Synthesis and Characterization of High-Temperature Fluorine-Containing PMR Polyimides

Low-Temperature Terpolymerizable Benzoxazine Monomer Bearing Norbornene and Furan Groups: Synthesis, Characterization, Polymerization, and Properties of Its Polymer

There is an urgency to produce novel high-performance resins to support the rapid development of the aerospace field and the electronic industry. In the present work, we designed and consequently synthesized a benzoxazine monomer (oHPNI-fa) bearing both norbornene and furan groups through the flexible benzoxazine structural design capability. The molecular structure of oHPNI-fa was verified by the combination characterization of nuclear magnetic resonance spectrum, FT-IR technology, and high-resolution mass spectrum. The thermally activated terpolymerization was monitored by in situ FT-IR as well as differential scanning calorimetry (DSC). Moreover, the low-temperature-curing characteristics of oHPNI-fa have also been revealed and discussed in the current study. Furthermore, the curing kinetics of the oHPNI-fa were investigated by the Kissinger and Ozawa methods. The resulting highly cross-linked thermoset based on oHPNI-fa showed excellent thermal stability as well as flame retardancy (T_d10 of 425 °C, THR of 4.9 KJg^-1). The strategy for molecular design utilized in the current work gives a guide to the development of high-performance resins which can potentially be applied in the aerospace and electronics industries.

Processable PMR Poly(Pyrrolone-Imide)s Matrix Resins and their Short Carbon Fiber-Reinforced Composites

Processable poly(pyrrolone-imide)s (PPI) were prepared via PMR process from diethyl ester of 4,4′-(hexafluoroisopropylidene)diphthalic acid (6FDE), 3,3′, 4,4′-tetraaminodiphenyl ether (TADPE), p-phenylenediamine ( p-PDA) and monoethyl ester of cis-5-norbornene- endo-2,3-dicarboxylic acid (NE) using methyl alcohol as solvent. The homogenous PPI matrix resin solutions with 32 wt.% solid content had the low absolute viscosities in the range of 80-90 mPa s at 25 °C. The matrix resin solutions were stable for a period of > 2 months at the refrigerator temperature (4 °C) and showed good adhesion on carbon fibers. The matrix resin solutions could be thermally converted to B-stage end-capped prepolymer, which was then thermally processed to yield the fully-cured PPI. Experimental results demonstrated that the fully-cured PPI exhibited good thermal stability with glass transition temperatures of >400 °C and the thermal decomposition temperature of 525-537 °C. The onset temperatures of the DMA storage modulus curve for PPI-20 was as high as 395 °C and the storage modulus retention was 71% at 370 °C. The short carbon fiber-reinforced PPI composites (CF/PPI) were also fabricated. The CF/PPI composites showed excellent thermal stabilities and good mechanical properties, with glass transition temperature in the range of 413-421 °C and the storage modulus retention of 76-87% at 370 °C.

Synthesis and Properties of PMR Matrix Resins of Poly(Pyrrolone-Benzimidazole)s

PMR type of poly(pyrrolone-benzimidazole) copolymers (PPBI) were synthesized by the polycondensation of monoethyl ester of cis-5-norbornene-endo-2,3-dicarboxylic acid (NE), diphenyl-isophthalate (DPIP), diethyl ester of 4,4′-oxydiphthalic acid (ODPE) and 3,3′-diaminobenzidine (DAB) or 3,3′,4,4′-tetraamindiphenyl ether(TAD) in a mixing solution of anhydrous ethyl alcohol and N -methylpyrrolidone (NMP) under different temperature and pressure procedures. The resulting resin solution showed an excellent solubility in polar organic solvents and good stability at room temperature, while the corresponding PPBI molded powder and molded plate could be prepared by undergoing amidation, imidization, cyclization and crosslinking reactions when the reaction temperature would be increased from 150 to 350°C, especially, the crosslinking structure formed by the reverse Dials-Alder reaction at 270-290°C under 2.5-3.5 MPa pressure displayed by the pressure meter. The chemical reactions and properties of the resulting PPBI molded powders and molded plates were studied by means of FT-IR, TGA, DMA methods, and the results indicate that the PPBI materials obtained hold excellent thermal stability and processability, the initial decomposition temperature > 600°C and its T g defined by the peak temperature in tan δ curve from the DMA method is 448°C (DAB) or 423°C (TAD) for PPBI-20 molded plate.

Insights into the Mechanism and Kinetics of Thermo-Oxidative Degradation of HFPE High Performance Polymer

The growing requisite for materials having high thermo-oxidative stability makes the design and development of high performance materials an active area of research. Fluorination of the polymer backbone is a widely applied strategy to improve various properties of the polymer, most importantly the thermo-oxidative stability. Many of these fluorinated polymers are known to have thermo-oxidative stability up to 700 K. However, for space and aerospace applications, it is important to improve its thermo-oxidative stability beyond 700 K. Molecular-level details of the thermo-oxidative degradation of such polymers can provide vital information to improve the polymer. In this spirit, we have applied quantum mechanical and microkinetic analysis to scrutinize the mechanism and kinetics of the thermo-oxidative degradation of a fluorinated polymer with phenylethenyl end-cap, HFPE. This study gives an insight into the thermo-oxidative degradation of HFPE and explains most of the experimental observations on the thermo-oxidative degradation of this polymer. Thermolysis of C-CF3 bond in the dianhydride component (6FDA) of HFPE is found to be the rate-determining step of the degradation. Reaction pathways that are responsible for the experimentally observed weight loss of the polymer is also scrutinized. On the basis of these results, we propose a modification of HFPE polymer to improve its thermo-oxidative stability.

Synthesis and Characterization of Soluble Polyimides Derived from the Polycondensation of 2,6-bis(4-amino-2-trifluoromethylphenoxy-4'-benzoyl)pyridine with Some Aromatic Dianhydrides

A new aromatic diamine monomer containing both pyridine and fluorine, 2,6-bis(4-amino-2-trifluoromethylphenoxy-4 '-benzoyl)pyridine (BAFP), was successively synthesized by the nucleophilic substitution reaction of 2,6-bis(4,4'-dihydroxybenzoyl)pyridine with 2-chloro-5-nitro-trifluoromethylbenzene in the presence of k2CO 3 in N, N-dimethylacetamide, and followed by reduction with SnCl2 and HCl in ethanol. The polycondensation of BAFP with four aromatic dianhydrides afforded a series of novel aromatic polyimides containing both pyridine and fluorine. The reaction was conducted by the one-step thermal imidization method. The resulting polyimides were characterized for inherent viscosity, solubility, and thermo-oxidative stability. The polyimides exhibited excellent solubility in various solvents such as N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO) and chloroform. The glass-transition temperatures ( Tg) were in the range of 206—227°C. The polyimides displayed good thermal stability, e.g. the temperatures at the 5% weight loss range were at 487—543°C in nitrogen and 463—521°C in air, respectively. Wide-angle X-ray diffraction measurements revealed that the polyimides were predominantly amorphous.