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PCL Blocks (pcl + block)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Selected Abstracts

Melt Structure and its Transformation by Sequential Crystallization of the Two Blocks within Poly(L -lactide)- block -Poly(, -caprolactone) Double Crystalline Diblock Copolymers

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2006
I. W. Hamley
Abstract Summary: Sequential crystallization of poly(L -lactide) (PLLA) followed by poly(, -caprolactone) (PCL) in double crystalline PLLA- b -PCL diblock copolymers is studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS). Three samples with different compositions are studied. The sample with the shortest PLLA block (32 wt.-% PLLA) crystallizes from a homogeneous melt, the other two (with 44 and 60% PLLA) from microphase separated structures. The microphase structure of the melt is changed as PLLA crystallizes at 122,°C (a temperature at which the PCL block is molten) forming spherulites regardless of composition, even with 32% PLLA. SAXS indicates that a lamellar structure with a different periodicity than that obtained in the melt forms (for melt segregated samples). Where PCL is the majority block, PCL crystallization at 42,°C following PLLA crystallization leads to rearrangement of the lamellar structure, as observed by SAXS, possibly due to local melting at the interphases between domains. POM results showed that PCL crystallizes within previously formed PLLA spherulites. WAXS data indicate that the PLLA unit cell is modified by crystallization of PCL, at least for the two majority PCL samples. The PCL minority sample did not crystallize at 42,°C (well below the PCL homopolymer crystallization temperature), pointing to the influence of pre-crystallization of PLLA on PCL crystallization, although it did crystallize at lower temperature. Crystallization kinetics were examined by DSC and WAXS, with good agreement in general. The crystallization rate of PLLA decreased with increase in PCL content in the copolymers. The crystallization rate of PCL decreased with increasing PLLA content. The Avrami exponents were in general depressed for both components in the block copolymers compared to the parent homopolymers. Polarized optical micrographs during isothermal crystallization of (a) homo-PLLA, (b) homo-PCL, (c) and (d) block copolymer after 30 min at 122,°C and after 15 min at 42,°C. [source]

Synthesis, Sequential Crystallization and Morphological Evolution of Well-Defined Star-Shaped Poly(, -caprolactone)- b -poly(L -lactide) Block Copolymer,

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 5 2006
Jing-Liang Wang
Abstract Summary: Well-defined star-shaped poly(, -caprolactone)- b -poly(L -lactide) copolymers (PCL- b -PLLA) were synthesized via sequential block copolymerization, and their molecular weights and arm length ratio could be accurately controlled. Both differential scanning calorimetry and wide angle X-ray diffraction analysis indicated that the crystallization of both the PLLA and PCL blocks within the star-shaped PCL- b -PLLA copolymer could be adjusted from the arm length of each block, and both blocks mutually influenced each other. The sequential isothermal crystallization process of both the PLLA and PCL blocks within the PCL- b -PLLA copolymers was directly observed with a polarized optical microscope, and the isothermal crystallization of the PCL segments was mainly templated by the existing spherulites of PLLA. Moreover, the PLLA blocks within the star-shaped PCL- b -PLLA copolymer progressively changed from ordinary spherulites to banded spherulites when the arm length ratio of PCL to PLLA was increased while concentric spherulites were observed for the linear analog. Significantly, these novel spherulites with concentric or banded textures and the morphological evolution of the spherulites have been observed for the first time in the PCL- b -PLLA block copolymers. [source]

Crystallization and Ring-Banded Spherulite Morphology of Poly(ethylene oxide)- block -Poly(, -caprolactone) Diblock Copolymer

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2004
Shichun Jiang
Abstract Summary: The crystallization behavior of crystalline-crystalline diblock copolymer containing poly(ethylene oxide) (PEO) and poly(, -caprolactone) (PCL), in which the weight fraction of PCL is 0.815, has been studied via differential scanning calorimeter (DSC), wide-angle X-ray diffraction (WAXD), and polarized optical microscopy (POM). DSC and WAXD indicated that both PEO and PCL blocks crystallize in the block copolymer. POM revealed a ring-banded spherulite morphology for the PEO- b -PCL diblock copolymer. DSC heating curve for the PEO- b -PCL block copolymer. [source]

Copolymers based on poly(butylene terephthalate) and polycaprolactone- block -polydimethylsiloxane- block -polycaprolactone

POLYMER INTERNATIONAL, Issue 6 2010
Vesna V Anti
Abstract A series of novel thermoplastic elastomers, based on poly(butylene terephthalate) (PBT) and polycaprolactone- block -polydimethylsiloxane- block -polycaprolactone (PCL-PDMS-PCL), with various mass fractions, were synthesized through melt polycondensation. In the synthesis of the poly(ester-siloxane)s, the PCL blocks served as a compatibilizer for the non-polar PDMS blocks and the polar comonomers dimethyl terephthalate and 1,4-butanediol. The introduction of PCL-PDMS-PCL soft segments resulted in an improvement of the miscibility of the reaction mixture and therefore in higher molecular weight polymers. The content of hard PBT segments in the polymer chains was varied from 10 to 80 mass%. The degree of crystallinity of the poly(ester-siloxane)s was determined using differential scanning calorimetry and wide-angle X-ray scattering. The introduction of PCL-PDMS-PCL soft segments into the polymer main chains reduced the crystallinity of the hard segments and altered related properties such as melting temperature and storage modulus, and also modified the surface properties. The thermal stability of the poly(ester-siloxane)s was higher than that of the PBT homopolymer. The inclusion of the siloxane prepolymer with terminal PCL into the macromolecular chains increased the molecular weight of the copolymers, the homogeneity of the samples in terms of composition and structure and the thermal stability. It also resulted in mechanical properties which could be tailored. Copyright © 2010 Society of Chemical Industry [source]