Solubility of additives: Grafting of itaconic acid onto LDPE by reactive extrusion. II. Effect of stabilizers

Static and dynamic mixers set on the Brabender plastograph were used to investigate the grafting of itaconic acid (IA) onto low-density polyethylene (LDPE) by the reactive extrusion. The initiators of free-radical reactions were monoperoxide 2,5-dimethyl-2-hydroxy-5-tert-butylperoxy-3-hexyne and diperoxide 2,5-dimethyl-2,5-di(tert-butyl peroxy)-hexane. The reaction mix contained stabilizers of phenolic type as follows: 2,6-ditert-butyl-4-methyl phenol; ester of 3,5-ditert-butyl-4-hydroxyphenyl-propanoic acid and pentaerythritol; 4-alkoxy-2-hydroxy-benzophenone; and 1,4-dihydroxybenzene. The effect of stabilizers, which follow the radical mechanism on the grafting of IA and on the crosslinking, depends on their solubility in the polymer and the monomer. The stabilizers (e.g., 1,4-dihydroxybenzene) with increased affinity toward the monomer reduce the grafting yield and inhibit crosslinking. At 0.3–0.5 wt % of the stabilizer insoluble in the monomer, the grafting yield can be increased, while inhibiting the LDPE-g-IA crosslinking, irrespective of the peroxide used. Hence, classical stabilizers can initiate grafting reactions at raised concentrations, temperatures, and application of the shearing stresses. They also help to obtain a high-grafting yield and a reduced crosslinking degree. A stabilizer, having a close affinity toward LDPE, influences the LDPE-g-IA structure. The stabilizer content of 0.5 wt % transforms the topological structure of LDPE-g-IA into uniblock. Its molecular weight distribution (MWD) may be narrow (⁻M<INF>n</INF>/⁻M<INF>w</INF> &lt; 2) or broad (⁻M<INF>n</INF>/⁻M<INF>w</INF> > 2), depending on the concentration of the initiator used. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3439–3448, 2001