Amic Ethyl Ester Research Articles

Polyimide Fibers Obtained by Spinning Lyotropic Solutions of Rigid‐Rod Aromatic Poly(amic ethyl ester)s

AbstractSummary: Fibers were spun from a lyotropic solution of a high‐molecular‐weight (η = 5.89 g · dL−1), rigid‐rod, fully aromatic polyimide precursor polymer in a dry‐jet, wet‐spinning process in NMP. Acetone was identified as the coagulant of choice since fibers could be drawn extensively in this solvent, resulting in improved mechanical properties (tensile modulus: E = 17 GPa, strength at break: σbreak = 400 MPa, elongation at break: εbreak = 5.3%) and orientation, which was shown by WAXS patterns. SEM images showed a layered, skin‐core morphology without any visible fibrillation. Additional processing of these fibers by step‐wise hot‐drawing up to 400 °C under tension rendered oriented polyimide fibers with excellent mechanical properties. (E = 68 GPa, σbreak = 700 MPa, εbreak = 1%). An analysis of the WAXS diffraction patterns showed an improved orientation of the fibers in the axial and lateral directions; however, probably due to the CF3 side groups, the lateral distance was still too large for crystallization. SEM images of these imidized fibers showed, for the first time, a fibrillar morphology in addition to the typical, skin‐core, sheet‐like morphology.SEM image of the hot‐drawn fiber PI 4 (12). The image shows a skin‐core morphology which was delaminating into ribbons during preparation.magnified imageSEM image of the hot‐drawn fiber PI 4 (12). The image shows a skin‐core morphology which was delaminating into ribbons during preparation.

Influence of Chain Stiffness and Preparation Methods on the Efficiency of Polyimide Alignment Layers for Liquid Crystal Orientation

In this work the influences of chain stiffness, solution concentration, and preparation methods on the formation and efficiency of highly oriented polyimide alignment layers are investigated. To quantify the performance of the alignment layers in liquid-crystalline (LC) cells, the orientation of a calamitic bis-azo dye in a low-molecular-weight nematic LC guest–host mixture was employed. The degree of orientation was quantified by measuring the dichroic ratio (DRUV) of the dye with polarized UV spectroscopy. Alignment layers were prepared from precursors of polyimide polymers with different chain stiffnesses. Additionally, the effect of polymer solution concentration, denoted as low (approx. 2 wt%) and high (50 wt%), and orientation techniques (casting and shearing) were systematically investigated. Cells assembled with buffed polyimide alignment layers originating from 1.5 wt% solutions in N-methyl-2-pyrrolidone (NMP) of a rigid para-linked poly(amic ethyl ester) precursor polymer resulted in a very high DRUV of 15. This value can be compared to values obtained with commercially available flexible polyimide layers, which had a DRUV of only 8. Pretilt angles of selected cells were also measured and were found to be in the range of 0.7 to 5.1°.

Preparation of Well-oriented Poly(p-phenylene pyromelliteimide) Fiber via Shear-induced Orientation of Poly(amic ethyl ester) Precursor during Polymerization

The orientation of poly ( p-phenylene pyromelliteimide) (PPPI) molecules was examined by means of shearing during the gelation of poly(amic ethyl ester) (PAEE) precursor and thermal imidization. The polymerization of 1,4-phenylene diamine (PPDA) and 2,5-diethoxycarbonyl-1,4-benzenedicarbonyl chloride (DEBC), and that of N, N'-bis(trimethylsilyl)-1,4-phenylenediamine (N-silyl-PPDA) and DEBC yielded the PAEE gel during polymerization. With respect to the polymerization of PPDA and DEBC, 0.44 mol L-1 gave the highest DPn of PAEE at the gelation point, and the strong shear during gelation made the PAEE and ultimately PPPI molecular chains oriented in the planar mode. In contrast to this, the polymerization of N-silyl-PPDA and DEBC gave a higher DPn of PAEE at the gelation point than that of PPDA and DEBC. The strong shear stress applied to the PAEE gel, prepared at 0.50 mol L-1, induced the uni-axial orientation of the molecular chains, but the relaxation of the orientation occurred gradually with time. The addition of ethyl acetate to the gel prevented the relaxation of the chain orientation and accelerated the crystallization. As a result, uni-axial orientation of the PAEE molecular chains was induced along the shear direction in the gel rather than the planar mode, and ultimately the PPPI molecular chains were well-oriented.

Lyotropic para‐linked aromatic poly(amic ethyl ester)s

AbstractThe synthesis, characterization and application of lyotropic precursor polymers for polyimides, poly(amic ethyl ester)s (PAE) are presented. By the use of non‐coplanar and para‐linked monomers, rigid‐rod PAEs are synthesized in a typical polycondensation reaction yielding liquid crystalline solutions at concentrations of 30‐40 wt% in NMP at 100°C. These lyotropic solutions permit for the first time the fabrication of orientation PAE layers by shear which are thermally converted to the corresponding polyimide. The bulk orientation in the thin films is characterized by spectroscopic methods. In addition the lyotropic solution is spun into fibers in a dry‐jet wet spinning process. The obtained fiber orientation is characterized by tensile tests and wide angle X‐ray scattering.

Synthesis and Properties of Lyotropicpara-Linked Aromatic Poly(amic ethyl ester)s

The paper describes the synthesis and structure-property relations of para-linked aromatic poly(amic ethyl ester)s with the intention to realize lyotropic precursor solutions for rigid-rod polyimides. As compared to the commonly used flexible precursors, these preorganized precursors should be superior to obtain perfectly oriented polyimide films, orientation layers, and fibers. The poly(amic ethyl ester)s were synthesized by polycondensation of 2,5-diethylbis-(ethoxycarbonyl)terephthaloyl acid dichloride and several para-functionalized diamines bearing fluoro substituents, bulky side groups, or non-coplanar structures. Certain introduced structural modifications improve the solubility in NMP to concentrations up to 50 wt.-% and lyotropic nematic solutions could be obtained. Polymers without fluoro atoms in the ortho position to the polyamide bond have a strong tendency to form a birefringent gel at room temperature which turns into a shearable lyotropic phase above 50°C. This transformation was studied by temperature dependent FTIR spectroscopy and WAXS. However when the ortho position is fluorinated the precursors form a lyotropic phase at room temperature under shear. The macroscopic surface morphology of the dried gels of concentrated solutions is dramatically affected by the chain stiffness, para-Poly-(amic ester)s show a distinct wormlike morphology, indicating molecular order within the gel, whereas the corresponding flexible meta-poly(amic ester)s show a structureless, smooth surface.

Imidization and interdiffusion of poly(amic ethyl ester) precursors of PMDA/3,4?-ODA

Para-, meta-, and mixed isomeric poly(amic ethyl ester) precursors of the polyimide based on pyromellitic dianhydride (PMDA) and 3,4′-oxydianiline (3,4′-ODA) were synthesized. The intrinsic viscosity of each of the isomers was measured in an NMP solution and found to be less than corresponding isomers derived from PMDA and 4,4′-oxydianiline (4,4′-ODA) precursors with comparable molecular weight. The imidization and solvent retention were measured as a function of imidization temperatures, Ti using forward recoil spectrometry (FRES). For samples cast from a single solvent, either N-methyl pyrrolidone (NMP) or dimethyl sulfoxide (DMSO), no difference was observed in the temperature-dependent imidization behavior between the isomers. In all cases the imide fraction f increased as Ti increased, and reached a value of unity, i.e., full conversion at 400°C. At the same Ti, samples cast from DMSO showed a slightly higher f than samples cast from NMP. FRES and time of flight FRES (TOF-FRES) were used to measure the interdiffusion distance, w, of deuterium-labeled tracers into nondeuterated base layers of the polyimide of PMDA/3,4′-ODA treated at various Ti. The primary determinant of w for all isomers was Ti, and the particular isomer used as either the base or the tracer molecule did not seem to affect w. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2247–2258, 1998

Imidization and interdiffusion of poly(amic ethyl ester) precursors of PMDA/3,4′‐ODA

Para-, meta-, and mixed isomeric poly(amic ethyl ester) precursors of the polyimide based on pyromellitic dianhydride (PMDA) and 3,4′-oxydianiline (3,4′-ODA) were synthesized. The intrinsic viscosity of each of the isomers was measured in an NMP solution and found to be less than corresponding isomers derived from PMDA and 4,4′-oxydianiline (4,4′-ODA) precursors with comparable molecular weight. The imidization and solvent retention were measured as a function of imidization temperatures, Ti using forward recoil spectrometry (FRES). For samples cast from a single solvent, either N-methyl pyrrolidone (NMP) or dimethyl sulfoxide (DMSO), no difference was observed in the temperature-dependent imidization behavior between the isomers. In all cases the imide fraction f increased as Ti increased, and reached a value of unity, i.e., full conversion at 400°C. At the same Ti, samples cast from DMSO showed a slightly higher f than samples cast from NMP. FRES and time of flight FRES (TOF-FRES) were used to measure the interdiffusion distance, w, of deuterium-labeled tracers into nondeuterated base layers of the polyimide of PMDA/3,4′-ODA treated at various Ti. The primary determinant of w for all isomers was Ti, and the particular isomer used as either the base or the tracer molecule did not seem to affect w. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2247–2258, 1998

Imide—Dimethylsiloxane block copolymers: Design and synthesis of a permanent buried oxygen ion etch barrier

Imide—siloxane multiblock copolymers were investigated. A key feature of these copolymers is the preparation of bis(aminopropyl) oligomers via anionic ring-opening polymerization. The molecular weights of the oligomers ranged from 1000 to 5000 g/mol. The oligomers were coreacted with 4,4′-oxydianaline (ODA) and pyromellitic dianhydride (PMDA) diethyl ester chloride in a N-methyl-2-pyrrolidone/THF—solvent mixture in the presence of N-methylmorpholine. The resulting amic ethyl ester siloxane copolymers were isolated and washed to remove homopolymer contamination. Copolymer compositions, determined by 1H-NMR, ranged from 20 to 65 wt % siloxane content and the measured compositions were close to those charged. Solutions of the copolymers were cast and cured (350°C) to effect imidization, producing clear films. The films showed tough ductile mechanical properties with moduli varying with siloxane content. The copolymers displayed good thermal stability with decomposition temperatures in the proximity of 450°C. Multiphase morphologies were observed irrespective of siloxane block lengths or compositions. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 199–208, 1997

Imide?Dimethylsiloxane block copolymers: Design and synthesis of a permanent buried oxygen ion etch barrier

Imide—siloxane multiblock copolymers were investigated. A key feature of these copolymers is the preparation of bis(aminopropyl) oligomers via anionic ring-opening polymerization. The molecular weights of the oligomers ranged from 1000 to 5000 g/mol. The oligomers were coreacted with 4,4′-oxydianaline (ODA) and pyromellitic dianhydride (PMDA) diethyl ester chloride in a N-methyl-2-pyrrolidone/THF—solvent mixture in the presence of N-methylmorpholine. The resulting amic ethyl ester siloxane copolymers were isolated and washed to remove homopolymer contamination. Copolymer compositions, determined by 1H-NMR, ranged from 20 to 65 wt % siloxane content and the measured compositions were close to those charged. Solutions of the copolymers were cast and cured (350°C) to effect imidization, producing clear films. The films showed tough ductile mechanical properties with moduli varying with siloxane content. The copolymers displayed good thermal stability with decomposition temperatures in the proximity of 450°C. Multiphase morphologies were observed irrespective of siloxane block lengths or compositions. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 199–208, 1997

Crosslinked networks based on trimethoxysilyl functionalized poly(amic ethyl ester) chain extendable oligomers

We report here the synthesis and characterization of poly(amic ethyl ester) oligomers functionalized with trimethoxysilyl end-groups. The oligomers were prepared via the condensation of 1,1-bis(4-aminophenyl)-1-phenyl-2.2,2-trifluoroethane, diethyldichloromellitate and p-aminophenyltrimethoxysilane. The p-amino-phenyltrimethoxysilane was used to control both molecular weight and end-group functionality. These oligomers were thermally cured to form crosslinked networks. The resulting networks possesed T g in excess of 450°C and thermal decomposition temperatures in the proximity of 500°C. The formation of networks was confirmed by swelling studies. These oligomers offer an attractive processing alternative as low viscosity precursors to crosslinked polyimide networks.

Effects of chemical structure and precursor on optical properties, thermo-mechanical properties, and molecular orientation and order of thin films of stiff aromatic polyimides

Thin films of rigid poly(p-phenylene pyromellitimide) (PMDA-PDA) and semi-rigid poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA), prepared by thermal imidization of the respective poly(amic acid) and poly(amic ethyl ester) precursors, were characterized with respect to their optical, thermomechanical and structural properties. Both polyimides exhibit an unusually large anisotropy between the in-plane and out-of-plane refractive indices, with Δn ranging from 0.198 to 0.216 for PMDA-PDA and from 0.230 to 0.242 for BPDA-PDA, nearly independent of the nature of the initial polyimide precursor, film thickness, and film preparation method. PMDA-PDA films exhibit low coefficients of thermal expansion (CTE's) of 6.5 and 8.2 ppm/δC for the acid-derived and the ester-derived polyimides, respectively. In comparison, the BPDA-PDA films show CTE values of 4.3 and 18.0 for the acid-derived and ester-derived samples, respectively, despite the small differences in their optical anisotropies. Wide-angle x-ray diffraction patterns obtained in reflection and transmission for the various samples reveal a strong in-plane chain orientation for both PMDA-PDA and BPDA-PDA polyimides, with somewhat better intermolecular packing order for the ester-derived polyimide films. These effects of chemical structure and precursor on properties and structures of the polyimide films are discussed in light of recent theoretical considerations of semiflexible polymers.

Solvent and isomer effects on the imidization of pyromellitic dianhydride-oxydianiline-based poly(amic ethyl ester)s

The imidization behaviour of the isomeric poly(amic ethyl ester) (PAE) precursor molecules of the polyimide pyromellitic dianhydride—oxydianiline was followed using forward recoil spectrometry. The degree of imidization after 1 h at various temperatures was found to depend strongly on the spin-casting solvent. Films cast from dimethyl sulfoxide (DMSO) showed an imide fraction, f, which was independent of depth and of isomeric precursor (i.e. whether the precursor was para-PAE, meta-PAE or a random mixture of meta and para (mixed-PAE).) In films spun cast from N-methylpyrrolidone (NMP), however, fs for the para- and mixed-PAE were larger than that for the meta-PAE. In addition the fs for the para-PAE and mixed-PAE were found to be greater for films cast from NMP than from DMSO for any given thermal treatment. For the meta-PAE, f was independent of the casting solvent. Over an imidization temperature range of 180–280°C f was found to vary with depth, being lower than the bulk value over the first 3000 Å from the film surface. These observations appear to be related to a retention of the NMP with f being larger where NMP is retained.

Profiling Polyimide-Polyimide Interfaces

AbstractThe adhesion of spuncast polyimide layers is critical to the success of manufacturing multilayer polyimide structures. We have measured the interpenetration between a spuncast layer of the meta isomer of poly(amic ethyl ester) (PAE) precursor of PMDA 4,4′ ODA and the corresponding partially-imidized PAE base layer using forward recoil spectrometry (FRES). Measurements made with FRES show that interpenetration decreases rapidly as the base layer imide fraction f increased, with a corresponding decrease in adhesion measured with a T-peel test. In the region of f > 0.8, differences in interfacial adhesion are still observed while the interfacial widths are too narrow to be differentiated with FRES. For this reason, the use of other high resolution techniques for profiling the polyimide-polyimide interface such as nuclear reaction analysis, dynamic secondary ion mass spectrometry, and neutron reflectometry will be necessary to accurately correlate interpenetration with adhesion.

Para-linked aromatic poly(amic ethyl esters): precursors to rodlike aromatic polyimides. 1. Synthesis and imidization study

The synthesis and characterization of several para-linked aromatic poly(amic ethyl ester)s based on 2,5-bis(ethoxycarbonyl)terephthalic acid and several substituted 1,4-diaminobenzene and noncoplanar 4,4'-diaminobiphenylene derivatives are described. Depending on the degree and type of substitution, the precursors are soluble to high concentrations in solvents such as DMF or NMP without the addition of inorganic salts. TGA and FTIR measurements show that the imidization process for these materials is controllable and goes to completion

Structure and properties of thin films of binary rodlike/flexible polyimide mixtures

AbstractBinary mixtures of a rodlike poly(p‐phenylene pyromellitimide) (PMDA‐PDA) and a flexible 6F‐BDAF polyimide synthesized from hexafluoroisopropylidene diphthalic anhydride and 2,2‐bis(4‐aminophenoxy‐p‐phenylene) hexafluoropropane were prepared by solution‐blending of the meta‐PMDA‐PDA poly(amic ethyl ester) and 6F‐BDAF poly(amic acid) precursors, followed by solvent evaporation and thermal imidization. Mixtures containing different molecular weights of 6F‐BDAF poly(amic acid) were studied. The size scale of the phase separation, as measured by light scattering, is ca. 1 μm or smaller in most cases. The domain size is primarily set by the demixing of the precursor polymers during solvent evaporation, with no significant coarsening observed during the thermal imidization. The observed variation of the domain size with molecular and process parameters such as composition, molecular weight, and film thickness is discussed in terms of the miscibility of the precursor polymers, rate of solvent evaporation, and solidification. Dynamic mechanical thermal analysis and dielectric relaxation measurements indicate that the glass transition temperature of 6F‐BDAF is unaffected in all of the mixtures studied, indicating complete demixing of rodlike and flexible polyimides in agreement with theory. X‐ray photoelectron spectroscopy results show a strong surface segregation of 6F‐BDAF in mixtures containing as low as 10% by weight of the 6F‐BDAF component in the bulk. The mixtures with PMDA‐PDA as the major matrix component therefore exhibit excellent mechanical toughness, dimensional stability up to 500°C, low coefficients of thermal expansion (< ca. 10 ppm/°C), and low dielectric constants (<3.0). On the other hand, the surface properties of the mixtures are dominated by the flexible 6F‐BDAF, resulting in excellent polymer/polymer self‐adhesion (lamination) properties between fully imidized films.

Structure And Properties Of Binary Rodlike/Flexible Polyimide mixtures.

Abbstract:Binary mixtures of a rodlike poly(p-phenylene pyromellitimide) (PMDA-PDA) and a flexible 6F-BDAF polyimide synthesized from hexafluoroisopropylidene diphthalic anhydride and 2,2-bis(4-aminophenoxy-p-phenylene) hexafluoropropane were prepared by solution-blending of the meta-PMDA-PDA poly(amic ethyl ester) and 6F-BDAF poly(amic acid) precursors, followed by solvent evaporation and thermal imidization. The size scale of the phase separation, as measured by light scattering, is ca. I μm or smaller in most cases. Dynamical mechanical thermal analysis measurements indicate that the glass transition temperature of 6F-BDAF is unaffected in all of the mixtures studied, indicating complete demixing of rodlike and flexible polyimides in agreement with theory. X-ray photoelectron spectroscopy results show a strong surface segregation of 6F-BDAF in mixtures containing as low as 10% by weight of the 6F-BDAF component in the bulk. The mixtures with PMDA-PDA as the major matrix component therefore maintain excellent bulk properties of rodlike polymers, i.e., high modulus to 500°C, and low coefficients of thermal expansion (< ca. 10 ppm/°C). On the other hand, the surface properties of the mixtures are dominated by the flexible 6F-BDAF, resulting in excellent polymer/polymer self-adhesion (lamination) properties between fully imidized films.