Polymeric chelates

The chloromethyl group is another highly reactive group when substituted in an aromatic nucleus. When introduced into the rhodium acetyl-acetonate ring system, the chloromethyl group is so reactive that instead of the tris(chloromethyl) chelate, polymeric products were formed (48) ... 

TMED, (CH3)2NCH2CH2N(CH3)2. B.p. 122 C a hygroscopic base which forms a hydrocarbon-soluble stable chelate with lithium ions and promotes enhanced reactivity of compounds of lithium, e.g. LiAlH4, UC4H9, due to enhanced kinetic basicity of the chelate. Used in polymerization catalysts, tetramethyl lead, TML 5 lead tetramethyl. 

Ion-exchange resins are categorized by the nature of functional groups attached to a polymeric matrix, by the chemistry of the particular polymer in the matrix, and by the porosity of the polymeric matrix. There are four primary types of functionaHty strong acid, weak acid, strong base, and weak base. Another type consists of less common stmctures in specialty resins such as those which have chelating characteristics. 

Addition of one mole of P,P -dipheny1methy1enediphosphinic acid to tetraisopropyl titanate gives a chelated product, the solutions of which can be used as a primer coat for metals to enhance the adhesion of topcoats, eg, alkyds, polyalkyl acylates, and other polymeric surface coating products, and improve the corrosion resistance of the metal to salt water (102). 

A typical recipe for batch emulsion polymerization is shown in Table 13. A reaction time of 7—8 h at 30°C is requited for 95—98% conversion. A latex is produced with an average particle diameter of 100—150 nm. Other modifying ingredients may be present, eg, other colloidal protective agents such as gelatin or carboxymethylcellulose, initiator activators such as redox types, chelates, plasticizers, stabilizers, and chain-transfer agents. 

Calcium Chelates (Salicylates). Several successhil dental cements which use the formation of a calcium chelate system (96) were developed based on the reaction of calcium hydroxide [1305-62-0] and various phenohc esters of sahcyhc acid [69-72-7]. The calcium sahcylate [824-35-1] system offers certain advantages over the more widely used zinc oxide—eugenol system. These products are completely bland, antibacterial (97), facihtate the formation of reparative dentin, and do not retard the free-radical polymerization reaction of acryhc monomer systems. The principal deficiencies of this type of cement are its relatively high solubihty, relatively low strength, and low modulus. Less soluble and higher strength calcium-based cements based on dimer and trimer acid have been reported (82). 

The formulation of calcium chelate materials is based upon the formation of a low-solubiUty chelate between calcium hydroxide and a sahcylate. Dycal utilizes the reaction product of a polyhydric compound and sahcyhc acid. Other sahcyhc acid esters can be similarly used. Vehicles used to carry the calcium hydroxide, extenders, and fillers may include mineral oil, A/-ethyl- -toluenesulfonamide [80-39-7] and polymeric fluids. The filler additions may include titanium dioxide [13463-67-7] zinc oxide, sihca [7631-86-9], calcium sulfate, and barium sulfate [7727-43-7]. Zinc oxide and barium sulfate are useflil as x-ray opacifying agents to ensure a density greater than that of normal tooth stmcture. Resins, rosin, limed rosins, and modified rosins may serve as modifiers of the physical characteristics in both the unset and set states. 

A number of papers have appeared on the removal of heavy metals in the effluents of dyestuff and textile mill plants. The methods used were coagulation (320—324), polymeric adsorption (325), ultrafiltration (326,327), carbon adsorption (328,329), electrochemical (330), and incineration and landfiU (331). Of interest is the removal of these heavy metals, especiaUy copper by chelation using trimercaptotria2ine (332) and reactive dyed jute or sawdust (333). 

Prepa.ra.tion, The preparation of amorphous high (99%) 1,2-polybutadiene was first reported iu 1981 (27). The use of a heterocycHc chelating diamine such as dipiperidine ethane iu the polymerization gave an amorphous elastomeric polymer of 99.9% 1,2 units and a glass-transition temperature of +5°C. In a previous description (53,54) of the use of a chelating diamine such as A/A/N(N -tetramethylethylene diamine, an 80% 1,2-polybutadiene with a glass-transition temperature of —30°C was produced. 

Studies in the photoinitiation of polymerization by transition metal chelates probably stem from the original observations of Bamford and Ferrar [33]. These workers have shown that Mn(III) tris-(acety]acetonate) (Mn(a-cac)3) and Mn (III) tris-(l,l,l-trifluoroacetyl acetonate) (Mn(facac)3) can photosensitize the free radical polymerization of MMA and styrene (in bulk and in solution) when irradiated with light of A = 365 at 25°C and also abstract hydrogen atom from hydrocarbon solvents in the absence of monomer. The initiation of polymerization is not dependant on the nature of the monomer and the rate of photodecomposition of Mn(acac)3 exceeds the rate of initiation and the initiation species is the acac radical. The mechanism shown in Scheme (14) is proposed according to the kinetics and spectral observations ... 

The quantum yield of the initiation process (<, ) is quite low 8 x 10, indicating the great stability of the chelate ring toward photolysis. However, the quantum yield of photodecomposition 4>d) under similar condition is 2 X 10, which is higher than It is clear, therefore, that not every molecule of Mn(acac)3 that is decomposed initiates polymerization apparently, ex-... 

Photoinitiation of polymerization of MMA and styrene by Mn(facac)3 was also investigated, and it was shown that the mechanism of photoinitiation is different [33] from that of Mn(acac)3 and is subject to the marked solvent effect, being less efficient in benzene than in ethyl acetate solutions. The mechanism shown in Schemes (15) and (16) illustrate the photodecomposition scheme of Mn(facac)3 in monomer-ethyl acetate and monomer-benzene solutions, respectively. (C = manganese chelate complex.)... 

Kaeriyama and Shimura [34] have reported the photoinitiation of polymerization of MMA and styrene by 12 metal acetylacetonate complex. These are Mn(acac)3, Mo02(acac)2, Al(acac)3, Cu(bzac)2, Mg(acac)2, Co(a-cac)2, Co(acac)3, Cr(acac)3, Zn(acac)2, Fe(acac)3, Ni(a-cac)2, and (Ti(acac)2) - TiCU. It was found that Mn(a-cac)3 and Co(acac)3 are the most efficient initiators. The intraredox reaction with production of acac radicals is proposed as a general route for the photodecomposition of these chelates. 

Aliwi and coworkers have investigated many vanadium (V) chelate complexes as photoinitiators for vinyl polymerization [36-43]. The mixed ligand complex of chloro-oxo-bis(2,4-pentanedione) vanadium (V). VO(a-cac)2 Cl is used as the photoinitiator of polymerization... 

The polymerization of MMA photoinitiated by al-koxo-oxo-bis(8-quinolyloxo) vanadium (V) complex [VOQ2 OR] has also been studied [38,39]. The alkyloxo radical ( OR) formed from the photodecomposition of the chelate (A = 365) nm at 25°C) was found to be the initiating species ... 

Metal chelates are known to decompose upon heating to generate free radicals, which can abstract hydrogen atoms from the polymeric backbone producing an active site where grafting can take place. 

Finally, there is active interest in developing catalyst systems, both ballistic and polymerization, that would promote combustion stability at high pressures (especially in metal-free systems for smokeless applications) and allow processing lattitude for relatively large motors. The ferric-based systems currently being used fall short of these performance measures. Compounds that form complex structures with the metal chelate to reduce its activity to acceptable levels seem to be most promising. Interestingly, the use of an antibiotic has been cited in this context [19],... 

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