Styrene in methanol

When the source of initiation is altered from ionising radiation to UV, analogous additive effects to those previously discussed have been found. For reasonable rates of reaction, sensitisers such as benzoin ethyl ether (B) are required in these UV processes. Thus inclusion of mineral acid or lithium perchlorate in the monomer solution leads to enhancement in the photografting of styrene in methanol to polyethylene or cellulose (Table V). Lithium nitrate is almost as effective as lithium perchlorate as salt additive in these reactions (Table VI), hence the salt additive effect is independent of the anion in this instance. When TMPTA is included with mineral acid in the monomer solution, synergistic effects with the photografting of styrene in methanol to polyethylene are observed (Table VII) consistent with the analogous ionising radiation system. 

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 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,...

Acid enhancement in the radiation grafting of styrene in methanol to cellulose (4), wool (3) and in preliminary work with the polyolefins (5 6) has been proposed as being predominantly due to such reactions. 

A solution of styrene in methanol to impregnate wood samples, followed by polymerization, was used by Furuno and Goto (1979). Penetration of the monomer into the cell wall was determined by solvent extraction of samples after polymerization. This removed lumen located polymer, whilst leaving the cell wall bound polymer in place. This showed that the concentration of cell wall bound polymer increased in proportion to the monomer content in methanol, up to a maximum of 80% of the monomer in the solvent. No cell wall penetration was observed for treatment with neat monomer. This was also found for bulking of the wood, as determined from external dimensions of the samples. Improvements in ASE were obtained as a result of the presence of cell wall bound polymer. To achieve similar ASE values with lumen located polymer required very high polymer loadings. 

Polymeric steric stabilizer such as poly(vinylpyrrolidone) (PVPo),poly(acrylic acid), poly(hydroxypropyl)cellulose, etc., are used to prepare monodisperse polymer in dispersion polymerization of monomers such as alkyl acrylates and methacrylates, and styrene in polar media. AB and ABA block copolymers are a second type of steric stabilizer which can be used in dispersion polymerization. For example, the poly(styrene-h-ethylene oxide) was recently used by Winnik et al. [6] in the dispersion polymerization of styrene in methanol. 

Ligno Styrene, acrylonitrile Grafting of styrene in methanolic solution [190,... 

Further work on the mechanism of the acid enhancement in both UV and gamma ray grafting is reported. The copolymerisation of styrene in methanol and dioxan to cellulose is used as model system. Acid enhances grafting and homopolymer formation in both radiation systems. Analysis of the homopolymer from the grafting runs indicates that acid reduces the chain length, but increases the numbers, of grafted chains. 

Recently inclusion of mineral acid in the grafting solution was found to enhance the grafting yields for a typical system such as the copolymerisation of styrene in methanol to cellulose in the presence of gamma rays (13). The acid effect now appears... 

In like manner, inclusion of mineral acid in the photo-sensitised grafting of styrene in methanol to cellulose enhances the polymerisation yields significantly (Figure 2). The results obtained with phosphoric and sulfuric acids were consistent with earlier data (13,14). Dioxan is also a useful solvent for these reactions when uranyl ion is used as sensitiser. However dioxan is not as efficient as methanol for the grafting reaction. The grafting in dioxan exhibits a Trommsdorff peak at 60% monomer concentration. The results in Figure 2 also show that the unsensitised process does occur in dioxan as in other solvents, but... 

Table I. UV Grafting of Styrene in Methanol to Cellulose in Presence of Organic Acids and Anhydrides (1 %) ...

Figure 1. Grafting of styrene in methanol to cellulose with uranyl nitrate (1%) for 24 h at 24 cm from 90-W lamp using the following additives...

UV- or y-radiation-induced grafting of cellulose films with styrene in methanol solution was significantly enhanced in the presence of H2SO4, lithium salts, urea, and other organic compounds and polyfunctional monomers... 

The addition of phenylselenenyl chloride to a-substituted styrenes in methanol is stereoselective and gives the product of anti addition of the phenylseleno and methoxy groups to the double bond. The (E)-alkcnc gives the (/ , S )-products while (Z)-alkenes give (S, S )-products28. 

Thus, Criegee 11) prepared the oxythallation adduct of styrene in methanol which he decomposed at 130°C. to give products which result from solvolysis of the carbon-thallium bond with (HI) and without (IV)... 

Polyfunctional monomers (divinylbenzene and tri-methylol propane triacrylate) are shown to be novel additives for enhancing the radiation copolymerisation of styrene in methanol to the polyolefins. 

In preliminary work (19), divinylbenzene (DVB) has been reported to be a useful additive for enhancing the above grafting reactions. These early data (19) indicate that there are possible common mechanistic pathways between the acid effect and the DVB process. More detailed DVB studies are discussed in this paper for enhancing the radiation grafting yields of styrene in methanol to films of polyethylene and polypropylene. The work has been extended to include the use of other polyfunctional monomers such as tri-methylol propane triacrylate (TMPTA) as additives. The possibility of being able to use these additives for copolymerisation of monomers to naturally occurring trunk polymers such as cellulose will also be considered. 

Table Comparison of Cellulose with Polypropylene as Trunk Polymers for Acid Enhancement in Radiation Grafting of Styrene in Methanol...

The optimum in the copolymerisation process occurs at 50% monomer concentration with both additives. The behaviour of sulfuric acid in these reactions is representative of the most reactive of the mineral acids (12). A comparison of TMPTA with H SO (0.2 M) also indicates that similar trends in enhancement in radiation grafting to polyethylene film are observed with both additives (Table III). Again, when polypropylene film is used as backbone polymer (Table IV), acid and DVB show similar increases in grafting yield with styrene in methanol, however in this system, it is interesting to note that the concentration of monomer at the position of the Trommsdorff peak does not vary for neutral and acidified grafting solutions but changes from 30% to 35% when DVB is additive. 

Styrene in methanol radiation grafted to polyethylene film (0.12 mm) at 4.1x10 rad/hr to dose of 2.4x10 rad in air. 

Copol3nners prepared by radiation grafting styrene in methanol to polypropylene powder. Sulfonation time, 45 min. 

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