Suman Kumar Sen

Solubility improvements in aromatic polyimides by macromolecular engineering

Polyimides are proved to be an important class of polymers due to their outstanding set of physical and chemical properties. However, this class of polymers suffers from poor processability, which limits their scope of application. This review article deals with approaches that have been undertaken by different researchers to improve the processability of this class of polymers. Mostly, these are synthetic approaches using new diamine and dianhydride monomers that reduce the interchain interaction of the final poyimide by flexibilizing the polymer chain or increasing the fraction free volume. Accordingly, the structural factors that are responsible for better processability are discussed and representative diamine and diahydride structures are tabulated under different categories. Major efforts towards development of soluble polyimides but maintaining excellent mechanical and thermal properties have been done by our group and are also covered in this article.

Synthesis, Characterization and Properties of New Fluorinated Poly(imide siloxane) Co-polymers from 4,4′-(Hexafluoro-isopropylidene)diphthalic Anhydride

Several new poly(imide siloxane)s co-polymers have been prepared by the reaction of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with commercially available 4,4′-oxydianiline (ODA) and with five different novel trifluoromethyl-substituted diamines, each with 20 wt% aminopropyl-terminated polydimethylsiloxane (APPS). The poly(imide siloxane)s are well characterized by different spectroscopic, thermal, mechanical and electrical techniques. The synthesized polymers exhibit good solubility in different organic solvents. The 1H-NMR indicates that the siloxane incorporation is about 17–19% for polymers 1a–f. These poly(imide siloxane) films show low water absorption rate (0.88–0.09%) and a low dielectric constant (2.43–2.58) at 1 MHz. The polymers show very good thermal stability, even up to 419°C for 5% weight loss in synthetic air and a glass transition temperature of up to 230°C. All poly(imide siloxane)s formed tough transparent films, with a tensile strength of up to 79 MPa, a modulus of elasticity of up to 1.38 GPa and elongation-at-break of up to 30%. Thermal, mechanical and dielectric properties of these polymers have been evaluated and compared with their non-siloxane analogues.

Synthesis of New Poly(biphenylene oxide) with Pendent Trifluoromethyl Group

A new AB type of monomer 4′-fluoro-3,5-dimethyl-3′-trifluoromethyl-biphenyl-4-ol has been synthesized that leads to a new poly(arylene ether) by self polycondensation reaction. The monomer and the polymer have been well characterized by elemental analyses, FT-IR and NMR spectroscopy. Both FT-IR and NMR spectra of the polymers did not show any terminal phenoxy group indicating high conversion. The polymer showed glass transition at 278°C and very good thermal stability in synthetic air. GPC results indicate high molar mass development; Mw = 53200 and MWD = 2.29.

Synthesis and Characterization of Semifluorinated Aromatic Copoly(ether amide)s

Two new semifluorinated aromatic copoly(ether amide)s have been synthesized by direct polycondensation reaction of 5-t-butyl isophthalic acid (TIPA) with two different aromatic diamines; bis-2,2-[4-{2′-trifluoromethyl-4′-(4″-aminophenyl) phenoxy}phenyl]isopropylidene (BTAPPI) and bis-9,9-[4-{2′-trifluoromethyl-4′-(4″-aminophenyl)phenoxy}phenyl]fluorenylidene (BTAPPF) and, 4,4′-oxydianiline (ODA) as a comonomer in all cases. These polymers showed very good solubility in organic solvents like DMF, DMAc, NMP and pyridine. The polymers showed very good thermal stabilities, the temperature for 10% wt loss in nitrogen and air were upto 422°C and 412°C, respectively. The copoly(ether amide)s synthesized exhibited glass transition temperature (Tg) 248 (BTAPPI-ODA-TIPA) and 263°C (BTAPPF-ODA-TIPA). DMA analysis showed very good retention of storage modulus of the polymer up to Tg. The copoly(ether amide) films were flexible with tensile strength up to 91 MPa, elongation at break up to 15% and modulus of elasticity up to 1.69 GPa depending on amine used and the exact repeating unit structure. These copoly(ether amide)s were less crystalline in nature in comparison to the homopolyamide synthesized using ODA as diamine but more crystalline than the homopolyamide synthesized using BTAPPI and BTAPPF as diamines. Water absorption study showed hydrophobic nature of the polymers. The copoly(ether amide)s showed non-Newtonian (pseudoplastic) behavior at higher applied shear rate.