Reevaluation of Tetrahydrophthalic Anhydride as an End Cap for Improved Oxidation Resistance in Addition Polyimides

Meador, Mary Ann B.; Frimer, and Aryeh A.; Johnston, James C.

doi:10.1021/ma0353078

Cited by 6 publications

(16 citation statements)

References 19 publications

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“…Aromatization of 11e yields 17e , whose spectral data has been previously reported . Full aromatization of compounds 11a , 11c and 11d yields o - methylphthalimide 17a , whose partial NMR data could be extracted from the reaction mixture.…”

Section: Methodsmentioning

confidence: 95%

“…We recently reported our studies on 1,2,3,6-tetrahydrophthalic (THP) end-capped bisimides 5 (Figure ) that contain no bridging methylene group at all . This structure was first investigated by TRW and NASA in the 1980s and found to yield composites with thermal oxidative stability (TOS) values better than PMR-15, but which were quite frangible and brittle. , No explanation for these peculiar results was given, however.…”

Section: Introductionmentioning

confidence: 99%

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Methylated Tetrahydrophthalic Anhydrides as End Caps in Addition Polyimides

2010

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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.

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Section: Methodsmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Methylated Tetrahydrophthalic Anhydrides as End Caps in Addition Polyimides

2010

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“…Though NE has been used as a vital component in many HPPs, − , the vulnerability of the cross-links formed from this end-cap at high temperatures limits its application above 600 K. − This is ascribed to the presence of multiple aliphatic centers that are susceptible to oxidation. ,− Another drawback of nadic end-cap is the requirement of high temperature (600 K) and pressure (200–500 psi) for the curing. − High pressure is essential for the formation of a polymer network devoid of voids . Plenty of research has been done to improve the curing conditions and thermo-oxidative stability of nadic end-capped polymers. − However, most of these newly developed end-caps failed to deliver a balance between thermal and mechanical properties. − To improve the thermo-oxidative stability and curing conditions of nadic end-capped polymers, a thorough knowledge of the cross-link structure and cross-linking mechanism is vital.…”

Section: Introductionmentioning

confidence: 99%

Polymerization Mechanism and Cross-Link Structure of Nadic End-Capped Polymers: A Quantum Mechanical and Microkinetic Investigation

Kunnikuruvan

Parandekar²,

Prakash³

et al. 2017

Macromolecules

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The applications of norbornene or nadic end-capped high performance polymers (HPPs) are manifold and have been discussed in the literature for more than two decades. The cross-links formed from nadic end-cap determine the mechanical and thermal properties of these polymers. In spite of extensive studies, the cross-link structure and the cross-linking mechanism of nadic end-capped polymers remain elusive. Quantum chemical computations together with microkinetic modeling are used here to elucidate these aspects. Various possible polymerization pathways that contribute to the final cross-link structure of nadic end-capped polymers are proposed, and the distribution of cross-link structures is computed. The cross-linking mechanisms are modeled considering radical initialization, chain propagation, and termination, and our computations identify the most active cross-linking mechanism. The results of our study are then compared with the available experimental data.

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“…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.…”

Section: ■ Introductionmentioning

confidence: 99%

“…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 …”

Section: Introductionmentioning

confidence: 99%

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

Kunnikuruvan¹,

Parandekar²,

Prakash³

et al. 2016

J. Phys. Chem. B

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The growing requisite for materials having high thermo-oxidative stability makes the design and development of high performance materials an active area of research. Fluorination of the polymer backbone is a widely applied strategy to improve various properties of the polymer, most importantly the thermo-oxidative stability. Many of these fluorinated polymers are known to have thermo-oxidative stability up to 700 K. However, for space and aerospace applications, it is important to improve its thermo-oxidative stability beyond 700 K. Molecular-level details of the thermo-oxidative degradation of such polymers can provide vital information to improve the polymer. In this spirit, we have applied quantum mechanical and microkinetic analysis to scrutinize the mechanism and kinetics of the thermo-oxidative degradation of a fluorinated polymer with phenylethenyl end-cap, HFPE. This study gives an insight into the thermo-oxidative degradation of HFPE and explains most of the experimental observations on the thermo-oxidative degradation of this polymer. Thermolysis of C-CF3 bond in the dianhydride component (6FDA) of HFPE is found to be the rate-determining step of the degradation. Reaction pathways that are responsible for the experimentally observed weight loss of the polymer is also scrutinized. On the basis of these results, we propose a modification of HFPE polymer to improve its thermo-oxidative stability.

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Reevaluation of Tetrahydrophthalic Anhydride as an End Cap for Improved Oxidation Resistance in Addition Polyimides

Cited by 6 publications

References 19 publications

Methylated Tetrahydrophthalic Anhydrides as End Caps in Addition Polyimides

Methylated Tetrahydrophthalic Anhydrides as End Caps in Addition Polyimides

Polymerization Mechanism and Cross-Link Structure of Nadic End-Capped Polymers: A Quantum Mechanical and Microkinetic Investigation

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

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