- Ring-opening polymerization
polymer chemistry, ring-opening polymerization is a form of addition polymerization, in which the terminal end of a polymer acts as a reactive center, where further cyclic monomers join to form a larger polymer chain through ionic propagation. The treatment of some cyclic compounds with catalysts brings about cleavage of the ring followed by polymerization to yield high-molecular-weight polymers. Exemplary polymers produced by this method include Nylon 6and polyethylene oxide.
When the reactive center of the propagating chain is a
carbocationthe polymerization is called cationic ring-opening polymerization and when the active center is a carbanionthe reaction is an anionic ring-opening polymerization.
A different type of ring-opening polymerization, based on
olefin metathesis, uses catalysts rather than cationic or anionic propagation.
One example of an anionic ring-opening polymerization is the
living polymerizationof the aziridineN-"methanesulfonyl-2-methylaziridine" with the sulfonamide "N-benzyl methanesulfonamide" (1) and potassium hexamethyldisilazide(2)(Fig. 1) ["Living Ring-Opening Polymerization of N-Sulfonylaziridines: Synthesis of High Molecular Weight Linear Polyamines" Ian C. Stewart, Cameron C. Lee, Robert G. Bergman, and F. Dean Toste J. Am. Chem. Soc.; 2005; 127(50) pp 17616 - 17617; (Communication) DOI: 10.1021/ja0554357 [http://pubs3.acs.org/acs/journals/doilookup?in_doi=10.1021/ja0554357 Abstract] [http://www.cchem.berkeley.edu/~toste/publications/ianasap.pdf Article link] ] . The disilazide actives the anionic initiatorby proton exchange which reacts in chain initiationwith an aziridine monomerin a ring-opening reaction (DMF, 40°C). In the chain propagationstep the negatively charged end of the growing polymer chain continues to react with monomeruntil it is depleted. The reaction is chain terminated when methanolis added and the active chain end is destroyed. The polymerization is considered living because the polydispersityis low and no evidence is found of branching. In this particular concept the sulfonylgroups can be removed by organic reductionwith naphthalene(7), lithiummetal and methanolto the free polyamine8. This procedure offers an alternative to a cationic ring-opening polymerization of oxazolines with anionicinitiators and subsequent acid hydrolysisof the acylgroups.
Ring opening metathesis polymerization
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