The phase mixing studies on moisture cured polyurethane-ureas during cure D.K. Chattopadhyay a , B. Sreedhar b , K.V.S.N. Raju a, * a Organic Coatings and Polymers Division, Indian Institute of Chemical Technology, Taranaka, Hyderabad 500 007, India b Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500 007, India Received 23 August 2005; received in revised form 21 February 2006; accepted 18 March 2006 Abstract Moisture cured polyurethane-urea (MCPU) is one of the industrially important polymers that shows good thermal, mechanical and weathering properties and is widely used in the reactive hot melt adhesives and coatings. Structural variation of the building blocks, i.e. soft, hard segment and chain extender structure on the phase mixing characteristics during cure in polyether based moisture-cured polyurethanes (MCPUs) has been investigated. Variations in the soft segment structure like polyethylene glycol (PEG), polypropylene glycol (PPG) and polytetramethylene glycol (PTMG) and hard segment like toluene diisocyanate (TDI) or isophorone diisocyanate (IPDI) were made. The effect of isocyanate content (NCO:OH ratio 1.6:1 and 2:1) as well as various aliphatic diol and aromatic diamine chain extenders were also compared. The phase mixing phenomenon during network growth was evaluated by differential scanning calorimetry (DSC) and a correlation was drawn for the degree of cure with the phase mixing property. The change in modulus and thermal stability with the cure advancement were measured by dynamic mechanical and thermal analysis (DMTA) and thermogravimetric analysis (TGA). A correlation was made for the soft, hard segment and chain extender structure to the phase mixing phenomenon during cure. The rate of phase mixing was found to be dependent on the subtle variations in molecular architecture. q 2006 Elsevier Ltd. All rights reserved. Keywords: Polyurethane; Moisture cure; Phase mixing 1. Introduction Moisture cured polyurethane-ureas (MCPUs) are widely used in the sealant production, high performance coating sector as well as reactive hot melt adhesive industries. They provide the functional groups necessary for curing with atmospheric moisture. The attractive mechanical properties of MCPUs results from the microphase-mixed morphology brought about by the solid state posture reaction of the hard segment. Partial mutual insolubility of different chemical sequences in the block copolymer results in biphasic morphology. One of the microphases is derived from the macrodiol and is generally referred to as the soft micro-domain or phase that imparts softness and extensibility. It is relatively immiscible with the other phase derived from the diisocyanate and chain extender and is referred as hard micro-domain or phase, which provides cohesive strength to the polymer matrix. During the urea network maturation, soft and hard microphase mixes, and provides a delicate balance between the phase mixing and phase separation. Therefore, by suitable variation in chemical structure, composition and synthetic conditions, it is possible to obtain tough, high-strength polymer with an extremely wide range of mechanical and thermal properties. In fact, it is this tremendous ability to readily modify the properties of these materials by variation in chemical structure and composition that has stimulated the enormous technological and scientific interest in these polymers. Thus, in principle, it is possible to tailor the thermal, mechanical, and optical properties of MCPUs to meet specific performance criteria [1]. Cure of MCPU advances with progress of time and produces crosslink networks by the diffusion of moisture, nucleophilic attack and generation of primary amine that further react to produce urea bonds [2,3]. As the chemical reaction proceeds, urea chain length increases and the interaction parameters between the polyether soft and polyurea hard segment also changes. Such changes lead to a transition from an initially homogeneous state into a microphase mixed state. The major drawback of MCPU coatings is the formation of side products on storage and if these reactions are significant, both pot stability and shelf life are expected to be dramatically affected. The presence of side products, for example allophanate Polymer 47 (2006) 3814–3825 www.elsevier.com/locate/polymer 0032-3861/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2006.03.092 * Corresponding author. Tel.: C91 4027202080. E-mail addresses: kvsnraju@iict.res.in (K.V.S.N. Raju), drkvsnraju@ yahoo.com (K.V.S.N. Raju).