Chemical and molecular structure of poly(vinyl chloride)

Abstract

Poly(vinyl chloride) presents a number of detects er 1,OO monomer units (m.u.), as follows: 4 — 6 ch].oromethy]. branches; 0.4 2.4 chioroethyl branches; 0.4 — 1.6 bu— tyl branches (uncertain value); 0.18 2.4 long branches (un. certain value); 6 7 head—t.o.head structures (uncertain va lue) ; 1.4 3 total double bonds ; 0.07 — 0.27 internal double bonds. The structure of internal unsaturation as allylic and ketochloroallylic chlorides is discussed. Labile chlorine atoms, 0.6 2.5 per 1,000 monomer units, were found, from which: 0.5 2.5 allylic chlOrine (CiA) or ketochioroallylic chlorine (C1COA) and 0.16 1 chlorine at tertiary carbon (C1T) (uncertain value). A general mechanism is proposed which explains the formation of unsaturated groups found in NMR and 13C NMR spectra. During polymerization some de'fects can undergo further transformations. The chlorination process of poly(vin.yl chloride) involves partially the chlorine addition reaction to the intermediary formed double bond. Raman spectroscopy supplies comparative data with NMR and lB regarding the chain configuration. Rotation isomery and its consequences upon the reactions of the poly(vinyl chloride) in solide state are discussed. This paper presents the main worldwide progresses which have been made since the last International Symposium on PVC in Lyon (1976), towards the elucidation of the chemical and molecular structure of this polymer. Branchin In 1977 it seemed that with the works published by Rigo (1) Abbas (2) and Bovey (3), the branching problem has been elucidated, as it was established that the preponderent structure of branchings is of chlorometh.yl type, .CH2-CHC]...CH(CH2C1)—CH2—. This structure is repeated on the rnacromoleculer chain with a frequency of 5 branches per 1,000 monomer units (5/1,000 m. u.) along with a low frequency of long branches, about 0.5/1,000 m.u. (Ref.4). The main direct data were based on 13C NMR measurements on PVC reduced with lithium aluminum hydride (LiA1H4). Analysing by gas chromatography the products formed as a result of the T—ra— diolysis of polyethylene obtined by LiA1H4 reduction of PVC, SchrSder and Byrdy (5 & 6) reported that in emulsion polymerization intramolecular 1,5 transfer leading to the formation of butyl branches is more pronounced than in bulk or suspension polymerization, and this fact could explain the higher concentration of butane found in the radiolysis products. Later on Starnes (7) demonstrated that the reduction with LiA1H4 presents serious disadvantages caused by the incomplete removal of chlorine, by the lack of reproductibility and side reactions leading to supplementary double bonds, as well as by the appearance of some 13C NMR signa's of unknown o— rigin. A NS2 mechanism was proposed, in which the reaction rate of different chain segments is not equal. Monade CHC1 group reacts 3.8 times faster with LiA1}14 than r-dyade CHC1 group. This behaviour was explained by the diffe—