Resin polymeric structure

Suspension Polymerized Particulate Resin Supports -Structural and Morphological Variants... 

Dase-catalyzed phenol-formaldehyde resins polymerized with a mole ratio of formaldehyde to phenol greater than one pose an interesting molecular weight characterization problem. This system is a dynamic one with active methylol end groups. Branched and crosslinked structures are formed, and in general, the separation of the resin from the reaction mixture is difficult. Figure 1 illustrates the chemical nature of a resole resin. 

Obviously, the way to heterogeneous enantioselective catalysis is open when chiral ligands are introduced into the polymers. This idea was first proposed by Okamoto and Still (231). However, the first catalytic results were published by Cazaux and Caze (235). These authors use the asymmetric Mo(VI) complex (9) covalently bound to a cross-linked polystyrene resin for the enantioselective epoxidation of geraniol. Unfortunately, the enantiomeric excess obtained was low—far below that obtained with the Ti-tartrate catalyst (Section II,B). Moreover, the polymeric structure appeared to be unstable. 

A large variety of polymeric structures can be obtained depending on the polymerization reaction and the curing agents involved. This can lead to versatile resins that can cure slowly or very quickly at room or at elevated temperatures. 

Finally, the acetone acetal is removed by acid hydrolysis. Because free sugars are difficult to isolate it is convenient to use an acidic resin known as Dowex . The resin (whose polymeric structure is discussed in Chapter 52) can simply be filtered off at the end of the reaction and the solid product isolated by lyophilization—evapora tion of water at low pressure below freezing point. The yield is quantitative. 

Polymers with a 3-D disordered structure are systems described as resins with a disordered cross-linked polymeric structure (Scheme 7). 

Chelate ion exchangers are based on the selective complex formation between a metal ion and a chelating ligand anchored onto the resin s polymeric structure. 

Elastomeric Modified Adhesives. The major characteristic of the resins discussed above is that after cure, or after polymerization, they are extremely brittle. Tims, the utility of unmodified common resins as structural adhesives would be very limited For highly cross-linked resin systems to be useful structural adhesives, they have to be modified to ensure fracture resistance. Modification can be effected by the addition of an elastomer which is soluble within the cross-linked resin. Modification of a cross-linked resin in this fashion generally decreases the glass-transition temperature but increases the resin flexibility7, and thus increases the fracture resistance of the cured adhesive. Recently, structural adhesives have been modified by elastomers which are soluble within the uncured structural adhesive, but then phase separate during the cure to form a two-phase system The matrix properties are mostly retained the glass-transition temperature is only moderately affected by the presence of the elastomer, yet the fracture resistance is substantially improved... 

The simple concept of thermal regeneration when applied in practice is found to involve resin equilibria which are complex. Some of the variables which influence the properties are the detailed polymeric structure of the resins, the acidity and the basicity of the functional groups, the ratio of acidic to basic groups, the resin affinities for counter-ions, the pH. the ionic strength, and temperature... 

The hydroxymethylation of phenols with formaldehyde is called the Lederer-Manasse reaction. This reaction must be carefully controlled, since it is possible for the para and both ortho positions to be substituted and for each of these to be rearylated, so that a polymeric structure 45 is produced. However, such polymers, which are of the Bakelite type (phenol-formaldehyde resins, 45), are of considerable commercial importance. 

Polymeric Systems. - Since polymer systems are extensively discussed elsewhere in this volume only selected examples will be quoted which indicate how polymeric structures can influence photophysical phenomena. For example, fluorescence polarization has been used to monitor polymer cure in resin mixtures when a... 

Combined TGA-DTA measurements of the catalysts revealed that the polymeric structure of these materials is stable up to 300 °C this was confirmed by monitoring the morphology of the materials by electron scanning microscopy. To establish that these resins were not leaching the active Ru or Rh catalyst, they were subjected to... 

Gamma irradiation curing of epoxy resins for structural adhesives — Radiation cure polymerization of commercial diglycidyl ether of bisphenol F epoxy resin has been achieved using Co-60 irradiation source, compounding the monomer with and onium salt catalyst [9],... 

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