Chain-reaction polymer acrylics

Chain reactions carried out on one type of monomer give rise to homopolymers when using two types of monomer the situation is more complicated. For example, polymerising mixtures of vinyl chloride with acrylate esters gives rise to a range of molecules, the first of which are relatively rich in acrylate molecules formed later, when the amount of acrylate monomer is relatively depleted, are richer in vinyl chloride. In a number of instances, reactions of this kind can be used to prepare polymers containing monomers which will not homopolymerise, e.g. maleic anhydride and stil-bene (vinylbenzene). 

If this mechanism is strictly followed the chain length and hence the value of 02-uptake (see below) increases linearly with the substrate concentration and (initiation rate)"1/2 (i.e., in radiolytic studies the dose rate) and in charged polymers also on the pH (cf. Ulanski et al. 1996a). In polymers, the chain reaction may mainly proceed intramolecularly (Ulanski et al. 1996a Janik et al. 2000). An example for an efficient intramolecular autoxidation is poly(acrylic acid) [reactions (34)-(36) Ulanski et al. 1996a], In these autoxidation reactions, hydroperoxides are formed which, in some cases, are quite unstable [e.g. reaction (37) see also Leitzke et al. 2001],... 

The chain reaction process can be used as a diagnostic aid to determine whether free radicals are generated from a drug when irradiated. Acrylamide is an acrylic monomer, which is widely used in gel electrophoresis, as a polymer formed in situ by peroxide or UV-initiated polymerization. This monomer is a water soluble solid, more easily handled than most other vinyl monomers, and the progress of its polymerization can be readily followed by measuring its contraction in volume utilizing dilatometry, or its increase in viscosity in a viscometer. Details of this experimental technique can be found in Moore and Burt (18). 

Sodium polyacrylate is produced by the reaction between acrylic acid (H2C=CHC00H) and its sodium salt (H2C=CHC00Na). The product of this reaction is a long-chain copolymer consisting of alternate units of acrylic acid and sodium acrylate. A copolymer is a polymer made of two different monomers, in this case, acrylic acid and sodium acrylate. What makes this polymer different from most other... 

Acrylic adhesives cure by addition polymerization reactions. These chain reactions are initiated by the formation of free radicals that result in the adhesive curing by way of a very rapid polymer chain growth. This cure chemistry is significantly more rapid than a typical cure curve (i.e., condensation type) found in epoxy and urethane adhesives. A comparison of the cure profile of condensation (epoxy and urethane) versus addition... 

Radical chain reactions are particularly suited to the synthesis of polymers, and there is one example of a polymerization that is worth including here since it demonstrates very nicely the effect of electron-withdrawing or -donating substituents on radical reactivity. When a mixture of vinyl acetate and methyl acrylate is treated with a radical initiator, a rather remarkable polymerization takes place. The polymer produced contains alternating vinyl acetate and methyl acrylate monomers along the length of its chain. 

It was shown subsequently that the effect of polymer stereoregularity is related to the double helical structure of PMMA. Thus, while the simple statistical model is effective for interpreting TOF-SIMS spectra of polymers having isolated chains, it is not for a polymer having the structure of isotactic PMMA. The crystal structure of iso-PMMA has acrylate groups rotated toward the center of the double helix in close proximity to each other. Also, LB films of iso-PMMA show the double helical structure. Therefore there are many possibilities for cross-chain reactions in iso-PMMA films deposited on a surface. A combinatorial spreadsheet analysis was done to determine... 

Similar to the biguanide structures, Dizman et al. created l,4-diazabicyclo[2.2.2]octane (DABCO)-based stmctures carrying two quaternary ammonium charges with butyl and hexyl alkyl extensions (C12). The monomer was assembled by multiple nucleophilic substitution reactions. Polymers were formed by free radical polymerization in water. These polymers, much like the biguanide acrylate and pyridinium polymers, combined hydrophobidty and cationic charge on the same monomer. One difference is that the cationic charge was also separated from the backbone of the polymer by a long alkyl chain. As with the pyridine polymers, the hexyl alkyl monomers were found to be the most effective biocides. 

Electrically neutral substituents in macromolecular chains exhibit no peculiarities with respect to low-molecular-weight compounds in terms of constitution, nomenclature, or, in general, modes of reaction. Polymers with substituents having ionizable bonds are called polyelectrolytes. Polyelectrolytes can dissociate to form a polyion and an oppositely charged gegenion. They can be polyacids, such as poly(acrylic acid)... 

Kolb and Meier [43] prepared a malonate derivative of methyl 10-undecenoate, which was polymerised further with 1,6-hexanediol using titanium (IV) isopropoxide as a catalyst. This polymalonate, bearing a C9 aliphatic side chain with terminal double bonds, was then subjected to grafting by ruthenium-catalysed cross-metathesis reactions with acrylates or thiol-ene addition reactions. This functionalisation enabled a subsequent Passerini multi-component reaction [44] using the pendant carboxylic-acid moiety of the modified polymers that resulted from the thiol-ene addition of 3-mercaptopropionic acid into the initial double bonds of the polymer. 

Polyethylene (PE) is a group of polymers resulting from the polymerization of ethylene by chain reaction. Polyethylene can be either a homopolymer or a copolymer, and either linear or branched. Homopolymer PE is based mostly on ethylene monomer. In PE copolymers, on the other hand, ethylene can be copolymerized with short aUtenes or with compounds having polar functional groups, such as vinyl acetate (VA), acrylic acid (AA), ethyl acrylate (EA), methyl acrylate (MA), or vinyl alcohol (VOH) see Fig. 11.2. When... 

In addition polymerization, the polymer molecule grows by the addition of one new monomer at-a-time via a chain reaction. The addition reaction occurs through the opening of double or triple bonds in the monomer. Each new monomer unit creates an active site for the next attachment. The net reaction is shown in Figure 1.1. Many plastics are formed in this manner. Some of the plastics created by addition polymerization include polyethylene, polyvinyl chloride (PVC), acrylics, polystyrene, polytetrafluoroethylene and polyoxymethylene (acetal). 

The most important chain-growth polymers are polyolefins and other vinyl polymers. Examples of the former are polyethylene, and polypropylene, and examples of the latter are poly(vinyl chloride), polystyrene, poly(vinyl alcohol), polyacrylonitrile, and poly(methyl acrylates). The most common stepwise reactions are condensation polymerizations. Polyamides, such as nylon 6-6, which is poly(hexamethylene adipamide), and polyesters, such as poly(ethylene terephthalate), are the most important commercial condensation polymers. These polymers were originally developed for use in fiber manufacture because of their high melting points but are now used also as thermoplastics. Polycarbonate is an engineering plastic that is made from bisphenol A and phosgene by a stepwise reaction. 

Figure 2.3 Reactions that can occur during a polymerisation reaction with acrylates. Y is an acrylate ester side group (or the acid itself). Intramolecular transfer to polymer leads to a branched chain (2a). Intermolecular transfer to polymer results in a shorter chain (species 1) and reinitiates a dead polymer chain and results in a branched chain (2b). The backbone radical can undergo /S-scission that results in two shorter chains (species 3 and 4). The unsaturated species 3 can undergo copolymerisation resulting in species 5 (after van Herk, 2001).

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