Polycyclotrimerization

All polymerization reactions were carried out under dry nitrogen using standard Schlenk technique. A typical example of experimental procedure for the polycyclotrimerization of 1 is given here To a thoroughly baked and carefully evacuated 15-mL Schlenk tube with a three-way stopcock on the sidearm was placed 14.5 mg (0.025 mmol) TaBrs under nitrogen in a glovebox. Then freshly distilled toluene 

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The polycyclotrimerization of difunctional isocyanates (or NCO-terminated prepolymers) produces polymer networks containing heterocyclic, thermostable per-hydro-1,3,5-triazine-2,4,6-trione (isocyanurate) rings as crosslinks ... 

Recently polycyclotrimerization of isocyanates has found successful applications in the preparation of high temperature resistant cellular plastics, coatings and elastomers. 

A comprehensive review on the synthesis and the polycyclotrimerization of cyanates was published in the USSR in 1977 (with 160 references) [3], More than 50 dicyanates... 

Individual oligomeric BPA/DC cyclotrimerizates were separated by the HPLC gradient-elution technique in THF/H20 [13], The step-growth mechanism of the polycyclotrimerization was supported by quantitative analysis of the results. 

Scheme 17 Synthesis of hyperbranched polymer through diyne polycyclotrimerization...

Scheme 19 Proposed mechanism for tantalum-catalyzed alkyne polycyclotrimerization...

Table 2 Analysis of the products [hb-P32(m)] obtained from the polycyclotrimerizations of aliphatic diynes 32(m) with different lengths (m) of methylene spacers3 ...

Scheme 24 Synthesis of hb-PAs by (co)polycyclotrimerization of aryldiynes (with monoynes)...

Structural analysis of the homopolymers by spectroscopic methods confirmed that the diynes had undergone [2 + 2 + 2] polycyclotrimerizations by forming new benzene rings from their acetylenic triple bonds. The ratio of the 1,2,4- to 1,3,5-isomers of the trisubstituted benzene rings was estimated to be 2.2 1. Careful evaluation of the 111 NMR spectra unveiled that the number of terminal triple bonds in the final hb-PAs was much smaller than that in an ideal hyperbranched structure produced by the diyne polycyclotrimer-ization. This result suggests that intra-sphere ring formation might have been involved in the cyclotrimerization polymerization. 

In the polycyclotrimerization reaction, the mean field theory usually fails to describe the structure build-up. According to the mean field theory, the degree of polymerization can be defined in terms of the cyanate conversion by the relation... 

Cyanate ester (CE) resins are the key monomers for a new type of high-performance polymer. They were developed by Hi-Tek Polymers during the 1980s, then Rhone-Poulenc, and now Ciba-Geigy. The polycyclotrimerization... 

Equation 3 is often used in the literature to account for the kinetic behavior of several common dicyanate monomers (25, 26). The autocatalytic character of cyanate polycyclotrimerization is now quite well established we noticed that it was especially enhanced in samples with a large surface directly exposed to air (24, 27, 28). The kinetics of DPEDC blends were more difficult to describe because they were perturbed by several residual impurities in the monomer. Together with adventitious air moisture, the latter increased gel conversion with respect to the theoretical value (0.5). 

In contrast to these unreactive modifiers, the additives that were likely to react with cyanates (ATBN via its secondary amine function, and PES5003P via its phenol function) were shown to appreciably accelerate their cure, even in its very first steps. Phenols (12) usually react with cyanates to yield iminocarbonates the latter are generally proposed as intermediates in the polycyclotrimerization mechanism ... 

For PES4100P and PES5003P, the conversions at the cloud point were respectively 0.44 and 0.40 for Tx = 180 °C. Once again, we conclude that phase separation is unlikely to influence the polycyclotrimerization kinetics. 

Cross-linking involving cyclopolymerization or polycyclotrimerization of the aromatic nitrile in the precursor is accomplished by thermal curing as illustrated by the following reaction ... 

To analyse the phase separation process during reaction it is necessary to describe the distribution of oligomer species in the pre-gel stage. Assuming an ideal polycyclotrimerization [91-94], the distribution in the pre-gel stage may be described by the equation [95,96]... 

Thus, thermal and heat resistance, as well as physicomechanical and physicochemical properties of high-modulus and low-modulus polyurethane isocyanurates, synthesized by OEC and TDl polycyclotrimerization and migration MDC polymerization with diamine were studied. The influence of the ratio of these components on the mentioned properties is also studied. It is shown that polyurethane isocyanurates synthesized in the selective reactions of polycyclotrimerization and polymerization possess quite high physicomechanical and physicochemical properties. 

Scheme 9.10 Ru-catalyzed polycyclotrimerization of an ABP monomer as described by Liu ef al. [23]. (Copyright American Chemical Society 2009. Reproduced with permission.)...

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