Phenylethynyl-terminated imide oligomers derived from thioetherdiphthalic anhydride isomers with decreased melt viscosities

A series of oligomers based on the mixture of thioetherdiphthalic anhydride isomers and 4,4′-oxydianiline with 4-phenylethynylphthalic anhydride as reactive endcapping reagent were prepared. The calculated molecular weights were in the range of 1150–5070 g mol−1 with different degrees of polymerization ( n = 1, 3, 5, 7, and 9). The effect of molecular weight of the aromatic oligomers on their processability and solubility as well as the thermal and mechanical properties of the thermal-cured polyimides (PIs) was systematically investigated. The typical oligomer (Oligo-1) could be melted at temperatures of 289–334°C to yield stable molten fluid with melt viscosity below 1.0 Pa s. The melt viscosity of the oligomers increased with the increasing molecular weight. After thermally curing at 370°C, the thermoset PIs exhibited good thermal properties. The glass transition temperatures of oligomers measured by differential scanning calorimetry were in the range of 286–326°C, and the temperature of 5% weight loss was higher than 524°C. The cured films also showed good mechanical properties with tensile strength above 72 MPa and modulus more than 2.5 GPa.

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.

Highly soluble phenylethynyl-endcapped imide oligomers derived from thioetherdiphthalic anhydride isomers

Novel imide oligomers (calculated molecular weights: 1250–5000 g mol−1) based on the mixture of thioetherdiphthalic anhydride isomers ( m-TDPA) with 2-phenyl-4,4′-diaminodiphenyl ether ( p-ODA) in the presence of 4-phenylethynylphthalic anhydride (PEPA) as reactive endcapping agent were prepared. Then pyromellitic dianhydride (PMDA) was introduced to the polymerization of m-TDPA/ p-ODA (mole m-TDPA:molePMDA = 1:1). The effect of molecular weights and polymer chemical structures of the aromatic oligomers on their processability and solubility as well as the thermal and mechanical properties of the thermal-cured polyimides (PIs) was systematically investigated. All the oligomers showed good solubility (more than 30 wt%) in N-methyl-2-pyrrolidone and very low melt viscosities. The minimum melt viscosities of Oligo-5 was 61.5 Pa s at 321°C. The melt viscosity of the oligomers increased with the increase of molecular weight. After thermally curing at 370°C for 1 h, the thermoset PIs exhibited good thermal properties. The glass transition temperatures of oligomers measured by differential scanning calorimetry were in the range of 264–337°C, and the temperature of 5% weight loss was higher than 505°C. The cured films also demonstrated good mechanical properties with tensile strength and modulus greater than 52 MPa and 2.9 GPa, respectively.