LARC-TPI polyimides

Figure 23 Lap shear strength determination (a) test specimen recommended in ASTM D1002 standard (b) multilayer process used to bond titanium alloy coupons with thermoplastic Larc TPI polyimide adhesive.

Fig. 2. Fig. 2. LARC polyimides where LARC stands for Langley Research Center, (a), LARC-TPI from 3,3 -diarninoben2oplienone and B IDA (b),...

Various melt-fusible polyimides whose T s range from 250 to 350°C are avadable as mol ding powders or pellets. LARC-TPI was developed by... 

St. Clair [36] synthesized and evaluated the properties of a semi-2-IPN comprising Thermid 600 (an acetylene terminated imide oligomer from National Starch and Chemical Company) and LaRC-TPI (a thermoplastic polyimide with a Tg of 257 °C). The composition having the ratio of 65 35 of thermosetting Thermid 600 to LaRC-TPI showed the best flexural strength at ambient temperature [36]. 

LARC TPI Langley Research Center Thermoplastic Polyimide... 

LARC TPI is a linear polyimide prepared with BTDA and 3,3 -diaminobenzo-phenone. The polyamide acid intermediate was used to prepare a semi-IPN with the PMR-15 reactants. After curing the blend exhibited a twofold Tg and an improved value of Glc (Table 8). 

Polyimides for microelectronics use are of two basic types. The most commonly used commercial materials (for example, from Dupont and Hitachi) are condensation polyimides, formed from imidization of a spin-cast film of soluble polyamic acid precursor to create an intractable solid film. Fully imidized thermoplastic polyimides are also available for use as adhesives (for example, the LARC-TPI material), and when thermally or photo-crosslink able, also as passivants and interlevel insulators, and as matrix resins for fiber-reinforced-composites, such as in circuit boards. Flexible circuits are made from Kapton polyimide film laminated with copper. The diversity of materials is very large readers seeking additional information are referred to the cited review articles [1-3,6] and to the proceedings of the two International Conferences on Polyimides [4,5]. 

Bell et al. [1] synthesized an exhaustive number of position isomers of diaminodi-phenylmethane (MDA), diaminodiphenyl ether (DDE) and diaminobenzophenone (DBF) and demonstrated that the meta linked diamines gave polyimides with markedly lower glass transition temperatures (Tg) than those of para- aksA structure. Interestingly, or/to-linked structures were ineffective in decreasing Tg probably because of possible steric restriction imposed on the rotational freedom of main chains. Melt fusible LARC-TPI developed by NASA is based on this discovery and is composed of 3,3 -DBP and 3,3, 4,4 -benzophenonetetracarboxylic dianhydride (BTDA). Diamines containing one or more stable linkages between aromatic rings such as —O—, —S—, —SO2 -, CO—, —C(CH3)2—, and —C(CF3)2—, have been used to synthesize many tractable polyimides. Some of the standard procedures to prepare these diamines are described below. 

During the last several years, a thermoplastic condensation polyimide (PI) was developed at NASA Langley Research Center (49). Prom the reaction between BTDA (3,3, 4,4 -benzophenonetetracarboxylic acid dianhydride) and DABP (3,3 -diamino benzophenone), the polyimide LARC-TPI (Pig. 7) was prepared by Bell et al. (49). Later, St. Clair (50) used LARC-TPI as an adhesive for titanium. The adhesion of titanium and PI has been studied by Nightman et al. (51) with XPS (ESCA) and PT-IR techniques. 

Polyphenylquinoxaline (PPQ) and Polyimide (LARC-TPI) adhesive systems were evaluated for titanium metal bond characteristics in various environments. Each polymer was chemically analyzed prior to fabrication into glass reinforced films and bonded into titanium test coupons. 

LARC-2 (LARC-TPI) - This is a thermoplastic polyimide supplied by NASA Langley which was added to Phase II portion of the program. All other adhesive system candidates, except PPQf were not suitable for full evaluations of Phase II, and to maintain two systems in this study LARC-TPI was screened to Phase I requirements then added to Phase II. This polymer is the reaction product of pyromellitic dianhydride (PMDA) and 3,3, 4,4 -benzophenone tetra-... 

One of the most successful thermoplastic polyimides has been LARC-TPI, developed by the National Aeronautics and Space Administration (NASA) in the United States. The polymer is commercially available. Table 3 shows some of the very reasonable properties obtained from this adhesive. As indicated, the abihty both to maintain mechanical properties at elevated temperatures and indeed retain mechanical integrity for long periods of time are clearly apparent. 

In addition to LARC-TPI, further recent developments have included the polyimide sulphones, polysiliconeimides and polyetherimides. All three have been evaluated and have shown promise for adhesive bonding apphcations. 

Larc-TPI, Thermoplastic polyimide resin, Mitsui Chemicals America, Inc. 

LARC-TPI Gulf Oil Company/Mitsui Toatsu Chemicals Thermoplastic polyimide. 

Chow et al. investigated the isoimide to imide conversion process with commercial Larc-TPI samples [25]. As illustrated in Fig. 11, the reaction of 3,3, 4,4 -benzophenone tetracarboxylic acid dianhydride 18 and 3,3 -carbonylbisbenze-neamine 19 leads to polyamic acid 20. Dehydrocyclisation to poly(isoiniide) 21 is then performed in solution by adding dicyclohexylcarbodiimide (DCC) or trifluoroacetic acid anhydride. Polymer 21 is generally processed fi om its solutions in polar organic solvents, dried and converted to polyimide 22 by thermal isomerisation. 

Figure 12 Chemical formulae of polyimides belonging to the Larc TPI series Fare TPl-ODA 23, Larc TPI-SO2 24 and Larc TPI-IA 25.

The high melt viscosity of Larc-TPI at 350°C (10 Pas) prohibits its use as an adhesive for bonding metallic or laminate skins on core honeycombs to make high strength sandwich structures. The work of Chow et al. discussed in Section 4.3.2.2 demonstrates that the melt viscosity of the poly(isoimide) form 21 of Fare TPI is of the order of 10 Pas at 240-250°C, compared to 2 x 10 Pas for polyimide 22 [25]. A semi-crystalline form of Larc-TPI has been obtained by chemical imidisation of the polyamic acid with acetic anhydride and triethylamine [63]. The differential scanning calorimetric curve exhibits an endotherm at 274°C due to melting of the crystalline sites. The value of the initial inherent viscosity (0.22 dl g ) indicates, however, that the lower melt viscosity also results from lower molecular weight polymer. 

Table 3 Lap-shear strength of Ti/Ti test specimens bonded with polyimides of the Larc-TPI series as a function of the test temperature before and after thermal ageing in air at 204°C...

Fig. 33 summarises the typical data discussed in the present section in order to compare the best performing polyimide adhesives at temperatures exceeding 200°C. It can be seen that condensation polyimides (Nolimid 380 and FM 34B ) seem to work better in ageing tests between 260 and 300°C. The thermoplastic polyimides Larc lA and Larc-TPI exhibit excellent adhesive properties between 200 and 232°C, whereas the BMI FM 32 can be used up to 200-230°C. 

In contrast, the consumption of polyimides has increased in the electronic industry, especially for the fabrication of flexible circuitry and its associated tape automated bonding process. High level of adhesion and thermoplasticity are the prominent parameters for these applications. Compared to aerospace applications, electronics imposes new requirements because of the exposition to high temperatures that is generally fimited to short-time exposures at 350 to 400°C. In the aerospace industry, Larc-TPI performs well to bond Kapton to itself as to... 

CIBA-GEIGY s XU 218, are commercially available. An experimental thermoplastic polyimide, Larc-TPI, is not... 

Other properties of Pis were also improved by the diimide additives [135]. The dielectric constant, e of PI from BDSDA and 2,2 -bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (BDAF) reduced appreciably by additives shown in Fig. 44. The results are as listed in Table 5. Furthermore, the addition of 10 wt% AN-BDSDA-AN into BDSDA-ODA m-PDA polyimide caused a decrease in the saturation moisture content from 1.52% for the neat PI to 1.27%. Positron annihilation spectroscopy proved that a decreased free volume is responsible for the reduced water uptake. Also, a slightly increased in modulus and a decreased CTE were caused by the 5% addition of AN-6FDA-A into LARC-TPI in both the undrawn and drawn states. 

A few Pis are commercially available in adhesive form as the polyamide acid with the most popular being FM 34B —18. Another is the polyamide acid form of LARC-TPI which can be formulated and used to prepare adhesive tape. Several other polyimides, as discussed in a review on aromatic polyimide adhesives and bonding agents,are also available. 

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