J. S. Velickovic

Thermogravimetric characterisation of poly(methyl methacrylate) photopolymerised by colloidal cadmium sulphide

The thermal stability of poly(methyl methacrylate) (PMMA) photopolymerised using colloidal cadmium sulphide as the photoinitiator was studied by thermogravimetry (TG) and differential TG (DTG).The thermal stability of the CdS initiated PMMA was greater than that of conventional radically polymerised PMMA and approached that of anionically prepared PMMA. The DTG curve of the CdS initiated PMMA was a composite of four peaks, three of which correspond to the three peaks observed in the DTG curve of standard radically prepared PMMA. It is suggested that the additional peak arises from a new mode of depolymerisation initiation, that is, from chain end unsaturation introduced into the polymer chain during polymerisation initiation with the colloidal CdS.

The polymerisation kinetics of lower dialkyl itaconates

SUMMARY: The free radical polymerisation kinetics of diethyl- (DEI), dipropyl- (DnPI), dibutyl- (DnBI), and dihexyl itaconate (DHI) in the bulk were studied in the temperature range from 50 to 70 C. The concentration of the initiator, 2,2 -azoisobutyronitrile (AIBN), was varied between 0.02 and 0.085 mol/dm 3 . The rate of polymerisation (Rp), degree of polymerisation (DP), overall polymerization rate constant (K), the ratio of the propagation and termination rate constants (kp/kt 1/2 ), as well as the chain transfer constant to monomer (CM) were determined. The values of Rp, K, and kp/kt 1/2 of the investigated monomers all increase with increasing size of the alkyl group in the ester substituent, whereas CM decreases when going from the dimethyl to the dihexyl ester. The values of CM are larger than the corresponding values for the alkyl esters of methacrylic acid.

On the thermolysis of poly(chloroalkyl methacrylates) and poly(chloroalkyl acrylates): Part 1—Poly(2,2,2-trichloroethyl methacrylate)

The thermal degradation of poly(2,2,2-trichloroethyl methacrylate). PTCMA, in the absence and presence of O2 was studied and compared with that of poly(ethyl methacrylate), PEMA. In the absence of O2 the two polymers behaved quite differently. Apart from unzipping, PTCMA became partially insoluble due to intermolecular crosslinking at T 240°C both polymers degraded effectively by depolymerization. O2 prevented crosslinking of PTCMA and retarded unzipping (shift of onset to higher temperature). It was inferred from product analysis that at T < 240°C the thermolysis of PTCMA is initiated by decomposition of pendant groups. Primary bond cleavage at various positions in the side groups, results in the formation of free radicals. In the presence of O2, hydrogen abstraction from CH2 groups in the polymer backbone generates carbon centered radicals which can be converted into oxyl radicals . The latter can give rise to main-chain scission. Apart from the monomer, the main volatile compounds formed in the presence of O2 are: 2,2,2-trichloroethyl pyruvate, CH3COCOOCH2CCl3 and 2-methyl-oxirane carbonic acid 2,2,2-trichloroethyl ester, Mechanisms concerning the initiation of thermolysis of PTCMA are proposed on the basis of the various thermolysis products.

Isothermal bulk polymerization ofp-alkylaryl methacrylates by DSC

The course and kinetics of free radical polymerization in bulk ofp-alkylphenyl methacrylates with AIBN initiator were studied by DSC, in the temperature range 348–373 K. The enthalpy of polymerization, the residual monomer content, as well as the overall reaction rate constants and the activation energies were determined. The similar values of the overall rate constants indicate that the relatively small alkyl substituents inp-position of the phenyl ring affect the polymerization rate to a very small, if any, extent.ZusammenfassungMittels DSC wurden im Temperaturbereich 348–373 K Reaktionsweg und Kinetik der radikalischen Raumpolymerisation vonp-Alkylphenylmethacrylaten mit AIBN Initiator untersucht. Dabei wurden die Polymerisationsenthalpie, der Monomerrest-gehalt als auch die Geschwindigkeitskonstanten und die Aktivierungsenergien der Gesamt-reaktion bestimmt. Ähnliche Werte für die Gesamtgeschwindigkeitskonstanten weisen darauf hin, daß die relativ kleinen Alkylsubstituenten inp-Stellung des Phenylringes die Polymerisationsgeschwindigkeit nur in sehr kleinem Maße — wenn überhaupt — beeinflussen.

The thermal degradation of poly(di-n-hexyl itaconate) prepared in the presence of n-dodecyl mercaptan

Abstract The preparation of poly(di- n -hexyl itaconate) (PDHI) in the presence of the chain transfer agent n -dodecyl mercaptan resulted in polymers of increased thermal stability, owing to the suppression of the number of chain terminal double bonds. The polymers were characterised by Fourier transform IR (FTIR) spectroscopy and gel permeation chromatography. The differential thermogravimetry (DTG) curves of all the PDHI samples had two peaks, showing that degradation occurred in two stages. The area of the lower-temperature DTG peak correlated with the number of terminal double bonds.

The thermal degradation kinetics of dextran and pullulan

The effect of molar mass and, in the case of dextran, of the degree of branching on the thermal degradation kinetics of dextran and pullulan was studied in the presence and absence of oxygen. Although the initial mass loss of the dextran samples occurred at higher temperatures than that of the pullulan samples, the overall thermal degradation activation energies were lower for dextran than for pullulan. In the case of dextran the thermal stability was found to decrease with molar mass and degree of branching. The molar mass of pullulan, in the range of 104 to 105 g/mol, appeared to have no significant influence on the thermal characteristics of the samples.ZusammenfassungIn und ohne Gegenwart von Sauerstoff wurde der Einfluß der Molekülmasse, im Falle von Dextran auch der Einfluß des Verzweigungsgrades auf die thermische Zersetzungskinetik von Dextran und Pullulan untersucht. Obwohl der anfängliche Masseverlust der Dextranproben bei höheren Temperaturen eintrat als bei den Pullulanproben, ist die Gesamtaktivierungsenergie der thermischen Zersetzung für Dextran niedriger als für Pullulan. Im Falle von Dextran sinkt die thermische Stabilität mit der Molekülmasse und dem Verzweigungsgrad. Die Molekülmasse von Pullulan scheint im Bereich 104 bis 105 g/mol keinen signifikanten Einfluß auf die thermischen Merkmale der Proben zu haben.

DSC analysis of compatibility of poly(phenyl methacrylate) and some poly(xylenyl methacrylates)

Glass transition temperatures of blends of (1) poly-(phenyl methacrylate) and poly(2,3-xylenyl methacrylate), (2) poly-(phenyl methacrylate) and poly(2,6-xylenyl methacrylates and (3) poly-(2,3-xylenyl-) and poly(2,6-xylenyl methacrylate) were measured. The data obtained suggest the existance of compatibility for blends of poly(xylenyl methacrylates) mentioned and incompatibility for both poly(phenyl methacrylate)/poly(xylenyl methacrylate) systems.ZusammenfassungEs wurden die Glasumwandlungspunkte von Gemischen aus (1) Poly-(phenylmethacrylat) und Poly(2,3-xylolylmethacrylat), (2) Poly-(phenylmethacrylat und Poly(2,6-xylolylmethacrylaten) und (3) Poly-(2,3-xylolyl-) und Poly(2,6-xylolylmethacrylat) vermessen. Die erhaltenen Angaben weisen auf Kompatibilität für die Gemische aus den genannten Poly-(xylolylmethacrylaten) sowie auf Inkompatibilität für Poly(phenylmethacrylat)/Poly(xylolylmethacrylat)-Systemen hin.

DSC investigation of isothermal bulk copolymerization of alkylaryl methacrylates

The free radical copolymerization of phenyl methacrylate (PhMA) witho-methylphenyl-methacrylate(o-MPhMA) ando-ethylphenyl methacrylate (o-EPhMA) was carried out and the enthalpies of copolymerization, overall rate constants and copolymerization parameters were determined for different molar ratios of comonomers in the temperature range 353–373 K.ZusammenfassungEs wurde die radikalische Kopolymerisation von Phenylmethacrylat (PhMA) mito-Methylphenylmethacrylat (o-MPhMA) undo-Ethylphenylmethacrylat (o-EPhMA) durchgeführt und im Temperaturbereich 353–373 K für verschiedene Molverhältnisse der Komonomere die Enthalpien der Kopolymerisation, die resultierende Geschwindigkeitskonstante und die Kopolymerisationsparameter bestimmt.

The thermal degradation kinetics of poly(chlorethylmethacrylates)

The thermal degradation kinetics of poly(2-mono-, 2,2-di- and 2,2,2-trichlorethyl methacrylate) and of the non-chlorinated poly(ethyl methacrylate) were studied by TG in the absence and presence of oxygen. The overall thermal degradation energy, determined by the Flynn-Wall method, increases with increasing chlorine content of the polymer when the degradation is performed in the absence of oxygen, while the trend is reversed in the presence of oxygen. Competition between the two major non-oxidative thermolysis reactions, depolymerization and crosslinking, could be monitored by DTG. Generally, the thermal stability of the investigated polymers is reduced by oxygen.ZusammenfassungMittels TG wurde in Gegenwart und in Abwesenheit von Sauerstoff die Kinetik des thermischen Abbaues von Poly(2-mono, 2,2-di- und 2,2,2-trichlorethylmethacrylat) und des nichtchlorierten Poly(ethylmethacrylat) untersucht. Die mit der Flynn-Wall Methode bestimmte Gesamtenergie des thermischen Abbaues steigt mit wachsendem Chlorgehalt des Polymers, wenn der Abbau ohne Sauerstoff erfolgt. In Gegenwart von Sauerstoff wird dieser Trend genau umgekehrt. Mittels DTG konnten die zwei wichtigsten nichtoxidativen Thermolysereaktionen, Depolymerisierung und Vernetzung, als kompetitive Reaktionen nachgewiesen werden. Ganz allgemein wird die thermische Stabilität der untersuchten Polymere durch Sauerstoff herabgesetzt.

Poly(dialkoxyethyl itaconates)

The oxidative and non-oxidative degradation of poly(di-methoxy-), poly(di-ethoxy-), poly(di-iso-propoxy-) and poly(di-n-butoxyethyl itaconate) were investigated by thermogravimetry. Characteristic degradation temperatures and apparent activation energies of degradation were determined for the non-oxidative degradation of all the investigated polymers. It was not possible to determine these characteristics in the presence of oxygen as the degradation was accompanied by a secondary exothermic reaction. Based on examination of the monomers, it is supposed that the exothermic reaction is a repolymerisation of the monomers released during the earlier stages of polymer degradation.