S. V. Jankiewicz

Insolubilisation of biologically active materials with novel radiation graft copolymers

Abstract The use of radiation grafting to immobilise a typical enzyme, trypsin, is reported. The technique involves radiation grafting to a backbone polymer a monomer containing an appropriate functional group to which the enzyme is bonded. In the present work, p-nitrostyrene has been grafted to representative trunk polymers, polypropylene and PVC, the nitro group in the resulting copolymer converted to the isothiocyanato derivative to which trypsin is attached. Of importance to this insolubilisation process, especially for radiation sensitive backbone polymers, is the inclusion of additives which enhance grafting. A new class of additives which increase the grafting yields is reported using as representative backbone polymers, naturally occurring cellulose and synthetic low density polyethylene. The new additives are specific metal salts such as LiClO4. The reactivity of these salts in grafting enhancement has been compared with that of mineral acid which has previously been used as an additive to increase grafting yields in both preirradiation and simultaneous techniques. A new model for grafting enhancement in the presence of the metal salts as well as acids is proposed whereby increased grafting yields are attributed to increased partitioning of monomer into the graft region in the presence of ionic solutes. The value of these additives in preparing copolymers suitable for general reagent insolubilisation reactions is discussed.

Mechanistic aspects of the acid and salt effect in radiation grafting

Abstract The enhancement of radiation grafting or photografting yields found in the presence of either acid or neutral salt has been attributed to a “salting out” of monomer from the solution into the grafting region within the polymer substrate. Measurements using a swelling/leaching technique and tritium labelled styrene, have shown that the rate of transfer adn the equilibrium distribution are dependent on the polarities of the monomer, substrate and solvent as well as the concentrations of ionic solute and monomer. Molecular weight studies and the effect of other additives confirmed the proposed mechanism. A number of other additives exhibited specific radiolytic chemical effects. These usually reduced the grafting yield.

Acid effects in radiation polymerisation and grafting reactions

Abstract The addition of mineral acid to solutions of styrene in dioxan enhances the radiation polymerisation yield of polystyrene. Gel permeation chromatographic analysis of the resulting homopolymer shows that Mn values are significantly reduced by acid inclusion. When radiation polymerisation is carried out in the presence of a trunk polymer such as cellulose or polyethylene (i.e. grafting conditions), the same acid effect on Mn is observed in the monomer solution. A mechanism for this acid effect in both radiation polymerisation and grafting is proposed based on the formation of shorter chain oligomers. This mechanism has been extended to monomer/solvent systems other than styrene in dioxan and is also shown to be consistent with previously reported general acid effects in the radiolysis of binary mixtures.

The role of partitioning of reagents in grafting and curing reactions initiated by ionizing radiation and UV

Experimental evidence involving monomer absorption studies using tritiated styrene is shown to support the proposal that additives such as mineral acids and certain inorganic salts when dissolved in the monomer solution enhance radiation grafting yields by a mechanism involving partitioning of reagents. Photoinitiators such as benzoin ethyl ether and its methyl analogue are reported as new additives for grafting of styrene in methanol to cellulose and polypropylene initiated by ionizing radiation. The partitioning concept is shown to be relevant in analogous UV grafting and curing processes.

Radiation and photografting as complementary techniques for immobilizing bioactive materials

Abstract The technique of radiation grafting to immobilize a typical enzyme, trypsin, to three representative backbone polymers namely polypropylene, PVC and polystyrene, is described. The process involves the simultaneous grafting of p-nitrostyrene to the polymer, the nitro group subsequently being converted to its isothiocyanato derivative to which trypsin is attached. For this immobilization work, the utilization of additives which enhance grafting is shown to be an advantage. Typical of the additives used are mineral acids (≈0.1M) and polyfunctional monomers (≈1% v/v), the two acting in a synergistic fashion when used together. A new class of additives, namely metal salts such as LiClO 4 , which also increase grafting yields has now been discovered. The reactivity of these salts in grafting enhancement is compared with that of mineral acid. A new model for the modus operandi of metal salts as well as acids in grafting enhancement is proposed whereby increased grafting yields are attributed to increased partitioning of monomer into the graft region in the presence of ionic solutes. The significance of using these additives to prepare radiation copolymers for enzyme immobilization is discussed. In addition to ionizing radiation, UV is also shown to be of value as an initiator for the preparation of graft copolymers for enzyme immobilization, however the presence of sensitizer in the copolymer may limit the photografting method. The possibility of using radiation curing processes involving electron beam (EB) and high powered (300 W/inch) UV sources for immobilization work has been explored and found to be feasible. The curing system possesses great potential for the current immobilization work since complete polymerization is achieved in a fraction of a second.

Polymer Modification by Radiation Grafting in the Presence of Salt Additives and its Application in Enzyme Immobilization

A novel radiation grafting method for modifying polymers of use in biomedical work is discussed. The procedure involves the use of particular inorganic salts as additives for accelerating the radiation grafting process. Styrene is used as typical monomer in these studies with cellulose, the polyolefins and PVC as representative backbone polymers. Two radiation grafting techniques are examined, namely pre-irradiation and simultaneous methods. The parameters affecting the observed grafting enhancement in the presence of these salt additives are treated. The results are compared with analogous data previously obtained with other additives, including acids. A new model for the mechanism of enhancement in radiation grafting in the presence of acids and/or salts is proposed. A typical biomedical application of the salt grafting technique for enzyme immobilization is briefly discussed.