Synthesis of stretchable polyetherimides containing multiple alkyl side chains David H. Wang a,b, * , Zhihao Shen b , Stephen Z.D. Cheng b , Frank W. Harris b, ** a University of Dayton Research Institute, Dayton, OH 45469-0168, USA b The Maurice Morton Institute of Polymer Science, The University of Akron, Akron, OH 44325-3909, USA Received 28 December 2006; received in revised form 20 February 2007; accepted 21 February 2007 Available online 24 February 2007 Abstract Two series of diamine monomers, i.e., 4-[3,4,5-tris(n-alkan-1-yloxy)benzyl]-3,5-diaminobenzoate and 2,2 0 -bis{4-[3,4,5-tris(n-alkan-1-yloxy) benzoate]}-4,4 0 -biphenyldiamines containing multiple alkyl side chains, were synthesized in which the length of the alkyl side chains was varied from 5 to 18 ethylene units. Polyetherimides (PEIs) were prepared from these two diamines and bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydrides (BisADA) using a one-step method in 1-chloronaphthalene. All the polymers possessed good solubility in chlorinated solvents. The high-molecular weight PEIs could be solution cast into transparent, tough films. The polymers containing the side chains which were at least 16 methylene units could be crystallized. The melting points of the crystals increased as the length of the side chains increased. The glass transition temperatures (T g s) of the PEIs decreased as the length of the side chains increased due to an internal plasticizing effect of the alkyl side chains. The PEIs containing multiple alkyl side chains showed excellent drawability with much higher elongations but lower tensile strengths and mod- uli compared with the commercial PEI, Ultem Ò 1000. The film’s in-plane refractive index parallel to the drawing direction (n // ) increased and its in-plane refractive index perpendicular to the drawing direction (n t ) decreased during drawing mainly due to the orientation of main chains in the drawing direction. The film’s in-plane birefringence increased with the drawing ratios. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Polyetherimides; Alkyl side chains; Birefringence 1. Introduction Polyetherimides (PEIs) have been prepared via aromatic nucleophilic substitution reactions [1]. Polymerization was carried out in dimethyl sulfoxide (DMSO)/toluene, N,N- dimethylformamide (DMF), N,N-dimethylacetamide (DMAc) or 1-methyl-2-pyrrolidinone (NMP) using moderate reaction conditions. PEIs were also synthesized from the diaminee dianhydride reaction. The majority of PEIs are non-crystalline and their glass transition temperatures (T g s) range from 200 to 280  C [2]. PEIs are injection moldable and exhibit high strengths and moduli, good ductility, excellent thermal stability, and flame resistance as well as good electrical properties. These basic properties make them outstanding high perfor- mance engineering thermoplastics. Ultem Ò 1000 is the most important PEI being sold by the General Electric Co. [3]. The polymer has also been used as a graphiteefiberecomposite matrix resin. n O N O O O N O O Ultem ® 1000 * Corresponding author. University of Dayton Research Institute, 330 College Park Avenue, Dayton, OH 45469-0168, USA. Tel.: þ1 937 255 9114; fax: þ1 937 258 8075. ** Corresponding author. E-mail addresses: huabin.wang@wpafb.af.mil (D.H. Wang), fharris@ uakron.edu (F.W. Harris). 0032-3861/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2007.02.053 Polymer 48 (2007) 2572e2584 www.elsevier.com/locate/polymer