This invention relates to a process for producing a polymeric product by the polymerisation of at least one olefinic compound in the form of an olefin or a compound including an olefinic moiety by contacting the at least one olefinic compound with a polymerisation catalyst. The catalyst comprises the combination of a source of a Group IV to VI transition metal; and a ligating compound of the formula (R.sup.1).sub.mX.sup.1(Y)X.sup.2(R.sup.2).sub.n.The process is characterised therein that when R.sup.1 and R.sup.2 are independently a hydrocarbyl group or a heterohydrocarbyl group which contains at least one non-polar substituent, the olefinic compound is contacted with the polymerisation catalyst at a reaction temperature from and above 70.degree. C.; and where R.sup.1 and R.sup.2 are independently a hydrocarbyl group or a heterohydrocarbyl group which contains no substituent, the olefinic compound is contacted with the polymerisation catalyst at a reaction temperature from and above 90.degree. C.