Cyclic compounds polymers

The kinetics of this type of polymerization are the same as for simple condensation for this reason, the use of the term polycondensation is perhaps more appropriate. Unless kinetic evidence suggests otherwise, polymerizations involving the formation of chain polymers from cyclic compounds, following ring scission, are classed as condensation polymerizations. Some important con-... 

Acyclic diene molecules are capable of undergoing intramolecular and intermolec-ular reactions in the presence of certain transition metal catalysts molybdenum alkylidene and ruthenium carbene complexes, for example [50, 51]. The intramolecular reaction, called ring-closing olefin metathesis (RCM), affords cyclic compounds, while the intermolecular reaction, called acyclic diene metathesis (ADMET) polymerization, provides oligomers and polymers. Alteration of the dilution of the reaction mixture can to some extent control the intrinsic competition between RCM and ADMET. 

The process proceeds through the reaction of pairs of functional groups which combine to yield the urethane interunit linkage. From the standpoint of both the mechanism and the structure type produced, inclusion of this example with the condensation class clearly is desirable. Later in this chapter other examples will be cited of polymers formed by processes which must be regarded as addition polymerizations, but which possess within the polymer chain recurrent functional groups susceptible to hydrolysis. This situation arises most frequently where a cyclic compound consisting of one or more structural units may be converted to a polymer which is nominally identical with one obtained by intermolecular condensation of a bifunctional monomer e.g., lactide may be converted to a linear polymer... 

In Section 3 of this chapter it was mentioned that polymers obtained by intermolecular condensation of bifunctional monomers may often be prepared alternatively by an addition polymerization of a cyclic compound having the same composition as the structural unit. Typical examples are shown in Table III. The processes indicated are appropriately regarded as addition polymerizations. Each of these polymers may also be prepared through the condensation of suitable bifunctional monomers. The dimethylsiloxane polymer, for example, may be prepared, as indicated in Table I (p. 45), through the condensation of dimethyl dihydroxysilane formed by hydrolysis of the di-chlorosilane... 

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... 

Other cyclic compounds such as the N-carboxyanhydrides of a-amino acids,and lactams may be polymerized similarly with regeneration of an amino group at each step. According to the mechanism postulated, the number of polymer molecules formed should equal the number of initiator molecules (e.g., ROH) introduced, and the average number of monomers per polymer molecule should equal the ratio of monomer consumed to initiator. 

Abandoning the hunt for linear, fiber-forming molecules, he turned to polymer ring compounds. Before Carothers, cyclic compounds were so difficult to make that no one studied them, but his group had tasted scientific blood and was happily publishing papers. When they discovered a series of ring compounds that produce synthetic scents, Du Pont sold the compounds to the perfume industry. The cyclic compounds were the last of Carothers fundamental scientific studies. After completing them, he drifted for a while, unclear as to what direction his research should take. 

In Olin s attempts to derivatize dilithiated products of o-carborane with chlorosilanes for further reaction with ammonia, it was observed that cyclic compounds, instead of polymers, were produced by the interaction of the substituents on the adjacent carbon atoms in the o-carborane units.11 However, when a linear dimethoxy intermediate of m-carborane was reacted as an equimolar mixture with dichlorosilane in the presence of the catalyst FeCl3, the quantitative evolution of CH3C1 was observed... 

The final class of polymers containing carboranyl units to be mentioned here is the polyphosphazenes. These polymers comprise a backbone of alternating phosphorous and nitrogen atoms with a high degree of torsional mobility that accounts for their low glass-transition temperatures (-60°C to -80°C). The introduction of phenyl-carboranyl units into a polyphosphazene polymer results in a substantial improvement in their overall thermal stability. This is believed to be due to the steric hindrance offered by the phenyl-carborane functionality that inhibits coil formation, thereby retarding the preferred thermodynamic pathway of cyclic compound formation (see scheme 12). 

Polymers are formed via two general mechanisms, namely chain or step polymerisation, originally called addition and condensation, respectively, although some polymerisations can yield polymers by both routes (see Chapter 2). For example, ring opening of cyclic compounds (e.g., cyclic lactides and lactams, cyclic siloxanes) yield polymers either with added catalyst (chain) or by hydrolysis followed by condensation (step). Many polymers are made via vinyl polymerisation, e.g., PE, PP, PVC, poly(methyl methacrylate) (PMMA). It could be argued that the ethylenic double bond is a strained cyclic system. 

Here, lipase-catalyzed ring-opening polymerization of cyclic compounds giving polymers other than polyesters is described. l,3-Dioxan-2-one, six-membered cyclic carbonate, was polymerized in the presence of lipase catalysts (Fig. 13)... 

Cyclic polymers form nearly 50 per cent of the product while the tetramer, octamethylcyclotera siloxane (I) constitutes the main cyclic compound. Now the polymerisation of the tetramer is done by heating at 150-200°C with a trace of sodium hydroxide and a very small amount of non-functional material so as to control the Molecular weight. The products obtained is a highly viscous gum having no elastic properties. 

Title Fluorine-Containing Cyclic Compound, Fluorine-Containing Polymer Compound, Resist Material Using Same, and Method for Forming Pattern... 

Fluorine-Containing Cyclic Compound, Fluorine-Containing Polymer Compound... 

The emphasis in the approaches to boron nitride [10043-11 -5], BN, precursors has been concentrated on cyclic compounds. There have been recent reports of trimethylsilyl-substituted aminoboranes being evaluated as B—N precursors. These are linear borylamines containing up to four boron atoms. Compounds were also synthesized with free —NH2 groups amenable to condensation with either dihaloboranes or dihaloborazines (65) and offering suitable monomers for linear B—N polymer synthesis and borazine-ring-linking applications. 

A very important field of polymerization, stereospecific polymerization, was opened in 1955. In this year, Natta and his coworkers (1—3) polymerized a-olefins to crystalline isotactic poly-a-olefins with the Ziegler catalyst, and Pruitt and Baggett (4,5) polymerized dl-propylene oxide to crystalline polypropylene oxide, which was later identified as an isotactic polymer by Price and his coworkers (6,7). Since then, a large number of compounds including both unsaturated and cyclic compounds were polymerized stereospecifically and asymmetrically. Development of the stereospecific polymerization stimulated... 

The product consists uf various amounts of high polymer (.r is very large) and discrete cyclosilanes with n = 5-35. This is the largest homologous series of cyclic compounds now known except for the cycloalkanes. Although these compounds are formally saturated, they behave in some ways as aromatic hydrocarbons. They can be reduced to amon ladicals. and EPR spectra indicate that the unpaired electron is delocalized over the entire ring. 06... 

The necessity for postulating combination steps raises questions regarding the nature of the intermediates which may be formed from acetylene and then reacted to form carbon. Various types have been suggested, such as aromatics, fulvene-type cyclic compounds, and highly unsaturated aliphatics. There is evidence for formation of all such types in thermal reactions of acetylene, but not enough is known of their chemistry to determine which might be of most significance as an intermediate under combustion conditions. It is probable that no one type actually controls the reaction. Parallel with the chemical question here, there is an important physical question of whether the nucleus for the ultimate carbon particle is a droplet of liquid polymer or a small bit of solid. 

This reaction also plays a role in the degradation of polysulfides. A back-biting mechanism as shown in equation 6 results in formation of the cyclic disulfide (5). Steam distillation of polysulfides results in continuous gradual collection of (5). There is an equilibrium between the linear polysulfide polymer and the cyclic disulfide. Although the linear polymer is favored and only small amounts of the cyclic compound are normally present, conditions such as steam distillation, which remove (5), drive the equilibrium process toward depolymerization. 

Figure 6-3. The principal problem associated with the formation of cyclic compounds is in the control of intramolecular as opposed to intermolecular reactions. The open circles represent sites that can react with each other. Intramolecular reaction leads to a cyclic compound, whereas intermolecular reaction leads to oligomers and polymers.

The ratio of linear to cyclic molecules is shifted heavily in favor of cyclic compounds in equilibrated 3,3,3-trifluoropropylmethylsiloxane polymers (31) which consist of 86 wt % of rings and 14% of chains. 

Dienes are cyclized by intramolecular metathesis. In particular, cyclic alkenes 43 and ethylene are formed by the ring-closing metathesis of the a,co-diene 46. This is the reverse reaction of ethenolysis. Alkene metathesis is reversible, and usually an equilibrium mixture of alkenes is formed. However, the metathesis of a,co-dienes 46 generates ethylene as one product, which can be removed easily from reaction mixtures to afford cyclic compounds 43 nearly quantitatively. This is a most useful reaction, because from not only five to eight membered rings, but also macrocycles can be prepared by RCM under high-dilution conditions. However, it should be noted that RCM is an intramolecular reaction and competitive with acyclic diene metathesis polymerization (ADMET), which is intermolecular to form the polymer 47. In addition, the polymer 47 may be formed by ROMP of the cyclic compounds 43. 

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