Precyclised and Linear Polymers

E-104 glass fabric carrier impregnated with Larc-TPI polyamic acid. The cure cycle is carried out under a pressure of 2.1 MPa by heating the assembly from the ambient to 343°C at a rate of 8°C min followed by 1 h at that temperature. A postcure treatment at 343°C for 4-6 h is applied to the assemblies that are subsequently tested at temperatures higher than the Tg. 

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. 

The lap shear strength values listed in Table 3 show that Larc-IA exhibits the best adhesive properties up to 204°C before and after thermal ageing at that temperature but Larc-TPI remains better when adhesion is measured at 232°C. 

To date, no high molecular weight condensation polyimide combines excellent adhesive properties, easy processability without volatile evolution and low 

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