Synthesis of Cyclic Polymers

Furthermore, Kricheldorf made the following statement All step-growth polymerizations possess the fundamental tendency to yield cycles as stable end products with linear chains being the reactive intermediates or end products of side reaction [183]. 

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The catalyst Cl2Ru(PCy3)2(=CHCH=CPh2), c.f., Figure 1.8, is obtained in a yield of 88%. In the same way, catalysts, where the metal atom is in a ring, can be synthesized. This type of catalysts is suitable for the synthesis of cyclic polymers (26). The synthesis route is shown in Figure 1.9. 

Synthesis of Cyclic Polymers Using Addition Polymerization. 126... 

Synthesis of Cyclic Polymers by Ring-Opening Polymerizations. 154... 

Fig. 5 Synthesis of cyclic polymer using polymerization of styrene with cyclic initiator...

Fig. 33 Synthesis of cyclic polymer by ring closure methasesis...

Many works on the synthesis of cyclic polymers and block copolymers using kinetically controlled ring-expansion polymerizations of cyclic monomers, such as lactones and lactides with various types of cyclic tin initiators, were reviewed by Kricheldorf [147,148]. Kricheldorfs group continued the synthesis of cyclic polymers, and their recent works have focused on the following. Polycondensations of 4,4/-difluorodiphenylsulfone with tris(4-hydroxy phenyl)ethane were performed in DMSO to give multi-cyclic poly(ether sulfone)s derived from tris(4-hydroxyphenyl)ethane [149]. 

A similar solid state method for the preparation of cyclic polymer has been reported. This method involves the synthesis of cyclic polymer obtained by a combination of inter-alkylation and intra-alkylation, i.e., cyclization of 11-bromo-decanoic acid. The cyclic polymer can be liberated from an anionic exchange resin. Thus, this method has the advantage that the cyclic product from the mixture after reaction is easily produced, as indicated in Fig. 50 [161]. 

Many different linking agents and functional groups have been proposed for the synthesis of cyclic polymers using homodifunctional groups. However, the general strategy followed by most authors is similar and can be outlined as follows ... 

Scheme 12.12 Early example of the synthesis of cyclic polymers using the insertion of /S-butyrolactone into cyclic tin initiator [50].

The synthesis and the study of intrinsic properties of well-defined cyclic synthetic polymers are still a challenge in polymer science. Approaches for their preparation were first concentrated on polymers exhibiting linear ring-chain equilibria. This corresponds to polymers containing functional groups in their backbone chain such as poly(dimethylsilox-anes) (PDMSs), polyethers, polyesters, and so forth. The synthesis of cyclic polymers from carbon-carbon chains free... 

One of the most widely used methods for the synthesis of cyclic polymers of controlled size and narrow dispersity is based on the end-to-end chain coupling of a,co-difunctional linear polymer precursors in highly dilute reaction conditions. This method offers a series of significant advantages it may be used both for polymers with in-chain reactive functions and for systems having no functional groups in their backbone such as saturated carbon-carbon bond polymers. The absence of potentially... 

In 2005, Laurent and Grayson successfully achieved synthesis of cyclic polymers through ring closure by taking advantage of CuAAC as the coupling chemistry. Starting from... 

Kudo, H., Makino, S., Kameyama, A., and Nishikubo, T. (2005) Synthesis of cyclic polymers ring-expansion reaction of cyclic S-dithioester with thiiranes. Macromolecules, 38,5964-5969. 

In the next section, we will first discuss synthesis of the linear polymer precursors with homodifunctional or heterodifunctional groups, and second, we will discuss the synthesis of cyclic polymers via a ring-closure reaction. 

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