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In polymer chemistry, ring-opening polymerization (ROP) is a form of chain-growth polymerization, in which the terminal end of a polymer chain acts as a reactive center where further cyclic monomers can react by opening its ring system and form a longer polymer chain (see figure). The propagating center can be radical, anionic or cationic. Some cyclic monomers such as norbornene or cyclooctadiene can be polymerized to high molecular weight polymers by using metal catalysts. ROP continues to be the most versatile method of synthesis of major groups of biopolymers, particularly when they are required in quantity. The driving force for the ring-opening of cyclic monomers is via the relief of bond-angle strain or steric repulsions between atoms at the center of a ring. Thus, as is the case for other types of polymerization, the enthalpy change in ring-opening is negative. Cyclic monomers that are polymerized using ROP encompass a variety of structures, such as: *alkanes, alkenes, *compounds containing heteroatoms in the ring: * *oxygen: ethers, acetals, esters (lactones, lactides, and carbonates), and anhydrides, * *sulfur: polysulfur, sulfides and polysulfides, * *nitrogen: amines, amides (lactames), imides, N-carboxyanhydrides and 1,3-oxaza derivatives, * *phosphorus: phosphates, phosphonates, phosphites, phosphines and phosphazenes, * *silicon: siloxanes, silathers, carbosilanes and silanes. ==History== Ring-opening polymerization (ROP) has been used since the beginning of the 1900s in order to synthesize polymers. Synthesis of polypeptides which has the oldest history of ROP, dates back to the work in 1906 by Leuchs. Many years later came the method of the ROP of anhydro sugars, providing polysaccharides, including synthetic dextran, xanthan gum, welan gum, gellan gum, diutan gum, and pullulan. Mechanisms and thermodynamics of ring-opening polymerization was further established in the 1950s. The first high-molecular weight polymers (Mn up to 105) with a repeating unit were prepared by ROP as early as in 1976. Nowadays, ROP plays an important role in industry such as production of nylon-6. ROP can introduce functional groups such as ether, ester, amide, and carbonate into the polymer main chain, which cannot be achieved by vinyl polymerization affording polymers only with C-C main chain. Polymers obtained by ROP can be also prepared by polycondensation in most cases, but following controlled radical polymerization is possible in ROP, which is difficult in polycondensation. Recently, development of novel monomers and catalysts has enabled polymer chemists to control molecular weights, structure, and configuration of the polymers precisely. Cyclic carbonates undergo both cationic polymerization and anionic polymerization to afford the corresponding polycarbonates, which are expected as biocompatible and biodegradable polymers. Recently, ultra high molecular weight bisphenol A polycarbonate (> 2,000 kDa) has been synthesized by ROP of a large-membered bisphenol A-based cyclic carbonate. The resulted polymer can be used as engineering plastics due to its thermal stability and high impact resistance. When the reactive center of the propagating chain is a carbocation, the polymerization is called cationic ring-opening polymerization. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ring-opening polymerization」の詳細全文を読む スポンサード リンク
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