Presence Of Peroxide Initiator Research Articles

Advances in peroxide‐initiated graft modification of thermoplastic biopolyesters by reactive extrusion

AbstractWe report recent advances in the solvent‐free reactive extrusion of thermoplastic biopolyesters, in the presence of peroxide initiators and tri‐functional cross‐linking/ chain extending agents. The resulting compounds have improved processability and properties compared to the starting materials, including higher melt strength due to long‐chain branching, higher crystallinity, faster crystallization kinetics, and improved mechanical properties. We demonstrate that these strategies are effective in thermoplastic biopolyesters, such as poly(lactide) (PLA) and various poly(hydroxyalkanoates) (PHAs), including poly(hydroxybutyrate) (PHB), and medium‐chain length PHAs. In addition to the improvements in properties, this approach has significant benefits in polymer processing operations, including blend compatibilization, and foaming. We also demonstrate that crosslinked PLA particles prepared by reactive extrusion using peroxide and a tri‐functional coagent, serve as very effective nucleating additives, resulting in crystallization half‐times as low as 1 min, and heat deflection temperature as high as 140°C. These modifications do not have adverse effects on the hydrolytic degradation characteristics of PLA.

Polar stationary phases based on poly(oligo ethylene glycol)diacrylates for capillary gas chromatography

New stationary phases for capillary columns in GC are synthesized and studied. The phases are prepared by depositing oligo(ethylene glycol)diacrylates on the column walls and subsequent polymerization (crosslinking) in the presence of peroxide initiators. It is shown that stationary phases based on monomers with molecular weights of 10 kDa or higher exhibit separation properties similar to those of conventional stationary phases based on polyethylene glycol (PEG); however, their thermal stability is higher because they have a higher degree of crosslinking and a more ordered structure of the crosslinked polymers than the respective parameters of phases based on native PEG.

New fluorinated polymers bearing pendant phosphonic groups for fuel cell membranes: Part 1 synthesis and characterizations of the fluorinated polymeric backbone

Radical copolymerizations of chlorotrifluoroethylene (CTFE) with vinyl ethers such as 2-chloroethyl vinyl ether (CEVE) and ethyl vinyl ether (EVE) were performed at 75 °C in the presence of peroxide initiator. Three copolymers were obtained and characterized by means of both NMR and elemental analysis. Then, the chlorine atoms in the side chains were converted into iodine atoms by nucleophilic substitution, which was monitored by 1H NMR spectroscopy. A series of five copolymers with different amounts of iodine atoms in the side chains were thus obtained. These copolymers exhibited molecular weight values of about 25,000 g mol −1, and the thermal analysis of the copolymers showed a starting degradation from about 220 °C. The T g values were in the range of 34–41 °C and showed a linear dependence versus the content of iodine atoms.

Sterically hindered aliphatic amines in the controlled synthesis of polystyrene

The kinetic features of radical polymerization of styrene in the presence of primary and secondary aliphatic amines combined with benzoyl peroxide and the molecular-mass characteristics of the resulting polymers were studied. In the presence of peroxide initiators, aliphatic amines, as potential sources of stable aminoxyl radicals, provide the synthesis of polystyrene with a controlled molecular mass without gel effect at a relatively high rate.

Morphology of Nylon12/natural rubber blends compatibilized by reactive processing

The reactive blending of 60 wt% polystyrene (PS) and 40 wt% natural rubber (NR) was carried out in the presence of peroxide initiator (0.5 phr; phr is part per hundred polymer bases (e.g., 60 : 40 PS/NR; 80 : 20 Nylon12/NR)), so the blend was called PSNR05. The reactive blend produced 26% gel and showed the reduction of glass transition temperature of polystyrene indicating the presence of PS-g-NR. The reactive blend PSNR05 as well as commercial styreneethylene-butylene-styrene block copolymer (SEBS) and the block copolymer with grafted maleic anhydride (SEBS-g-MA) were added to compatibilize Nylon12 (80 wt%) and NR (20 wt%) blends at various contents (1-16 phr). Interfacial tensions of the ternary blends were calculated. The reactive PSNR05 should encapsulate NR phase in Nylon12 matrix more readily than SEBS-g-MA and SEBS. In contrast to the prediction, core-shell morphology observed by SEM and TEM revealed that not only the dispersion of particles having a NR core with SEBS or PSNR05 shell occurred, but also the inclusion of Nylon12 in NR particles with PSNR05 or SEBS at the interfaces, such that Nylon12, PSNR05 and SEBS became core and NR was shell in the Nylon12 matrix of the ternary blends, while in the blend with SEBS-g-MA (which is capable of reaction between MA and the amide group in Nylon12), the core-shell morphology was as expected. The average particle sizes (including NR and compatibilizer) tended to increase with SEBS and PSNR05 content, although the sizes were still in the submicron range. On the other hand, the blends with increasing SEBS-g-MA showed reduction of the average particle sizes which were relatively lower than those of the other blends with PSNR05 and SEBS. The morphologies of ternary blends having SEBS and PSNR05 were not significantly different so that the reactive blending technique is potentially an easier way to prepare the compatibilizer.

Thermal and induced decompositions of N-alkoxycarbonyldihydropyridines: end product analysis and EPR spectra of azacyclohexadienyl radicals

Hydrogen abstraction from N-alkoxycarbonyldihydropyridines generated azacyclohexadienyl radicals (pyridinyl radicals) which are characterised by EPR spectroscopy. In the presence of peroxide initiators, N-alkoxycarbonyl-1,2-dihydropyridines decomposed with production of pyridine, the corresponding alkyl formate, alkyl benzoate and alkanol being formed as the major products. Absence of cyclised products in experiments with substrates containing hex-5-enyl, pent-4-enyloxy etc. units demonstrates that radical production must be minor and that N-alkoxycarbonylazacyclohexadienyl radicals do not readily undergo β-scission of the exocyclic N–C bond. The most probable mechanism is a direct 1,2-elimination of formate. The alcohols which accompanied the other products are probably formed by hydrolysis of the formates and benzoates. Analogous chemistry is displayed by N-alkoxycarbonyl-1,4-dihydropyridines at higher temperatures where 1,4-elimination of formate is too rapid for homolytic radical production to compete.

The effect of diethylphosphite and of diethylphosphine oxide on polydimethylvinylsiloxanes

A study has been made of the effect of diethylphosphite and diethylphosphine oxide on various polydimethylvinylsiloxanes in the presence of peroxide initiators, platinum catalysts and UV-irradiation. It was found that reactions of polydimethylvinylsiloxanes with diethylphosphite and diethylphosphine oxide in the presence of peroxide initiators (benzoyl peroxide and tertiary butyl peroxide) and platinum catalysts (Pt: C and H 3PtCl 6·6H 2O) and azoisodibutyronitrile (ABN) are unaccompanied by phosphorylation of polydimethylvinylsiloxanes at high temperatures. It is only by UV-irradiation that partial phosphorylation of polydimethylvinylsiloxanes with diethylphosphine oxide takes place, though the process is a very complex one.

Interaction of diethylphosphite and diethylphosphine oxide with vinyl-containing organocyclosiloxanes

The interaction of diethylphosphite (DEP) and diethylphosphine oxide (DEPO) with vinyl-containing organocyclosiloxanes has been investigated in the presence of peroxide initiators, under UV-irradiation, and without initiators at 20, 80 and 145°. The reaction of organocyclosiloxanes containing the vinyl group with DEP and DEPO proceeds in two directions: with siloxane bond opening in the ring under the action of the phosphorus component, and with the addition of DEP and DEPO to the double bond of the siloxane component. The addition of DEP to the vinyl group occurs only in the presence of peroxide initiators, while the addition of DEPO takes place in the presence of initiators as well as without them at 80°, and also under UV irradiation.

Some aspects of polypropylene functionalization by free radical reactions

Hydrocarbon/monomer combination products are detected by GC-MS in the reaction of 2-methylundecane with α-methylstyrene (MES) in the presence of peroxide initiators. On this basis, functionalization experiments of isotactic polypropylene (IPP) and of atactic polypropylene (APP) with MES, diethylfumarate and diethylamaleate have been carried out in solution and in bulk, in the presence of dicumylperoxide. The extent of functionalization, determined by i.r. spectroscopy, depends on the microstructure of the macromolecule being 0.5–1.0% by weight for IPP and 3.0–8.0% by weight for APP. In all functionalization experiments of IPP and APP, partial thermal degradation is observed but crosslinking is negligible.

Contribution to the mechanism of copolymerization of phenylvinyl alkyl ethers and thioethers with maleic anhydride

AbstractThe equilibrium constants of the charge‐transfer complex monomers of phenylvinyl alkyl ethers (I) and thioethers (II) with maleic anhydride (MAn) were determined by the transformed Benessi—Hildebrand NMR method, and it was found that the bulkiness of alkyl groups had no significant influence on the equilibrium constant. The rate of copolymerization, however, was largely dependent on the bulkiness of the alkyl groups in the phenylvinyl alkyl ether series. The rate of copolymerization of I (R = Et; sec‐Bu) and II (R = Et; sec‐Bu) with MAn was proportional to the square root of AIBN concentration, and intrinsic viscosity of poly‐I (R = Et)‐co‐MAn was proportional to the reciprocal square root of AIBN concentration. Spontaneous copolymerization did not occur, but I (R = Et) copolymerizes with MAn in the presence of oxygen; II did not copolymerize with MAn in the presence of oxygen; nor in the presence of peroxide initiators. In the copolymerization of I (R = Et) and MAn, it was found that molecular weight increases with conversion. By applying the generalized model described by Shirota and co‐workers, the reactivity ratios k1c/k12 and k2c/21 for copolymerization of I (R = Et) and II (R = Et) with MAn were calculated from the change of copolymerization rate with monomer feed at constant total monomer concentration.

Effect of oxygen on the polymerization of vinyl chloride. II. Polymer properties

AbstractThe bulk and suspension polymerizations of vinyl chloride have been carried out in the presence of small known amounts of added oxygen at 54°C in the presence of peroxide initiators. The concentrations of oxygen were in the range 0–1240 ppm for 1‐gal bulk polymerization systems and 0–400 ppm for 15‐gal suspension polymerization systems. The thermal stabilities of the polymers prepared in the presence of oxygen were lower than those prepared under corresponding oxygen‐free conditions. The average molecular weights of bulk polymers isolated at relatively low conversions were reduced in the presence of oxygen, and the infrared spectra of the polymers were altered. The significance of the decreased thermal stabilities of the polymers prepared in the presence of oxygen is discussed briefly in relation to the possible sites of initiation of dehydrochlorination.

Radical reaction of methallyl chloride and polychloromethanes with?-elimination of chlorine atom

A study was made of the radical reaction of methallyl chloride with CCl4 and CHCl3 in the presence of peroxide initiators. On the basis of the structures of the isolated products and certain kinetic data a reaction mechanism was proposed with the postulatedβ-elimination of the chlorine atom from the intermediate radicals.