Investigation on the gelation behavior of biodegradable poly(butylene succinate) during isothermal crystallization process

The early stage of polymer crystallization may be viewed as physical gelation process,i.e.,the phase transition of polymer from liquid to solid.Determination of the gel point is of significance in polymer processing.In this work,the gelation behavior of poly(butylene succinate)(PBS) at different temperatures has been investigated by rheological method.It was found that during the isothermal crystallization process of PBS,both the storage modulus(G′) and the loss modulus(G″) increase with time,and the rheological response of the system varies from viscous-dominated(G′G″),meaning the phase transition from liquid to solid.The physical gel point was determined by the intersection point of loss tangent curves measured under different frequencies.The gel time(t_c) for PBS was found to increase with increasing crystallization temperature.The relative crystallinity of PBS at the gel point is very low(2.5%-8.5%) and increases with increasing the crystallization temperature.The low crystallinity of PBS at the gel point suggests that only a few junctions are necessary to form a spanning network,indicating that the network is"loosely"connected,in another word,the critical gel is soft.Due to the elevated crystallinity at gel point under higher crystallization temperature,the gel strength S_g increases, while the relaxation exponent n decreases with increasing the crystallization temperature.These experimental results suggest that rheological method is an effective tool for verifying the gel point of biodegradable semi-crystalline polymers.     

HYDROGEN-BONDING INDUCED CHANGE OF CRYSTALLIZATION BEHAVIOR OF POLY（BUTYLENE SUCCINATE） IN ITS MIXTURES WITH BISPHENOL A

In the present work, the blend of poly（butylene succinate） （PBS） and bisphenol A （BPA） was prepared by solution mixing, and the intermolecular interactions between the two components were characterized by a combination of nuclear magnetic resonance （NMR） and Fourier transform infrared spectroscopy （FTIR）. The results showed that intermolecular hydrogen-bonding forms between the carbonyl group of PBS and phenol hydroxyl of BPA. With the increase of BPA content, more hydrogen bonds were formed. The effect of hydrogen bonding on the crystallization behavior of PBS was investigated by differential scanning calorimetry （DSC） and polarized optical microscopy （POM）. The results showed that the overall isothermal crystallization kinetics and the spherulite growth rate of PBS decrease with the increase of BPA content, while the PBS spherulite size increases with BPA content.     

Hydrogen bonding interaction and crystallization behavior of poly (butylene succinate‐co‐butylene adipate)/thiodiphenol complexes

The poly (butylene succinate‐co‐butylene adipate) (PBSA)/thiodiphenol (TDP) complexes were prepared by melt blending. Intermolecular hydrogen bonding between carbonyl group of PBSA and hydroxyl group of TDP formed as verified by a combination FTIR and peak fitting technique. As a result, the crystallization temperature, melting temperature, crystallinity and crystallization rate of PBSA decreased with addition of TDP, implying impeded crystallization and reduced lamellar thickness. On the basis of Lauritzen–Hoffman analysis, the fold surface energy (σ_e) and work of chain folding (q) were increased by TDP incorporation. POM observation exhibited concentric ring‐banded spherulites for samples with 10 and 20 wt% TDP. A peculiar ring‐banded pattern with discrepant band spacing was obtained for the first time by addition of 30 wt% TDP, whose formation mechanism remains to be discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Thermal degradation kinetics of the biodegradable aliphatic polyester, poly(propylene succinate)

The preparation of the biodegradable aliphatic polyester poly(propylene succinate) (PPSu) using 1,3-propanediol and succinic acid is presented. Its synthesis was performed by two-stage melt polycondensation in a glass batch reactor. The polyester was characterized by gel permeation chromatography, ¹H NMR spectroscopy and differential scanning calorimetry (DSC). It has a number average molecular weight 6880 g/mol, peak temperature of melting at 44 °C for heating rate 20 °C/min and glass transition temperature at −36 °C. After melt quenching it can be made completely amorphous due to its low crystallization rate. According to thermogravimetric measurements, PPSu shows a very high thermal stability as its major decomposition rate is at 404 °C (heating rate 10 °C/min). This is very high compared with aliphatic polyesters and can be compared to the decomposition temperature of aromatic polyesters. TG and Differential TG (DTG) thermograms revealed that PPSu degradation takes place in two stages, the first being at low temperatures that corresponds to a very small mass loss of about 7%, the second at elevated temperatures being the main degradation stage. Both stages are attributed to different decomposition mechanisms as is verified from activation energy determined with isoconversional methods of Ozawa, Flyn, Wall and Friedman. The first mechanism that takes place at low temperatures is auto-catalysis with activation energy E = 157 kJ/mol while the second mechanism is a first-order reaction with E = 221 kJ/mol, as calculated by the fitting of experimental measurements.     

Multiblock copolymers composed of poly(butylene succinate) and poly(1,2-propylene succinate): Effect of molar ratio of diisocyanate to polyester-diols on crosslink densities, thermal properties, mechanical properties and biodegradability

In order to study the relationship between structure and properties, multiblock copolymers composed of poly(butylene succinate) (PBS) and poly (1,2-propylene succinate) (PPSu) have been synthesized by chain-extension at various molar ratios of hexamethylene diisocyanate (HDI) to polyester-diols, which have been abbreviated as R-values in this paper. Molecular weights of soluble fractions, gel fractions and crosslink densities have been determined. Thermal properties, mechanical properties and biodegradability have been studied and correlated with R-values. Crystallization of copolymers becomes difficult with increasing R-value. Tensile strength, flexural strength and flexural modulus tend to increase with increasing R-value up to 1.2, and vary little when R-value increases from 1.2 to 1.3, then decrease with further increase in R-value. Impact strength achieves a maximum value at R-value of 1.3. Biodegradation rate reaches a minimum value when R-value is 1.1. Biodegradation has been studied systematically by attenuated total reflectance Fourier transform infrared (ATR-FTIR), ¹H NMR and SEM.     

一种抗偏头痛复方制剂体外溶出度的比较研究

 A novel in vitro dissolution profile was developed for formulated drug in combinational form containing naproxen sodium (NAP) and sumatriptan succinate (SUMA). This study was performed to understand the dissolution of the drug in the physiological temperature and pH. Dissolution testing was performed using USP 29 type II testing apparatus rotating at 50 r/min, in 900 mL deaerated buffer （pH 1.2, 4.5 and 6.8） which was maintained at (37±0.5) ℃. Quantification was performed using a developed and validated high performance liquid chromatographic (HPLC) method. Aceclofenac (ACE) was used as internal standard. SUMA, ACE and NAP were eluted at 4.8, 5.7 and 7.9 min, respectively. As expected for enteric coated immediate release (IR) tablets, the dissolution of NAP and SUMA was rapid and essentially complete within 2 h using phosphate buffer (pH 6.8). The comparison of the dissolution profiles was realized by model independent approach using a difference factor (f1), similarity factor (f2) and dissolution efficiency (DE). Statistical results showed the profiles were similar to the reference and the test products. Hence, this method demonstrated to be adequate for in vitro studies of NAP and SUMA in the combinational dosage form, since there is no official monograph, collaborating to the official codes.     

The crystal structure of calcium succinate monohydrate

The crystal structure of calcium succinate monohydrate, Ca(C₄H₄O₄)·H₂O, has been determined by single crystal X-ray diffraction. The crystals are monoclinic witha=11.952(2),b=9.691(2),c=11.606(2)Å, =108.81(1)°, space group C2/c,Z=8,V=1272.49 ų,d _m =1.80, andd _c =1.818 Mg m^–3. The structure was refined by full-matrix least-squares techniques toR=0.027,R _w =0.040, for 829 reflections with13(I). Ca is coordinated to seven oxygen atoms, and the coordination polyhedron is best described as a pentagonal bipyramid. One carboxylate group in the succinate ion is bonded to three different Ca ions, forming a four-membered chelate ring with one Ca ion is bonded to three different Ca ions, forming a four-membered chelate ring with one Ca ion and unidentate bridge bonds to two other Ca ions. The other carboxylate group is bonded to two Ca ions through unidentate bonds. The structure is highly polymeric. The general structural features are nearly identical to those of calcium adipate monohydrate.Certain commercial materials and equipment are identified in this paper to specify the experimental procedure. In no instance does such identification imply recommendation or endorsement by the National Institute of Standards and Technology or the ADA Health Foundation or that the material or equipment identified is necessarily the best available for the purpose.     

生物降解高分子材料聚丁二酸丁二醇酯的改性研究进展

生物降解高分子材料被公认为是聚丙烯、聚乙烯等传统高分子材料造成"白色污染"的问题的重要解决方法之一。聚丁二酸丁二醇酯是重要的可生物降解的脂肪族聚酯之一,因与传统的聚丙烯、聚乙烯高分子材料具有相近的物理和力学性能,从而引起科学与工业界的广泛重视。然而,与大多数脂肪族聚酯一样,PBS材料也存在着加工、种类少、性能应用上的缺点。因此,对其通过改性拓宽用途范围的研究报道也随之增多。本文从化学、物理等改性的手段方法为着眼点,分类阐述了近些年来生物降解高分子材料聚丁二酸丁二醇酯改性研究现状与进展。     

Thermal degradation mechanism of poly(ethylene succinate) and poly(butylene succinate): Comparative study

Two aliphatic polyesters that consisted from succinic acid, ethylene glycol and butylene glycol, —poly(ethylene succinate) (PESu) and poly(butylene succinate) (PBSu)—, were prepared by melt polycondensation process in a glass batch reactor. These polyesters were characterized by DSC, ¹H NMR and molecular weight distribution. Their number average molecular weight is almost identical in both polyesters, close to 7000 g/mol, as well as their carboxyl end groups (80 eq/10⁶ g). From TG and Differential TG (DTG) thermograms it was found that the decomposition step appears at a temperature 399 °C for PBSu and 413 °C for PESu. This is an indication that PESu is more stable than PBSu and that chemical structure plays an important role in the thermal decomposition process. In both polyesters degradation takes place in two stages, the first that corresponds to a very small mass loss, and the second at elevated temperatures being the main degradation stage. The two stages are attributed to different decomposition mechanisms as is verified from the values of activation energy determined with iso-conversional methods of Ozawa, Flyn, Wall and Friedman. The first mechanism that takes place at low temperatures, is auto-catalysis with activation energy E = 128 and E = 182 kJ/mol and reaction order n = 0.75 and 1.84 for PBSu and PESu, respectively. The second mechanism is nth-order reaction with E = 189 and 256 kJ/mol and reaction order n = 0.68 and 0.96 for PBSu and PESu, respectively, as they were calculated from the fitting of experimental results.     

聚琥珀酸丁二酯的辐射交联及其生物降解性

对聚琥珀酸丁二酯（PBS1）采用两步法辐照，比其它辐照法得到的凝胶含量高，这是由于在室温下预先辐射所形成的交联网络结构减少了聚合物的降解。交联后的PBS1有较高的耐热变形性。通过酶降解试验和土需求量法降解实验，PBS1有很高的生物降解性，即使它产生了很高的交联结构。在65℃时，酶的降解率最高。由于交联样品所含有的交联网络结构阻碍它的降解，交联PBS1的生物降解失重低于未交联样品。