Non-Stoichiometric Polycondensations

Based on the definition of conversion given in Eq. (8.1), (or Eq. 4.1), and according to the correlation between DPn and conversion p (Eq. 8.2), a polycondensation should yield the highest molar mass, when  

In Flory s classical theory of step-growth polymerization[l] only points (1) and (2) were considered, and thus, textbooks usually comment that polycondensations of a-b monomers olfer the best chance for reaching high molar masses, because they possess a built in perfect stoichiometry. This apparently straightforward logic is supported by calculations of Flory (Eq. 4.3., Chap. 4), who found that stoichiometric imbalance in 02 + 2 polycondensations reduces the DPn. For instance, an excess of the 02 monomer has the consequence that after complete conversion of the monomers telechelic a-terminated oligomers or low polymers are formed. The DP decreases, when then excess of 2 increases. 

On the other hand, it has been found over the past 20 years that the highest molar masses of polycondensates reported in the literature were obtained from non-stoichiometric 02 + 2 polycondensations. This discrepancy results firom the fact in Flory s theory (and thus in all textbooks based on it) the role of end-biting cyclization is ignored. Polycondensations of a-b monomers exclusively yield oligomers and polymers terminated by one a and on b function, an optimum scenario for efficient cyclization, unless the growing chains are extremely stiff, but soluble or meltable. In the case of an 2 + 2 polycondensation only 50 % of aU 

Kricheldorf, Polycondensation, DOI 10.1007/978-3-642-39429-4 8, Springer-Verlag Berlin Heidelberg 2014 

Polycondensations of 02 + 2 monomer combinations may be subdivided into three categories according to their kinetic properties. 

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However, non-stoichiometric polycondensations are of interest for the preparation of telechelic oligomers and polymers. For example, OH-terminated oli-go(ether sulfone)s were prepared by several research groups [9-11], because their high Tgs and good solubilities render them useful building blocks for (multi)block-copolymers. Numerous other telechelic oligoethers were reported in the literature [9, 10], but a complete listing and discussion were not intended in this book. 

To the best knowledge of the author, non-stoichiometric polycondensations of this class have not been studied yet, A recently published speculative discussion[12] of suitable monomer combinations should not be repeated in this book. 

Presumably, the oldest non-stoichiometric polycondensation of class III is a synthesis poly(phenylene sulfide), PPS, which was patented in 1967 by Edmonds and Hill [25]. The first(nonintended) synthesis of low molar mass PPs was found by... 

In summary, two conclusions may be drawn. First, non-stoichiometric polycondensations of class ni may give much higher molar masses than polycondensations of a-b monomers. Second, the kinetic course of the polymerizations deviate largely from that of a normal step-growth polymerization, and the term non-stoichiometric polycondensation is rather a formal label than a correct terminology. In the extreme case, when cyclization is totally suppressed, class III polymerization exactly obeys the definition of an aa + condensative chain polymerizaion . This term was proposed by lUPAC, and numerous condensative chain polymerizations are known from a-b monomers as discussed in Chap. 16. 

Whereas for oa + 2 polycondensations the equimolar and equrfunctional feed ratio is necessarily identical, both feed ratios are quite different in oa + polycondensations and yield different architectures. Therefore, three different regimes of non-stoichiometric polycondensations may be defined ... 

Non-Stoichiometric polycondensations according to the scenarios (1) were not systematically studied. [a2]l[b feed ratios < 1.0/1.0 yield hyperbranched oligomers, which after complete conversion of the a functions possess numerous b" end groups. Syntheses of Novolac from formaldehyde with excess of phenol are example of such a polycondensation (see Chap. 2). Numerous examples are mentioned in the literature dealing with equimolar polycondensations (see Chap. 10). To the best knowledge of the author, non-stoichiometric polycondensations according to scenario (3) were never systematically studied. Several examples of non-stoichiometric polycondensations according to (2) were published in connection with syntheses of multicyclic polymers from equifunctional polycondensations (see Chap. 12). 

In this chapter we summarize the various methods of calculation which are reported in the literature, we show that when the polycondensation is stoichiometric no correction is needed and we propose new relations for cases where the balance between reactive groups is non-stoichiometric. 

To obtain polymer chains bearing at both ends the same function, say A, it is necessary to carry out to high conversion the reaction of a non-stoichiometric mixture of AA and BB. This procedure also allows some control of the molecular weight of the polycondensate since the well-known equation... 

Finally, it should be emphasized that all the theoretical considerations presented above also apply to syntheses of hyper branched polymers as discussed in Chap. 11. Cyclization limits the chain growth according to Eqs. (7.13) or (7.14), it reduces the dispersity compared to Flory s calculations (see Sect. 4.3) and the law of self-dilution (Eq. (7.11)) is also valid together with the RZDP. Furthermore, the existence of a permanent competition of cyclization and chain growth in KC polycondensations is decisive for a proper understanding of non-stoichiometric poly condensations as discussed in Chap. 8. 

Interfacial polycondensation can yield polymers with high molecular weights at high reaction rates. Since the interfacial technique is a non-equilibrium method, the critical dependence of high molecular weight on exact stoichiometric equivalence between diol and dichloridate inherent in bulk and solution methods is removed. The limitation of this method is the hydrolysis of the acid chloride in the alkaline aqueous phase. 

Non-catalytic thermal decarbonylation of quinones proceeded for 9,10-anthraquinone (ANQ), 9,10-phenanthrenequinone (PHQ), 1,4-and 1,2-naphthoquinone(NPQ) and p-benzoquinone (BNQ) in the presence of atmospheric hydrogen at 500- 600 C. ANQ or PHQ decar-bonylated in the presence of hydrogen to form fluorenone (FLR) at the first step, followed by successive hydrodecarbonylation and hydrocracking to form biphenyl and benzene. In the case of 1,4-NPQ, the reaction did not proceed in any obvious stoichiometric relation. Only 60- 70 % of 1,4-NPQ decarbonylated and was hydrogenated yielding styrene, ethylbenzene, toluene, benzene and lower hydrocarbons the remainder polymerized or partly polycondensed. Similar, or less selective results were obtained for 1,2-NPQ and p-BNQ. Analyses of kinetic treatments are reported for the consecutive reaction schemes of ANQ or PHQ as well as of FLR. The kinetic parameters for decarbonylation, polymerization, polycondensation reactions of quinones are discussed. 

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