Stannous octoate catalyst effect

Data Showing Stannous Octoate Catalyst Effect Polymers 9 11... 

A common way of controlling the opening of cells is the use of a gelation catalyst. Stannous octoate (SO) is one such catalyst. Figure 3.14 shows the effects of SO on air flow. This illustration is particularly appropriate since our purpose is to build a device through which fluids will pass. 

Synthetic routes include anionic, cationic, zwitterionic, and coordination polymerization. A wide range of organometallic compounds has been proven as effective initiators/catalysts for ROP of lactones Lewis acids (e.g., A1C13, BF3, and ZnCl2) [150], alkali metal compounds [160], organozinc compounds [161], tin compounds of which stannous octoate [also referred to as stannous-2-ethylhexanoate or tin(II) octoate] is the most well known [162-164], organo-acid rare earth compounds such as lanthanide complexes [165-168], and aluminum alkoxides [169]. Stannous-2-ethylhexanoate is one of the most extensively used initiators for the coordination polymerization of biomaterials, thanks to the ease of polymerization and because it has been approved by the FDA [170]. 

By setting the temperature of the reaction medium at 60 C from the beginning of the IPN formation, the PUR synthesis is accelerated, and that of the methacrylic system begins after the usual inhibition period. The competition between the two processes can still favour the complete formation of PUR before appreciable radical copolymerisation may have taken place, though the kinetic curves may change or even cross. For this reason, a second factor, the content of PUR catalyst, is varied too with less stannous octoate, the formation of the first network is more or less delayed, even at 60 C, and counterbalances to some extent the effect of temperature. In such a case, the conversion of the methacrylic phase may proceed further before higher or even post-gel conversions are reached for polyurethane. Thus, IPNs in which both networks have been formed more or less simultaneously, are obtained by this... 

Organotin compounds are effective catalysts for the isocyanate-hydroxyl reaction. Tin catalysts have a slight odour, and low amounts are required to achieve a high reaction rate. Examples of organotin catalysts are stannous octoate, stannous oleate, dibutyltin dilaurate and dibutyltin di-2-ethylhexoate. They are often used in conjunction with small concentrations of antioxidants such as tertiary-butyl catechol resorcinol and tartaric acid. 

A similar reaction of tetraphenyl pyrophosphate with propylene oxide leads to an 80% yield of the corresponding insertion product, as an oily liquid. The reaction time was six hours at 70 °C. purity, 96.7% by HPLC. Magnesium chloride and stannous octoate were also shown to be effective catalysts for this insertion reaction. 

Poly(lactic acid)s can be synthesized by two methods (i) polyeondensation of lactic acids and (ii) ROP of LAs [1, 3, 8, 54, 55], Figure 8.3 shows the synthesis of PLLA, PDLA, and their block copolymers [11], Tin-based catalysts such as tin (II or IV) chloride and tin (II) bis-2-ethyUiexanoic acid (stannous octoate or tin octoate) were reported to effectively increase the molecular weight of the resulting PLAs up to an order of 10 and 10 g mol for polyeondensation [56,57] and ROP [58-61], respectively. Moreover, bulk polymerization in the presence of these catalysts aids in avoiding racemization and transesterification during the ROP of LA. 

Organometalhc compounds based on lead, tin, bismuth and zinc are also used to catalyse a urethane reaction. Bismuth and zinc carboxylates are used because of the toxicity and disposal problems of lead and tin. Nowadays, alkyl tin carboxylates, oxides and mercaptide oxides such as dibutyltin dUaurate (DBTDL),dioctyltin mercaptide, stannous octoate and dibutyltin oxide are used successfully in all types of polyurethane applications (Table 6.4), among which DBTDL was found to be the most widely used catalyst. The catalytic effect of organometaUic compounds is due to their capacity to form a complex with the isocyanates and polyols. The catalysis mechanism involves interaction of the metal cation with isocyanate and hydroxyl groups, followed by rearrangement of the resulting complex to yield the final urethane product. 

Very often mixtures of the two types are used, because the tertiary amine-based catalysts tend to catalyze the blowing reaction preferentially, and the metal salts—like dibutyltin dilaurate or stannous octoate—promote the gelling reaction more. Moreover it has been found that these two types of catalysts have a synergistic effect when used together. 

This homopol)TTierization is carried out in the presence of a catalytically effective amount of a suitable metal-containing catalyst such as stannous octoate (stannous-2-ethylhexoate — Sn(CgHi502)2) or stannous oxalate. Typically the catalyst levels are reported as monomerxatalyst molar ratios. Level vary widely depending on the catalyst but stannous octoate is preferably used from 15,000 1 to 40,000 1. The polymerization is carried out in the presence of an initiator such as an alkanol, a... 

Tabka and Widmaier (16,17) imdertook the study of the interactions of azo-bis(isobutyronitrile) (AIBN), firee-radical initiators with stannous and stannic organotin polyurethane catalysts. These workers found a synergistic effect of stannous octoate on the AIBN on the radical polymerization (qv) of methyl methacrylate, increasing the reaction rate and shortening the gelation time. While there was a severe deactivation of the tin(II) atom by the AIBN, there was no measurable effect using organotin(IV) stannic catalysts. 

As mentioned in Section 8.4.3.1., the majority of hydroxy groups in a polyether triol are secondary groups and are comparatively unreactive towards isocyanates. It is therefore necessary to select a catalyst which favours the formation of urethane links relatively more than the formation of gas by the reaction of isocyanate and water. Tin compounds (e.g., stannous octoate and dibutyltin dilaurate) are particularly effective in this respect (cf.. Table 14.3) and are very widely used. In addition to the primary isocyanate-polyol and isocyanate-water reactions, several secondary reactions occur during the preparation of foam. As shown in Section 14.4, the final product may contain allophanate, biuret, isocyanurate and uretidione links. It will be appreciated that in a polymeric system, which is based on a diisocyanate, all of these links (except uretidione) represent points of branching or cross-linking. These secondary reactions are particularly favoured by tertiary amines (e.g., triethylenediamine and 4-dimethylaminopyridine) and these catalysts therefore contribute to the final cross-linking of the foam and hence to the achievement of, for example, a low compression set. Mixtures of tin compounds and tertiary amines are more... 

The gums may be converted to rubber-like products by reaction with an alkoxysilane such as a tetraalkoxysilane, trialkoxysilane or polyalkoxysilox-ane. By a suitable choice of catalyst, cure may be effected at room temperature in times ranging from 10 minutes to 24 hours stannous octoate and dibutyltin dilaurate are particularly satisfactory. The reactions which take place with tetraethoxysilane illustrate the cross-linking process ... 

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