Four-arm, star-shaped poly(D,L-lactide) (PDLLA) oligomers of controlled molar mass and narrow molar mass distribution were successfully synthesized by use of an ethoxylated pentaerythritol initiator. Derivatization of the terminal hydroxyl groups with either methacrylic anhydride (MAAH) or 2-isocyanatoethyl methacrylate (IEM) to yield PDLLA-M (M = methacrylate end group) and PDLLA-UM (UM = urethane methacrylate end group), respectively, was monitored by in situ Fourier transform infrared (FTIR) spectroscopy. Photo-cross-linking of the functional oligomers yielded networks with high gel contents (>95%). The glass transition temperature (T(g)) of these networks was strongly dependent on prepolymer molar mass, and networks based on low molar mass precursors were more rigid than the networks obtained from higher molar mass oligomers. The tensile strength (TS) and Young's modulus of the PDLLA-M samples, approximately 7 and 17 MPa, respectively, were significantly lower than the values of 19 MPa (TS) and 113-354 MPa (Young's modulus) for the PDLLA-UM samples. The introduction of terminal hydrogen-bonding sites that were adjacent to the photo-cross-linking site resulted in higher performance poly(lactide)-based bioadhesives.

A new family of associating polymers based on four-arm, star-shaped poly(D,L-lactide) (PDLLA) containing peripheral complementary hydrogen-bonding sites is described. Hydroxy-terminated, four-arm, star-shaped PDLLAs of controlled molar mass were functionalized with complementary DNA base pairs, adenine (A) and thymine (T), to obtain PDLLA-A and PDLLA-T, respectively. 1H NMR spectroscopy confirmed quantitative functionalization and the subsequent formation of PDLLA-A and PDLLA-T hydrogen-bonded complexes. Job's analysis revealed a 1:1 optimal stoichiometry for the hydrogen-bonded complexes, and the association constant (Ka) that was determined using the 1H NMR-based Benesi-Hildebrand treatment was 84 M(-1) for the low molar mass complementary polymers. Furthermore, the PDLLA-based hydrogen-bonded complexes exhibited higher solution viscosities compared to the corresponding non-hydrogen-bonded precursors, which further confirmed strong complementary multiple-hydrogen-bonding associations between the star-shaped polymers with terminal adenine and thymine groups. Moreover, variable-temperature 1H NMR studies demonstrated the thermoreversibility of the hydrogen-bonded PDLLA-based complexes in solution.

SPONSOR/MONITOR'S ACRONYM(S) 9. SPONSORING/MONITORING AGENCY NAME(S) AND A SPONSOR/MONITOR'S REPORT NUMBER(S) DDRESS(ES) DISTRIBUTION/AVAILABILITY STATEMENTAppr ed for public release; distribution is unlimited. ov Self-assembly processes and subsequent photo-cross-linking were used to generate cross-linked, ordered microporous structures on the of well defined four-arm star-shaped poly(D,L-lactide) (PDLLA) thin films. The four-arm star-shaped PDLLAs were synthesized using a humid environment, and upon solvent evaporation ns between molar mass, polymer solution viscosity, and pore dimensions were established. The average pore dimension decreased with increasing polym ution concentration, and a linear relationship was observed between relative humidity and average pore dimensions. Highl rdered microporous structures were also developed on four-arm star-shaped methacrylate-modified PDLLA (PDLLA-UM) t in films. Subsequent photo-cross-linking resulted in more stable PDLLA porous films. The photo-cross-linked films were insoluble, and the honeycomb structures were retained despite solvent exposure. Free-standing, structured PDLLA-UM thin f s were obtained upon drying for 24 h. Ordered microporous films based on biocompatible and biodegradable polym h as PDLLA, offer potential applications in biosensing and biomedical applications. ReceiVed January 31, 2006. In Final Form: July 31, 2006 Self-assembly processes and subsequent photo-cross-linking were used to generate cross-linked, ordered microporous structures on the surfaces of well defined four-arm star-shaped poly(D,L-lactide) (PDLLA) thin films. The four-arm star-shaped PDLLAs were synthesized using an ethoxylated pentaerythritol initiator. Solutions of the PDLLAs were cast in a humid environment, and upon solvent evaporation, ordered honeycomb structures (or breath figures) were obtained. Correlations between molar mass, polymer solution viscosity, and pore dimensions were established. The average pore dimension decreased with increasing polymer solution concentration, and a linear relationship was observed between relative humidity and average pore dimensions. Highly ordered microporous structures were also developed on four-arm star-shaped methacrylate-modified PDLLA (PDLLA-UM) thin films. Subsequent photocross-linking resulted in more stable PDLLA porous films. The photo-cross-linked films were insoluble, and the honeycomb structures were retained despite solvent exposure. Free-standing, structured PDLLA-UM thin films were obtained upon drying for 24 h. Ordered microporous films based on biocompatible and biodegradable polymers, such as PDLLA, offer potential applications in biosensing and biomedical applications. SUPPLEMENTARY NOTES

The fabrication of enhanced hydrophobic surfaces via simple and inexpensive means will be discussed. Regular arrays of microscale pores were prepared in polymer matrices via the spontaneous assembly of water-vapor condensation, the so-called breath figure method. Using these regular arrays of pores as templates, the analogous array of pillars (inverse pores) was transferred to polymeric films. These microtextured surfaces have greatly enhanced the hydrophobicity of the polymer when measured by the contact angle. This method of producing super-hydrophobic textured surfaces should be amenable to high-throughput, low-cost manufacturing of many polymeric surfaces.

Four‐armed, star‐shaped poly(D,L‐lactide) (PDLLA) was synthesized and terminally‐functionalized with either adenine or thymine complementary hydrogen bonding groups (PDLLA‐A and PDLLA‐T, respectively). The strong hydrogen bonding led to increased viscosity below the dissociation temperature of the hydrogen bonds. Rheology confirmed that these bonds were thermally reversible, with a sharp reduction in viscosity near 100 °C. PDLLA, PDLLA‐A, and PDLLA‐T were melt electrospun with no significant change in fiber diameter (all between 3.6 and 4.0 µm). However, a blend of PDLLA‐A and PDLLA‐T formed fibers with an average diameter of 9.8 ± 2.0 µm, resulting from the hydrogen bond associations. Also, the phospholipid 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphoethanolamine (POPE) was melt electrospun at 200 °C and formed uniform fibers with average fiber diameter of 6.5 ± 2.0 µm.

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