The present invention provides a process for crystallizing a polymer having at least 20 mole percent of hydroxyalkanoate repeat units, comprising admixing the polymer and a compound of the formula R.sup.1--C(O)N(R.sup.2).sub.2, R.sup.1--C(O)NH--(R.sup.3)--NHC(O)--R.sup.1, R.sup.1--NHC(O)NH--(R.sup.3)--NHC(O)NH--R.sup.1, R.sup.1--NHC(O)--R.sup.2, R.sup.1--NHC(O)--(R.sup.3)--C(O)NH--R.sup.1, R.sup.1--C(O)NH--(R.sup.3)--C(O)NH--R.sup.1, R.sup.1--NHC(O)NH--(R.sup.3)--C(O)NH--R.sup.1, R.sup.1--NHC(O)NH--(R.sup.3)--NHC(O)--R.sup.1, or a combination thereof, at a first temperature, which is from about 5.degree. C. to about 15.degree. C. above the melting point of the polymer; and cooling the polymer at a second temperature, which is from about the glass transition temperature of the polymer to about the melting point of the compound. The present invention also provides a composition comprising a polymer having at least about 20 mole percent of hydroxyalkanoate repeat units, and a compound of the formula R.sup.1--C(O)N(R.sup.2).sub.2, R.sup.1--C(O)NH--(R.sup.3)--NHC(O)--R.sup.1, R.sup.1--NHC(O)NH--(R.sup.3)--NHC(O)NH--R.sup.1, R.sup.1--NHC(O)--R.sup.2, R.sup.1--NHC(O)--(R.sup.3)--C(O)NH--R.sup.1, R.sup.1--C(O)NH--(R.sup.3)--C(O)NH--R.sup.1, R.sup.1--NHC(O)NH--(R.sup.3)--C(O)NH--R.sup.1, R.sup.1--NHC(O)NH--(R.sup.3)--NHC(O)--R.sup.1, or a combination thereof.