The crystal structure of poly(m‐phenyulene isophthalamide) was determined by x‐ray analysis. The triclinic cell, with a = 5.27 Å, b = 5.25 Å, c (fiber axis) = 11.3 Å, α = 111.5°, β = 111.4° and γ = 88.0° and space group P1, contains one monomeric unit. The crystal density is 1.47 g/cc. The molecules in the crystal are contracted by 1 Å per monomeric unit from the fully extended conformation, and the planes of the benzene rings and adjacent amide groups make angles of about 30°. The crystal is composed of molecular chains connected by NH···O hydrogen bonds along the a and b axes forming a “jungle gym” network structure. The low tensile modulus of this polymer as compared with that of poly(p‐phenylene terephthalamide) is attributed to the contracted molecular conformation.

ABSTRACT:Intimate relationship between the thermal behavior and the structural change has been clarified for the first time by an organized combination of isothermal DSC thermogram and FT/IR spectra measured for the stabilization reaction of an acrylonitrile (AN)/methacrylic acid (MAA) copolymer. In an early stage of the isothermal exothermic thermogram measured by DSC under air, a flat region or the induction period of the cyclic structure formation was found to exist, which is immediately followed by the two stages of steep heat evolution and the slow heat release. Based on the IR spectral changes observed during this thermal reaction, the induction stage was found to be associated with the reaction of methacrylic acid groups with the adjacent nitrile groups and the steep heat evolution region with the propagation of the cyclic structure and dehydrogenation of the polyacrylonitrile (PAN) chain sequences to give an unsaturated ladder structure. An activation energy for this initiation reaction of the cyclic structure formation was evaluated to be ca. 26 kcal/mo! by an Arrhenius plot.KEY WORDS Polyacrylonitrile / Methacrylic Acid / DSC / FT/IR / Precursor / Carbon Fiber / Stabilization / Induction Period / Polyacrylonitrile (PAN) contammg acidic comonomers are the most commonly used precursors for carbon fibers because of the excellent performance of PAN based carbon fibers. 1 Production process of PAN based carbon fibers involves a stabilization of oriented acrylic fibers and a carbonization of them at elevated temperature. 2 Stabilization is the most important process which converts PAN to an infusible and nonflammable fiber by heating at 200-----300°C for about one hour in an oxidative atmosphere. Thus stabilized fibers can be heated up to carbonization temperature (1000-2000°C) in an inert gas atmosphere. 2 A number of studies 5 -zs have been reported concerning the stabilization of PAN since the proposition of the fully hetero aromatic cyclic structure for the stabilized PAN in 1950. 4 The subject of stabilization was reviewed by Bashir 40 years after this first proposition. 3 PAN copolymers containing acidic comonomers work as a good precursor and gives high quality carbon fibers. The role of comonomers in the stabilization reaction was said to lower the initiation temperature of cyclization reaction. 1 Grassie and coworkers 27 · 28 studied by DTA method the effects of some comonomers on lowering the stabilization temperature. Some acidic comonomers, e.g., itaconic acid, methacrylic acid (MMA), and acrylic acid, lower the exothermic peak temperature and also decrease the peak height in the following order: itaconic acid> methacrylic acid> acrylic acid > acrylamideIn this way the degree of reduction of the exothermic peak temperature may be useful as a measure of the effect of comonomers in stabilization reaction. On the other hand, the effects of comonomers on the t To whom all correspondence should be addressed. 36 • 37 developed a kinetic model including the two rate processes so as to simulate the he...

the sequence distribution, ~8% in the polymer composition, and ~50 % in the monomer feed are shown for a VC1-BMA copolymer. Errors of ~18% in the sequence distribution, ~4% in the polymer composition, and ~1 % in the monomer feed are shown for a BD-MMA copolymer. Large errors are not expected in any of the variables, but erroneous reactivity ratios may also arise from a cumulation of smaller errors.The effect on predicted reactivity ratios of an ~2% error in all variables is also shown in Table V for both the VC1-BMA and BD-MMA copolymers. It is doubtful that errors of this degree would occur in all variables simultaneously, but the error range found indicates the experimental care that must be taken in using this approach. Accurate measurement of variables will, however, give favorable reactivity ratio comparisons as shown in Table II. ConclusionsReactivity ratios may be predicted in copolymer systems susceptible to sequence distribution measurements by accurately knowing the monomer feed, the copolymer composition, and the copolymer sequence distribution. Reactivity ratios can be obtained with a minimum amount of polymer synthesis and may be used to predict desired copolymer compositions. The singlecopolymer reactivity ratio technique could possibly be used to illustrate shifts in reactivity ratios attributed to penultimate effects or polymerization mixture polarity changes.The single-copolymer reactivity ratio method may prove to be valuable in specific systems where accurate sequence distribution data can be obtained and the use of conventional methods for finding reactivity ratios is not practical.

Structural Studies of Polyethers, [-(CH,)m-O-]n. SUMMARY:The structure of polyoxacyclobutane has been studied by x-ray diffraction and infrared absorption methods, and three crystal modifications have been found. The molecular conformation of modification I is essentially planar zigzag, fiber period being 4.80 A. Modification I1 is trigonal, R3c-C:,, a = 14.13 A, and c (fiber axis) = 8.41 A; nine molecular chains of a T,GT,G type pass through a unit cell. Modification I11 is orthorhombic, C222,-Dz, a = 9.23 A, b = 4.82 A, and c (fiber axis) = 7.21 A; two molecular chains of a (T,G,), type pass through the center and the corner of a unit cell.The transitions among these three modifications were studied and discussed. Modification I is stable only in the presence of water. Modification I11 is the most stable form, and this is consistent with the antiparallel arrangement of the strong dipole-moments of the COC groups. Modification I1 is stable only as oriented samples. ZUSAMMENFASSUNG: Die Struktur von Polyoxacyclobutan wurde mit Rontgenstrahlbeugungs-und Ultrarotabsorptionsmethoden untersucht. Dabei wurden drei Kristallmodifikationen gefunden. Modifikation I hat im wesentlichen eine ebene Zickzackkonformation mit einer Faserperiode von 4,80 A. Modifikation I1 ist trigonal, R3c-C&, a = 14,13 A,und c (Faserachse)= 8,41 A; neun Molekiilketten vom Typ T3GT3c gehen durch eine Elementarzelle. Modifikation I11 ist orthorhombisch, C222,-D;, a = 9,23 A, b = 4,82 A,und c (Faserachse) = 7,21 A; zwei Molekiilketten vom Typ (T,G,), laufen durch das Zentrum und die Ecke einer Elementarzelle.Die Ubergange zwischen diesen drei Modfiationen werden untersucht und erortert. Modifikation I ist nur in Gegenwart von Wasser bestandig. Modfiation I11 ist die stabilste Form, was durch die antiparallele Anordnung der starken Dipolmomente der COC-Gruppen zu erklaren ist. Modifikation I1 ist nur in orientierten Proben stabil.