Tuning the mechanical properties and degradation properties of polydioxanone isothermal annealing

Polydioxanone (PPDO) is synthesized by ring-opening polymerization of p-dioxanone, using stannous octoate as the catalyst. The polarized optical micrograph (POM) shows thes pherulite growth rate of PPDO decreases with an increase in the isothermal crystallization temperature. PPDO is compression-molded into bars, and PPDO bars are subjected to isothermal annealing at a range of temperatures (Ta = 50, 60, 70, 80, 90, and 100 °C), and correspond to three different annealing times (ta = 1h, 2h, 3h). The effect on PPDO is investigated by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). With an increase in Ta and ta, the grain size and the degree of crystallinity also increase. Meanwhile, the tensile strength is significantly improved. The PPDO bars (90 °C, 2 h) reach the maximum crystallinity (57.21%) and the maximum tensile strength (41.1 MPa). Interestingly, the heat treatment process does not result in serious thermal degradation. It is observed that the hydrolytic degradation of the annealed PPDO is delayed to some extent. Thus, annealed PPDO might have potential applications, particularly in the fields of orthopedic fixation and tissue engineering.     

Oxidation of polycaprolactone to induce compatibility with other degradable polyesters

Chemical modification of poly(?-caprolactone) PCL by oxidation with potassium permanganate in solution was investigated. According to the data obtained from Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance ¹H NMR, after the oxidation reactions the PCL chains exhibited new functional groups (vinyl and hydroxyl) and possible intermolecular recombination, producing an oxidized-polycaprolactone (PCL-OX). Solution viscometry indicated that degradation also occurred during the oxidation reactions (∼30% drop in viscosity average molecular weight was detected). Differential scanning calorimetry (DSC) also indicated that PCL was chemically modified and degraded. The successive self-nucleation/annealing (SSA) treatment confirmed that a reduction (or interruption) in linear crystallizable sequences occurred. The immiscibility of blends of PCL with other degradable polyesters, such as poly(p-dioxanone) PPDX (PCL/PPDX 90:10 w/w), was shown by the invariability of the relevant thermal transitions as determined by DSC and FT-IR and NMR analysis. However, the blend prepared with oxidized PCL (PCL-OX/PPDX, in the same composition range) did not display signs of thermodynamic miscibility but showed an interesting thermal behaviour demonstrated by changes in the crystallization temperatures of both phases, and by the melting behaviour of the PCL-OX in the blend. These results together with spectroscopic analysis show that the oxidation of PCL induces physical interactions and/or compatibilisation among the phases of this blend.     

聚二氧杂环己酮合成可吸收缝合线体外降解研究

通过检测缝线的力学性能、分子量、失重、大分子取向和结晶度变化研究了聚二氧杂环己酮可吸收缝合线（ＰＤＳ）在体外的初期（４星期）降解过程。研究结果表明，本文工艺条件下研制的ＰＤＳ缝线在体外降解过程中随着分子量和大分子取向程度下降，力学性能明显下降，４星期时强度基本消失。分子量明显下降而失重变化很小的结果，证明ＰＤＳ缝线的酯水解在链中和链端等活性，水解的几率只与水分子的可及程度相关。ＷＡＸＤ和ＤＳＣ测试结果表明，随着体外降解进行，缝线原晶区基本保持不变，无定形区产生新的有序区，并且含量不断增加和完善。采用结晶高聚物微原纤结构模型解释ＰＤＳ缝线无定形区在水中的降解机理与研究结果相吻合。ＰＤＳ缝线的体外降解机理与聚羟基乙酸（ＰＧＡ）缝线基本相同     

高分子量聚对二氧环己酮改进聚DL-乳酸柔韧性的研究

为了提高DL-聚乳酸(PDLLA)的柔韧性,将10～20wt%不同比例的由本课题组自主合成的高分子量聚对二氧环己酮(PPDO)加入到PDLLA基体中,对共混物的微观两相形态、力学性能、热学性能和表面性质、降解性能等物化性质进行了研究.实验结果表明,PPDO加入后,在PDLLA/PPDO共混物的柔韧性得到显著提高的同时,共混物表面亲水性相应提高,降解速率也随之加快.