Ring-opening polymerization initiation

Rates of reaction (Rp) in ring opening polymerizations initiated by alkali metals are typically proportional to a fractional order of the initiator and close to first order in cyclosiloxane ... 

Ring-opening polymerizations initiated by anionic reagents... 

Setting of materials based on this chemistry set by ring-opening polymerization initiated by a three-component photoinitiator system consisting of camphorquinone. 

Figure 10.4 reports the MALDI-TOF mass spectrum of a PEG sample obtained by ring-opening polymerization (initiator potassium ethanolate, termination by ethanol). " The comparison between the values for M and M ... 

Burd, C., and Week, M. 2005. Self-sorting in polymers. Macromolecules 38 7225-7230. Celiz, A. D., and Scherman, O. A. 2008. Controlled ring-opening polymerization initiated via self-complementary hydrogen-bonding units. Macromolecules 41 4115-4119. 

Scheme 3. Synthesis of optically enriched substituted e-caprolactones by ring opening polymerization initiated by Sn(Oct)2.

Fig. 1 Synthetic approaches towards peptoids by either (a) solid-phase submonomer synthesis or (b-d) ring-opening polymerization initiated by nucleophiles such as (b) amines in solution, (c) amines on solid-phase resins, or (d) IV-heterocyclic carbenes in solution...

The key initiation step in cationic polymerization of alkenes is the formation of a carbocationic intermediate, which can then interact with excess monomer to start propagation. We studied in some detail the initiation of cationic polymerization under superacidic, stable ion conditions. Carbocations also play a key role, as I found not only in the acid-catalyzed polymerization of alkenes but also in the polycondensation of arenes as well as in the ring opening polymerization of cyclic ethers, sulfides, and nitrogen compounds. Superacidic oxidative condensation of alkanes can even be achieved, including that of methane, as can the co-condensation of alkanes and alkenes. 

One product is poly(2-ethyl-2-oxa2oline) (PEOX). It is prepared by the ring-opening polymerization of 2-ethyl-2-oxazoline (19) with a cationic initiator (48) (eq. 6). 

Nylon-6 is the polyamide formed by the ring-opening polymerization of S-caprolactam. The polymerization of S-caprolactam can be initiated by acids, bases, or water. Hydrolytic polymerization initiated by water is often used in industry. The polymerization is carried out commercially in both batch and continuous processes by heating the monomer in the presence of 5—10% water to temperatures of 250—280°C for periods of 12 to more than 24 h. The chemistry of the polymerization is shown by the following reaction sequence. 

Fig. 9. Initiation of epoxy cure. Irradiation of a triaryl sulfonium salt produces a radical cation that reacts with an organic substrate RH to produce a cation capable of releasing a proton. The proton initiates ring-opening polymerization. X = BF , PFg, AsFg, and SgFg. ...

The cationic ring opening polymerization of oxolane (THF) or of N-substituted aziridines can be initiated by oxocarbenium salts [42]. The methacrylic ester unsaturation is insensitive to cationic sites, and polyoxolanes (poly-THF) macromonomers are obtained in good yields. 

The use of an unsaturated anionic initiator—such as potassium p-vinyl benzoxide—is possible for the ring opening polymerization of oxirane [43]. Although initiation is generally heterogenous, the polymers exhibit the molecular weight expected and a low polydispersity. In this case, the styrene type unsaturation at chain end cannot get involved in the process, as the propagating sites are oxanions. 

By means of a ring-opening polymerization of the condensation type Vlasov et al. [50] synthesized polypeptide based MAIs with azo groups in the polymeric backbone. The method is based on the reaction of a hydracide derivative of AIBN and a N-carboxy anhydride. Containing one central azo group in the polymer main chain, the polymeric azo initiator was used for initiating block copolymerizations of styrene and various methacrylamides. 

Intramolecular rearrangement of the initially formed radical may occur occasionally (e.g. backbiting - Section 4.4.3) or even be the dominant pathway (e.g. cyelopolymerization - Section 4.4.1, ring-opening polymerization - Section 4.4.2). These pathways can give rise to branches, rings, or internal unsaturation in the polymer chain. 

Commercial end functional polymers have been converted to alkoxyamincs and used to prepare PKO-Worri-PS.040 The hydroxyl group of alkoxyamine 284 was used to initiate ring-opening polymerization of caprolactonc catalyzed by aluminum tris(isopropoxide) and the product subsequently was used to initiate S polymerization by NMP thus forming polycaprolactone-Wodr- P8.641 The alternate strategy of forming PS by NMP and using the hydroxyl chain end of the product to initiate polymerization of caprolactonc was also used. 

Yamashita, Y. Random and Black Copolymers by Ring-Opening Polymerization. Vol. 28, pp. 1-46. Yamazaki, N. Electrolytically Initiated Polymerization. Vol. 6, pp. 377-400. 

The preparation of poly( -caprolactone) given below is a bulk ring-opening polymerization of -caprolactone initiated by Ti(OBu)4 in the presence of... 

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