Crystallizable Poly Research Articles

Triple-Shape Effect of Copolymer Networks Based on Poly(ω-pentadecalactone) and Poly(ε‑caprolactone) Segments Applying a Programming Procedure with an Adjusted Temperature Profile

ABSTRACTA triple-shape material based on the two crystallizable segments poly(ω‑pentadeca-lactone) and poly(ε-caprolactone) was synthesized by crosslinking star-shaped precursors. A newly developed programming procedure (TSCP2) was applied in order to achieve triple-shape behavior. The application of this modified triple-shape creation procedure enabled triple-shape capability by influencing the crystallization behavior of the two switching segments in these copolymer networks, which partly show no two distinct and separated melting points. The influence of molecular weight and content of the poly(ε-caprolactone) segment on the triple-shape effect programmed by application of TSCP2 was investigated.

“Design of Poly(ethylene glycol)-Polycaprolactone Diblock Micelles with RGD Targeting Ligands and Embedded Iron Oxide Nanoparticles for Thermally-activated Release”

ABSTRACTA thermally-activated micelle consisting of a crystallizable poly(caprolactone), PCL, core and a poly(ethylene glycol), PEG, corona was developed to contain magnetic nanoparticles and anti-cancer agent doxorubicin as well as display a targeting RGD peptide. This system has the potential to target cancer cells, deliver combination hyperthermia and chemotherapy, and offer magnetic resonance imaging contrast. The micelles self-assemble in aqueous solutions and form a crystalline core with a melting transition ranging from 40 to 50 °C, depending on the length of the PCL blocks, with dynamic light scattering showing micelle sizes typically ranging from 20 to 100 nm, depending on block lengths and added drug or nanoparticles. The micelles become unstable as they are heated above their melting point, creating a thermally-activated drug release mechanism. By adding magnetite (Fe3O4) nanoparticles into the PCL core, the micelles can be heated using an externally applied AC magnetic field to induce hyperthermia in combination with the thermally-activated drug release. The polymers and magnetic nanoparticles (MNPs) were synthesized and characterized in our laboratories. The melting transitions of the PCL micelle cores were investigated using microcalorimetry. The heating of nanoparticles and magnetomicelles was conducted using a custom-built hyperthermia coil capable of generating fields of several hundred Oersteds at frequencies ranging from 50 to 450 kHz. Heating of MNPs was maximized at high field intensities. RGD peptides were attached to the PEG corona using maleimide chemistry, and the ability of the RGD-derivatized micelles to target integrin-expressing cells was investigated using fluorescent dye PKH26 to identify the localization of micelles in cultured human kidney (293) cells in vitro. The crystallizable (and meltable) cores in these micelles were designed to overcome drug leakage common in liposome systems and release the drug on demand after a period of time for localization to integrin receptors.

Synthesis of high‐impact biodegradable multiblock copolymers comprising of poly(butylene succinate) and poly(1,2‐propylene succinate) with hexamethylene diisocyanate as chain extender

AbstractBlock copolymers demonstrate excellent thermal and mechanical properties superior to their corresponding random copolymers and homopolymers. However, it is difficult to synthesize block copolymers comprising of different polyester segments by copolycondensation due to the serious transesterification reaction. In this study, multiblock copolymers comprising of two different polyester segments, i.e. crystallizable poly(butylene succinate) (PBS) and amorphous poly(1,2‐propylene succinate) (PPSu), were synthesized by chain‐extension with hexamethylene diisocyanate (HDI). Amorphous PPSu segment was incorporated to improve the impact strength of PBS. The copolymers were characterized by GPC, laser light scattering (LLS), NMR, DSC, and mechanical testing. The results of 13C NMR spectra suggest that multiblock copolymers with regular sequential structure have been successfully synthesized. The data of DSC and mechanical testing indicate that block copolymers possess excellent thermal and mechanical properties with satisfactory tensile strength and extraordinary impact strength achieving upto 1900% of pure PBS. The influence of PPSu ratio and chain length of both the segments on the thermal and mechanical properties was investigated. The incorporation of an amorphous soft segment PPSu imparts high‐impact resistance to the copolymers without obviously decreasing the melting point (Tm). The favorable mechanical and thermal properties of the copolymers also depend on their regular sequential structure. At the same time, the introduction of amorphous PPSu segment enhances the enzymatic degradation rate of the multiblock copolymers. Copyright © 2009 John Wiley & Sons, Ltd.

Birefringence in heat-mechanical modified freshly moulded polyester fibers

The article submits new experimental data concerning to the role of combined thermo-mechanical treatments on the structural development of freshly moulded uncrystallized but crystallizable poly (ethylene terephthalate) (PET) fibers. The object of the present work is PET as a thermoplastic polymer with a large practical application. The report is devoted to the influence of the heat-mechanical modification temperature on the structure rearrangement in uniaxially orientated amorphous PET. The heat-mechanical modification of the investigated yarns and the optical measurements were realized by specialized gears constructed and built in the author's laboratories. The fibers heat-mechanical modification includes samples annealing at constant temperature above their glass transition temperature (Tg) without strain stress. The yarn annealing has been followed from well defined uniaxially strain-loading with values from 0 MPa up to 30 MPa during two minutes. The optical measurements were carried out by an optical system using a polarization microscope and a CCD camera. The obtained experimental data has been analyzed by Mocha-1.2 (Jandel Scientific) software. There are established dependences between the heat-mechanical modification mode and the structural rearrangements running in the studied PET samples.

Cylinder‐to‐rod‐to‐sphere evolution of complex micelles in solution and their corresponding solvent‐induced crystallization process

AbstractIn a previous paper, we investigated the solvent‐induced crystallization of films made up of spherical micelles, which were prepared by mixing polystyrene‐block‐poly(acrylic acid) and polystyrene‐block‐poly(2‐vinylpyridine)‐block‐poly(ethylene oxide) in the neutral solvent N,N‐dimethylformamide (DMF). In the work reported in the present paper, we further studied the cylinder‐to‐rod‐to‐sphere evolution of complex micelles in solution and their corresponding solvent‐induced crystallization process. The initial morphology of the micelles in the solution was cylindrical due to a rapid growth of micelles with high unimer concentration, and spheres became the dominant form after storage at room temperature for a longer time. Regular square platelets can form after a certain period of treatment for all micelles in DMF vapor for sufficient time. However, the kinetics of their solvent‐induced crystallization process is quite different. The aggregation and subsequent nucleation of poly(ethylene oxide) blocks are determined by the distribution of crystallizable poly(ethylene oxide) blocks in the films. Copyright © 2010 Society of Chemical Industry

In Situ X‐Ray Scattering Studies of Poly(ε‐caprolactone) Networks with Grafted Poly(ethylene glycol) Chains to Investigate Structural Changes during Dual‐ and Triple‐Shape Effect

The dual- and triple-shape effects of multiphase polymer networks that contain two crystallizable chain segments have been assessed in situ by combining X-ray measurements with thermomechanical investigations. The studied polymer, named CLEG, is a multiphase polymer network of crystallizable poly(ε-caprolactone) (PCL) with grafted poly(ethylene glycol) (PEG) side chains. Wide-angle (WAXS) and small-angle X-ray scattering (SAXS) measurements were combined with temperature-controlled in situ tensile testing experiments. This integrated approach enables systematic investigation and interpretation of relevant structural features during the programming procedures and the thermally-induced recovery process. Main results concern the combined effect of PCL and PEG crystals on shape fixation, the specific role of low-melting PCL crystallites in the fixation of the low temperature temporary shape, and the different orientation behavior of PCL and PEG crystals during certain stages of the programming procedure. These results demonstrate that crystal orientation effects are dominant for the PCL crystals. The effects of the low temperature PCL crystals could only be investigated when synchrotron radiation was applied. These findings indicate the great potential of in situ X-ray investigations for the creation of design-relevant knowledge about the microscopic foundations of dual- and triple-shape effects in appropriate polymer systems.

Well-Defined Oxide Core−Polymer Shell Nanoparticles: Interfacial Interactions, Peculiar Dynamics, and Transitions in Polymer Nanolayers

Interfacial interactions, chain dynamics, and glass and melting transitions were studied in well-defined core-shell nanoparticles with amorphous silica or crystalline alumina cores and noncrystallizable poly(vinyl pyrrolidone) (PVP) or crystallizable poly(ethylene glycol) (PEG) shells. Varying particle composition caused regular changes in the shell thickness from 1 to 2 nm (monomolecular layer) up to 90 nm. Far- and mid-IR spectroscopy allowed us to register hydrogen bonding and, tentatively, Lewis/Brønsted (LB) interfacial interactions as well as changes in the dynamics and conformational state of the polymer chains as a function of the nanoshell thickness. Their most pronounced peculiarities were found for the monomolecular polymer layers. The LB interactions were stronger with the alumina substrate than silica. DSC analysis was performed, and the data obtained were in agreement with the spectroscopic data. Unlike the bulk polymer, the PVP monolayer was characterized with an extraordinarily large dynamic heterogeneity within the glass transition while broadening the transition range and varying the activation energy by an order of magnitude. The PEG monolayer adsorbed on silica was totally amorphous, whereas a highly crystalline one with the anomalously thin lamellae, down to 3 nm thick, was adsorbed on an alumina surface, presumably as a result of the quasi-heteroepitaxial crystallization process.

In vivo evaluation of the angiogenic effects of the multiblock copolymer PDC using the hen's egg chorioallantoic membrane test

Multiblock copolymers with shape-memory capability attracted tremendous interest as promising candidate materials for smart, degradable implants. In the present study the hen's egg-chorioallantoic membrane test (HET-CAM test) was used to investigate the angiogenic properties of a thermoplastic, biodegradable multiblock copolymer PDC composed of poly(p-dioxanone) hard segments (PPDO) and crystallizable poly(ε-caprolactone) switching segments (PCL), whereby PPDO and PCL homopolymers were investigated as controls. According to our HET-CAM test data, only PDC induced significant microvessel attraction and formation in the contact area of the test specimen after 48 hours of incubation showing newly formed blood vessels along the outer edge of the material. In contrast, no newly formed blood vessels were observed around the PPDO or PCL specimen after the same incubation period. These in vivo results indicate that the multiblock copolymer PDC possibly possesses an angiogenic effect and it can induce blood vessel formation in its direct vicinity when it is implanted in vivo.

In vivo degradation behavior of PDC multiblock copolymers containing poly(para-dioxanone) hard segments and crystallizable poly(epsilon-caprolactone) switching segments

AbstractThe degradation behavior of biodegradable multiblock copolymers (PDC) containing poly(p-dioxanone) hard segments (PPDO) and crystallizable poly(epsilon-caprolactone) switching segments (PCL) synthesized via co-condensation of two oligomeric macrodiols with an aliphatic diisocyanate as junction unit was explored in in vivo and in vitro experiments. The in vitro experiments for enzymatic degradation resulted that the poly(epsilon-caprolactone) segments are degraded faster, than the poly(p-dioxanone) segments. During degradation the outer layer of the test specimen becomes porous. Finally non-soluble degradation products in form of particles were found at the surface. This observation is in good agreement with the in vivo studies, where the non-soluble degradation products in the periimplantary tissues showed a diameter of 1 – 3 micron.

Self-assembly of graft polyurethanes having both crystallizable poly(ε-caprolactone) blocks and soft poly(n-butyl acrylate) segments

We report the self-assembly behavior of graft polyurethanes combining in its structure soft lateral poly(n-butyl acrylate) (PnBuA) chains with rigid and crystallizable polycaprolactone (PCL) segments. Segmented polyurethanes microphase separated into high-glass transition temperature PCL hard and low-glass transition temperature PnBuA soft domains. The variation of the microstructure as a function of the hard segment content (ratio hard to soft segments) within the structure has been studied by using atomic force microscopy. Additionally, the crystallization mechanism appeared to be directly related to the properties of the substrates forming parallel lamellar structures on hydrophilic substrates and perpendicular lamellae with hydrophobic substrates.

Surface micellization of poly(2-oxazoline)s based copolymers containing a crystallizable block

The micellization on surfaces of copoly(2-oxazoline) diblock copolymers consisting of a crystallizable poly(2-nonyl-2-oxazoline) (pNonOx) block linked to a poly(2-ethyl-2-oxazoline) (pEtOx) block is investigated. Those micelles are not pre-existing in the initial ethanol solution but are formed during the spin-coating process by the evaporation of the solvent inducing the precipitation of the less soluble pNonOx block. The morphology and size of the surface micelles vary according to the pNonOx molar fraction in the copolymers. Reorganization of the micelles and evolution of the surface energies after a thermal annealing are also studied.

Synthesis, Characterization, Crystalline Morphologies, and Hydrophilicity of Brush Copolymers with Double Crystallizable Side Chains

Novel brush copolymers with poly(2-hydroxyethyl methacrylate) (PHEMA) as polymer backbone and diblock copolymer consisting of crystallizable poly(e-caprolactone) (PCL) and poly(ethylene oxide) (PEO) as side chains were synthesized successively by the combination of ring-opening polymerization (ROP) and coupling reaction. The molecular weights of poly(2-hydroxyethyl methacrylate)-graft-poly(e-caprolactone) (PHEMA-g-PCL) brush copolymers were controllable, and the molecular weight distributions were in the range of 1.28−1.32. The coupling reaction efficiency of hydroxyl-terminated mPEO (mPEO-OH) with PCL-OH in the PHEMA-g-PCL to produce poly(2-hydroxyethyl methacrylate)-graft-poly(e-caprolactone)-block-poly(ethy lene oxide) (PHEMA-g-(PCL-b-PEO)) ranged from 85.2% to 94.3%. The investigation of the melting and crystallization demonstrated that the values of crystallization temperature (Tc), melting temperature (Tm), and the degree crystallinity (Xc) of PHEMA-g-PCL were enhanced with the chain length increase...

Morphology of a highly asymmetric double crystallizable poly(ε-caprolactone-b-ethylene oxide) block copolymer

The morphology of a highly asymmetric double crystallizable poly(epsilon-caprolactone-b-ethylene oxide) (PCL-b-PEO) block copolymer has been studied with in situ simultaneously small and wide-angle x-ray scattering as well as atomic force microscopy. The molecular masses Mn of the PCL and PEO blocks are 24,000 and 5800, respectively. X-ray scattering and rheological measurements indicate that no microphase separation occurs in the melt. Decreasing the temperature simultaneously triggers off a crystallization of PCL and microphase separation between the PCL and PEO blocks. Coupling and competition between microphase separation and crystallization results in a morphology of PEO spheres surrounded by PCL partially crystallized in lamella. Further decreasing temperature induces the crystallization of PEO spheres, which have a preferred orientation due to the confinements from hard PCL crystalline lamella and from soft amorphous PCL segments in different sides. The final morphology of this highly asymmetric block copolymer is similar to the granular morphology reported for syndiotactic polypropylene and other (co-) polymers. This implies a similar underlying mechanism of coupling and competition of various phase transitions, which is worth further exploration.

Synthesis and characterization of diblock copolymers based on crystallizable poly(ε-caprolactone) and mesogen-jacketed liquid crystalline polymer block

Diblock copolymers comprising crystallizable poly(ε-caprolactone) and poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) were synthesized by ring-opening polymerization of ε-caprolactone and subsequent atom transfer radical polymerization (ATRP) of MPCS. The molecular structure of the copolymers was confirmed by 1H NMR spectroscopy and GPC. Kinetic study of ATRP showed that the polymerization proceeded in a controlled way up to high conversions. Three series of diblock copolymers were obtained with relatively narrow polydispersity indices (PDI≤1.11) and PCL blocks of 8000, 12,900, and 22,800 molecular weights, respectively. The existence of microphase separation was identified by differential scanning calorimetry (DSC) and directly observed through transmission electron microscopy (TEM). The melting behavior of PCL block was significantly affected by the length of PCL block and composition of PMPCS. The thermotropic liquid crystalline behavior was examined by polarized optical microscopy (POM) and DSC. The result showed that the diblock copolymer exhibited liquid crystalline behavior when the degree of polymerization (DP) of PMPCS block was not less than 44.

Synthesis and characterization of polyurethane–urea nanoparticles containing methylenedi‐p‐phenyl diisocyanate and isophorone diisocyanate

AbstractWater‐based polyurethane–urea (WPUU) nanoparticles containing 4,4′‐methylenedi‐p‐phenyl diisocyanate (MDI) and isophorone diisocyanate (IPDI) were synthesized by a stepwise prepolymer mixing process, that is, the consecutive formation of hydroxyl‐terminated and isocyanate‐terminated polyurethane prepolymers. The reaction behavior, chemical structure, and consequent morphology of the polyurethane prepolymers and WPUU were investigated with Fourier transform infrared (FTIR), gel permeation chromatography, and NMR techniques with MDI concentrations ranging from 0 (pure IPDI) to 50% with respect to the total moles of isocyanate. Wide‐angle X‐ray diffraction and differential scanning calorimetry patterns showed that the crystallinity of WPUU, which mostly originated from crystallizable poly(tetramethylene adipate) polyol, was significantly affected by the MDI content. Both the crystallinity and melting temperature of WPUU decreased as the MDI content increased. Deconvoluted relative peak areas of the carbonyl region in the FTIR spectrum revealed that the effect of hydrogen bonding among the hard segments became favorable as the MDI content increased, whereas the hydrogen bonding of the soft segments significantly decreased. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4353–4369, 2004

Non-conventional injection molding of poly(lactide) and poly(epsilon-caprolactone) intended for orthopedic applications.

Biodegradable polymers such as poly(lactide) (PLA) and poly(epsilon-caprolactone) (PCL) are increasingly used in biomedical applications as temporary implants. However, melt processing of these materials in particular of PLA is difficult due to the temperature sensitivity. Within this study, PLA and PCL were injection molded conventionally and by using the process shear controled orientation in injection molding (SCORIM) in order to investigate the effect of processing parameters on the physical properties of the moldings. Therefore, flexural testing, differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), molecular weight (MW) and orientation measurements were performed. PLA showed high sensitivity to melt temperature. In the case of amorphous poly(DL-lactide), the molecular weight and subsequently the ductility is substantially reduced by processing at higher melt temperatures. In the case of crystallizable poly(L-lactide), higher melt temperatures and shear induced by the SCORIM process resulted in enhanced crystallinity, which compromised the mechanical properties. Generally, SCORIM processing improved the mechanical properties, in particular the ductility, by orientating the molecular structure. PCL was shown to be less sensitive to shear and temperature than PLA. Stress at yield and stiffness are more improved by SCORIM processing. However, the processing temperature in combination with the grade used proved to be influential for the mechanical properties of resulting moldings.

Synthesis and Solid State Properties of Novel Fluorescent Polyester Star Polymers

AbstractTwo novel tetra‐ and hexahydroxy functionalized perylene chromophores have been used as initiators for the Sn(oct)2 catalyzed ring‐opening polymerization of different lactones. The arms of the resulting star polymers were comprised of either crystallizable poly(L‐lactide) or poly(ε‐caprolactone) arms or of amorphous poly[γ‐(tert‐amyl)‐ε‐caprolactone] chains. The star polymers were investigated by differential scanning calorimetry, X‐ray scattering and dynamic mechanical and optical spectroscopy. Whereas the thermal properties of the poly(ε‐caprolactone) stars were barely affected by the star topology, crystallization of the poly(L‐lactide) stars was strongly hindered by the star‐shaped architecture. Interestingly, for the amorphous poly[γ‐(tert‐amyl)‐ε‐caprolactone] stars a decrease in Tg with increasing chain length was found, reflecting the declining influence of the rigid perylene core on segmental mobility with increasing arm length. While the solid state and solution optical properties of high molar mass polyester stars were identical, the excitation and fluorescence emission spectra of spin‐coated films of the low molecular weight polymers revealed a red shift, pointing towards perylene – perylene interactions in these samples. The optical spectroscopy experiments suggested that arm length, rather than the number of arms, is the most important parameter determining encapsulation and preventing aggregation of the perylene core moieties in the solid state.magnified image

Interrelation between side chain crystallization and dynamic glass transitions in higher poly( n-alkyl methacrylates)

Calorimetric and dielectric results for crystallizable poly( n-alkyl methacrylates) (PnAMA) with C=12, 16 and 18 alkyl carbons per side chain are presented. Degree of crystallization D cal and melting peak temperature T M are estimated from conventional DSC measurements. For poly( n-hexadecyl methacrylate) ( C=16) the influence of isothermal crystallization is studied by DSC as well as TMDSC. Changes in dielectric relaxation strength Δ ε and α peak shape during crystallization are investigated. Effects of side chain crystallization on the complex dynamics of PnAMA are discussed. The results are related to the relaxation behavior of lower nanophase-separated PnAMA with two co-existing glass transitions, the conventional glass transition ( a or α) and the polyethylene-like glass transition ( α PE) within alkyl nanodomains formed by aggregated alkyl rests. It is shown that amorphous as well as semicrystalline PnAMA can be understood as nanophase-separated polymers with alkyl nanodomains having a typical dimension of 1–2 nm. The results are compared with the predictions of simple morphological pictures for side chain polymers. X-ray scattering data for the amorphous and semicrystalline PnAMA are included in the discussion. Common aspects of nanophase-separated systems in both states as well as differences caused by crystallization are discussed. Indications for the existence of rigid amorphous regions are compiled. Different approaches to explain a similar increase of T g( α PE)—the glass temperature of the amorphous alkyl nanodomains—and T M—the melting temperature of crystalline alkyl nanodomains—with side chain length are considered. Pros and cons of both approaches, based on increasing order within the alkyl nanodomains and confinement effects in nanophase-separated systems, are discussed. Main trends concerning crystallization and cooperative dynamics are compared with those in other systems with self-assembled nanometer confinements like microphase-separated blockcopolymers or semicrystalline main chain polymers.

Compatiblization of Polymers via Coalescence from Their Common Cyclodextrin Inclusion Compounds

We have found, when inherently immiscible polymers are included as guests in the narrow channels of their common inclusion compounds (ICs) formed with host cyclodextrins (CDs) and then these polymer-1/polymer-2-CD-IC crystals are washed with hot water to remove the host CD lattice and coalesce the guest polymers, that intimately mixed blends of the polymers are obtained. This behavior had been observed previously by us for the crystallizable poly(e-caprolactone) (PCL)/poly(l-lactic acid) (PLLA) pair, where in the coaelsced blend PCL and PLLA crystallinity was completely and nearly completely suppressed, respectively. Here we report similar observations made on the polycarbonate (PC)/poly(methyl methacrylate) (PMMA) pair, which are respectively difficult to crystallize and amorphous. PC/PMMA blends coalesced from their common γ-CD-ICs are amorphous and generally exhibit single glass transitions at temperatures (Tg) between those of pure PC and PMMA. Interestingly, a 1:4 molar PC:PMMA blend coalesced from i...

Crystallizations of poly(ethylene terephthalate co ethylene isophthalate)

Crystallization behaviors of crystallizable poly(ethylene terephthalate co ethylene isophthalate) with different molar ratios of polyethylene terephthalate (PET) to polyethylene isophthalate (PEI) were studied both non-isothermally and isothermally by differential scanning calorimetry (DSC). Avrami and Ozawa plots were used to describe the non-isothermal crystallizations. However, the Avrami treatment cannot predict the mechanisms of non-isothermal crystallizations for the above copolyesters, while the Ozawa explanation can be taken to reveal that the non-isothermal crystallization is dominated by heterogeneous nucleation. The activation energies of crystallization were calculated from the Kissinger equation. The copolyester 90/10 shows synergistic effects on non-isothermal crystallization, in that it has the lowest activation energy of crystallization. Isothermal crystallizations were explained by Avrami plots. From lower degrees of supercooling to higher ones, the crystals of the copolyesters grow from low dimension to multidimensions, but the crystallization rates become lower. The percentage of spherulite growth of the copolyester 100/0 (PET homopolymer) is higher than that of the other copolyesters under the same degree of supercooling. Equilibrium crystallization temperatures (T0c) and melting temperatures (T0m) were postulated respectively. T0c and T0m decrease with the increasing composition of PEI, indicating that the equilibrium crystals of the copolyesters become imperfect. With involvement of PEI, the copolyester is not likely crystallizable perfectly and the crystal becomes less perfect.