K.S. Minsker

Correlations between the chemical structure and the thermal stability of polyvinylchloride. A review

The main ideas about the new theory of PVC decomposition are described; they tackle such key questions as the chemical structure and the contents of anomalous groupings in the PVC, their effects on the thermal stability of the products, and the kinetics of HCl elimination. In contrast with the generally accepted β-allyl chloride activation of the PVC decomposition was developed the concept of oxygen-containing groups having the structure ∼C(O)CHCHCHCl∼ playing a decisive part. Real PVC macromolecules have been shown to contain 10−4 mole per base-mole of PVC of the latter, which are the cause of the low thermal stability. The purity of the monomer, the presence of oxygen in the reaction zone, the polymerization temperature, and other factors have been established to have a significant influence on the content of the ∼C(O)CHCHCHCl∼ groups in PVC.

Rapid method for determining molecular characteristics of polyisobutylene

Abstract Results are given of determining molecular characteristics of polyisobutylene using a combination of a liquid chromatograph and a double bond analyser (ADS-4). The possibilities offered by the method are compared with those well known for determining MW and MWD of polyisobutylene.

Polymerization of ethylene in the presence of alkoxy-(aroxy)titanium trichlorides and tri-isobutylaluminium☆

Abstract In polymerization of ethylene in the presence of alkoxy-(aroxy)titanium trichloride-tri-isobutylaluminium catalytic systems, the introduction of the RO-groups in the Ti 4+ compound has the effect of causing rapid stabilization of the active centres and the appearance of a long period of polymerization, at a constant rate with the simple kinetic relationship w pol = k p ·[catalyst]·[C 2 H 4 ]. The catalytic activity of the systems is dependent on the nature of the RO substitunt in the ROTiCl 3 : : p -BrC 6 H 4 O>C 6 H 5 O>C 12 H 25 O>C 4 H 9 O. The ROTiCl 3 R 3 Al catalytic systems have a number of characteristic properties, from which the conclusion may be drawn that the RO groups function as “micro-carriers” of active centres.

Photochemical degradation of polyvinylchloride

Abstract Fresh light has been thrown on some novel features of the photochemical degradation of PVC. Crosslinking of the macromolecules and the formation of chromophore groups in PVC as well as the total interaction of thermostabilizers with HCl, leading to a major change in the mechanical properties of the material, do not take place in the entire volume of the material, but only in thin (up to 0·005 cm) surface layers on the side exposed to irradiation. Highly effective stabilization of PVC towards the action of UV light is obtainable by increased protection of the surface of PVC materials by means of thermostabilizers that are HCl acceptors.

Conversions of structural groups during the degradation of vinylchloride and vinylacetate polymers

Abstract Industrial and laboratory samples of PVC and PVA contain 5 × 10 −3 mole/mole polymer of unsaturated end groups, however, PVA, unlike PVC is practically free from internal 〉C=C〈 bonds. It was established that at the initial stages overall-deacetylation of PVA only takes place as a result of statistical elimination of CH 3 COOH from macromolecules. During thermal degradation of PVC structural groups undergo conversion to form polyconjugated sequences. Statistical elimination of CH 3 COOH from PVA, in the same way as that of HCl from PVC k s = 0·8 × 10 −7 sec −1 , 175°) is independent of the type of polymer sample and takes place with a rate constant of k s = 0·7 × 10 −8 sec −1 (175°). Crosslinking of PVA macromolecules, in contrast with PVC, occurs readily at the initial stages of polymer degradation, when no long polyene sequences are formed and occurs by mechanisms different from those of PVC: the process takes place as the result of terminal and internal 〉C=C〈 bonds formed by thermal degradation of the polymer, or as the result of intermolecular deacetylation, etc.

The degradation of polyvinyl chloride in presence of phosphorus-containing plasticizers☆

Abstract The introduction of plasticizers based on orthophosphoric acid esters into PVC significantly changes the thermal and thermo-oxidative degradation processes occuring in the polymer, consisting in HCl elimination, and formation of a conjugated double bond system and of statistical, isolated, C=C double bonds. Phosphate plasticizers intensify the thermal decay of PVC. The thermo-oxidative degradation may be retarded or on the other hand, substantially accelerated by phosphates. The process kinetics are determined by the nature and amount of plasticizer in the polymer composition and also by the decomposition products. As a result, the efficiency of metal-containing thermostabilizer-HCl acceptors and antioxidant-stabilizers is determined to an appreciable extent by the nature of the phosphate plasticizer being used.

Ziegler-Natta catalysts and the reactive centres composition during the stereospecific polymerization of α-olefins

The chemisorption of (CH3)2AlCl on the crystal surfaces of the α- and β-modifications of TiCl3 have been calculated by the “atom-atom” potentials method. The reactive centres were found to have the same composition for 80% α-TiCl3 and 30% β-TiCl3; their amounts diminished when the temperature was raised. These results agree with those given in the literature about the yields of stereospecific α-olefin polymers over the catalytic systems containing the α- and β-forms of TiCl3.

Reaction of alkylaluminum chlorides with water

1. In the reaction of (C2H5)2AlCl and C2H5AlCl2 with water (1∶1 molar ratio) under mild conditions, donor-acceptor complexes are formed, in which the water molecule is coordinated by the aluminum atom. Sesquiethylaluminum chloride in its reaction with water behaves as a mixture of monochloro and dichloro derivatives. 2. Benzene and toluene increase the tendency of ethylaluminum chlorides towards hydrolysis and, in the case of C2H5AlCl2 the Al-Cl2 and Al-C bonds are cleaved, whereas only the Al-C bond is cleaved in (C2H5)AlCl. 3. The reaction of (C2H5)2AlCl and C2H5AlCl2 with water in diethyl ether is accompanied by the hydrolysis of Al-C bonds and leads to the etherates of the corresponding alumoxanes. 4. The donor-acceptor complexes obtained are modified Lewis acids. The low acidity of these complexes explains their selectivity in electrophillc reactions.

Stabilization of polyvinyl chloride using epoxide compounds

Abstract It was shown that the addition of epoxide compounds (EC) to PVC containing an inert heat stabilizer (Ba, Ca or Na stearates) reduces the rate of separation of HCl from PVC macromolecules. Dehydrochlorination of PVC in the presence of EC is only inhibited as a result of the formation of polyconjugated systems, the rate of statistical separation of HCl remaining constant. During the breakdown of PVC by the action of heat in a mixture with EC the oxyrane ring reacts with ketochlorallyl groups (KCAG) of polymer macromolecules with the formation of a 1,3-dioxalane group, which does not affect the heat stability of the polymer. A reduction in the rate of HCl liberation during the breakdown of PVC stabilized by EC in solid phase in the presence of Ba, Ca or Na stearates is due to complex formation between EC and KCAG of polymer macrochains.

On the nature of the activity of the systems C2H5AlCl2-alcohol in the cationic polymerization of olefins☆

A study has been made of some physico-chemical properties and of the activity of the systems C2H5AlCl2-alcohol in isobutylene polymerization (transformation of isobutylene models). A quantum chemical calculation has been carried out for some models of active centres in these systems. The calculated data agree with the experimental results, which points to the carbocationic activity of alcohol.