Design of Co-Cured Multi-Component Thermosets with Enhanced Heat Resistance, Toughness, and Processability via a Machine Learning Approach

Designing heat-resistant thermosets with excellent comprehensive performance has been a long-standing challenge. Co-curing of various high-performance thermosets is an effective strategy, however, the traditional trial-and-error experiments have long research cycles for discovering new materials. Herein, a two-step machine learning (ML) assisted approach is proposed to design heat-resistant co-cured resins composed of polyimide (PI) and silicon-containing arylacetylene (PSA), that is, poly(silicon-alkyne imide) (PSI). First, two ML prediction models are established to evaluate the processability of PIs and their compatibility with PSA. Then, another two ML models are developed to predict the thermal decomposition temperature and flexural strength of the co-cured PSI resins. The optimal molecular structures and compositions of PSI resins are high-throughput screened. The screened PSI resins are experimentally verified to exhibit enhanced heat resistance, toughness, and processability. The research framework established in this work can be generalized to the rational design of other advanced multi-component polymeric materials.

Chemorheological Monitoring of Cross-Linking in Slide-ring Gels Derived From α-cyclodextrin Polyrotaxanes

Despite hundreds of studies involving slide-ring gels derived from cyclodextrin (CD)-based polyrotaxanes (PRs), their covalent cross-linking kinetics are not well characterized. We employ chemorheology as a tool to measure the gelation kinetics of a model slide-ring organogel derived from α-cyclodextrin/poly (ethylene glycol) PRs cross-linked with hexamethylenediisocyanate (HMDI) in DMSO. The viscoelastic properties of the gels were monitored in situ by small-amplitude oscillatory shear (SAOS) rheology, enabling us to estimate the activation barrier and rate law for cross-linking while mapping experimental parameters to kinetics and mechanical properties. Gelation time, gel point, and final gel elasticity depend on cross-linker concentration, but polyrotaxane concentration only affects gelation time and elasticity (not gel point), while temperature only affects gelation time and gel point (not final elasticity). These measurements facilitate the rational design of slide-ring networks by simple parameter selection (temperature, cross-linker concentration, PR concentration, reaction time).

Phenylethynyl-terminated oligoimides with ultra-low melt viscosity derived from 1,4-bis(3,4-dicarboxy phenoxy)benzene dianhydride

Most of the existing polyimide oligomers for resin transfer molding (RTM) processing exhibited high melt viscosity, which can only maintain below 1 Pa·s at 280°C for 2 h, leading to very high process temperatures. So novel RTM-type oligomers with lower and stable melt viscosities are more desirable. Three series of thermoset oligoimides derived from 1,4-bis(3,4-dicarboxy phenoxy)benzene dianhydride and three different aromatic diamines were prepared herein. The diamines included 4,4′-oxydianiline, 2,2′-bis(trifluoromethyl)benzidine (TFDB), and 2-phenyl-4,4′-diaminodiphenyl ether ( p-ODA). 4-Phenylethynylphthalic anhydride was used as an endcapping reagent. Effects of the chemical structures and molecular weights of the oligoimides on their aggregated structures, melt processability, and the thermal and mechanical properties of the cured films were then systematically investigated. X-Ray diffraction results indicated that ODA series oligoimides and TFDB series oligoimides showed crystallinity in various degrees. However, the asymmetric p-ODA enables the p-ODA series oligoimides to exhibit amorphous forms. It was found that the p-ODA-based oligoimide with a molecular weight of 750 g mol−1 showed very low melt viscosity of 1 Pa·s even at 210°C, and the melt viscosity could maintain below 1 Pa·s after isothermal aging for 2 h at any temperature in the range of 200–280°C by rheological measurements. The cured film also showed a high glass transition temperature of 355°C by dynamic mechanical analysis, very good thermal stability by thermogravimetric analysis, and good mechanical properties. It might be more suitable for RTM processes in the future.

An improved simplified approach for curing kinetics of epoxy resins by nonisothermal differential scanning calorimetry

The curing kinetics of two different types of commercial epoxy resins were investigated by means of nonisothermal differential scanning calorimetry (DSC) in this work. The complex curve of measured heat flow of CYCOM 970 epoxy resin was simplified with the method of resolution of peak. Two typical autocatalytic curing reaction curves were gained and the kinetic parameters of the curing process were demonstrated by combination of those two reactions. The Kissinger method was adopted to obtain the values of the activation energy. The parameters of curing kinetic model were acquired according to the fitting of Kamal model. Isothermal DSC curve of CYCOM 970 epoxy resin obtained using the experimental data shows a good agreement with that theoretically calculated. Then, 603 epoxy resin was investigated by the simplified method and the kinetic parameters were received through the same procedure. The nonisothermal DSC curve tested according to the recommended cure cycle of 603 epoxy resin is also consistent with the calculated results. This improved simplified approach provides an effective method to analyze the curing kinetics of the epoxy resins with complex DSC curves as similar to this study.

Thermal curing of novel carborane-containing phenylethynyl terminated imide oligomers

The thermal behavior of novel carborane-containing phenylethynyl terminated imide model compound and resultant resin systems was studied in this paper.