An atactic polypropylene comb-block polyolefin comprising two blocks including a polyolefin backbone and atactic polypropylene combs pendant to the backbone having a weight average molecular weight of at least 8000 g/mole and a crystallinity of less than 20%, where the atactic polypropylene comb-block polyolefin has comb number of at least 2. The atactic polypropylene comb-block polyolefin is made by contacting at a temperature within a range from 20 to 70° C. propylene with a first metallocene precursor to form vinyl-terminated atactic polypropylene to form vinyl-terminated atactic polypropylene, then contacting at a temperature within a range from 40 to 150° C. the vinyl-terminated atactic polypropylene with ethylene, propylene, or both and a second metallocene precursor to form the backbone.