Methylated Tetrahydrophthalic Anhydrides as End Caps in Addition Polyimides

Abstract

Thermolysis of methylenedianiline (MDA) 1,2,3,6-tetrahydrophthalic (THP) bismides up to 371 °C, produces aromatic product, with a concomitant lowering in cross-linking. This aromatization is responsible for both the improved thermal oxidative stability of THP end-capped polyimides and their substantial frangibility. In the hope of inhibiting precuring aromatization, 2,3-dimethyl, 3,3-dimethyl, and 1,2,3-trimethyl THP analogues were synthesized and reacted with MDA in a 2:1 ratio, heating gradually from 204 to 371 °C. In the lower temperature range, monoimide transforms to bisimide. At temperatures above 320 °C, cross-linking predominates;generally reaching ∼30% at 371 °C, though it was as much as 69% for 3,3-dimethyl THP. The surprising facility of cross-linking in the latter was correlated to the double bond length of the trans imide formed via thermal enolization. The aromatization (2-25%) observed in these methylated systems at higher temperatures presumably results from oxidative decarboxylation of the pendant methyls, which is the preferred pathway for degradation after cross-linking.

Stereospecific mono- and difluorination of the C7-bridge of norbornenes

“…The X-ray structure of diacid 5 is shown in Fig. 2 (the full X-ray analysis, performed as previously described [38], is available in Supporting Information).…”

“…The numbering of the various carbons and attached hydrogens appears in Schemes 1 and 5. X-ray spectroscopy was carried out as previously described [38] on a single crystal of the sample. Unless otherwise indicated, all the solvents and reagents were commercially available in high purity and used as received.…”

Insights into the Mechanism and Kinetics of Thermo-Oxidative Degradation of HFPE High Performance Polymer

“…7,15,16,23−33 Many of these studies were focused on the improvement of thermo-oxidative stability of the existing polymers by chemical modifications of different molecular fragments of the polymer. 7,24,[26][27][28]34 Among various possible chemical modifications, fluorination of the polymer backbone is identified as a good strategy to improve the thermo-oxidative stability of the polymer. 8,29,30,35−37 In addition to the improved thermo-oxidative stability fluorination of the polymer backbone can also increase the T g of the polymer.…”

“…In order to understand the mechanism and factors affecting the degradation of such polymers, various experimental and theoretical studies were performed. ,,,− Many of these studies were focused on the improvement of thermo-oxidative stability of the existing polymers by chemical modifications of different molecular fragments of the polymer. ,,− , Among various possible chemical modifications, fluorination of the polymer backbone is identified as a good strategy to improve the thermo-oxidative stability of the polymer. ,,,− In addition to the improved thermo-oxidative stability fluorination of the polymer backbone can also increase the T g of the polymer . Improved properties of fluorinated polymers is attributed to the high bond strength, low polarizability of the C–F bond and small size of the fluorine atom …”

Novel Interecting Blends Based on Amino Terminited Oligoimides by Using Michael Addition Reaction‐II

“…Recently, the interest has accelerated in tailoring chemistry of polyimide So as to approach the optimum balance of properties required for ease of processing. Many aspects of research pertinent to various polyimides have been well documented [2][3][4][5][6][7][8] .…”