Patent ID: 7420023

Claim:
A process for producing a modified buten-1-based polymer comprising the step of modifying a buten-1-based polymer satisfying the following requirements (a), (b), (c) and (d): (a) a crystalline resin having a melting point (Tm-D) of 0 to 100° C., the melting point being defined as a top of a peak observed on a highest-temperature side in a melting endothermic curve obtained by a differential scanning calorimeter (DSC) when a sample is held in a nitrogen atmosphere at −10° C. for 5 min and then heated at a temperature rise rate of 10° C./min; (b) a stereoregularity index represented by [mmmm]/([mmrr]+[rmmr]) of 20 or less; (c) following formulae 20%<[ mmmm]≦ 90%, and [ mmmm ]≦(90−2 ×[rr ]) %; and (d) a weight-average molecular weight (Mw) of 10,000 to 1,000,000 and a ratio (Mw/Mn) of weight-average molecular weight to number-average molecular weight of 4.0 or less, with a radical polymerization initiator and an organic acid.