TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The reactive end groups are selected from anhydrides, carboxylic acids, esters, amines, alcohols, isocyanates, epoxides, olefins, or dienes. The olefinic organic acid end caps are maleic acid groups. The compound (I) is bisphenol A dianhydride, the compound (III) is diaminopolysiloxane (DAPS), and the compound (II) is H2N-(CH2)4-(O-(CH2)4)n-O-(CH2)4-NH2 (XTJ-452).    TECHNOLOGY FOCUS - POLYMERS - Preferred Method: The method (M1) further involves heating the layer of a low-melt polymer to a second temperature effective to crosslink the low-melt polymer and form a hermetic seal with the substrate and to repair the cracks or deformations in the substrate. The substrate is a polyimide insulation layer of an electrical wire. The low-melt polymer comprises a poly(amic acid) (PAA), where the second temperature is effective to convert the PAA into a repair polyimide layer and form covalent bonds between the repair polyimide layer and the polyimide insulation. The low-melt polymer comprises a polyimide with reactive end groups, where at the second temperature the polyimide with reactive end groups reacts through its reactive end groups with itself to crosslink and form a repair polyimide that is hermetically sealed to the substrate. The low-melt polymer layer comprises a mixture of at least two poly(amic acids) (PAAs), where the mixture of PAAs melts at a lower temperature than at least two of the at least two PAAs. The low-melt polymer is formed from a reaction mixture of monomers, where at least 15 wt.% of the monomers is fully aliphatic. The first temperature is 70-150 degrees C, and the second temperature is 130-300 degrees C. The second temperature is effective to crosslink the low-melt polymer and form a polyimide with no melt temperature or a melt temperature higher than its cure temperature. The heating steps involve heating the low-melt polymer layer with an electrical heater apparatus for repairing wire insulation, where the apparatus comprises: an upper heating element having a heating edge in the form of a semicircle; a lower heating element having a heating edge in the form of a semicircle; where the upper and lower heating elements oppositely disposed and adapted to engage to surround and heat polymer insulation of an electrical wire; and where the upper and lower heating elements mechanically coupled through a hinge and each electrically coupled to an electrical power source device. The polyimide has a melting temperature of less than 150 degrees C before the curing step. The method (M2) further involves reacting the diamine and dianhydride with an olefinic cross-linker, where the olefinic cross-linker is selected from acrylic acid, methacrylic acid, allyl alcohol, allyl amine, maleic anhydride, or vinyl amine (preferably maleic acid), where the reaction is carried out in the reaction mixture at less than 100 degrees C to form a poly(amic acid) (PAA) in solution; casting the PAA solution into a film on a substrate; and heating the film to imidize the PAA to a polyimide. In the method (M2), at least 60% of reactants in the polymerization reaction mixture are the compound (I)-(III). Preferred Components: The low-melt polymer layer comprises a cross-linker selected from acrylic acid, methacrylic acid, allyl alcohol, allyl amine, maleic anhydride, or vinyl amine or a residue of acrylic acid, methacrylic acid, allyl alcohol, allyl amine, maleic anhydride, or vinyl amine end capped on the low-melt polymer. The polyether block is a polyether block of formula -(2-6C)alkyl-(O-(2-6C)alkyl-)nO-(2-6C)alkyl-, and the polysiloxane block is a polysiloxane of formula -(2-6C)alkyl-O-Si(CH3)2-(O-Si(CH3)2-)nO-Si(CH3)2-O-(2-6C)alkyl-. The low-melt polymer has a melting temperature of less than 150 degrees C. In the low-melt polymer, at least 15 (preferably 15-60)% of carbon atoms are aliphatic carbon atoms. In the low-melt polymer or poly(amic acid) (PAA), 15-60% of carbon atoms are in polyether or polysiloxane blocks. EXAMPLE - No suitable example given.