Influence of lithium chloride on the morphology of flexible slabstock polyurethane foams and their plaque counterparts Ashish Aneja a , Garth L. Wilkes a, * , Ersin Yurtsever b , Iskender Yilgor b a Polymer Materials and Interfaces Laboratory, Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0211, USA b Department of Chemistry, Koc University, Sariyer 80910, Istanbul, Turkey Received 18 July 2002; received in revised form 18 October 2002; accepted 22 October 2002 Abstract In continuing efforts to understand urea phase connectivity in flexible polyurethane foams and its implications on physical properties, LiCl is used to alter the phase-separation behavior of slabstock foams. Comparisons are also drawn with plaque counterparts, which are prepared using the same polyol, isocyanate, and chain extender (water). LiCl is shown to alter the solid-state phase separation behavior of the foams and the plaques in a similar manner. This is confirmed using multiple characterization techniques, which provide information at different scale lengths. The foams and plaques with and without LiCl are shown to possess a microphase separated morphology with interdomain spacings of ca. 100 A ˚ . SAXS and TEM reveal that addition of LiCl reduces the urea aggregation behavior, typical in slabstock polyurethane foams, leading to a loss in the urea phase macro connectivity. Hard segment ordering, as studied by WAXS and FTIR, is shown to be of a similar nature in the plaque and foam, which do not incorporate LiCl. Addition of LiCl leads to a loss in the segmental packing behavior, or micro level connectivity of the urea phase, in both the plaques and corresponding foams, as inferred from WAXS and FTIR. The LiCl additive interacts with the polyol soft segments in an insignificant manner as shown from FTIR and DMA. In addition, foams containing LiCl are found to possess more intact cell windows due to the influence of LiCl on reaction kinetics as well as its effect on the precipitation of the urea phase. The experimental observations are supported by quantum mechanical calculations using a density functional theory approach, where molecular interactions between LiCl and model ether, urethane, and urea compounds are investigated. Interaction geometries of most stable complexes and their stability energies are calculated. Stability energies of ether/LiCl, urethane/LiCl, and urea/LiCl were determined to be 2 189, 2 617, and 2 687 kJ/mol, respectively, reinforcing that LiCl interacts predominantly with urea hard segments and in a minimal manner with the polyol soft segments. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: Polyurethanes; Foam; Microphase separation 1. Introduction One of the many applications of polyurethanes (PU) [1,2] lies in the area of flexible foams [1,3], which are used in many areas. Their preparation involves simultaneously occurring isocyanate – water and isocyanate – polyol reac- tions. The ‘blow’ reaction, in which water reacts with an isocyanate (functionality ¼ 2), leads to the formation of urea based hard segments (HS). In the ‘gelation’ reaction, an isocyanate group reacts with a terminal hydroxyl group of a polyol (functionality . 2) to form urethane linkages, which covalently bond the urea hard segments to the polyol soft segments (SS). As these reactions proceed, the morphology of flexible PU foams develops over several scale lengths. The exotherms associated with these reactions as well as the carbon dioxide generated in the blow reaction helps to expand the foaming mixture into a final cellular structure. Cell sizes in flexible PU foams are typically a few hundred microns in dimensions. The morphology development in the struts of the foam takes place at a much smaller scale length as compared to the cellular structure. The presence of a microphase separated morphology in flexible PU foams was first confirmed using small angle X-ray scattering (SAXS) by Wilkes and coworkers [4]. Their work suggested the formation of urea microdomains separated from the polyol phase with an interdomain spacing of ca. 100 A ˚ . Ever since, SAXS has been a widely utilized technique to understand the fine structure of PU foams [3,5,6]. The presence of morphological features at a scale length 0032-3861/03/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0032-3861(02)00781-4 Polymer 44 (2003) 757–768 www.elsevier.com/locate/polymer * Corresponding author. Tel.: þ 1-540-231-5498; fax: þ1-540-231-9511. E-mail address: gwilkes@vt.edu (G.L. Wilkes).