Impact of plasticizers and tackifiers on the crystallization of isotactic poly(1-butene)

Crystallization of a semi-crystalline polyolefin in the presence of low molecular weight modifiers was quantified by differential scanning calorimetry and optical microscopy. The polyolefin was a commercial grade of isotactic poly(1-butene) (iPB). Two modifiers were used: an oligomeric plasticizer, designated HOAO, which decreased the glass transition temperature (T_g) of the system, and an oligomeric tackifier, designated HOCP, which increased T_g. Binary iPB/modifier blends containing 10% or 20% by weight of HOAO or HOCP were examined to determine how their addition affects T_g, while ternary iPB/HOAO/HOCP blends containing 10% or 20% by weight of total modifier were examined to determine the effects of dilution by using a ratio of HOAO to HOCP that matched the T_g of iPB. The addition of modifier decreased the nucleation rate, spherulitic crystal growth rate, and final crystallinity of each blend. However, only the nucleation rate showed a dependence on the type of modifier, with nucleation retarded more by HOCP than by HOAO. A Hoffman-Weeks analysis of the melting point as a function of crystallization temperature confirmed that the driving force for nucleation was reduced, and that the effect was larger for HOCP. An Avrami analysis of the bulk crystallization kinetics was consistent with these observations, as the Avrami exponents were in the range of 3-4.     

Effect of molecular weight on the polymorphic transformation of isotactic poly(1-butene)

The effect of molecular weight on the polymorphic transformation of isotactic poly(1-butene)(iPB) under room temperature had been investigated by fourier transform infrared spectroscopy(FT-IR). The phase transformation time, phase transformation rate and phase transformation time difference between phase I and phase II at a given transformation degree were used to analysis the phase transformation kinetics of iPB aging at room temperature. The results show that the reduction of phase II can occur quickly at room temperature and seem less dependent on the molecular weight. However, the molecular weight has great effect on the formation of phase I. When the phase transformation degree for phase I reach 90%, a distinct transformation time difference can be observed. In order to clearly explain the difference in the reduction of phase II and the growth of phase I, a phase transformation model from the chain conformation level for iPB with different molecular weight have been drawn. DSC analysis was used to support the proposed model.     

Solvent vapor annealing induced polymorphic transformation of polybutene-1

Solvent annealing is a facile method for changing the aggregated microstructure and physical properties of polymer materials. In this paper, we addressed the effects of solvent vapor annealing, including chloroform and water vapor, on the polymorphic transformation in both hot-pressed film and electrospun nonwoven of isotactic polybutene-1 (PB-1) by means of in situ Fourier transform infrared spectroscopy (FTIR). The pretty rapid transition rate caused by the increased motion of molecular chains under chloroform vapor is associated with a lowest crystallinity. Also, a decreased crystallinity with the crystal transition occurred in electrospun nonwovens resulting from the relaxation of the stretched molecular chains into amorphous state rather than realignment into crystal form I predominating the crystal transition process.     

Nucleation effect of cyclodextrin inclusion complexes on the crystallization of isotactic poly(1‐butene)

The β‐cyclodextrin (β‐CD) and γ‐cyclodextrin (γ‐CD) inclusion complexes (ICs) with four kinds of polyolefin were prepared. The crystallization behavior of isotactic poly(1‐butene) (iPB‐1) blended with these CDs and ICs was investigated by differential scanning calorimetry, polarized optical microscopy, and wide‐angle X‐ray diffraction. The iPB‐1 blended with the ICs was found to exhibit higher crystallization temperature (T_C), smaller spherulites, and faster crystallization rate than neat iPB‐1. These results indicate that the ICs can act as nucleating agent on the crystallization of iPB‐1 and induce the accelerated crystallization. The guest molecules of ICs play an important role in the nucleation effect of ICs on the crystallization of iPB‐1. ICs with polyolefin having higher T_C as guest molecules have higher nucleation effect than the one with polyolefin having lower T_C as guest molecules. And, the CDs and ICs induce different crystal form of iPB‐1. The crystal of iPB‐1 blended with CDs is defective, whereas the crystal of iPB‐1 blended with ICs is more perfect. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 389–395, 2010     

Luminescence studies in polymers—IV. Effect of orientation,tacticity and crystallinity on polystyrene and polyvinylcarbazole fluorescence

The fluorescence spectra of amorphous atactic, amorphous isotactic and crystallized isotactic polystyrene films have been compared. The effect of chain orientation has also been analysed on amorphous atactic samples. The results show that the fluorescence yield increases with crystallinity at room temperature and 77°K. The contribution of excimer fluorescence at 77°K increases according to the sequence: atactic < atactic oriented < isotactic amorphous < isotactic crystallized. An increase of the fluorescence yield with crystallinity was also observed for polyvinylcarbazole samples although the contribution of excimer fluorescence at 77°K is independent of crystallinity for this polymer. The results are interpreted in terms of energy migration.     

Direct Fabrication of Porous Isotactic Poly‐1‐Butene With Form I From the Melt Using CO2

The deformation of isotactic poly‐1‐butene (iPB‐1) matrix, during the CO₂‐assisted foaming process, makes the iPB‐1 melt crystallize into form I rather than form I′, which crystallizes after annealing under high‐pressure CO₂ without foaming. The result provides a new strategy to directly obtain porous iPB‐1 with stable form I from iPB‐1 melt.     

不同结晶度的乙二醇及其水溶液玻璃化转变与焓松弛

为了考察晶体成分对无定形成分玻璃化转变和结构松弛行为的影响,利用差示扫描量热法(DSC),结合低温显微技术,研究了乙二醇(EG)及其50％水溶液在不同结晶度时的玻璃化转变和焓松弛行为.采用等温结晶方法控制骤冷的部分结晶玻璃体中的晶体份额.DSC结果表明,对于部分结晶的EG,只有单一的玻璃化转变过程,而对于50％EG,当结晶度不同时,不同程度地表现出两次玻璃化转变（无定形相Ⅰ和无定形相Ⅱ）.相Ⅰ的玻璃化转变温度和完全无定形态的含水EG的玻璃化转变温度相一致;相Ⅱ的玻璃化转变温度要比此温度约高6 ℃.低温显微观察结果印证了DSC实验结果.DSC等温退火的实验和KWW(Kohlrausch-Williams-Watts)衰变函数分析结果表明,EG无定形和50％EG中的两种无定形有不同的焓松弛行为.     

Characterization of annealed isotactic polypropylene in the solid state by 2D time‐domain 1H NMR

Two‐dimensional time‐domain ¹H NMR was used to investigate annealed isotactic polypropylene in the solid phase. The spin–lattice relaxation in the laboratory frame and in the rotating frame were correlated with the shape of the free induction decay to identify and characterize relaxation components over the temperature range −120 to 120 °C. Several phase transitions were observed, and three distinct solid phases, with different chain mobilities, were detected. Two of these phases were identified as regions with different mobilities within the crystalline phase. The third phase was characterized by a high degree of isotropy in molecular motion. This phase, identified as the amorphous phase, appeared as the polymer was heated above a low‐temperature (−45 °C) phase transition. All transitions observed at higher temperatures occurred exclusively in this phase. About one‐third of the polymer chains reside between crystalline lamellae, whereas the majority form amorphous regions outside fibrils of multilamellar structure. Furthermore, the glass‐to‐rubber transition, occurring above −15 °C, consists of three stages. During the first stage, between −15 °C and 15 °C, regions with an increased segment mobility (labeled intermediate phase) appear gradually within the amorphous phase. At 15 °C, the intermediate phase consists of ∼10% of the polymer units, or one‐third of the polymer units constituting the amorphous phase. Between 15 °C and 25 °C, the intermediate phase increases rapidly to 18%. This is associated with the appearance of semiliquid and liquid regions, likely within the intermediate phase. Polymer chain segments (and possibly entire chains) involved in the liquidlike phases exhibit heterogeneous molecular motion with a correlation frequency higher than 10⁶ Hz. These two stages of glass‐to‐rubber transition occur within amorphous regions outside multilamellar structures. The third stage of the glass transition, appearing above 70 °C, is associated with the upper glass transition and occurs within the interlamellar amorphous phase. Finally, on a timescale of 100 ms or less, spin diffusion does not couple the amorphous regions outside fibrils with crystalline and amorphous regions within multilamellar fibrils. However, on a timescale of hundreds of milliseconds to seconds, all different regions within isotactic polypropylene are partially coupled. It is proposed that the relative magnitude of the crystalline magnetization, as observed in the T_1ρ experiment, is a good measure of polymer crystallinity. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2487–2506, 2000     

Deformation-induced morphology evolution during uniaxial stretching of isotactic polypropylene: effect of temperature

The effects of draw temperature on the deformation-induced morphology evolution of isotactic polypropylene in terms of crystal orientation, degree of crystallinity, crystal size in the direction normal to chain axis, long spacing, and the deformation behavior at the crystal lattice and lamellae scale were investigated using differential scanning calorimetry, two-dimensional wide-angle X-ray diffraction, and small-angle X-ray scattering, respectively. The results revealed that the thermal behaviors are associated with the deformation-induced morphology evolution, and the morphology evolution is strongly temperature dependent. At low strain, crystal fragmentation takes place at all the draw temperature range studied; at high strain, after crystal fragmentation the draw temperature shows different effects on the morphology evolution: at low temperature (25 °C), fragmentation of the crystal blocks continues; at medium temperatures (80 and 110 °C), the broken crystal blocks remain stable and the unfolded chains and disentangled chains in amorphous region crystallize into crystal blocks with crystal size almost identical to that of the original broken ones; at high temperatures (130 and 140 °C), not only the unfolded chains and disentangled chains in amorphous region crystallize into crystal blocks, but also these small broken crystal blocks melt and recrystallize and the new crystal blocks formed possess larger crystal size than those of the original broken ones.     

Correlation between crystallization kinetics and microdomain morphology in block copolymer blends exhibiting confined crystallization

The crystallization kinetics of poly(ethylene oxide) (PEO) blocks in poly(ethylene oxide)‐block‐poly(1,4‐butadiene) (PEO‐b‐PB)/poly(1,4‐butadiene) (PB) blends were previously found to display a one‐to‐one correlation with the microdomain morphology. The distinct correlation was postulated to stem from the homogeneous nucleation‐controlled crystallization in the cylindrical and spherical PEO microdomains, where there existed a direct proportionality between the nucleation rate and the individual domain volume. This criterion was valid for confined crystallization in which the crystallization was spatially restricted within the individual domains. However, it was possibly not applicable to PEO‐b‐PB/PB, in that the melt mesophase was strongly perturbed upon crystallization. Therefore, it may be speculated that the crystal growth front developed in a given microdomain could intrude into the nearby noncrystalline domains, yielding the condition of cooperative crystallization. To establish an unambiguous model system for verifying the existence of microdomain‐tailored kinetics in confined crystallization, we crosslinked amorphous PB blocks in PEO‐b‐PB/PB with a photoinitiated crosslinking reaction to effectively suppress the cooperative crystallization. Small‐angle X‐ray scattering revealed that, in contrast to the noncrosslinked systems, the pre‐existing domain morphology in the melt was retained upon crystallization. The crystallization kinetics in the crosslinked system also exhibited a parallel transition with the morphological transformation, thereby verifying the existence of microdomain‐tailored kinetics in the confined crystallization of block copolymers. Homogeneous nucleation‐controlled crystallizations in cylindrical and spherical morphologies were demonstrated in an isothermal crystallization study in which the corresponding crystallinity developments followed a simple exponential rule not prescribed by conventional spherulitic crystallization. Despite the effective confinement imposed by the crosslinked PB phase, crystallization in the lamellar phase still proceeded through a mechanism analogous to the spherulitic crystallization of homopolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 519–529, 2002; DOI 10.1002/polb.10121     

Effect of Polymerization Temperature on Propylene Polymerization with Cs-symmetric Metallocene Catalyst

The synthesis of bridged ansa metallocenes usually gives a diastereomeric mixture ofracemic and meso metallocene isomers and in many cases the meso form is about 50 % ofthe product of metallocene synthesis"'. The amount of desired racemic isomer is ratherpoor and can be separated from the meso isomer by fractional crystallization'. The racemicansa-metallocene isomer acts as catalyst for propylene polylnerization to produce isotacticpolypropylene (PP) while the corresponding meso isomer gives a…     

Nanosized gismondine grown in colloidal precursor solutions

A colloidal molecular sieve with GIS-type structure was prepared from aged aluminosilicate precursor solutions containing tetramethylammonium (TMA) hydroxide under hydrothermal treatment at 100 degrees C. The nucleation and the development of the GIS zeolite structure were studied by dynamic light scattering, scanning electron microscopy, X-ray diffraction, Raman and infrared spectroscopies, and liquid-state NMR spectroscopy. It is shown that the aging at room temperature leads to the formation of subcolloidal particles that incorporate TMA cations and form larger aggregates. After an extended heating of 13 days, a complete transformation from amorphous precursor material to crystalline GIS-type colloidal particles is observed. The mean hydrodynamic radius of the crystalline GIS particles is in the range of 30-50 nm. The specific template-framework interactions influence the spectral features of the TMA cations incorporated in the zeolite structure, thus making possible the use of the corresponding Raman spectra and 13C NMR data for the examination of the crystallinity of GIS-type colloidal particles stabilized in water.     

全同立构聚丁烯-1溶液浇铸膜直接生成晶型Ⅰ结构

作为一种半结品性的聚烯烃材料．全同立构聚丁烯-1(iPB-1)的结晶存在Ⅰ,Ⅱ．Ⅲ和Ⅰ’4种品型,其中,晶型Ⅰ和Ⅰ’是由3／1螺旋链堆砌的六方晶胞结构,晶型Ⅱ是由11／3螺旋构象链堆砌的四方晶胞结构,晶型Ⅱ则是由4/1螺旋链堆砌而成的正交品胞结构．通常溶液结晶得到品型Ⅲ和晶型Ⅰ’,在高压条件下从本体结品也可得到晶型．     

Heat conduction in a two-dimensional spherulite

The anisotropy of thermal conduction in a spherulite is calculated for a two-phase model. The problem of the temperature distribution due to cooling of a spherulite suddenly heated at one point is solved. An analytical result is given and isothermal contours are calculated for wide ranges of thermal conduction anisotropy and cooling time. Experiments with spot-heated isotactic polypropylene (i-PP) and isotactic polystyrene (i-PS) spherulites were conducted using a laser pulse and a needle as heat sources. The isotherms were recorded using a thin coating of a heat-sensitive indicator substance, and then by comparison with theoretical isotherm patterns the heat conduction anisotropy of a PP spherulite was estimated. Additional measurements of heat conduction coefficients of at least two polymer films characterized by different crystallinity permit calculation of the thermal conductivity of the amorphous phase, and the conductivities of single crystals along chains and perpendicular to the chains. The results show that the heat is transferred mainly along the primary bonds of polymer chains. However, the morphology of sperulites and lamellas plays an important role.     

Aggregation and thermoresponsive properties of new star block copolymers with a cholic acid core

Poly(allyl glycidyl ether) (PAGE) and poly(ethylene glycol) (PEG) blocks were sequentially grown via anionic polymerization to form four block copolymer arms on a cholic acid (CA) core, yielding star block copolymers (CA(AGE(8)-b-EG(n))(4)) with low polydispersities (ca. 1.05). The introduction of PAGE segments into CA(PEG)(4) significantly reduced their crystallinity. The polymers can aggregate in water at room temperature above their critical aggregation concentration. The copolymers are thermoresponsive; their behavior in aqueous solutions was studied by the use of UV-visible spectroscopy, dynamic light scattering, and transmission electron microscopy. Their cloud points vary from 13 to 55 °C with increasing length of the PEG segments. Double thermoresponsive behavior was observed with short PEG segments because of a two-step transition process: small micelles are formed upon heating and then further aggregate into micellar clusters through the association of PEG chains.     

Rheooptical Fourier transform infrared spectroscopy of the deformation behavior in quenched and slow‐cooled isotactic polypropylene films

Emerging technological applications for complex polymers require insight into the dynamics of these materials from a molecular and nanostructural viewpoint. To characterize the orientational response at these length scales, we developed a versatile rheooptical Fourier transform infrared (FTIR) spectrometer by combining rheometry, polarimetry, and FTIR spectroscopy. This instrument is capable of measuring linear infrared dichroism spectra during both small‐strain dynamic deformation and large‐strain irreversible deformation over a wide temperature range. The deformation response of quenched and slow‐cooled isotactic polypropylene (iPP) is investigated. In quenched iPP, under dynamic oscillatory strain at an amplitude of ～0.1%, the dichroism from the orientation of the amorphous chains is appreciably less than that from the crystalline region. At large irreversible strains, we measured the dichroic response for 12 different peaks simultaneously and quantitatively. The dichroism from the crystalline peaks is strong as compared to amorphous peaks. In the quenched sample, the dichroism from the crystalline region saturates at 50% strain, followed by a significant increase in the amorphous region dichroism. This is consistent with the notion that the crystalline regions respond strongly before the yield point, whereas the majority of postyielding orientation occurs in the amorphous region. Our results also suggest that the 841 cm^?1 peak may be especially sensitive to the ‘smectic’ region orientation in the quenched sample. The response of the slow‐cooled sample at 70 °C is qualitatively similar but characterized by a stronger crystalline region dichroism and a weaker amorphous region dichroism, consistent with the higher crystallinity of this sample, and faster chain relaxation at 70 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2539–2551, 2002     

Studies on the α and β forms of isotactic polypropylene by crystallization in a temperature gradient

Samples of isotactic polypropylene (PP) were zone-solidified in temperature gradients up to 300°C/cm at growth rates down to 3 μm/min. Oriented α-type spherulites were obtained only by nucleation. While β nucleation is extremely rare, the β phase is easily initiated by growth transformations along the oriented α front. Since the β phase was found to grow considerably faster than the α phase, the α-to-β transformation points diverge across the sample, interrupting growth of the oriented α fibrils. This causes subsequent nucleation to yield teardrop-shaped α spherulites. Differential scanning calorimetry (DSC) studies of zone-solidified PP show the β-phase to be favored by slow growth rates, high temperature gradients, and large degrees of superheat in the melt—all of which tend to suppress nucleation. Differential thermograms of largely β-PP obtained at a heating rate of 1°C/min show the actual melting and recrystallization of the β spherulites into the α form.     

In situ FT-IR spectroscopic study on the conformational changes of isotactic polypropylene in the presence of supercritical CO2

The conformational changes of isotactic polypropylene (iPP) under supercritical CO₂ condition with different pressure and temperature have been carefully studied by in situ Fourier-transform infrared spectroscopy (FT-IR). Analysis of the corresponding spectra shows that the conformational ordering by supercritical CO₂ results in the intensity enhancement of the regularity bands of iPP. Due to the high CO₂ concentration and strong intermolecular interaction, iPP can reach an equilibrium state in a short time at high CO₂ pressure. The equilibrium time increases with soaking temperature. After supercritical CO₂ treatment, two mechanisms, the formation of short helix from amorphous phase and the extension of short helix into long one, happen simultaneously. The latter mechanism undergoes quickly at the beginning of induced conformational changes and then slows down, resulting in the slight increase of crystallinity. At the same time, the conformational ordering in amorphous phase happens continuously until a thermodynamic equilibrium. In summary, in the presence of supercritical CO₂, the conformational ordering of iPP chains occurs exclusively in the amorphous region, with no impact on the crystal part.     

Hydrolysis of post-consume poly(ethylene terephthalate) with sulfuric acid and product characterization by WAXD, C NMR and DSC

Post-consume PET was hydrolysed with commercial sulfuric acid (96%) with varying reaction times (5-120 min). The structure of the material obtained was analysed by ¹³C NMR, DSC, and WAXD and the results were correlated with reaction time. ¹³C NMR shows a decrease in chain size with reaction time and an increase in the number of carboxyl groups at the end of the chains. The correlation of DSC and WAXD data indicates the presence of structures of different sizes and an increase in crystallinity with reaction time. The structure of the samples hydrolysed for 5-60 min is less ordered than those of the samples hydrolysed for 60-120 min because the amorphous phase is predominantly quickly dissolved. Dissolution of the crystalline phase is favoured by the increase in reaction time. In this process, the crystalline memory retained in the dissolution of the crystalline phase behaves as nucleation sites which form smaller and more ordered structures compared to those obtained with shorter reaction times.     

Mechanical relaxation in polypropylene as a function of polymorphism and degree of lamella orientation

Mechanical relaxation data as a function of temperature (ca. 1 Hz) have been obtained for several samples of isotactic polypropylene crystallized from the melt, which exhibit both α and β forms as well as varying degrees of lamella orientation. The samples ranged in morphology from an unoriented sample showing only the α form to one highly oriented having approximately 90 per cent the β form. Results for the logarithmic decrement Δ and loss modulus G″ are that the low temperature (ca. ?75°C) and glass temperature (ca. 0°C) relaxations show little or no sensitivity to orientation in the α form, but that the intensity of the two processes is different in the α form than in the β form for samples of nearly equal overall per cent crystallinity. In both Δ and G″, the low-temperature peak decreased and the glass temperature peak increased in intensity as the fraction of β form crystallinity present increased. Data for the high-temperature relaxation (ca. 80°C) indicate a dependence upon orientation and/or crystal form in addition to a dependence upon per cent crystallinity.