: The ultimate crystalline modulus of poly(oxymethylene) was estimated by using the Raman longitudinal acoustic mode and small-angle X-ray scattering. In this paper we emphasize the sensitivity of the calculated modul...
An infrared spectroscopic investigation of ethylene-methacrylic acid copolymers and their sodium salts has been carried out. All the copolymers studied were based on a parent copolymer containing 4.1 mol % of methacry...
An infrared spectroscopic investigation of ethylene-methacrylic acid copolymers and their sodium salts has been carried out. All the copolymers studied were based on a parent copolymer containing 4.1 mol % of methacrylic acid groups. This was then neutralized to various extents (from 0 to 78%) with sodium hydroxide. The per cent ionization was determined from the integrated absorbance of the 1700 cm-1 un-ionized carbonyl stretching band. Temperature-dependent infrared studies showed that the behavior of the un-ionized acid groups over the entire range of ionization is quantitatively comparable to that of low molecular weight carboxylic acids in nonpolar solvents. A monomer-dimer equilibrium exists among the acid groups and they are almost completely in the form of hydrogen-bonded dimers at room temperature. The heat of dissociation of the dimers was found to be 11.6 kcal mol-1. Thus each hydrogen-bond has a bond strength of 5.8 kcal mol-1. Infrared dichroism studies established that there is a significant amount of crystallinity even at the highest degree of ionization, that the hydrogen bonds are intermolecular in nature, and that the ionized carboxylate groups have a preferred orientation out of the plane of the main chain of the copolymer.
Thermogravimetric analysis is typically employed to study degradation and curing processes. The work presented here will show that thermogravimetry (TG) can also be used to probe other types of thermal processes. In p...
Thermogravimetric analysis is typically employed to study degradation and curing processes. The work presented here will show that thermogravimetry (TG) can also be used to probe other types of thermal processes. In particular, TG can be used to determine glass transitions T g in certain polymers. A premise of the technique is that low molecular weight species can be imbibed into a polymer sample. Upon heating, major gas evolution will take place in the glass transition region and such gas evolution can be utilized as an indicator of T g . This technique is particularly beneficial for determining T g values of semicrystalline polymers without major modifications of crystallinity. To demonstrate the concept, studies were carried out in two phases. Phase one looked at well characterized amorphous polymers using several solvents to show that the technique does indeed work. In phase two it was established that glass transitions of semicrystalline polymers could be detected.
A review has been attempted in this article of the multidisciplinary character of the development of high performance fibrous materials. The effort has focused on both the theoretical recognition of the possibility of...
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A review has been attempted in this article of the multidisciplinary character of the development of high performance fibrous materials. The effort has focused on both the theoretical recognition of the possibility of such materials and a recounting of significant aspects of the art for producing fiber with high performance characteristics. A knowledge of the primary valence bonds in a basic molecule, the atom configuration along the backbone of the molecule and the valence angles permits one to utilize spectroscopic inputs to compute the theoretical maximum modulus of elasticity in a given ideal fiber structure. An infinite replication of such molecules, all parallel one with the other is envisioned as this ideal structure. In order to obtain the ultimate modulus values, it is necessary to know the three-dimensional arrangements between chains, knowledge which is usually derived from X-ray diffraction studies. The ultimate tenacity, on the other hand, is dependent on some approximation of the intermolecular potential between polymer chains. The Morse potential, 61 a strictly empirical relation describing the force of separation of polymer segments, has proved to be one of the simpler methods for obtaining an estimate of ultimate tenacity. Other intermolecular potentials may or may not provide similar estimates. The Morse potential provides an explicit elongation at the point of break if this is based on maximum force of separation. It varies with the value of U 0 , the dissociation energy, and a parameter a , characteristic of an inverse length which is determined in turn by spectroscopic data. Based on the initial work of Flory, lattice techniques may be utilized for understanding and describing the development of order in infinite molecules when the ordering process is subjected to an external biasing probability imposed by the presence of some type of an ordering field. One could envision the macroscopic picture of extensional and stretching flows and similar ma
Poly(ethylene terephthalate) (PET) structure and morphology were modified and set during a continuous false twist solvent texturing process. Three yarn types were included in this study: partially oriented yarn (Pou),...
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Poly(ethylene terephthalate) (PET) structure and morphology were modified and set during a continuous false twist solvent texturing process. Three yarn types were included in this study: partially oriented yarn (Pou), high speed spun yarn (HSSY), and an experimentally extruded yarn known as quenched high speed spun yarn (QHSSY). A prototype continuous false twist solvent texturing machine was used to produce textured samples (thermally as well as with solvents). Excessive extensibility of POY was virtually eliminated by drawing on the machine in the same zone as the solvent treatment, but this action reduced solvent diffusion into the filaments. HSSY crystallinity increased slightly, about 8% during solvent texturing, the main reason being a large amount of initial crystallinity for the feed yarn. QHSSY was most suitable for solvent texturing, since it initially contains a large amount of oriented noncrystalline material that is crystallized during texturing. Textured QHSSY set by solvent plus heat, in comparison with heat only, increased significantly in percent crystallinity and crystallite dimensions.
Delocalized carbanions have proved to be useful synthetic tools in the preparation of many compounds including new monomers. Abstraction of a proton alpha to a double bond can be accomplished through the use of strong...
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Delocalized carbanions have proved to be useful synthetic tools in the preparation of many compounds including new monomers. Abstraction of a proton alpha to a double bond can be accomplished through the use of strong metalating agents such as n-Butyllithium/tetramethyl-ethylenediamine (n-BuLi/TMEDA) or Lochmann's base system (n-BuLi/potassium-tert-butoxide in pentane). The use of Lochmann's base system instead of n-BuLi/TMEDA possesses a twofold advantage - reaction times are on the order of minutes instead of days or weeks leading to significantly higher yields and conjugated olefins can be successfully metalated. Thus 2,3-dimethyl-1,3-butadiene can easily be converted to 2,3-dimethylene-1,3-butadiene dianion.
The synthetic utility of delocalized carbanions resulting from the abstraction of a proton alpha to a double bond has been established using strong metalating agents such as n-butyllithium/tetramethylethylene diamine ...
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The synthetic utility of delocalized carbanions resulting from the abstraction of a proton alpha to a double bond has been established using strong metalating agents such as n-butyllithium/tetramethylethylene diamine (n-BuLi/TMEDA), or Lochmann's base system (n-BuLi/potassium-t-butoxide in pentane). Lochmann's base system has been shown to cause allylic metalation of conjugated dienes, with the notable exception of isoprene where the butyl anion adds to the conjugated diene instead of abstracting the alpha proton. However, metalation of 2,3-dimethyl-1,3-butadiene proceeds cleanly and quickly (10 min. ) to dianion in yields of greater than 80%. A synthetic scheme for the preparation of 2,3-disubstituted-1,3-butadienes and 1,4-butanediols has been identified as a desirable goal. These compounds are useful in preparing disubstituted polybutadienes, and condensation polymers.
作者：
Runt, J.Rim, P.B.Pennsylvania State Univ
Polymer Science Program University Park PA USA Pennsylvania State Univ Polymer Science Program University Park PA USA
This paper reviews the determination of polymer/polymer interaction parameters chi from experimental melting point data with emphasis on two major areas. The first concerns variation of morphology with blend compositi...
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This paper reviews the determination of polymer/polymer interaction parameters chi from experimental melting point data with emphasis on two major areas. The first concerns variation of morphology with blend composition which can restrict attempts to calculate chi if non-equilibrium melting points are used. The second area of interest involves processes such as lamellar thickening during thermal analysis which can seriously impair determination of 'true' crystalline melting points.
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