Polymeric macromolecules, irradiation

So-called prepolymerization is frequently used to achieve a very high purification a monomer that has already been purified by the normal methods is polymerized to about 10-20% conversion by heating or irradiation, or if necessary by addition of initiator. It is then separated from the polymer by fractional distillation under nitrogen. Impurities that affect the initiation (e.g., by reaction with the initiator or its fragments) or that react with the growing macromolecules (causing chain termination or chain transfer) are thereby removed. 

Radiations ionisantes et macromolecules. 3e Partie. Irradiation des solutions de polymeres. Synthese des copolymeres greffes. Ind. plastiques mod. (Paris) 9, n° 2, 34 (1957). 

Another example of a Pc-based 1-D polymer is that reported by Armstrong and co-workers [158], They prepared a Pc with eight styrene-type polymerizable sites at the end of the peripheral substituents. This molecule forms highly ordered, rod-like aggregates at the air-water interface that can be transferred onto solid supports. Irradiation of the thin films affords polymerization between the olefin moieties of adjacent molecules by photostimulated [2 + 2] cycloaddition. The rod-like Pc macromolecules were conveniently studied by matrix-assisted laser desorp-tion/ionization (MALDI-TOF) spectrometry and atomic force microscopy (ATM), the latter showing rods with lengths up to 290 nm. 

The formation of keto-phosphonate structure within macromolecule leads to the removal of internal unsaturation. Triallyl cyanurate and ionizing irradiations [210] made a E-P block copolymer-PE blend thermally stable. Triallyl cyanurate increases the crosslinking density probably due to addition reactions between polymeric and allyl radicals produced by ionizing radiation. The addition of 2,2,4-trimethyl-l,2-di-hydroquinoline and bis[4(l-methyl-1-phenylethyl)pheny 1]-amine stabilized a PE-EPDM blend against heat [211]. Popov et al. [212] studied the ozone effect on PE-iPP blend. The oxidation rate was detected in relation to... 

Moreover, the polymerization of MMA, photoinitiated by poly(AVBP-co-St), proceeds at a lower rate than that promoted by the low-molecular-weight analogue AIBP and is enhanced in solvents where the macromolecules are more expanded, thus reducing free radical recombinations [60]. The presence of cage recombinations in this type of systems is also substantiated by the occurrence of a very efficient crosslinking when films of poly(VBP-ca-DMAS) are subjected to UV irradiation [54]. 

Upon ultraviolet irradiation in solution, N,N -nonamethylene-blsdlmethylmaleimide polymerizes into high molecular weight macromolecules with cyclobutane rings in the main chain. The reaction could be sensitized by acetophenone and was quenched by oxygen, ferrocene, and 3,3,4,4-tetramethyl-l,2-diazetine-l,2-dioxide. Stem-Volmer plots were linear for all chromophore concentrations and were dependent on the chromophore concentration. Linear quenching relations can be obtained in the following cases (Scheme IV). 

Nakamura, Sakata and Kichuchi 48> have compared the thermal and photochemical crosslinking of poly (vinyl cinnamate). The critical hardening value required is approximately 1.3 crosslinks per macromolecule possessing a degree of polymerization of 1400. The minute amount of crosslinking required to insolubilize poly(vinyl cinnamate) makes the study of the process difficult insight can be obtained only by inference. Furthermore, Nakamura and Kikuchi 44> reported that the quantum yield of the disappearance of the double bonds in poly(vinyl cinnamate) decreased rapidly with irradiation time. Extrapolation to zero time of exposure indicated a quantum yield of 0,34. It therefore seems hazardous to base conclusions on observations of products which result from long irradiation times. 

Sugihara, S.H. Ito, S. Irie, S. Ikeda, I. Synthesis of thermoresponsive shell cross-linked micelles via living cationic polymerization and UV irradiation. Macromolecules 2010,43 (4), 1753-1760. 

Spadaro et al. - polymerized methyl methacrylate (MMA) monomers in the presence of acrylonitrile-butadiene rubber by y-irradiation at a temperature of 70°C. For pure MMA, a total dose of 4 kGy is enough to complete polymerization and further irradiation (6.3 kGy) leads to a degradation of PMMA macromolecules. On the contrary, for PMMA/ABN blends, a higher dose... 

Besides the above noted polymerization techniques photocuring is a special process that transforms a multifunctional monomer into a crosslinked macromolecule by a chain reaction initiated by reactive species generated by UV irradiation [77]. Three basic components are needed for photocuring ... 

Hydrogels can be prepared conveniently with the aid of yrays, starting with aqueous solutions of the respective monomer [16]. The process consists of two radiation-induced steps (i) polymerization of the monomer and (ii) crosslinking of the polymer formed in the first step (see Section 5.2.1). In fact, the process can commence with the OH radical-induced polymerization of monomers. With prolonged irradiation, the initially formed macromolecules such as poly(vinyl pyrrolidone) and polyacrylamide undergo crosslinking by OH radical attack [15,115]. 

The grafted copolymers are obtained from macromolecules of polymer of A, in which are formed active centers that can then initiate polymerization of another monomer B. The active centers in polymer A may be formed by the reaction with free radicals arising from the deeomposition of reaction initiators, and also during the irradiation, oxidation and under influence of ultrasounds, etc. 

Elimination of a smaller molecule from two or more molecules gives condensed product. These products may be used in the synthesis of larger molecules, macromolecules or even polymerized products. Microwave irradiation helps in the formation of these products with a variety of properties in limited time and with excellent... 

Naphthalene excitation by UV-light in glassy cellulose triacetate films induces formation of polymeric free radicals, polymer chain break and addition of naphthalene fractures to macromolecules. In the absence of oxygen, the naphthalene consumption rate increases in direct proportion to UV-light intensity, whereas the rate of polymeric chain breaks varies in proportion to quadratic intensity. The process is initiated by singly excited triplet naphthalene molecules localized in the structural matrix zones, where they are incapable of irradiative deactivation. The features of phototransformation are explained in the framework of the hetero-nanophase kinetic model of the process, taking into account the radiationless translation of triplet excitation energy to naphthalene molecules present in the zones, where sensitization is absent and only triplet state deactivation is performed. 

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