Thermoset polymers phase separation

Semi-IPNs were prepared by the sol-gel technique through in situ polymerization of BMI in thermoplastic polyetherimide (PEI) as well as in polysulfone (PSF) (Kurdi and Kumar 2006). Structure and properties of semi-IPN membranes could be varied by controlling the thermoset BMI microdomain size interpenetrating within a thermoplastic polymer network. The size of this microdomain depended on the polymerization time of BMI and on the degree of thermoset/thermoplastic phase separation. These semi-IPN membranes showed an improved Tg but a decrease in their thermal stability and could be used for Oj-emiched-air applications where high selectivity is not required. At ambient temperature, it was possible to increase the permeance of semi-IPN membranes. 

Typically IPNs exhibit some degree of phase separation in their structure depending on how miscible the component polymers are. However, because the networks are interconnected such phase separation can occur only to a limited extent, particularly by comparison with conventional polymer blends. Polymer blends necessarily have to be prepared from thermoplastics IPNs may include thermosets in their formulation. 

Williams, R.J.., Rozenberg, B. A. and Pascault, J.-P. Reaction Induced Phase Separation in Modified Thermosetting Polymers. Vol. 128, pp. 95-156. 

It is our intention to present strategies based on chemically induced phase separation (CIPS), which allow one to prepare porous thermosets with controlled size and distribution in the low pm-range. According to lUPAC nomenclature, porous materials with pore sizes greater than 50 nm should be termed macroporous [1]. Based on this terminology, porous materials with pore diameters lower than 2 nm are called microporous. The nomination mesoporous is reserved for materials with intermediate pore sizes. In this introductory section, we will classify and explain the different approaches to prepare porous polymers and to check their feasibility to achieve macroporous thermosets. A summary of the technologically most important techniques to prepare polymeric foams can be found in [2,3]. 

To overcome these problems a gradient oven was presented which allows one to find rapidly the real phase separation gap for a given set of polymer and solvent. These results may serve as general guidelines for the preparation of a wide variety of solvent-modified and macroporous thermosets with tailored morphologies via CIPS. 

The precursors of thermosetting polymers are usually one of the ingredients of complex formulations. They may be present in very small amounts, as in the manufacture of abrasive disks where the thermoset acts as an aggluti-nant in medium amounts, as in the case of filler-reinforced thermosets or as the only components, in formulations used for encapsulation purposes. Apart from fillers, fibers, pigments, etc., some formulations contain rubber or thermoplastic modifiers that phase-separate upon the polymerization reaction (cure). 

An interesting method of eliminating the undercure caused by vitrification when using microwave radiation is to modify the formulation, including the use of polar thermoplastic that phase-separates during cure (Chapter 8). The thermoplastic material can convert microwave energy into heat, which enables the thermosetting polymer to devitrify and reach full cure. 

Liquid-crystalline polymers (LCP) can be used in thermoset systems as initially miscible modifiers that phase-separate during cure. 

---