Immersion grafting

Fig. 11.6 Schematic depiction of surface photografting processes (a) continuous grafting [91], (b) immersion grafting [97], (c) vapor-phase grafting. Adapted from Ogiwara et al. [98] with permission from John Wiley Sons, Inc.

The formation of appreciable quantities (up to "oQ0% based on the initial additive concentration) of the grafted substituted hydroxylamine O W0PP as from reaction 7) in photo-degrading PPH can be demonstrated by indirect methods (10, 11). For example after the rapid loss of the initial concentration of a piperidine or its nitroxide in PPH film, heating the film immersed in isooctane for several hours at 100 C in the presence of oxygen causes the re-appearance of nitroxide in appreciable quantities as measured by e.s.r. spectroscopy (ll). This nitroxide most likely results from a reaction analogous to reaction 8 (l2). In addition we have observed the ) N-0-C band (at 1306 cm 1) in the infrared spectrum of irradiated, nitroxide-containing PP films by Fourier Transform IR spectroscopy (ll)., ... 

The uniformity of these hyperbranched PAA grafts on PE films was studied by forming derivatives with visible and fluorescent dyes. These hyperbranched films were modified by treating an activated 3-PAA/PE film with an amine terminated p-methyl red dye (MR) 9 or with a dansyl amine 10 to form MR/3-PAA/PE or dansyl/3-PAA/PE films, respectively. Visual inspection under a light or fluorescence microscope showed that the methyl red-labeled and fluorescently labeled films were uniform in color and fluorescence. The methyl red/3-PAA/PE film derivafive showed a responsive color change wifh change in pH. The MR labeled 3-PAA/PE film was red after immersion in an acidic ethanol solution and yellow after treatment with a basic ethanol solution. 

Grafting of Vinyl Monomer by Trapped Radicals in Irradiated Polymer. The polymer is preirradidated in vacuo or in the presence of an inert gas and then immersed in monomer. The trapped free radicals in the irradiated polymer can then initiate graft polymerization. 

Table I. Grafting of Preirradiated Foam Immersed in Monomer"...

Homopolymer was formed by both methods of grafting however, the amount was considerably greater with the immersion method. When the time of grafting in solution was increased beyond 30 minutes, the extent of grafting continued to increase, but there was a tendency for the homopolymer to crosslink and become embedded in the foam. When this occurred, beads of crosslinked homopolymer were trapped in the cells of the foam, and they could not be removed by subsequent washing. 

Acrylonitrile is reported to change properties of Nylons by grafting (14,18, 20,21,37,58,62). It is worthwhile to call the attention to Hargreaves work who studied extensively the subject. A 25% solution of acrylonitrile in a 15% solution of zinc chloride was used as immersion media. A flow diagram for radiation polymerization of liquid material is presented (27). 

Simply heating the fibers at 80-120° C in the presence of air might also create active centers for subsequent grafting by immersion in acrylic or methacrylic esters (143). 

By chemical agents, indirect grafting on Nylon in liquid phase is frequently referred to in the bibliography. The most common reagent is air (144) or ozone, under controlled conditions, in order to avoid deterioration on the mechanical properties of the fiber, which is then immersed in the monomer. Hence, styrene (145-149), vinylidene chloride (146), vinyl acetate (146), acrylic and methacrylic acids (149), methyl methacrylate (146), acrylonitrile (146,148,149), 2-methyl-5-vinylpyridine (149) were successfully employed as grafting comonomers. 

N-Halogenation as the preliminary step of indirect grafting on polyamide backbone is another interesting method which was studied with good results by Bamford and co-workers (150). The N-chlorination was undertaken by immersion for several minutes at room temperature in an aqueous solution of sodium hypochlorite to which acetic acid was added until reaching pH 4—4.5, followed by washing with distilled water and drying in vacuum at 40° C. N-Bromination... 

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