Monomers and Oligomers

The monomers which are most widely used for photopolymerization processes are acrylates. The reason is that they polymerize fast and, by introducing chemical modifications in the ester group, materials with very different properties may be obtained without sacrifying too much of the polymerization rate. Methacrylates generally polymerize more slowly but, due to the stiffer main chain, yield harder products. 

Other systems include styrene/unsaturated polyesters and thiol-ene compositions These will not be discussed here. 

With monoacrylates (functionality f = 2), linear chains are obtained, and upon the addition of di- and/or triacrylates (f = 4 or 6, respectiiiely) crosslinked networks are formed. In order to avoid the presence of free monomer in the cured product, monoacrylates are sometimes omitted. 

The acrylic esters of the lower mono-, di- or trialcohols or the lower ethylene or propylene glycols are liquids of low viscosity and, especially with the lower alcohols, of repellent odor. They are often used in coating formulations as reactive diluents for the much more viscous oligomers. References to their toxicological properties can be found in Refs and 

Oligomers serve to reduce the volatility, toxicity, odor, polymerization shrinkage and to improve the properties of the cured material. 

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Figure C2.3.11 Key surfactant stmctures (not to scale) in emulsion polymerization micelles containing monomer and oligomer, growing polymer particle stabilized by surfactant and an emulsion droplet of monomer (reservoir) also coated with surfactant. Adapted from figure 4-1 in [67],...

Resins. As mentioned above, both furfural and furfuryl alcohol are widely used in resin apphcations. Another resin former, 2,5-furandimethanol [1883-75-6] (BHME), is prepared from furfuryl alcohol by reaction with formaldehyde. It is usually not isolated because oligomerization occurs simultaneously with formation (competing reaction). Both the monomer and oligomers are very reactive owing to difuntionahty, and are used primarily as binders for foundry sand (72) and fiberglass insulation (147,148). 

Liquid-Injection Molding. In Hquid-injection mol ding (LIM), monomers and oligomers are injected into a mold cavity where a rapid polymerization takes place to produce a thermoset article. Advantages of these processes are low cost, low pressure requirement, and flexibiHty in mold configuration. Conventional systems, such as isocyanate with polyol, release Htfle or no volatiles. The generation of substantial volatiles in the mold is obviously undesirable and has represented a significant obstacle to the development of a phenoHc-based LIM system. A phenoHc LIM system based on an... 

Vinyl ethers can also be formulated with acryHc and unsaturated polyesters containing maleate or fumarate functionaHty. Because of their abiHty to form alternating copolymers by a free-radical polymeri2ation mechanism, such formulations can be cured using free-radical photoinitiators. With acryHc monomers and oligomers, a hybrid approach has been taken using both simultaneous cationic and free-radical initiation. A summary of these approaches can be found in Table 9. 

R. H. Marchessault, S. Coulombe, T. Hanai, and H. Monkawa, Monomers and Oligomers from Wood, Transactions of Technical Section of the TR52, 1980 pubhshed ia Pulp and Paper Canada 81(6), 1980. 

Peculiar characteristics of chitins and chitosans are hemostatic action, anti-inflammatory effect, biodegradability, biocompatibihty, besides antimicrobial activity, retention of growth factors, release of glucosamine and M-acetylglucosamine monomers and oligomers, and stimulation of cellular activities [11,12,295-297]. 

This is clo.sely related to the Tertiary radical synthesis" scheme for the preparation of organocobalt porphyrins, in which alkenes insert into the Co—H bond of Co(Por)H instead of creating a new radical as in Eq. (13). If the alkene would form a tertiary cobalt alkyl then polymerization rather than cobalt-alkyl formation is observed. " " " The kinetics for this process have been investigated in detail, in part by competition studies involving two different alkenes. This mimics the chain transfer catalysis process, where two alkenes (monomer and oligomers or... 

Polymer Devolatilization, Eractionation, and Plasticization Supercritical fluids may be used to extract solvent, monomers, and oligomers from polymers, including biomaterials. After extraction the pressure is reduced to atmospheric, leaving little residue in the... 

Many analytical techniques are in use for the qualitative and quantitative evaluation of monomers and oligomers extracted from PA6 (GC, differential refrac-tometry, IR, PC, SEC, HPLC, RPLC, etc.). FTIR has been used for quantitative analysis of caprolactam oligomer content (extract %) in polyamide-6 [113], The method, which involves a 3h extraction in boiling methanol, is suitable for process control and plant environment. Kolnaar [114] has used FTIR characterisation of fractional extracts with pentane, hexane, and heptane of HDPE for blow moulding applications. Vinyl acetate in packaging film has similarly been determined by quantitative FUR. 

There are various theories on the structure of these species and their size. Some authors have assumed the presence of monomers and oligomers up to pentamers, with the open structure of ice I, while others deny the presence of monomers. Other authors assume the presence of the structure of ice I with loosely arranged six-membered rings and of structures similar to that of ice III with tightly packed rings. Most often, it is assumed that the structure... 

Schweikart KH, Malinovskii VL, Yasseri AA, Li J, Lysenko AB, Bocian DF, Lindsey JS (2003) Synthesis and characterization of bis(S-acetylthio)-derivatized europium tripledecker monomers and oligomers. Inorg Chem 42 7431-7446... 

Synthesis. Functionalized monomers (and oligomers) of sebacic acid (SA-Me2) and 1,6 -bis(/ -carboxyphenoxy)hexane (CPH-Me2) were synthesized and subsequently photopolymerized as illustrated in Figure 1. First, the dicarboxylic acid was converted to an anhydride by heating at reflux in methacrylic anhydride for several hours. The dimethacrylated anhydride monomer was subsequently isolated and purified by dissolving in methylene chloride and precipitation with hexane. Infrared spectroscopy (IR), nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis results indicated that both acid groups were converted to the anhydride, and the double bond of the methacrylate group was clearly evident. 

Monomer/Oligomer Synthesis. The first two steps in the four step reaction sequence of Figure 1 are capable of producing both monomer and oligomer. The first step, aromatic nucleophilic substitution, is a polymer forming reaction under the correct stoichiometric conditions. In order to favor the formation of monomer with a small amount of oligomer, the substitution was carried out at a 4 1 ratio of diol to dichlorodiphenyl sulfone. This led to a predominantly monomeric product (IV) with only the requirement that the excess diol be removed from the product to eliminate the potential presence of low molecular weight species in later reactions. 

In this paper methods are described for preparing the 1,3,5-triethynylbenzene monomer and oligomers. Evidence is then presented to support the theory that these diacetylene oligomers tend to thermally cure by an aromatization reaction. 

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