Add-catalyzed polymerization

Yold has determined by IR spectroscopy that the degree of silicon oxide network connectivity increases with increasing H O/TEOS mole ratio for add-catalyzed polymerizations in bulk solutions (21). These results, if applicable to the membrane in situ add-catalyzed polymerizations described herein, serve to reinforce our conclusion that a more highly-coordinated silicon oxide structure exists within microcomposites produced with short immersion times according to procedure A, or according to the slow stepwise TEOS addition in procedure B. In either case, more initial hydrolysis water molecules per alkoxide molecule are available to promote this situation. General Conclusions... 

The problem of irreversible termination in Lewis add catalyzed polymerizations is still controversiaL Many authors have address themselves to this problem however, solutions have b%n propo for only a few spedalized systems. The action of impurities is usually invoked to explain the fact that many cationic polymerizations stop far before all the monomer has been consun d. 

Nijenhuis, A.J., Grijpma, D.W., Pennings, A.J., 1992. Lewis add catalyzed polymerization of l-Lactide. Kinetics and mechanism of the hulk polymerization. Macromolecules 25, 6419-6424. 

Fig. 60. Synthesis of poly(thiophene methine)s add-catalyzed polymerization of thiophene and an aldehyde.

Indole undergoes add-catalyzed dimerization the 3H-indoIium ion acts as an electrophile and attacks an unprotonated molecule to give the dimer (46). Protonation of the dimer in turn gives an electrophilic species from which a trimeric product can be derived (77CPB3122). Af-Methylisoindole undergoes acid-catalyzed polymerization, indicating that protonation at C-1 gives a reactive electrophilic intermediate. 

Enzyme-catalyzed polymerization reactions have an important characteristic that is not found elsewhere. Once the enzyme has added a monomeric unit to the growing chain, it can either dissociate and recombine at random with other growing termini, or it can remain attached to the same chain and add further residues. Enzymes that dissociate between each addition and distribute themselves among all the termini are termed distributive. Those that process along the same chain without dissociating are termed processive. These terms apply also to degradative enzymes such as exonucleases. 

The aliphatic poly(ether lactonejs are a group of synthetic polymers with high elasticity and high tissue absorptivity [293]. The ether function in the polymer backbone adds flexibility to the ester chain. Ring-opening polymerization of l,4-dioxan-2-one yields an elastic polymer, polydioxanone, with a tensile strength similar to that of human tissue [294]. Polydioxanone has been successfully used to prepare monofilament sutures, with a flexibility superior to that of PGA sutures [294]. Recently, the lipase-catalyzed polymerization of polydioxanone was demonstrated [295]. 

Iodine. Iodine successfully initiates or catalyzes polymerization of A-vinyl carbazole, vinyl ethers, and styrenes. It adds to double bonds to form 1,2-diiodosubstituted ethanes which are subsequently ionized in the presence of excess iodine [69,149-151]. Stopped-flow UV studies dem-... 

Compressed liquid or supercritical carbon dioxide has been recognized as a useful alternative reaction medium for radical and ionic polymerization reactions (see Chapter 4.5). Many of the benefits associated with the use of SCCO2 in these processes apply equally well to polymerizations relying on a metal complex as the chain-carrying species. However, the solubility of the metal catalyst and hence the controlled initiation of chain growth add to the complexity of the systems under study. Furthermore, many of the environmental benefits would be diminished if subsequent conventional purification steps were needed to remove the metal from the polymer. Nevertheless, the interest in metal-catalyzed polymerizations is increasing, and some promising systems have been described. 

How the aliphatic monomers are incorporated into the suberin polymer is not known. Presumably, activated m-hydroxy adds and dicarboxyfic adds are ester-ified to the hydroxyl groups as found in cutin biosynthesis. The long chain fatty alcohols might be incorporated into suberin via esterification with phenylpro-panoic acids such as ferulic acid, followed by peroxidase-catalyzed polymerization of the phenolic derivative. This suggestion is based on the finding that ferulic acid esters of very long chain fatty alcohols are frequently found in sub-erin-associated waxes. The recently cloned hydroxycinnamoyl-CoA tyramine N-(hydroxycinnamoyl) transferase [77] may produce a tyramide derivative of the phenolic compound that may then be incorporated into the polymer by a peroxidase. The glycerol triester composed of a fatty acid, caffeic add and co-hydroxy acid found in the suberin associated wax [40] may also be incorporated into the polymer by a peroxidase. 

Since only Ta and Nb catalysts, which are not tolerant to polar groups, are available for the polymerization of sterically crowded disubstituted acetylenes, it is generally difficult to directly synthesize disubstituted acetylene polymers that have a highly polar substituent such as a hydroxy group. Recently, the synthesis of poly[l-phenyl-2-(p-hydroxyphenyl)acetylene] has been achieved by the polymerization of l-phenyl-2-(p-r-butyldimethylsiloxyphenyl)acetylene (11) and the subsequent add-catalyzed deprotection reaction. ... 

The reaction of MA with free radicals can find a place at a number of places in this book. Since during the radical-catalyzed polymerization such a process occurs, the major segment of these types of reactions are naturally covered in the polymerization section. However, above and beyond the polymer aspects of the reactions, some reactions are known which add radicals to The double bond of MA to give monomeric products. Since some of these radical generating processes have been photoinitiated, it is suitable to discuss them as a part of this section. 

Lipase-catalyzed polymerization between an achiral dk rboxylic add and a primary glycol in an aqueousorgank mixture was reported [32J. A polycondensation of achiral 10-hydroxydecanoic acid catalyzed by lipase in benzene has also been claimed, however no convincing evidence was presented [33]. 

It has been proven that the polyreaction occtrrs mainly at amine end groups and the reaction can be catalyzed by the carboxyl groups. In reaction [9], a tetrahedral intermediate, similar to that occurring in the add-catalyzed hydrolysis, is involved (see Seaion 4.14.5.1.1, Scheme 7). Intermediate amidine groups may also be generated. As a matter of fact, amidines are reported to be present in the polymerization of CL and tl-caprylolactam initiated by the corresponding amino adds. ... 

Polymerization initiated by phosphoric or metaphosphoric add, or their alkylammonium salts, in the absence of water, proceeds probably through a hydrolytic mechanism. Indeed, phosphoric acid at the polymerization temperatures rmdetgoes dehydration and the lactam amide group is then hydrolyzed. The resultant diphosphoric add catalyzes both hydrolysis and propagation. 

The second type of chemically amplified depolymerization resist mechanism depends upon the incorportation of C-O bonds into the polymer backbone which can be cleaved by either hydrolysis or addolysis. This concept was first advanced by Crivello, who proposed that polymers such as polycarbonates and polyesters could undergo photo-induced add catalyzed hydrolysis reaction in polymeric film (9, 76). Although polymers could be designed to undergo catalytic chain cleavage in the presence of add, such an approach depends upon the inclusion of stoichiometic amounts of water in the polymer film. Uttle further work was reported on this concept until recently, when a new system for dissolution inhibition was described based upon the hydrolysis of polysilyl ethers in a novolac resin (24). 

Radical, cationic, anionic, and metal catalyzed polymerizations of butadiene are known—and there are three possible products of the polymerization (Figure 21.12). Initial addition of a radical to butadiene gives exclusively the allyl radical, which has two resonance forms. The more stable resonance form adds further butadiene to give 1,2-polybutadiene. The less inherently stable, but also less sterically hindered, form adds further butadiene to give cis- or tra s-l,4-polybutadiene. 

A monomer is a reactive molecule that has at least one functional group (e.g. -OH, -COOH, -NH2, -C=C-). Monomers may add to themselves as in the case of ethylene or may react with other monomers having different functionalities. A monomer initiated or catalyzed with a specific catalyst polymerizes and forms a macromolecule—a polymer. For example, ethylene polymerized in presence of a coordination catalyst produces a linear homopolymer (linear polyethylene) ... 

Although sulfonyl chlorides add readily to unactivated olefins, with vinylic monomers telomeric and/or polymeric products were observed. This difficulty has been overcome by carrying out the addition in the presence of catalytic amounts of CuCl2, so as to provide a general and convenient synthesis of /5-chlorosulfones (Asscher-Vofsi reaction)63. For the copper-catalyzed system a redox-transfer mechanism has been suggested in which the... 

When catalyzed by acids, low molecular weight aldehydes add to each other to give cyclic acetals, the most common product being the trimer. The cyclic trimer of formaldehyde is called trioxane, and that of acetaldehyde is known as paraldehyde. Under certain conditions, it is possible to get tetramers or dimers. Aldehydes can also polymerize to linear polymers, but here a small amount of water is required to form hemiacetal groups at the ends of the chains. The linear polymer formed from formaldehyde is called paraformaldehyde. Since trimers and polymers of aldehydes are acetals, they are stable to bases but can be hydrolyzed by acids. Because formaldehyde and acetaldehyde have low boiling points, it is often convenient to use them in the form of their trimers or polymers. 

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