STUDIES ON NATURAL RUBBER (PART X)
GRAFT COPOLYMERIZATION OF ACRYLIC ACID AND METHACRYLIC ACID ONTO NATURAL RUBBER
1971 Volume 44 Issue 4 Pages 375-381
Details
1971 Volume 44 Issue 4 Pages 375-381
Graft copolymerization of acrylic acid and methacrylic acid onto natural rubber was investigated in toluene using radical initiators. As initiators benzoyl peroxide (BPO) and azobisisobutyronitrile (AIBN) were effective for acrylic acid and BPO was more effective than AIBN for methacrylic acid. Generally, acrylic acid seemed to be more easily grafted than methacrylic acid.
Graft copolymerization of acrylic acid: The degree of grafting increased or reached a constant with increasing initiator concentration, monomer concentration and polymerization time. However, it was inversely proportional to the volume of polymerization solvent. The grafting efficiency was 90-95% independent of any variables except in the range of the high monomer concentration. The curves of the total conversion and the percent monomer grafting against the monomer concentration had maxima, but the other variables had the same effects as they had on the degree of grafting. The most adequate polymerization temperature was 80°C.
Graft copolymerization of methacrylic acid: The degree of grafting showed the same tendency as in the case of acrylic acid. The grafting efficiency increased with increasing BPO concentration and became approximately 60% irrespective of the polymerization time, if the monomer concentration was not extremely low or it was not at the very initial stage. However, it was inversely proportional to the volume of polymerization solvent and the polymerization temperature. As for the total conversion and the percent monomer grafted the total conversion was proportional to the polymerization temperature and the curve of the percent monomer grafted against the monomer concentration had a maximum. Other variables had almost the same effects as they had on the graft efficiency.
The appearance of graft copolymers obtained were similar both for acrylic acid and methacryic acid. They became less elastic, tough and lumpy, as the degree of grafting increased. With increasing degree of grafting the degree of swelling and the amount of soluble part became smaller in benzene, but greater in water and ethanol. This tendency was more remarkable in methacrylic acid-grafted copolymers than acrylic acid-grafted copolymer.
