Beta relaxation in polyimides

Sun, Ze; Dong, Lisong; Zhuang, Yugang; Cao, Lin-Ying; Ding, Mengxian; Feng, Zhaochi

doi:10.1016/0032-3861(92)90684-o

Cited by 72 publications

(48 citation statements)

References 16 publications

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“…The first transition around 150 o C displayed the β relaxation, which was related to the sub-glass transition [16][17][18][19]. At the higher temperature around 290 o C, the second transitions (α relaxation) of the two kind of fibers were observed, which were generally regarded as the maximum of glass transition in the polymer and higher than that of E′ curve.…”

Section: Fig 2 Tga Curves Of Pi Fibersmentioning

confidence: 97%

The properties, morphology and structure of BPDA/ PPD/ BOA polyimide fibers

Huang

Gao²,

et al. 2012

E-Polymers

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A family of random copoly(amic acid)s (coPAAs) containing the 2-(4-aminophenyl)-5-aminobenzoxazole (BOA) moiety were synthesized in DMAc, followed by dry-jet wet spinning process into as-spun PAA fibers. The modified polyimide (PI) fibers were obtained from PAA fibers after imidized and drawn in a furnace. The mechanical properties of fibers were improved by incorporating BOA into BPDA/PPD backbone. SEM photo showed that the cross-section of each stage fibers was round and voids free. Besides, the "skin-core" and microfibrillar structure were not observed. The thermal properties of PI fibers were also investigated. The results showed that the PI fibers owned excellent thermal stability, moreover, the dimensional stability and the microphase separation of fibers were improved by heat-drawn stage. The T g were found to be around 290℃ by TMA and DMA. The X-ray (WAXD and SAXS) experiments indicated that the longitudinal stacks, the molecular orientation and the structural homogeneity of PI fiber were improved in the preparation process of fibers.

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Section: Fig 2 Tga Curves Of Pi Fibersmentioning

confidence: 97%

The properties, morphology and structure of BPDA/ PPD/ BOA polyimide fibers

Huang

Gao²,

et al. 2012

E-Polymers

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“…It appears around 58, 85, 61 and 69°C for P1, P2 P3 and P4, respectively, at 1Hz. β Transition of polyimides was assigned to the segmental motion in diamine or dianhydride moiety [53,54], but may comprise larger portions of the structural unit that respond in a correlated manner [55,56] or can ultimately involve the entire repeating segment, as it is the case of rigid systems. The intensity of γ and β relaxations of P1-P4 decreases with temperature reflecting an apparent loss of net dipolar correlation with increasing thermal energy.…”

Section: Dielectric Relaxation Behaviourmentioning

confidence: 99%

Local and segmental motion in highly transparent and low-k poly(ether-imide) films

Damaceanu

Brumă

2014

J Polym Res

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One series of poly(ether-imide)s containing oxadiazole units have been studied with respect to the relationship between the chains structure and their physical properties, particularly thermal transitions and dielectric behavior with emphasis on the local and segmental motion, and optical clarity. High-temperature solution polycondensation reactions of an oxadiazole-containing diamine with different bis(etheranhydride)s resulted in easy soluble polymers with high molecular weights. The variation of the real and imaginary parts of the dielectric permittivity in a large frequency range, from 10 to 10 6 Hz, and in a wide temperature domain, from −150 to 250°C of the tough free-standing films prepared from these polymers was registered. The dielectric constant values, measured at room temperature and in the frequency domain of 10 Hz −1 MHz, were lower or comparable with those of Kapton HN film measured under similar conditions. The dielectric spectroscopy data were corroborated with the dynamo-mechanical analysis ones to highlight the subglass and glass relaxations encountered in these polymer films. The γ and β sub-glass viscoelastic and dielectric relaxations were explored in order to understand their molecular origins, being discussed in correlation with polymers repeating unit structure. The optical transparency of the poly(ether-imide) films has been also studied, to survey their potential for use as flexible substrates in electronic and optical devices.

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“…[14,[23][24][25][26] This is due to the complex molecular architecture of PIs which gives rise to the occurrence of at least three mechanical relaxations. The process with the lowest transition rate (longer timescale) showing up to highest temperatures is designed as a arelaxation and it is ascribed to the cooperative glass/rubber transition (only partially visible here).…”

Section: Dynamic Mechanical Analysismentioning

confidence: 99%

“…In PIs, b-relaxation has been generally attributed to a local dynamics arising from both oscillations of the imide rings and rotations of the para-phenylene segments in the diamine moieties due to phenyl-nitrogen conjugation (see Figure 5). [24,27] In other words, the brelaxation results from local bond rotations along the polyimide backbone of complex rigid segments composed of a para-phenylene unit and an adjacent imide group which respond in correlated manner. Moreover, since the rotation of one rigid chain segment does not influence the conformation of the other segments, both small free volume and rather low activation energy are required.…”

Section: Dynamic Mechanical Analysismentioning

confidence: 99%

“…Moreover, since the rotation of one rigid chain segment does not influence the conformation of the other segments, both small free volume and rather low activation energy are required. [24] In this framework, the correlation among the local motions of the single units within the rigid segment might be source for the existence of complex relaxation process. As concerning the g-relaxation, although it was first related to the presence of water molecules linked to the polar groups in polyimides, [28,29] a direct correlation with non-cooperative oscillations and pflipping motion of the phenoxy groups in the diamine sequence has been then proven.…”

Section: Dynamic Mechanical Analysismentioning

confidence: 99%

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Indication of Local Phase Separation in Polyimide/Silica Hybrid Polymers

Bartolotta

Calandra

2010

Macro Chemistry & Physics

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PI/SiO2 hybrid polymers involving the in situ generation of SiO2 particles through the sol/gel route have emerged as promising materials in many fields of modern technology thanks to their unique structural characteristics. In this paper their structural and dynamic properties were investigated by FT‐IR and DMTA as a function of SiO2 content. All data consistently highlight a loosening of polymeric structure due to the presence of SiO2 nanoparticles and suggest a silica‐induced structural change most probably due to a sub‐micrometer scale SiO2 phase separation. Our results demonstrate how the analysis of sub‐glass γ‐relaxation dynamics can be exploited to investigate sub‐micro phase segregation in such materials.magnified image

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Beta relaxation in polyimides

Cited by 72 publications

References 16 publications

The properties, morphology and structure of BPDA/ PPD/ BOA polyimide fibers

The properties, morphology and structure of BPDA/ PPD/ BOA polyimide fibers

Local and segmental motion in highly transparent and low-k poly(ether-imide) films

Indication of Local Phase Separation in Polyimide/Silica Hybrid Polymers

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