Molecular packing density in the crystalline state of semi‐rigid chain polymers. I: Polyimides

Abstract

Published data on crystal lattice unit cell parameters were used to calculate molecular packing density coefficients (Kc) in the crystalline state for a series of polyimides. The values of Kc were shown to decrease, the larger the chain cross‐section thickness, and the lower the ratio of chain persistence length to chain thickness.

Precise Analysis of Thermal Volume Expansion of Crystal Lattice for Fully Aromatic Crystalline Polyimides by X-ray Diffraction Method: Relationship between Molecular Structure and Linear/Volumetric Thermal Expansion

“…Based on the above discussion, the weight density of a PI crystal is expected to be strongly related to its CVE. On the other hand, it is plausible to expect that the volume fraction of the crystal’s free volume will be correlated to some extent with its CVE. , In Figures a and b, the CVEs of all of the studied PIs are plotted against their volume fraction and absolute weight density, respectively. Herein, the volume fraction was calculated based on the van der Waals volume of the repeating unit (Supporting Information).…”

Accelerated Discovery of High-Refractive-Index Polyimides via First-Principles Molecular Modeling, Virtual High-Throughput Screening, and Data Mining

“…One path to narrowing down compound space is to maximize the polarizability for systems from the same compound family, for which the number density is similar. Given that this is known to be the case for PIs, we pursue this path and focus our search on highly polarizable PI candidates …”

“…We obtain V vdW using Slonimskii's method detailed in ref 54 and K p using the support vector regression (SVR) machine learning model introduced in ref 46 (except during the prescreening of individual residues R 1 and R 2 discussed in the following section, for which we simply employ a constant K p of 0.75 that is typically found in PIs 55 ). We obtain the asymptotic limit for the polymers via a linear extrapolation scheme as outlined in ref 46.…”

“…Given that this is known to be the case for PIs, we pursue this path and focus our search on highly polarizable PI candidates. 55 For this, we create a PI library based on 29 building blocks and bonding rules shown in Figure 3, which we select following empirical expertise with regard to promise and synthetic feasibility. The building blocks can be divided into linkers (B1−B6) and (hetero)aromatic moieties (B7−B29).…”

The relationship between nonexponential relaxation and molecular stiffness in aromatic model compounds

“…Similarly to the case of the narrow polystyrene fractions, 12 the experimental values of ␤ for the model compounds change continuously in the interval from 0.65 to 0.49 with no evidence for preference of one of the theoretical values, ␤ ϭ3/5 or 3/7, expected for systems in which the relaxation is dominated by short-range or by long-range interactions, respectively. 8 It can be seen ͑Table I͒, however, that the ␤ values tend to decrease with increasing chain stiffness as expressed through the mean length of the virtual bond: 19,20 ͗l͘ϭL/(nϩ1). Here, L is the molecular contour length 15 ͑i.e., that corresponding to its full extension͒ ͑Table I͒, and n is the number of intramolecular swivels permitting unhindered internal rotation.…”