A Molecular Dynamics Study of Crosslinked Phthalonitrile Polymers: The Effect of Crosslink Density on Thermomechanical and Dielectric Properties

Abstract

Abstract:In this work, molecular dynamics (MD) and molecular mechanics (MM) simulations are used to study well-equilibrated models of 4,4 -bis(3,4-dicyanophenoxy)biphenyl (BPh)-1,3-bis(3-aminophenoxy)benzene (m-APB) phthalonitrile (PN) system with a range of crosslink densities. A cross-linking technique is introduced to build a series of systems with different crosslink densities; several key properties of this material, including thermal expansion, mechanical properties and dielectric properties are studied and compared with experimental results. It is found that the coefficient of linear thermal expansion predicted by the model is in good agreement with experimental results and indicative of the good thermal stability of the PN polymeric system. The simulation also shows that this polymer has excellent mechanical property, whose strength increases with increasing crosslink density. Lastly and most importantly, the calculated dielectric constant-which shows that this polymer is an excellent insulating material-indicates that there is an inverse relation between cross-linking density and dielectric constant. The trend gave rise to an empirical quadratic function which can be used to predict the limits of attainable dielectric constant for highly crosslinked polymer systems. The current computational work provides strong evidence that this polymer is a promising material for aerospace applications and offers guidance for experimental studies of the effect of cross-linking density on the thermal, mechanical and dielectric properties of the material.

Statistical Analyses of Inverse Miniemulsion Acrylic Acid Polymerizations for Encapsulation of Hydrophilic Compounds

“…For thermal stability, the model presented a correlation coefficient value (R) of 0.84, indicating that the model was able to describe fairly well the experimental results with 6° of freedom. The positive effect of reaction temperature and crosslinker content on the thermal stability is probably related to the increase of the molecular weight averages and crosslinking density, as also observed in the literature for other crosslinked polymer materials . Besides, synergetic effects could also be observed between the initial AA content and the reaction temperature and initial EGDMA content.…”

“…The positive effect of reaction temperature and crosslinker content on the thermal stability is probably related to the increase of the molecular weight averages and crosslinking density, as also observed in the literature for other crosslinked polymer materials. [22][23][24][25] Besides, synergetic effects could also be observed between the initial AA content and the reaction temperature and initial EGDMA content. This indicates that the AA effect on thermal stability depends on the reaction temperature and EGDMA content, as both variables affect the formation of the linear PAA segments and crosslinking density.…”

Benzoxazine Containing Fluorinated Aromatic Ether Nitrile Linkage: Preparation, Curing Kinetics and Dielectric Properties

“…The variations of dielectric constant and dielectric loss with regard to frequency for poly(FAEN-Bz) cured at various temperatures were presented in Figure 14. Dielectric properties for polymers are mainly influenced by relaxation mechanisms and dielectric polarization in bulk of the composites [48]. It can be observed from Figure 14a that dielectric constant was frequency dependent for poly(FAEN-Bz) polymers and decreased with increasing the frequency.…”

Polycyanurates via Molecular Dynamics: In Situ Crosslinking from Di(Cyanate Ester) Resins and Model Validation through Comparison to Experiment

“…This approach is similar to that of Chua et al in the simulated crosslinking of phthalonitriles. 27 The initial addition step and propagation steps were given a relative rate of 1 and the cyclization a relative rate of 100. The cutoff distance was increased to 7 Å for the cyclization step to account for the larger distance involved with a fully extended linear trimer.…”