Multicyclic polymers

The other extreme is the formation of networks (gels) by polycondensations conducted in bulk or at IMCs 1.0 mol/L. Flory [3] has calculated two simple Eqs. (12.1) and (12.2), which correlate the critical conversion (pcr) at which gelation becomes detectable with the functionahty n (or f in Rory s work) of the b monomers. He found that equifunctional polycondensatzions of 02 + 3 monomers will form gels at a. 71.5 % in theory and 76-77 % in real experiments [4—6]. He attributed the difference to the occurrence of a few cyclization reactions. For 2 + 4 monomer combinations a pcr of 58 % was calculated as theoretical value, and a of 63 % was found by Stockmayer et al. [7] for 

Kricheldorf, Polycondensation, DOI 10.1007/978-3-642-39429-4 12, Springer-Verlag Berlin Heidelberg 2014 

About ten years ago the author speculated that between the extremes mentioned above a third set of reaction conditions and a third group of reaction products might exist, namely reaction conditions yielding soluble multicyclic polymers. Such polycondensations yield a complex mixture of reaction products which cannot satisfactorily be characterized by classical spectroscopic methods such as IR-, NMR and NMR spectroscopy. Mass spectrometric methods such as Fast-Atom-Bombardment, and above all, MALDI-TOF mass spectrometry are required, and even these methods do not answer all questions concerning the structure of the reaction products. Hence, a systematic exploration of this new working field was not feasible before the year 2000, i. e. before powerful MALDI-TOF mass spectrometer became commercially available. 

Perfect multicycles free of functional end groups. They can only exist for even-numberd DPs. They are the result of anequifunctional polycondensation under (nearly) ideal conditions with almost quantitative conversion (e.g. B4C8 in Formula 12.3, bottom). 

Multicyclic polymers bearing one functional b group (Formulas 12.2 and 12.3, top). Such multicycles are typical for odd-membered DPs and almost quantitative conversion. 

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Scheme 18.10 Construction of multicyclic polymers with repeating segments. Linearly connected (a) spiro-type and (b) bridged-type, and (c) networked bridged-type.

Kricheldorf, H. R., Cyclic and Multicyclic Polymers by Three-Dimensional Polycondensation. Acct. Chem. Res. 2009, 42, 981-992. 

Sugai, N., Heguri, H., Ohta, K. et al. (2010) Effective click construction of bridged- and rpiro-multicyclic polymer topologies with tailored cyclic prepolymers (lyk/o-telechelics). Journal of the American Chemical Society, 132, 14790-14802. 

E) Equifunctional feed ratios -I- moderate IMC s (e.g., 0.01-0.1 moI/L) yield multicyclic polymers free of functional groups at 100 % conversion (see Chap. 12). 

G) [a2]/[ n] > equifunctional + high IMC s yield gels and multicyclic polymers having a groups at molar ratios close to equifunctional or yield branched oligomers at very high [a l b ratios... 

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). 

HB polymers derived from ab monomers can only form one cyclic element, so that the architecture changes from tree-shaped to sun-shaped with increasing conversion. Yet, hb polymers based on a2 -I- b monomers may contain two or more cyclic moieties at high conversions. Such jx)lymers may be considered as multicyclic polymers having hb side chains (see Chap. 12). 

Multicyclic polymers having two or more b" functions. These multicycles result from polycondensations with molar 2/ 3 ratios < 1.5/1.0 and quantitative conversion of a (see Formulas 12.2 and 12.3). 

Multicyclic polymers having both a" and b" functions. Such multicycles indicate incomplete conversion regardless of the feed ratio. 

For the description of multicyclic polymers prepared by + />4 polycondensation, in principle, the same type of structural formulas and sum formulas can be used designed for 02 + 3 polycondensates (Formulas 12.5). However, two characteristic differences should be emphasized. First, depending on the stereochemical properties of the monomers even the bridged bicyclic monomers may yield isomers. As illustrated by scheme (a) in Formulas 12.6 (top), 64 monomers based on a tetravalent carbon such as pentaerythritol and its derivatives [e.g. (b) and (c) in Formulas 12.6] cannot form isomers. Yet, for the bicyclic monomers of tetrafunctional benzene derivatives two or three isomers may exist. The condensation of a non-symmetrical monomer, such as tetrahydroxy spirobisindane (TTSBI) with flexible 02 monomers may yield 8 isomeric dimers [18]. In other words, the exponential increase of the number of isomers with higher DPs is steeper than in the case of 02 + 3 polycondensates. The second characteristic difference is the fact, that in 02 + / 4 polycondensations monofuctional multicycles (analogous to those in Formulas 11.2 and 12.3, top) cannot be formed. Hence, only four not five different classes of multicycles exist ... 

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