Synthesis of novel polyimides from dianhydrides with flexible side chains - Polyimides and Other High Temperature Polymers - page 73

Figure 4. Synthesis route to C m -OADA.

) [24] were prepared by bis-Diels-
Alder reaction from maleic anhydride and 1,4-dialkyloxy-2,3,5,6-tetrakis
(bromomethyl)benzene, which had been synthesized from duroquinone as a start-
ing material via consecutive reduction, alkylation with n-bromoalkane and side-
chain bromination of methyl groups using N-bromosuccinimide (NBS), as shown
in Figure 4. Bis-Diels-Alder reaction was conducted to obtain monomeric dianhy-
drides below 80°C under a nitrogen flow. The reaction mixtures were dehydrated
by treating with acetic anhydride, and then recrystallized from acetic anhydride or
CH 2 Cl 2 /petroleum ether mixed solvent. After separation, crystalline materials
were obtained with anhydride peaks at 1844, 1783 cm -1 in the FT-IR spectra. The
NMR peaks at 0.9~1.8 ppm were regarded as the ones from alkyl side chains.
And we also confirmed that doublets at ca. 2.5 and 3.5 ppm were split by the
geminal hydrogen atom of the alicyclic unit in the monomers.

Other monomeric dianhydrides ( C m -OADA

2.2. Polymerization
The polymerization reactions were carried out by one or two-step method and the
chemical structure of new polyimides and their codes are listed in Figure 5.
The typical one-step method was as follows. To a solution of diamine in freshly
distilled N-methylpyrrolidinone (NMP), equimolar dianhydride was added at
room temperature under an argon atmosphere with 10% solid content (w/v). The
reaction mixture was heated at 70~80°C for 2 hours. Then the solution tempera-
ture was slowly raised to 180°C and kept there for an additional 12 hours. In the
two-step method, poly(amic acid)s were first prepared from reactions of dianhy-
dride monomers with diamines in NMP and subsequently cyclized with triethyl-
amine and acetic anhydride at room temperature.