Motional heterogeneity and phase separation of semi-interpenetrating networks and mixtures based on functionalised polyurethane and polymethacrylate prepolymers Jelena C ˇ ulin a , Ivan S ˇ mit a , Mladen Andreis a , Zorica Veksli a, * , Alojz Anz ˇlovar b , Majda Z ˇ igon b a RuCer Bos ˇkovic ´ Institute, Bijenic ˇka c. 54, HR-10000 Zagreb, Croatia b National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia Received 6 April 2004; received in revised form 11 October 2004; accepted 1 November 2004 Available online 23 November 2004 Abstract Semi-interpenetrating polymer networks (SIPNs) and polymer mixtures (1:1 mass ratio) based on segmented polyester polyurethane (PU) with carboxylic groups and methacrylic copolymer (PM) with tertiary amine groups were studied by the electron spin resonance (ESR) spin label method. The concentration of functional groups varied from 0 to 0.45 mmol g K1 in both prepolymers. The ESR spectra of spin labelled PM component were used to characterise the heterogeneity of segmental motion and transitions due to the additional polymer interactions imposed by complementary functional groups. The results were deduced from the temperature dependent ESR spectra. Two component spectra reflect the effect of PU chains on segmental motion of the PM component below the macroscopic glass transition temperature, T g . The ratio of the fast and slow component was related to the complex polymer–polymer interaction or extent of miscibility. Restrictions of segmental motion of PM chains increase with functional groups concentration and above certain concentration (0.25 mmol g K1 ) PM segments in the network assess faster motion suggesting a change in the local packing density and domain structure. An increased miscibility and disorganisation of the ordered domains are confirmed by the loss of spherulitic morphology and crystallinity at higher functional groups concentration. PU/PM mixtures reveal similar motional behaviour as SIPNs of the same composition. However, the differences in the fractional amount of fast and slow motions confirm better interpenetration and interaction of the two polymers in the SIPNs. The results of motional heterogeneity and polymer interactions were complemented with the T g s. q 2004 Elsevier Ltd. All rights reserved. Keywords: Functionalized polyurethane–polymethacrylate semi-interpenetrating networks; Heterogeneity; ESR 1. Introduction Interpenetrating polymer networks, IPNs, and semi- interpenetrating polymer networks, SIPNs, based on polyurethanes offer a route for preparation of versatile materials with wide spectrum of properties [1]. The fundamental phenomena associated with the IPNs is the phase separation during the preparation. Many factors determine the phase separation and the properties of IPNs: the method of preparation, prepolymer miscibility, compo- sition, chain structure, crosslinking density, domain size and crystallinity. Interpenetrating polymerisation is a way of blending two polymers where at least one of the polymers is crosslinked in the presence of another to produce a mixture of fine morphology [2,3]. In order to improve polymer miscibility by noncovalent interactions additional functional groups are incorporated in the backbone of constituent polymers [4–8]. Additional interactions influence the change of morphology and consequently mechanical and thermal properties [4,5]. Micro or nanoheterogeneous morphology of IPNs and SIPNs as a consequence of incomplete mixing is reflected in the broad glass transition. Differences of packing density within domains and local composition allow heterogeneity of segmental motions around glass transition temperature, T g . Those multiple segmental motions can explain engin- eering performance of the material, namely mechanical 0032-3861/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2004.11.011 Polymer 46 (2005) 89–99 www.elsevier.com/locate/polymer * Corresponding author. Tel: C385 1 4561 111; fax: C385 1 4680 245. E-mail address: veksli@rudjer.irb.hr (Z. Veksli).