Crystallization and ring-banded spherulite morphology of poly(ethylene oxide)-block-poly(epsilon-caprolactone) diblock copolymer

The crystallization behavior of crystalline-crystalline diblock copolymer containing poly(ethylene oxide) (PEO) and poly(epsilon-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 or the PEO-b-PCL diblock copolymer.

Synthesis of a novel structural triblock copolymer of poly(gamma-benzyl-L-glutamic acid)-b-poly(ethylene oxide)-b-poly(epsilon-caprolactone)

A novel structural triblock copolymer of poly(gamma-benzyl-L-glutamic acid)-b-poly(ethylene oxide)-b-poly(epsilon-caprolactone) (PBLG-PEO-PCL) was synthesized by a new approach in the following three steps: (1) sequential anionic ring opening polymerization (ROP) of ethylene oxide and epsilon-caprolactone with an acetonitrile/potassium naphthalene initiator system to obtain a diblock copolymer CN-PEO-PCL with a cyano end-group; (2) conversion of the CN end-group into NH2 end-group by hydrogenation to obtain NH2-PEO-PCL; (3) ROP of gamma-benzyl-L-glutamate-N-carboxyanhydrides (Bz-L-GluNCA) with NH2-PEO-PCL as macroinitiator to obtain the target triblock copolymer. The structures from CN-PEO precursor to the triblock copolymers were confirmed by FT-IR and H-1 NMR spectroscopy, and their molecular weights were measured by gel permeation chromatography. The monomer of Bz-L-GluNCA can react almost quantitatively with the amino end-groups of NH2-PEO-PCL macroinitiator by ROP.

Study on crystalline morphology of poly(L-lactide)-poly(ethylene glycol) diblock copolymer

Crystallization behavior, structural development and morphology evolution in a series of diblock copolymers Of poly(L-lactide)-blockpoly(ethylene glycol) (PLLA-b-PEG) were investigated via differential scanning calorimetry, wide-angle X-ray diffraction, polarized optical microscopy and atomic force microscopy. In these copolymers, both blocks are crystallizable and biocompatible. It was interesting that these PLLA-b-PEG diblock copolymers could form spherulites with banded textures, which was undercooling dependent. Single crystals with an abundance of screw dislocations were also observed via AFM. Such results indicated that these ringed spherulites and single crystals were formed during the crystallization of the PLLA blocks.

Synthesis and characterization of RGD peptide grafted poly(ethylene glycol)-b-poly(L-lactide)-b-poly(L-glutamic acid) triblock copolymer

Advances in tissue engineering require biofunctional scaffolds that can provide not only physical support for cells but also chemical and biological cues needed in forming functional tissues. To achieve this goal, a novel RGD peptide grafted poly(ethylene glycol)-b-poly(L-lactide)-b-poly(L-glutamic acid) (PEG-PLA-PGL/RGD) was synthesized in four steps (1) to prepare diblock copolymer PEG-PLA-OH and to convert its -OH end group into -NH2 (to obtain PEG-PLA-NH2), (2) to prepare triblock copolymer PEG-PLA-PBGL by ring-opening polymerization of NCA (N-carboxyanhydride) derived from benzyl glutamate with diblock copolymer PEG-PLA-NH2 as macroinitiator, (3) to remove the protective benzyl groups by catalytic hydrogenation of PEGPLA-PBGL to obtain PEG-PLA-PGL, and (4) to react RGD (arginine-glycine-(aspartic amide)) with the carboxyl groups of the PEG-PLA-PGL. The structures of PEG-PLA-PGL/RGD and its precursors were confirmed by H-1 NMR, FT-IR, amino acid analysis, and XPS analysis. Addition of 5 wt % PEG-PLA-PGL/RGD into a PLGA matrix significantly improved the surface wettability of the blend films and the adhesion and proliferation behavior of human chondrocytes and 3T3 cells on the blend films. Therefore, the novel RGD-grafted triblock copolymer is expected to find application in cell or tissue engineering.

Formation of a unique crystal morphology for the poly(ethylene glycol)-poly(epsilon-caprolactone) diblock copolymer

The crystallization behaviors of the poly(ethylene glycol)-poly(epsilon-caprolactone) diblock copolymer with the PEG weight fraction of 0.50 (PEG(50)-PCL50) was studied by DSC, WAXD, SAXS, and FTIR. A superposed melting point at 58.5 degrees C and a superposed crystallization temperature at 35.4 degrees C were obtained from the DSC profiles running at 10 degrees C/min, whereas the temperature-dependent FTIR measurements during cooling from the melt at 0.2 degrees C/min showed that the PCL crystals formed starting at 48 degrees C while the PEG crystals started at 45 degrees C. The PEG and PCL blocks of the copolymer crystallized separately and formed alternating lamella regions according to the WAXD and SAXS results. The crystal growth of the diblock copolymer was observed by polarized optical microscope (POM). An interesting morphology of the concentric spherulites developed through a unique crystallization behavior. The concentric spherulites were analyzed by in situ microbeam FTIR, and it was determined that the morphologies of the inner and outer portions were mainly determined by the PCL and PEG spherulites, respectively. However, the compositions of the inner and outer portions were equal in the analysis by microbeam FTIR.

Composition dependence of the crystallization behavior and morphology of the poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer

The crystallization behavior and morphology of the crystalline-crystalline poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer (PEO-b-PCL) was studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), small-angle X-ray scattering (SAXS), and hot-stage polarized optical microscope (POM). The mutual effects between the PEO and PCL blocks were significant, leading to the obvious composition dependence of the crystallization behavior and morphology of PEO-b-PCL. In this study, the PEO block length was fixed (M-n = 5000) and the weight ratio of PCL/PEO was tailored by changing the PCL block length. Both blocks could crystallize in PEO-b-PCL with the PCL weight fraction (WFPCL) of 0.23-0.87. For the sample with the WFPCL of 0.36 or less, the PEO block crystallized first, resulting in the obvious confinement of the PCL block and vice versa for the sample with WFPCL of 0.43 or more. With increasing WFPCL, the crystallinity of PEO reduced continuously while the variation of the PCL crystallinity exhibited a maximum. The long period of PEO-b-PCL increased with increasing WFPCL from 0.16 to 0.50 but then decreased with the further increase of WFPCL due to the interaction of the respective variation of the thicknesses of the PEO and PCL crystalline lamellae.

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.

The influence of nucleating agent on crystallization behavior and properties of polypropylene and its copolymer with ethylene

The influences of nucleating agent EDBS on crystallization behavior and properties of polypropylene UP) and its copolymer with a small amount (4. 48 %, molar fraction) of ethylene (CPP) were studied. DSC results indicated that the crystallization temperature of iPP and CPP samples with 0.5 % (mass fraction) EDBS obviously increased and the degree of crystallinity of these samples became higher. In addition, adding small amount of EDBS enhanced the crystallization of the low isotacticity and low molecular weight segments of the CPP. PLM results showed that their spherulite size decreased markedly, and as a result, the transmittance and haze of the films were all improved.

Polydispersity of ethylene sequence length in metallocene ethylene/alpha-olefin copolymers. I. Characterized by thermal-fractionation technique

In this article, the polydispersity of the ethylene sequence length (ESL) in ethylene/alpha-olefin copolymers was studied by atomic force microscopy (AFM) and the thermal-fractionation technique. The crystal morphology observation by AFM showed that morphology changed gradually with decreasing average ESL from complete lamellae over shorter and more curved lamellae to a granular-like morphology, and the mixed morphology was observed after stepwise crystallization from phase-separated melt. This result indicated that the ethylene sequence with different lengths crystallized into a crystalline phase with a different size and stability at the copolymer systems. The thermal-fractionation technique was used to characterize the polydispersity of ESL. Three of the following statistical terms were introduced to describe the distribution of ESL and the lamellar thickness: the arithmetic mean (L) over bar (n), the weight mean (L) over bar (w), and the broadness index I = (L) over bar (w)/(L) over bar (n). It was concluded that the polydispersity of ESL could be quantitatively characterized by the thermal-fractionation technique. The effects of temperature range, temperature-dependent specific heat capacity C-p of copolymer, and the molecular weight on the results of thermal fractionation were discussed,

The polydispersity of ethylene sequence in metallocene ethylene/alpha-olefin copolymers III: crystallization and melting behavior of short ethylene sequence

Crystallization and melting behavior of short ethylene sequence of metallocene ethylene/alpha -olefin copolymer with high comonomer content have been studied by standard DSC and modulated-temperature differential scanning calorimetry (M-TDSC) technique. In addition to high temperature endotherm around 120 degreesC, a low temperature endotherm is observed at lower temperatures (40-80 degreesC), depending on time and temperature of isothermal crystallization. The peak position of the low temperature endotherm T-m(low) varies linearly with the logarithm of crystallization time and the slope, D, decreases with increasing crystallization temperature T-c. The T-m(low) also depends on the thermal history before the crystallization at T-c, and an extrapolation of T-m(low) (30.6 degreesC) to a few seconds has been obtained after two step isothermal crystallization before the crystallization at 30 degreesC. The T-m(low) is nearly equal to T-c, and it indicates that the initial crystallization at low temperature is nearly reversible. Direct evidence of conformational. entropy change of secondary crystallization has been obtained by using M-TDSC technique. Both the M-TDSC result and the activation energy analysis of temperature dependence suggest that crystal perfection process and conformational entropy decreasing in residual amorphous co-exist during secondary crystallization.

Nonisothermal crystallization kinetics: poly(ethylene terephthalate)-poly(ethylene oxide) segmented copolymer and poly(ethylene oxide) homopolymer

The nonisothermal crystallization behavior of polyethylene oxide (PEO) in poly(ethylene terephthalate)poly(ethylene oxide) (PETPEO) segmented copolymer and PEO homopolymer has been studied by means of differential scanning calorimetry, as well as transmission electron microscope. The kinetics of PEO in copolymer and PEO homopolymer under nonisothermal crystallization condition has been analyzed by Ozawa equation. The results show that Ozawa equation only describes the crystallization behavior of PEO-6000 homopolymer successfully, but fails to describe the whole crystallization process of PEO in copolymer because the secondary crystallization in the later stage could not be neglected. Due to the constraint of PET segments imposed on the PEO segments, a distinct two stage of crystallization of PEO in copolymer has been investigated by using Avrami equation modified by Jeziorny to deal with the nonisothermal crystallization data. In the case of PEO-6000 homopolymer, good linear relation for the whole crystallization process is obtained owing to the secondary crystallization does not occur under our experimental condition. (C) 2001 Elsevier Science Ltd. All rights reserved.

Characterization and ionic conductivity of an amorphous comblike polymer - II: Based on ethylene maleic anhydride copolymer backbone with monoethyl ether of poly(ethylene glycol) of M-W=550 as side chain

Using a graft modification method, a comblike polymer host (CBPE550) was synthesized by reacting monomethyl ether of poly(ethylene glycol) (PEGMA) with ethylene-maleic anhydride copolymer (EMAC) and endcapping the residual carboxylic acid with methanol. The product was characterized by IR and elementary analysis. Result showed that the product was amorphous and semi-ester product is accord with reaction equation. There were two peaks in the plot of the ionic conductivity against Li salt concentration. The plot of log a against 1/(T - T-0) shows a dual VTF behavior when using the glass transition temperature of PEO of side chain as T beta. The comblike polymer is a white rubbery solid. It can be well-dissolved in acetone. (C) 1999 Elsevier Science Ltd. All rights reserved.

Studies on blends of LLDPE and ethylene-methacrylic acid random copolymer

Blends of linear low-density polyethylene (LLDPE) and poly(ethylene-co-methacrylic acid) (EMA) random copolymer were studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and excimer fluorescence. In binary blends, crystallization of EMA was studied, and no modification of crystal structure was detected. In excimer fluorescence measurements, emission intensities of blends of EMA and naphthalene-labeled LLDPE were measured. The ratio of the excimer emission intensity (I-D) to the emission intensity of the isolated "monomer" (I-M) decreases upon addition of EMA, indicating that PE segments of EMA interpenetrate into the amorphous phase of LLDPE. (C) 1998 Published by Elsevier Science Ltd,. All rights reserved.

Effect and mechanism in compatibilization of poly(styrene-b-2-ethyl-2-oxazoline) diblock copolymer in poly(2,6-dimethyl-1,4-phenylene oxide) poly(ethylene-ran-acrylic acid) blends

The compatibilization effect of poly(styrene-b-2-ethyl-2-oxazoline) diblock copolymer, P(S-b-EOx), on immiscible blends of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and poly(ethylene-co-acrylic acid) (EAA) is examined in terms of phase structure and thermal, rheological and mechanical properties, and its compatibilizing mechanism is investigated by Fourier-transform infrared spectroscopy. The block copolymer, synthesized by a mechanism transformation copolymerization, is used in solution blending of PPO/EAA. Scanning electron micrographs show that the blends exhibit a more regular and finer dispersion on addition of a small amount of P(S-b-EOx). Thermal analysis indicates that the grass transition of PPO and the lower endothermic peal; of EAA components become closer on adding P(S-b-EOx), and the added diblock copolymer is mainly located at the interface between the PPO and EAA phases. The interfacial tension estimated by theological measurement is significantly reduced on addition of a small amount of P(S-b-EOx). The tensile strength and elongation at break increase with the addition of the diblock copolymer for PPO-rich blends, whereas the tensile strength increases but the elongation at break decreases for EAA-rich blends. This effect is interpreted in terms of interfacial activity and the reinforcing effect of the diblock copolymer, and it is concluded that the diblock copolymer plays a role as an effective compatibilizer for PPO/EAA blends. The specific interaction between EAA and polar parts of P(S-b-EOx) is mainly hydrogen bonding. (C) 1998 Elsevier Science Ltd. All rights reserved.

Study on a comb-like polymer electrolyte based on the backbone of ethylene-maleic anhydride copolymer

A comb-like polymer host(CBPE) as polymer electrolyte was synthesized by reacting poly(ethylene glycol) monomethyl ether (PEGME) with ethylene-maleic anhydride copolymer(EMAC) and endcapping the residual carboxylic acid with methanol. The synthetic process was followed by IR and the amorphous product characterized by IR and elemental analysis. There were two peaks in the plot of the ionic conductivity against Li salt concentration. The plot of log sigma vs. 1/(T - T-0) may exhibit dual VTF behavior when using the glass transition temperature of PEO of side chain as T-0. The comb-like polymer is a white rubbery solid which dissolves in acetone. (C) 1998 Elsevier Science B.V. All rights reserved.