Ring-scission polymerization

The kinetics of this type of polymerization are the same as for simple condensation for this reason, the use of the term polycondensation is perhaps more appropriate. Unless kinetic evidence suggests otherwise, polymerizations involving the formation of chain polymers from cyclic compounds, following ring scission, are classed as condensation polymerizations. Some important con-... 

A methylaluminum diphenolate such as 3e also exhibits an accelerating effect on the polymerization of P-lactone, and the extent of acceleration depends on the mode of the ring scission. For example, in the polymerization of P-butyrol-actone (p-BL, 300 equiv) initiated with 1 (X=Cl) in CH2CI2 at room temperature, the addition of 3e (1 equiv) brought about a 2-times acceleration (Fig. 47, ). The Mn (5100 [Mw/Mn=l.l] at 22% conversion 288 h) of the polymer formed in the absence of 3e and that (15,600 [Mw/Mn=1.2] at 57% conversion 384 h) of the polymer obtained in the presence of 3e were close to the expected values (5700 and 14,700, respectively) from the initial P-BL-to-1 (X=C1) mole ratio and the monomer conversion by assuming that every molecule of 1 produced one polymer molecule. In contrast, the polymerization initiated with... 

Anionic polymerization. For some heterocyclic monomers the unique chemical structure of the growing species follows unequivocally from the monomer structure. However, in many cases isomeric structures have to be taken into account. For instance, for symmetrical monomers, like thietane, the carbanion but not the thiolate anion was proposed (4). Unsymmetrically substituted monomers can provide active species by a- or B- ring scission. Unusual structure of activated monomer was proposed for NCA and lactams. These structures can not be distinguished by spectrophotometric methods, and application of H- or 13C-NMR looks more promising. 

Ring-type monomers such as cyclic ethers, lactams, and lactones can be polymerized via ring scission reactions to high-molecular-weight polymers. 

This cyclic compound can then undergo a ring-scission polymerization, in which the polymer is formed without splitting out a small molecule (e.g., water), because the small molecule had been eliminated previously in the cyclization step. 

A tetrafunctional telechelic polymer (possessing reactive end groups see Section 4.5) is made by ring scission polymerization of propylene oxide (PO) on pentaerythritol (PE). 

Ring-scission polymerization of norbornene (1,3-cyclopentylenevinylene) prodnces a rubber, polynorbornene, that was introdnced in 1976 in France and has since been offered in other conntries. The monomer norbornene is made by the Diels-Alder condensation of ethylene with cyclopentadiene ... 

A variety of aliphatic polyesters of molecular weight near 1000 are made with terminal hydroxyl groups to form the basis for urethane polymers. A ring-scission polymerization has been used for one such material (Table 17.1). A product that is less likely to crystallize on aging can be made if a copolymer of a-methyl caprolac-tone and caprolactone is made. Some commercially important polyesters produced by plants and animals are discussed in Chapter 15. 

Although polymers with the —P=N— backbone were produced as long ago as the 1890s by ring-scission polymerization of (NPCljls, moisture hydrolyzes the polymer to a brittle material. 

Why are most of the new thermoplastics with high heat distortion tan-peratures heterochain polymers rather than carbon chain polymers Why is not ring-scission polymerization used more often for them ... 

These ring opening reactions proceed via Si-C (or in the latter case, Si-Si) bond scission. Another type of ring-opening polymerization involves C=C bond scission (eq. 12) [52]. 

NMR studies on the alkoxide initiators confirm that all the lactones polymerize via an acyl— oxygen scission, including /3-PL (which, by contrast, opens at the alkyl—oxygen bond with (251)). Monomer coordination and subsequent ring opening may be observed by 111 NMR spectroscopy. Coordination is also observed with 7-BL and 7-VL, although these adducts are stable to insertion and polymerization does not proceed. 

It is believed that polymerization occurs via a chain polymerization where ring opening occurs via complete scission of the carbon-carbon double bond through the reaction with metal carbene precursors giving an active carbene species (structure 5.60). 

---