Poly(urea ester): A family of biodegradable polymers with high melting temperatures

Abstract

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 ...

Fabrication of Food-Safe Water-Resistant Paper Coatings Using a Melamine Primer and Polysiloxane Outer Layer

“…Figure shows the FTIR spectra of the printed paper (a) and cup paper (b) at various stages during the fabrication process. The melamine C–N stretching in IR for the melamine-primed paper overlapped with that from the uncoated paper at 1553 cm –1 . The melamine–PDMS-primed paper exhibits several characteristic peaks corresponding to the PDMS.…”

“…The melamine C–N stretching in IR for the melamine-primed paper overlapped with that from the uncoated paper at 1553 cm –1 . 39 The melamine–PDMS-primed paper exhibits several characteristic peaks corresponding to the PDMS. For example, the peak at 1260 cm –1 corresponds to the stretching vibration of the −CH 3 groups in the Si–CH 3 moieties of PDMS, whereas the peak at 798 cm –1 represents the −CH 3 rocking and Si–C stretching of PDMS.…”

“…Melamine is a FDA-approved material for food-contact applications (tolerable level is 0.63 mg/kg of body weight, per day) that exhibits superior binding to paper because it is a strong hydrogen donor as well as an acceptor, thus providing it with excellent performance as a primer. Meanwhile, the use of PDMS–isocyanate (NCO) enables the chemical grafting of PDMS to melamine via a biodegradable urea linkage formed as a result of a reaction between the NCO and amine groups of PDMS and melamine, respectively . In the absence of melamine, the bonding between PDMS and paper would be weak, and the PDMS could be readily washed away from the paper.…”

“…Meanwhile, the use of PDMS−isocyanate (NCO) enables the chemical grafting of PDMS to melamine via a biodegradable urea linkage formed as a result of a reaction between the NCO and amine groups of PDMS and melamine, respectively. 39 In the absence of melamine, the bonding between PDMS and paper would be weak, and the PDMS could be readily washed away from the paper. As a result, water-resistant-coated paper bears PDMS as its outer layer that is firmly held onto the paper substrate by an intermediate melamine layer.…”

Influence of Short-Range Scrambling of Monomer Order on the Hydrolysis Behaviors of Sequenced Degradable Polyesters

“…Although there has been an increasing effort in studying structure and function in SCPs, − little is known about the sensitivity of properties to sequence errors. Synthetic advances have aided in both the expansion in the number and types of SCPs − and the studies of the bulk properties, − solution properties, ,,− and complex behaviors − of these materials. Still, there has been less effort to date in trying to understand the effects of sequence errors.…”