| The objective of this research was to investigate the effect of introducing multiple alkyl side chains, i.e., three to six side chains per repeat unit, on the properties of aromatic polyimides, polyetherimides and polyesters. The approach to the polyimides involved the synthesis of two series of diamine monomers, i.e., 2,2′ -bis4-[3,4,5-tris(n-alkan-1-yloxy)benzoate]-4,4 ′-biphenyldiamines and bis4-[3,4,5-tris(n-alkan-1-yloxy)benzyl]-4,4 ′-diamino-2,2′-biphenyldicarboxylates. Thus, diamines containing multiple alkyl side chains were synthesized in which the length of the alkyl side chains was varied from 5 to 18 carbon atoms. Polyimides were prepared from the diamines and pyromellitic dianhydride (PMDA), 3,3′4,4′-biphenyltetracarboxylic dianhydride (BPDA), 2,2′-dibromo-4,4′,5,5 ′-biphenyltetracarboxylic dianhydride (DBBPDA), and 2,2 ′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), using a one-step method in 1,2-dichlorobenzene or 1-chloronaphthalene. Most of the polymers had good solubility in chlorinated solvents. The high-molecular-weight polyimides could be solution cast into flexible, tough films, except for those based on PMDA. The side chains that contained at least 10 carbon atoms crystallized. The melting points of the crystalline regions increased as the length of the side chains increased. Variable temperature (VT), solid state 13C nuclear magnetic resonance (NMR) showed that the polyimide containing C 18 side chains crystallized at room temperature. A wide angle X-ray diffraction (WAXD) study showed that the spacing between the main chains increased as the number of carbon atoms in the side chains increased. Several of the polyimides were used to prepare alignment layers for liquid crystal displays. The films generated liquid crystal pretilt angles that ranged from 6 to 90°. Two series of polyetherimides containing multiple alkyl side chains were also prepared from 2,2′ -bis4-[3,4,5-tris(n-alkan-1-yloxy)benzoate]-4,4 ′-biphenyldiamines, 4-[3,4,5-(n-alkan-1-yloxy)benzyl]-3,5diaminobenzoates and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BisADA). The moduli and tensile strengths of these polymers were lower than those of the commercial polyetherimide Ultem®, but the elongations were higher. Finally, a series of bis4-[3,4,5-tris(n-alkan-1-yloxy)benzyl]-4,4 ′-dihydroxy-2,2′-biphenyldicarboxylate monomers was prepared in which the length of the alkyl side chains was varied from 5 to 12 carbon atoms. The monomers were polymerized with 2,2′ -bis(trifluoromethyl)-4,4′-biphenyldicarboxylic acid and terephthalic acid. The polyesters obtained were soluble in common solvents, such as chloroform and tetrahydrofuran (THF). |
