Light stabilization

Yellowing behavior is important in particular for the practical applications of PS and SAN, Table 3.4. Articles that are exposed to UV radiation (louvers for fluorescent lamps, bill boards, etc.) have to be stabilized against harmful UV influence [86]. 

Light stabilization is mandatory for SB and ABS because of their butadiene content. Combinations of UVA with HALS lead to a notable improvement of mechanical properties during service of the components. The good light-protective effect of the UVA/HALS combination is attributed to the observed synergism, where the UV absorber protects the interior layers and HALS provides the necessary surface protection. This goes hand in hand with significant improvement in color behavior [86]. 

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The 2-imino-4-thiazolines may be used as ultraviolet-light stabilizers of polyolefin compositions (1026). 2-Aminothiazole improves adhesive properties of wood to wood glue (271). Cbmpound 428 exhibits antioxidant properties (Scheme 242) (1027). Ammonium N-(2-thiazolyl)dithio-carbamate (429) is a bactericide and fungicide used in industrial products such as lumber, paint, plastics, and textiles (1037). Compound 430 is reported (1038) to form an excellent volume of foam coating in aluminum pans when ignited with propane. 

ALKYLPHENOLS] (Vol 2) Hindered-amine light stabilizers (HALS)... 

Uv-curable polymers Uv devices Uvilon Uvithane 893 Uv light stabilizers... 

Sesamex [51-14-9] (Sesoxane) (30) is a synergist oflow toxicity, acute oral LD q (rat) = 2000 2270 mg/kg, for pyrethrins and allethrin. 6,7-Dihydroxy 4-methylcoumarin has been offered as an antioxidant for phenoHcs and polymers, and as an anthelmintic. 2,4,5-Trihydroxybutyrophenone has been available as an antioxidant and light stabilizer for polyolefins, waxes, and foods. Isoflavones, eg (31), have been patented as components of antioxidant compositions for foods and cosmetics (qv) (97). 

Diazo Coupling Reactions. Alkylphenols undergo a coupling reaction with dia2onium salts which is the basis for the preparation of a class of uv light stabilizers for polymers. The interaction of orxv i -nitrobenzenediazonium chloride with 2,4-di-/ r2 -butylphenol results in an azo-coupled product (30). Reduction of the nitro group followed by m situ cyclization affords the benzottiazole (31) (19). 

The major use of this compound is in the production of mordant and acid dyes. 2-Amino-4-nitropheno1 also has found limited use as an antioxidant and light stabilizer in butyl mbbers and as a catalyst in the manufacture of hexadiene. The compound has been shown to be a skin irritant and continuous exposure should be avoided. Toxicological studies indicate that it is nonaccumulative (162). 

As a pharmaceutical, methyl salicylate is used in liniments and ointments for the relief of pain and for rheumatic conditions. As a flavor and fragrance agent, it is used in confectioneries, dentifrices, cosmetics, and perfumes. Other commercial applications for methyl salicylate are as a dye carrier, as a uv-light stabilizer in acrylic resins, and as a chemical intermediate. The May 1996 price was 5.50/kg (18). 

Hindered Amines. Hiadered amines are extremely effective ia protecting polyolefins and other polymeric materials against photodegradation. They usually are classified as light stabilizers rather than antioxidants. 

Most of the commercial hindered-amiae light stabilizers (HALS) are derivatives of 2,2,6,6-tetramethylpiperidine [768-66-1] (15). 

Oligomeric hindered amine light stabilizers are effective thermal antioxidants for polypropylene. Thus 0.1% of A[,Af-bis(2,2,6,6-tetramethyl-4-piperadinyl)-l,6-hexanediamine polymer, with 2,4,6-trichloro-l,3,5-triazine and 2,4,4-trimethyl-2-pentaneainine [70624-18-9] (35) (Fig. 5), protects polypropylene multifilaments against oxidation when exposed at 120°C in a forced-air oven (22) for 47 days. 3,5-Di-/ l -butyl-4-hydroxytoluene [128-37-0] (0.1%) affords protection for only 14 days. 

Nearly all of the benzal chloride produced is consumed in the manufacture of benzaldehyde. Benzaldehyde (qv) is used in the manufacture of perfume and flavor chemicals, dyes, and pharmaceuticals. The principal part of benzotrichloride production is used in the manufacture of benzoyl chloride (see Benzoic acid). Lesser amounts are consumed in the manufacture of benzotrifluoride, as a dyestuff intermediate, and in producing hydroxybenzophenone ultraviolet light stabilizers. Benzotrifluoride is an important intermediate in the manufacture of herbicides, pharmaceuticals, antimicrobial agents, and the lampreycide, 4-nitro-3-(trifluorometh5l)phenol [88-30-2]. 

The exterior durabiHty of relatively stable coatings can be enhanced by use of additives. Ultraviolet absorbers reduce the absorption of uv by the resins and hence decrease the rate of photodegradation. Eurther improvements can be gained by also adding free-radical trap antioxidants (qv) such as hindered phenols and especially hindered amine light stabilizers (HALS). A discussion of various types of additives is available (113). 

The process of post-chlorinating PVC was carried out during World War II in order to obtain polymers soluble in low-cost solvents and which could therefore be used for fibres and lacquers. The derivate was generally prepared by passing chlorine through a solution of PVC in tetrachloroethane at between 50°C and 100°C. Solvents for the product included methylene dichloride, butyl acetate and acetone. These materials were of limited value because of their poor colour, poor light stability, shock brittleness and comparatively low softening point. 

As a safety glass interleaver, poly(vinyI butyral) (Butacite, Saflex) is extensively used because of its high adhesion to glass, toughness, light stability, clarity and moisture insensitivity. 

Further improvement in light stability may be achieved by addition of small quantities of ultraviolet absorbers. Typical examples include phenyl salicylate, 2,4-dihydroxybenzophenone, resorcinol monobenzoate, methyl salicylate and stilbene. 

This tri-isocyanate is reported to impart good light stability and weather resistanee in polyurethane eoatings and is probably the most widely used aliphatic isocyanate. A number of other aliphatic polyisocyanates have been introduced recently in attempts to produce polyurethanes with improved light stability. Amine derivatives of diphenylmethane are made by reacting aniline of toluidines with formaldehyde. These can lead to a mixture of di-isoeyanates, the diphenylmethane di-isocyanates (MDIs) of commerce. Triphenylmethane-pp p"-tny tri-isocyanate is produced from leucorosaniline. 

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