Enhancing the Crystallization Performance of Poly(L-lactide) by Intramolecular Hybridizing with Tunable Self-assembly-type Oxalamide Segments

In this work, hydroxyl-terminated oxalamide compounds N^(1),N^(2)-bis(2-hydroxyethyl)oxalamide(OXA1) and N^(1),N^(1)′-(ethane-1,2-diyl)bis(N^(2)-(2-hydroxyethyl)oxalamide(OXA2) were synthesized to initiate the ring-opening polymerization of L-lactide for preparation of oxalamide-hybridized poly(L-lactide)(PLA_(OXA)), i.e., PLA_(OXA1) and PLA_(OXA2). The crystallization properties of PLA were improved by the self-assembly of the oxalamide segments in PLA_(OXA) which served as the initial heterogeneous nuclei. The crystal growth kinetics was studied by HoffmanLauritzen theory and it revealed that the nucleation energy barrier of PLA_(OXA1) and PLA_(OXA2) was lower than that of PLA. Consequently, PLA_(OXA) could crystallize much faster than PLA, accompanied with a decrease in spherulite size and half-life crystallization time by 74.8% and 86.5%(T=125 ℃), respectively. In addition, the final crystallinity of PLA_(OXA1) and PLA_(OXA2) was 6 and 8 times higher, respectively, in comparison with that of neat PLA under a controlled cooling rate of 10 ℃/min. The results demonstrate that the hybridization of oxalamide segments in PLA backbone will serve as the self-heteronucleation for promoting the crystallization rate. The higher the content of oxalamide segments(PLA_(OXA2) compared with PLA_(OXA1)) is, the stronger the promotion effect will be. Therefore, this study may provide a universal approach by hybridizing macromolecular structure to facilitate the crystallization of semi-crystalline polymer materials.

Preparation and Stability Evaluation of Size-Controllable PDHCA-β-CD Nanoparticles as Drug Carrier

A novel biocompatible polymer was prepared by grafting the derivate of β-cyclodextrin （6-SH-β-CD） onto poly（3,4-dihydroxycinnamic acid） （PDHCA） via Michael addition. PDHCA-β-CD nanoparticles were prepared by the self-assembly of amphiphilic PDHCA-β-CD polymer with N,N-dimethylformamide （DMF） as good solvent and water as poor solvent. The PDHCA-β-CD nanoparticles were monodispersed with spherical morphology as shown in the scanning electron microscopic （SEM） images in accord with the result of dynamic light scattering （DLS） measurement. The size of the nanoparticles could be controlled from 60 to 180 nm by tuning the grafting degree （GD） of PDHCA-β-CD polymer and also significantly influenced by the amount of water used during the process. These as-prepared nanoparticles were stable without any significant change in the particle size after six-months＇ storage and even after being irradiated by UV at 2〉280 nm for hours. The formation mechanism of PDHCA-β-CD nanoparticles was explored. The content of doxombicin （DOX） loaded onto the nanoparticles was up to 39% with relatively high loading efficiency （approximately 78.8% of initial DOX introduced was loaded）. In vitro release studies suggested that DOX released slowly from PDHCA-β-CD nanoparticles. These features strongly support the potential of developing PDHCA-β-CD nanoparticles as carriers for the controlled delivery of drug.