Tertiary chlorine poly

As indicated previously, points of branching are also thought to feature in the degradation of poly(vinyl chloride). It was seen in Section 4.2.4. that branching which occurs during polymerization of vinyl chloride is likely to result in the formation of a tertiary chlorine atom. The high reactivity of tertiary chlorine in heterolytic reactions suggests that a branch point is a favourable site for unimolecular elimination. 

Two-step synthetic routes to poly(/i-aminoborazines) from /i-chloroborazines involve initial nucleophilic reaction of the /i-chloroborazine with appropriate linking reagents followed by a deamination reaction of the as-obtained /i-aminoborazine. The 5-tiichloroborazine undergoes nucleophilic attack by ammonia or amine derivatives on the boron atom linked to chlorine atoms. For the same reasons previously quoted a tertiary amine (e.g., Et3N) must be added to precipitate the corresponding hydrochloride. 

The block copolymerization involving 3-pinene has also been investigated [37]. This strategy involved the synthesis of a poly(pPIN) bearing tertiary chloride end groups and the attachment of poly(THF) blocks by their activation, as shown in Fig. 2.9 for chains with a single chlorinated site, thus giving a di-block structure. 

Commercially available poly(vinyl chloride) contains small amounts of different abnormal structures (defects) which may originate from synthesis. Such groups are random unsaturation (allylic chlorines) [316, 317,710,956,957] chain end groups [2, 3, 357, 710, 955, 1431, 2052] branch points (tertiary-bonded chlorine atoms) [2,3, 319, 357, 995,1514,2052-2054] head-to-head units [3,309,357,710] and oxidized structures [3,317,357,700]. It has been estimated that the number of defects per 1000 monomer units in commercial poly(vinyl chloride) samples are [357] 4-6 chloromethyl branches, 0.4-2.4 chloroethyl branches, 0.4-1.6 butyl branches (value uncertain), 0.18-2.4 long branches (value uncertain), 6-7 head-to-head structures (values uncertain), 1.4-3 total double bonds and 0.08-0.27 internal double bonds. Labile chloride atoms have been estimated at 0.6-2.5 per 1000 monomer units of which 0.5-2.5 are allylic chlorine or ketochloroallylic chlorine and 0.16-1.0 are chlorine at tertiary carbon (value uncertain). The possible structures of these defects are given in Table 3.12. 

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