Color lightness and highly organosoluble fluorinated polyamides, polyimides and poly(amide–imide)s based on noncoplanar 2,2 0 -dimethyl-4,4 0 -biphenylene units Der-Jang Liaw * , Ching-Cheng Huang, Wen-Hsiang Chen Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan, ROC Received 5 November 2005; received in revised form 7 January 2006; accepted 11 January 2006 Abstract A new diamine monomer containing noncoplanar methyl substitution, 2,2 0 -dimethyl-4,4 0 -bis(2-trifluoromethyl-4-aminophenoxy)biphenyl (DBTFAPB) was successfully synthesized and used in the preparation of a series of polyamides and polyimides by direct polycondensation with various aromatic dicarboxylic acids and tertacarboxylic dianhydrides. A new noncoplanar dicarboxylic acid monomer containing noncoplanar methyl substitution, 2,2 0 -dimethyl-4,4 0 -bis(2-trifluoromethyl-4-trimellitimidophenoxy)biphenyl (DBTFTPB) was also successfully synthesized by refluxing the diamine, DBTFAPB, with trimellitic anhydride in glacial acetic acid. A series of new poly(amide–imide)s were prepared directly from DBTFTPB with various diamines in N-methyl-2-pyrrolidinone (NMP). All the polymers exhibited excellent solubility in solvents, such as N- methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), pyridine, tetrahydrofuran (THF), cyclohexanone and g-butyrolactone at room temperature or upon heating at 70 8C. Inherent viscosities of the polymers were found to range between 0.60 and 1.34 dL g K1 . Gel permeation chromatography (GPC) of the polymers showed number-average and weight- average molecular weight up to 7.3!10 4 and 17.9!10 4 , respectively. These polymers showed that the glass transition temperatures were between 230 and 265 8C, and the 10% mass loss temperatures were higher than 460 8C in nitrogen atmosphere. All the polymers could be cast into flexible and tough films from DMAc solutions. They had a tensile strength in the range of 82–124 MPa and a tensile modulus in the range of 1.9–2.9 GPa. These polymers exhibited low dielectric constants ranging from 2.87 to 4.03, low moisture absorption in the range of 0.29–3.20%, and high transparency with an ultraviolet–visible absorption cut-off wavelength in the 347–414 nm range. q 2006 Elsevier Ltd. All rights reserved. Keywords: Noncoplanar; Dielectric constant; Birefringence 1. Introduction Aromatic polyamides, polyimides and poly(amide–imide)s have been noted for their excellent characteristics such as thermal stability, electrical properties and chemical resistance as well as their high strength and high modulus as fibers [1,2]. However, the main drawbacks of these classes of aromatic polymers are their insolubility and high glass transition temperature that cause difficulties in both synthesis and processing [3,4]. Therefore, several approaches have been made through synthetic modification by the incorporation of flexible linkages [5,6], bulky pendant groups [7–9] and noncoplanar biphenylene moieties [10–12] into the polymer backbones. The 2,2 0 -dimethyl biphenylene moiety could be considered as a rod-like structure. The substitution at the 2- and 2 0 -positions of the biphenyl moiety appears to force the two phenyl rings into adopting a noncoplanar conformation. This has resulted in disrupted crystal packing, enhanced solubility and optical transparency [11–15]. Recently, considerable attention has been devoted to the synthesis of fluorine- containing polymers. Incorporation of the bulky fluorine groups serves to increase the free volume of the polymers, thereby improving some properties like solubility, gas permeability [16], optical transparency [17,18] and flame resistance [19]. In addition, it also reduces the moisture absorption, crystallinity, dielectric constant and color. In this study, we successfully prepared two novel monomers, 2,2 0 -dimethyl-4,4 0 -bis(2-trifluoromethyl-4-amino- phenoxy)biphenyl (DBTFAPB) and 2,2 0 -dimethyl-4, 4 0 -bis(2-trifluoromethyl-4-trimellitimidophenoxy)biphenyl Polymer 47 (2006) 2337–2348 www.elsevier.com/locate/polymer 0032-3861/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2006.01.028 * Corresponding author. Fax: C886 2 23781441/C886 2 27376644. E-mail addresses: liaw@ch.ntust.edu.tw (D.-J. Liaw), liaw8484@yahoo. com.tw (D.-J. Liaw).