Grafting of styrene to polyethylene

Both Odian and Silverman models satisfactorily explain most of the observed results in all solvents (Tables I-III, VI) used in the present study, however there are some exceptions especially when solvents other than the alcohols are used (Table VI). Thus the Odian mechanism is not consistent with the DMF data nor can the Silverman model account for the acetone results. In addition, in further preliminary studies with grafting of styrene to polyethylene (10) in solvents other than those reported here both Odian and Silverman mechanisms are deficient. The problem is that possible contributions from the radiation chemistry of the components in the grafting reaction need to be considered in formulating a complete mechanism for the overall process. 

Figure 1. Effect of divinylbenzene on grafting of styrene to polyethylene film in methanol at dose rate of 4,1 X rad/h to total dose of 2,5 X 10 rad. Key O, styrene-methanol , styrene-methanol-divinylbenzene (1% v/v).

W.J. Chappas and J. Silverman, The effect of acid on the radiation-induced grafting of styrene to polyethylene, JoRad.Phys.Chemo 14 847 (1979). 

Table 4. Synergistic effect of acid with polyfunctional monomers in the radiation grafting of styrene to polyethylene, (a)... 

Table II. Synergistic Effect of Acid and DVB on the Grafting Efficiency of Styrene to Polyethylene Film Initiated by Ionising Radiation3...

Hoffman, A. S. Irradiation grafting of styrene to high pressure and low pressure polyethylene films. J. Polymer Sci. 34, 461 (1959). 

A similarly poor efficiency in extraction can also be seen in Fig. 11, where the extraction result for the product obtained by the radiation grafting of styrene onto polyethylene terephthalate)(PET) fibers13 is shown. In this case the unreacted PET can be extracted after most of PS homopolymer has been extracted by repeated solution-precipitation of the sample. It should be mentioned here that the solution procedure is also necessary to extract the unreacted PET. Such a solution-precipitation procedure is also necessary for nylon-styrene13 and poly(vinyl chloride)-acrylo-nitrile14 graft products so as to remove the homopolymers to a sufficient extent. 

The latter effect has not yet been investigated quantitatively. So far, only one interesting paper49 by Odian and Kruse has been reported who performed a mathematical analysis of the grafting of styrene to irradiated polyethylene films for different ratios between the diffusion and the grafting rates. For stationary graft polymerization they derived the following equation ... 

A theory for this acid effect has been developed essentially from the wool and cellulose work (3,4). Recently, in a brief communication, we reported analogous acid enhancement effects in the radiation grafting of monomers such as styrene in methanol to nonpolar synthetic backbone polymers like polypropylene and polyethylene (5). In the present work, detailed studies of this acid enhancement effect are discussed for the radiation grafting of styrene in various solvents to polyethylene. The results are fundamentally important since most of the experiments reported here have been performed in solvents such as the low molecular weight alcohols which, unlike cellulose and wool systems, do not swell polyethylene. 

TABLE IV. Effect of Acid Structure in Methanol to Polyethylene.a Grafting of Styrene in ... 

TABLE V. Effect of Acid on Homopolymer Formation in the Radiation Grafting of Styrene in Methanol to Polyethylene.0... 

Figure 1. Grafting of styrene in methanol to polyethylene at various dose rates total dose 0.2 X 10 rads. (V) 0.117 X 10s rad/hr, without HsSOk (Y) with 0.1 N H S04 (0)0.196 X 10s rad/hr, without HsSOi (9) with 0.1N H2SOi ( ) 0.279 X 106 rad/hr, without ( ) with 0.1N ffsS04 ( ) 0.546 X 10 rad/hr,...

TABLE VII. Effect of Dose Rate in the Presence of Acid on the Grafting of Styrene in DMF to Polyethylene. 

TABLE VIII. Effect of Acid in Methanol to in the Radiation Grafting of Styrene Polyethylene using Open Tubes.a ... 

The parameters which predominantly influence the acid effect in radiation grafting of styrene monomer to polyethylene film are the structure of solvent, the concentration of monomer and the dose rate. Because these three variables are inter-related, it is difficult to predict, a priori, the conditions required to yield an optimum in grafting. In this respect the type of solvent used is particularly important. 

Figure 2. Grafting of styrene in DMF to polyethylene in the presence of HtSOt at various concentrations total dose 0.5 X 10s rad at dose rate 0.080 X 10s rad/hr...

Polymer radicals can also be produced by the irradiation of a polymer-monomer mixture with ionizing radiation. Thus, the interaction of ionizing radiation with polyethylene-styrene produces radical centers on polyethylene, and these initiate graft polymerization of styrene to produce poly(ethylene-gra/i-styrene) [Rabie and Odian, 1977]. 

Although benzophenone derivatives have found application in a number of photopolymerization processes (10), these have usually involved cross-linking reactions induced by energy transfer from photo-exdted benzophenones to groups (e.g. cinnamate) attached to the polymer chains. In such cases, the benzophenones act as sensitisers and not as photoinitiators. An e>fample in which hydrogen abstraction by photoexdted benzophenone has been utilized for photoinitiation is the ultra-violet induced grafting of styrene on to polyethylene (8,45). Recently, extensive studies concerned with photoinitiation of vinyl polymerization by benzophenone derivatives in homogeneous media have been carried out, and are described in detail below. 

An Important observation recently made concerning acid and salt effects In UV and radiation grafting to polyethylene Is that In Che swelling of polyethylene In Che presence of methanolic solutions of styrene, partitioning of styrene Into polyethylene Is significantly Improved by the Inclusion of mineral acid or lithium salt In the grafting solution. Styrene labelled with tritium was used for these sophisticated experiments which Indicate chat most swelling occurs within Che first few minutes of exposure of backbone polymer... 

The new additives are polyfunctional monomers, which are exemplified by divlnylbenzene (DVB) and trlmethylol propane triacrylate (TMPTA) and are used in concentrations of 1% (v/v). When these polyfunctional monomers are added to the monomer solution, the results show that the gamma ray grafting of styrene in methanol to polyethylene is enhanced to a comparable degree to that of inclusion of acid (Table VII). The polyfunctionality of DVB and TMPTA is obviously Important in these reactions, since the number of grafting sites in the system is potentially enhanced by the Increase in... 

Table VII. Comparison of Acid with Polyfunctlonal Monomers as Additives for Enhancing UV and Ionizing Radiation Grafting of Styrene In Methanol to Polyethylene Film...

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