Condensation polymers cyclic

Keywords Chain-growth polymerization Condensation polymers Cyclic polymers jt-Conjugated polymers Polycondensation... 

In 1930, in one of many pioneering studies, Carothers showed that certain condensation polymers could be cyclic or macrocyclic rather than exclusively linear. In addition to this very important observation, he showed that thermolysis in vacuo of certain polymers could also yield macrocyclic materials. Quite a number of papers have been published on this subject since that time, especially dealing with the chemistry of phthalate " , isophthalate " ", and terephthalate esters Many of these structures are tabulated at the end of this... 

Innumerable derivatives have been prepared by the standard techniques of organic chemistry. The organosilanes tend to be much more reactive than their carbon analogues, particularly towards hydrolysis, ammonoly-sis. and alcoholysis. Further condensation to cyclic oligomers or linear polymers generally ensues, e.g. ... 

The chemical and physical properties of the polymers obtained by these alternate methods are identical, except insofar as they are affected by differences in molecular weight. In order to avoid the confusion which would result if classification of the products were to be based on the method of synthesis actually employed in each case, it has been proposed that the substance be referred to as a condensation polymer in such instances, irrespective of whether a condensation or an addition polymerization process was used in its preparation. The cyclic compound is after all a condensation product of one or more bifunctional compounds, and in this sense the linear polymer obtained from the cyclic intermediate can be regarded as the polymeric derivative of the bifunctional monomer(s). Furthermore, each of the polymers listed in Table III may be degraded to bifunctional monomers differing in composition from the structural unit, although such degradation of polyethylene oxide and the polythioether may be difficult. Apart from the demands of any particular definition, it is clearly desirable to include all of these substances among the condensation... 

Id. Cyclic Condensation Polymers.—The foregoing discussion has proceeded under the assumption that the only products of bifunctional condensation are open chain polymer molecules—an assumption which obviously will not be exactly valid since cyclic polymers must always occur to some extent. The nature of the error introduced by this assumption will be examined in the course of the following discussion of cyclic polymer components. 

Tetramethylammonium chloride (2 mg) and 5 (1. Og) were placed in a vial, sealed, and heated in an oil bath at 107°C for 65 h. H-NMR analysis of the colorless, viscous grease showed the ratio of signals at 4.6 and 3.90ppm as ca. 60/1. The small amount of cyclic dimer formed (GC anlaysis) was removed by Kugelrohr distillation (up to 100°C/0.05 mm). 19F-NMR featured the internal/ terminal CF2CH20 group ratio as ca. 83/1. Size-exclusion chromatography showed the major peak with Mn, =26,700 and Mw =52,800, consistent with condensation polymer 7. 

Cyclic oligomers of condensation polymers such as polycarbonates and polyesters have been known for quite some time. Early work by Carothers in the 1930s showed that preparation of aliphatic cyclic oligomers was possible via distillative depolymerization [1, 2], However, little interest in the all-aliphatics was generated, due to the low glass transition temperatures of these materials. Other small-ring, all-aliphatic cyclic ester systems, such as caprolactone, lactide... 

Materials that are constructed from organic polymers such as polyethylene, polystyrene, polyisoprene (natural rubber and a synthetic elastomer) and poly(vinyl chloride) are common features of our daily lives. Most of these and related organic polymers are generated from acyclic precursors by free radical, anionic, cationic or organometallic polymerisation processes or by condensation reactions. Cyclic precursors are rarely used for the production of organic polymers. 

Polyester, a condensation polymer, can be produced by chainwise, acid-catalyzed ring openings of cyclic ester (lactone) without expulsion of small molecules, and also by stepwise polycondensation of ohydroxycarboxylic acid. 

With the development of polymer science and synthesis of newer polymers, this definition of condensation polymer was found to be inadequate. For example, in polyurethanes, which are classified as condensation polymers, the repeat unit has the same net composition as the two monomers-that is, a diol and a diisocyanate, which react without the elimination of any small molecule. Similarly the polymers produced by the ring-opening polymerization of cyclic monomers, such as cyclic ethers and amides, are generally classified as condensation polymers based on the presence of fimctional groups, such as the ether and amide linkages, in the polymer chains, even though the polymerization occurs without elimination of any small molecule. 

Two basic types of condensation polymers are possible. Nylon-6,6 is the typical example of the poly condensation of two bifunctional monomers, adipic acid and hexamethylenediamine. This type of polycondensation is generally referred to as the AABB reaction. In contrast, polycondensation of one difunctional monomer is referred to as an AB reaction. The AABB-type polycondensation has the advantage that the stoichiometry is fixed by salt formation. In contrast, AB polyamides are usually prepared by ring-opening polymerization of a cyclic lactam. This reaction requires only a catalytic amount of water, because the water required for ring opening is replenished by the simultaneously occurring polycondensation ... 

Poly(ethylene terephthalate) is the condensation polymer made from terephthalic acid and ethylene glycol. The acid or its dimethyl ester is obtained by the oxidation of -xylene, a product from catalytic reforming of naphtha. The glycol is obtained from ethane via the corresponding cyclic oxide. With the availability of purified terephthalic acid since the 1960s direct esterification of the acid in a continuous process is used in commercial production of the polyester [31] ... 

Under the standard conditions formaldehyde is gaseous. However, its molecules can interact with each other by a mechanism similar to nucleophilic attack. The oxygen of the carbonyl group behaves as the nucleophilic atom (see the next scheme). The product of such a reaction is a polymer, the white powder called paraformaldehyde. Hence, formaldehyde can be provided either in the form of the water solution formol or as paraformaldehyde powder. Pure formaldehyde gas for use in chemical reactions can be prepared by heating paraformaldehyde under vacuum. Similarly, the molecules of acetaldehyde can condense into cyclic trimers giving the substance known as paraldehyde. 

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