Stabilization with organotins

Figure 3.3.4 Reaction of an organotin stabilizer with t-buty hydroperoxide. (Reproduced from reference 6, copyright 2003, John Wiley Sons, Ltd.)...

Organotin stabilizers with a complex mercapto group structure were recommended in the patent [219], where the X-group in the compound R2SnX2 possesses the composition ... 

In Reaction (16), a lead stabilizer is shown at the degradation site interfering with HCl-catalyzed eUminafron (Reaction 15). It could as readily be a mixed metal complex or a complex of organotin stabilizer with calcium stearate. 

Alkyltin Intermedia.tes, For the most part, organotin stabilizers are produced commercially from the respective alkyl tin chloride intermediates. There are several processes used to manufacture these intermediates. The desired ratio of monoalkyl tin trichloride to dialkyltin dichloride is generally achieved by a redistribution reaction involving a second-step reaction with stannic chloride (tin(IV) chloride). By far, the most easily synthesized alkyltin chloride intermediates are the methyltin chlorides because methyl chloride reacts directiy with tin metal in the presence of a catalyst to form dimethyl tin dichloride cleanly in high yields (21). Coaddition of stannic chloride to the reactor leads directiy to almost any desired mixture of mono- and dimethyl tin chloride intermediates ... 

Section 3 shows that many optically active organotin compounds with an asymmetric tin atom as only chiral center can be made. This fact is already strong evidence for the optical stability of those compounds. Furthermore, their optical rotation does... 

Organotin compounds with Sn atoms bearing a double bond appear in Table 6. These compounds are usually unstable at room temperature or when exposed to air. Attachment of sterically crowded groups to the tin atom greatly contributes to the stabilization of these compounds. 

Concentration levels of heat stabilizers in various PVC products are in the range 1.5-3.0% for metal soaps and 0.3-2.5 % for organotin stabilizers (Pospfsil, 1990c). Aliphatic (22) or mixed aliphatic/aromatic phosphites (23, 24) are used together with polyols (e.g., pentaerythritol or sorbitol) and acid scavengers as co-stabilizers in PVC (Pospfsil, 1990c). 

Rigid PVC is polymerized at 55-70°C and then compounded with organotin stabilizer, acrylic processing aid, lubricants, and optionally with rubbery impact modifier. 

This section deals with the stabilization of PVC by organotin stabilizers having different alkyl groups (methyl, ethyl, n-butyl, n-octyl, etc.) and different ligands (carboxylates, mercaptides, etc.), the mechanism of reaction and the evaluation of stability by yellowness index and conductivity. 

Scheme 3.3.3 Proposed mechanism of exchange of chloride atoms in PVC by mercaptide groups of organ-otin stabilizers coordination ofallylic chlorine by organotin mercaptide with subsequent rearrangement to a non-allylic structure...

While control and 2.5% organotin stabilizer containing films are transparent, films with 5% organotin stabilizer are opaque white, indicating limited solubility of organotin stabilizer in PVC. ... 

Brecker, L.R. Mechanism of organotin stabilization of poly(vinyl chloride). 1. The structure and equilibria of alkyltin alkyl mercaptopropionates and their compatibility with PVC. In Plastics Plastics on My Mind, Proceedings Antec 1998 Brookfield, Society of Plastic Engineering Vol. 3, 33291. 

Organotin Compounds—These offer good overall stabilization with excellent clarity and complete freedom from sulfide staining. They are more expensive than the common barium-cadmium types as a result of the higher tin metal prices. The commercially important tin stabilizers include various dibutyltin and dimethyltin salts of maleate half esters, alkyl mercaptans, and thioacids, as well as certain monoalkyltin derivatives. Certain... 

Carbon radicals generated by the polymerization of methyl methacrylate do not undergo displacement reactions with the Sn-S, Sn-O, Sn-C, or Sn-Cl bonds of typical organotin stabilizers (73). However, PVC stabilization caused by scavenging of chlorine atoms by organotins has not been ruled out experimentally (73). Furthermore, the ability of... 

Treatment with organotin stabilizers improves the color of thermally degraded PVC (100,105). This effect was attributed to the destruction of complexes formed from polyenes and HC1 (100,105) and, in the case of the organotin mercaptides, to the addition of free mer-... 

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