Stereochemical structure‐property relationships in polynorbornene from simulation

Abstract

Single‐chain Monte Carlo simulations of polynorbornene were carried out for three stereochemical isomers. These simulations employed custom force field parameters derived from ab initio and semi‐empirical quantum calculations. The scaling of intrinsic viscosity with molecular weight was determined from these simulations. An unusually large variation in this scaling was obtained, which is attributed to the large degree of steric hindrance inherent in this form of polynorbornene that retains the bicyclo‐heptane ring in the backbone. The same scaling was measured for three commercial samples of this polymer produced using three different catalysts. The simulation and experimental results were consistent and the former were used to estimate the stereochemical configuration of the commercial samples. The simulation results for a stereoregular isomer of polynorbornene were also consistent with previous RIS model results. These structure‐property relationships extracted from the simulations are potentially useful in the commercialization of polynorbornene for interlayer dielectric applications in electronic packaging.

RIS Model of the Helix‐Kink Conformation of Erythro Diisotactic Polynobornene

“…Primarily, the intramolecular torsional barriers and backbone steric hindrance determines the polymer conformation while the surrounding polymer produces only minor structural perturbation. [3,4] Similar isolated chain simulations have been used previously to accurately reproduce experimental conformations in other polymer systems that do not have strong inter-chain interactions. [20][21][22] The modeled erythro diisotactic PNB chain began either in its extended conformation (torsion angles at 1808) or at random conformations where the torsion angles were randomly and uniformly selected from the trans (1808) and gauche (AE608) states.…”

“…Simulation of PNB without this alternating bridge-head carbon showed a much less extended conformation that was similar to a random coil conformation. [3] While this previous work did include the investigation of the relative probabilities of occurrence of various RIS, it did so without including the long-range effect seen in this work. [4] Therefore it did not produce a quantitatively accurate RIS model.…”

“…Of the various catalysts studied, only the Pd catalyst produces a similar scaling. [3] In the same simulation study, the intrinsic viscosity scaled with molecular weight of the nonstereoregular polymer at just above the 1=2 power indicating a random coil conformation. This same scaling was observed experimentally for the ''naked'' Ni-catalyzed polymer indicating that this catalyst likely produced an atactic polymer.…”

“…[8][9][10] However, previous simulations and their comparison to viscometry experiments indicate that the Pd-catalyzed polymer is likely the erythro diisotactic configuration. [3] The simulation of only this configuration produces a polymer with a highly extended conformation where the polymer dimensions scale as nearly the square of the molecular weight. Of the various catalysts studied, only the Pd catalyst produces a similar scaling.…”

“…These scaling values compare well to their experimental scaling of approximately 2 determined from intrinsic viscosity. [3,4] Rotational Isomeric States Model RIS models are used to describe the microstructure of isolated polymer chains in detail as a function of their torsional angle distributions. [34,35] Additionally, RIS models can be used to generate initial conformations in periodic boundary conditions where combinations of subsequent minimizations and/or dynamics are used to relax the structure to simulate bulk behavior.…”