Syndiotactic 1,2-polybutadiene with Co-CS2 catalyst system. I. Preparation,properties, and application of highly crystalline syndiotactic 1,2-polybutadiene

Highly crystalline syndiotactic 1,2-polybutadiene (s-PB) having melting point (mp) up to 216°C was obtained by using a Co(acac)₃-AIEt₃-CS₂ catalyst. The polymer with mp 208°C was found to have 99.7% 1,2 content and 99.6% syndiotacticity by ¹H and ¹³C-NMR measurements. The s-PB can be molded by addition of a stabilizer such as 2,6-di-t-butyl-4-hydroxymethylphenol into fiber, film, and various shaped articles. The physical properties presented in the present article include stress-strain and dynamic mechanical behavior. The highly crystalline syndiotactic 1,2-polybutadiene was applied to a carbon fiber and UBEPOL VCR (cis-1,4-polybutadiene reinforced by fibrous syndiotactic 1,2-polybutadiene).     

Syndiotactic 1,2-polybutadiene with Co-CS2 catalyst system. III. 1H- and 13C-NMR study of highly syndiotactic 1,2-polybutadiene

The ¹H and ¹³C-NMR spectra of highly crystalline syndiotactic 1,2-polybutadiene (s-PB) are discussed in order to clarify the mechanism of butadiene polymerization with cobalt compound–organoaluminum–CS₂ catalysts. Cis opening of the double bonds in the syndiotactic polymerization is affirmed by the study of the copolymer from perdeuteriobutadiene and cis,cis-1,4-dideuteriobutadiene. S-PB (mp 210°C) has 99.7% 1,2 units, 0.3% isolated cis-1,4 units, and 99.6% syndiotacticity. Polymer ends (2-methyl-3-butenyl group and conjugated diene structure) are also determined. The differences in free energy of activation between 1,2 and cis-1,4 propagation and between syndiotactic and isotactic propagation are 14.0 and 9.6 kcal/mol, respectively, for Co(acac)₃-AlEt₃-AlEt₂Cl-CS₂, and 6.7 and 5.7 kcal/mol, respectively, for the aluminum-free Co(C₄H₆)(C₈H₁₃)CS₂ system. The conformation of s-PB in o-dichlorobenzene at 150°C is described by the sequence (tt)_1.6(gg)(tt).     

Syndiotactic 1,2-polybutadiene with Co-CS2 catalyst system. II. Catalysts for stereospecific polymerization of butadiene to syndiotactic 1,2-polybutadiene

Butadiene is polymerized by cobalt compound–organoaluminum–CS₂ catalysts to give highly crystalline syndiotactic 1,2-polybutadiene (s-PB) having melting point up to 216°C. An aluminum-free catalyst, Co(C₄H₆)(C₈H₁₃)-CS₂, is also effective. Syndiotactic polymerization with Co(C₄H₆)(C₈H₁₃)-CS₂ is not interrupted by the addition of protic substances such as water and alcohol, but is influenced by donor or acceptor substances. The donor molecule, e.g., dimethylsulfoxide or dimethylformamide, decreases the stereoregularity, i.e., syndiotacticity and 1,2 content. An acceptor molecule of organoaluminum with appropriate acidity such as AlEt₃-AlEt₂Cl or tetraethylaluminoxane increases the molecular weight, stereoregularity, and yield of the polymer. In the presence of CS₂ a mixture of cis-PB and s-PB was obtained by using Co(octoate)₂-AlEt₂Cl-H₂O, with molar ratio H₂O/Co less than unity. In the case of H₂O/Co > 1, only cis-PB was obtained. By the addition of donor substances such as ester, ether, nitrile, and AlEt₃, s-PB was obtained even when H₂O/Co > 1. The amount and ratio of cis-PB and s-PB are dependent upon the nature and amount of the additives.     

Thermally induced polymerization of isobutylene in the presence of SnCl4: Kinetic study of the polymerization and NMR structural investigation of low molecular weight products

The polymerization reactivity of isobutylene/SnCl₄ mixtures in the absence of polar solvent, was investigated in a temperature interval from −78 to 60 °C. The mixture is nonreactive below −20 °C but slow polymerization proceeds from −20 to 20 °C with the initial rate r₀ of the order 10⁻⁵ mol · l⁻¹ · s⁻¹. The rate of the process increases with increasing temperature up to ∼10⁻² mol · l⁻¹ · s⁻¹ at 60 °C. Logarithmic plots of r₀ and M̄_n versus 1/T exhibit a break in the range from 20 to 35 °C. Activation energy is positive with values E = 21.7 ± 4.2 kJ/mol in the temperature interval from −20 to 35 °C and E = 159.5 ± 4.2 kJ/mol in the interval from 35 to 60 °C. The values of activation enthalpy difference of molecular weights in these temperature intervals are ΔH_Mn = −12.7 ± 4.2 kJ/mol and −38.3 ± 4.2 kJ/mol, respectively. The polymerization proceeds quantitatively, the molecular weights of products are relatively high, M̄_n = 1500–2500 at 35 °C and about 600 at 60 °C. It is assumed that initiation proceeds via [isobutylene · SnCl₄] charge transfer complex which is thermally excited and gives isobutylene radical‐cations. Oxygen inhibits the polymerization from −20 to 20 °C. Possible role of traces of water at temperatures above 20 °C is discussed. It was verified by NMR analysis that only low molecular weight polyisobutylenes are formed with high contents of exo‐ terminal unsaturated structures. In addition to standard unsaturated groups, new structures were detected in the products. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1568–1579, 2000     

Synthesis,conformation transition,liquid crystal phase,and self‐assembled morphology of thermosensitive homopolypeptide

Thermosensitive diethylene glycol‐derived poly(L ‐glutamate) homopolypeptides (i.e., poly‐L ‐EG₂‐Glu) with different molecular weights (MW) (M_n,GPC = 5380–32520) were synthesized via the ring‐opening polymerization (ROP) of EG₂‐L ‐glutamate N‐carboxyanhydride (EG₂‐Glu‐NCA) in N,N‐dimethylformamide solution at 50 °C. Their molecular structure, conformation transition, liquid crystal (LC) phase behavior, lower critical solution temperature (LCST) transition, and morphology evolution were thoroughly characterized by means of FTIR, ¹H NMR, gel permeation chromatography, differential scanning calorimetry, wide angle X‐ray diffraction, polarized optical microscope, transmission electron microscope, and dynamic light scattering. In solid state, the homopolypeptide poly‐L ‐EG₂‐Glu presented a conformation transition from α‐helix to β‐sheet with increasing their MW at room temperature, while it mainly assumed an α‐helix of 80–86% in aqueous solution. Poly‐L ‐EG₂‐Glu showed a thermotropic LC phase with a transition temperature of about 100 °C in solid state, while it gave a reversible LCST transition of 34–36 °C in aqueous solution. The amphiphilic homopolypeptide poly‐L ‐EG₂‐Glu self‐assembled into nanostructures in aqueous solution, and their critical aggregation concentrations decreased with increasing MW. Interestingly, their morphology changed from spherical micelles to worm‐like micelles, then to fiber micelles with increasing MW. This work provides a simple method for the generation of different nanostructures from a thermosensitive biodegradable homopolypeptide. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Multimodal sorption of nonionic dyes with two amino groups by various polymers from water

Sorption isotherms of nonionic dyes with two amino groups (one anthraquinone dye and two azo dyes) on various polymers from water were measured at 40–90°C (Nylon-6 and cellulose film) and at 95°C (polyester microfiber). The isotherms were curved, convex to upward, in the range of low dye concentration C_s in water and almost linear in the range of medium to saturated C_s. The isotherms measured at low temperature (40°C for cellulose, 40–60°C for Nylon-6, and at 95°C for polyester) were satisfactorily described by considering three concurrent modes of sorption. They are Nernst type partitioning and bimodal Langmuir sorption (sorption by the higher affinity sites with a small saturation value and that by the lower affinity sites with a large saturation value). However, for the sorption of the anthraquinone dye and one azo dye by Nylon-6 film at high temperature (80–90°C), the amount of dye sorbed by the high affinity site decreased to negligibly small. Accordingly, the isotherms were expressed well by simple dual-sorption model. © 1995 John Wiley & Sons, Inc.     

Preparation and some properties of nylon 46

Nylon 46 was synthesized from the salt of 1,4-diaminobutane and adipic acid. High molecular weight polymers could be obtained by reaction for 1 hr at 215°C in a closed system and at least for 1 hr in vacuo at a temperature in the range 290–305°C. The reactions at 290°C were found to have taken place in the solid state and those at 305°C in the melt. The highest molecular weights (M?_w ca. 45,000) were obtained by reaction at 290°C with a nylon salt with a pH of 7.8–8.0. The molecular weight characteristics were studied with end-group analysis, viscometry, light scattering, and ultracentrifugation. The polymers were found to be gel-free and monodisperse (M?_w/M?_n ～ 1.15). Films could be cast from formic acid. From x-ray diffraction patterns, measured on such films, spacings of 3.74 and 4.30 Å were calculated, whereas a long period of 66 Å was also found. The infrared spectra showed all the usual amide bands of even–even polyamides. The melting temperature was found to vary between 283 and 319°C, depending on the thermal history of the sample. Water absorption measured on a cast film showed this to be very hygroscopic (7.5% at 65% RH), while a highly crystalline sample absorbed only little water (1.6% at 65% RH).     

Thermal stability of shear-induced precursor structures in isotactic polypropylene by rheo-X-ray techniques with couette flow geometry

Combined in situ rheo-SAXS (small-angle X-ray scattering) and -WAXD (wide-angle X-ray diffraction) studies using couette flow geometry were carried out to probe thermal stabilty of shear-induced oriented precursor structure in isotactic polypropylene (iPP) at around its normal melting point (162 °C). Although SAXS results corroborated the emerging consensus about the formation of “long-living” metastable mesomorphic precursor structures in sheared iPP melts, these are the first quantitative measures of the limiting temperature at which no oriented structures survive. At the applied shear, rate = 60 s⁻¹ and duration t_s = 5 s, the oriented iPP structures survived a temperature of 185 °C for 1 h after shear, while no stable structures were detected at and above 195 °C. Following Keller's concepts of chain orientation in flow, it is proposed that the chains with highly oriented high molecular weight fraction are primarily responsible for their stability at high temperatures. Furthermore, the effects of flow condition, specifically the shear temperature, on the distributions of oriented and unoriented crystals were determined from rheo-WAXD results. As expected, at a constant flow intensity (i.e., rate = 30 s⁻¹ and duration, t_s = 5 s), the oriented crystal fraction decreased with the increase in temperature above 155 °C, below which the oriented fraction decreased with the decrease in temperature. As a result, a crystallinty “phase” diagram, i.e., temperature versus crystal fraction ratio, exhibited a peculiar “hourglass” shape, similar to that found in many two-phase polymer–polymer blends. This can be explained by the competition between the oriented and unoriented crystals in the available crystallizable species. Below the shear temperature (155 °C), the unoriented crystals crystallized so rapidly that they overwhelmed the crystallization of the oriented crystals, thus depleting a major portion of the crystallizable species and increasing their contribution in the final total crystalline phase. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3553–3570, 2006     

Lactones ofFerula gigantea

The following substances have been isolated from an acetone extract ofFerula gigantea B. Fedtsch.: a coumarin — umbelliferone, C₉H₆O₂, mp 230–233°C; and sesquiterpene lactones — talassin A, C₂₅H₃₀O₇, mp 188–191°C; malaphyllinin, C₂₄H₂₄O₇, mp 231–235°C; malaphyll, C₂₉H₃₂O₉, mp 212–213°C; and malaphyllin, C₂₆H₂₈O₉, mp 216–218°C. Structures have been proposed for three new sesquiterpene lactones on the basis of an analysis of their spectral characteristics.     

Electrical and self‐heating properties of UHMWPE‐EMMA‐NiCF composite films

Conductive polymer composites (CPC) containing nickel‐coated carbon fiber (NiCF) as filler were prepared using ultra‐high molecular weight polyethylene (UHMWPE) or its mixture with ethylene‐methyl methacrylate (EMMA) as matrix by gelation/crystallization from dilute solution. The electrical conductivity, its temperature dependence, and self‐heating properties of the CPC films were investigated as a function of NiCF content and composition of matrix in details. This article reported the first successful result for getting a good positive temperature coefficient (PTC) effect with 9–10 orders of magnitude of PTC intensity for UHMWPE filled with NiCF fillers where the pure UHMWPE was used as matrix. At the same time, it was found that the drastic increase of resistivity occurred in temperature range of 120–200 °C, especially in the range of 180–200 °C, for the specimens with matrix ratio of UHMWPE and EMMA (UHMWPE/EMMA) of 1/0 and 1/1 (NiCF = 10 vol %). The SEM observation revealed to the difference between the surfaces of NiCF heated at 180 and 200 °C. Researches on the self‐heating properties of the composites indicated a very high heat transfer for this kind of CPCs. For the 1/1 composite film with 10 vol % NiCF, surface temperature (T_s) reached 125 °C within 40 s under direct electric field where the supplied voltage was only 2 V corresponding to the supplied power as 0.9 W. When the supplied voltage was enough high to make T_s beyond the melting point of UHMWPE component, the T_s and its stability of CPC films were greatly influenced by the PTC effect. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1253–1266, 2009     

Poly[3,3-bis(hydroxymethyl) oxetane]—an analog of cellulose: Synthesis,characterization, and properties

Poly[3,3-bis(hydroxymethyl)oxetane], PBHMO, was prepared in high molecular weight (η_inh up to 5.2) by polymerizing the trimethylsilylether of 3,3-bis(hydroxymethyl)oxetane with the i-Bu₃Al–0.7 H₂O cationic catalyst at low temperature, followed by hydrolysis. PBHMO is crystalline, very high melting (314°C) and highly insoluble, much like its analog, cellulose. It is soluble in 75% H₂SO₄ at 30°C, being 65% converted to the acid sulfate ester; these conditions are useful for viscosity measurement, since the degradation rate is low and at least an order of magnitude less than for cellulose in this solvent. PBHMO can be prepared as oriented films and fibers using the lower melting diacetate (184°C) which can be melt or solution (CHCl₃) fabricated and then the oriented forms saponified to oriented PBHMO. BHMO can be directly polymerized to low molecular weight, perhaps somewhat branched, PBHMO (η_inh 0.1) with trifluoromethanesulfonic acid catalyst at room temperature. Poly(3-methyl-3-hydroxymethyloxetane), (PMHMO), prepared in high molecular weight (η_inh up to 3.8) by the same method used for PBHMO, is more soluble and lower melting (165°C) than PBHMO, appears to be atactic and can be compression molded at 195°C to a tough, clear film which is readily oriented. Copolymers of BHMO with MHMO are crystalline over the entire composition range with a linear variation of T_m with composition, a new example of isomorphism in the polymer area.     

Flavonoids of inflorescences of Calendula officinalis

By column chromatography on polyamide sorbent, the inflorescences of pot marigold calendula have yielded eight substances of flavonoid nature: two aglycons — quercetin (C₁₅H₁₀O₇, mp 309–311°C) and isorhamnetin (C₁₆H₁₂O₇, mp 314–316°C); six glycosides, of which three have been identified as isoquercetin (C₂₁H₂₀O₁₂, [α] _D ²⁰ ?36° in methanol, mp 218–220°C), isorhamnetin 3-O-β-D-glucoside (C₂₂H₂₂O₁₂, [α] _D ²⁰ ?59° in dimethylformamide, mp 193–195°C), narcissin (C₂₈H₃₂O₁₆, [α] _D ²¹ ?28° in dimethylformamide, mp 180–182°C), and three substances that have proved to be new and have been called calendoflaside (C₂₈H₃₂O₁₅, [α] _D ²¹ ?85° in methanol, mp 192–195°C; calendoflavoside (C₂₈H₃₂O₁₆, [α] _D ²⁰ ?106° in methanol, mp 189–192°C), and calendoflavobioside (c₂₇H₃₀O₁₆, [α] _D ²⁰ ?105° in methanol, mp 194–197°C).     

8,13-Epoxylabd-14-en-19-oic acid — A component of the needles ofPinus sylvestris

8,13-Epoxylabd-14-en-19-oic [(mannoyl oxide)-19-oic] acid, mp 64–66°C, [α]_D ?39.2° (c 1.0; ethanol) has been isolated from the needles ofPinus sylvestris. The following derivatives have been obtained: methyl 8,13-epoxylabd-14-en-19-oate, with mp 83–85°C, [α]_D ?43.2° (c 1.2; ethanol); 8,13-epoxylabd-14-en-19-ol, an oil, [α]_D ?10.9° (c 1.0; ethanol), n _D ²⁵ 1.5025, cyclohexylammonium salt with mp 113–115°C, [α]_D ?29.3° (c 1.0; ethanol); and 8,13-epoxydihydrolabd-14-en-19-oic acid with mp 61–63°C, [α]_D ?23.1° (c 1.0; ethanol). The structures of the compounds were established by IR, mass, PMR, and¹³C NMR spectroscopy.     

Purification and Characterization of Pectin Lyase Produced by Aspergillus terricola and its Application in Retting of Natural Fibers

An indigenously isolated fungal strain identified as Aspergillus terricola with assigned fungal strain number MTCC 7588 has been used as source for pectin lyase production. The extracellular pectin lyase was purified to homogeneity from the culture filtrate of A. terricola by ion exchange and gel filtration chromatography. The determined molecular weight was 35 ± 01 kDa. The K _m and k _cat (turnover) values of the purified enzyme at 37 °C using citrus pectin as the substrate were found to be 1.0 mg/ml and 110.0 s⁻¹, respectively. The pH and temperature optima of the enzyme were 8.0 and 50 °C, respectively. The retting ability of the purified pectin lyase for natural fibers viz. Cannabis sativa and Linum usitatissimum has been demonstrated for the first time.     

Polybromostryl macromers and their anionic polymerization

The decomposition of polybromostyryl carbanions (PBS^?), obtained by anionic polymerization of 4-bromostyrene in tetrahydrofuran (THF), was investigated in the dark in a temperature range of ?6–?21°C. It was accompanied by the evolution of bromine anions and by the formation of polymeric allylic carbanions (λ_max = 575 nm; ε_max = 6800 eq^?1·L·cm^?1). The reaction mechanism was elucidated. The rate constant of the unimolecular rate-determining step of the process was 1.3 × 10^?5 s^?1 and 9.7 × 10^?5 s^?1 at ?21 and ?6°C, respectively. Its apparent energy of activation E_app = 18.38 Kcal/mol. The polybromostyrenes with allylic carbanions at their ends may decompose further. Their “dark” decomposition yielded 1,3-butadiene-1,3-diphenyl-macromers. The mechanisms of decomposition of the PBS^? carbanions and the dark decomposition of the polybromostyryl allylic carbanions are analogous. The rate constant of the latter process was 2.5 × 10^?6 s^?1 at ?6°C. The anionic polymerization of prepared macromers can be initiated in THF at ?78°C by α-methylstyryl carbanions, which do not react, however, with PBS^? carbanions. “Comblike” polymacromers were prepared in which each branch had a molecular weight of about 50,000. The overall molecular weight of the polymacromer was estimated to be about 1 × 10⁶. It has been assumed that the 2–1 mode of addition to the diene group of the macromer is predominant during its polymerization. The 3–4 mode of addition followed by proton shift represents the termination step. The 4–3 mode of addition was ruled out on the basis of spectroscopic evidence.     

Association of polyacrylonitrile prepared by low-temperature,solution polymerization with an organometallic catalyst

The weight-average molecular weights of polymers of acrylonitrile prepared by a free-radical initiator and an organometallic catalyst have been determined by lightscattering measurements in N,N-dimethylformamide, dimethyl sulfoxide, and dimethylacetamide at 25°C. and in dimethyl sulfoxide at 140°C. The apparent molecular weights of the polymers prepared with the NaAlEt₃S(i-Pr) catalyst in DMF at ?78°C. (referred to as high-melting polymers) changed from 54,800, 82,700, and 480,000 when measured in DMF at 25°C. to 36,000, 41,600, and 225,000 when measured in DMSO at 140°C., whereas the molecular weights of the free-radical polymers remained unchanged. Furthermore, from results obtained in DMSO at 140°C., The intrinsic viscosity–molecular-weight relationships were found to be identical for the high-melting and the free-radical polymer and in substantial agreement with an equation reported by Cleland and Stockmayer. The apparent decrease in molecular weight of the high-melting polymer from 25 to 140°C. indicates rather clearly that the high-melting polymers are associated in DMF at 25°C. The “aggregates,” even though present only at low concentrations, raised the weight-average molecular weight markedly but affected the number-average molecular weight only slightly, thus giving a high M?_w/M?_n ratio. It appears likely that when temperature and solvent are such that association does not occur, linear PAN's will have approximately the same intrinsic viscosity–molecular weight relationship (subject of course to slight change by polydispersity). The often reported abnormal molecular weight of samples prepared by solution polymerization especially at low temperatures, may be attributed to branching, or to an association, as reported here. The nature of association of PAN in dilute solution is also discussed.     

Macromorphology of polypropylene homopolymer tacticity mixtures

The macromorphology of isotactic/atactic (iPP/aPP) and isotactic/syndiotactic (iPP/sPP) polypropylene mixtures is examined by optical microscopy. The spherulitic macrostructure of equimolecular weight [weight‐average molecular weight (M_w) = 200k] iPP/aPP blends is volume‐filling to very high aPP concentrations when the crystallization temperature is 130 °C. Similar spherulitic macrostructures (spherulite size and volume‐filling nature) are observed for iPP homopolymer and a 50/50 iPP/aPP blend at low crystallization temperatures (115–135 °C). At higher crystallization temperatures (140–145 °C), a equimolecular weight (M_w = 200k) 50/50 iPP/aPP blend exhibits nodular texture that blurs the spherulitic boundaries. Double temperature jump experiments show that the nodular texture is due to melt phase separation that develops prior to crystallization. The upper critical solution temperature (UCST) of a 50/50 iPP/aPP blend (M_w = 200k) lies below 155 °C, and the blend is miscible at conventional melt processing temperatures. The UCST behavior is controlled by the blend molecular weight and aPP microstructure. aPP microstructures containing increased isospecific sequencing (although still noncrystalline) exhibit a reduced tendency for phase separation in 50/50 mixtures (M_w = 200k) and the absence of nodular texture at low undercoolings (140–145 °C). Equimolecular weight (M_w = 200k) 50/50 iPP/sPP mixtures exhibit phase‐separated texture at all crystallization temperatures. The size scale of the phase‐separated texture decreases with decreasing crystallization temperature because of a competition between crystallization and phase separation from a melt initially well mixed from the initial solution blending process. Extended melt annealing experiments show that the 50/50 iPP/sPP mixture (M_w = 200k) is immiscible in the melt at conventional melt processing temperatures. The iPP/sPP pair shows a much stronger tendency for phase separation than the iPP/aPP polymer pair. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1947–1964, 2000     

Temperature dependence of radiation effects in polyethylene: Cross‐linking and gas evolution

High‐density polyethylene (HDPE) and low‐density polyethylene (LDPE) were irradiated in vacuo at 30–220 and 30–360°C, respectively, with γ‐rays at doses of 10–400 kGy. Temperature dependence of cross‐linking and gas evolution was investigated. It was found that cross‐linking was the predominant process up to 300°C and the gel point decreased smoothly with temperature. The increase of G(x) with temperature was likely attributed to the temperature effect on addition of radicals to the double bonds present in the polymer. Above 300°C, the gel fraction at a given dose decreased remarkably with temperature and turned to zero at 360°C. The molecular weight variation determined with gel permeation chromatography (GPC) indicated the enhanced degradation at 360°C by radiation. G‐values of H₂ increased with temperature and varied with dose. The compositions of the C₁–C₄ hydrocarbons evolved depended on the structures of side branches. Raising the temperature favored the formation of unsaturated hydrocarbons, and the yield of unsaturated relative to saturated hydrocarbons decreased with dose. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1541–1548, 1999     

Superdrawing of polytetrafluoroethylene virgin powder above the static melting temperature

A new two‐stage draw technique was successfully applied to the superdrawing of polytetrafluoroethylene (PTFE) virgin powder. A film, compression‐molded from powder below the melting temperature (T_m = 335 °C), was initially solid‐state coextruded to an extrusion draw ratio (EDR) of 6–20 at 325 °C, about 10 °C below the T_m. These extrudates from the first‐stage draw were further drawn by a second‐stage pin draw in the temperature (T_d) range of 300–370 °C that covers the static T_m. The maximum achievable total draw ratio was ～60 at a T_d = 300 °C and increased rapidly with increasing T_d, reaching a maximum of 100–160 at a temperature window between 340 and 360 °C, depending on the initial EDRs. At yet higher T_d's, the ductility was lost as a result of melting. The high ductility of the PTFE extrudates at such high temperatures was ascribed to the improvement of interfacial adhesion and bonding between the deformed powder particles upon the first‐stage extrusion combined with the rapid heating of only a portion of the extrudate followed by the elongation at a high rate. The highly drawn fibers were highly crystalline (χ_c ≤ 87%) and showed high chain orientation (f_c ≤ 0.997) and a large crystallite size along the chain axis (D₀₀₁₅ ≤ 160 nm). The molecular draw ratio, estimated from the entropic shrinkage above the T_m, was close to the macroscopic deformation ratio independently of the initial EDRs. These results indicate that the draw was highly efficient in terms of chain extension, orientation, and crystallization. Thus, the maximum tensile modulus and strength achieved in this work were 102 ± 5 and 1.4 ± 0.2 GPa, respectively, at 24 °C. These tensile properties are among the highest ever reported on oriented PTFE. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1995–2004, 2001     

Application of zone-drawing and zone-annealing method to poly(p-phenylene sulfide) fibers

A zone-drawing and zone-annealing treatment was applied to poly(p-phenylene sulfide) fibers in order to improve their mechanical properties. The zone-drawing (ZD) was carried out at a drawing temperature of 90°C under an applied tension of 5.5 MPa, and the zone-annealing (ZA) was carried out at an annealing temperature of 220°C under 138.0 MPa. The differential scanning calorimetry (DSC) thermogram of the ZD fiber had a broad exothermic transition (T_c = 110°C) attributed to cold-crystallization and a melting endotherm peaking at 286°C. The T_c of the ZD fiber was lower than that (T_c = 128°C) of the undrawn fiber. In the temperature dependence of storage modulus (E′) for the ZD fiber, the E′ values decreased with increasing temperature, but increased slightly in the temperature range of 90–100°C, and decreased again. The slight increase in E′ was attributable to the additional increase in the crosslink density of the network, which was caused by strain-induced crystallization during measurement. The resulting ZA fiber had a draw ratio of 6.0, a degree of crystallinity of 38%, a tensile modulus of 8 GPa, and a tensile strength of 0.7 GPa. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1731–1738, 1998