F. Tüdős

Study of the thermal oxidation of polyolefines—IX: Some differences in the oxidation of polyethylene and polypropylene

Abstract In the thermal oxidations of polyethylene (PE) and polypropylene (PP), both similarities and differences are found. In the initial stage, the ratio of the hydroperoxide formed and the amount of oxygen absorbed is independent of both the nature of the polymer and the actual reaction conditions. With increased conversion, however, this ratio decreases to a greater extent in the case of PE than for PP. Most of the carbonyl groups formed in the PE chain during oxidation are ketones and carboxyls, but in PP there are also carbonyls with different structure. The amount of carbonyl groups in PE is approximately 1.5 times that observed for PP. The number of scissions involving considerable molecular weight decrease is higher for PE than for PP: for identical conversions, the ratio of scissions is S PE / S PP ∼ 6.

Polymer degradation by elimination—I. Thermal degradation of poly(vinyl chloride) and kinetic treatment of the process

Abstract The kinetics of the overall process of the thermal degradation of dissolved poly(vinyl chloride), taking place under oxygen-free conditions, have been studied. On the basis of the experimental data concerning dehydrochlorination and polyene formation, it has been supposed that the overall thermal degradation process consists of a special chain ( zip -) reaction. The initiating step of this reaction is the random decomposition of the monomeric units. The chain propagation consists of series of allyl activated decomposition steps resulting in the formation of conjugated double bonds. The small kinetic chain length is, however, the consequence either of the existence of special polymer sequences along which degradation can proceed, or the possibility of a reaction step interrupting the propagation of activation. The kinetic treatment of the process has been accomplished, based on the assumption of special polymer sequences. Relationships have been obtained concerning the conversion of dehydrochlorination, as well as the concentration and length distribution of polyenes. The calculated results are in good agreement with the experimental data; the real physical and chemical significance of the probability factor appearing in these results has not yet been decided.

Study of the thermal oxidation of polyolefines—VIII: Volatile products of polypropylene thermal oxidation

Abstract In the oxidation of isotactic polypropylene, qualitative and quantitative studies were made of organic volatile products by gas chromatographic methods. Experimental results and further data have been compared. Most of the products formed during degradation are acetone, and other ketones and aldehydes. Propylene, acetic acid and 2.4-dimethyl furane have also been identified. The products are formed in an accelerating kinetic process. There was linear relationship between the volatile products measured and the amount of oxygen consumption: approximately 2% of the oxygen absorbed is built into low molecular weight organic carbonyl compounds.

Kinetics of copolymerization—II. Kinetic investigation of the polymerization of methyl acrylate in solution☆

Abstract The kinetics of methyl acrylate polymerization initiated by azobisisobutyronitrile were investigated in dimethylformamide at 40–60. The polymerization was 1/2 order with respect to initiator; the rate of initiation was independent of the initial concentration of monomer. The rate and the overall rate constant of polymerization strongly depend on the medium: the overall rate constant decreases with increase of solvent concentration. The solvent dependence of overall rate constant can adequately be described by the hot radical theory.

Study of the thermal oxidation of polyolefins—III: Pressure and temperature dependence of the rate of oxygen absorption☆

Abstract The kinetics of oxygen absorption by high pressure polyethylene (PE) have been studied between 8 and 650 torr oxygen pressure and in the temperature range 140 to 180°. The mechanism of thermal oxidation has been described and the equation for the rate of oxygen absorption has been derived. The rate equation has been studied in the initial stage and at points of the maximum rate of oxygen absorption. Some rate constant combinations (characteristic of the process) and their temperature dependence have been determined from experimental data. The pressure dependence of the initial and maximum rates of oxygen absorption, in the pressure range investigated, is well described by the proposed mechanism.

Investigation of the effect of nitroso compounds on free radical polymerization

Abstract A study was made on the effects of nitroso compounds on the free radical polymerizations of styrene and methyl methacrylate. Kinetic investigations showed that the aromatic C-nitroso compounds are such strong inhibitors of free radical polymerization that relative reactivity cannot be evaluated by the usual way. In a polymerization system containing initiator, vinyl compound and nitroso compound, two main reaction-paths for the nitroso compounds are to be considered, viz. 1. a. free radical addition to the −NO group; 2. b. direct interaction between the nitroso and vinyl compounds. On the basis of the derived kinetic relationship, the investigated aromatic C-nitroso compounds can be divided into two main groups, viz. 1. 1. p -nitroso aniline and its N-substituted derivatives; 2. 2. other substituted derivatives of nitroso-benzene.

Investigation of decomposition of azoisobutyronitrile in the melt and in the solid state

Abstract An investigation has been made of the decomposition of solid and molten azoisobutyronitrile (AIBN). Below the melting point, the decomposition is first very slow; then a brief period of autocatalysis is followed by a gradual reduction in rate; when melting occurs, acceleration occurs again as the proportion of molten material increases. It appears that there is a crystal-form of AIBN favourable for decomposition; the rate for this form is considerably greater than for AIBN in solution. It is proposed that there is an energy-chain decomposition in which there is transfer of energy from excited tetramethylsuccinodinitrile to a neighbouring molecule of AIBN.

Polymer degradation by elimination—III. The probability—theoretical treatment of the elimination assuming a reaction step interrupting the propagation of activation

Abstract The probability—theoretical treatment of the model formed for the interpretation of the thermal degradation of poly(vinyl chloride) has been accomplished. Chain termination is assumed to occur by a reaction step interrupting the propagation of activation. The discussion has been performed both without limitations to the values of the rate constants, and in the simplified case supposing β ⪢ α . It has been found, that the alternative formulation of the chain termination led to the same results; the good agreement of these with the experimental data supports the assumptions of the model; it does not solve, however, the problem of the real physical and chemical significance of the probability factor appearing in the results. The treatment is to be applied also for other polymers degrading by elimination, as well as for certain polymer-analogous reactions.

The kinetics of radical polymerization—XXVII. Investigation of the radical reactivity of 3,3′- and 4,4′-disubstituted azobenzenes in the polymerization of vinylacetate

Abstract A study was made on the inhibition by some 3,3′- and 4,4′-disubstituted azobenzenes of the polymerization of vinylacetate initiated by azoisobutyronitrile at 50°. The inhibitory effects of these substances can be attributed to their ability to engage in radical addition giving a less reactive hydrazyl type radical. The mechanism of the inhibition has been established by ESR and kinetic (stoichiometric) measurements. The value of k 5 / k 2 (characteristic of the reactivity of an inhibitor) was determined for 9 substituents. The radical reactivity of the aromatic azo group was decreased by electron donor substituents and increased by electron acceptors. The substituent effect can be well interpreted by the Hammett equation; the value of the reaction constant was ϱ = +0.53.