Crystallization Of Copolymers Research Articles

Face-On and Edge-On Orientation Transition and Self-Epitaxial Crystallization of All-Conjugated Diblock Copolymer

The orientation transition and self-epitaxial crystallization of all-conjugated diblock copolymers poly(p-phenylene)-block-(3-hexylthiophene) (PPP-b-P3HT) were systematically investigated by in situ temperature-resolved two-dimensional grazing incidence X-ray diffraction (2D GIXD) in step-by-step heating and cooling process. B39T18 was selected; the results of 2D GIXD showed that the PPP block crystal adopted a face-on orientation while the crystallization of P3HT block was hindered in as-casted films. Three different molecular orientations transition were obtained in self-epitaxial crystallization circles. First, P3HT crystallize with edge-on during the heating process and induced the PPP blocks crystallized with edge-on during the cooling process. Then, the as-casted film was heated in the melting temperature region of PPP blocks and isothermally crystallized. The partial melting of PPP blocks promoted the P3HT blocks crystallize in a face-on due to the steric limitation effect; PPP blocks crystallized ...

Terminal modification of polymeric micelles with π-conjugated moieties for efficient anticancer drug delivery

High drug loading content is the critical factor to polymeric micelles for efficient chemotherapy. Small molecules of cinnamic acid, 7-carboxymethoxy coumarin and chrysin with different π-conjugated moieties were immobilized on the terminal hydroxyl groups of PCL segments in mPEG-PCL micelles to improve drug loading content via the evocation of π-π stacking interaction between doxorubicin (DOX) and polymeric micelles. The modification of π-conjugated moieties enhanced the capability of crystallization of mPEG-PCL block copolymers. The drug loading content increased dramatically from 12.9% to 25.5% after modification. All the three modified mPEG-PCL micelles were nontoxic to cells. Chrysin modified polymeric micelles exhibited the most efficient anticancer activity. The in vivo anticancer activity of 10 mg/kg DOX dose of chrysin modified micelle formulation for twice injections was comparable to that of 5 mg/kg dose of free DOX·HCl for four injections under the circumstance of same total DOX amount. The systemic toxicity of DOX loaded chrysin modified micelles was significantly reduced. This research provided a facile strategy to achieve polymeric micelles with high drug loading content and efficient anticancer activity both in vitro and in vivo.

Crystallization of Double Crystalline Diblock Copolymer by Dynamic Monte Carlo Simulation

SummaryWe report dynamic Monte Carlo simulation results on the crystallization of double crystalline A‐B diblock copolymer, wherein the melting temperature of A‐block is higher than B‐block. Crystallization of A‐block precedes the crystallization of B‐block upon cooling from a homogeneous melt. The interaction between A‐type and B‐type units is modelled as the repulsive interaction to represent their mutual immiscibility. The morphological development is controlled by the interplay between crystallization and microphase separation. With increasing segregation strength, we observe a gradual decrease in crystallinity accompanying with smaller and thinner crystals. During crystallization, A‐block crystallizes first and creates confinement for the crystallization of the B‐block. Thus, crystallization of B‐block slows down, influencing the overall crystal morphology. With changing block composition, we observe a non‐monotonic trend in the crystallization behaviour (viz., crystallinity, lamellar thickness) of A‐block when B‐block composition is significantly higher than A‐block. This non‐monotonic trend is attributed to the dilution effect of the B‐block.

Influense of the high-voltage conductivity on peculiarity of polarization ferroelectric polymer on based vinylidenefluoride

The phenomena of high-voltage polarization and conductivity in oriented vinylidenefluoride and tetrafluoroethylene copolymer films have been investigated. It was shown that under certain electric fields, injection of carriers from the material of electrodes appears The barrier for holes injection in the copolymer was found to be lower than that for electrons. It results in more effective screening of the external field near the anode than near cathode. Electrones, ejected from cathode, creating negative charge by trapping on the surface. It is shown that the electrons injected from cathodes create a negative homocharge on the copolymer surface and then become captured on the surface shallow traps. Their nature has been studied by the x-ray photoelectron spectroscopy. It was shown that these traps may consist of chemical defects in the form of new functional groups formed by reactions of surface macromolecules with sputtered atoms of aluminum. The asymmetric shape of hysteresis curves was explained by the difference in mobility of injected holes and electrons. These factors caused appearance of "non-closed" hysteresis curves for fluorine-containing polymer ferroelectrics. Hysteresis phenomena observed at low electric fields (below coercive ones) are to associate with the behavior of the domains localized in the ordered regions formed during secondary crystallization of copolymers.

Crystallization and Mechanical Properties of Poly(l-lactide)-Based Rubbery/Semicrystalline Multiblock Copolymers

The crystallization and mechanical properties of triblock and multiblock copolymers containing 70 vol % semicrystalline poly(l-lactide) (L) and 30 vol % rubbery poly(ethylene-co-ethylene) (E/EE) were investigated. The multiblock copolymer was synthesized directly from the triblock copolymer (denoted LE/EEL). Specifically, the dihydroxyl-terminated LE/EEL served as a macromonomer in a step-growth polymerization in which stoichiometric quantities of sebacoyl chloride were added, resulting in (LE/EEL)⟨3.6⟩, a multiblock copolymer with an average of 3.6 triblock copolymer units connected together. Additionally, triblock and multiblock copolymers were blended together in order to systematically tune ⟨n⟩ and uncover the role of block number on properties. Dynamic mechanical analysis (DMA) indicated that despite differences in ⟨n⟩, all samples had an order-to-disorder transition temperature TODT ≈ 190 °C, which is above the melting temperature (Tm) of poly(l-lactide). Small-angle X-ray scattering measurements (S...

A new approach to increase toughness of synthesized PP/EPR in-reactor blends by introducing a copolymerization step under low ethylene concentration

Complex microstructure of the polypropylene/ poly(ethylene-co-propylene) in-reactor blends has been the subject of many studies. In this work simple two-step polymerization procedure was considered and effects of adding another copolymerization step with low ethylene concentration were investigated. The blends microstructure and morphology as well as mechanical properties were studied. The blends were characterized using dynamic mechanical thermal analysis (DMTA), gel permeation chromatography (GPC), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and temperature gradient elution fractionation (TGEF). It was found that adding an extra copolymerization step under low ethylene concentration caused considerable increase in the blends toughness, elongation at break and the number of very small dispersed particles in the polypropylene matrix. The mentioned polymerization step produced copolymers having long polypropylene sequences capable to take part in crystallization of polypropylene matrix, suggested acting as linkage between rubber and polypropylene phases. Although the amorphous copolymer related to the additional copolymerization step had a role in decreasing the average size of dispersed phase, the difference in crystallizable copolymer microstructure suggested had a key role in marked enhancement of mechanical properties.

Effect of Level of Crystallinity on Melt Memory Above the Equilibrium Melting Temperature in a Random Ethylene 1-Butene Copolymer

A strong memory effect of crystallization has been observed in melts of random ethylene copolymers even above the equilibrium melting temperature. Melt memory is correlated with self-seeds that increase the crystallization rate of ethylene copolymers. The seeds are associated with molten ethylene sequences from the initial crystals that remain in close proximity and are unable to diffuse quickly to the randomized melt state. Fast diffusion is restricted by topological chain constraints (loops, knots, and other entanglements) that build in the intercrystalline region during crystallization. The effect of topological constraints on melt memory, or on number of remaining self-seeds in the melt, is analyzed studying the melting and subsequent crystallization of a model ethylene 1-butene copolymer with 2.2 mol% ethyl branches prepared with different levels of crystallinity. There is a critical threshold level of crystallinity of 6–12% to observe the effect of melt memory on the subsequent crystallization rate of this copolymer. A faster development of the initial crystallinity may more efficiently trap knots and loops around the crystallites, leading to a lower crystallinity threshold than for slow or isothermally crystallized copolymers.

Investigating Effects of Using Mixtures of Two External Electron Donors on Microstructure and Properties of Polypropylene/Poly(ethylene‐co‐propylene) in‐Reactor Blends Based on Ziegler–Natta Catalyst

Novel results on using mixtures of two external electron donors “phenyltriethoxysilane (donor A)” and “cyclohexylmethyldimethoxysilane (donor C)” in the synthesis of polypropylene/poly (ethylene‐co‐propylene) in‐reactor blends were presented. Thermal gradient elution fractionation (TGEF) was carried out to separate crystallizable copolymer fractions from the blends. FTIR, DSC, DMTA, and SEM were used to analyze the microstructure of the blends and separated fractions. Although using donor A as pure decreased the catalyst activity and molecular weight, using “donor A” in combination with donor C had a synergistic effect on the molecular weight of polypropylene homopolymers and the blends. The glass transition temperature (Tg) of the blend rubbery phase was the lowest in the case of the blend based on pure donor A because of formation of higher sequences of polyethylene and the Tg increased with increasing donor C concentration. PP–PE copolymer concentration and impact strength were found to be higher in the case of the blend based on donor ratio of A/C: 75/25 than other blends.

Dinonylphenyl end-capped poly(ethylene glycol)-b-polystyrene: synthesis and its unusual crystalline and self-assembly behaviors

Block copolymers, dinonylphenyl end-capped polyethylene glycol-b-polystyrene (DNPE-PEO-b-PSs) were synthesized in a one-step atom transfer radical polymerization (ATRP) of styrene. The PEO block in the DNPE-PEO-b-PS samples (volume fraction of PS: 66.8–93.2 %) was found to be amorphous, which contrasts with DNPE-PEO precursor, traditional methoxide end-capped polyethylene glycol-b-polystyrene (PEO-b-PS) and dinonylphenyl end-capped poly-(ethylene glycol)-b-poly(fluorinated methyl methacrylate)(DNPE-PEO-b-PFMAs). Meanwhile, DNPE-PEO-b-PSs display an intriguing self-assembly behavior in solution. Block copolymer particles with mesoporous internal structures are directly formed by self-assembly of DNPE-PEO-b-PS in tetrahydrofuran/water solutions. It is proposed that DNPE end group has an important effect on the crystallization of the block copolymers as well as their self-assembly behaviors in solution.

Crystallization and Thermal Properties of PLLA–PEG 600/Clay Nanocomposites

This study explored the crystallization and thermal properties of copolymers of polylactic acid–polyethylene glycol (Mn: 600) (PLLA–PEG 600 copolymer) nanocomposites with added montmorillonite (clay). The d-spacing of the hydrophilic montmorillonite was increased by using a quaternary ammonium salt. The salt was used to modify montmorillonite via ion exchange. The modified montmorillonite was then evenly dispersed in the matrix of the PLLA–PEG 600 copolymer to synthesize the nanoscale polymer via solution casting method. Thermogravimetric analysis and differential scanning calorimetry were used to measure the thermal properties of the PLLA–PEG 600 copolymers with various proportions of added clay. Wide-angle X-ray diffraction was used to identify the crystal structure and lattice displacements of PLLA–PEG 600 copolymer and the copolymer with added clay. Using polarized optical microscopy and transmission electron microscopy, the crystal growth and size of PLLA–PEG 600 copolymer with various proportions of added clay, as well as the dispersion of the clay, were observed. Adding clay to PLLA–PEG 600 copolymer improved its thermal properties and crystallinity without changing its original crystal structure.

Morphology, Crystal Structure and Charge Transport in Donor–Acceptor Block Copolymer Thin Films

We studied structure and charge transport properties of thin films of donor-acceptor block copolymers, poly(3-hexylthiophene-block-perylene bisimide acrylate), using a combination of X-ray scattering, AFM and vertical charge transport measurements in diode devices. Block copolymer self-assembly and crystallization of the individual components are interrelated and different structural states of the films could be prepared by varying preparation conditions and thermal history. Generally the well-defined microphase structures found previously in bulk could also be prepared in thin films, in addition alignment induced by interfacial interactions was observed. Microphase separated block copolymers sustain ambipolar charge transport, but the exact values of electron and hole mobilities depend strongly on orientation and connectivity of the microdomains as well as the molecular order within the domains.

Crystallization and Phase Segregation of Multifunctional Multiblock Copolymers in Spin Coated Thin Films Altered by Diurethane Junction Units

SummaryA multiblock copolymer named PDC is composed of crystallizable oligo(p‐dioxanone) (OPDO) and oligo(ε‐caprolactone) (OCL) as hard and switching segments. PDC has been synthesized via connecting two oligomeric macrodiols using a diisocyanate linker such as 2,2(4), 4‐trimethyl‐hexamethylene diisocyanate (TMDI) or 1,6‐hexamethylene diisocyanate (HDI). In this work, the surface morphologies of spin coated thin films from two PDCs (PDC‐HDI and PDC‐TMDI) were investigated via in‐situ atomic force microscopy (AFM) to examine how the diisocyanate linkers affect the balance between crystallization and phase segregation behavior. The results demonstrated that in PDC‐HDI, the crystallization of poly(ε‐caprolactone) (PCL) crystals provoked a “break out” from the phase segregated morphology. On contrary, the crystallization of PCL crystals in PDC‐TMDI was strictly confined in the phase segregated morphology.

Effect of an alpha-phase nucleating agent on the crystallization kinetics of a propylene/ethylene random copolymer at largely different supercooling

The effect of addition of 0.1wt% phosphate-ester based alpha-phase nucleating agent on the crystallization of a random propylene-based copolymer with 3.9mol% ethylene has been investigated by fast scanning chip calorimetry (FSC). Main purpose of the work was the evaluation of the effect of the nucleating agent on the bimodal temperature dependence of the crystallization rate of propylene-based polymers caused by a change of the nucleation mechanism from heterogeneous to homogeneous nucleation on lowering the temperature to below about 60°C. Presence of the nucleation agent in the copolymer of the present study accelerates crystallization only in the high-temperature range of predominant heterogeneous nucleation, but does not affect the crystallization rate in the low-temperature range of homogeneous nucleation. The observed decrease of the minimum crystallization half-time due to the addition of the nucleation agent, from 0.2s in case of the unmodified copolymer to 0.04s in case of the copolymer containing the nucleating agent, is paralleled by an increase of the critical cooling rate required to inhibit crystallization on continuous cooling to below the glass transition temperature from 102 to 103Ks–1. The study is completed by an analysis of the effect of addition of the nucleation agent on the spherulitic superstructure.

Modeling Thermal Properties for Copolymers Covering a Comonomer Composition Range up to 20%

Differential scanning calorimetry (DSC) analysis for ethylene/propylene copolymers synthesized in the whole composition range with a supported metallocene catalyst has been carried out. The melting/crystallization process can be determined both in the ethylene and propylene rich regions covering a comonomer composition range of up to 20%. Two peaks are detected showing two different transitions (Tm1 and Tm2). A procedure is developed for modeling DSC melting curves by using a model previously reported by Kissin. Two contributions are considered for the copolymer crystallization in connection with a random comonomer distribution. Such model favourably describes experimental DSC curves and Tm1 and Tm2 values. The obtained parameters follow a regular trend in accordance with its physical meaning. Standard deviation for melting temperatures reveals accurate calculated values. The analysis of the parameter trend allows a fit against composition and predicting melting temperatures, yielding also accurate values.

Effect of block asymmetry on the crystallization of double crystalline diblock copolymers.

Monte Carlo simulation on the crystallization of double crystalline diblock copolymer unravels an intrinsic relationship between block asymmetry and crystallization behaviour. We model crystalline A-B diblock copolymer, wherein the melting temperature of A-block is higher than that of the B-block. We explore the composition dependent crystallization behaviour by varying the relative block length with weak and strong segregation strength between the blocks. In weak segregation limit, we observe that with increasing the composition of B-block, its crystallization temperature increases accompanying with higher crystallinity. In contrast, A-block crystallizes at a relatively low temperature along with the formation of thicker and larger crystallites with the increase in B-block composition. We attribute this non-intuitive crystallization trend to the dilution effect imposed by B-block. When the composition of the B-block is high enough, it acts like a "solvent" during the crystallization of A-block. A-block segments are more mobile and hence less facile to crystallize, resulting depression in crystallization temperature with the formation of thicker crystals. At strong segregation limit, crystallization and morphological development are governed by the confinement effect, rather than block asymmetry. Isothermal crystallization reveals that the crystallization follows a homogeneous nucleation mechanism with the formation of two-dimensional crystals. Two-step, compared to one-step isothermal crystallization leads to the formation of thicker crystals of A-block due to the dilution effect of the B-block.

Unusual crystallization behavior of isotactic polypropylene and propene/1-alkene copolymers at large undercoolings

During the investigation of the crystallization of metallocene isotactic polypropylene and copolymers with low amount of 1-butene and 1-hexene at large undercoolings, an unexpected behavior has been found. Random copolymers crystallize faster than the homopolymer between 80 and 40 °C, while at high temperatures the overall crystallization rates follow the expected trend. On the basis of structural and morphological evidences we suggest that the overall structuring kinetics of the homopolymer is slowed down by the concomitant formation of mesophase and monoclinic structures. This effect is absent in the copolymers because the branched counits retard the development of mesophase.

Influence of Metastable States on Electrophysical Properties in Ferroelectric Crystalline Polymers

The poling and local piezoresponse mechanism has been investigated in ferroelectric polymers. Isotropic 94/6 composition vinylidenefluoride and tetraflouroethylene copolymer films is formed from acetone at room temperature by slow evaporation of solvent. The copolymer crystallization results in metastability (nonequilibre) form at high overcooling temperatures. IR spectroscopy shows occurrence of isomers with conformation TGTG-, T3GT3G- and (TT)n. The local piezoresponse shows that ferroelectric domains include crystals areas as well as nonordered phase. After annealing by heating to 150 oC was found conformation changes in polymer chain: T3GT3G- TGTG- and T3GT3G- (TT)n. It is show that the regular conformation chains length rising after annealing. Polarization value decreasing kinetic was investigated by piezoresponse force microscopy method.

Crystallization and thermal characterization of biodegradable tri-block copolymers and poly(ester-urethane)s based on PCL and PLLA

Abstract In this paper the crystallization behavior of biodegradable linear tri-block copolymers PLLA-b-PCL-b-PLLA and their corresponding poly(ester-urethane)s was studied and related to their thermal stability. A series of tri-block copolymers was synthesized by ring opening polymerization of l -lactic acid thus using PCL block with constant molecular weight of about 8000 g/mol and varying the amount of PLLA. The poly(ester-urethane)s were synthesized by polycondensation of the tri-block copolymers with hexamehylene diisocyanate. The crystallinity nature of the polymers was investigated by wide angle X-ray diffraction (WAXD) measurements allowing the determination of the cell structure parameters. Furthermore, the kinetic of the crystallization process from the melt was studied with differential scanning calorimetry (DSC) measurements and by using the Avrami equation to describe the process in terms of crystallization growth and rate. Finally, the thermal degradation of the tri-block copolymers as well as of the poly(ester-urethane)s was investigated by dynamic thermogravimetric analysis (TGA). It was found that the differences on the molecular structure in terms of block copolymer composition, molecular weight, crystallinity and the presence of urethane bonds, affect the degradation behavior of each block.

How different mesophases affect the interactive crystallisation of a block co-oligomer

An effective method for fabrication of long range ordered micro- and nanostructures on surfaces is to control the interactive crystallisation of block copolymers. In this study, the influence of different initial mesophases of a double crystalline polyethylene-block-poly (ethylene oxide) (PE-b-PEO) diblock co-oligomer on the interactive crystallisation process was studied using synchrotron radiation X-ray diffraction (SAXS/WAXD), in situ optical microscopy and differential scanning calorimetric analysis (DSC). According to the applied annealing procedure, different PE-b-PEO initial mesophases, i.e., disordered, cylindrical and spherical, have been induced. In all cases, the subsequent PEO crystallisation disrupted these initial microdomains and transformed them into crystalline lamellar morphologies with the same long periods. However, the different initial mesophases significantly affected the PEO crystallisation kinetics due to different topological confinements. An initial disordered mesophase induced the highest PEO crystallisation rate because PEO nucleation and crystal growth were limited only by chain diffusion. For an initial spherical or cylindrical mesophase, decreased PEO crystallisation rates were observed. Here, the chain diffusion was decreased by the microdomain structure. For an initial cylindrical mesophase, the earlier formed PE crystals act as a template for the subsequent PEO crystallisation and, thus, increased the PEO crystallisation as compared to the spherical mesophase where the PE was amorphous. This study demonstrates that the topological confinement of the block copolymer's initial mesophase strongly influences the crystallisation kinetics and, thus, the structures formed at the surface of drop-casted films.

Crystallization in Sequence-Defined Peptoid Diblock Copolymers Induced by Microphase Separation

Atomic level synthetic control over a polymer's chemical structure can reveal new insights into the crystallization kinetics of block copolymers. Here, we explore the impact of side chain structure on crystallization behavior, by designing a series of sequence-defined, highly monodisperse peptoid diblock copolymers poly-N-decylglycine-block-poly-N-2-(2-(2-methoxyethoxy)ethoxy)ethylglycine (pNdc-b-pNte) with volume fraction of pNte (ϕNte) values ranging from 0.29 to 0.71 and polydispersity indices ≤1.00017. Both monomers have nearly identical molecular volumes, but the pNte block is amorphous while the pNdc block is crystalline. We demonstrate by X-ray scattering and calorimetry that all the block copolypeptoids self-assemble into lamellar microphases and that the self-assembly is driven by crystallization of the pNdc block. Interestingly, the microphase separated pNdc-b-pNte diblock copolymers form two distinct crystalline phases. Crystallization of the normally amorphous pNte chains is induced by the preorganization of the crystalline pNdc chains. We hypothesize that this is due to the similarity of chemical structure of the monomers (both monomers have linear side chains of similar lengths emanating from a polyglycine backbone). The pNte block remains amorphous when the pNdc block is replaced by another crystalline block, poly-N-isoamylglycine, suggesting that a close matching of the lattice spacings is required for induced crystallization. To our knowledge, there are no previous reports of crystallization of a polymer chain induced by microphase separation. These investigations show that polypeptoids provide a unique platform for examining the effect of intertwined roles of side chain organization on the thermodynamic properties of diblock copolymers.