Elena Hamciuc

Fluorinated heterocyclic polyamides

Abstract New thermostable fluorinated heterocyclic polyamides have been synthesized by low-temperature solution polycondensation of various aromatic diamines which contain phenylquinoxaline or 1,3,4-oxadiazole units, with a diacid chloride containing imide rings, hexafluoroisopropylidene (6F) group and methylene bridges. These polymers are readily soluble in polar amidic solvents, such as N-methylpyrrolidinone (NMP) and dimethylformamide (DMF) and can be cast into flexible thin films from solutions. They show high thermal stability with decomposition temperature being above 350°C and glass transition temperature in the range of 260–306°C, good electrical insulating properties with dielectric constant being in the range of 3.3–3.6 and tough mechanical properties.

Synthesis and study of new silicon-containing polyoxadiazoles

A series of new poly-1,3,4-oxadiazoles has been synthesized by polycondensation reaction of hydrazine sulfate with a mixture of a dicarboxylic acid containing unsaturated bonds and a dicarboxylic acid containing silicon, by using methanesulfonic acid/phosphorus pentoxide as a reaction medium. These polymers were highly thermostable but they were only soluble in strong inorganic acids such as sulfuric or methanesulfonic ones. An alternative way was followed by using the corresponding dihydrazides containing unsaturated bonds and the corresponding diacid chloride containing silicon that reacted in N-methylpyrrolidinone (NMP) to give soluble silicon-containing unsaturated polyhydrazides, which were cyclodehydrated either by thermal or chemical treatment to give the corresponding polyoxadiazoles. Very thin coatings of polyhydrazides and polyoxadiazoles were deposited onto silicon wafers and they showed a very smooth surface, free of pinholes, when studied by atomic force microscopy (AFM). Some polyoxadiazole films showed strong blue photoluminescence.

New Silicon-Containing Poly(Imide-Amide)s

New aromatic silicon-containing poly(imide-amide)s have been synthesized by solution polycondensation of various aromatic diamines having ether bridges between phenylene rings with a diacid chloride containing silicon. These polymers are easily soluble in polar amidic solvents such as N-methyl-pyrrolidinone or dimethylformamide and can be cast into thin flexible films or coatings from such solutions. They show high thermal stability, with an initial decomposition temperature above 410°C and a glass transition temperature in the range of 251-285°C. Very thin polymer films deposited by the spincoating technique onto silicon wafers showed a smooth, pinhole-free surface in atomic force microscopy investigations.

The effect of the rotation hindrance on physical properties of some heterocyclic polyamides containing pendent imide groups

Conformational parameters of a series of heterocyclic polyamides with pendent imide groups were calculated by the Monte Carlo method with allowance for hindered rotation. Several physical properties of these polymers, such as solubility, glass transition temperature and initial decomposition temperature were experimentally measured and discussed in relation with the rigidity of their chains. Some relationships have been shown.

Influence of the Conformational Parameters on Physical Properties of Some Polyamides Containing Phenylquinoxaline Rings

Conformational parameters of some heterocyclic polyamides containing phenyl-substituted quinoxaline rings have been calculated by the Monte Carlo method taking into consideration the hindered rotation produced by the side phenyl groups. Several physical properties such as solubility, glass transition temperature, initial decomposition temperature and dielectric constant have been studied with regard to the rigidity of the chains of these polymers, and their relationships have been shown.

New Poly(Imide‐Ether‐Amide)s Based on Epiclon

Epiclon, 5‐(2,5‐dioxotetrahydrofurfuryl)‐3‐methyl‐3‐cyclohexenyl‐1,2‐dicarboxylic acid anhydride, reacted with p‐aminobenzoic acid to give a dicarboxylic acid containing imide rings. This was further treated with thionyl chloride to give the corresponding diacid chloride having epiclon units and imide rings. New poly(imide‐ether‐amide)s have been synthesized by a solution polycondensation reaction of this diacid chloride with various aromatic diamines having ether bridges between phenylene rings. These polymers are easily soluble in polar amidic solvents such as N‐methylpyrrolidinone or dimethylformamide and can be cast into thin flexible films or coatings from such solutions. They show high thermal stability, with initial decomposition temperature being above 350°C and glass transition temperature in the range of 223°C–238°C.

Poly(1, 3, 4-Oxadiazole-Amide)s Containing Pendent Phenoxy Groups

A series of new poly(1, 3, 4-oxadiazole-amide)s have been synthesized by solution polycondensation of aromatic diamines containing preformed 1, 3, 4-oxadiazole rings with phenoxyterephthalic diacid chloride or by the reaction of the same diacid chloride with p-aminobenzhydrazide resulting in a polyhydrazide-amide which was cyclodehydrated to the corresponding oxadiazolic structure. The new polymers were soluble or partially soluble in polar amidic solvents, were stable up to 375–400 °C in air and had a glass transition temperature in the range of 225–272 °C.

Environmentally friendly fire-resistant epoxy resins based on a new oligophosphonate with high flame retardant efficiency

Advanced flame retardant epoxy resins, environmentally friendly, with different contents of a new oligophosphonate (PFR), were prepared using dicyandiamide as a hardener and 1,1-dimethyl-3-phenylurea as an accelerator. PFR, with a high phosphorus content, was synthesized by polycondensation reaction of phenylphosphonic dichloride with a phosphorus-containing bisphenol, namely bis((6-oxido-6H-dibenz[c,e][1,2]oxaphosphorinyl)-(4-hydroxyaniline)methylene)-1,4-phenylene. The bisphenol was prepared by reacting 9,10-dihydro-oxa-10-phosphaphenanthrene-10-oxide with an imine bisphenol resulting from the condensation of 4-aminophenol with terephthalaldehyde. The structure and morphology of cured epoxy resins were evaluated by Fourier transform infrared spectroscopy and scanning electron microscopy (SEM) analysis, respectively. Differential scanning calorimetry analysis revealed that cured epoxy resins containing PFR possessed slightly higher glass transition temperatures than phosphorus-free cured epoxy resin. Thermogravimetric analysis and limiting oxygen index values indicated that the incorporation of PFR into epoxy resin substantially enhanced the thermal stability and flame retardancy of the char layer at high temperature. The surface morphology of the char residue was studied by SEM measurements. The kinetic processing of thermogravimetric data was carried out using Friedman and Vyazovkin methods. The lifetime prediction analysis established that the fire-resistant phosphorus-containing epoxy resins could be used at a constant temperature of 200 °C up to 620–630 minutes. The new PFR can be successfully used as a very efficient flame retardant for improving the fire-resistance properties of epoxy resins.

Silica-containing fluorinated poly(amide-imide) hybrid films

New silica-containing hybrid films were prepared using a fluorinated poly(amide-imide) having hydroxyl groups and tetraethoxysilane, via the sol–gel technique. The polymer was synthesized by solution polycondensation reaction of a mixture of two diamines, 4,4′-diamino-4′′-hydroxy-triphenylmethane and 1,3-bis(4-aminophenoxy)benzene (molar ratio 3/7), with a fluorinated diacid chloride containing imide rings, 2,2-bis[N-(4-chloroformylphenyl)phthalimidyl]hexafluoroisopropane. To improve the compatibility between the polymer and silica, the pendant hydroxyl groups of the polymer were reacted with 3-(triethoxysilyl)propyl isocyanate. The hybrid films were flexible, tough, and exhibited high thermal stability, having the initial decomposition temperature above 420 °C. The surface morphology of the hybrid films was investigated by scanning electron microscopy. Dynamic mechanical analysis and dielectric spectroscopy revealed subglass transitions, γ and β, and an α relaxation corresponding to the glass transition temperature. Electrical insulating properties were evaluated on the basis of dielectric constant and dielectric loss and their variation with the frequency and temperature. The values of the dielectric constant at 10 kHz and 20 °C were in the range of 3.18–3.48. The influence of the silica content on the polymer properties was examined.

Study of Aromatic Polyimides Containing Cyano Groups

Aromatic polyimides containing cyano groups have been synthesized by solution polycondensation reaction of an aromatic diamine having cyano and ether groups, with various aromatic dianhydrides containing flexible groups such as carbonyl and hexafluoroisopropylidene. The properties of these polyimides were compared with those of related polymers based on rigid aromatic dianhydrides, such as biphenyltetracarboxylic and pyromellitic dianhydride, and the same cyano containing diamine. The polymers were easily soluble in polar organic solvents, such as N-methylpyrrolidinone, N,N-dimethylacetamide and N,N-dimethylformamide and exhibited remarkable film forming ability, except for polyimide derived from pyromellitic dianhydride. They showed high thermal stability, with initial decomposition temperature being above 400 °C and glass transition temperature in the range of 210—260 °C. Conformational rigidity parameters of these polymers have been calculated by Monte Carlo method with allowance for hindered rotation. Several physical properties such as solubility and glass transition temperature are discussed in relation to the structure of the polymers and rigidity of their chains. The calculation of parameters of conformational rigidity showed that the glass transition temperature values (220—230 °C) increase with the increase of the rigidity. The polymers based on pyromellitic dianhydride form a separate group having the glass transition temperature values above 250 °C.