PROBLEM TO BE SOLVED: To provide a conjugated diene-based polymer capable of obtaining a polymer composition excellent in fuel cost saving property when formulating a filler, especially silica and to provide a method for producing the conjugated diene-based polymer and to a polymer composition obtained by formulating the conjugated diene-based polymer with silica and to provide a method for producing the polymer composition.;SOLUTION: The conjugated diene-based polymer has a monomer unit based on a conjugated diene and a group represented by formula (I) (wherein R1 and R2 are each independently a hydrocarbon group, a hydrocarbon-oxy group or a hydroxy group; m is an integer of 0-10; A1 is a polar functional group not having active hydrogen). The conjugated diene-based polymer is characterized in that the peak area of a molecular weight peak on the lowest molecular weight is 50% when total area of molecular weight distribution curve obtained by gel permeation chromatography measurement is defined as 100%.;COPYRIGHT: (C)2008,JPO&INPIT
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