F.-U. Schafer

Poly(ether urethane)/poly(ethyl methacrylate) interpenetrating polymer networks: Morphology, phase continuity and mechanical properties as a function of composition

The composition range of polyurethane (PUR)/poly(ethyl methacrylate) (PEMA) interpenetrating polymer networks was investigated with respect to morphology and phase continuity using mechanical and dynamic mechanical methods and transmission electron microscopy (TEM). Dynamic mechanical data revealed one main tanδ transition with a shoulder for the intermediate compositions from 70:30 to 40:60 indicating a semi-miscible system. For the remaining compositions only one peak, indicating a higher degree of miscibility was observed. The storage and elastic moduli were related to the Davies, Kerner and Budiansky modulus-composition models. The Budiansky modulus-composition model, which indicates phase inversion at the mid-range composition, resulted in the best fit. However, it was found that the shape of the modulus versus composition curves was strongly temperature-dependent. In previous studies, not much attention had been given to the temperature at which the modulus-composition studies were conducted. Tensile testing revealed a strong synergistic effect at the 70:30 PUR/PEMA composition with maxima occurring at this composition for both the elongation at break and the toughness index. The tensile strength increased in a three-step regime corroborating the dynamic mechanical thermal analysis results. TEM micrographs confirmed a co-continuous system at the 70:30 to 40:60 PUR/PEMA mid-range compositions.

Poly(ether urethane)/poly(ethyl methacrylate) IPNs with high damping characteristics : The influence of the crosslink density in both networks

Interpenetrating polymer networks (IPNs) with a controlled degree of microphase separation were synthesized from a poly(ether urethane) (PUR) and poly(ethyl methacrylate) (PEMA). The influence of the crosslink density of both networks was investigated in the 70:30 PUR/PEMA IPN. The extent of damping was evaluated by dynamic mechanical thermal analysis. Mechanical properties were studied using tensile testing and hardness measure-ments. Control of crosslinking was successful in tailoring the damping profile. Higher crosslinking in the first-formed network (polyurethane) seemed to increase slightly the area under the linear loss modulus curve, LA, whereas no influence was obvious when changing the crosslink density in the second network. TGA studies revealed improved thermal properties for the IPNs with a higher crosslink density in the PUR network. TEM micrographs confirmed a finer morphology for the materials with a higher crosslink density in the PUR, whereas increasing the crosslink density in the PEMA network resulted in a decrease of phase mixing.

Modulated differential scanning calorimetry: XI. A characterisation method for interpenetrating polymer networks

Abstract Quantitative analysis of the differential of heat capacity with temperature, d C′ p d t , signal from modulated-temperature differential scanning calorimetry (M-TDSC) allows the extent of phase mixing to be calculated for interpenetrating polymer networks (IPNs). A new characterisation method for interpenetrating polymer networks is proposed in which the d C′ p d T signal was used to analyse phase structure and composition. It is believed that the d C′ p d T with temperature signal will become a useful tool and a powerful complement to solid-state NMR, scattering and direct nonradiative energy-transfer methods for analysing the morphology of IPNs.

Miscibility and fracture behaviour of epoxy resin-nitrated polyetherimide blends

Abstract Nitrated polyethermide (NI-PEI) was obtained by chemically modifying a commercially available polyetherimide (PEI) and was characterized by nuclear magnetic resonance and infra-red spectroscopies, elemental analysis and viscometry. NI-PEI and NI-PEI/PEI mixtures were blended with an epoxy resin (MY0510) which was cured with 3,3′-diaminodiphenolsulfone. The morphology and fracture behaviour of these blends were examined by dynamic mechanical thermal analysis and by a three-point bending fracture test. A two-phase morphology exists with substantial toughening occurring at PEI and NI-PEI concentrations of 5 and 10 wt%.

TMXDI-based poly(ether urethane)/polystyrene interpenetrating polymer networks : 2. Tg behaviour, mechanical properties and modulus-composition studies

Abstract In this, the second of two papers on a series of simultaneous polyurethane (PUR)/polystyrene (PS) interpenetrating polymer networks (IPNs), the T g behaviour, mechanical properties and modulus–composition relations have been studied. A gross phase morphology over the full IPN composition range was indicated by two separate loss factor peaks from dynamic mechanical thermal analysis (DMTA). Both DMTA and modulated-temperature differential scanning calorimetry (MT-d.s.c.) measurements revealed that the T g of the PS transition increased with decreasing PS content in the IPN. This was explained by an increase in interactions between the PUR hard segments and the π -electrons of the PS phenyl rings. Despite the phase-separated morphology, materials with good mechanical properties were obtained. The tensile properties and the Shore hardness results were comparable to similar semi-miscible PUR/PEMA IPNs. The Budiansky modulus–composition relation resulted in the best fit with the experimental data, indicating phase inversion at mid-range compositions. Modulus–composition studies, indicating that phase inversion occurred at the 30:70 PUR/PS IPN composition, corroborated the electron microscopy findings from the first paper in this series.

Mechanical and morphological study of polyurethane/polystyrene interpenetrating polymer networks containing ionic groups

The viscoelastic and mechanical properties and the morphology of polyurethane (PUR)/ olystyrene (PS) interpenetrating polymer networks (IPNs) containing ionic groups have been investigated. Dynamic mechanical thermal analysis (DMTA) revealed a pronounced change in the viscoelastic properties upon the introduction of ionic groups. For the 70 : 30 and 60 : 40 PUR/PS IPN compositions, the DMTA data changed from a dominant PUR to a dominant PS loss factor peak. Higher intertransition loss factor values indicated a significant improvement of IPN component mixing with increasing ionic content. The stress at break values increased only moderately, whereas sharp rises in Youngs modulus and hardness values were found at 2 wt % ionic groups. At the same time, the strain at break values decreased by half. Scanning and transmission electron microscopy (TEM) indicated a grossly phase-separated morphology for the 70 : 30 PUR/PS IPN without ionic groups. With increasing methacrylic acid (MAA) content, the PS phase domain sizes decreased. At 2 wt % of ionic groups, a TEM micrograph showed interconnected PS phase domains resembling a network structure.

Modulated differential scanning calorimetry : 12. Interphase boundaries and fractal scattering in interpenetrating polymer networks

Abstract The morphology of polyurethane (PU)–poly(methyl methacrylate) (PEMA) interpenetrating polymer networks (IPNs) were investigated by means of small-angle X-ray scattering (SAXS) and modulated-temperature differential scanning calorimetry (M-TDSC) techniques. Based on the analysis method employed by Tan et al. [Polymer 1997;38:4571], the interfacial thickness in the IPNs was calculated from SAXS data. The conclusion is that the interfacial thickness is zero and there are sharp domain boundaries in the PU-PEMA IPNs. M-TDSC results show that the PU-PEMA IPNs have a multi-phase morphology with a diffuse interphase region. The M-TDSC results are in agreement with DMTA and TEM findings. The M-TDSC, TEM and DMTA results, therefore, conflict with those obtained from the analysis of the SAXS data. We believe that the analysis method employed by Tan et al. is questionable for IPNs.

TMXDI-based poly(ether urethane)/polystyrene interpenetrating polymer networks: 1. Morphology and thermal properties

Abstract In this, the first of two papers on the full composition series of simultaneous polyurethane (PUR)/polystyrene (PS) interpenetrating polymer networks (IPNs), the morphology and thermal properties are investigated. For the first time in IPN preparations, tertiary aliphatic m-tetramethylxylene diisocyanate (TMXDI) was used in the PUR hard segment. An investigation of the reaction kinetics of the 60:40 PUR/PS IPN composition by Fourier transform infrared (FTi.r.) spectroscopy, using a heated cell unit, confirmed that the PUR was the first network formed. Scanning (SEM) and transmission (TEM) electron microscopy indicated a grossly phase-separated morphology. The phase domain sizes at the outer composition ranges (90:10, 80:20, 70:30 and 10:90 PUR/PS IPNs) were smaller (20–300 nm) than at the mid-range compositions (300 nm-6 μmm). SEM and TEM showed phase inversion to occur at a composition between the 30:70 and 20:80 PUR/PS IPNs. Comparing the immiscible PUR/PS IPN composition series with a similar semi-miscible PUR/PEMA IPN series revealed that in addition to phase domain sizes, the domain shape and the definition of the phase boundaries are of importance in assessing the miscibility of IPNs. No significant improvement in the thermal decomposition profile was observed for the IPN compared to the respective homonetworks.

Damping Characteristics of Polyurethane-Based Simultaneous Interpenetrating Polymer Networks

A brief overview of damping with polymers is given. The highest energy absorbing potential of polymers is centred around their glass transition temperature (T g ). In order to broaden the transition, partially miscible polymer pairs with fairly widely separated T g s can be used to give broad and high transition regions. This can be obtained by the use of interpenetrating polymer network (IPN) technology. The damping ability of the IPNs was assessed from the tan δ and loss modulus versus temperature curves. The area under the linear tan δ curve (TA) and the loss modulus equivalent (LA) were calculated and correlated with the IPN composition. An incompatible polyurethane/polystyrene IPN was chemically modified by internetwork grafting and the use of compatibilizers, resulting in a high and broad transition with tan δ values > 0.3 over 80°C and 135°C respectively. Conducting a stirred polymerization of a 60:40 PUR/PS IPN resulted in a very complicated morphology with phases within phases within phases, Values for tan δ were greater than 0.3 from −19°C to 145°C combined with a high TA area of 85.4 K. The influence of the composition on the damping ability was studied in a semicompatible polyurethane/polyethyl methacrylate IPN. At the 70:30 composition, a broad temperature range (> 130°C) of tan δ values greater than 0.3 and a high TA area of 62.1 K resulted. LA was found to increase with increasing PEMA content, but with values well below those expected from applying the linear rule of mixing to LA of the homonetworks. TEM micrographs further elucidated the multiphase morphologies.

High-resolution thermogravimetric analysis of polyurethane/poly(ethyl methacrylate) interpenetrating polymer networks

Thermal degradation of a series of polyurethane/poly(ethyl methacrylate) interpenetrating polymer networks and their constituent networks were studied by three modes of thermogravimetric analysis: the conventional method, the constant reaction rate method, and the dynamic rate technique. The best understanding of the degradation mechanism was achieved by the last method, which allows much better resolution of overlapping events. In addition, the weight losses correspond well with the results obtained from the constant reaction rate analysis, but are achieved in shorter times.