High Performance Polymers

To improve the melt processability of poly(phthalazinone ether sulfone ketone) (PPESK), we prepared a series of blends for PPESK with poly(ether ether ketone) oligomer (O-PEEK). The phase behavior, thermal stability, rheological and mechanical properties of the blends were investigated by means of scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis and capillary rheometry. The results show that a homogeneous microstructure was formed and all the blends were full miscible over the composition range investigated. Using O-PEEK as a processing aid can markedly improve the processability of the PPESK. In spite of the slight decrease in T _g and mechanical strength, the blends still had good heat-resistant and mechanical properties.

Epoxy-terminated polydimethylsiloxanes (E-PDMSs) of different molecular weight M _n were proved to undergo inclusion complexation into the inner cavity of β-cyclodextrin (β-CD), resulting in polyrotaxanes (PRots). The dethreading of the macrocycle was prevented by blocking the siloxane chain with a bulky substituent derived from 4-aminophenyltriphenyl methane (APhTPhM). As revealed by thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy (SEM), wide-angle X-ray diffraction and statistical analysis of SEM images, the thermal properties and the morphology of polyrotoxanes are dependent upon M _n, β-CD/E-PDMS molar ratio and the presence of free β-CD in the complexes.

The synthesis and characterization of polymers containing ketimine linkages in the main chain (P1—P6) are reported. Two ketimine polymers additionally containing a nitrogen-nitrogen double bond in the side chain were synthesized by melt polycondensation of so-called `Solvent Brown 1' with p-dibenzoylbenzene and trans-1,2-dibenzoylethylene (P3, P6), respectively. The properties of these polymers were compared with four ketimine polymers without pendent N=N bonds. Polymers were characterized by elemental analysis, FT-IR, NMR, UV-vis and photoluminescence (PL) spectroscopy. Calculated energy gaps for blends of these polymers with poly(methyl methacrylate) PMMA was 2.0 eV. Photoluminescence emission spectra of polyketimines in solution are characterized by one band in the 450—560 nm range. Polymers with N=N bond in the side chain (P3, P6) in DMA solution exhibit bathochromic shift of the emission band of about 60 nm. Additionally, the photoluminescence spectra of the polyketimines blended with PMMA were also determined. Polymers P3 and P6 blended with PMMA are about 120 nm hypsochromically shifted with respect to the PL spectra of P3 and P6 measured in DMA solution.

A new siloxane-containing monomer, 5,5¹-exo-(1,1,3,3,5,5-hexamethyl-trisiloxane -1,5-diyl) bisbicyclo[2,2,1]heptene-2,3-endo-dicarboxylic anhydride (3) was synthesized by the hydrosilylation reaction of 1,1,3,3,5,5-hexamethyl-trisiloxane (1) and cis-5-norbornene-endo-2,3-dicarboxylic anhydride (2). A series of organosoluble polysiloxaneimides (PI 5a-e) was prepared from the dianhydride 3 and several aromatic diamines 4 by a one-step high-temperature polycondensation method and the structures were characterized by IR and NMR. The effects of the main chain siloxane groups on the properties of PIs were evaluated by solubility, thermal stability and dielectric properties in addition to optical and water adsorption. The PIs were readily soluble in polar aprotic solvents such as NMP, DMAc and CHCl ₃ at room temperature, except PI 5a, which was only soluble in polar amide type solvents at elevated temperature. PIs 5a-e had glass transition temperatures between 138 and 251°C in N₂ and the 5% weight loss temperature ranged from 460 to 470°C under air. The PIs could be cast into flexible and tough films from DMAc solution. The films had tensile strengths of 44—52 MPa, tensile moduli of 0.56—0.68 GPa and elongations at break from 5.8—7.9%. The PI films exhibited good optical UV-vis transparency with wavelength cutoff of 269—289 nm and transmittances over 90% at 400 nm, and dielectric constants of about 2.76—2.65 with low water adsorption (0.3—0.4%).

Poly(1,3,4-oxadiazole-ether)s containing isopropylidene, hexafluoroisopropylidene, cyclohexylidene, fluorene, phthalide or phenylquinoxaline groups have been prepared by nucleophilic substitution polymerization technique of 2,5-bis( p-fluorophenyl)-1,3,4-oxadiazole with various aromatic bisphenols. The thermal decomposition behavior of the polymers was studied using thermogravimetric analysis in air, at several heating rates: 6, 10 and 14° C min . The polymers showed high thermo-oxidative stability with decomposition temperature corresponding to 5% weight loss above 380°C. The kinetic processing of data was carried out using the Coats—Redfern, Reich—Levi, Flyn—Wall and Kissinger methods.

The viscometric behavior of polyacrylonitrile solutions in dimethylformamide at 25°C has been examined at high dilutions. The reduced viscosity—concentration curves are strongly dependent on the flow conditions, being influenced by the viscometer capillary size. The observed viscosity abnormality in the extremely dilute concentration regime is also due to the adsorption phenomena on the viscometer wall surface and to conformational changes of macromolecules in solution.

Inorganic—organic hybrid nanocomposites were prepared by the following steps: (1) homogeneous dispersion of various percentages (1 to 5% w/w) of organically modified montmorollonite clay in epoxy matrix resin; (2) the resulting homogeneous epoxy—clay hybrids were modified with 10 wt.% of hydroxyl-terminated polydiemthyl siloxane (HTPDMS) using γ -aminopropyltriethoxysilane (γ APS) as coupling agent in the presence of dibutyltindilaurate catalyst; and (3) the siliconized epoxy—clay prepolymers were further modified separately with 10 wt% of three different cyanate ester monomers and cured with diaminodiphenylmethane. The chemical interactions between epoxy, clay, HTPDMS and cyanate ester were confirmed by Fourier transform infrared spectral analysis. The values obtained from differential scanning calorimetry and dynamic mechanical analysis showed that there was a significant loss of glass transition temperatures in the resulting hybrid epoxy nanocomposite systems compared with that of neat epoxy system. The inorganic clay mineral and the formation of thermally stable oxazolidinone structures and siloxane linkages during curing led to significant improvement in the thermal properties of the resulting nanocomposites. A decreasing trend was identified in the resulting nanocomposites from their values of dielectric constant and dielectric loss by the incorporation of clay, HTPDMS and cyanate ester in the epoxy resin. The intercalation/exfoliation structure was studied using X-ray diffraction analysis and the homogeneous/heterogeneous morphology was studied using scanning electron microscopy analysis in the resulting nanocomposites.

A series of novel poly(sulfoxide-urethane)s (PSUs) with enhanced thermal stability and good solubility were prepared by two different processes from 2,2^' -sulfoxide bis(4-methyl phenol) with commercially available diisocyanates. In the first process the PSU_a-d were prepared by solution polymerization in dry N,N-dimethylacetamide (DMAc) under gradual heating. In the second process, the PSU_1-4 were synthesized under reflux conditions. The resulting polymers exhibited inherent viscosities in the range of 0.19—1.10 dL g^-1 and 0.13—0.79 dL g ^-1 for PSU_a-d and PSU_1-4, respectively. All of the polymers were characterized by Fourier transform infra-red spectroscopy and elemental analyses. The PSUs exhibited a good solubility in a variety of polar solvents. The glass transition temperatures of the PSU_a-d as determined by differential scanning calorimetry (DSC) were in the range 154—200³C. The 10% weight loss temperatures of the PSU _a-d as determined by dynamic thermogravimetric analysis were found to be in the range 235—305³C in argon atmosphere.

This paper examines the compressive and tensile strength of Kevlar-29/Derakane composites using as-received Kevlar-29 and a thermally enhanced version of the fiber. Previous studies have shown that thermal enhancement results in a form of Kevlar-29 with significantly better compressive strength at a cost of 10—20% of its tensile strength. This study compared the mechanical properties of unidirectional composites made using as-received and thermally enhanced forms of Kevlar-29 fibers. The composites made with the thermally treated fiber showed a decrease in tensile strength roughly proportional to the difference in tensile strength of the fibers. Although the improvement in the compressive strength of the composites made with the thermally treated fibers was statistically significant, it was less than anticipated. A change in predominant failure mechanism also occurred with most as-received fiber-based composites failing from a debonding/pull-out mechanism, while composites made with the thermally enhanced fiber failed primarily from microbuckling with attendant splitting.