Cyclic polymers radical polymerization

The double bond of maleic anhydride may undergo free radical polymerization with the proper initiator. Polymers of maleic anhydride (or copolymers made with another monomer) are commercially available (Polysciences). They consist of a linear hydrocarbon backbone (formed from the polymerization of the vinyl groups) with cyclic anhydrides repeating along the chain. Such polymers are highly reactive toward amine-containing molecules. 

The importance of intramolecular cyclization was emphasized when Butler and coworkers found that the radical polymerization of N, N, N, /V-diallyldimethylammonium chloride (DADMAC) gave soluble, uncrosslinked polymers with little or no unsaturation (Eq. 6-101) [Butler and Angelo, 1957 Butler and Ingley, 1951 Wandrey et al., 1999]. There is a very low tendency for radical IV to propagate intermolecularly and undergo crosslinking. The predominant reaction is intramolecular cyclization, and the product is a linear product with cyclic structures in the backbone. The reaction is referred to as alternating intra/intermolecular polymerization or cyclopolymerization. 

The most important feature of ionizing radiations is, as the term implies, ionization to give ionic intermediates in irradiated systems. Though radiation-induced radical polymerization had long been studied, it is only a decade since radiation-induced ionic polymerization was first found. In 1957, Davison et al. obtained polymer from isobutene, which is known not to be polymerized by radical catalysts, by irradiating at low temperature with y-rays (7). Before long, the radiation-induced polymerization of styrene was proved to proceed as an ionic mechanism in suitable solvents (2,3,4). Since these pioneering researches, the study of the chemical kinetics of radiation-induced ionic polymerization has been extended to several vinyl, diene and cyclic monomers. 

MALDI-TOF mass spectrometry analysis of poly(methyl acrylate) prepared by the free-radical polymerization of methyl acrylate (MA) in the presence of a cyclic dixanthate under y-ray irradiation revealed that there are at least three distributions, i.e., molecular mass for [ 1-(MA) -H]+ of cyclic polymers, [1-(MA) -THF-H]+, and [1-(MA) -(THF)2-H]+ of linear polymers were observed. The relative content of the cyclic polymers markedly increases at a lower temperature, which may be related to the reduced diffusion rate and the suppressed chain-transfer reaction at the low reaction temperature [39]. 

The above examples of free-radical ring-opening polymerization, which have been explored by Bailey and Endo, produce polymers containing ketonic carbonyl and/or ester groups in the main chain. In addition, these cyclic monomers can be copolymerized with vinyl monomers by free-radical mechanism. Thus, the variety of the polymers produced by radical polymerization has been enlarged. 

The versatility associated with nitroxide-mediated polymerizations, in terms of both monomer choice and initiator structure, also permits a wide variety of other complex macromolecular structures to be prepared. Sherrington201 and Fukuda202 have examined the preparation of branched and cross-linked structures by nitroxide-mediated processes, significantly the living nature of the polymerization permits subtlety different structures to be obtained when compared to traditional free radical processes. In addition, a versatile approach to cyclic polymers has been developed by Hemery203 that relies on the synthesis of nonsymmetrical telechelic macromolecules followed by cyclization of the mutually reactive chain ends. In a similar approach, Chaumont has prepared well-defined polymer networks by the cross-linking of telechelic macromolecules prepared by nitroxide-mediated processes with bifunctional small molecules.204... 

Cationic and radical polymerizations of norbornene yield only low molecular weight oligomers [169,170]. Ring-opening metathesis polymerization (ROMP) of strained cyclic olefins was first reported in the 1950s [171] and is of industrial importance. Attempts were made to prepare 193 nm resist polymer by ROMP of functionalized norbornenes and tetracyclododecenes (Fig. 75) [168,251]. Hydrogenation of the unsaturated backbone was necessary to afford ther-mooxidative stability and to reduce OD at 193 nm. Use of tetracyclododecene... 

The third platform of resists for ArF lithography is the ester-protected acrylate/ah-cyclic polymer hybrid platform (XLII), which was pioneered at BeU labs. The polymerization route to polymers of this platform is free radical copolymerization... 

---