High solubility and optical transparency of novel polyimides containing 3,3 0 ,5,5 0 -tetramethyl pendant groups and 4-tert-butyltoluene moiety Chenyi Wang, Xiaoyan Zhao, Guang Li * , Jianming Jiang State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Material Science and Engineering, Donghua University, Shanghai 201620, China article info Article history: Received 25 February 2009 Received in revised form 19 April 2009 Accepted 24 April 2009 Available online 13 May 2009 Keywords: Polyimides Solubility Optical transparency Dielectric constant abstract A series of novel polyimides (3a–d) were prepared from 3,3 0 ,5,5 0 -tetramethyl-4,4 0 -diaminodiphenyl- 4’’-tert-butyltoluene (1) with four aromatic dianhydrides via a one-step high-temperature poly- condensation procedure. The obtained polyimides showed excellent solubility, with the dissolvability at a concentration of 10 wt% in most amide polar solvents and chlorinated solvents. Their films were nearly colorless and exhibited high optical transparency, with the UV cutoff wavelength in the range of 322–350 nm and the wavelength of 80% transparency in the range of 395–414 nm. They also showed low dielectric constant (2.72–2.91 at 1 MHz) and low water absorptions (0.37–0.62%). Moreover, these polyimides possessed high glass transition temperatures (T g ) (above 321  C) and good thermal stability with 10% weight loss temperatures in the range of 526–547  C in nitrogen atmo- sphere. In comparison with the analogous polyimides non-containing 3,3 0 ,5,5 0 -tetramethyl pendant groups, the resultant polyimides 3a–d showed better solubility, higher optical transparency and lower dielectric constant. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Aromatic polyimides (PIs) exhibit excellent thermal, mechanical and electrical properties and have been used in microelectronic, aviation, liquid crystal display and other industries [1–8]. They could be synthesized from the conventional polycondensation of A–A and B–B monomers, namely, an aromatic diamine and an aromatic dianhydride. However, most PIs like other aromatic and heterocyclic polymers are often insoluble and infusible in fully imidized form due to their rigid chain characteristics and strong interchain actions, thus leading to processing difficulties. Purely commercial PIs derived from PMDA or BPDA, for instance, are soluble only in a few strongly protic acids. Meanwhile, the wholly aromatic PIs often have strong absorption in the visible region observed from their UV–visible spectra and are pale yellow or deep reddish yellow because of their highly conjugated aromatic struc- tures and/or the intermolecular charge–transfer complex (CTC) formation [9]. However, highly optical transparency is also one of the most attractive properties of PIs materials for optical applica- tions. To overcome these problems, much research effort have been focused on the synthesis of soluble and optically transparent PIs without much deterioration of their own excellent properties. Several successful approaches including insertion of flexible linkage and bulky substituents on the main chain or utilization of noncoplanar or unsymmetrical monomers have been developed [10–16]. Recently, considerable attention has been devoted to the fluo- rinated PIs, especially the trifluoromethyl-containing poly(ether imide)s (PEIs) [17–28]. These fluorinated PEIs are usually prepared derived from the trifluoromethyl-substituted bis(ether amine)s [21–28]. It was found that the incorporation of bulkily fluorinated groups into macromolecular backbones resulted in great benefits for improving polymer solubility as well as optical and dielectric performance, which attributed to the small dipole and the low polarizability of the C–F band as well as the increase in free volume. However, some of these fluorinated PEIs derived from PMDA and BPDA still showed a limited solubility. For example, Yang studied a series of fluorinated PEIs derived from 4,4 0 -bis(4-amino-2-tri- fluoromethylphenoxy)- benzophenone, 1,4-bis(4-amino-2-trifluo- romethylphenoxy)naphthalene and 2,5-bis(4-amino-2-trifluorome thylphenoxy)-tert-butylbenzene [22,25,26]. These materials derived from BPDA were almost insoluble in most common solvents. Moreover, the T g of these PEIs also have a much decreased value compared with the standard aromatic PIs because of intro- ducing amount of flexible ether linkages into polymer backbones (two ether linkages in each repeated unit). Insulating materials for microelectronics should not only have low dielectric constant and moisture absorption, but also should possess high T g to withstand the elevated processing temperatures. * Corresponding author. Tel.: þ86 021 67792830; fax: þ86 021 67792798. E-mail address: lig@dhu.edu.cn (G. Li). Contents lists available at ScienceDirect Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab 0141-3910/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2009.04.032 Polymer Degradation and Stability 94 (2009) 1526–1532