Multiple sol-gel transitions of PEG-PCL-PEG triblock copolymer aqueous solution

An aqueous solution of a poly(ethylene glycol)-polycaprolactone-poly(ethylene glycol) (PEG-PCL-PEG) with a composition of EG13CL23EG13 undergoes multiple transitions, from sol-to-gel (hard gel)-to-sol-to-gel (soft gel)-to-sol, in the concentration range 20.0∼35.0 wt.-%. Through dynamic mechanical analysis, UV-vis spectrophotometry, small angle X-ray scattering, differential scanning calorimetry, microcalorimetry and 13C NMR spectroscopy, the mechanism of these transitions was investigated. The hard gel and soft gel are distinguished by the crystalline and amorphous state of the PCL. The extent of PEG dehydration and the molecular motion of each block also played a critical role in the multiple transitions. This paper suggests a new mechanism for these multiple transitions driven by temperature changes.

Synthesis and characterization of PCL/PEG/PCL triblock copolymers by using calcium catalyst

Triblock copolymer PCL-PEG-PCL was prepared by ring-opening polymerization of epsilon-caprolactone (CL) in the presence of poly(ethylene glycol) catalyzed by calcium ammoniate at 60 degreesC in xylene solution. The copolymer composition and triblock structure were confirmed by H-1 NMR and C-13 WR measurements. The differential scanning calorimetry and wide-angle X-ray diffraction analyses revealed the micro-domain structure in the copolymer. The melting temperature T-c and crystallization temperature T-c of the PEG domain were influenced by the relative length of the PCL blocks. This was caused by the strong covalent interconnection between the two domains. Aqueous micelles were prepared from the triblock copolymer. The critical micelle concentration was determined to be 0.4-1.2 mg/l by fluorescence technique using pyrene as probe, depending on the length of PCL blocks, and lower than that of corresponding PCL-PEG diblock copolymers. The H-1 NMR spectrum of the micelles in D2O demonstrated only the -CH2CH2O- signal and thus confirmed. the PCL-core/PEG-shell structure of the micelles.

Fabrication using a rapid prototyping system and in vitro characterization of PEG-PCL-PLA scaffolds for tissue engineering

n the field of tissue engineering new polymers are needed to fabricate scaffolds with specific properties depending on the targeted tissue. This work aimed at designing and developing a 3D scaffold with variable mechanical strength, fully interconnected porous network, controllable hydrophilicity and degradability. For this, a desktop-robot-based melt-extrusion rapid prototyping technique was applied to a novel tri-block co-polymer, namely poly(ethylene glycol)-block-poly(epsi-caprolactone)-block-poly(DL-lactide), PEG-PCL-P(DL)LA. This co-polymer was melted by electrical heating and directly extruded out using computer-controlled rapid prototyping by means of compressed purified air to build porous scaffolds. Various lay-down patterns (0/30/60/90/120/150°, 0/45/90/135°, 0/60/120° and 0/90°) were produced by using appropriate positioning of the robotic control system. Scanning electron microscopy and micro-computed tomography were used to show that 3D scaffold architectures were honeycomb-like with completely interconnected and controlled channel characteristics. Compression tests were performed and the data obtained agreed well with the typical behavior of a porous material undergoing deformation. Preliminary cell response to the as-fabricated scaffolds has been studied with primary human fibroblasts. The results demonstrated the suitability of the process and the cell biocompatibility of the polymer, two important properties among the many required for effective clinical use and efficient tissue-engineering scaffolding.

双结晶性PEG-PCL两嵌段共聚物的合成，结晶行为和形态

聚乙二醇－聚ε-己内酯两嵌段共聚物（PEG-PCL）由于其在生物医用材料中的潜在应用而受到广泛的关注。然而，研究表明这类嵌段共聚物的许多性质，如药物渗透性，降解性能和机械性质等，都要受到它们的结晶行为与聚集态结构的显著影响。而在本课题开始之前，还没有关于PEG-PCL的结晶行为与形态的系统研究报道。因此，本文希望通过对PEG-PCL两嵌段共聚物结晶行为与形态的研究，能为这类生物降解高分子材料的工业应用提供一定的科学依据。本文使用辛酸亚锡为催化剂，甲氧基聚乙二醇（mPEG）为大分子引发剂，合成了一系列分子量分布比较窄，PCL质量百分含量为0.16-0.93的PEG-PCL两嵌段共聚物。两嵌段共聚物中的PEG段分子量固定为5000，共聚物的组成通过改变PCL链段的长度来调节。本文使用DSC，WAXD，常温或变温FTIR详细研究了PEG-PCL的结晶和熔融行为，使用偏光显微镜（POM）观察了PEG-PCL的结晶形态及结晶生长行为，利用SAXS研究了PEG-PCL的微观形态，得出了如下结果：（1）WAXD与FTIR的结果表明，两嵌段共聚物中的PEG与PCL形成微相分离的结晶微区，不存在两者的共晶或混晶。PCL含量为0.23-0.87的两嵌段共聚物中都能观察到的PEG与PCL的结晶。变温FTIR结果显示，当PCL含量低于或等于0.36，两嵌段共聚物中的PEG先从熔体中结晶；反之，当PCL含量等于或大于0.43，则熔体中PCL结晶先出现。（2）DSC结果表明，随着PEG-PCL中PCL段长度的增加，PCL段的结晶和熔融温度显著增加；相反，PEG段的结晶和熔融温度则显著降低。当PCL的质量分数由0增加至0.93，PEG的结晶度从79%降低至0，然而PCL的结晶度却不是单调变化，而是出现一个最大值。（3）在POM下观察PEG-PCL的36 oC等温熔体结晶过程，当PCL质量分数不超过0.36时，在偏光显微镜下只能观察到PEG球晶；而当PCL质量分数大于或等于0.56时，只能观察到PCL球晶；PCL含量为0.43和0.50的两种两嵌段共聚物中观察到了一种独特的同心球晶，同心球晶的中心部分形态类似于PCL球晶，而外部则类似于PEG球晶。PEG球晶与PCL球晶生长速率受PCL含量的影响显著：当PCL质量分数从0增加至0.50，PEG球晶的生长速率大大降低；然而，PCL球晶的生长速率却不是单调变化，而是在PCL质量分数为0.62时达到最大值。（4）SAXS结果表明，结晶后的PEG-PCL的微区结构是由交替的PEG与PCL的层状微区组成。共聚物的长周期在PCL质量分数为0.50时达到最大值。当PCL质量分数由0增加至0.50时，由于PCL层厚度的显著增加，共聚物的长周期显著增加；而当PCL含量由0.50继续增加至0.87，由于PEG层厚度的急剧降低，又使得共聚物的长周期迅速降低。（5）首次利用POM和微区红外光谱详细研究了PEG-PCL50/50(w/w)同心球晶的形成过程，发现同心球晶的形成是由于一种独特的结晶动力学造成的。另外，即使同心球晶的中心和外部的形态差别巨大，但是红外显微镜结果显示，两部分的组成却是相同的。

Development of hydrophilic nanocarriers for the charged form of the local anesthetic articaine

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Poly(epsilon-capralactone)/poly(ethylene oxide) diblock copolymer .2. Nonisothermal crystallization and melting behavior

The nonisothermal crystallization behavior and melting process of the poly(epsilon-caprolactone) (PCL)/poly(ethylene oxide) (PEG) diblock copolymer in which the weight fraction of the PCL block is 0.80 has been studied by using differential scanning calorimetry (DSC). Only the PCL block is crystallizable, the PEO block with 0.20 weight fraction cannot crystallize. The kinetics of the PCL/PEO diblock copolymer under nonisothermal crystallization conditions has been analyzed by Ozawa's equation. The experimental data shows no agreement with Ozawa's theoretical predictions in the whole crystallization process, especially in the later stage. A parameter, kinetic crystallinity, is used to characterize the crystallizability of the PCL/PEO diblock copolymer. The amorphous and microphase separating PEO block has a great influence on the crystallization of the PCL block. It bonds chemically with the PCL block, reduces crystallization entropy, and provides nucleating sites for the PCL block crystallization. The existence of the PEO block leads to the occurrence of the two melting peaks of the PCL/PEO diblock copolymer during melting process after nonisothermal crystallization. The comparison of nonisothermal crystallization of the PCL/PEO diblock copolymer, PCL/PEO blend, and PCL and PEO homopolymers has been made. It showed a lower crystallinity of the PCL/PEO diblock copolymer than that of others and a faster crystallization rate of the PCL/PEO diblock copolymer than that of the PCL homopolymer, but a slower crystallization rate than that of the PCL/PEO blend. (C) 1997 John Wiley & Sons, Inc.

Processing of polycaprolactone and polycaprolactone-based copolymers into 3D scaffolds and their cellular responses

Synthetic polymers have attracted much attention in tissue engineering due to their ability to modulate biomechanical properties. This study investigated the feasibility of processing poly(varepsilon-caprolactone) (PCL) homopolymer, PCL-poly(ethylene glycol) (PEG) diblock, and PCL-PEG-PCL triblock copolymers into three-dimensional porous scaffolds. Properties of the various polymers were investigated by dynamic thermal analysis. The scaffolds were manufactured using the desktop robot-based rapid prototyping technique. Gross morphology and internal three-dimensional structure of scaffolds were identified by scanning electron microscopy and micro-computed tomography, which showed excellent fusion at the filament junctions, high uniformity, and complete interconnectivity of pore networks. The influences of process parameters on scaffolds' morphological and mechanical characteristics were studied. Data confirmed that the process parameters directly influenced the pore size, porosity, and, consequently, the mechanical properties of the scaffolds. The in vitro cell culture study was performed to investigate the influence of polymer nature and scaffold architecture on the adhesion of the cells onto the scaffolds using rabbit smooth muscle cells. Light, scanning electron, and confocal laser microscopy showed cell adhesion, proliferation, and extracellular matrix formation on the surface as well as inside the structure of both scaffold groups. The completely interconnected and highly regular honeycomb-like pore morphology supported bridging of the pores via cell-to-cell contact as well as production of extracellular matrix at later time points. The results indicated that the incorporation of hydrophilic PEG into hydrophobic PCL enhanced the overall hydrophilicity and cell culture performance of PCL-PEG copolymer. However, the scaffold architecture did not significantly influence the cell culture performance in this study.

Melt electrospinning of polycaprolactone and its blends with poly(ethylene glycol)

Melt electrospinning is one aspect of electrospinning with relatively little published literature, although the technique avoids solvent accumulation and/or toxicity which is favoured in certain applications. In the study reported, we melt-electrospun blends of poly(ε-caprolactone) (PCL) and an amphiphilic diblock copolymer consisting of poly(ethylene glycol) and PCL segments (PEG-block-PCL). A custom-made electrospinning apparatus was built and various combinations of instrument parameters such as voltage and polymer feeding rate were investigated. Pure PEG-block-PCL copolymer melt electrospinning did not result in consistent and uniform fibres due to the low molecular weight, while blends of PCL and PEG-block-PCL, for some parameter combinations and certain weight ratios of the two components, were able to produce continuous fibres significantly thinner (average diameter of ca 2 µm) compared to pure PCL. The PCL fibres obtained had average diameters ranging from 6 to 33 µm and meshes were uniform for the lowest voltage employed while mesh uniformity decreased when the voltage was increased. This approach shows that PCL and blends of PEG-block-PCL and PCL can be readily processed by melt electrospinning to obtain fibrous meshes with varied average diameters and morphologies that are of interest for tissue engineering purposes. Copyright © 2010 Society of Chemical Industry

Nonisothermal crystallization behavior of poly (L-lactide)-poly(ethylene glycol) dibloick copolymer

The nonisothermal crystallization behavior of poly (L-lactide)-poly(ethylene glycol) ( PLLA-PEG) diblock copolymer was studied by means of real-time WAXD, DSC and POM, and Ozawa equation was used to analyze the kinetics of PLLA-PEG under nonisothermal crystallization conditions. During the crystallization of the high-T-m block (PLLA), the low-T-m block (PEG) acts as a noncrystalline diluent, and the crystallization behavior of PLLA obeys the Ozawa theory. When the PEG block begins to crystallize, the PLLA phase is always partially solidified and the presence of the spherulitic microstructure of PLLA profoundly restricts its crystallization behavior, which results in that the overall crystallization process does not obey the Ozawa equation. Furthermore, the study of the crystalline morphology of PLLA-PEG at different cooling rates indicates that when the cooling rate is from low to high, the crystalline morphology undergoes a transformation from the ring-banded spherulites to the typical Maltese cross spherulites, which experiences the mixed crystalline morphologies of ring-banded and typical Maltese cross spherulites, and the spherulitic size becomes smaller.

Polymersomes, smaller than you think : ferrocene as a TEM probe to determine core structure

By incorporating ferrocene into the hydrophobic membrane of PEG-b-PCL polymersome nanoparticles it is possible to selectively visualize their core using Transmission Electron Microscopy (TEM). Two different sizes of ferrocene-loaded polymersomes with mean hydrodynamic diameters of approximately 40 and 90 nm were prepared. Image analysis of TEM pictures of these polymersomes found that the mean diameter of the core was 4–5 times smaller than the mean hydrodynamic diameter. The values obtained also allow the surface diameter and internal volume of the core to be calculated.

钙催化剂在生物降解脂肪族聚酯合成中的应用

生物降解高分子在环境保护以及组织工程、药物控制释放、骨固定等医药领域有着广泛的应用。特别是以聚丙交酷（PLA）、聚乙交酯（PGA）、聚。一己内酯（PCL）以及它们的共聚物为代表的化学合成生物降解高分子材料，由于具有优异的性能、可以大规模生产、成本较低等优点，得到了人们广泛的关注。作为生物医用材料，对无毒性的要求很严。而现在所用的脂肪族聚酯大都是用金属盐、金属有机化合物等作为催化剂合成出来的，不可避免残留一些催化剂所用的金属元素。研究表明，即使是已经获得美国FDA批准的，现在用得最普遍的辛酸亚锡所残留的锡也可能引起一些细胞毒性。因此对毒性小且活性高的催化剂的研究是非常有意义。钙离子对人体是没有毒性的，因而这几年已引起了人们的兴趣，但文献中报道的钙催化剂，如CaHZ等，催化活性尚不够让人满意。本文对高效的钙催化剂在生物降解脂肪族聚酯中的应用进行详细的研究，得到了一些有意义的结论：1、用EO和PO处理的有机氨钙催化剂（Ca／EO和Ca／PO）聚合了CL和LLA。发现CL聚合速度很快，M／I=650时70℃反应3h后收率已达到90％以上，LLA的聚合速度比CL要慢，M／I=650、70℃反应10h后收率才达到90％以上。以上聚合反应有明显的活性聚合的特点：反应初期Mv和收率和聚合时间呈线性关系；Mv在一定范围内和M／I成线性关系。2、用红外、原子吸收和核磁共振等分析手段阐明了有机氨钙催化剂的结构：结构，而且这两个催化剂的活性中心分别是均是Ca-O键。CL和LLA的开环聚合可能是以配位一插入的机理进行的。3、用C。／PO催化剂聚合LLA时有一定程度的消旋化反应发生，曳NMR研究表明相当于88％的LLA和12％外消旋以共聚。提高反应温度到110℃时比旋光度只有-125℃说明消旋化反应比较严重。4、用C。／PO催化剂先聚合CL再聚合LLA的方法合成了PCL-PLA两嵌段共聚物，并用泊NMR，13C NMR，GPC，DSC，WAXD进行了表征。其绝对和相对分子量可以通过M／I和投料比进行控制。定量碳谱图表明有较严重的消旋化反应发生，相当于84％的LLA和16％外消旋LA共聚。DSC和似XD分析表明，PLA段的分子量小时PLA段不结晶，当PLA段的分子量达到一定程度（3000以上）后PCL一PLA嵌段共聚物有相分离现象发生。5、以各种分子量的PEG为引发剂用氨钙催化剂和开环聚合CL，合成了一系列PCL-PEG-PCL三嵌段共聚物，并用妞NMR，laCNMR，GPC，DSC，做XD进行了表征。聚合物的结构可以通过改变PEG的分子量和CL／PEG投料比来调整。从DSC和wAXD分析可以得出以下几个结论：PCL-PEG-PCL嵌段共聚物有相分离现象发生，形成PCL和PEG微相区域；PEG段的结晶行为受先结晶的PCL段的影响；PCL段的分子量越大PEG段的Tc和Tm越低，其结晶度越低。6、以各种分子量的PEG为引发剂用氨钙催化剂80℃下开环聚合LLA24小时，合成了一系列PLA-PEG-PLA三嵌段共聚物，和别的催化剂比起来温度低得多，反应时间也短得多。可以通过改变PEG的分子量和CL／PEG投料比来调整聚合物的结构。DSC和WAXD分析表明，PLA-PEG-PLA三嵌段共聚物中PEG段的结晶能力受PLA段的影响非常大：当PEG段的分子量很小时（如1000）很难结晶；即使当PEG段的分子量较大时如果PLA段的分子量达到一定程度时PEG段同样也不结晶；而且PLA段的结晶行为受本身分子量的影响比较大，其Tc和伽随着分子量增加有较大的提高。7、合成了MPEG-PLA两嵌段共聚物，发现合成PLA段的分子量大的聚合物比较困难，MPEG-PCL两嵌段共聚物很难合成。DsC和WAXD分析表明，PLA段对MPEG段结晶有一定程度的影响，但是比三嵌段共聚物的影响要小得多。8、用荧光光谱和IHNMR研究了上面合成出的几个样品的胶束行为。发现cmc由大到小的顺序为MPEG（5000）-PLA（5100），PLA（3050）-PEG（4600）-PLA（3050），PCL（2270）-PEG（5000）-PCL（2270），PCL（4600）-PEG（4600）-PCL（4600）。PCL-PEG-PCL三嵌段共聚物在水中形成了具有核一壳结构的胶束。9、以苯甲醇处理的有机氨钙催化剂开环聚合了CL。泊NMR谱图表明得到的聚合物具有苯端基。这一结果为用硝苯基乙醇代替苯甲醇制备催化剂，然后开环聚合CL或LA得到硝基苯端基的脂肪族聚酯打下了实验基础。

聚3—羟基丁酸酯与聚丙撑碳酸酯共混体系研究

本论文对完全生物降解聚（3—羟基丁酸酯）（PHB）和聚丙撑碳酸酯（PPC）共混体系进行了全面研究，目的是提高PHB的综合性能，加深对共混高聚物的基本物理问题的认识，进一步明晰高聚物的结构和性能之间的关系.1.在分析判断PPC的热降解机理的基础上，对PPC进行了封端处理，阻止了以端羟基回咬“解拉链”方式引起的热降解，增加了PPC热降解反应活化能，显著地提高了PPC的稳定性（提高30K以上）.2.经热性能和形态结构等方面的表征，PHB/PPC共混体系为不相容体系，直接在PHB中加入PPC不能改善PHB的韧性和其它力学性能.3.PCL-PEG-PCL嵌段共聚物能够作为PHB/PPC的增容剂，在PHB/PPC共混体系中加入PCL-PEG-PCL三嵌段共聚物能显著减小分散相的平均尺寸.4.选用增塑剂对PPC进行增塑能够在很大范围内（80K）调节PPC的玻璃化转变温度，使PPC表现出弹性体的特性，拓宽了PPC的应用范围.5.增塑剂1,2丙二醇碳酸酯（PGC）对PHB有一定的增塑作用，但不能明显改善PHB的力学性能.6.增塑后的PPC是PHB的良好增韧剂，使PHB由脆性断裂转变为韧性断裂，最佳增韧效果可使PHB的抗冲击强度由36J/m增加到70PHB/30PPC/20PGC的307J/m，增加8倍.7.增塑后的PPC能够实现对PHB增韧，是增塑剂使得PPC在冲击实验条件下仍然保持弹性体的性质，由此引发空洞化、多重银纹和剪切屈服共存的增韧方式提高PHB的性能.

双结晶性嵌段共聚物的合成及结晶形貌研究

众所周知，嵌段共聚物聚乙二醇一聚L-丙交酯（PEG-LLA）、聚乙二醇一聚ε-己内酯（PEG-PCL）中的两个嵌段都是结晶性的，用它们作为结晶一结晶型嵌段共聚物的代表来研究结晶行为和结晶结构是很有意义的，但由于它们的结晶行为比结晶一非晶型的嵌段共聚物要复杂得多，因而至今相关报道很少。本论文合成了不同分子量的聚乙二醇一聚L-丙交酯两嵌段共聚物并对其结晶行为和形貌进行了详细的表征，具体研究结果如下：（1）DSC结果显示，嵌段共聚物中PLLA晶体和PEG晶体共存，并在升温和降温过程中显示出各自的熔融温度（Tm）和结晶温度（Tc），PEG链段的Tm都低于均聚物PEG的Tm，并且随着PLLA链段分子量的增加而降低。另一方面，均聚物PEGSO00的Tc要高于共聚物中的PEG链段Tc的。此外，嵌段共聚物中PEG链段的Tc都随着PLLA链段长度的增加而降低。（2）结果显示，嵌段共聚物的谱图恰好是两个均聚物PEG和PLLA谱图的叠加。这说明在嵌段共聚物中同时存在两个嵌段PEG链段和PLLA链段的相分 离的结晶微区。（3）在110℃或120℃时，不同分子量的嵌段共聚物PEG-PLLA都可以形成环带结晶形貌。偏光显微镜下的周期性的明暗交替消光与原子力显微镜观察到的表面的周期性的凸凹起伏都是由于PLLA片晶沿着球晶的半径方向作周期性扭曲造成的。（4）AFM观察环带球晶发现，凸起部分（ridge）的PLLA片晶以Edge-on方式堆砌，凹下部分（valley）的PLLA片晶主要是以Flat-on的方式堆砌。可见，AFM图像可以更直观的表现出球晶的结构和形态。好M还观察到了嵌段共聚 物的菱形单晶形貌，并发现在单晶中心伴有明显的螺旋位错结构。（5）在110或120℃时，先结晶的PLLA嵌段的片层为PEG的结晶提供了受限环境。PEG的结晶在微米尺度上虽然不会改变嵌段共聚物单晶的形貌，但会增加了单晶的片层厚度。本论文还合成了不同分子量的聚乙二醇一聚s一己内酷两嵌段共聚物并对其结晶行为和形貌进行了详细的表征，具体研究结果如下：（1）DSC结果显示，在嵌段共聚物中，固定PEG嵌段的长度时，随着PCL嵌段长度的增加，PCL嵌段的结晶温度和融温度变化不大，PEG嵌段的结晶温度和熔融温度变化很大。（2） POM结果显示，在不同的结晶温度下，PEG5000-PCL1000形成的球晶类似PEG均聚物的结晶形貌，PEG5000-PCL9000和PEG5000-PCL26000形成的球晶类似于均聚物PCL的结晶形貌，说明嵌段长度对整个结晶形貌的影响很大。（3）PEG5000-PCL5000显示出一种独特的结晶形貌一同心双球晶结晶形貌。同心双球晶的中心和外部分属于PCL嵌段和PEG嵌段的结晶。在同心双球晶的形成过程中，PEG嵌段从同心双球晶的中心一先结晶的PCL晶体片层开始生长，然后以较快的结晶速率冲破PcL球晶，形成自己独立的结晶微区结构。（4）在25，52℃等温结晶后，PEG5000-PCL5000和PEG5000-PCL9000的好M图片上呈现出一种独特的结晶形貌一纤维状或称羽毛状的结晶形貌，这属于PCL链段的结晶形貌。PEG5000-PCL16000和PEG50OO一PCL260OO由于其较长的PCL嵌段，导致其形貌大体上类似于均聚物PcL8000的树枝状形貌。PEG5000-PCLI000呈现有取向的条带结晶结构，类似于均聚物PEG5000的结晶形貌。（5）在36℃等温结晶后，PEG5000-PCL5000和PEG5000-PCL9000的AFM图片上呈现出的树枝状结构宽厚，肥大，这也许是因为PEG作为溶剂或稀释剂促进了PCL嵌段的结晶，使其晶体尺寸增加。

Study of the synthesis, crystallization, and morphology of poly(ethylene glycol)-poly(is an element of-caprolactone) diblock copolymers

Poly(ethylene glycol) -poly(epsilon-caprolactone) diblock copolymers PEG-PCL were synthesized by ring-opening polymerization of c-caprolactone using monomethoxy poly(ethylene glycol) as the macroinitiator and calcium ammoniate as the catalyst. Obvious mutual influence between PEG and PCL crystallization was studied by altering the relative block length. Fixing the length of the PEG block (M-n = 5000) and increasing the length of the PCL block, the crystallization temperature of the PCL block rose gradually from I to about 35 degreesC while that of the PEG block dropped from 36 to -6.6 degreesC. Meanwhile, the melting temperature of the PCL block went up from 30 to 60 degreesC, while that of the PEG block declined from 60 to 41 degreesC. If the PCL block was longer than the PEG block, the former would crystallize first when cooling from a molten state and led to obviously imperfect crystallization of PEG and vice versa. And they both crystallized at the same temperature, if their weight fractions were equal. We found that the PEG block could still crystallize at -6.6 degreesC even when its weight fraction is only 14%. A unique morphology of concentric spherulites was observed for PEG5000-PCL5000.