Polymer stabilization overview

This chapter is a comprehensive overview of the progress in the field of generation, chemistry, and application of nitroxyl radicals and their precursors, for example, hindered amines of the 2,2,6,6-tetramethy1-piperidine series. Because of the importance of nitroxyl radicals to polymer stabilization, this application is discussed at length, while the others are touched upon briefly. 

To become an effective UV stabilizer UVAs must strongly absorb, for polymers, harmful UV light. They have to be able to transfer the absorbed light in harmless energy and they have to be active during the service life of the polymer. An overview of the currently in use classes of UVAs is given in Scheme 17.1. The UV absorption characteristics of these classes of UVAs are shown in several publications (for example, see Refs [4-6]). The UV absorption of these molecules depends, besides on the type, also on their substitution [4]. 

Poly(p-pheny lene)s, PPPs, constitute the prototype of rigid-rod polymers and are currently being intensively investigated [1]. The key role of PPPs follows from their conceptually simple and appealing molecular structure, from their chemical stability, and from their superior physical properties [2], In turn, this is the result of important advances made in aromatic chemistry over the last few years. The following section gives an overview of the most common methods to generate poly(p-phenylene)s via different synthetic approaches. 

Soluble polymers are widely used to control the state of dispersion of fine-particle suspensions. Depending on the polymer, and how it is applied, they can serve to enhance stability (dispersants) or to promote aggregation of the particles (flocculants). The topics covered in this chapter are intended as an overview of the use of polymers for stability control in mineral-particle suspensions with particular emphasis on flocculation processes. A brief discussion of stabilisation by polymers is included for completeness. 

From electronic back to optical properties, in the final Chapter 15, Rajca and Miyasaka provide an overview of the synthesis of molecules with highly anne-lated, chiral, 3t-conjugated systems, primarily of the helicene-type. Tremendous progress has been made in the synthesis of helicenes however, the corresponding helical, ladder-type polymers remain a significant and attractive challenge. In addition to the synthesis, the configurational stability (barriers for racemization) and chirooptical properties are described and discussed in depth in this chapter. In this context, perspectives for isotropic materials with molecule-based chirooptical properties are outlined. 

Camino, G. Costa, L. Luda, M. P. Overview of fire retardant mechanism, Polymer Degradation and Stability, 1991, 33(2), 131-154. 

MABS polymers (methyl methacrylate-acrylonitrile-butadiene-styrene) together with blends composed of polyphenylene ether and impact-resistant polystyrene (PPE/PS-I) also form part of the styrenic copolymer product range. Figure 2.1 provides an overview of the different classes of products and trade names. A characteristic property is their amorphous nature, i.e. high dimensional stability and largely constant mechanical properties to just below the glass transition temperature, Tg. 

Chemical breakdown usually involves oxidative chain reactions that cause embrittlement of semicrystalline polymers and discoloration of poly(vinyl chloride) and polymers with aromatic groups. The reactions are complicated by the presence of transient intermediates and by rates that depend on minute concentrations of molecular defects, impurities and additives. They also depend on several important piiysi-cal factors outlined in this brief overview of polyolefin degradation, two of these factors, the transfer of excitation energy and the transport of products and protectants, play a major role in stabilization processes. 

In this chapter, the theories as well as the experimental justification for the mechanism of stabilization and destabilization of colloidal dispersions are outlined. Interacting forces between colloidal particles are analyzed and an overview of experimental methods for assessing the dispersion and relevant properties is given. The stabilization and flocculation of dispersions in the presence of surfactants and polymers is discussed in the last two sections. 

There is much to learn and admire in the hindered amine story. Chemists can take pride in how effectively they have worked together across national boundaries to make hindered amine stabilizers an important product group for the stabilization of polymers. This introduction is a modest effort to review some of the early history of stable-free radicals including triacetoneamine-N-oxyl. This chapter was intended to serve primarily as an introduction to the hindered amine review which took place at the symposium and intentionally avoids covering material which other participants were expected to present. It is a "light-touch" overview. 

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