Stabilization of HTPBs

Stabilizers are chemicals used for maintaining the polymer s strength, flexibility and toughness during their processing and life-time thus they should preserve the polymer s original molecular structure. In other words, stabilization aims to retain the original molecular architecture in spite of the effect of heat, stress, chemical environment and irradiation. Stabilizers are classified as  

Degradation of polymers starts with a formation of free radicals, R, caused by structural defects, temperature, stress, etc. Examples of labile bonds that break creating R are listed in Table 2.6. Once R is formed, the radical degradation process is initiated it abstracts the most labile H-atom in the stabilizer or polymer. In the presence of O2, R transforms into peroxy radical, ROO, which accelerates the autocatalytic process. The alkyl-peroxy radicals dominate the propagation step of degradation. Usually polymers 

Tinuvin 312 = UV absorber for PEST and PC, N-(2-ethoxyphenyl)-N -(2-ethylphenyl)-ethylene diamide 

Several books and other publications on the stabilization of polymers have been mentioned in this chapter. In addition, two patents are noteworthy. The one by Hamilton discusses protection of polymer blends against transesteri-fication. For example,blends of PC with semi-crystalline PEST (e.g., PET) finds application in the automotive industry. Since the resistance to solvents depends on the PET crystallinity, which decreases with advancing transreactions, its control is essential. The patent specifies addition of a sUyl phosphate compound for inhibiting the ester-carbonate interchange. The stabilization is achieved by deactivation of the residual metaUic catalyst in the reaction with silyl phosphate stabilizers or their mixture. 

The second patent addresses several types of degradation mechanism, of the engineering or specialty polymers. Thus, oxidative, thermal and/or 

---

The degradability and stabilization of HTPBs was discussed in Sections 2.6 and 2.7. Now, the influence of one macromolecular blend component on another is of interest. Evidently, in totally immiscible blends the inter-species... 

---