High Performance Polymers

In this article, initial steps were taken in the study of processing mixtures of a polymer and a preceramic polymer to produce a hybrid material that contains a region of gradual transformation from a polymer to a ceramic. It is thought to be a first step toward the eventual development of a hybrid that is graded from a polymer matrix composite to a ceramic matrix composite. Thermal analysis, elemental analysis, and morphology characterization of blends of RD-730 preceramic polymer, which converts to silicon carbide upon pyrolyzation, and Matrimid A/B polymer which is a bismaleimide were carried out as a function of cure cycles. The cure cycles were chosen to vary the resin viscosity at specific times during processing in order to affect the amount of phase separation of the two resins. These results were then used to make conclusions on how processing parameters affected the miscibility of the two resins and the likelihood of producing a hybrid having mechanical and thermal properties that fall between those of the two constituents. High RD-730 loadings were achieved without phase inversion, the glass transition temperature (T_g) of the blended material was shown to be significantly influenced by a post-cure, and a spatial gradient in RD-730 concentration was noted.

Here, for the first time, we report the synthesis of a new class of optically active polymers, poly(amide-thioester-imide)s (PATEI)s, containing flexible and anticorrosion linkages. Step growth polymerization of a novel diamine with diacids containing amino acid and trimellitylimide groups in tetrabutylammonium bromide, in the molten state, which acts as a molten ionic salt medium, was carried out. The obtained polymeric materials were of the nanoscale size and were assembled by filamentary particles as shown by field-emission scanning electron microscopy micrographs, which were distributed uniformly and randomly, with an average nanosize diameter of about 40 nm. The polymeric samples were readily soluble in a variety of common organic solvents and formed low-colored and flexible thin films via solution casting. The values of absorption edge wavelength (λ₀) were determined by ultraviolet–visible spectroscopy, and all of the resulting PATEI films exhibited high-optical transparency. According to x-ray diffraction patterns, all the PATEIs were amorphous. The structure of PATEIs were also characterized by Fourier-transform infrared spectroscopy, Proton-nuclear magnetic resonance, elemental, and thermogravimetric analysis techniques. The effect of ultrasound on the morphology of polymers was also investigated. This study confirmed that the size of polymer particles decreased and there was a change in their morphology.

Series of aromatic polyamides containing azo groups have been synthesized by the phosphorylation polycondensation of a new dicarboxylic acid (E)-1-(4-(4-(3-carboxypyridylazo)thiocarbamoylaminophenyl-sulfonyl)phenyl)-3-(3-carboxypyridylazo)-thiourea and various diamines. Poly(azo-sulfone-amide)s (PASAs) were characterized using spectroscopic techniques, solubility, molar mass, electrical conductivity, mechanical strength, nonflammability, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) studies. PASAs possessed fine solubility in polar solvents and high molar mass 70 × 10³–75 × 10³ gmol⁻¹. These polyamides showed fibrous structure according to field-emission scanning electron microscopy (FESEM). Thermal and nonflammability data indicated that PASAs were fairly stable above 500°C having initial weight loss of around 525–531°C, 10% of gravimetric loss in the range of 542–563°C, own high glass transition temperature 257–267°C and limiting oxygen index (LOI) values (35–47%). The polymers also demonstrated higher tensile strength (61.10–74.29 MPa) and elongation at break (1.49–1.57). FESEM images displayed fibrous morphology of the PASAs. Moreover, polyamides showed superior electrical conductivity (1.45–1.92 S cm⁻¹). Fine balance of the properties render the new PASAs potential engineering plastics for a number of aerospace relevance.

The problem of phase separation in polycarbosilane (Starfire resin)–Matrimid thermoset blend structures, designed for thermal protection applications, was addressed in this study. The structural design of the compatibilizers synthesized via a hydrosilylation–deprotection sequence was primarily based on a polymer structure with a nonpolar segment consisting of a carbosilane unit and a polar segment with a bisphenol-type moiety. Besides the homopolymer, block copolymers with varying contents of the polycarbosilane unit and the bisphenol A unit were synthesized and characterized. Curing experiments on the blends of Starfire resin–Matrimid incorporating 1–5% of the compatibilizers were performed followed by morphological characterization of the cured resin plaques. The effectiveness of the compatibilizers was assessed by the StarFire domain size and the distribution of cured specimens was examined in the scanning electron micrographs. Results indicated that the compatibilizers that were more effective in minimizing phase separation were relatively more polar and comprised a larger fraction of the phenolic functional units. In fact, the blend composition incorporating 5% of the homopolymer compatibilizer with the largest fraction of the polar bisphenol A unit was highly effective in providing a homogeneous distribution of very small StarFire domains, that is, fairly uniform domain sizes of the order of 5 µm or less.

The compound bispropargyl ether of bisphenol-A (BPEBPA) is prepared using phase transfer catalyst. Different copper salts like cuprous chloride (CuCl), cupric chloride dihydrate (CuCl₂.2H₂O), copper sulphate pentahydrate (CuSO₄.5H₂O), basic copper carbonate (CuCO₃.Cu(OH)₂), cupric acetate monohydrate ((CH₃COO)₂Cu.H₂O), and cupric oxide (CuO) are blended separately with BPEBPA (1%, w/w) and the curing characteristics of these materials are investigated using differential scanning calorimetry (DSC). The presence of copper salt in BPEBPA shifts the curing temperature to a lower temperature region. The materials are thermally cured and the structural characterisation and the thermal properties of these cross-linked materials are investigated using Fourier-transform infrared (FTIR) spectrophotometer and thermogravimetric analyzer (TGA). Of the different copper salts investigated, the presence of copper sulphate pentahydrate in BPEBPA increases the thermal stability of the cured BPEBPA. The thermal degradation products of thermally cured pure BPEBPA and copper salts containing BPEBPA are studied using TG-FTIR. The phenols, substituted phenols, carbon monoxide (CO), carbon dioxide (CO₂), and alkenes are major volatiles evolved during the thermal degradation of these materials.

In order to improve the dielectric and overall properties of cyanate ester (CE) resin, octa(aminopropyl)silsesquioxane (POSS-NH₂) was used to modify CE. A series of POSS-NH₂/CE hybrids containing different contents of polyhedral oligomeric silsesquioxane (POSS) were elaborated by melt casting and then curing. The curing kinetics and reaction mechanisms of the resin systems were studied using Fourier-transform infrared (FT-IR). Dielectric properties, thermal stability, and hot/wet resistance of the hybrids have been investigated. FT-IR results show that both temperature and POSS content may influence the curing reaction of CE. POSS-NH₂ mainly displays the catalytic effect at higher temperature (220°C). Dielectric results indicate that NC1 containing 1 wt% of POSS displays not only the lowest dielectric constant but also the lowest dielectric loss. The increase in POSS content leads to significant increase in glass transition temperature (T_g) at lower POSS content (≤5 wt%). However, further increase in POSS content (>5 wt%) does not lead to great increase in T_g. Besides, all the POSS-NH₂/CE hybrids show lower water absorption than that of CE.

Hybrid nanocomposites (NCs) produced by the dispersion of zinc oxide (ZnO) nanoparticles (NPs) in thermoplastic poly(amide-imide)s (PAIs) are designed and synthesized using ultrasonic-assisted technology. ZnO NPs were functionalized with 3-aminopropyltriethoxysilane (KH550) coupling agent to increase the hydrophobic nature of NPs. Reaction of diamine containing N-(4-hydroxyphenyl) benzamide and a diacid chloride comprising pyromellitoyl-bis-l-isoleucine segments at low temperature provided the polymeric matrix with well-designed groups. Surface treatments of ZnO NPs gave a better dispersion and enhancing possible interactions of NPs with functional units of polymer matrix. The surface-modified ZnO NPs were dispersed uniformly in the PAIs matrix using ultrasonic irradiation. The obtained NCs were characterized by Fourier-transform infrared spectroscopy, x-ray powder diffraction, atomic force microscopy, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and thermogravimetry analysis. The FE-SEM and TEM pictures confirmed the globular-like structures for NCs.

A series of aniline-based bifunctional benzoxazines (BZs) were synthesized using solventless or solvent method via the Mannich condensation reactions. The chemical structures of these BZs were confirmed using Fourier-transform infrared and proton-nuclear magnetic resonance spectroscopies. The polymer blends were prepared by mixing silicon-containing arylacetylene (poly(dimethylsilyleneethynylenephenyleneethynylene) (PSA)) resin with BZ in weight ratios at 110°C until a homogeneous viscosity liquid was obtained. The resultant blends were characterized by solubility tests, rheological analyses, differential scanning calorimetry, dynamic mechanical analyses and thermogravimetric analyses. The good solubility and low melt viscosity of the blends indicated excellent processability. The curing reactions resulted in the formation of interpenetrating polymer networks. The cured blends exhibited high glass transition temperatures (T _g s) and thermal stabilities. The compressive strength and flexural strength of the blend casts improved when compared with pristine PSA.

Two thermoplastic polyimides were controllably synthesized with similar molecular weight from 2,3,3′,4′-oxydiphthalic anhydride (3,4′-ODPA) or 2,3,3′,4′-thioetherdiphthalic anhydride (3,4′-TDPA) with 4,4′-diaminodiphenyl ether (ODA) by a one-step method of m-cresol. The solubility and mechanical properties of these polymers were investigated for comparison. The thermal and melt processable properties of these polymers were examined carefully by differential scanning calorimetry, thermogravimetric analysis (TGA), rheometer and melt index, and so on. It was found that the glass transition temperature (T_g) of 3,4′-TDPA/ODA was about 15°C lower than that of 3,4′-ODPA/ODA, the melt indices of 3,4′-TDPA/ODA at different temperatures were higher than those of 3,4′-ODPA/ODA, while the minimum melt viscosity of 3,4′-TDPA/ODA was lower than those of 3,4′-ODPA/ODA. Furthermore, TGA results showed that 3,4′-TDPA/ODA had different degradation mechanism in air compared with 3,4′-ODPA/ODA. The long-term thermooxidative stability results showed that 3,4′-TDPA/ODA had better thermal oxidative stability than 3,4′-ODPA/ODA at 410°C for 6 h in air, which could be associated with the results of apparent activation energy (E_a) of polymers calculated by TGA dynamics. The natural bond orbital charge of ethero atoms (S or O), and energy gap of the corresponding model compounds were also obtained by computational simulation to correlate with polymer properties.

Bismaleimide–allyl phenol polymer system exhibiting shape memory characteristics and possessing transition temperature of up to 220°C (T_trans) was synthesized by coreacting 2,2-bis 4[(4-maleimidophenoxy)phenyl]propane (BMIP) and o,o′-diallylbisphenol A (DABA) with a bismaleimide-end-capped poly(tetramethyleneoxide) (BMI-PTMO). BMI-PTMO that served as shape memory polymer was synthesized and characterized using Fourier-transform infrared (FTIR), nuclear magnetic resonance, chemical analysis and size exclusion chromatography. The cured network containing varying proportions of poly(tetramethyleneoxide) was synthesized by varying the concentration of BMI-PTMO in the ternary blend. Cure characteristics were investigated by FTIR, differential scanning calorimetry and rheometry. Elastic memory composites were processed using carbon fabric from varying blend composition at fixed resin to reinforcement ratio. PTMO enhanced the flexibility of the network. The system as a whole possessing high transition temperature, its storage modulus decreased with increase in PTMO content. The polymer possessed good shape recovery characteristics and the recovery time decreased with increasing concentration of the shape memory component. The system showed shape recovery of 88–98% in about a minute at T_trans. The extent of shape recovery was a direct function of PTMO concentration. The recovery time showed an inverse relationship to the modulus ratio.

The purpose of this study was to evaluate how barium-containing glass filler (BGF) reinforcement and pretreatment methods affect shear bond strength (SBS) of poly(ether ether ketone) (PEEK) to resin cement. PEEK composites with various amounts of BGF (10, 20, 30 and 40 wt%) were prepared as PEEK-BGF10, PEEK-BGF20, PEEK-BGF30 and PEEK-BGF40. Afterward, PEEK and PEEK-BGF40 specimens were treated with hydrofluoric acid, sulfuric acid (H₂SO₄), silica coating and polishing, respectively. Acrylic hollow cylinders were luted with Dentex dual-curing resin cement to the specimens. Finally, SBS measurements were conducted with a universal testing machine. The introduction of BGFs greatly enhanced SBS of PEEK to resin cement. After simply polishing with 150 grit silicon carbide papers (G150), PEEK-BGF40 exhibited the SBS value up to 19.73 ± 4.30 MPa, similar to the PEEK treated with H₂SO₄ etching. Scanning electron microscopy and x-ray photoelectron spectroscopy were used to investigate the surface morphological and chemical changes in PEEK and PEEK-BGF composites before and after surface treatment. The results indicate that the introduction of BGF particles plays a key role in improving the adhesion between PEEK and resin cement. This study provides a new method to enhance the adhesion to PEEK without breaking its surface structure, which encourage further research in PEEK composite application in dentistry.