Heterocyclic polymers, literature

Heterocyclic polymers containing the 1,4-dioxane ring have been mentioned only briefly in the literature. Cationic addition polymerization of 1,4-dioxene (151) produces polymer (152 Scheme 48) which, along with other poly(l,2-dialkoxyethylenes), is reported to form polymeric complexes with poly(methacrylic acid) (79MI11109). 

Heterocycle-forming polymerization reactions have been the most extensively reviewed of the three methods for obtaining heterocyclic polymers. A series of monographs are available that cover the literature through 1971 quite well (B-72MI11109). These monographs have served to provide an excellent foundation for our efforts. Whenever possible, we have cited more recent references, especially any reviews. It is the purpose of this section to depict succinctly the rich variety of chemistry that has been employed to form heterocyclic polymers of this type. This section, then, is a capsule summary of most of the heterocycles that have been generated concomitant with formation of a polymer. 

As shown in Fig. 2, oidy some epoxy-phenolic compositions and a limited number of heterocyclic polymers exhibit long-term thermal stability at 200°C and higher temperatures. In the heterocyclic series, only polybenzimidazoles, polyimides and polyphenylquinoxahnes have been subjected to extensive testing at high temperature. Several classification schemes are commonly used in the literature to represent these polymers. In the following discussion, the polymer chemistry is presented in the form... 

An impressive amount of data published in the literature indicates, based on TGA, that many heterocyclic polymers can be used at temperatures more than 350—4(X) °C. All experiments conducted later with these polymers, in actual long-term thermal operations, showed that heat-resistant polymers exhibit only a very short-term thermal stability at the onset of degradation revealed by TGA. In actual use, the thermal stability of a given polymer is approximately 150 to 2(X) °C less than the value provided by dynamic TGA. However, it is worth noting that significant differences exist between materials such as films and adhesives. In the former case, the surface area subjected to pyrolysis or oxidation is far greater than the periphery of an adhesive joint. 

Cyclophosphazenes are a fascinating group of inorganic heterocyclic compounds whose chemistry is multi-faceted, well developed and reasonably well understood. They are closely related to the linear poly-phosphazenes this relationship is unlike any other existing between ring-polymer systems. Although cyclic siloxanes and polysiloxanes have a close interrelationship, the number and types of cyclophospha-zene derivatives that are known, together with their exact counterparts in polyphosphazenes, underscore the utility of cyclophosphazenes as models for the more complex polyphosphazenes. The literature on cyclophosphazenes has appeared earlier in the form of books (1,2), chapters of books (3-5), authoritative compilations of data (6,7), and several reviews (8-21). The current literature on this subject is reported annually in the Specialist Periodic Reports published by the Royal Society of chemistry (22). This review deals mostly with chlorocyclo-... 

Attention was then turned to aromatic heterocyclic ladder polymers other than BBL. Due to the complexities in their synthesis, ladder polymers were not reported extensively in the literature at that time. A sample of polyfluoflavine (I) having an inherent viscosity in methanesulfonic acid of 2.5 was obtained from professor C. S. Marvel at the University of Arizona. The ladder polymer was prepared [5] from the A-B polycondensation of 2,3-dihydroxy-6,7-diamino-quinoxaline hydrochloride in PPA. Transparent blue sheets were observed on precipitation of this polymer from methanesulfonic acid, and when collected and dried, it formed gold films much like the color of the BBL films. It was felt at that time that all ladder polymers of sufficient molecular weight would form precipitated films. 

The oxolane (tetrahydrofuran) ring system can be incorporated into polymers either by polymerization of the suitably substituted heterocycle itself or by addition polymerization of a dihydrofuran derivative. A prime example of the former case is found in the utilization, as a component of adhesives and coatings for example, of the acrylate (38) and methacrylate (39) esters of tetrahydrofurfuryl alcohol. Although the bulk of the investigations concerning these monomers is recorded in the patent literature, a detailed study of the polymerization behavior of ester (39) has appeared (74MI11101) that indicates it is a fairly typical methacrylate monomer. 

Unsaturated tetrahydropyran derivatives have received only cursory attention in the literature as heterocyclic monomers. 2,3-Dihydropyran and several of its substituted derivatives apparently undergo cationic polymerization in a manner typical of vinyl ethers (72MI11103), while tetrahydropyranyl esters of methacrylic acid (123) are fairly typical free radically polymerizable monomers (Scheme 35) (74MI11105). The THP group was used in this study as a protecting group for the acid functionality, and it was found that deprotection of polymers (124) could be accomplished under extremely mild conditions. 

Although any coordination polymerisation involves a monomer coordination in each step, literature data that might concern complex formation between the monomer heteroatom and the metal atom at the active site are rather scant. This is due to the lability of such complexes of monomers with active sites if they were stable enough, they would not undergo any further rearrangement, which might lead to polymer chain growth. Thus, models have been studied that have consisted of a metal complex, of no effectiveness as a catalyst, and a monomer, or of a catalyst and a non-polymerisable heterocycle. 

Heterocycles have played a significant role in conjugated polymers and in the last three decades enormous amount of literature on these molecules has been made available. This section will review some of the recent understandings of this class of conjugated species both in the well-defined oligomeric form as well as in a higher polymeric form. 

Table 13.4.2. Summary regarding literature information on thermal decomposition of polymers containing heterocyclic groups [2],...

Thermal properties of some other polymers containing heterocycles are reported in literature. For example, the polymers containing triazine networks substituted with perfluoro-rt-propyl or perfluoroalkyloxy groups do not decompose easily upon heating. These types of polymers are used as heat resistant oils, and several studies on their thermal decomposition are available in literature [21-23]. 

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