Random and block copolyimides made of biphenyltetracarboxylic dianhydride (BPDA) and 3,3'-diaminodiphenylacetylene (intA), p-phenylenediamine (PDA), and 4,4'-oxydianiline (ODA) were prepared. Random copolyimides were prepared by adding BPDA into an N-methylpyrrolidone (NMP) solution of diamine mixtures, followed by thermal imidization. The ratio of PDA and intA or ODA was 7:3. Block copolyimides were prepared by the reaction of amine-terminated BPDA/PDA units and anhydride-terminated BPDA/intA (or ODA) units. The ratio of PDA and intA or ODA was also set at 7:3. For the polyimides containing internal acetylene units, exotherms appeared on DSC measurements starting from 320C, which shows that crosslinking is occurring. Cold-drawing of polyamide acid films gave polyimide films with a higher modulus. High-temperature treatment to induce crossblinking did not lower the high modulus afforded by the cold-drawing. Crosslinking afforded a higher Tr, and a higher modulus at higher temperatures. Laminate processing was performed at 400C with a pressure of 100kgcm"2. The copolyimides containing internal acetylene units gave laminate films whose interfaces are strongly bonded through the crosslinking reaction. It was confirmed that the laminate films maintained the high modulus afforded by crosslinking.
Colorless, heat resistant polyimide films derived from 2,3,3′,4′-biphenyltetracarboxylic dianhydride
