As one of the environmental problems, 'white pollution' is caused by the accumulation of nondegradable polymer materials. Recycling is one solution, however, creating biodegradable polymers would be more feasible for many applications. 1-6 If those biodegradable polymers exhibit similar properties to the nonbiodegradable ones then they should be more commercially competitive. 7-9 Among those biodegradable polymers developed so far, aliphatic polyesters are the best-known and they are already widely utilized in many applications (e.g., drug delivery carriers, medical implants, and tissue scaffolding) 10-15 since the ester linkages in aliphatic polyesters are hydrolytically or enzymatically degradable. 16,17 However, most of the biodegradable aliphatic polyesters exhibit low melting temperatures (T m ) and subpar mechanical properties. For instance, the T m of poly(e-caprolactone) is around 60 8C. 18 On the contrary, aromatic polyesters have high T m values (e.g., the T m of polyethylene terephthalate is as high as 260 8C 19 ) and show competitive mechanical properties but they are typically nonbiodegradable.The aim of this study is to bridge the gap between the aliphatic and the aromatic polyesters and to create biodegradable polymers with higher T m values. Inclusion of the urethane or urea group into polymer backbones can enhance the crystallization/aggregation of polymer chains. 20 Furthermore, urea groups can also be degraded by proteases, such as papain. 21,22 Therefore, we explored a class of polymer, namely poly(urea ester)s (PUEs), via polycondensation of dimethyl esters (DMEs) and di(hydroxyalkyl) urea (DHAU, Scheme 1). In a PUE polymer chain, the ester groups offer biodegradability while the urea groups provide hydrogenbonding which should increase the T m and/or enhance the performance. Mulhaupt and co-workers reported previously the preparation of PUEs based on polyether polyols through an N,N 0 -carbonylbiscaprolactam route but only crosslinked materials were prepared. 23 Du et al. also synthesized nonbiodegradable liquid crystalline PUEs. 24 To the best of our knowledge, this work would be the first one creating biodegradable thermoplastic PUE.Since amino groups react with urea at elevated temperatures and hydroxy groups are much less reactive, 25 we posited that DHAUs could possibly be prepared from amino alcohols (AAs) and urea. A series of DHAUs with different alkylene lengths between the urea group and the hydroxy group were prepared: DHAU-4, DHAU-5, and DHAU-6 (Scheme 1). The reactions of urea with 4-amino-1-butanol (AA-4), 5-amino-1pentanol (AA-5), and 6-amino-1-hexanol (AA-6) were performed at 150 8C. In all these reactions the conversions were essentially quantitative within 24 h. The crude products were precipitated in acetone to remove the monosubstituted by-products and the remaining AAs. The isolated yields of DHAUs were all around 80%. The melting points of these DHAUs range from 110 to 128 8C.By transesterification polymerization, DHAUs react with DMEs to form PUEs (Scheme 1). It is of ...