Cyclic polymers functionalized linear precursors

A cyclic polydimethylsiloxane was also prepared by the end-to-end reaction, i.e., a,ft)-dianion-functionalized polymers, which are then cyclized simply by reaction with a difunctional electrophile to give a cyclic polymer. The cyclic polydimethylsiloxane was synthesized from a commercially available o. tw-dihydroxy-polydimethylsiloxane (M = 2.460 g/mol). The Unear precursor was deprotonated using sodium hydride in dilute THF (< 10 2 M) and then end-coupled using a dichlorosilane coupUng agent (Fig. 53). The uncy-clized anionic linear precursors are then removed by a macroporous anion exchange resin. The successful cyclization and purification is monitored by IR and 29Si NMR, GPC, and MALDI-TOF mass [176],... 

The unimolecular homodifunctional approach involves the coupling of identical functionalities on opposite ends of the same polymer chain. The linear precursors for this unimolecular approaches are very accessible synthetically, because of the numerous polymerization methods from bis-functional initiators that allow termination of opposite chain ends with identical functional groups. However, the practical application of this route is limited by the paucity of homocoupling reactions that are efficient enough to enable the generation of high-purity cyclic polymers. 

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... 

Narrow-polydispersity cydic poly(caprolactone) was synthesized by cyclization of linear precursors prepared via ring-opening polymerization bom an azido-functionalized initiator, followed by end-group modification to attach a terminal alkyne. Click coupling afforded the cyclic polymer in high... 

The Huisgen click cycloaddition reaction has been explored for the cyclization of linear poly(styrene) precursors prepared by ATRP. Using an optimized slow, continuous addition technique, nearly quantitative yields of the cyclic polymer can be achieved without the need for fractionation or further purification. The versatility of ATRP provides extremely well defined linear precursors and enables the incorporation of diverse functionality. As a demonstration of this versatility, acetoxystyrene was polymerized, cyclized, and hydrolyzed to yield macrocylic poly(hyroxystyrene). This cyclic polymer is extremely useful as the phenols on each repeat unit can be easily modified to incorporate further functionality, such as the quantitative esterification described. We are currently investigating the attachment of bifurcated... 

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