Larc adhesives

LARC-TPI is a linear thermoplastic PI which can be processed ia the imide form to produce large-area, void-free adhesive bonds. Mitsui Toatsu Chemicals, Inc., has obtained Hcense to produce this product commercially for appHcations such as adhesives, films, mol ding compounds, etc. These are thermooxidatively stable and show essentially no loss ia weight at 300°C ia air. Weight loss does not exceed 2—3% after isothermal aging ia air at 300°C for 550 h. 

St. Clair et. al. investigated a series of maleimide and nadimide terminated polyimides and developed LARC-13 [8,9]. Changing the terminal group from maleimide to nadimide, the value of the lap shear strength of a titanium lap shear joint increased from 7 to 19 MPa [9]. They also added an elastomeric component to the adhesive formulation. The introduction of 15 wt% of a rubbery component, ATBN (amine terminated butadiene nitrile polymer) and ADMS (aniline terminated polydimethyl siloxane) enhanced the adhesive properties as follows 19 MPa to 25 MPa (ATBN) titanium T-peel strength 0.2 kN/m to 1.4... 

More recently, St. Clair and co-workers176) reported the use of aromatic amine terminated polydimethylsiloxane oligomers of varying molecular weights in an effort to optimize the properties of LARC-13 polyimides. They observed the formation of two phase morphologies with low (—119 to —113 °C) and high (293 to 318 °C) temperature Tg s due to siloxane and polyimide phases respectively. The copolymers were reported to have improved adhesive strengths and better thermal stabilities due to the incorporation of siloxanes. 

Trichloroethylene is an excellent extraction solvent for greases, oils, fats, waxes, and tars and is used by the textile processing industry to scour cotton, wool, and other fabrics (lARC 1979 Kuney 1986 Verschueren 1983). The textile industry also uses trichloroethylene as a solvent in waterless dying and finishing operations (McNeill 1979). As a general solvent or as a component of solvent blends, trichloroethylene is used with adhesives, lubricants, paints, varnishes, paint strippers, pesticides, and cold metal cleaners (Hawley 1981 lARC 1979 McNeill 1979). 

Various consumer products found to contain trichloroethylene include typewriter correction fluids, paint removers/strippers, adhesives, spot removers, and rug-cleaning fluids (Frankenberry et al. 1987 LARC 1979). 

According to the 1981-83 United States National Occupational Exposure Survey (NOES, 1997), as many as 125 000 workers in the United States were potentially exposed to dimethylformamide (see General Remarks). Occupational exposures to dimethylformamide may occur in the production of the chemical, other organic chemicals, resins, fibres, coatings, inks and adhesives. Exposure also may occur during use of these coatings, inks, adhesives, in the synthetic leather industry, in the tanning industry and in the repair of aircraft (Ducatman et al., 1986 lARC, 1989). 

Dimethyl hydrogen phosphite is used as a flame retardant on nylon 6 fibres, as a chemical intermediate in the production of pesticides and in lubricant additives and adhesives. No data on occupational exposure levels were available. A potential source of exposure to this chemical is from its occurrence as a degradation product of the chemical intermediate trimethyl phosphite and of pesticides such as trichlorphon and malathion (lARC, 1990). 

Methylaziridine is a reactive alkylating agent that is used as an intermediate in the production of polymers, coatings, adhesives, textiles and paper finishes (lARC, 1975). 

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]. 

LARC/MIP-3Q, Exodus 2 Lymphoid tissue, liver, thymus, EC, EOS, appendix, tonsil, PBL, monocytes and DC Constitutive Inhibits BM progenitor proliferation Induces memory T adhesion, attracts DC... 

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. 

Besides the condensation PI, there have been two new types of addition Pi s ethynl (acetylenic) and norbornene (nadic) end-capped PI. The acetylene-terminated PI (ATI) was first reported by Bilow and co-workers (52) and the nadic-terminated PI (NTI) (Pig. 8) was derived from the work of Lubowitz (33). An NTI prepared at NASA Langley Center has been designated as LARC-13 (34). When LARC-13 was compared with ATI as the adhesive for titanium, the lap shear... 

C. More recent adhesive work has shown that LARC-TPI has good resistance to aircraft solvents, moisture, and... 

NTI with a molecular weight of llOO g/mole, prepared from the reaction of appropriate molar amounts of BTDA, 3,3 -diaminodiphenylmethane, and nadic anhydride in N,N-dimethylformamide, was evaluated as a high temperature adhesive (eq. 7). This material has been referred to as LARC-13. The nadic group on NTI undergoes a thermally... 

Recent studies at NASA Langley Research Center have been directed towards the toughening of higher temperature thermoset addition polyimides (4,5). ATBN and silicone elastomers have been incorporated into an addition polyimide adhesive, LARC-13 (6,7), which is a candidate for bonding metals such as titanium and graphite/polyimide... 

The synthetic route for preparing the addition polyimide adhesive LARC-13 is displayed in Fig. 1. Appropriate quantities of 3,3 -methylenedianiline (m,m -MDA)f nadic anhydride (NA), and 3,3, 4,4 -benzophenone-tetracarboxylic acid dianhydr ide (BTDA) are combined in an amide solvent at a concentration of 50% solids by weight to form a 1300 molecular weight amic acid. This amic acid prepolymer is used as the adhesive resin and is later cured to the cross-linked polyimide by the removal of solvent,... 

Results from room temperature and elevated temperature lap shear testing of the elastomer-modified LARC-13/titanium bonds are presented in Table 1. After 500 hr at elevated temperature, all four adhesive formulations were reduced in strength compared to LARC-13 control specimen. However, it should be noted that the silicon-containing adhesives showed improved strengths at 260 C after aging at elevated temperature. Such behavior is probably due to additional cross-linking. 

In order to study the effects of varying the length of the elastomer chain on the properties of LARC-13 adhesive, a series of polymers were prepared using the ATS elastomer (Fig. 2). Resins were prepared with a concentration of 15% (w/w) elastomer using four ATS elastomers containing chain repeat units of 10, 41, 63 and 105. (ATS with repeat unit of 105 was used in studies previous to this.) Incorporation of these four elastomers into the LARC-13 backbone caused a reduction in the amic acid viscosity as shown in Table 4. This phenomenon was observed previously and was especially pronounced for the polymer containing 10 repeat units in the elastomer (ATS q). ... 

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