A process for producing a modified olefin polymer in an extruder having a feed zone, a melting zone, optionally a mixing zone and optionally a die zone, comprising: introducing a stream of an olefin polymer which is a homopolymer of propylene or a copolymer of propylene having a melt flow rate, measured according to ISO 1133 under a load of 2.16 kg and at a temperature of 230°C, of 0.1 to 50 g/10 min into the feed zone of the extruder; introducing a stream of a free radical generator directly into the feed zone or the melting zone or the mixing zone, if present, of the extruder; introducing a stream of a functionally unsaturated compound chosen from (i) a bifunctionally unsaturated monomer selected from the group consisting of divinyl compounds, allyl compounds, dienes, aromatic or aliphatic bis (maleimide), aromatic or aliphatic bis (citraconimide) and mixtures thereof or polymer; or (ii) a bifunctionally or multifunctionally unsaturated polymer directly into the feed zone or the melting zone or the mixing zone, if present, of the extruder; extruding the mixture in the extruder at a temperature which is greater than the decomposition temperature of the free radical generator and the melting temperature of the olefin polymer but less than the decomposition temperature of the olefin polymer thereby producing the modified olefin polymer in the extruder; and, optionally, passing the melt of the modified olefin polymer through the die zone to a pelletiser whereby the modified olefin polymer is having - a F 30 melt strength of at least 3.4 cN and - a melt extensibility of at least 170 mm/s. introducing a stream of an olefin polymer which is a homopolymer of propylene or a copolymer of propylene having a melt flow rate, measured according to ISO 1133 under a load of 2.16 kg and at a temperature of 230°C, of 0.1 to 50 g/10 min into the feed zone of the extruder; introducing a stream of a free radical generator directly into the feed zone or the melting zone or the mixing zone, if present, of the extruder; introducing a stream of a functionally unsaturated compound chosen from (i) a bifunctionally unsaturated monomer selected from the group consisting of divinyl compounds, allyl compounds, dienes, aromatic or aliphatic bis (maleimide), aromatic or aliphatic bis (citraconimide) and mixtures thereof or polymer; or (ii) a bifunctionally or multifunctionally unsaturated polymer directly into the feed zone or the melting zone or the mixing zone, if present, of the extruder; (i) a bifunctionally unsaturated monomer selected from the group consisting of divinyl compounds, allyl compounds, dienes, aromatic or aliphatic bis (maleimide), aromatic or aliphatic bis (citraconimide) and mixtures thereof or polymer; or (ii) a bifunctionally or multifunctionally unsaturated polymer directly into the feed zone or the melting zone or the mixing zone, if present, of the extruder; extruding the mixture in the extruder at a temperature which is greater than the decomposition temperature of the free radical generator and the melting temperature of the olefin polymer but less than the decomposition temperature of the olefin polymer thereby producing the modified olefin polymer in the extruder; and, optionally, passing the melt of the modified olefin polymer through the die zone to a pelletiser - a F 30 melt strength of at least 3.4 cN and - a melt extensibility of at least 170 mm/s.