A comprehensive study of the structure and properties has been performed for copolymers of propylene‐1‐hexene, CiPH, and propylene‐ethylene, CiPE, synthesized by an isotactic metallocene catalyst system. The comonomer content constitutes the most important factor affecting the structure and properties of these CiPH and CiPE copolymers, although the length of the comonomer is also very important. Thus, a considerable decrease in crystallinity is observed in the two kinds of copolymers as the comonomer content increases. The structure in the CiPH copolymers evolves, however, from the typical, monoclinic crystal lattice to mesomorphic‐like, ordered entities for the highest 1‐hexene molar fraction, whereas in the CiPE copolymers the structural evolution with molar fraction goes from a monoclinic lattice to an almost amorphous material. All of these variations in crystal structure significantly influence the viscoelastic and mechanical behavior of these CiPH and CiPE copolymers. Consequently, the location and intensity of the different relaxation mechanisms, as well as the rigidity parameters (storage and Young's moduli and microhardness) and deformation mechanism are strongly dependent upon composition.
Comb‐like copolymers based on a polyolefin backbone of poly(10‐undecene‐1‐ol) (PUol) with poly(ε‐caprolactone) (PCL) side chains are synthesized in two steps. After synthesis of PUol by metallocene‐catalyzed polymerization, the side‐chain hydroxyl functionalities of this polar polyolefin are used as an initiator for the ring‐opening polymerization (ROP) of ε‐caprolactone (CL). In this context, copolymers with different lengths of PCL grafts are prepared. The chemical structure and the composition of the synthesized copolymers are characterized by 1H and 13C NMR spectroscopy. It is shown that the hydroxyl end groups of PUol act effectively as initiating sites for the CL ROP. Size‐exclusion chromatography (SEC) measurements confirm the absence of non‐attached PCL and the expected increase in molar mass after grafting. The thermal and decomposition behaviors are investigated by DSC and thermogravimetric analysis (TGA). The effect of the length of the PCL grafts on the crystallization behavior of the comb‐like copolymers is investigated by DSC and wide‐angle X‐ray scattering (WAXS).
Biodegradable copolymers were prepared by ring‐opening polymerization of sequentially added ε‐caprolactone and DL ‐lactide in the presence of ethylene glycol or poly(ethylene glycol), using zinc metal as catalyst. Polymerization was performed in bulk and yielded block copolymers with predetermined PEG/PCL/PLA segments. The obtained polymers were characterized by 1H NMR, SEC, IR, DSC, TGA, and X‐ray diffraction. Data showed that the copolymers preserved the excellent thermal behavior inherent to PCL. The crystallinity of PLA‐containing copolymers was reduced with respect to PCL homopolymer. The presence of both hydrophilic PEG and fast degrading PLA blocks should improve the biocompatibility and biodegradability of the materials, which are of interest for applications as substrate in drug delivery or as scaffolding in tissue engineering.
Block copolymerization of ε‐caprolactone and DL ‐lactide initiated by dihydroxyl PEG. 相似文献
The thermal properties, morphological development, crystallization behavior, and miscibility of semicrystalline PCL and its 25, 50, and 75 wt% blends with amorphous PPF in spin‐coated thin films crystallized at various crystallization temperatures (Tc) from 25 to 52 °C are investigated. The surface roughness of PPF/PCL (?PCL = 75%) films increases with increasing Tc and consequently the adsorption of serum proteins is also increased. No significant variance is found in surface hydrophilicity or in mouse MC3T3‐E1 cell attachment, spreading, and proliferation on PPF/PCL (?PCL = 75%) films crystallized isothermally at 25, 37, and 45 °C, because of low ridge height, nonuniformity in structures, and PPF surface segregation. 相似文献
Fullerene capped poly(ε‐caprolactone)s (PCLs), namely single‐ and double‐fullerene end‐capped PCLs with different fullerene content, were successfully synthesized. The effect of the fullerene end on the crystallization behavior and mechanical properties of the PCL was studied. The aggregation behavior of the fullerene moieties at the end of the PCL chain was also studied. It was found that the aggregated fullerenes have two kinds of effect on the crystallization behavior of the PCL i.e., confinement effect and nucleating effect. The fullerene content shows a certain balance between the confinement effect and the nucleating effect on the crystallization rate of PCL. It was also found that the mechanical properties of the fullerene end‐capped PCLs are strongly related to the content of fullerene and the mode of end‐capping style: either single or double end‐capping.
Vis‐breaking or rheology control is an important technical process to improve the processability of impact poly(propylene) copolymers (IPCs). In the vis‐breaking process the molar mass and its dispersity are reduced and the crystallinity changes and polar carbonyl functionalities are introduced due to the reaction of the polymer with peroxide. Although the fundamental principles of vis‐breaking are well understood, not much research has been devoted to the investigation of the molecular changes brought about by the vis‐breaking process. In the present study, the effect of vis‐breaking on the molecular parameters of IPCs is elucidated using advanced fractionation methods. After the analysis of the bulk sample properties, the samples are fractionated using preparative temperature rising elution fractionation and the fractions are analyzed by Fourier transform infrared spectroscopy, differential scanning calorimetry, crystallization analysis fractionation, and high temperature high performance liquid chromatography techniques. For the first time, an effective multidimensional analytical approach is established to study compositional heterogeneities in vis‐broken IPC materials.
Summary: A binary blend of poly (L ‐lactide) (PLLA) and poly(ε‐caprolactone) (PCL) of composition 70:30 by weight was prepared using a twin screw miniextruder and investigated by differential scanning calorimetry (DSC), optical microscopy and scanning electron microscopy (SEM). Ternary 70:30:2 blends were also obtained by adding either a diblock copolymer of PLLA and poly(oxyethylene) (PEO) or a triblock PLLA‐PCL‐PLLA copolymer as a third component. Optical microscopy revealed that the domain size of dispersed PCL domains is reduced by one order of magnitude in the presence of both copolymers. SEM confirmed the strong reduction in particle size upon the addition of the copolymers, with an indication of an enhanced emulsifying effect in the case of the PLLA‐PEO copolymer. These results are analyzed on the basis of solubility parameters of the blend components.
Optical micrograph of M3EG2 blend melt quenched at 125 °C. 相似文献
Summary: Polybenzoxazine (PBA‐a)/poly(ε‐caprolactone) (PCL) blends were prepared by an in situ curing reaction of benzoxazine (BA‐a) in the presence of PCL. Before curing, the benzoxazine (BA‐a)/PCL blends are miscible, which was evidenced by the behaviors of single and composition‐dependant glass transition temperature and equilibrium melting point depression. However, the phase separation induced by polymerization was observed after curing at elevated temperature. It was expected that after curing, the PBA‐a/PCL blends would be miscible since the phenolic hydroxyls in the PBA‐a molecular backbone have the potential to form intermolecular hydrogen‐bonding interactions with the carbonyls of PCL and thus would fulfil the miscibility of the blends. The resulting morphology of the blends prompted an investigation of the status of association between PBA‐a and PCL under the curing conditions. Although Fourier‐transform infrared spectroscopy (FT‐IR) showed that there were intermolecular hydrogen‐bonding interactions between PBA‐a and PCL at room temperature, especially for the PCL‐rich blends, the results of variable temperature FT‐IR spectroscopy by the model compound indicate that the phenolic hydroxyl groups could not form efficient intermolecular hydrogen‐bonding interactions at elevated temperatures, i.e., the phenolic hydroxyl groups existed mainly in the non‐associated form in the system during curing. The results are valuable to understand the effect of curing temperature on the resulting morphology of the thermosetting blends.
SEM micrograph of the dichloromethane‐etched fracture surface of a 90:10 PBA‐a/PCL blend showing a heterogeneous morphology. 相似文献
Graft copolyesters with a PCL backbone and PLLA side chains were successfully prepared in three steps avoiding transesterification. First ε‐caprolactone was polymerised with 1,6‐hexane diol as initiator to obtain hydroxytelechelic oligo(ε‐caprolactone)s. These diols were then subjected—in the second step—to polycondensation with L ‐malic acid yielding in linear poly[oligo(ε‐caprolactone)L ‐malate] having secondary hydroxyl functions in the side chain. For both reactions scandium triflate Sc(OTf)3 was used as a catalyst. In the third step various amounts of L ‐lactide were grafted from the polymer backbone using Zn(oct)2 as catalyst. The successful reaction was confirmed by NMR and SEC (size exclusion chromatography) analysis. Further the thermal properties of the graft copolymers with different graft lengths were determined via differential scanning calorimetry.
Macromolecular complexes of sodium poly(α,L ‐glutamate) (PGNA) (molecular weight (MW) 1, 49 and 71 k) and ethylene oxide‐propylene oxide tri‐block copolymer (MW 8 400) have been prepared by a novel method involving dehydration of reverse micelles (DRM method). This series of complexes was compared with the complexes of PGNA (MW 1, 49 and 71 k)/ethylene oxide‐propylene oxide random and tri‐block copolymers prepared by the common method involving evaporation of aqueous mixtures (EAM method). By the DRM process fifteen times more copolymer was incorporated in the pure macromolecular complex than by the EAM process. CD spectra of the EAM series of complexes showed formation of α‐helical PGNA conformation as evidenced by the observation of +ve peak at 194 nm and two –ve peaks at 201 and 221 nm. Formation of the α‐helical conformation is further supported by FT‐IR spectroscopy. On the other hand, CD spectra of the DRM macromolecular complexes showed neither α‐helical nor random conformation, and the spectra may be attributed to a distorted helical PGNA conformation. DSC studies revealed that the copolymers in EAM macromolecular complexes were intimately blended with PGNA, while in the DRM series only 65% of the copolymer were blended at the molecular level, with the rest present as a pure copolymer domain. 23Na NMR spectra of both series of complexes showed presence of free sodium ions indicative of dissociated Na+—O dipolar interactions in aqueous solution. Hydrophobic interaction between PGNA and copolymer remained intact even in very dilute solutions of both series of complexes as observed by strong 2D‐NOESY 1H NMR correlation between β and γ CH2 groups of PGNA and CH2 groups of copolymers. However, in the DRM series, only the CH2 groups of PEO blocks of the PEO‐PPO‐PEO copolymer showed the 2D‐NOESY 1H NMR correlation indicating that only the PEO blocks are involved in the complex formation. The PPO block that had no interaction with PGNA may have formed pure PPO domains. NMR data combined with the DSC, CD and FT‐IR data suggest that the structure of both series of macromolecular complex is a composite composed of copolymer molecules intimately interacting with PGNA chains. Interactions between β and γ groups of PGNA side groups with CH2 groups of the copolymer are involved in forming the complex. 2D‐NOESY 1H NMR correlation further indicate that both the DRM and EAM series of macromolecular complexes are stable in water for at least seven weeks. 相似文献
Summary: The ternary thermosetting blends composed of epoxy resin, poly(ethylene oxide) (PEO) and poly(ε‐caprolactone) (PCL) were prepared via in situ polymerization of epoxy monomers in the presence of the two crystalline polymers, PEO and PCL. DSC results showed that the binary blends of epoxy with PEO (and/or PCL) are fully miscible in the entire composition in the amorphous state. FTIR indicates that there were interchain specific interactions between the crosslinked epoxy and the linear polymers in the binary blends and the hydrogen bonding interactions between epoxy and PCL are much weaker than those between epoxy and PEO. The difference in the strength of interchain specific interactions gives rise to the competitive hydrogen bonding interactions in the ternary blends of epoxy, PEO and PCL, which were evidenced by the results of FTIR. The results of optical microscopy and DSC showed that in the ternary blends PCL component separated out with inclusion of PEO. The formation of the specific phase structures is ascribed to the competitive interchain specific interactions among the crosslinked epoxy, PEO and PCL.
Phase boundary diagram of epoxy, PEO and PCL ternary blends. 相似文献
Poly(ε‐caprolactone)/silica nanocomposites were prepared by the in situ technique. The molecular weight of the polymer was slightly reduced on increasing the amount of filler. Most likely, the silica nanoparticles affected the action of the polymerisation catalyst. Furthermore, it was found that especially for high filler content the silica nanoparticles showed a trend to form aggregates. The non‐isothermal crystallisation of these hybrid organic/inorganic materials was studied. The crystallisation rates seemed to increase upon increasing the content of silica nanoparticles in the composites. When the silica content was above 5 wt.‐%, the molecular weight of the polymer in the hybrids decreased, and the increase in the crystallisation rates was attributed to both the nucleating effect of the nanoparticles and the lower molecular weight. The modified Avrami and Ozawa model were used to study the crystallisation kinetics. It was found that both of the models gave satisfactory results. The nucleation activity of the filler was estimated. The effective activation energy for the non‐isothermal crystallisation was calculated using the isoconversion method of Friedman and the results were compared to those from Kissinger's method. The activation energy was found to decrease upon increasing the filler content, showing that the crystallisation is favoured.
Novel fullerene‐ and polyhedral oligomeric silsesquioxane‐ (POSS) double end‐capped poly(ε‐caprolactone) (PCL) were successfully synthesized. The crystallization behavior of the fullerene‐ and POSS‐ double end‐capped PCL and the effect of aggregation of the POSS and fullerene moieties on the crystallization of PCL were thoroughly studied. The aggregation of the fullerene moieties has much larger confinement effect on the crystallization of PCL than that of POSS. The successful incorporation of two nano‐sized objects, that is, fullerene and POSS, into the PCL matrix may introduce their merits, so that PCL can attain multi‐functional properties.
Summary: The thermal behaviour of poly(propylene terephthalate) modified with 2,2‐bis[4‐(ethylenoxy)‐1,4‐phenylene]propane terephthalate) units (PPT/BHEEBT copolymers) was investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and hot‐stage optical microscopy (MO). Good thermal stability was found for each sample. The thermal analysis carried out using the DSC technique showed that the Tm of the copolymers decreased with the increment in BHEEBT unit content. This was different from the Tg which, on the contrary, increased. Wide‐angle X‐ray diffraction measurements allowed the identification of the PPT crystalline structure in each semicrystalline sample. Multiple endotherms were shown in the PPT/BHEEBT samples, due to melting and recrystallisation processes, similarly to PPT. The of the copolymers was derived from the application of the Hoffman‐Weeks' method. The isothermal crystallisation kinetics were analysed according to Avrami's treatment. The introduction of BHEEBT units was found to decrease the crystallisation rate compared to pure PPT. Values of the Avrami's exponent n close to 3 were obtained for PPT/BHEEBT6 and PPT/BHEEBT12, regardless of Tc, in agreement with a crystallisation process originating from pre‐determined nuclei and characterised by three‐dimensional spherulitic growth. As a matter of fact, for these two copolymers, space‐filling spherulites were observed through optical microscopy at all Tcs. The heat of fusion (ΔHm) was correlated to the specific heat increment (Δcp) for samples with different degrees of crystallinity, and the results were interpreted on the basis of the existence of an interphase, whose amount was found to depend mainly on composition, despite the thermal treatment applied to the polymer also playing an important role.
Calorimetric curves of PPT, PBHEEBT homopolymers and their random copolymers after melt quenching. 相似文献
Poly(vinyl alcohol)‐graft‐poly(ε‐caprolactone) (PVA‐g‐PCL) was synthesized by ring‐opening polymerization of ε‐caprolactone with poly(vinyl alcohol) in the presence of tin(II) 2‐ethylhexanoate as a catalyst in dimethyl sulfoxide. The relationship between the reaction conditions of the solution polymerization and the chemical structure of the graft copolymer was investigated. The degree of substitution (DS) and degree of polymerization (DP) of the PCL side chains were roughly controlled by varying the reaction periods and feed molar ratios of the monomer and the catalyst to the backbone. PVA‐g‐PCL with a PCL content of 97 wt.‐% (DP = 22.8, DS = 0.54) was obtained in 56 wt.‐% yield. The graft copolymer was soluble in a number of organic solvents, including toluene, tetrahydrofuran, chloroform, and acetonitrile, which are solvents of PCL. The molecular motion of the graft copolymer from 1H NMR measurements appears to be restricted to some extent at 27–50°C, however the 1H NMR signal intensities measured at temperatures higher than ca. 50°C reflect the actual chemical structure of the graft copolymer as determined by elemental analysis. The graft copolymer having a short PCL side chain (DP = 4.4, DS = 0.15) was amorphous. The melting temperature of a sample with relatively high PCL content (DP = 22.8, DS = 0.54) was observed at 39°C. Thermogravimetric analysis revealed that the thermal stability of PVA was improved by introducing PCL side chains. The surface free energies of the air‐side of a graft copolymer film, as calculated by Owens' equation using contact angles, were comparable to that of PCL homopolymer. 相似文献
New hydrophilic networks combining poly(ethylene glycol) (PEG) and β‐cyclodextrin (β‐CD) have been prepared. Both components are linked by reacting PEG chains previously end‐capped with isocyanate groups and β‐CD, forming urethane links. Networks of molar compositions (β‐CD/PEG) ranging from 1/4 to 1/14, and with four different molar masses (400, 600, 900, and 1 350 g · mol?1) of the end‐capped PEG precursor have been synthesized. The networks have good thermal stability and low glass transition temperatures. Crystallinity has only been detected for the two higher molar mass PEG precursors. The swelling properties of these hydrogels depend on the chain lengths of the PEG precursor and also on the temperatures.
A series of supramolecular degradable inclusion complex (IC) films were formed by threading α‐cyclodextrin (α‐CD) molecules over poly(ε‐caprolactone) (PCL) according to the designed ratio of α‐CD–PCL. Due to containing both α‐CD–PCL inclusion crystallites and uncovered PCL crystallites, the resulting supramolecular α‐CD–PCL IC partial films displayed a shape memory effect. The properties of the materials were investigated by 1H NMR, X‐ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and swelling measurement. It was found that the casting temperature and solvent have great influence on the formation and properties of the α‐CD–PCL partial ICs. The modes of complexes on different conditions were proposed. In addition, the introduction of inclusion structure accelerates the degradation of materials strongly.
Biodegradable and photocurable block copolymers of ε‐caprolactone and L ‐lactide were synthesized by polycondensation of PLLA diol ( = 10 000 g · mol?1), PCL diol ( = 10 000 g · mol?1), and a chain extender bearing a coumarin group. The effect of copolymer composition on the thermal and mechanical properties of the photocured copolymers was studied by means of DSC and cyclic tensile tests. An increase in Young's modulus and a decrease in the tensile strain with increasing PLLA content was observed for the block copolymers. Block copolymers with high PCL content showed good to excellent shape‐memory properties. Random copolymers exhibited Rf and Rr values above 90% at 45 °C for an extremely large tensile strain of 1 000%.
Summary: The synthesis of α,ω‐di(2‐methyl‐6‐pyrenyl‐2‐succinimidylhexanoic ester)poly(ethylene oxide) (Py(S)‐EOn‐(S)Py) was obtained by a new radical reaction between 4‐pyrenylbutanoate N‐hydroxysuccinimidyl ester and α,ω‐dimethacrylate poly(ethylene oxide). The reason for the choice of such bulky groups is a possible application of this reaction to the synthesis of polyrotaxane from polypseudorotaxane. Two reaction media were examined, heterogeneous in water at room temperature using persulfate as initiator, or homogeneous in DMSO at 60 °C using AIBN as initiator. Structural characterization of the functionalization products was carried out by SEC, MALDI TOF, and NMR spectroscopies. It was shown that two types of α,ω‐dipyrenyl PEO could be obtained, one corresponding to the expected product (Py(S)‐EOn‐(S)Py), the other corresponding to the same structure but without the succinimidyl substituent (Py(H)‐EOn‐(H)Py). It was also shown that in the soluble system macrocycles could be formed and this last aspect has been assigned to intramolecular interactions existing between the pyrenyl groups. An interesting aspect of this synthesis is the possibility to find conditions giving high yields without crosslinking and fairly reduced amount of coupling.
Surface patterning was carried out by the epitaxial crystallization of biodegradable PCL on a HOPG, and the surface morphologies were observed by atomic force microscopy. Edge‐on view lamellae were aligned along the HOPG lattice to display stripe patterns in the threefold symmetry. The intervals of stripe patterns composed of ridges and valleys increased with an increase in the crystallization temperature. Enzymatic degradation of the PCL nanopattern allowed the different depth profiles of the fringed structure. The persistence length of the nanopattern could be tuned by the molecular weight of PCL.
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