Damping properties and morphology of polyurethane/vinyl ester resin interpenetrating polymer network

Abstract

A series of polyurethane/vinyl ester resin simultaneous and gradient interpenetrating polymer networks (PU/VER IPN and gradient IPN), cured at room temperature, were synthesized by introducing acrylic esters as VER’s comonomers. The effects of thermodynamic factor, kinetic factor, component ratio and gradient techniques on their damping properties were studied by DMA. It was found that the damping properties of general PU/VER (St) IPN with styrene (St) as VER’s comonomer are improved by introducing acrylic esters instead of St. When the relative polymerization rates of the networks are close, 80:20, 70:30 and 60:40 PU/VER (BMA) IPNs with butyl methacrylate (BMA) as VER’s comonomer have excellent damping properties. The gradient IPN with better damping properties than simultaneous IPNs was obtained by adjusting the gradient techniques. The $\text{tan}\text{δ}$ values of the gradient IPN with the time interval of 3 h and the component ratios of 50:50–60:40–70:30 are higher than 0.3 from −57 °C to higher than 90 °C, and its $\text{tan}\text{δ}$ values are higher than 0.5 from −36 to 54 °C. The results of EDX revealed that the gradient structure is formed in transition regions of gradient IPN. The results detected by TEM and AFM showed that the phase ranges of PU/VER (BMA) IPNs and gradient IPN obtained are both in nanometer scale. Furthermore, the relationship of microstructure and damping properties was studied.

Introduction

Material damping is one of the most effective solutions to the problem of vibration and noise. Viscoelastic polymers as damping materials have attracted many researchers in recent years because of their high damping values around the glass transition temperature (T_g) [1], [2]. But the useful damping temperature range of a homopolymer usually covers 20–30 °C for acoustical frequency ranging from 20 to 20 000 Hz, which is rather narrow for practical applications. In fact, the $\text{tan}\text{δ}$ values of good damping materials are higher than 0.3 for a temperature range of at least 60 °C [3]. In order to improve the damping capabilities of polymers, many techniques, such as polymer blends, copolymers, and interpenetrating polymer networks (IPNs or IPN) have been employed. Among them, IPN, a novel type of polymer alloys consisting of two or more crosslinked polymers held together by physical entanglement, has been the promising technique of preparing materials with broad T_g ranges and excellent damping performances because of mutual entanglement, forced compatibility, synergism of the networks and cellular, dual-phase continuous microstructure [4], [5].

Gradient IPN is mixture of crosslinked polymers in which the concentration of one network changes across the section of a sample. So, it may be regarded as a combination of an infinite number of layers of IPN, whose compositions and properties vary gradually from the surface to the core of the sample. As a result, the properties of the system differ from those of both individual network and IPN prepared by the traditional method. It was shown that gradient IPN had a broad maximum of mechanical loss tangent ($\text{tan}\text{δ}$) spanning a temperature range from 273 to 373 K [6]. Gradient IPN is obtained by the method of sequential curing, so it cannot be prepared by traditional method in the system cured at room temperature in which the process of diffusion and curing of the monomers forming the second network is simultaneous.

In the previous work [7], the polyurethane/poly(methyl methacrylate) gradient IPN cured at room temperature was obtained by casting the mixture of different component ratios in a mold at various times and the detected results showed that the gradient IPN revealed many sublevel transitions. In this paper, a series of polyurethane/vinyl ester resin (PU/VER) simultaneous and gradient IPNs were synthesized by this method. For PU/VER IPN, a great deal of research has been concentrated on their synthesis, morphology and mechanical properties, but seldom on their damping properties [8], [9]. And there is still few literature about damping properties of gradient IPN [6]. Generally, styrene (St) is VER’s comonomer, which may result in the poor compatibility and damping properties of PU/VER (St) IPN (St is VER’s comonomer) because PU and polystyrene (PSt) are incompatible thermodynamically [10]. Wang et al. [11] improved the compatibility and mechanical properties of PU/VER IPN by introducing methyl methacrylate (MMA) as grafted VER’s comonomer. In this paper, in order to improve the compatibility and damping properties of PU/VER IPN, different acrylic esters were introduced into VER’s comonomer system. The effects of thermodynamic factor, kinetic factor, component ratio of IPN and techniques of gradient IPN on their damping properties were studied. Furthermore, the relationship of microstructure and damping properties was studied.