Spontaneous Molecular Orientation of Polyimides Induced by Thermal Imidization. 3. Component Chain Orientation in Binary Polyimide Blends

Abstract

The degrees of uniaxial and in-plane molecular orientation for homopolyimides (PI) and PI/PI binary blends were estimated from the absorption dichroism of perylenetetracarboxydiimide (PEDI) bound to the main chains. Thermal cure of a slightly drawn film of poly(amic acid) (PAA) derived from 3,4,3,′4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA), BPDA/PDA, showed marked spontaneous orientation toward the stretching direction. The dependence on the chain structure revealed that in addition to the chain stiffness (linearity) the molecular packing is an important factor for the spontaneous orientation behavior. In a miscible binary blend system composed of semirigid BPDA/ PDA labeled with PEDI and flexible BPDA/ODA (ODA: 4,4′-oxydianiline), the extent of spontaneous orientation for the labeled BPDA/PDA chains decreased with increasing BPDA/ODA content in the blends. From the result, the marked spontaneous orientation behavior of homo-BPDA/PDA is interpreted as a kind of "cooperative phenomenon" where the neighboring chains promote the molecular orientation of each other in the cure process. Effects of film thickness, amount of residual solvent, cure method, and heating rate on the extent of spontaneous orientation were also discussed for the homo-BPDA/PDA system.

A rod-like fluorinated polyimide as an in-plane birefringent optical material 2: Control of optical retardation using spontaneous molecular orientation

“…Similar results were obtained by Nakagawa [15] and Hasegawa et al [9] for semi-rigid polyimides. In their experiments, PAA films were uniaxially drawn at room temperature and then thermally cured at higher temperatures.…”

“…However, the elongation behavior of polyimide films and the mechanism of the molecular orientation of this method has been unclear. Hasegawa et al reported that for semi-rigid polyimides, the degree of molecular orientation of uniaxially drawn PAA films is markedly enhanced by thermal imidization, based on measurements of the absorption dichroism and refractive indices [8,9]. This phenomenon coincides well with our findings, and their investigations are helpful in understanding the spontaneous orientation behavior of polyimide molecules with rigid or semi-rigid structures.…”

Structural Study on Aromatic Poly(amic n-alkyl ester)s and Their Derivatives by Solid-State Imidization II. Effect of Unremoved Alkyl Chains Attached by Ether Linkage

“…1. As pointed out by Hasegawa et al [9], stiff polyimide chains have strong tendency to spontaneous molecular orientation during the thermal imidization, which was interpreted as a cooperative phenomenon because the neighboring chains promote the molecular orientation each other. The segregation of PPPI in the imidization of PA-8 with destructing the layered structure may be explained by this cooperative phenomenon.…”

Preparation and Performance of Nano-hybrids Synthesized from Polyimide and Silica

“…Till now, much research has carried out to develop the properties of PI [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Among the PIs, rigid PI from BPDA and PDA (Scheme 1) is a unique type of PI because of its high modulus, increased tensile modulus by cold drawing, remarkable spontaneous in-plane orientation, low water sorption, low stress relaxation co-efficient and minimum coefficient of thermal expansion [18][19][20][21]. So far, no research has been carried out to observe the thermal and mechanical properties of rigid PI from BPDA, PDA and silica hybrids through in-situ sol-gel process.…”