Condensation polymer crosslinking

The second step is the condensation reaction between the methylolphe-nols with the elimination of water and the formation of the polymer. Crosslinking occurs hy a reaction between the methylol groups and results in the formation of ether bridges. It occurs also by the reaction of the methylol groups and the aromatic ring, which forms methylene bridges. The formed polymer is a three-dimensional network thermoset ... 

Covalent polymeric networks which are completely disordered. Continuity of structure is provided by an irregular three-dimensional network of covalent links, some of which are crosslinks. The network is uninterrupted and has an infinite molecular weight. Examples are vulcanized rubbers, condensation polymers, vinyl-divinyl copolymers, alkyd and phenolic resins. 

The topological structure of condensation polymers is predetermined by the functionality of the initial monomers. If all of them are bifunctional then linear polymers are known to form. Branched and crosslinked molecules are prepared only when at least one of the monomers involves three or more functional groups. 

Condensation polymerizations (polycondensations) are stepwise reactions between bifunctional or polyfunctional components, with elimination of small molecules such as water, alcohol, or hydrogen and the formation of macromo-lecular substances. For the preparation of linear condensation polymers from bifunctional compounds (the same considerations apply to polyfunctional compounds which then lead to branched, hyperbranched, or crosslinked condensation polymers) there are basically two possibilities. One either starts from a monomer which has two unlike groups suitable for polycondensation (AB type), or one starts from two different monomers, each possessing a pair of identical reactive groups that can react with each other (AABB type). An example of the AB type is the polycondensation of hydroxycarboxylic acids ... 

The high-molecular-weight products formed by the condensation of phenols with carbonyl compounds (especially with formaldehyde) are known as phenolic resins. They are mixtures of structurally nonuniform compounds that are initially soluble and fusible but which can become crosslinked (cured) by subsequent reactions. One distinguishes between acid- and base-catalyzed condensations, since they lead to different end products the properties of the condensation polymer are also affected by the mole ratio of phenol to formaldehyde. 

A new transesterification stanoxane catalyst, tin (di(chlorodimethylsiloxy)-tin chlor-odimethylsilane), has been used to incorporate ethyl acrylate into the condensation polymer of 2,2-bis(hydroxymethyl)propionic acid. This catalyst is preferable because it allows the reaction to proceed under milder conditions than those using a condensation esterification reaction route and makes it likely for product crosslinking side reactions to occur. 

Besides the thermal condensation, many publications describe the use of acid catalysts (CF3COOH [77], POCI3, polyphosphoric acid [78]) to carry out the polymer analogous cyclization. The occurrence of soluble products shows that the intramolecular cyclization is greatly favored over an intermolecular condensation step (crosslinking). 

Because die silicon of the vinyl silane-containing acrylic polymers is attached directly to the backbone of the polymer, it is expected that the silanols will be less able to condense and crosslink than the less sterically encumbered silanols of the MTIPS latexes. The vinyl silane signal did not change in intensity during cure. 

Gelation processes, such as crosslinking linear chains or condensation of /-functional monomers A/ (where A reacts with A) with /> 2 are quite different from either linear condensation polymers or hyperbranched polymers. Linear condensation polymers (made from AB monomers, -where A only reacts with B) and hyperbranched polymers (made from... 

If the fiber is to be ironed, its Tg should be above 200°C. Branching and crosslinking are nndesirable since they inhibit crystalline formation. Even so, some crossfinkmg may be present to maintain a given orientation, snch as desired in permanent press clothing. While most fibers are made from condensation polymers, new treatments allow some fibers to be made from olefinic materials snch as polypropylene (Table 3). 

Condensed systems start to behave as polymers after a certain molecular mass has been attained and a network of macromolecular entanglements or chemical nodes has been formed [57]. In consideration of condensed polymers, it is especially important to describe the sections of the macromolecule between the points of chemical crosslinking or entanglements [56]. The deformability and mobility of these sections largely determine the macroscopic properties of polymers [57, 104]. The general physical grounds that account for the fractality of these chain sections are considered next in relation to epoxy polymers. 

Polyvinyl - methyl- ether Vinyl chloride polymers Urea- and melamineform-aldehyde condensates (uncured) Crosslinked (cured, vulcanized) polymers... 

Polymer 2 (Fig. 4.1) is an example of a condensation polymer where a difionctional cyclophosphazene can react with an organic or an inorganic difiinctional reagent to afford a linear polymer. These polymers contain the cyclophosphazene ring as a repeat motif in the polymer backbone. These polymers have also been termed cyclolinear polymers. In this type of polymers also, the scope for variation is considerable, although in practice this has not been realized. Polymers of the type 3 (Fig. 4.1) are examples of in-termolecularly crosslinked cyclophosphazenes. These are reminiscent of thermoset polymers such as phenol-formaldehyde or melamine-formaldehyde resins. The presence of the cyclophosphazene units in the crosslinked matrix is expected to impart special properties. However, this family of polymers also has not yet fulfilled the promise that they seem to hold. 

This is now interpreted to mean that the polymer particles initially formed were internally more completely condensed and crosslinked at the higher pH. Polymerization involves three simultaneous processes ... 

When considering the use of MA in condensation polymers, it is automatic to think of unsaturated polyesters. In fact, the demand for MA is keyed primarily to the growth of these resins. In 1980, about 172 MM lb of MA were used to produce polyester resins in the United States.This represented approximately 52% of the 330 MM lb of MA demand in the United States in 1980 (see Sec. 1.4.1). MA is also very useful in other condensation polymers, including about 6 MM lb in alkyd resins. The value of using MA to prepare, crosslink, and/or modify condensation and addition polymers is discussed in this chapter. In recent times, the synthesis of maleinated vinyl esters and maleimide resins have had significant study. Because of this interest, we also give some attention to the use of MA in vinyl ester and maleimide technology. 

Bisisomaleimide, hexamethylene, rearrangement to bisimide, 89 Bismaleimides aliphatic, crosslinked, 511 alkenylphenols condensation, 514 aromatic cycloaddition reactions, 266 azomethine condensations, 515 condensation polymer modifiers, 511 crosslinking monomers, 91 crotonitrile condensations, 515 dialdoximes condensation, 514... 

Branched and crosslinked condensation polymers are produced when the reaction mixture includes tri-functional monomers as well as bi-functional ones. The incorporation of a single tri-fimctional monomer into a chain generates a branch point. As we increase the fraction of tri-functional monomers, branching becomes more prevalent and the resulting molecules more complex. When sufficient tri-fimctional monomers are present we create a three-dimensional crosslinked network. Figure 1.12 shows the general outline of the effects of tri-fimctional monomers on condensation polymers. 

Simultaneous IPNs involve monomers or reactive oligomers and crosslinkers of two or more reactive systems. These systems are generally chosen such that the reaction of one component does not interfere with or is involved with the reactions of the second component. Otherwise, grafting reaction would compete with interlocking ring formation as the method of compatibilization. An example of a simultaneous IPN is the reaction of free radical polymers (such as polyacrylates) in the presence of condensation polymers such as polyurethanes, as has been the subject of many investigations [171-174]. A PU/PMMA simultaneous IPN exhibited transparency and showed only limited phase separation below 30% PMMA [171]. This IPN... 

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