Preparation of condensation polymers

There have come into prominence in the past few years fast, low-temperature processes for the preparation of condensation polymers (12, 22),... 

Hydrazines and hydrazides have been known for some time to react with aromatic and aliphatic isocyanates to give the expected products. Recently this type of reaction was used for the preparation of condensation polymers from diisocyanates and dihydrazides and hydrazine (64). 

Although the mechanism of condensation reactions is generally simple, the preparation of condensation polymers with useful molecular weight can be very difficult and can require very precisely controlled reaction conditions because of the very high reaction yields needed, as shown by Equation 31. 

Although the procedures for the preparation of condensation polymers are analogous in many respects to those for the condensation reactions of monofunctional compounds, some additional factors must be taken into account if one wishes to attain high molecular weights in polycondensations. These are essentially consequences of Eqs. 4.1, 4.2, 4.3, 4.4, 4.5, 4.8, and 4.9. Firstly, the condensation reaction must be specific and proceed with the highest possible yield. 

K. C. Stueben is a Senior Research Scientist at Union Carbide s Technical Center in Bound Brook, New Jersey. He received his Ph.D. from the Polytechnic Institute of New York in 1960. His research experience has encompassed a number of areas, including micellar catalysis, synthetic paper, polymer flammability, exploratory adhesives, radiation curable pressure sensitive adhesives and both laboratory and plant scale preparation of condensation polymers, latexes and industrial chemicals. He is the author of numerous papers, chapters and patents in these fields. Dr. Stueben is currently Director of the Adhesion Society s course on Adhesion. 

In all the preceding polymerization methods we have seen how to utilize the double bond in an unsaturated organic compoimd to link many molecules together into a polymeric chain. Also, in all of these processes the polymer was produced starting from a single monomer. In contrast in this section we will look at polymers that are prepared from the reaction of two difunctional monomers with each other. In all the polymerization reactions that we have seen so far there was no side-product formation. For example, ethylene was converted into polyethylene acrylonitrile was converted into polyacrylonitrile and so on. During this conversion the entire stmc-tural unit of the monomer was incorporated into the polymer without any side-product formation. However, in the preparation of condensation polymers a small molecule (such as water or methanol) is eliminated as the side-product. Another important difference is that condensation polymerization is usually a step-growth polymerization. This means that the polymerization proceeds in a series of steps. To make this point clear let us recall the polymerization of ethylene by the free-radical method. In the free-radical process the polymerization of various chains are initiated by the... 

Figure 4 Synthetic scheme for the preparation of condensation polymers.

Polymers from hydroxy-substituted fatty acids or esters, derived from fats and oils and bifunctional compounds, have been reported [277]. The fat- and glyceridic oil-derived monomers used represent an inexpensive and readily obtainable monomer source for the preparation of condensation polymers from hydroxy- or amino-substituted fatty acids (e.g. 12-hydroxystearic acid) with difunctional compounds (e.g. diamines, polyamines, amino alcohols, diols, polyols, diacid chlorides, diisocyanates, phosgene, etc.). 

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. 

The most interesting aminomethyl derivative of condensation polymers that we have prepared to date Is derived from direct reduction of poly(2-cyano-l,3-phenylene arylene ether), 20. Enchainment of benzonitrile repeat units Is accomplished by coupling 2,6-dichlorobenzonitrile with the potassium salt of bisphenol-A copolymers with lower nitrile contents can be produced by copolycondensation of bisphenol-A, 2,6-dichlorobenzonitrile and 4,4 -dichlorodiphenyl sulfone.21 The pendent nitrile function provides an active site for further elaboration. 

The conventional route to prepare I generally involves a high temperature melt polymerization of hexachlorocyclotriphosphazene, or trimer (IV). Recent studies have demonstrated the effectiveness of various acids and organometalllcs as catalysts for the polymerization of IV (8). Alternate routes for the preparation of chloro-polymer which do not involve the ring opening polymerization of trimer have been reported in the patent literature (9. 10). These routes involve a condensation polymerization process and may prove to be of technological importance for the preparation of low to moderate molecular weight polyphosphazenes. 

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... 

The range of monomers which can be employed is largely dictated by the physical chemistry of the emulsion system. For instance, monomers must be sufficiently hydrophobic to allow the formation of stable w/o HIPEs. In addition, most systems which have been studied have used polymerisation methods which require either an initiation step, or addition of a catalyst. This is due to the fact that the first step in the preparation of the polymer is the preparation of HIPE this can only proceed satisfactorily in the absence of any significant degree of polymerisation. Thus, it can be seen that radical addition polymerisation is suitable for the synthesis of PolyHIPE polymers, whereas condensation polymerisation can be more problematical. Also, the latter reactions often generate water as the by-product, hence the aqueous component of the HIPE is inhibiting to the polycondensation. 

In this section, we shall discuss some of the more useful procedures for the preparation of high polymers, starting with examples involving condensation reactions. 

A variety of polyester-condensation polymers are made commercially. Ester interchange (Section 18-7 A) appears to be the most useful reaction for preparation of linear polymers ... 

Polyethylene is formed by addition of C2H4 molecules, which are merely linked together without the elimination of any reactant atoms. When other polymers are formed, molecules are linked together, and particular atoms break loose to form additional products. When water (H20) is the additional product, the reaction is called a condensation reaction. Often the reactants are not simple hydrocarbons but are more complex organic molecules. The formation of nylon is a condensation polymerization reaction. In Activity 5.5 students will prepare a condensation polymer and use it to create a macrosculpture. 

Calculations at the MP2/6-31G //MP2/6-31G level indicates that the C2h fully planar structure is about 8 kcal/mol more stable than the C2V perpendicular form (a transition state). Likewise, condensation reactions with isatins have suggested the involvement of the superelectrophile 86 (eq 21).40 This superelectrophilic chemistry has been successfully applied in the preparation of hyperbranched polymers and other macromolecules 40b d Other... 

In the case of condensation polymers such as PET, it is often possible to reverse the polymerization process and convert the polymer back to its constituent monomers. The monomers can then be purified and used to prepare new polymer. PET is converted back to ethylene glycol and dimethyl terephthalate by heating the polymer with methanol. This is exactly the reverse of the reaction that is used to prepare the polyester ... 

As outlined in the previous chapters, the preparation of silicone polymers involves first the preparation of organosilicon halides or esters, secondly the hydrolysis of an appropriate mixture of these intermediates, and finally the condensation or rearrangement of the polymers to achieve the desired molecular arrangement. Only in the first step is there a choice of preparative methods the second and third steps are carried out in much the same way, regardless of how the intermediates were made. From the standpoint of synthesis, the problem therefore comes down to the preparation of the methyl-, ethyl-, and phenylchlorosilanes or ethoxysilanes. Of these the methyl compounds are the most important, because they are used directly for the water-repellent treatment and are the only intermediates required for the oils, elastomers, and some types of resin. 

Some attempts were made to prepare nitrate esters of condensation polymers, but in most cases these gave low molecular weight solid products. Typical of this work was the study carried out by the Naval Powder Factory on hydroxylated polyamides. 

When MFC are prepared from blends of condensation polymers as a result of chemical reaction (additional condensation and transreactions) taking place at the... 

As with condensation polymers many examples of biochemically formed vinyl addition polymers, such as the poly-cis-isoprene found in the sap of rubber trees, were known long before we were able to replicate these materials even in the laboratory. Our ability to initiate and control the preparation of vinylic polymers on a laboratory scale came in the early 1930s, substantially later than the commercialization of phenol-formaldehyde condensation polymers. Since then, however, starting with the synthesis of polyethylene, then poly(vi-nyl chloride) (PVC), synthetic rubbers and polystyrene, the scale of production of this class of polymer has outstripped the polycondensation class by more than an order of magnitude. Table 23.1 displays some representative production figures to illustrate this. 

The polymeric amides, polyamides, are an especially important class of condensation polymers. Nylon is the best known polyamide. It is prepared by heating anhydrous hexa-methylenediamine with anhydrous adipic acid, a dicarboxylic acid. This substance is often called nylon 66 because the parent diamine and dicarboxylic acid each contain six carbon atoms. 

Polyesters, polyetherimide, melamine-formaldehyde, polyurethanes, polyurethane-ureas and polyamides (nylons) are examples of condensation polymers prepared by REX. " Because a small molecule is produced in condensation reactions, vent ports are employed. Between the ports are melt sealing screw sections, to prevent back mixing of volatilizing melt. Sealing screw sections are constructed by a right handed-left handed sequence of screw elements. Another chemistry feature of step-growth reactions is their sensitivity to errors in stoichiometric feed proportions. This poses problems with solid feed materials, which are normally converted to liquid form for more... 

The economic impact of synthetic polymers is too great to send them to the end of the book as a separate chapter or to group them with biopolymers. We regard polymers as a natural part of organic chemistry and pay attention to them throughout the text. The preparation of vinyl polymers is described in Chapter 6, polymer stereochemistry in Chapter 7, diene polymers in Chapter 10, Ziegler-Natta catalysis in Chapter 14, and condensation polymers in Chapter 20. 

Our cooperation with Sheats also extended into the area of condensation polymers of cobalticinum salts.92 Ionic polyesters were prepared by melt-phase transesterification of 1,1 bis(carbethoxy)cobalticinium hexafluorophosphate with various diols. Low molecular-weight polysters were formed. However, attempts to prepare polyamides by melt condensations of alkylene diammonium salts of l,l -bis(carboxy)cobalticinium PFg salts resulted in decomposition.92... 

Preparation of synthetic polymers. The polymerisation process (chemical joining of monomers) generally occurs by means of one of the three major mechanisms, namely, addition polymerisation, condensation polymerisation and rearrangement polymerisation. 

Preparation of linear polymers. Into a 5 L, three-necked flask equipped with an overhead stirrer, an argon inlet tube and a condenser are placed 89.57 g (0.621 mole) frans-eyelohexanedimethanol, 39.52 g (0.334 mol) 1,6-hexanediol, and 1.8 L distilled tetrahydrofuran. The mixture is stirred until all solids have dissolved then, 200 g (0.942 mole) 3,9-bis (ethylidene 2,4,8,10-tetraoxaspiro [5,5] undecane) is added. The polymerization is initiated by the addition of 2 mL of a solution of p-toluenesulfonic acid (20 mg/mL) in tetrahydrofuran. 

In addition, there has been an increasing interest in new synthetic methods for the preparation of well-defined polymers with controlled chain-end functional groups [23], such as telechelic polymers, which are characterized by the presence of reactive functional groups placed at both chain ends. These materials can then be used as precursors in the synthesis of block copolymers, as modifiers of the thermal and mechanical properties of condensation polymers, as precursors in the preparation of polymer networks, and as compatibilizers in polymer blends [24]. 

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