Maleimide adhesive

Bis-maleimide resins composed of BMI and diamines have been reported in the early 1960s in the patent literature. Since that time, a number of patents have appeared describing improvements in their properties and uses [3]. Although many bis-maleimide resins are commercially developed, relatively few reports of their use as adhesives are to be found in scientific journals [4-10]. Improvements of maleimide resins are mirrored in the improvements of thermosetting polyimides. For example, the method of in situ polymerization of monomer reactants (PMR method) was developed [6]. 

Maleimides have three principal reaction pathways. These are radical addition to vinyl compounds the Michael addition with compounds having active hydrogens and the Diels-Alder reaction with dienes (Fig. 3). Any of the three can be tools for forming thermosetting adhesives. 

BMI also reacts with dienes to form Diels-Alder adducts [12]. When BMI reacts with a a,(n-biscyclopentadienyl compound or other bis-diene resin, the bis-maleimide chain is extended by the Diels-Alder reaction. Bis-maleimide, chain extended with bis-diene, is not used in adhesives. However, as the Diels-Alder reaction is reversible, there may be a possibility of recyclability of the cured resin by depolymerization of the backbone (Fig. 6). 

As already mentioned, aromatie polymers are thermally stable but aliphatic portions of them are not as thermally stable. Typical maleimide resins have aliphatic units. This is inevitable because the Michael addition was used to prepare the maleimide-based oligomers. On the other hand, if an adhesive consists of a linear thermoplastic polymer, it is not usable at temperatures above its softening temperature. Introdueing chemical crosslinking is one way to prevent thermal weakening of a material. 

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... 

JP 05125345 (Japanese) 1993 Poly(vinyl butyral) blend adhesive composition for flexible printed circuit boards Ube Industries, Japan H Inoe, S Takabayashi, T Muramatsu, T Funakoshi Formulated resins having good flexibility and heat resistance are useful adhesives for polyimide/Cu foil laminated circuit boards Maleimide-terminated siloxane-imide block copolymers were formulated with poly(vinyl butyral) and melamine resins to give adhesive compositions. 

JP 05306386 (Japanese) 1993 Heat-resistant adhesive composition Ube Industries, Japan H Inoe, S Takabayashi, T Muramatsu, T Hirano Resin formulation useful for bonding Cu foils to polyimide films for electronic applications Heat-resistant adhesives were formulated to include imide-siloxanes with softening points <300° C. Diaminopolysiloxanes and aromatic amines were used maleimide termination also utilized. 

The nadimide and maleimide end-capped oligomers belong to the family of thermosetting telechelic oligomer precursors of thermostable networks shown in Fig. 1. These products were developed in order to fulfill the requirements of the aerospace industry in the domain of high performance adhesives and matrices for laminates. 

The aspects relevant to the use of rosin as such, or one of the derivatives arising from its appropriate chemical modification as monomer or comonomer [12-14], have to do with the synthesis of a variety of materials based on polycondensations and polyaddition reactions of structures bearing such moieties as primary amines, maleimides, epoxies, alkenyls and, of course, carboxylic acids. These polymers find applications in paper sizing, adhesion and tack, emulsification, coatings, drug delivery and printing inks. 

LV) [65]. These maleimide additives appear to be relatively unreactive during the initial anaerobie eure. As the adhesive is exposed to high temperatures the methacrylate backbone degrades and the methacrylates can then copolymerize with the maleimides, forming a more heat-resistant matrix [66],... 

---