12 15 pentathiaheptane 1 17 dithiol 3 3 mercapto 2 2 mercaptoethyl thio propyl thio propyl thio 2 2 mercaptoethyl thio propane 1 thiol 3 3 u2032 dithiobis propane 1 2 dithiol 7 11 bis mercaptomethyl 3 6 9 12 15 pentathiaheptane 1 17 dithiol 7 12 bis mercaptomethyl 3 6 9 10 13 16 hexathiaoctadecane 1 18 dithiol 5 7 dimercaptomethyl 1 11 dimercapto 3 6 9 trithiaundecane 4 7 dimercaptomethyl 1 11 dimercapto 3 6 9 trithiaundecane 4 8 dimercaptomethyl 1 11 dimercapto 3 6 9 trithiaundecane 1 1 3 3 tetrakis mercaptomethylthio propane 1 1 2 2 tetrakis mercaptomethylthio ethane 4 6 bis mercaptomethylthio 1 3 dithiane and 2 2 2 bis mercaptodimethylthio ethyl 1 3 dithietane these polysulfide compounds may also have hydroxyl groups replacing hydrosulfide groups according to another embodiment the polymerizable composition according to the present invention may comprise a mixture of a hals anti yellowing additive of formula vii viii or ix and a sulfide anti yellowing additive of formula x xiii xiv or xv as defined above the weight ratio of hals anti yellowing additive to sulfide anti yellowing additive may range from 1 4 to 4 1 preferably from 1 2 to 2 1 the amount of anti yellowing additive s in the polymerizable composition according to the present invention may be from 0 05 to 1 by weight preferably.