2,2, 6,6-Tetramethylpiperidine derivatives

In the present study possible modes of action of a relatively new class of light stabilizers, the Hindered Amine Light Stabilizers (HALS, tetramethylpiperidine derivatives, TMP) will be discussed. Certain members of this group have a light stabilizing effect superior in many fields of application to that of previous additives. They are effective in both thick layers and fibers13 12. 

An aspect of particular interest is the performance of hindered amines in protective coatings such as lacquers. Weathering tests in our application laboratories have shown that a tetramethylpiperidine derivative (HALS 1) has in fact a very good protective effect. 

For this reason we have concentrated on the study of ketone photolysis in the presence of oxygen and the interaction of the oxygen-centered radicals arising in this reaction with certain tetramethylpiperidine derivatives. ... 

In similar electrochlorination experiments, propionaldehyde [86], ethylene [87], tetramethylpiperidine derivatives [88], amines [89], acetone [90], and polymers [91] have been converted into chloro derivatives. Mechanistic studies have aimed at elucidating the role of chloronium intermediates [92], water [93], and of redox mediators such as Ce +[94] in the electrochlorination process. 

Several examples are known of N—O coordination of iV-hydroxypiperidines resulting in three-membered chelate rings on deprotonation (14). The crystal structures and Mo NMR studies of some complexes of MoVI containing this grouping have appeared.46"4 A similar coordination mode was observed in the crystal structure of a Pdn complex of the 2,2,4,4-tetramethylpiperidine derivative.49... 

Actually, triacetonamine still remains the only starting compound for the synthesis of 2,2,6,6-tetramethylpiperidine derivatives. The main methods of its preparation are given in Scheme 2. A summary of methods of synthesis for triacetonamine and other hindered piperidines are summarized in (15). 

By now a large number of 2,2,6,6-tetramethylpiperidine derivatives has been prepared. These are mostly compounds having substituents in the four-position of a piperidine ring, and their... 

Formyl-2,2,6,6-tetramethylpiperidine-l-oxyl obtained by the reaction given below could have been of great importance for the synthesis chemistry of 2,2,6,6-tetramethylpiperidine derivatives. But, after its synthesis had been reported, there is no evidence of its utilization (28). ... 

In Scheme 5 are given the structures of some 2,2,6,6-tetramethylpiperidine derivatives which are effective polymer stabilizers. The analysis of the structures of these compounds allows the formulation of the design principles of polymer stabilizers based on hindered amines in general and hindered piperidines in particular (38,51). 

It is a fact that while research on UV stabilizers has advanced to products which significantly improve the weatherability of polymeric materials, the exact processes by which the various classes of stabilizers fulfill their functions are not entirely certain. This especially holds for the very important class of Jlindered Mine Light Stabilizers (HALS, tetramethylpiperidine derivatives, TMP). 

The results obtained for the non-inhibited and N-H inhibited photooxidation are shown in Figure 1. The amine used was the tetramethylpiperidine-derivative ... 

Tetramethylpiperidine derivatives are capable of acting in both ways according to our findings, these additives react very efficiently with peracid radicals. In addition, they are expected to accumulate at hydroperoxide sites by complex formation ( 1, 2). This means they are partly located at the sites where photooxidation is initiated. The respective complex formation constants are... 

D.W. Grattan, D.J. Carlsson, and D.M. Wiles, Polyolefin photo-stabilisation mechanisms. Reaction of tetramethylpiperidine derivatives in model systems, Polym. Degrad. Stab. 1979, 1, 69-84. 

As alluded to above, a second class of light stabilizers, the hindered amine light stabilizers (HALSs), provide additional stability to polymers and can function even in thin film or in sample surfaces. The chemistry of HALSs is based on the 2,2,6,6-tetramethylpiperidine derivatives (Fig. 5). Unlike UVAs, HALSs have no significant UV absorption and... 

For polyolefins, hindered amine-based on 2,2,6,6-tetramethylpiperidine derivatives are gaining importance as light stabilisers [14,17]. They are effective as antioxidants at low and moderate temperatures [18]. Hindered amine light stabilisers have a synergistic effect in combination with aliphatic phosphites under photo-oxidative conditions [19]. 

Hindered Amine Ethers. This imusual new family of flame retardants (or synergists) was discovered by Ciba, which had been exploring the light stabilizer family of 2,2,6,6-tetramethylpiperidine derivatives (see UV Stabilizers). The A(-alkoxy or cycloalkoxy derivatives appear to have flame-retardant action particularly in polyolefins. One member of this group, where the A -cyclohexyloxy-2,2,6,6-tetramethylpiperidinyl group is attached to an oligomeric pol5mier chain, has been in market development as Ciba s NOR 116 (144). 

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