Self Polymerization

Aromatic and aliphatic isocyanates can undergo self polymerization to form stable resinous trimer structures. The reaction is catalyzed by many materials including calcium acetate, potassium acetate, sodium formate, sodium carbonate, sodium methoxide, triethylamine, oxalic acid, sodium benzoate in dimethylformamide, and a large number of soluble metal 

Some isocyanates also react with themselves to form thermally reversible dimer structures, the so-called uretidinediones. Such self reaction is apparently confined to aromatic isocyanates, and is illustrated with phenyl isocyanate in Fig. 8.4. The dimerization reaction is catalyzed vigorously by trialkyl phosphines and less by tertiary amines such as pyridine. 

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With some reaetions whieh have a signifieant rate at ambient temperature, e.g. eatalysed reaetions, oxidations or self-polymerization of eertain polymers, severe hazards may be assoeiated with an elevation in temperature. 

Butadiene CH2=CHCH= H2 Cu Acetylide, Vinyl Acetylene Ethylene Air (Peroxides) > 300 114 Inhibitor — t-Butyl Catechol — 115ppm Activation 12.0 429 Self-polymerization above RT or press... 

Methyl Acrylate CH2=CHCOOCH3 Non-inhibitors such as Biphenyl, Bibenzyl, Tri-phenyl, etc Methyl Acrylate Vap plus air > Ambient > 120 Inhibitor—H ydro quino ne or Methyl Ether of Hydro-quinone 10-20ppm. Store Store below 10° no inert atmosphere. No sparks 18.58-18.8 463 Self polymerizing above ambient press temp accelerates polymerization... 

Methyl Methacrylate CH2=C(CH3)COOCH3 Impure Methyl-Methacrylate Vap in Air 2.1 to 12.5% > Ambient > 110 Inhibitor-Hydroquinone or Methyl Ether of Hydro-quinone. Shield from light avoid sparks. Store in cool place 13.3-13.8 421 Self-polymerizing initiated by visible light at 20 to 40°... 

Styrene C6H5CH=CH2. Alkali Peroxy compds Vap in Air 1.1 to 6.1% > Ambient > Ambient Inhibitor—Methyl Ether of Hydroquinone—10-15 ppm, Phenol Subst-Hydroxyl Amine, etc. Store below 70°F. Avoid sparks in. vap/air mixt 17.4-17.8 490 Soln polymerization catalyzed with w or Ti tetrachloride. Also self polymerization... 

Vinyl Chloride CH2=C HC1 Acrylates, Styrene, W, or oxidizing agents. Forms the Poly-peroxide which decomps exo-thermally at RT Air Vap Monomer. In Air 4.0 to 22.0% or 3.6 to 33.0% > Ambient > Ambient Inhibitor—Phenol (25-100 ppm). Store under press in a cool place. No sparks 22.9 472 Self-polymerizes, catalyzed by oxygen... 

Vinylidene Chloride CH2=CC12. Monomer forms unstable peroxides by autooxidation therefore, no oxidg agents or w Air Vap Monomer In Air 7.0 to 16.0% > Ambient > Ambient Inhibitor—Methyl Ether of Hy droquino ne (100 ppm) Transport store under. inert gas in a cool, dry place. No sparks -18.0 570 Self-polymerizing, easily copolymerizes with with Acrylates Styrene. Polymerization catalyzed by light or w... 

The sequential growth and branching involved in the preparation of dendrimers had been considered by Flory many years before they were actually prepared. Flory developed a sound understanding of the kind of processes that would occur in the self-polymerization of a molecule of the type ABj most of which have been shown to be correct by the relatively recent experimental studies. In particular, the existence of a limit to growth was predicted. This limit has become known as the starburst limit, and is the reason for the highly monodisperse nature of fully developed dendrimers. 

Allylchlorosilanes reacted with naphthalene to give isomeric mixtures of poly-alkylated products. However, it was difficult to distill and purify the products for characterization from the reaction mixture due to the high boiling points of the products and the presence of many isomeric compounds. The alkylation of anthracene with allylchlorosilanes failed due to deactivation by complex formation w ith anthracene and the self-polymerization of anthracene to solid char. 

Kramer, I. R. H. McLean, J. W. (1952). Alterations in the staining reactions of dentine resulting from a constituent of a new self-polymerizing resin. 

Several pathological self-polymerizing systems have been biophysi-cally characterized sufficiently to permit identification of protein or peptide species that could serve as molecular targets in a structure-activity relationship. These include transthyretin (TTR) [73-76], serum amyloid A protein (SAA) [77], microtubule-associated protein tau [78-80], amylin or islet amyloid polypeptide (IAPP) [81,82], IgG light chain amyloidosis (AL) [83-85], polyglutamine diseases [9,86], a-synuclein [47,48] and the Alzheimer s (3 peptide [87-96]. A variety of A(3 peptide assay systems have been established at Parke-Davis to search for inhibitors of fibril formation that could be therapeutically useful [97]. 

Pool the fractions containing protein. Adjust the enzyme concentration to lOmg/ml for the conjugation step (see next section). The periodate-activated enzyme may be stored frozen or freeze-dried for extended periods without loss of activity. Do not store the preparation in solution at room temperature or 4°C, since precipitation will occur over time due to self-polymerization. 

CHEMICAL Ability to self-polymerize Uncontrolled polymerization... 

Polymerization, the reaction of monomer to produce polymer, may be self-polymerization (e.g., ethylene monomer to produce polyethylene), or copolymerization (e.g.,... 

McKelvey etal. (1959) investigated the reaction of epoxides with cellulose in alkaline conditions, reporting that alkaline cellulose reacted readily once the concentration of sodium hydroxide was sufficiently high. However, no evidence was found of reaction between cotton yarn and cellulose with a range of epoxides under a variety of reaction conditions. It was concluded that the apparent reactivity of cellulose with epoxides was primarily due to alkaline swelling of the cellulose, self-polymerization of the epoxide monomers then occurring within the interior structure of the fibres. It was also noted that the reactivity with phenol OH groups was very low (e.g. only 1 % conversion of ethylene oxide with various phenols). 

A number of flammable liquids and gases used in processing facilities are stored in refrigerated vessels. Common among these are liquefied gases, such as liquefied natural gas (LNG) and anhydrous ammonia, and a number of reactive or self-polymerizing liquids, such as acrylic acid and organic peroxides. 

Kim et al. [67], used the self-polymerized heterometallic polymeric salen complexes 26-32 as efficient catalysts for kinetic resolution of terminal epoxides with phenols to give a-aryloxy alcohols in high yields (38-43%) and ee (92-99%) (Scheme 17). These catalysts were recycled up to three times without any loss in their performance. 

Polymers XL-XLIII are commercially available. XL and XLI are referred to as poly-etheretherketone (PEEK) and polyetherketone (PEK), respectively. XLII and XLIII are known as bisphenol A polysulfone and poly ethersulf one, respectively. Polymers XLI and XLIII can be synthesized not only using the combination of A—A and B—B reactants, but also by the self-polymerization of appropriate A—B reactants. 

High surface area hexagonal mesoporous Ge also can be prepared with oxidative self-polymerization chemistry of [Ge9] clusters [48]. This synthetic route does not require external oxidants such as ferrocenium or linking Ge(lV) centers and occurs in the presence of cationic surfactant (iV-eicosane-A ,A -dimethyl-A -(2-hydroxyethyl)ammonium bromide, EDMHEABr) as stmcture-directing agent. The polymerization reaction proceeds through the slow oxidative coupling of (Ge9)-clusters and seems to be accompanied by a two-electron process (2). The electron acceptors in this case appear to be the surfactant molecules or the solvent. 

The ability of using mixed [Geg.nSin]" clusters as starting building blocks, which are soluble in ethylenediamine, allowed us to prepare mesoporous Ge/Si alloy semiconductors. These structures were synthesized as described above by the oxidative self-polymerization of mixed [Geg.nSin]" clusters with the assistance of self-assembled cationic surfactants (3). 

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