Polyolefins reaction with acids

A series of reactions with gases have been selected for the rapid quantification of many of the major products from the oxidation of polyolefins. Infrared spectroscopy is used to measure absorptions after gas treatments. The gases used and the groups quantified include phosgene to convert alcohols and hydroperoxides to chloroformates, diazomethane to convert acids and peracids to their respective methyl esters, sulfur tetrafluoride to convert acids to acid fluorides and nitric oxide to convert alcohols and hydroperoxides to nitrites and nitrates respectively. 

Additives in polyolefins which improve their application properties affect the crosslinking whenever they take part in the generation of free radicals or enter the propagation reactions.With the presence of fillers with acid sites, peroxides are, e.g., decomposed by an ionic medmnism and formation of a crosslinked structure in polyethylene is suppressed. To remove such an eff t, acid centres should be neutralized by basic substances. 

Available compounds of this type include polyolefin backbones with carboxylic acid, polyacrylic acid end groups and maleic anhydride, polybutadiene, also functionalized with maleic anhydride, and unsaturated polymeric silane compounds. As with other coatings, reactions depend on the filler/coating/matrix chemistry. Carboxylic acid groups will react as for their short chain counterparts, unsaturated polymer chains will enter into crosslinking processes, for example during the vulcanization of rubber, and maleic anhydride groups lead to reaction with the filler surface. 

Kim et al. studied the reaction of a pre-blend of PS and poly(styrene-g-glycidyl methacrylate) (PS-g-GMA) with two types of reactive polyolefins, poly(ethylene-ran-acrylic acid) (PE-r-AA) and poly(propylene-g-acrylic acid) (PP-g-AA), respectively. PE-r-AA reduced more efficiently than PE-g-AA the domain size, when the amount of PS-g-GMA in the PS phase was increased. This observation was explained by the phase separation of die PAA grafts in the PP-g-AA compatibilizer (Fig. 4.16), which restricted the availability of the AA units for reaction with PS-g-GMA. In contrast, the random distribution of the acid units along the PE chains was favorable for their reaction with the epoxy groups of PS-g-GMA at the interface [107]. 

Mixtures of a titanium complex of saturated diols, such as TYZOR OGT, and a titanium acylate, such as bis- -butyl-bis-caproic acid titanate, do not have a yellowing or discoloring effect on white inks used to print polyolefin surfaces (506). The complexes formed by the reaction of one or two moles of diethyl citrate with TYZOR TPT have an insignificant color on their own and do not generate color with phenol-based antioxidants (507). The complexes formed by the addition of a mixture of mono- and dialkyl phosphate esters to TYZOR TBT are also low color-generating, adhesion-promoting additives for use in printing polyolefin films (508). 

Polycondensation pol5mers, like polyesters or polyamides, are obtained by condensation reactions of monomers, which entail elimination of small molecules (e.g. water or a hydrogen halide), usually under acid/ base catalysis conditions. Polyolefins and polyacrylates are typical polyaddition products, which can be obtained by radical, ionic and transition metal catalyzed polymerization. The process usually requires an initiator (a radical precursor, a salt, electromagnetic radiation) or a catalyst (a transition metal). Cross-linked polyaddition pol5mers have been almost exclusively used so far as catalytic supports, in academic research, with few exceptions (for examples of metal catalysts on polyamides see Ref. [95-98]). 

Other Gas Reactions. Several other reactive gases or vapours were examined but found to be unsatisfactory. No ester formation ( 1745 cm"1) was found when oxidatized films were exposed to acetic acid or formic acid vapour. Alcohol/carboxylic acid reactions in the solid state have often been suggested as the source of ester products, but not substantiated (4,5). Gaseous ammonia reacted with carboxylic acid groups to give absorptions at 1550 cm"1 [-C(=0)-0 ] and 1300 cm"1 (NHi +). However, these absorptions were very broad and the method inferior to acid measurement by SF. Although N20 did not react with oxidized polyolefins, the reaction of N02 with oxi-... 

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