Nonisothermal melting and crystallization studies of homogeneous ethylene/α-olefin random copolymers

A study of nonequilibrium melting, nonisothermal, and isothermal crystallization behavior of ethylene/1-octene (EO) random copolymers, produced using metallocene catalysts has carried out. As branch (or defect) content increases, the nonisothermal and isothermal crystallization rates, melting temperatures, and heats of fusion decrease. There is also a branch length effect on melting temperature depression, the melting temperature depression of EO random copolymers with hexyl branches were significantly larger than those of ethylene/1-butene (EB) and ethylene/1-propene (EP) copolymers having ethyl and methyl branches, respectively. The melting temperatures of homogeneous random copolymers have been found to be always lower than those of fractions of heterogeneous copolymers, having approximately the same branch content and molecular weight. Hence, defect distribution in copolymer systems is at least as important a parameter as the defect content. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1893–1905, 1998     

Synthesis and characterization of copolymers based on poly(butylene terephthalate) and ethylene oxide‐poly(dimethylsiloxane)‐ethylene oxide

A series of thermoplastic elastomers based on ethylene oxide‐poly(dimethylsiloxane)‐ethylene oxide (EO‐PDMS‐EO), as the soft segment, and poly(butylene terephthalate) (PBT), as the hard segment, were synthesized by catalyzed two‐step, melt transesterification reaction of dimethyl terephthalate (DMT) with 1,4‐butanediol (BD) and α,ω‐dihydroxy‐(EO‐PDMS‐EO). Copolymers with a content of hard PBT segments between 40 and 90 mass % and a constant length of the soft EO‐PDMS‐EO segments were prepared. The siloxane prepolymer with hydrophilic terminal EO units was used to improve the miscibility between the polar comonomers, DMT and BD, and the nonpolar PDMS. The molecular structure and composition of the copolymers were determined by ¹H‐NMR spectroscopy, whereas the effectiveness of the incorporation of α,ω‐dihydroxy‐(EO‐PDMS‐EO) into the copolymer chains was verified by chloroform extraction. The effects of the structure and composition of the copolymers on the melting temperatures and the degree of crystallinity, as well as on the thermal degradation stability and some rheological properties, were studied. It was demonstrated that the degree of crystallinity, the melting and crystallization temperatures of the copolymers increased with increasing mass fraction of the PBT segments. The thermal stability of the copolymers was lower than that of PBT homopolymer, because of the presence of thermoliable ether bonds in the soft segments. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of PEO-PPO-PEO structure on the compressed ethylene-induced reverse micelle formation and water solubilization

Some of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) tri-block copolymers aggregate in p-xylene upon addition of ethylene and form reverse micelles at higher temperature at which the reverse micelles cannot be formed without addition of compressed ethylene. An abrupt increase of water solubilization is observed at a certain ethylene pressure. The effects of surfactant structure, such as the ratio of EO (EO weight percent) and the molecular mass, on the copolymer micellization and the solubilization of water in such systems are studied. For the copolymers with the same length of PO block, higher EO ratios facilitate the reverse micelle formation. However, as the EO ratio reaches 70%, it cannot form reverse micelles because the hydrophilicity is too high. For the copolymers with same composition, higher molecular weight is favorable to forming the reverse micelle due to the hydrophilic and folding effects, respectively. The reverse micelle solution can solubilize water with W₀ (molar ratio of water to EO segment) up to 4.1.     

Conductivities and some other properties of oxymethylene-linked 2-vinylpyridine-oxyethylene multiblock copolymers

Oxymethylene-linked 2-vinylpyridine-oxyethylene (2VP-EO) mulitblock copolymers doped with LiClO₄ or/and tetracyanoquinodimethane (TCNQ) showed ionic electronic and mixed (ionic-electronic) conductivity. Effects of the poly(oxyethylene) content and of the molar ratios of EO/Li and TCNQ/2VP on the conductivities of the complexes were studied. The optimum molar ratios of EO/Li and TCNQ/2VP were 10 and 1.0, respectively. The copolymers emulsified benzene/water systems and exhibited good phase-transfer catalysis properties in the Williamson reaction of solid potassium phenolate with n-butyl bromide. After neutralization with HCI solution, the copolymers showed polyelectrolyte solution properties.     

Solid polymer electrolytes based on nanocomposites of ethylene oxide–epichlorohydrin copolymers and cellulose whiskers

With the aim of developing ion‐conducting solid polymer electrolytes that combine high ionic conductivity with good mechanical properties, we prepared and investigated nanocomposites of LiClO₄‐doped ethylene oxide‐epichlorohydrin (EO‐EPI) copolymers and nanoscale cellulose whiskers derived from tunicates. We show that homogeneous nanocomposite films based on EO‐EPI copolymers, LiClO₄, and tunicate whiskers can be produced by solution‐casting THF/water mixtures comprising these components and subsequent compression‐molding. The Young's moduli of the nanocomposites thus produced are increased by a factor of up to >50, when compared to the copolymers, whereas the electrical conductivities experience only comparably small reductions upon introduction of the whiskers. The nanocomposite with the best combination of conductivity (1.6 × 10^?4 S/cm at room temperature and a relative humidity of 75%) and Young's modulus (7 MPa) was obtained with a copolymer having an EO‐EPI ratio of 84 : 16, a whisker content of 10% w/w, and a LiClO₄ concentration of 5.8% w/w. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2883–2888, 2004     

Crystallization behavior and rheological properties of polycarbonate and polypropylene blends

Crystallization behavior and rheological properties of blends of bisphenol-A polycarbonate (PC) and polypropylene (PP) prepared by screw extrusion have been investigated by differential scanning calorimetry (DSC), polarized-light microscopy, scanning electron microscopy, and a Rheometrics Mechanical Spectrometer. In the study of thermal analysis of PC-PP blends by DSC, double crystallization peaks were observed in the PC-rich compositions. In the study of spherulite of 7/3 PC-PP blend, large droplets (>25 μm) of PP were crystallized between 115°C and 105°C, and then small droplets (<10 μm) of PP were crystallized at about 90°C. This result is consistent with the double crystallization behavior such that heterogeneous and homogeneous nucleations have been observed at about 105°C and about 85°C, respectively, by DSC measurements. From the results of rheological properties of the PC-PP blends, the storage modulus of the PC-PP blends at low frequencies has larger value than that of the simple mixing rule. The elasticity increase from the simple mixing rule is consistent with the emulsion model for a dispersed system.     

Analysis of the solid phase copolymerization grafting process

Solid phase grafting, which is an emerging process for the production of graft copolymers, was analyzed and reviewed as an environmentally friendly and inexpensive graft copolymerization process. The effect of the process variables; amount of initiator, catalyst, interfacial agent, monomer, reaction temperature and reaction time were examined. Two graft copolymers, produced by solid phase grafting, were used to show differences in graft percentage by changing the process conditions. The two graft copolymers used were maleic anhydride graft onto polypropylene and acrylic acid graft onto polystyrene. A proposed mechanism was given for each example and characteristic bonds proposed in the PP-g-MA mechanism was positively identified by NMR spectroscopy. Graft levels of 4 wt% PS-g-AAc and 9.6 wt% PP-g-MA were obtained providing comparable or superior graft levels to other grafting processes. Successful scale-up of the solid phase technique proved that this process is efficient and marketable.     

Crystallization and morphology of starch-g-poly(1,4-dioxan-2-one) copolymers

The thermal transition, crystallization and spherulitic morphology of starch-g-poly(1,4-dioxan-2-one) copolymers were studied by means of differential scanning calorimetry (DSC) and polarized optical micrographs (PM). It is found that the graft structures of copolymers have obvious effects on the thermal and crystallization behaviors. Because there were more defect sites in the crystalline phase originating from the short grafted chains of poly(1,4-dioxan-2-one) (PPDO), the crystal structure of the copolymers was much less perfect than that of PPDO. PM revealed that the spherulitic morphology of the graft copolymers depended on graft structures and crystallization temperatures. From the single polarized micrograph of the graft copolymers it was observed clearly that the starch segments acted as nucleation sites. The Avrami equation was used to analyze the overall isothermal crystallization of the graft copolymers. Avrami exponents were almost constant at crystallization temperatures T_c ranging from 45 to 60 °C. Both the PM observation and the DSC investigation (crystallization rate constant, K values) indicated that the graft copolymers crystallize faster than pure PPDO, especially at higher crystallization temperatures.     

Biodegradable polymers for use in surgery — poly(ethylene oxide)/poly(ethylene terephthalate) (PEO/PET) copolymers: 2. In vitro degradation

The degradation mechanism of a series of poly(ethylene oxide)/poly(ethylene terephthalate) (PEO/PET) copolymers, synthesized as described in Part 1¹, has been studied in vitro. The need for the development of in vitro test methods for candidate biomaterials is set down. The effect of time, temperature, pH and selected enzymes on the rate and mechanism of degradation is elucidated. The degradation products are identified. The degree of degradation was monitored molecularly by gel permeation chromatography (g.p.c.) and end-group titration techniques. The composition of the copolymers was obtained using infra-red (i.r.) and nuclear magnetic resonance (n.m.r.) spectroscopy. Mass loss and water uptake data are also given. The mechanism of degradation is shown to be by hydrolysis. The effect of ethylene oxide (EO) and ⁶⁰Co γ-irradiation sterilization on the copolymers was investigated.     

改性高岭土/聚丙烯复合材料的热性能及非等温结晶行为研究

以自制的剥离高岭(MK)、原高岭土(K)以及聚丙烯(PP)和马来酸酐接枝聚丙烯(PP-g-MA)等作为基本原料,通过熔融挤出、注塑成型,制备PP复合材料。采用XRD、DSC、TG研究复合材料的非等温结晶行为、结晶动力学以及热降解性能。结果表明:高岭土的加入,使结晶温度、结晶度、热稳定性都有所提高,且结晶速率加快,具有异相成核作用。与原高岭土相比,改性高岭土更能促进PP复合材料的PP异相成核,促进PP稳态晶型(α晶型)的转变,结晶速率较快。与纯PP和PP/PP-g-MA复合材料相比,PP/改性高岭土复合材料的结晶峰温度、最大热降解温度分别提高了16.7、7.8、9.7、12.6℃。     

Simulation of mass and heat transfer of Quercus leaf particles during hydrothermal extraction

Mass and heat transfer models of Quercus leaf particles during hydrothermal extraction were developed in COMSOL Multiphysics. The main physical properties used in the model were measured. The results showed that the average particle size was 116.7 μm, and after soaking in water for 24 h, the average particle size increased to 127.3 μm. However, the average particle size increased from 116.7 to 132.8 μm after soaking in a 60% (v/v) ethanol solution for 40 min, and decreased to 127.3 μm after 60 min. The Quercus leaf particles have a higher ability to absorb ethanol solution than water. The simulations showed that it took 3.2 s for the ethanol concentration and 0.5 s for the temperature in the particles to tend stably after soaking in a 60% (v/v) ethanol solution at 40°C. From the edge of the particle to the centre, the increasing rates of ethanol concentration and temperature gradually slowed down, while the changing rates of the centre accelerated with the increase in solution concentration and temperature, respectively. When the particles soaked at the lowest concentration, the central concentration first reached stability, and at the lowest temperature, the centre temperature first stabilized.     

Domain structure and crystalline morphology of AB and ABA type block copolymers of ethylene oxide and isoprene cast from solutions

The domain structure and crystalline morphology of AB and ABA type block copolymers of ethylene oxide (EO) and isoprene (Ip) were investigated by using two kinds of casting solvents, non-selective (benzene) and selective (ethyl benzene) solvents. The domain structures of both types of block copolymers are identical, as in the case of amorphous block copolymers, depending mostly on the fractional compositions of each block segment but hardly on the sequence arrangements.When benzene is used as a cast solvent, the change of domain structure with increase of Ip fraction follows, in general, a role established for amorphous block copolymers, except for the fact that the EO segment is crystallizable so that the above role is considerably modified, especially when the EO fraction is dominant, to form spherulitic crystalline texture. The domain structure of mixed system of block copolymer with homo-PEO, cast from benzene solution, also follows the above role, simply depending on fractional composition as a whole, of each component, unless the molecular weight of the homopolymer is much larger than that of corresponding block segment.On the other hand, when ethyl benzene is used as a cast solvent, the domain structure is quite different from that cast from benzene solution, giving single crystal-like texture of EO segments on which Ip segments are segregated to form Ip layer even for a copolymer having an EO fraction as small as 20%. The above contrast of domain formation mechanism between the two kinds of casting solvents is interpreted in terms of an interrelation of two binodal surfaces, critical concentration of crystallization of EO segments and critical concentration of micelle formation of EO and Ip segments, in the phase diagram of the system at a given temperature.     

Synthesis, isothermal crystallization and micellization of mPEG-PCL diblock copolymers catalyzed by yttrium complex

Amphiphilic biodegradable mPEG-PCL diblock copolymers have been synthesized using rare earth catalyst: yttrium tris(2,6-di-tert-butyl-4-methylphenolate) [Y(DBMP)₃] in the presence of monomethoxy poly(ethylene glycol) (mPEG, M_n = 5000) as macro-initiator. The diblock architecture of the copolymers was thoroughly characterized by ¹H NMR, ¹³C NMR and SEC. The molecular weights of mPEG-PCLs can be well controlled by adjusting the feeding molar ratio of ?-CL to mPEG. Thermal and crystallization behaviors of the diblock copolymers were investigated by DSC and POM (polarized optical microscope). The crystallization property of mPEG-PCL block copolymers depends on the length of PCL blocks. As the molecular weight of PCL block increased, the crystallization ability of mPEG block was visibly restrained. Aqueous micelles were prepared by dialysis method. The critical micelle concentration of the copolymers, which was determined to be 0.9-6.9 mg/L by fluorescence technique, increased with the decreasing of PCL block length. The particle sizes determined by DLS were 30-80 nm increasing with the PCL block length. TEM images showed that these micelles were regularly spherical in shape.     

聚醚改性硅油表面性质的研究

对实验室自制聚醚改性硅油(以下简称硅醚)的表面张力及浊点进行测定,并对其表面性质的特征及趋势进行了研究。结果表明,随硅醚质量浓度的增加,硅醚水溶液的表面张力值下降,硅醚质量浓度增至约0.01 g/L后,表面张力值降幅渐缓,其表面张力最低值为29~42 mN/m;随着硅醚侧链聚醚中环氧丙烷链段所占比例增加,其水溶液的浊点略有下降,质量浓度约为0.1 g/L的硅醚以侧链聚醚结构n(EO)∶n(PO)=1∶4的硅醚的浊点最小,为9.5℃;随体系温度上升,质量浓度约为0.01 g/L的硅醚水溶液的表面张力降幅小于同样质量浓度的甲基硅油加乳化剂A25(硬脂醇/脂肪醇醚-25)的水溶液,并求得质量浓度约为0.01 g/L不同环氧乙烷与环氧丙烷摩尔比的硅醚的表面张力随体系温度下降的系数及方程,根据实验建立的方程所得的某温度下表面张力的计算值与实测值之间的平均相对偏差为7%。     

Kinetics and extent of low-temperature crystallization of ethylene–vinyl acetate copolymers

The enthalpies of fusion of two types of EVA copolymers containing 9 and 16% of vinyl acetate, respectively, were investigated by DSC. After melting, the samples were cooled down and held at 10, 15, 20, and 25°C for different periods of time from 15 min to 2.5 months (only at 20°C). The enthalpy of fusion increased over the 2.5-month period for 9.3 and 11.3 J/g, respectively. There was a new small melting peak on the endotherm of the aged sample whose position and size depended on aging temperature and aging time. During 2.5 months, the peak shifted toward higher temperature for 8°C. The enthalpy of fusion and corresponding degree of crystallinity changed linearly with the logarithm of time, as is the case in high-temperature annealing or secondary crystallization at high temperatures. The rate and the extent of low-temperature crystallization of ethylene copolymers depend on the comonomer content, sequence length distribution, and temperature. © 1996 John Wiley & Sons, Inc.     

Characterization and crystallization behavior of poly(ethylene‐co‐trimethylene terephthalate) copolymers

A series of poly(ethylene‐co‐trimethylene terephthalate) (PETT) copolymers were prepared by polycondensation. The synthesized PETT are block copolymers and the content of poly(trimethylene terephthalate) (PTT) units incorporated into the copolymers are always larger than that fed in the polymerization. The nonisothermal crystallization at the different cooling rates was studied by means of differential scanning calorimetry. The copolymers develop the crystallization later and show the lower melting temperature than the corresponding enriched homopolymers. The modified Avrami analysis fit well the nonisothermal crystallization of these polymers. The overall rate of crystallization of PTT is fastest and that of PET is slowest, whereas the copolymers are between them at the same cooling rate. The minor PET units incorporated into PTT polymer chains reduce the crystallization of PTT segments, but the present minor PTT units in the PET chains seem to accelerate the crystallization of PET segments. The Avrami exponent nvaries in the range of 3 – 4, indicating that the nonisothermal crystallization follows the homogeneous nucleation and two‐ to three‐dimensional growth mechanism. Wide angle X‐ray diffraction analysis explains that the PET and PTT units do not cocrystallize and it is considered as the enriched polymer segments to crystallize during crystallization. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

(EOXPOYEOX)型嵌段共聚物反胶团形成的影响因素

通过 (EO_XPO_YEO_X)型嵌段共聚物有机溶液的水增溶实验研究 ,探讨了溶剂、聚合物结构、离子强度和温度对增溶水量及临界胶团浓度 (CMC)的影响 .研究结果表明 ,正辛醇的加入不仅提高了嵌段共聚物 /对二甲苯体系的最大增溶水量 (W_{o ,max}) ,而且也增大了体系的CMC值 .lg(1/cmc)随聚合物分子单边EO数X增大而线性递增 ,表明亲水基EO的内聚能变在胶团化过程中起着重要作用 .实验研究范围内 ,溶液离子强度小于 1时 ,对反胶团的增溶作用有利 ,一定程度上增大了胶束粒径 .反胶团临界浓度的自然对数lnX_CMC与温度T成线性关系 .胶团化过程是一个自发的放热过程 ,并且是一个混乱度降低的熵减过     

Synthesis and characterization of fluorescein isothiocyanate (FITC)-labeled PEO-PCL-PEO triblock copolymers for topical delivery

We present the synthesis of fluorescein isothiocyanate (FITC)-labeled poly(ethylene oxide)-block-poly(?-caprolactone)-block-poly(ethylene oxide) (PEO-PCL-PEO) triblock copolymers and their applications for tracking the penetration behavior of FITC-labeled copolymers in the hairless mouse skin. In the first step, PEO-PCL diblock copolymers with different ratios of PCL to PEO (i.e., [CL]/[EO]) were prepared by ring opening polymerization of ?-caprolactone (CL), where monomethoxy poly(ethylene glycol) (mPEG, M_n = 2000 g mol⁻¹) was used as a macro-initiator. FITC was successively reacted with octadecylamine, isophorone diisocyanate (IPDI), and then used as a linker to obtain PEO-PCL-PEO triblock copolymers from the PEO-PCL diblock copolymers. In aqueous solution, both FITC-labeled triblock copolymers show two UV absorption peaks at 489 and 455 nm, attributed to the monomeric FITC and H-aggregated FITC moieties, respectively. Due to the strong H-aggregation of FITC in the copolymer of high [CL]/[EO], fluorescent emission intensities considerably decreased at high concentrations of the copolymer. FITC-labeled copolymers exhibited more sharper polarized optical and fluorescence microscopic images compared to the mixtures of FITC and unlabeled copolymer in both solid crystalline and multiple emulsion state. Furthermore, the Frantz diffusion cell test was carried out to demonstrate the penetration behavior of the FITC-labeled copolymers in the hairless mouse skin.     

Overall crystallization kinetics of polymorphic propylene-ethylene random copolymers: A two-stage parallel model of Avrami kinetics

The isothermal crystallization of propylene ethylene random copolymers evolves with a simultaneous formation of two polymorphic forms, monoclinic crystals (α form) and orthorhombic crystals (γ form). The relative content of each polymorph changes during crystallization and impacts the kinetics and mechanisms of growth. The content of γ crystals developed at high levels of transformation increases with the concentration of ethylene and with the crystallization temperature. In this work, the overall crystallization kinetics of copolymers with an ethylene content ranging from 0.8 to 7.5 mol% were followed by DSC and analyzed according to classical Avrami kinetics. For most copolymers, fits to single-stage nucleation and growth models were poor. Following structural models for lamellar growth that account for epitaxial γ branching from α surfaces, the experimental data were modeled with a parallel two-stage kinetic model with excellent fits up to ∼70% transformations. The Avrami exponents obtained from the fits are consistent with a linear spherulitic growth from pre-existing nuclei for the α stage and homogeneous nucleation (linear with time) for the γ stage, and strongly support the postulated structural growth model. The rate constants of each stage follow the expected temperature dependence. Attempts made to extract the interfacial free energies for α and γ crystals from the values of the rate constants are discussed.     

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.