Download the Poliigon Material Converter for Cinema 4D.

To install the material converter, copy the contents of the zip folder to a new folder on your hard drive. 

Go to the Script -> User Scripts -> Run Script... menu option within Cinema 4D and navigate to the folder you created in step 2. Select the Installer_Poliigon_Material_Converter file and the plugin will then be installed.

To run the converter plugin go to the Plugins -> Poliigon Material Converter menu option. Select the location of your textures then check that ProRender is assigned as the renderer and then click on 'Convert!'

To assign the newly imported material(s) to an object simply drag it from the material panel onto the target object.