Palladium(II)-catalyzed addition polymerizations of nadimides with linear alkyl and alicyclic pendant groups Binyuan Liu a, * , Xiaoya Wang a , Yige Wang a , Weidong Yan a , Huanrong Li a , Il Kim b, * a School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130, China b The WCU Center for Synthetic Polymer Bioconjugate Hybrid Materials, Division of Chemical Engineering, Pusan National University, Busan 609-735, Republic of Korea article info Article history: Received 2 February 2009 Received in revised form 30 March 2009 Accepted 1 April 2009 Available online 9 April 2009 Keywords: Catalysis Nadimides Palladium(II) catalysts Polymerizations Transition metal chemistry abstract Two series of polynadimides with pendant linear alkyl and alicyclic groups have been prepared by addi- tion polymerization of N-alkyl-exo-norbornene dicarboximides (nadimides; alkyl = propyl, butyl, pentyl, hexyl, cyclopropyl, cyclopentyl, cyclohexyl, and cycloheptyl) in the presence of palladium(II) catalyst. The catalytic reactivity of the nadimides strongly depends on the nature and the steric bulk of the pendant groups. Nadimides with alicyclic groups (except for N-cyclopropyl nadimides) exhibit higher reactivity than the nadimides with linear alkyl groups and substituents with the same number of carbons. The poly- nadimides with alicyclic groups present lower dielectric constants than those with linear alkyl groups. All resulting polynadimides exhibit better thermal stability than the unsubsitituted polynorbornenes. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Norbornene (NB) and its derivatives can be polymerized in three ways, depending on the catalyst used: ring-opening metath- esis polymerization (ROMP), cationic and/or radical polymeriza- tion, and vinyl polymerization [1]. Each method leads to its own polymer type, which is different in structure and properties from polymers made by the other two methods. Among these polymer types, vinyl-type polynorbornene (PNB) – which maintains its in- tact bicyclic structure in repeating units – has been considerably attracted because of its processibility and unique chemical and physical properties, such as excellent optical transparency, high thermal stability, high glass transition temperature (T g ), low mois- ture absorption, and low dielectric constant (k) [2,3]. These proper- ties make the materials attractive for electronic and optical applications. However, the polymer’s poor solubility in common organic solvents, its mechanical brittleness, and its low adhesion property present serious limitations towards potential applications [1,4]. Thus, much effort has gone into surmounting these limita- tions by incorporating functional pendant groups into the PNB backbone, such as alkoxysilyl, alkyl, and ester groups. The key problem with this approach, however, is that these modifiers often deteriorate the thermal stability [5–7] and/or dielectric properties of the polymers. Unfavorable changes to these properties are unde- sired for certain applications, like interlayer dielectric materials. Other than the aforementioned PNBs, poly(N-o/m/p-tolyl nadi- mide)s with aromatic imide groups display good solubility [8], and fluorinated polynadimides possess low dielectric constants (2.31) [9] while maintaining good thermal stability. Unfortunately, the NB derivatives with imide groups tend to have a lower rate of addition polymerization, requiring either longer reaction times or higher amounts of catalyst [8,9]. ROMP of nadimides with linear alkyl and alicyclic substituents has also been performed, and the resulting polymers show good thermal properties and gas separa- tions, as well as low dielectric constants [10]. In comparison to the extensive studies on ROMP of nadimides with linear alkyl and alicyclic pendant substituents, few reports have been published on vinyl addition polymerizations of these nadimides. Our interest is in forming functionalized PNBs with good solu- bility without deteriorating the high thermostabilities and low dielectric constants common to PNBs. As a means of achieving these targets, we reported a series of functionalized PNBs bearing dimethyl carboxylate groups, polymerized by a Pd(II) complex associated with weak SbF  6 counter ions. As expected, the PNBs bearing dimethyl carboxylate groups showed good solubility in common organic solvents; however, their thermal stability (360 °C at 5% weight loss) and dielectric properties (k = 3.0–3.5) were worse than those seen for the unsubstituted PNB [11]. These deficiencies impelled us to design new kinds of functional NB derivatives. Considering the merits of polynadimides synthesized by ROMP and the lower addition polymerization activity of the nadimides bearing aromatic moieties, we have designed a new ser- ies of nadimide monomers with linear alkyl and/or alicyclic pen- dant groups and subjected them to vinyl addition polymerization 1381-5148/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.reactfunctpolym.2009.04.002 * Corresponding authors. Tel.: +86 22 26564277 (B. Liu). Fax: +82 51 513 7720 (I. Kim). E-mail addresses: byliu@hebut.edu.cn (B. Liu), ilkim@pusan.ac.kr (I. Kim). Reactive & Functional Polymers 69 (2009) 606–612 Contents lists available at ScienceDirect Reactive & Functional Polymers journal homepage: www.elsevier.com/locate/react