RADIATION COPOLYMERISATION

The inclusion of mineral acid in the grafting solution has recently been shown to increase the radiation copolymerisation yield, particularly when styrene is grafted to trunk polymers like wool (3) and cellulose (4) i.e. polymers which readily swell in polar solvents such as methanol. This acid effect is important since for many copolymerisation reactions, relatively low radiation doses are required to yield finite graft. The process is particularly valuable for monomers and/or polymers that are either radiation sensitive or require high doses of radiation to achieve the required graft. 

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. 

More recent preliminary studies show that the grafting results for DVB and TMPTA can be extended to other polyfunctional monomers, including tetrafunctional compounds. The enhancement observed with these additives thus appears to be a general phenomenon in radiation copolymerisation and is of value in a preparative context since the radiation dose required to achieve a particular percentage graft can be significantly reduced with the consequence that potentially less radiation damage occurs in the backbone polymer. 

Recently a method was reported for enhancing the radiation grafting of monomers to polymers by the simple addition of mineral acid to the grafting solution >Under some experimental conditions organic acids act in the same manner >. Extensive work on this acid effect has been published for the radiation copolymerisation of styrene to cellulose wool, the polyolefins >PVC and polyesters. The acid effect has also been extended to the grafting of monomers other then... 

Graft copolymerisation of styrene on partially carboxymethylated cotton using gamma radiation. 

Graft copolymerisation is a unique method which is used for modifying the properties of the base polymer. A varieties of new properties can be imparted to the base polymer by implanting a number of suitable polymers. Various methods used for grafting are (i) Chemical method, (ii) Radiation method, and... 

The Acid Effect. The possible mechanistic role of hydrogen atoms in the current radiation grafting work becomes even more significant when acid is used as an additive to enhance the copolymerisation. At the concentrations utilised, acid should not affect essentially the physical properties of the system such as precipitation of the polystyrene grafted chains or the swelling of the polyethylene. Instead the acid effect may be attributed to the radiation chemical properties of the system. Thus Baxendale and Mellows (15) showed that the addition of acid to methanol increased G(H2) considerably. The precursors of this additional hydrogen were considered to be H atoms from thermalised electron capture reactions, typified in Equation 5. 

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. 

In the sensitised UV copolymerisation, radical pathways similar to the ionising radiation process are available for grafting (Equations (10-12,4,U0 + being representative sensitiser). 

Olefin-carbon monoxide co-polymers of the type (-RCH-CH2-CO-)n, known as polyketones, have a wide variety of interesting properties, such as thermoplasticity, flexibility, durability and high impact strength. The ketone function in the polymer makes them sensitive to UV radiation and as a consequence they are photodegradable and hence environmentally acceptable plastics. However their light sensitivity has limited their applications. They can be made by the copolymerisation of an alkene with carbon monoxide (Equation 27 see also Chapter 7, Section 7.7) ... 

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. 

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. 

With radiation grafting, there is also an additional mechanism for enhancement unique to acid and not applicable to the polyfunctional monomer additives. This process is particularly relevant to irradiations performed in air and involves the acid induced decomposition of peroxy species formed radiolytically in the backbone polymer, thus generating further sites where copolymerisation may occur (Equation 3). Current evidence (17) indicates that the contribution... 

Polyacrylamide gels are prepared by copolymerisation of acrylamide monomer (CH2=CHCO NH2) with a cross linking agent, usually N, N-methylene bisacrylamide, CH2(NHCOCH = CH2)2, in the presence of a catalyst accelerator-chain initiator mixture. This mixture may consist of freshly prepared ammonium persulphate as catalyst (0.1 to 0.3% w/v) together with about the same concentration of a suitable base, for example, dimethylamino propionitrile (DMAP) or N, N, N, N tetramethylene diamine (TEMED) as initiator. TEMED is most frequently used and proportional increases in its concentration speed up the rate of gel polymerisation. Photochemical polymerisation may be brought about by riboflavin in the presence of UV radiation. Gelation is due to vinyl polymerisation as shown below ... 

It Is the purpose of this paper to examine the role of functionality of MFA and MFMA In the enhancement process In reactions using the copolymerisation of styrene In methanol to the polyolefins under the Influence of UV as model system. The results will be extrapolated to ionising radiation work. In addition, synergistic effects Involving these MFAs and other additives in both UV and radiation grafting processes will be reported. The significance of the data In UV and electron beam curing reactions will be discussed. 

When ionising radiation is used as source of initiation for grafting instead of UV (10-14), analogous additive effects to those previously discussed, have been found. Thus Inclusion of sulfuric acid in methanollc solutions of styrene leads to an enhancement in copolymerisation to a polyolefin, such as polyethylene, when Irradiated by cobalt - 60 gamma rays (Table VI). 

Applied Spectroscopy 52, No.5, May 1998, p.692-701 INVESTIGATIONS OF RADICAL POLYMERISATION AND COPOLYMERISATION REACTIONS IN OPTICALLY LEVITATED MICRODROPLETS BY SIMULTANEOUS RAMAN SPECTROSCOPY, MIE SCATTERING, AND RADIATION PRESSURE MEASUREMENTS Musick J Popp J Trunk M Kiefer W Wurzburg,University... 

Details are given of the copolymerisation of maleimide derived UV stabilisers with aaylonitrile and styrene in the presence of NBR or SBR latexes. Thermomechanical properties and UV radiation resistance are discussed. 26 refs. USA... 

The radiation grafting properties of polypropylene using styrene in methanol as monomer system have been compared with those of the natural materials, cellulose and leather. Of the three, polypropylene is the most reactive trunk polymer (Table 2). Cellulose and leather exhibit comparable styrene grafting properties and all three trunk polymers show acid enhancement in copolymerisation especially in the 20-40% monomer concentration region. The polypropylene and cellulose data illustrate the... 

N.P. Davis, J.L. Garnett and S.V. Jankiewicz, Radiation grafting-modifications to cellulose by accelerated copolymerisation of monomers, Proc. 1st PRI Conference Radiation Processing for Plastics and Rubbe, Brighton, England, Paper 27.1 (1980, in press. 

Recently light-sensitive polymers were applied in two-phase polymer systems (Li et al, 2010). A light-sensitive polymer was synthesised by copolymerisation of A-isopropylacrylamide (a temperature-responsive monomer) with rV-vinyl-2-pyrrolidone and chlorophyUin sodium copper salt (light-sensitive monomers) (Wang et al., 2008). The polymer was used in a two-phase polymer system for the separation of protein (BSA) and amino acid (L-Tyr). The conformational change of the copolymer was induced by light applying laser radiation at 488 nm. About 98% of the copolymer was recovered after the separation. 

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