polyethylene. The crystal growth mechanism of initial folding on molecular nucleation followed by chain extension is applicable to both polymers and seems to be a general mechanism for crystallization of prepolymerized linear macromolecules. Differences arise from the branching mechanism of the spherulites. Annealing the striated surface created on fracture could be shown to lead to folded chain ripples of time and temperature dependent thickness. Fibrous crystals of smooth and shish-kebob-type appearance were grown from gaseous tetrafluoroethylene.

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Zusammenfassung Die Morphologie der extended chain-Lamellen und von faserigem Polytetrafluoräthylen wird elektronenmikroskopisch analysiert und mit Polyäthylen verglichen. Der Kristallwachstumsmechanismus anfänglicher Faltung bei molekularer Nukleation, gefolgt von Streckung der Ketten, kann auf beide Polymere angewendet werden und scheint ein allgemeiner Mechanismus der Kristallisation von polymerisierten linearen Makromolekülen zu sein. Unterschiede entstehen vom Verzweigungsmechanismus bei den Sphärolithen. Tempern der gestreiften Bruchflächen — so ließ sich zeigen-führt zu Riffeln von gefalteten Ketten mit zeit- und temperaturabhängigen Dicken. Faserige Kristalle vom glatten und vom Schaschlik-Typ wachsen von gasförmigem Polytetrafluoräthylen.

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For part I–VI of this series see J. Polymer Sci., Part A2, 2043–2113 (1969), Part VII, J. Polymer Sci., Part B,10, 57 (1972).

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Dedicated to ProfessorR. Hosemann on the occasion of his 60th birthday.     

Synthesis and characterization of certain aromatic polyfumaramides

Ten polyfumaramides based on p,p′-aromatic diamines and fumaric acid were synthesized by the phosphorylation method. The polymers were characterized by viscosity, solubility, infrared and UV-visible spectroscopy, and thermogravimetry. The fluorescence spectra of one of the polymers were studied. A model compound, fumaroyldianilide, was synthesized and characterized.     

Extended-chain crystals. IV. Melting under equilibrium conditions

Dilatometric melting experiments were performed on an extended-chain crystalline polyethylene with a broad molecular weight distribution and on four samples crystallized from fractionated polyethylenes. The melting curves were compared with computer calculations based on the assumption of eutectic separation. For the fraction of lowest molecular weight, agreement between experiment and calculation was achieved. The melting behavior of all other samples indicated that only for molecular weights up to 10,000–12,000 did eutectic separation occur. The higher molecular weight portion of each sample crystallized in the form of mixed crystals. Of the experimental maximum melting-point lowering of these mixed crystals, 0.1–0.9°C is due to the lower molecular weight diluents. Another 2–3°C lowering in melting point is due to the fact that the phase diagram of polyethylene mixed crystals has a minimum.     

Aromatic polyamides

Kinetics of the initial degradation of poly(1,3-phenylene isophthalamide) and of poly(chloro-2, 4-phenylene isophthalamide) has been studied by TG in inert as well as oxidative atmospheres. The information derived from the kinetic data is in agreement with our earlier reported studies on the degradation mechanism of these polyamides. The difference-differential method of Freeman-Carroll is shown to have problems when applied to high-char forming polymeric materials. The isoconversion method of Ozawa involving simple computations based on a particular reaction extent, is considered suitable for studying the complex degradation behavior of high-temperature and high-char forming polymer systems. Using this procedure, an activation energy of 215–230 kJ/mole is obtained for the initial degradation of the studied aromatic polyamides in inert and oxidative environments.     

Ferrocene-containing polyesters and polyamides

A series of ferrocene-containing polyesters and polyamides were prepared by refluxing 1,1′-dichlorocarbonylferrocene with various diols and primary diamines in xylene–pyridine solvent. The polyamides were all solids, but some of the polyesters were liquids. Reported are the infrared spectra and solubility characteristics of all the polymers and, where possible, the molecular weight and molecular weight distributions. In general, these polyamides and polyesters were of relatively low molecular weight (below 4000), but the polyesters were readily chain extended and crosslinked by di- and triisocyanates. Elemental analyses are reported for all the polymers prepared.     

Review: Auto-oxidation of aliphatic polyamides

The literature on oxidation kinetics of polyamides and model compounds has been reviewed in order to try to extract suitable information for non-empirical kinetic modeling. Polyamide characteristics are systematically compared to polyolefin ones, these latter being more extensively studied. From kinetic analysis point of view, it is shown that oxidation attacks predominantly α amino methylenes of which C–H bond is considerably weaker than the other methylenes. As a result, propagation by H abstraction is considerably faster in polyamides than in polyethylene for instance. Termination by radical combination is also very fast. Another cause of PA oxidizability is the instability of α amino hydroperoxides linked to the inductive effect of nitrogen. This instability is responsible for many key features of oxidation kinetics especially the absence of induction period.     

Photodegradable polyamides

Unique photodegradable polyamides have been prepared by solution polymerization of diphenyl α-truxillate or δ-truxinate with hexamethylene or nonamethylenediamine, followed by melt polymerization. Photochemical properties of resulted polyamides were studied spectroscopically and are discussed in terms of photoreversibility and monomeric derivatives for comparison. Solution viscosity of the polymer was decreased by irradiation with a high-pressure mercury lamp. The polymers from α-truxillic acid depolymerize by the action of monochromatic light of 224 mμ to give rise to cinnamyl groups faster than those from δ-truxinic acid. On the photodegradation of polyalkylene-δ-truxinamide, two types of scission of cyclobutane were found: symmetrical scission, giving rise to two cinnamyl groups, and a symmetrical scission, giving rise to one trans-stilbene and one fumaramide linkage. The intense absorption peak due to cinnamyl groups at 272 mμ of partially photodepolymerized films diminished by the action of 304 mμ light; this can be accounted for by the recombination of cinnamyl groups into cyclobutane ring and some unidentified crosslinking reactions. The photochemical behavior of cyclobutane in the polyamides studied proved to be consistent with that of monomeric derivatives reported previously. The study on thermal properties of the polymers by DTA and TGA revealed that this type of polyamide is quite stable as high as 350°C unless significant steric effects are involved.     

Phenothiaphosphine-containing polyamides and polyesters

Phosphorus-containing polyamides and polyesters, which had tricyclic fused rings (phenothia-phosphine rings) in the main chain, were prepared and the properties of the resulting polymers were examined. These polymers were obtained at highly reduced viscosities in satisfactory yields by the polycondensation of 2,8-dichloroformyl-10-phenylphenothiaphosphine 5,5,10-trioxide with aromatic diamines or bisphenols. The polyamides and polyesters were soluble in polar aprotic solvents such as dimethylacetamide and N-methyl-2-pyrrolidone; the polyesters were also soluble in chloroform. The polymers exhibited good heat resistance. The phenothiaphosphine-containing polyamides and polyesters self-extinguished immediately when flame was removed and were highly flame-resistant. The polyester obtained from bisphenol A showed a limiting oxygen index value of 43.5.     

Phenoxasilin-containing polyamides and polyesters

Silicon-containing polyamides and polyesters of a new type have been synthesized. They contain phenoxasilin rings with double-stranded structure. The polymers were synthesized by the interfacial polycondensation of 2,8-dichloroformyl-10,10-diphenylphenoxasilin with diamines and bisphenols, and were obtained in nearly quantitative yields. Their reduced viscosities were in the range of 0.53–1.47 dl g^?1 m dimethylformamide (DMF), m-cresol or chloroform. Some of the polyamides were soluble in polar aprotic solvents such as DMF and N-methyl-2-pyrrolidone (NMP) and the polyesters had good solubility in chloroform, phenol-sym tetrachloroethane (60:40 by wt %) and acidic solvents (m-cresol and nitrobenzene). The polymers hardly dissolved in cone. H₂SO₄ and some of them coloured in it. Only the polyester having sulphide bonds was soluble in benzene in addition to the above organic solvents. These polymers hardly degraded below 400° except for the polyamides derived from aliphatic diamines. The polymers from aliphatic diamines melted at 290–325°; the other polyamides and the polyesters decomposed without melting.     

Phenazasiline-containing polyamides and polyesters

A Phenazasiline ring was incorporated into a polymer backbone by polycondensation of 2,8-dichloroformyl-5,10-dihydro-5-methyl-10,10-diphenylphenazasiline (V) with aromatic diamines or bisphenols, and phenazasiline-containing polyamides and polyesters were obtained. The polyamides were prepared by low-temperature solution polycondensation in N-methyl-2-pyrrolidone (NMP) in the presence of lithium chloride. The polyesters were synthesized by interfacial polycondensation in a mixture of 1,2-dichloroethane and aqueous alkali in the presence of tetrabutylammonium chloride as an accelerator. These reaction conditions gave the corresponding polymers with high viscosities. The phenazasiline-containing polyamides exhibited good solubilities in polar aprotic solvents such as dimethylformamide, dimethylacetamide, and NMP, and also in m-cresol, although the polyesters showed limited solubilities in organic solvents. Under nitrogen, the phenazasiline-containing polyamides and polyesters showed little degradation below 400°C and had good heat resistance.     

Extended-chain crystals. II. Crystallization of polyethylene under elevated pressure

A report on crystallization of polyethylene at elevated pressures to an extended-chain morphology is presented. The crystals have been characterized by electron microscopy and density determination. Pressure, supercooling (temperature), and crystallization time have been varied to find the best conditions for production of perfect crystals. At 10–30°C supercooling completely crystallized polyethylene was obtained between 4.5 and 7 kb crystallization pressure in 1–8 hr. Analysis of fracture surfaces of samples crystallized for different lengths of time shows an increase in size and number of crystal lamellae and an improvement of extended chain crystals in the early stages of crystallization. A further improvement of the less well crystallized material between the lamellae occurs after 15 min of crystallization time.     

Substituted rod-like aromatic polyamides: Synthesis and structure-property relations

The synthesis and structure-property relations of a number of novel substituted paralinked aromatic homopolyamides and copolyamides are described. The synthesis of the polyamides was carried out by polycondensation of activated N,N'-bis-(trimethylsilyl) substitued aromatic diamines and aromatic diacid chlorides. In order to improve the solubility and to lower melting temperatures, novel arylsubstituted terephthalic acids moieties, such as p-terphenyl-2,5-dicarboxylic acid and o-terphenyl-2,5-dicarboxylic acid, were used in combination with substituted and noncoplanar diamines. Depending on the chemical structure, polyamides with very high solubility (up to 40% w/w) in polar aprotic solvents such as N,N-dimethylacetamide without the addition of inorganic salts were obtained. Lyotropic liquid crystalline behavior was observed for the first time in polyamides which contain noncoplanar biphenylene units.     

Dendritic aromatic polyamides and polyimides

The syntheses and properties of dendritic and hyperbranched aromatic polyamides and polyimides are reviewed. In addition to conventional stepwise reactions for dendrimer synthesis, an orthogonal/double‐stage convergent approach and dendrimer syntheses with unprotected building blocks are described as new synthetic strategies for dendritic polyamides. Hyperbranched polyamides and polyimides composed of various repeating units are presented. Besides the self‐polycondensation of AB₂‐type monomers, new polymerization systems with AB₄, AB₈, A₂ + B₃, and A₂ + BB′₂ monomers have been developed for hyperbranched polyamides and polyimides. The copolymerization of AB₂ and AB monomers is discussed separately with respect to the effects of branching units on the properties. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1293–1309, 2004     

N-methyl-substituted aromatic polyamides

A series of N-methyl-substituted aromatic polyamides derived from the secondary aromatic diamines 4,4′-bis(methylamino)diphenylmethane, 3,3′-bis(methylamino)diphenylmethane, 4,4′-bis(methylamino)benzophenone or 3,3′-bis(methylamino)benzophenone and isophthaloyl dichloride, and terephthaloyl dichloride or 3,3′-diphenylmethane dicarboxylic acid dichloride was prepared by high-temperature solution polymerization in s-tetrachloroethane. Compared with analogous unsubstituted and partly N-methylated aromatic polyamides, the full N-methylated polyamides exhibited significantly lower glass transition temperatures (T_g), reduced crystallinity, improved thermal stability, and good solubility in chlorinated solvents.