Condensation polymers types, monomers

In condensation polymers, the monomers are linked together by condensation reactions, like those used to form ester or amide links. Polymers formed by linking together monomers that have carboxylic acid groups with those that have alcohol groups are called polyesters. Polymers of this type are widely used to make artificial fibers. A typical polyester is Dacron, or Terylene, a polymer produced from the... 

Polymerization The bonding of two or more simple identical molecules termed monomers to form a polymer. Polymerization maybe by Condensation Polymer-type aert el Aerogel adopting a fibrous, polymeric morphology Porometry Characterization technique to determine the minimum pore diameter (hence its pore size distribution) in a material, by flowing a fluid (e.g., mercury) through its capillary porous network. 

Linear condensation polymers are produced when the constituent monomers contain two functional groups each. When a single monomer is polymerized, the product is made of chains whose repeat unit corresponds to the monomer. An example of this type is nylon 6, the structure of which is shown in Fig. 1.10. If two different monomers are polymerized, the result most often is a chain whose repeat unit corresponds to the two different monomers arranged alternately. An example of this type is nylon 66, the structure of which is shown in... 

The polymerization of AB -functional vinyl monomers is fundamentally different from the step-growth polymerization of AB2-monomers. Condensation of AB2-monomers results immediately in the formation of hyperbranched polymers since the reactivity of the end-groups are the same, regardless of what type of repeat unit (linear or dendritic) that is formed. 

Dendrimer synthesis involves a repetitive building of generations through alternating chemistry steps which approximately double the mass and surface functionality with every generation as discussed earlier [1-4, 18], Random (statistical) hyperbranched polymer synthesis involves the self-condensation of multifunctional monomers, usually in a one-pot single series of covalent formation events [31], Random hyperbranched polymers and dendrimers of comparable molecular mass have the same number of branch points and terminal units, and any application requiring only these two characteristics could be satisfied by either architectural type. Since dendrimer synthesis requires many defined synthetic and process purification steps while hyperbranched synthesis may involve a one-pot synthetic step with no purification, the dendrimers will necessarily be a much more expensive material to produce. 

The second common method of synthesising polymers (Fig. 5.3) is chain (addition) polymerisation. The most common type of addition polymer is based on ethene CH2 = CHj in which the monomer contains at least one double (tt) bond which on being activated, by free radical attack say, opens up to produce two single sigma bonds and the homopolymer poly(ethene). (Note in Fig. 5.3 the resultant polymer backbone is joined together by carbon-carbon bonds, unlike the condensation polymer systems (Fig. 5.1).)... 

This type of polymerisation generally involves a repetitive condensation reaction between two bt-functtonal monomers. These polycondensatton reacttons may resutt In the toss of some simple molecules as water, alcohol, etc., and lead to the formation of high molecular mass condensation polymers. 

Although we will not be discussing the mechanism of each type of step growth polymer because these reactions are very similar to the corresponding monomer chemistry, we should be aware of this analogy. For instance, an acid reacts with an alcohol under acid-catalyzed conditions by a certain well-studied and proven mechanism. This same mechanism is followed each time an ester linkage of a polyester is formed. One such transformation is outlined in Fig. 14.8. The equilibrium is shifted in the direction of the product by distillation of the water from the reaction mixture (and condensing it in a separate container—hence the name condensation polymers for this type). 

Most addition polymers are formed from polymerizations exhibiting chain-growth kinetics. This includes the typical polymerizations, via free radical or some ionic mode, of the vast majority of vinyl monomers such as vinyl chloride, ethylene, styrene, propylene, methyl methacrylate, and vinyl acetate. By comparison, most condensation polymers are formed from systems exhibiting stepwise kinetics. Industrially this includes the formation of polyesters and polyamides (nylons). Thus, there exists a large overlap between the terms stepwise kinetics and condensation polymers, and chainwise kinetics and addition (or vinyl) polymers. A comparison of the two types of systems is given in Table 4.1. 

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 formation of a condensation polymer is a stepwise process. Thus, the first step in the polycondensation of a hydroxycarboxylic acid (AB type) is the formation of a dimer that possesses the same end groups as the initial monomer ... 

Further intramolecular reaction of the poly(phenylene)-type polymer leads to more condensed polymers. Tour synthesized polymer 84 bearing a carbonyl moiety and a protected amino group in the phenylene rings by the reaction of boronate 83 and a dibromobenzene monomer. The polymerization takes place in the presence of a palladium catalyst in DME-H2O at 85 °C to give 84 that showed 3/n = 9850-28400 = 1.85-3.70) in 63-97% yields. The resulting polymer 84 is... 

The preparation of polymers from heterocyclic monomers that contain polymerizable functional groups undoubtedly constitutes the most common method of incorporating heterocycles into polymeric materials. Polymer-forming reactions are of two possible types addition reactions and condensation reactions. Addition monomers in general contain a site of unsaturation, i.e. a double or triple bond, through which polymerization occurs by successive single bond formation from one monomer to the next. With condensation monomers a bond is formed between two monomers with concomitant elimination of a... 

Monomer Purification. All polymers were prepared from either column purified or distilled monomers. The acrylate and methacrylate esters, styrene, and vinyl nitrile type monomers were purified by passing them through Rohm and Haas Amberlyst exchange resins (salt forms), while the diene monomers were either distilled directly from cylinders and condensed in a dry ice trap or alternatively caustic washed to remove the inhibitor. 

Even general AB-type monomers, affording polyamide, polyester, polyether, and so on, undergo chain-growth condensation polymerization if the polymer end group becomes more reactive than the monomer by virtue of the change of substituent effects between the monomer and polymer. Both the resonance effect and inductive effect of the nucleophilic site on the reactivity of the electrophilic site at the para and meta positions of the monomer are applicable, respectively. 

During the early 1960 s a new class of chemicals containing one or more double bonds was used to treat wood vinyl type monomers that could be polymerized into the solid polymer by means of free radicals (2). This vinyl polymerization was an improvement over the condensation polymerization reaction because the free radical catalyst was neither acidic nor basic, nor does the reaction leave behind a reaction product that must be removed from the final composite, such as water. The acid and base catalysts used with the other treatments degrade the cellulose chain and cause brittleness of the composite. Vinyl polymers have a large range of properties from soft rubber to hard brittle solids depending upon the groups attached to the carbon-carbon backbone. 

A polymerization that provides a transition into a discussion of gelation is the condensation of an excess of A-B with a small amount of an /-functional monomer, R-A/, that contains / equivalent functional groups of Type A, but no functional groups of Type B.[3 Linear chains are obtained when / is 1 or 2, but multichain condensation polymers are produced when/>2. At high conversion the polydispersity index depends only on/. 

Condensation polymers result from formation of ester or amide linkages between difunctional molecules. Condensation polymerization usually proceeds by step-growth polymerization, in which any two monomer molecules may react to form a dimer, and dimers may condense to give tetramers, and so on. Each condensation is an individual step in the growth of the polymer, and there is no chain reaction. Many kinds of condensation polymers are known. We discuss the four most common types polyamides, polyesters, polycarbonates, and polyurethanes. 

Condensation polymers of the polyester type were studied by Thiokol by using monomers originally developed by the Hooker Chemical Co. 

In this paper we report on the synthesis of new types of intrinsically conducting polymers using high-temperature reaction of condensation polymers and polyfunctional monomers. We shall show that the new polymers can be regarded as low-dimensional graphites both macroscopically and microscopically and discuss the change in their structural and electronic properties with heat-treatment temperature (HTT). 

End group analysis has been applied mainly to condensation polymers, since these materials must have relatively reactive end groups if they are to polymerize. If such polymers are prepared from two different bifunctional monomers the products can contain either or both end group types, and the concentrations of both are preferably measured for the most reliable molecular weight determinations. 

Many useful condensation polymers employ two bifunctional monomers, one having two functional groups of one type (e.g., a di-alcohol or diol), and the other having two complementary functional groups (e.g., a diacid). This type of polycondensation is often referred to as an A-A, B-B type, and gives only linear polymers. 

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