Appearance of double spherulites like concentric circles for poly(ϵ-caprolactone)-block-poly(ethylene glycol)-block-poly(ϵ-caprolactone)

Shiomi, Tomoo; Imai, Kiyokazu; Takenaka, Katsuhiko; Takeshita, Hiroki; Hayashi, Hisao; Tezuka, Yasuyuki

doi:10.1016/s0032-3861(00)00597-8

Cited by 85 publications

(73 citation statements)

References 19 publications

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“…Block copolymers, consisting of both crystalline and amorphous segments were widely recognized that their crystallization processes and the resulting crystal morphologies can be significantly influenced by microphase separation in melt [6,7]. However, block copolymers, consisting of different crystalline segments such as the double crystalline block copolymers, usually exhibit much more complicated crystallization behaviors [8,9], including confined crystallization [10][11][12][13], competitive or interactive crystallization and so on [14][15][16]. For these block copolymers, the overall crystallization behavior is influenced by block ratios, nucleation types, crystallization kinetics and characteristics of the individually folded chains [5,[17][18][19].…”

Section: Introductionmentioning

confidence: 99%

“…Recently, with the comprehensive investigations on crystallization process for block copolymers, the high order structures containing crystal lamellae were frequently discovered [6,[21][22][23][24][25], where several types of spherulites with unusual morphologies such as ring banded spherulite, spherical granular aggregates and double concentric spherulites have been reported [14,15,[26][27][28][29][30][31]. Especially, the double concentric spherulites were only found in poly(ethylene oxide)/poly(!-caprolactone) PEG/PCL block copolymer up to now [14,[26][27][28][29]. This complex morphology contains an initial spherulite in center and a concentric outside spherulite with different crystal structure.…”

Section: Introductionmentioning

confidence: 99%

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Poly(ethylene glycol)-poly(tetrahydrofuran)-poly(ethylene glycol) triblock copolymer : Synthesis, crystallization behavior and novel morphology

Wang¹,

Fan²,

Tian³

et al. 2013

Express Polym. Lett.

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Abstract. Poly(ethylene glycol)-poly(tetrahydrofuran)-poly(ethylene glycol) (PEG-PTHF-PEG) triblock copolymer was synthesized by ring-opening polymerization of ethylene oxide using sodium alcoholate of PTHF as the macroinitiator. Its crystallization behavior and formation mechanisms of different crystal structures were studied. The study showed that the molecular weight of PEG-PTHF-PEG exhibited a significant effect on its crystallization: that is, with the increase of the copolymer's molecular weight, the crystallizability of PTHF blocks decreased gradually, which led to the transition of copolymer from crystalline-crystalline to crystalline-amorphous. By adjusting the total molecular weight of triblock copolymer, the crystallization process can be effectively controlled, and as a result, different spherulite structures were obtained. Particularly, when PTHF blocks became amorphous, novel double concentric spherulites were observed. The morphological structures were studied by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), polarized optical microscopy (POM), and its crystalline process was investigated.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Poly(ethylene glycol)-poly(tetrahydrofuran)-poly(ethylene glycol) triblock copolymer : Synthesis, crystallization behavior and novel morphology

Wang¹,

Fan²,

Tian³

et al. 2013

Express Polym. Lett.

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“…1 If T m values of two blocks are close enough, we have a simultaneous crystallization of both blocks to result in a complicated morphology formation. [2][3][4][5][6][7][8] If T m of one block is enough higher than that of the other, we have a two-step crystallization; high-T m blocks crystallize first to form a crystallized morphology and subsequently low-T m blocks start to crystallize from this morphology. Therefore the crystallized morphology formed by high-T m blocks is a kind of spatial confinement for the subsequent crystallization of low-T m blocks, which will be qualitatively different from the confinement imposed by amorphous or glassy microdomains observed in crystallineamorphous diblock copolymers.…”

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confidence: 99%

Composition Dependence of Crystallization Behavior Observed in Crystalline-Crystalline Diblock Copolymers

Ikeda

Ohguma

Nojima

2008

Polym J

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The crystallization behavior of poly("-caprolactone) (PCL) blocks starting from a solid morphology formed in advance by the crystallization of polyethylene (PE) blocks (PE-crystallized morphology) in PCL-b-PE diblock copolymers has been investigated by a time-resolved synchrotron small-angle X-ray scattering (SR-SAXS) method as a function of composition (or volume fraction of PE blocks PE in the system). The PE-crystallized morphology and the crystallized state of PCL blocks (i.e., melting temperature and crystallinity of PCL blocks) were examined by static SAXS and differential scanning calorimetry methods, respectively. When PCL-b-PE with PE 0:58 was quenched from a microphase-separated melt into low temperatures T c (30 C T c 45 C), the PE block crystallized first to yield the PE lamellar morphology, an alternating structure consisting of thin PE crystals and amorphous PE + PCL layers, followed by the crystallization of PCL blocks starting from this PE lamellar morphology, where two different crystallization behaviors of PCL blocks were observed depending on T c ; at higher T c (! 40 C) the Avrami index was ca. 3, indicating a heterogeneous crystallization in 3D space. However, it was smaller ($ 2) at lower T c ( 38 C), suggesting a confined crystallization within the PE lamellar morphology. The temperature at which the crystallization mechanism changed was almost independent of PE in these copolymers. The late stage of PCL crystallization (or post-Avrami process) was not significantly dependent on PE and similar to that of crystalline homopolymers. For PCL-b-PE with PE ! 0:73, the PE block crystallized on the basis of molten microdomains to yield the PE-crystallized microdomain, and eventually PCL crystallization was confined within this microdomain for every T c at early and late stages. These results were consistent with our previous conclusions derived from the investigation of resulting morphology.KEY WORDS: Crystalline-Crystalline Diblock Copolymer / Composition / Crystallization Behavior / Synchrotron SAXS / Crystalline-crystalline diblock copolymers show a complicated morphology formation according to the melting temperature T m of constituent blocks when they are quenched from a microphase-separated melt into low temperatures.1 If T m values of two blocks are close enough, we have a simultaneous crystallization of both blocks to result in a complicated morphology formation.2-8 If T m of one block is enough higher than that of the other, we have a two-step crystallization; high-T m blocks crystallize first to form a crystallized morphology and subsequently low-T m blocks start to crystallize from this morphology. Therefore the crystallized morphology formed by high-T m blocks is a kind of spatial confinement for the subsequent crystallization of low-T m blocks, which will be qualitatively different from the confinement imposed by amorphous or glassy microdomains observed in crystallineamorphous diblock copolymers. [9][10][11] There are some studies so far on the morphology formation of double crystall...

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“…18 Dong reported that the conversion of monomers did not decrease when SnOct 2 was used much less. 4 Shiomi synthesized PCL-b-PEG-b-PCL triblock by the bulk ROP of "-caprolactone initiated with hydroxy groups at both chain ends of PEG without any catalyst at 200 C. 10 These observations show that a catalyst seems to be not indispensable in the ROP under suitable polymerization conditions. Ideally, if no catalyst and no solvent were needed, the resulting PTMC would be pure and favor its applications as biomaterials.…”

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confidence: 98%

“…1,3 This method was also used to synthesize OH-terminated polyesters, such as polycaprolactone, poly(lactide-co-glycolide), or polylactide, etc. [4][5][6][7][8][9][10][11][12] Several metal complexes have been usually chosen as catalysts, especially metal carboxylates and alkoxides, such as stannous octoate (SnOct 2 ) and aluminum isopropoxide. Herein, the alcohol is the real initiator whereas SnOct 2 acts as a Lewis acid catalyst to provide the ROP with a fast kinetics.…”

mentioning

confidence: 99%

Synthesis and Characterization of OH-Terminated Poly(trimethylene carbonate)s by Alcohol-Initiated Ring-Opening Polymerization in Melt Bulk without Using Any Catalyst

Zhuo

2004

Polym J

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ABSTRACT:OH-terminated poly(trimethylene carbonate)s (OH-PTMC) were synthesized by ring-opening polymerization (ROP) of trimethylene carbonate (TMC) in the melt bulk in vacuo at 120 C using an alcohol such as benzyl alcohol, 1,4-butanediol, ethanol, isopropanol, or tertiary butanol as a respective initiator in the presence or in the absence of acid catalyst (e.g. trifluoroacetic acid (TFA)). The products were characterized by 1 H NMR and GPC. Experiments showed that TFA was not indispensable under the polymerization conditions and that the ROP conformed to a pseudoliving polymerization. The molecular weights of products can be predicted based on the monomer conversion and the molar ratio of monomer to initiator practically participating in the polymerization. It was also demonstrated that the alcohol ability to initiate the ROP increased in the following order: ethanol > isopropanol > t-butanol whether using TFA or not. Part of isopropanol or t-butanol did not practically participate in the initiation step and the participating degree further decreased in the absence of TFA catalyst.KEY WORDS Ring-opening Polymerization / Alcohol Initiation / Pseudoliving Polymerization / Poly(trimethylene carbonate) / Functionalized End Group / Aliphatic polycarbonate, for example, poly(trimethylene carbonate) (PTMC), displays good biocompatibility, degradability by hydrolysis or enzyme and high elasticity at room temperature, and is one of the most important biodegradable polymers.1,2 Besides, OHterminated PTMC (OH-PTMC) is very useful in the synthesis of other biodegradable polymers. It can be used to initiate another comonomer to prepare multiblock copolymers. OH end group can be further transformed into other end groups to adjust the degradability, etc. Alcohol-initiated ring-opening polymerization (ROP) is a convenient method of choice for the preparation of OH-terminated PTMC.1,3 This method was also used to synthesize OH-terminated polyesters, such as polycaprolactone, poly(lactide-co-glycolide), or polylactide, etc.4-12 Several metal complexes have been usually chosen as catalysts, especially metal carboxylates and alkoxides, such as stannous octoate (SnOct 2 ) and aluminum isopropoxide. Herein, the alcohol is the real initiator whereas SnOct 2 acts as a Lewis acid catalyst to provide the ROP with a fast kinetics.13-15 However, these metal impurities remain in these materials and would result in an unpredicted trouble in body when these resulting materials were used as biomaterials though SnOct 2 is a permitted food additive in numerous countries. 16,17 On the other hand, considering the catalysis mechanism of Lewis acid of such metal complexes, trifluoroacetic acid (TFA) has been also chosen as a catalyst of the ROP of seven-or six-number cyclic carbonates in order to reduce the harmfulness of metal residue. 18In fact, in the absence of such catalysts, the ringopening reactions of seven-numbered cyclic carbonate also occurred.18 Dong reported that the conversion of monomers did not decrease when SnOct 2 was used much l...

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Appearance of double spherulites like concentric circles for poly(ϵ-caprolactone)-block-poly(ethylene glycol)-block-poly(ϵ-caprolactone)

Cited by 85 publications

References 19 publications

Poly(ethylene glycol)-poly(tetrahydrofuran)-poly(ethylene glycol) triblock copolymer : Synthesis, crystallization behavior and novel morphology

Poly(ethylene glycol)-poly(tetrahydrofuran)-poly(ethylene glycol) triblock copolymer : Synthesis, crystallization behavior and novel morphology

Composition Dependence of Crystallization Behavior Observed in Crystalline-Crystalline Diblock Copolymers

Synthesis and Characterization of OH-Terminated Poly(trimethylene carbonate)s by Alcohol-Initiated Ring-Opening Polymerization in Melt Bulk without Using Any Catalyst

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