Poly triad sequence distribution

A series of ethylene-vinyl chloride (E-V) copolymers was generated [27] by the reductive dechlorination of poly (vinyl chloride) (PVC) [28]. Each E-V copolymer has the same average chain length (approx. 1000 repeat units) and polydispersity. High-resolution solution NMR revealed [27] their random-like comonomer sequence distributions, which were quantitatively determined to the comonomer sequence triad-level (see chapter 2). E-V copolymers with less than 40% V units were observed [29] to crystallize, and the stabilities, structures and morphologies of their crystals were observed [29,30] and analyzed by DSC, X-ray and electron diffraction, and electron microscopy. 

Hz), is very close to that (190 Hz) determined for the CF carbon resonances of polydtFS, Since the CF carbon resonances of poly-aFS occur at 6 =92,1 and 6 =101 6 ppm and are not split appreciably by stereosequence effects, it seems that the CF carbon resonance patterns of the copolymers may be useful for sequence distribution measurements CF-carbon resonances of SSS and MSM triads should be observed at (6 =92.4 and 101.9 ppm) and (6 =94.3 and 103.2 ppm), respectively those associated with (MSS + SSM) triads should be observed in the vicinity of 6 =93 and 102,5 ppm. As can be seen in Figure 10, this seems to be the case for the copolymer containing 48 mole percent aFS the observed CF-carbon resonance pattern seems to be consistent with aFS triad fractions calculated for this sample, which are (SSM4MSS) > SSS" ... 

When polymerization of unsymmetrical monomers such as propylene occurs, addition can occur in a head-to-tail or a head-to-head shion to provide a variety of different structures. If two or more monomers are copolymerized, a variety of monomer sequences ((fyads, triads, tetrads, pentads, etc.) are possible as illustrated by the possible pentad monomer sequences for poly(l-chloro-l-fluoroethylene-co-isobulylene), (PCFEI), shown in Table 1. In general, it is possible to form copolymers having blodcs of monomers, a statistically random distribution of two monomers, and all possible compositional variations between these two extremes. In the example of PCFEI, it is possible to form pentads with five sequential E s, five sequential I s, and all permutations of E s and Fs between those extremes. The relative number of different monomer sequences provides information about the blockiness of the polymer, and is useful for determining the polymer s monomer composition. 

---