1. T. Hancock, English Patent 4768 (1823)
2. C. Hancock, English Patent 11, 147 (1846)
3. D.F. Oxley and D.J. H. Sandifor, Plast, Polym. 39, 288 (1971).
4. W.J. Schrenk, K.J. Cleereman and T. Alfrey, SPE Trans. 19, 192 (1963).
5. J.H. Saunders, J.A. Burroughs, L.P. Williams, D.H. Martin, J.H. Souther, R.L. Ballman and K.R. Lea, J. Appl. Polym., Sci. 191387 (1975).