Understanding the role of MAM molecular weight in the production of PMMA/MAM nanocellular polymers

Abstract

Nanostructured polymer blends with CO2-philic domains can be used to produce nanocellular materials with controlled nucleation. It is well known that this nanostructuration can be induced by the addition of a block copolymer poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) (MAM) to a poly(methyl methacrylate) (PMMA) matrix. However, the effect of the block copolymer molecular weight on the production of nanocellular materials is still unknown. In this work, this effect is analysed by using three types of MAM triblock copolymers with different molecular weights, and a fixed blend ratio of 90 wt% PMMA and 10 wt% of MAM. Blends were produced by extrusion. As a result of the extrusion process, a non-equilibrium nanostructuration takes place in the blends, and the micelle density increases as MAM molecular weight increases. Micelle formation is proposed to occur as result of two mechanisms: dispersion, controlled by the extrusion parameters and the relative viscosities of the polymers, and self-assembly of MAM molecules in the dispersed domains. On the other hand, in the nanocellular materials produced with these blends, cell size decreases from 200 to 120 nm as MAM molecular weight increases. Cell growth is suggested to be controlled by the intermicelle distance and limited by the cell wall thickness. Furthermore, a theoretical explanation of the mechanisms underlying the limited expansion of PMMA/MAM systems is proposed and discussed.

Low-density PMMA/MAM nanocellular polymers using low MAM contents: Production and characterization

“…1 shows the TEM images of the solid blends for all the contents of MAM and the three grades of MAM. It should be noted that the nanostructuration observed on these samples is obtained from a nonequilibrium process as the extrusion is [31]. The micelle nanostructuration is detected at contents from 10 wt% down to 0.5 wt%.…”

“…T g of the PBA phase was determined by DSC. More details about the characterization of the copolymers can be found elsewhere [31].…”

“…They obtained cell sizes below 200 nm at 10 MPa of saturation pressure with a 10 wt% of MAM, but with relative densities above 0.4. Bernardo et al [31] investigated the influence of the MAM molecular weight in the production of PMMA/MAM nanocellular polymers. They showed that reducing the MAM molecular weight allows decreasing the relative density up to 0.37, the cell size being around 200 nm.…”

“…In all the previously mentioned works, copolymer contents of at least 1 wt% were necessary to achieve a nanocellular structure, whereas the densities obtained were far away from the results obtained using pure polymers or nanoparticles as a nucleating agent. In an own previous work [31] we proposed that the presence of the micelles is a limiting parameter in the production of low density nanocellular materials based on PMMA/MAM blends. Besides, these copolymers are usually expensive and not easily available, and due to this, the high contents needed complicate its use as possible nucleating agents on the industrial production of nanocellular polymers.…”

Modeling the heat transfer by conduction of nanocellular polymers with bimodal cellular structures

“…For a value of = SD ϕ / 0.5, that is, a width of 100 nm with an average cell size of 200 nm, a difference of almost 1.5 mW/mK is predicted, that is, an increase of a 4.8% in the conductivity. Values of SD ϕ / of 0.5 and higher are usually detected in nanocellular materials [47,56,57], so this effect is important for the accurate prediction of the thermal conductivity of nanocellular polymers.…”