Zs. Fodor

The thermo-oxidative degradation of polyolefines—Part 10. Correlation between the formation of carboxyl groups and scission in the oxidation of polyethylene in the melt phase

Abstract Films of low density polyethylene have been degraded under an oxygen atmosphere at temperatures above the semicrystalline melting point. Time, conversion and temperature dependence of carboxyl group formation and chain scission have been studied. After induction periods we found linear dependences both in function of time and conversion. One third of absorbed oxygen forms carboxyl groups and the absorption of 3·57 mmol oxygen per monomer unit is needed for one chain scission. Maximum rates of carboxyl formation and chain scission have Arrhenius temperature dependence with 33·5 kcal/mole activation energy. The number of carboxyl groups and chain scissions are always practically the same; we assume that the isomerisation of secondary alkyl peroxy radicals simultaneously causes chain scission and carboxyl formation.

Polyisobutylene-containing block polymers by sequential monomer addition. IX: Poly(acenaphthylene-b-isobutylene-b-acenaphthylene)

Novel poly(acenaphtylene-b-isobutylene-b-acenaphtylene) (PAc-PIB-PAc) triblock copolymers exhibiting thermoplastic elastomer (TPE) properties have been prepared. The synthesis involved the addition of acenaphtylene (Ac) to living polyisobutylene dications (⊕PIB⊕) obtained by living isobutylene (IB) polymerization induced by the dicumyl methyl ether (DiCumOMe)/TiCl4 initiating system at-80°C. The triblocks contain very short polyacenaphtylene (PAc) blocks (Mn≈9,000) and consequently yield very soft, low modulus TPEs. Efforts to develop conditions for the living carbocationic polymerization (LC⊕Pzn) of Ac have failed.

Changes in molecular mass characteristics in the autooxidation of isotropic and oriented isotactic polypropylene films: Primary initiation of the kinetic chain

Autooxidation of polymers is accompanied by the destruction of the macromolecule, which leads finally to the deterioration of the polymer. In several publications1 − 7 it was pointed out that the autooxidation kinetics of isotropic isotactic polypropylene (isotropic IPP) differ considerably from those of the oriented material, the greatest difference being observed at the beginning of oxidation, the induction period of the latter being much longer than that of the former. With increasing degree of oxidation, the kinetic differences decrease or disappear. It was also pointed out2,3 that, at identical conversion, a greater proportion of initial strength remains in the oriented, than in the isotropic, samples and this proportion increases with the degree of stretching (λ). These data led to the conclusion that stretched macromolecules ‘resist’ destruction and oxidize more slowly than macromolecules having the compact conformation of the amorphous phase. These observations inspired the present work in which the oxidative destruction of macromolecules was directly followed, using the GPC method to investigate the change of the molecular mass distribution (MMD). The method was expected to yield information about the processes which take place during the induction period of IPP oxidation, during which the rate of oxygen uptake and the accumulation of product are too small to be followed by the usual methods. That is why the reason for the existence of the induction period has not been clarified so far in the uninhibited oxidation of the polyolefins. Any supplementary knowledge about the so far unexplored processes which take place during the induction period is essential in order to elucidate the nature of the phenomenon.

Quasiliving Carbocationic Polymerization. XVII. Synthesis Of Poly (Styrene-β-Isobutylene-β-Styrene)

Abstract Poly(styrene-b-isobutylene-b-styrene) has been synthesized by sequential carbocationic polymerization under quasiliving conditions at -90°C. The quasiliving synthesis was effected by first continuously and slowly condensing gaseous isobutylene (IB) to a bifunctional initiating system (p-dicumyl chloride/TiCl4) dissolved in a hexane-methylene chloride (60:40 v/v) mixture. After the quasiliving polyisobutylene (PIB) sequence had reached a desired molecular weight, styrene (St) was continuously and slowly added to produce the polystyrene (PSt) sequence. The products consisted of the target triblock. However, due to initiation by impurities and possibly to chain transfer to both IB and St, it also contained diblocks and small amounts of homopolymers. While the latter could be removed by selective fractionation, the triblocks and diblocks could not be separated. The mechanism of quasiliving polymerization leading to PIB/PSt blocks is discussed.

Thermo-Oxidation of Polyethylene Stabilized with Irganox 1010 and Tinuvin 622

Abstract Thermal oxidation of polyethylene stabilized with the mixture of Irganox 1010 and sterically hindered amine Tinuvin 622 confirmed that the occurrence of synergism or antagonism in the effect of sterically hindered amines towards antioxidants is concentration dependent. Provided that the concentration of phenolic antioxidant Irganox 1010 in polytheylene exceeds that of Tinuvin 622, synergism is observed at 185 and 190°C. Chemiluminescence, oxygen absorption method, nonisothermal differential scanning calorimetry (DSC) and differential thermal analysis (DTA) were used for testing of stabilizing efficiency of mixtures of stabilizers and the mutual correspondence of the results have been pointed out.

The effect of reaction conditions on LDPE oxidation

SummaryThe formation kinetics of functional groups and the kinetics of the molecular mass change were investigated in low density polyethylene oxidized under different conditions in static and dynamic equipments. The processes studied were found highly sensitive to the oxygen supply. With the increase of [O2] higher rate of oxidation and increasing fragmentation can be observed. If [O2] is reduced, crosslinking will dominate. Mechanical effect was significant only during the melting of the polymer. Under dynamic conditions, diffusion control was always found.

Changes of molecular weight in autooxidation of isotropic and oriented films of isotactic polypropylene

Abstract A trimolecular mechanism is postulated for the reaction of polypropylene with oxygen, which represents the first step initiating the kinetic chain of oxidation. Crosslinking of polypropylene observed experimentally in the initial stages of oxidation as well as the effects of polymer structure and of oxygen pressure are explained on this basis.