Co-reporter:Yonggang Shangguan;Jie Yang;Qiang Zheng
RSC Advances (2011-Present) 2017 vol. 7(Issue 26) pp:15978-15985
Publication Date(Web):2017/03/09
DOI:10.1039/C7RA01106G
A hybrid crosslinked network composed of covalent bonding and non-covalent bonding was constructed in nitrile rubber (NBR) by using the compound crosslinking agents dicumyl peroxide (DCP) and N,N-methylenebis acrylamide (MBA). DCP not only acted as a chemical crosslinking agent for NBR but also initiated MBA association onto the rubber chains. In addition to the crosslinked network of covalent bonds, the acylamino groups of MBA could associate reversibly into junctions between rubber chains to form additional hydrogen bonds. It was found that the total crosslinking density of NBR increased with the increasing MBA amount. Both dynamic mechanical analysis and dynamic rheological measurement results indicated that samples with more hydrogen bonding were more sensitive to deformation and temperature. For the vulcanized NBR samples with MBA, their glass transition temperature was higher than those of vulcanized samples only with DCP and slightly increased with increasing MBA amount. The existence of hydrogen bonding led to a shorter linear viscoelastic region in vulcanized NBR samples with MBA. In addition, compared with the samples vulcanized with only DCP, the vulcanized samples containing MBA presented a higher storage modulus in the low frequency region but a lower one in the high frequency region. These results indicated that the hydrogen bonding induced by MBA decreased both the motion ability of the chain segments between the crosslinking points and the energy dissipation generated by internal friction of the polymer chain.
Co-reporter:Yilan Ye, Shangguan Yonggang and Qiang Zheng
Polymer Chemistry 2016 vol. 7(Issue 1) pp:89-100
Publication Date(Web):12 Oct 2015
DOI:10.1039/C5PY01022E
Counterions play significant roles in the characteristics of polyelectrolytes, whereas many problems still remain unsolved. Among most previous research studies, counterions were too small to be “seen” by light scattering. In this article, we prepare macrocounterions which are single/double carboxylate ion-terminated polyethylene glycols (Mn ≈ 5000 g mol−1). The solution properties of polycations with macrocounterions are investigated through rheological, conductivity and dynamic light scattering measurement. On the basis of the scaling theory, the static and dynamic parameters of polyelectrolytes are analyzed over wide concentration ranges. In rheological measurement, a critical concentration () has been observed. When the concentration is below , the role of macrocounterions can be ignored; while above , macrocounterions determine the longest relaxation and prevent entanglement of polycations. Moreover, the same turning point exists in the dependence of conductivity and viscosity on the molar fraction of macrocounterions, which indicates that macrocounterions can't serve as brushes condensed on the polycation until their molar fraction is above the effective charge density of polyelectrolytes. In dynamic light scattering, we investigate the relaxation of polycations with macrocounterions on the length scale of electrostatic blobs, where the size of macrocounterions becomes significant. In comparison with ordinary polyelectrolytes, it is observed that both fast and slow diffusive relaxations of polycations with macrocounterions are significantly slowed down, and the fast mode relaxation becomes dominant. Since no independent relaxation of macrocounterions has been observed, it is supposed that the fast mode relaxation is the coupled relaxation of polycations and macrocounterions.
Co-reporter:Biwei Qiu, Feng Chen, Yonggang Shangguan, Yu Lin, Qiang Zheng and Xia Wang
RSC Advances 2016 vol. 6(Issue 28) pp:23117-23125
Publication Date(Web):23 Feb 2016
DOI:10.1039/C6RA01046F
In this work, the effects of β-nucleating agent and annealing treatment on the crystallization and amorphous phase in impact polypropylene copolymer (IPC) were profoundly displayed to reveal the toughening mechanism of the modified product. The toughness of β-nucleated IPC was improved dramatically compared with samples without nucleation agent. The chain mobility measured by dynamic mechanical analysis (DMA) in the rigid amorphous fraction (RAF) weakened with increasing annealing temperature, while that in the mobile amorphous fraction (MAF) strengthened under low annealing temperatures (not more than 124 °C) and then weakened at higher temperatures. On the one hand, the impact energy is effectively dissipated by slipping of loose β lamellae. On the other hand, the voids in loose β crystals multiply shear yielding. By contrast, dense α crystals in neat IPCs provide fewer voids and the major pathway of energy dissipation is crazing induced by soft dispersed particles. After annealing treatment, all the β-nucleated IPCs became brittle, which was mainly ascribed to the reduction of β crystals through β–α transformation.
Co-reporter:Feng Chen, Biwei Qiu, Bo Wang, Yonggang Shangguan and Qiang Zheng
RSC Advances 2015 vol. 5(Issue 27) pp:20831-20837
Publication Date(Web):12 Feb 2015
DOI:10.1039/C5RA00386E
For ordinary rubber toughened plastics, the introduction of rubber will inevitably bring about the severe decline in mechanical strength due to the low modulus and rigidity of elastomers. To fabricate toughened polypropylene (PP) materials without significant strength degradation, the poly(styrene-b-ethylene–propylene) diblock copolymer (SEP) was used as the third component in an isotactic polypropylene/ethylene–propylene random copolymer (iPP/EPR) to prepare a series of PP/EPR/SEP blends. The phase morphology, dynamic mechanical behavior, crystallization behavior and mechanical properties of PP/EPR/SEP blends were systematically investigated, and compared with PP/EPR blends. The dynamic mechanical analysis results revealed that SEP has good compatibility with both EPR phase and amorphous PP phase, which led to an improvement of interfacial adhesion between them. The mechanical properties testing results indicated that the introduction of SEP could effectively promote the brittle–ductile transition for PP/EPR blends and that PP/EPR/SEP blends presented a good toughness without strength loss. Considering the fact that the individual EPR or SEP could not achieve good toughening, it was proposed that SEP and EPR have a synergistic effect on toughening PP and a modified PP with balanced toughness and tensile strength can be achieved by simultaneously adding EPR and SEP into iPP.
Co-reporter:Yuhua Lv, Yu Lin, Feng Chen, Fang Li, Yonggang Shangguan and Qiang Zheng
RSC Advances 2015 vol. 5(Issue 56) pp:44800-44811
Publication Date(Web):11 May 2015
DOI:10.1039/C5RA06663H
The effects of intermolecular interaction between casting solvents and polymer chains on molecular entanglement and dynamics in solution-cast poly(methyl methacrylate)/poly(styrene-co-maleic anhydride) (PMMA/SMA) films were investigated by dynamic rheological measurement and broadband dielectric spectroscopy. A series of polymer blend films were cast from the mixed solvents composed of m-xylene and acetic acid with different mass ratio of acetic acid (Rac) at a solution concentration of 5 wt%, and in solutions the quantity of hydrogen bonding between PMMA and acetic acid was adjusted by Rac. FTIR results confirmed the existence of hydrogen bonding between carbonyl in PMMA and hydroxyl in acetic acid. Although the topological entanglement density of the resultant films decreased with increasing Rac, the α-relaxation peak shifted towards lower frequency and a higher glass transition temperature (Tg) appeared due to the increased cohesional entanglement in PMMA/SMA blend films induced by hydrogen bonding between PMMA and acetic acid. Furthermore, the dc conductivity decreased due to the more homogeneous structure in PMMA/SMA blend films cast from mixed solvents with higher Rac. Neither the width distribution of α-relaxation nor the dynamics of β-relaxation in these films was influenced by hydrogen bonding between PMMA and acetic acid due to the unchanged heterogeneity of the segmental dynamics and local environment of the segments. These results revealed that the hydrogen bonding between polymers/solvent during casting film can greatly influence the chain entanglement and molecular dynamics of the resultant polymer blends due to the memory effect of polymer chain.
Co-reporter:Feng Chen, Yonggang Shangguan, Yishu Jiang, Biwei Qiu, Guohang Luo, Qiang Zheng
Polymer 2015 Volume 65() pp:81-92
Publication Date(Web):18 May 2015
DOI:10.1016/j.polymer.2015.03.064
•PP/EPR/HDPE blends present a balanced toughness and rigidity improvement.•The interparticle distance takes a key factor of toughening by rubber.•A new toughening mechanism of increasing equivalent rubber content was proposed.Toughening with little rigidity loss was achieved by adding high density polyethylene (HDPE) into polypropylene/ethylene-propylene random copolymer (PP/EPR) blends to fabricate a series of PP/EPR/HDPE ternary blends with core–shell dispersed particles. Morphology observations revealed that the addition of HDPE leads to the appearance of core–shell dispersed particles in PP matrix, i.e., HDPE core encapsulated in EPR shell. Dynamic mechanical analysis results showed that the introduction of HDPE could increase glass transition temperature (Tg) and loss factor peak area of EPR in PP/EPR/HDPE blends, which is similar to the effect of adding EPR in PP/EPR. The shrinkage behavior results suggested that the increase of glass transition temperature of EPR was induced by the mismatch of thermal expansion coefficients of components and the larger peak area was ascribed to the stronger relaxation friction of EPR. According to percolation of stress volumes, the interparticle distance was proposed to be a key factor of toughening effect of rubber particles in thermoplastic and thereby a toughening mechanism about the equivalent rubber content was established to explain balanced toughness-strength improvement of PP/EPR/HDPE blends with core–shell particles. The rubber particles with core–shell structure lead to the increase of particle size and the decrease of interparticle distance on the premise of not increasing actual rubber content, resulting in a notable improvement of toughness, while the ‘hard’ core made from HDPE component provides a satisfied rigidity.
Co-reporter:Yu Lin;Yong-gang Shangguan 上官勇刚;Bi-wei Qiu
Chinese Journal of Polymer Science 2015 Volume 33( Issue 6) pp:869-879
Publication Date(Web):2015 June
DOI:10.1007/s10118-015-1637-8
By preparing homogenous blend samples with different degrees of chain entanglement, we report an anomalous contribution of chain entanglement to phase separation temperature and rate of poly(methyl methacrylate)/poly(styrene-co-maleic anhydride) (PMMA/SMA) blends presenting a typical lower critical solution temperature (LCST) behavior. The meltmixed PMMA/SMA blends with a higher chain entanglement density present a lower cloud point (Tc) and shorter delay time, but lower phase separation rate at the given temperature than solution-cast ones, suggesting that for the polymer blends with different condensed state structure, thermodynamically more facilitation to phase separation (lower Tc) is not necessarily equivalent to faster kinetics (decomposition rate). The experimental results indicate that the lower Tc of melt-mixed sample is ascribed to smaller concentration fluctuation wavelength (Λm) induced by higher entanglement degree, while higher entanglement degree in melt-mixed sample leads to a confined segmental dynamics and consequently a slower kinetics (decomposition rate) dominated by macromolecular diffusion at a comparable quench depth. These results reveal that the chain packing in polymer blends can remarkably influence the liquid-liquid phase separation behavior, which is a significant difference from decomposition of small molecular mixtures.
Co-reporter:Feng Chen, Biwei Qiu, Yonggang Shangguan, Yihu Song, Qiang Zheng
Materials & Design (1980-2015) 2015 69() pp: 56-63
Publication Date(Web):15 March 2015
DOI:10.1016/j.matdes.2014.12.052
•Toughness is influenced by the structure of dispersed particle.•The samples with different self-structure and size were prepared.•Toughness at different temperature is contributed by different factors.•A linear relationship describes the toughening mechanism at room temperature.The influence of the dispersed phase on impact properties of impact polypropylene copolymer (IPC) was systematically investigated by preparing a series of samples with different self-structure and size of dispersed particles. The impact test results at room temperature revealed that in case of rubber size below the critical value, the core–shell structure was dominant in the excellent impact strength though the impact strength was also affected by the size. For the impact strength at lower temperature, it seemed to be independent of the core–shell structure of dispersed particle and only dropped with the increase of rubber size. Compared with common polypropylene/ethylene–propylene rubber (PP/EPR) binary blend, IPC samples presented larger rubber sizes but higher impact strength at lower temperature, which was ascribed to the presence of ethylene propylene block copolymers (EbP) component. For describing the toughening mechanism of IPC at room temperature determined by size and self-structure of dispersed phase, a quantity linear relationship between toughness and rubber size was proposed.
Co-reporter:Bi-wei Qiu;Feng Chen;Yong-gang Shangguan 上官勇刚
Chinese Journal of Polymer Science 2015 Volume 33( Issue 1) pp:95-108
Publication Date(Web):2015 January
DOI:10.1007/s10118-015-1556-8
A series of ternary blends of polypropylene/ethylene-propylene random copolymer/ethylene-propylene segmented copolymer (HPP/EPR/EbP) whose microstructures are similar to those of impact polypropylene copolymer (IPC) were prepared in order to systematically investigate the effects of composition on microstructure and crystallization behavior of IPC. The observation of primary phase morphology reveals that the dispersed phase with core-shell structure could be rebuilt in certain composition and excessive EPR leads to a bicontinuous phase structure in ternary blends. After undergoing same quiescent crystallization including isothermal and non-isothermal crystallization, these blend samples exhibit special composition-dependent melting behavior, i.e., the melting point increases markedly with the increase of EPR content until it turns down at a critical content (about 30 wt%). The crystallization behavior is mainly ascribed to the different nucleation abilities. It is suggested that although the compatibility between EPR and HPP components becomes worse with the increase of EPR content due to the increased interfacial area and the decreased concentration of EbP, higher EPR content in the blend facilitates to heterogeneous nucleation except for the appearance of obvious bicontinuous phase structure.
Co-reporter:Feng Chen;Bi-wei Qiu;Ya-nan Ye;Yu-hua Lv
Chinese Journal of Polymer Science 2015 Volume 33( Issue 4) pp:633-645
Publication Date(Web):2015 April
DOI:10.1007/s10118-015-1616-0
We reported an approach to reconstruct the complex phase morphology of impact polypropylene copolymer (IPC) with core-shell dispersed particles and to optimize its toughness in approximate shear condition. The molten-state annealing results indicate that the phase structure with core-shell dispersed particles is unstable and could be completely destroyed by static annealing, resulting in the degradation of impact strength. By using a co-rotating twin screw extruder, we found that the dispersed particle with core-shell structure could be rebuilt in appropriate condition with the recovery of excellent impact strength due to both the huge interfacial tension during solidification and the great difference in viscosity of components. Results reveal that almost all the extruded IPCs show the impact strength 60%–90% higher than that of annealed IPCs at room temperature. And the twice-extruded IPC shows the highest impact strength, 446% higher than that of IPC annealed for 30 min. As for low temperature tests, the impact strength of extruded IPCs also increases by 33%–58%. According to adjusting the processing conditions including extrusion speed, extrusion frequency and temperature, an optimization of toughness was well established.
Co-reporter:Biwei Qiu, Feng Chen, Yonggang Shangguan, Lina Zhang, Yu Lin and Qiang Zheng
RSC Advances 2014 vol. 4(Issue 103) pp:58999-59008
Publication Date(Web):24 Oct 2014
DOI:10.1039/C4RA10682B
By introducing high density polyethylene (HDPE) into the dispersed phase of impact polypropylene copolymers (IPCs), the morphologies of IPC/HDPE blends were regularly tailored and consequently the tensile and impact properties were simultaneously improved. Morphological observations showed a series of multilayered core–shell dispersed particles when the content of HDPE was less than 40%, while the continuous network structure was observed beyond 40%. With an increase in the content of HDPE, the size of the core increased and the number of dispersed particles with incomplete encapsulated polyethylene (PE) cores rose. More valid ‘bridges’ made up of segmented ethylene–propylene copolymer (sEbP) appeared and connected the PE core and polypropylene (PP) matrix. Meanwhile, co-crystallization occurred in the core phase, between long ethylene chain segments of the joined HDPE and sEbP in multi-component IPCs. The increased HDPE in blends reduced defective co-crystals, and in turn led to a thicker average lamellar thickness and thinner amorphous thickness of PE. Partial inserted ethylene–propylene random sequences are constrained by narrowed PE amorphous layers. Hence, the connection between the PP matrix and the dispersed phase was strengthened by co-crystals, ‘bridges’ and restriction effects. The tensile strength of the blends was slightly enhanced with an increase in HDPE, while the greatly improved toughness was achieved at a HDPE content of 30 wt% and kept constant with more HDPE. Thus, the interactions rather than core–shell phase morphology are regarded as the predominate factor for the excellent properties.
Co-reporter:Yu Lin, Langping Liu, Jiaqi Cheng, Yonggang Shangguan, Wenwen Yu, Biwei Qiu and Qiang Zheng
RSC Advances 2014 vol. 4(Issue 39) pp:20086-20093
Publication Date(Web):14 Apr 2014
DOI:10.1039/C4RA00517A
We investigate the effects of silver (Ag) nanoparticles on the segmental and chain dynamics, physical aging and rheological behavior of polystyrene (PS) via a combination of broadband dielectric spectroscopy, calorimetry, and dynamic rheological measurement. The segmental dynamics of PS is found to be unchanged with increasing nanoparticle loading. After annealing below the glass transition temperature (Tg) for various time periods and measuring the recovered enthalpy values of PS, it is surprising that an acceleration and a suppression of the physical aging in PS/Ag-3% and 10% nanocomposites can be observed, respectively, corresponding to the decreased and increased calorimetric Tg, which can be interpreted by plasticizing and antiplasticizing effects. Furthermore, the filler reinforcement in rheological behavior is observed with increased weight fraction of Ag nanoparticles. The temperature-dependent horizontal shift factor reveals that the overall chain dynamics speed up in the presence of Ag nanoparticles. We also emphasize recent discrepancies in the prior studies of polymer nanocomposites and polymer thin films by comparing results.
Co-reporter:Feng Chen, Biwei Qiu, Yuhua Lv, Yonggang Shangguan and Qiang Zheng
RSC Advances 2014 vol. 4(Issue 101) pp:57935-57944
Publication Date(Web):30 Oct 2014
DOI:10.1039/C4RA09867F
Morphology evolution of the dispersed phase with a multilayered core–shell structure in impact polypropylene copolymer (IPC) during molten-state annealing was systematically studied through scanning electron microscopy (SEM), phase contrast microscopy (PCM) and dynamic rheological test. To demonstrate the evolution path of the dispersed phase comprised of ethylene-propylene random copolymer (EPR) and ethylene–propylene block copolymer (EbP) during annealing, different binary blends comprised of different fractions were prepared and their diffusion behavior during liquid–liquid phase separation was investigated. Compared with EPR, EbP presented a higher diffusion rate in propylene homopolymer (hPP) matrix, owing to its lower molecular weight and lower entanglement density. The statistical results of EbP and EPR domain sizes reveal that the coalescence of EbP is faster than that of EPR. In addition, the interaction parameters of EbP/hPP and EbP/EPR estimated using the Nishi–Wang equation show that EbP has a stronger affinity for hPP than EPR. Based on the diffusion rates, entanglement densities of components and great disparity in viscosity between EPR and hPP, a potential mechanism was proposed for the morphology evolution of core–shell dispersed particles in IPC during molten-state annealing.
Co-reporter:Ya-Nan Ye, Pei-Yuan Li, Yong-Gang Shangguan, Zhi-Sheng Fu, Qiang Zheng, Zhi-Qiang Fan
Chinese Chemical Letters 2014 Volume 25(Issue 4) pp:596-600
Publication Date(Web):April 2014
DOI:10.1016/j.cclet.2014.01.001
Both terminated functional isotactic polypropylene (iPP) and block copolymers containing iPP segment are desirable for commercial applications. This paper provides a convenient, highly-efficient method to prepare hydroxyl-terminated isotactic polypropylene (iPP-t-OH) and functional di-block copolymer containing the iPP segment through a combination of coordination polymerization and coupling reaction. The coordination polymerization was catalyzed by TiCl4/MgCl2/AlEt3 catalyst system using ZnEt2 as chain transfer agent. Further, the Zn-terminated iPP was oxidized and subsequently hydrolyzed to provide iPP-t-OH. Soxhlet extraction and 13C NMR were used to calculate the isotacticity of iPP-t-OH. The degree of polymerization and the number of hydroxyl groups at the chain end of iPP-t-OH were measured by GPC and 1H NMR. Despite the high molecular weight and heterogeneous reaction, iPP-t-OH is effectively linked with PEG-t-NCO to produce di-block copolymers. DSC analysis of the di-block copolymer shows an obvious decrease in Tm and Tc, which indicated that PEG was successfully linked to the terminal end of iPP.Hydroxyl-terminated isotactic polypropylene (iPP-t-OH) and functional di-block copolymer containing iPP segment were successfully prepared by a combination of coordination polymerization and coupling reaction.
Co-reporter:Yonggang Shangguan, Dameng Guo, Hui Feng, Yuan Li, Xiangjun Gong, Qianjin Chen, Bo Zheng, and Chi Wu
Macromolecules 2014 Volume 47(Issue 7) pp:2496-2502
Publication Date(Web):March 20, 2014
DOI:10.1021/ma500056m
Conventional mapping of a phase diagram of a polymer in a solvent requires a substantial amount of polymer (e.g., at least of the order of ∼100 mg of narrowly distributed samples with different molar masses) and may take months or even years to reach the true two phase equilibrium at each given temperature, especially when the polymer concentration is high. This is why good phase diagrams of polymer solutions are rare in the literature. To solve such a problem, we developed a Teflon microfluidic device to prepare and store a series of droplets (∼10 nL) at different polymer concentrations inside a glass capillary. The phase transition inside each polymer solution droplet sealed and isolated in immiscible fluorohydrocarbon could be quickly and precisely monitored by a newly developed small angle laser light scattering detector. Using poly(vinyl acetate) (PVAc) in isobutyl alcohol and in benzene as two examples, we demonstrated that a combination of microfluidic device and small angle light scattering enables us to map the phase diagram of a polymer in a given solvent within hours by using only a few mg of the sample because (1) each droplet contains no more than ∼10 μg polymer and (2) the phase-transition induced interchain association inside each droplet can be quickly and sensitively detected. We have demonstrated that two sets of a total of eight precisely mapped phase diagrams of four PVAc fractions in the two solvents can be reasonably scaled together to form a master curve.
Co-reporter:Yilan Ye, Yonggang Shangguan, Yihu Song, Qiang Zheng
Polymer 2014 Volume 55(Issue 10) pp:2445-2454
Publication Date(Web):13 May 2014
DOI:10.1016/j.polymer.2014.03.057
It is well-known that introduction of charged groups to poly(N-isopropylacrylamide) (PNIPAM) raises its phase transition temperature. However, the influence of charged groups on structural evolution and dehydration dynamics of weakly charged PNIPAM during phase transition still lacks systematic investigation. In the current study, armed with rheometer and two-dimensional Fourier transform infrared spectrometer (2D-FTIR), we investigated on mesoscopic and microscopic scales the phase transition of sodium poly(N-isopropylacrylamide-co-2-acrylamido-2-methylpropanesulfonate), abbreviated as poly(NIPAM-co-NaAMPS), with charge density of 1–10%. At ambient temperature, scaling exponent of poly(NIPAM-co-NaAMPS) varies from that of neutral polymer to polyelectrolytes as charge density increases. Above phase transition temperature, mesoscopic structure of poly(NIPAM-co-NaAMPS) varies from network of physical gel to viscoelastic liquid containing branched aggregates with increase of charge density, indicating increasing hindrance to intra/inter-chain association due to electrostatic repulsion. On a molecular level, poly(NIPAM-co-NaAMPS) exhibits distinctive microdynamic sequence of dehydration during phase transition, in contrast to neutral PNIPAM. In particular, sulfonate groups decouple the cooperative dehydration of alkyl and carbonyl groups, resulting in their distinctive phase transition temperature as well as temperature range. In analogy to hydration of proteins, it is proposed that the microdynamic sequence, implying the hydration stability of each group, is closely related to the density of hydration layer as well as influence of electrostatic field generated by charged groups. For poly(NIPAM-co-AMPS) with charge density of 3%, there still remains 72.3% of hydrogen bonds between carbonyl group and water at 60 °C, meanwhile a highly hydrated network forms with network strands 1–2 times as long as the copolymer chain length.
Co-reporter:Biwei Qiu, Feng Chen, Yu Lin, Yonggang Shangguan, Qiang Zheng
Polymer 2014 Volume 55(Issue 23) pp:6176-6185
Publication Date(Web):5 November 2014
DOI:10.1016/j.polymer.2014.09.060
•Core–shell structure in HPP/EPR/EbP blends can be constructed and regulated.•Propylene chain segments in EbP and HPP can form co-crystals.•Melting point is strongly related to nucleation behavior and phase structure.•Double depression of Tg,EPR and Tg,HPP reflects enhanced infiltration of chains.According to a two-step preparation technique consisting of temperature-gradient extraction fractionation (TGEF) and subsequent solution-mixing, a series of polypropylene/ethylene-propylene random copolymer/ethylene-propylene block copolymer (HPP/EPR/EbP) blends containing multilayered core–shell dispersed particle with bridges were prepared to explore the influences of dispersed phase on crystallization and dynamic mechanical behavior. The inner core of the core–shell dispersed particles was mainly composed of EbP with long ethylene chain segment, and the intermediate layer was EPR and outer layer was EbP with long propylene chain segment. The size and layer thickness of the core–shell dispersed particle could be regulated by varying the ratio of EPR/EbP. With the decrease of EbP content, the outer interfacial thickness of core–shell structure decreases and the blends presented elevated melting points, which might be ascribed to enhanced nucleation ability. Meanwhile, the special simultaneous depression of glass-transition temperatures (Tg) of HPP and EPR was observed in all HPP/EPR/EbP blends compared with the Tgs of neat components, which was attributed to the enlarging free volume by imperfect co-crystals and infiltration of long ethylene chain segments of EbP component at interface.
Co-reporter:Yu Lin, Yeqiang Tan, Biwei Qiu, Jiaqi Cheng, Wanjie Wang, Yonggang Shangguan, Qiang Zheng
Journal of Membrane Science 2013 Volume 439() pp:20-27
Publication Date(Web):15 July 2013
DOI:10.1016/j.memsci.2013.03.033
•Casting solution concentration significantly affects the segmental dynamics.•Segmental motion is dependent on casting solvents.•α-Relaxation time distribution is hardly affected by solvation effect.•Neither the dynamics nor the distribution width of β- and γ-relaxations is affected.The effects of solvent casting parameters on the molecular dynamics of poly(methyl methacrylate)/poly(styrene-co-maleic anhydride) (PMMA/SMA) blend films was investigated using broadband dielectric spectroscopy. Through changing the solvent type and solution concentration, blend film samples with different entanglement intensity were prepared, and they can significantly affect the glass transition temperature (Tg) and segmental dynamics of the films. In films cast from a methyl ethyl ketone (MEK) solution at various concentrations, Tg and relaxation time (τmax) increase with increasing solution concentration due to an increased entanglement density, decreased molecular mobility and entanglement recovery. No obvious distribution broadening is observed due to the unchanged heterogeneous dynamics. In the case of films cast from chloroform, MEK and tetrahydrofuran solution, Tg and τmax of the resultant films are hardly affected, while Tg and τmax of films cast from a N, N-Dimethylformamide (DMF) solution are much higher than the other three due to a higher entanglement degree and strong interaction contributions. Moreover, the poor dissolving capacity of DMF may result in more heterogeneous dynamics and subsequently a larger dc conductivity process and broader and more symmetric α-relaxation spectra. Neither the dynamics nor the distribution width of the subglass relaxation processes is affected by the casting solvent or solution concentration, indicating little change in the local environment of the segments.Graphical abstract
Co-reporter:Lei Jin, Yonggang Shangguan, Tao Ye, Hu Yang, Quanfu An and Qiang Zheng
Soft Matter 2013 vol. 9(Issue 6) pp:1835-1843
Publication Date(Web):17 Dec 2012
DOI:10.1039/C2SM27404C
A remarkable shear induced self-thickening of chitosan-graft-polyacrylamide aqueous solution was observed. After the polyelectrolyte solution presenting shear thinning was subjected to a high-rate shear for several minutes, their viscosities recovered and then a much higher zero shear viscosity than the original one appeared. Obviously, the self-thickening differs from conventional shear thickening or viscous recovery, as reported previously. The mechanism of self-thickening was investigated by rheological methods together with TEM, 1H NMR and DLS, etc. It was found that some aggregates exist in original chitosan-graft-polyacrylamide aqueous solution and the scale of such aggregations would become larger within several minutes after a strong shear. The thickening was proven to be the result of an enhanced scale of GPAM aggregation in aqueous solution, and the mechanism of aggregation was proven to be intermolecular hydrogen bonding effects. Besides, the shear-induced self-thickening appears to be facile, maintainable and easily controllable by changing the shear conditions.
Co-reporter:Yu Lin;Feng Chen;Min Zuo ;Qiang Zheng
Polymer International 2013 Volume 62( Issue 4) pp:676-683
Publication Date(Web):
DOI:10.1002/pi.4349
Abstract
The nonlinear phase-separation behavior of poly(methyl methacrylate)/poly(styrene-co-maleic anhydride) (PMMA/SMA) blends over wide appropriate temperature and heating rate ranges was studied using time-resolved small-angle laser light scattering. During the non-isothermal process, a quantitative logarithm function was established to describe the relationship between cloud point (Tc) and heating rate (k) as given by Tc = Alnk + T0, in which the parameter A, reflecting the heating rate dependence, is much different for different compositions due to phase-separation rate and activation energy difference. For the isothermal phase-separation process, an Arrhenius-like equation was successfully applied to describe the temperature dependence of the apparent diffusion coefficient (Dapp) and the relaxation time (τ) of the early stage as well as the late stage of spinodal decomposition (SD) of PMMA/SMA blends. Based on the successful application of the Arrhenius-like equation, the related activation energies could be obtained from Dapp and τ of the early and late stages of SD, respectively. In addition, these results indicate that it is possible to predict the temperature dependence of the phase-separation behavior of binary polymer mixtures during isothermal annealing over a range of 100 °C above the glass transition temperature using the Arrhenius-like equation. © 2012 Society of Chemical Industry
Co-reporter:Lei Jin, Yeqiang Tan, Yonggang Shangguan, Yu Lin, Bo Xu, Qiang Wu, and Qiang Zheng
The Journal of Physical Chemistry B 2013 Volume 117(Issue 48) pp:15111-15121
Publication Date(Web):November 15, 2013
DOI:10.1021/jp408782e
A special shear thinning phenomenon followed by static self-thickening in chitosan-graft-polyacrylamide (GPAM) aqueous solutions was investigated. This multiregion shear thinning can be defined as the first stage of the recently reported shear induced self-thickening (SIT) in our previous work. The three thinning regions (labeled as N1, N2, and N3) are considered very important, and they can reflex the complex variations of intermolecular interactions among and inside the aggregates in solution with increasing shear rate. To verify this multiregion shear thinning, a critical concentration of GPAM for this three-region shear thinning was first investigated. Shear recovery tests with the maximal shear rates located in the N1–N3 were carried out to ascertain the crucial role of shear thinning in SIT. The mechanisms of these three shear thinning regions were proposed based on the dependence of shear rheological behavior on various conditions in each region, including GPAM concentration, grafting ratio, temperature, added hydrogen bonding breaker, and salt. The above results confirm that N1 is due to the breakage of the interactions among hydrogen bonding aggregates, while N2 and N3 are attributed to the progressive destruction of the aggregates. As the first stage of SIT, shear thinning can markedly break the original aggregate and expose additional hydrogen bonding stickers to reform more aggregates with bigger size, resulting in the final higher viscosity.
Co-reporter:Yu Lin, Yeqiang Tan, Biwei Qiu, Yonggang Shangguan, Eileen Harkin-Jones, and Qiang Zheng
The Journal of Physical Chemistry B 2013 Volume 117(Issue 2) pp:697-705
Publication Date(Web):December 26, 2012
DOI:10.1021/jp3098507
The influence of annealing above the glass transition temperature (Tg) on chain entanglement and molecular dynamics of solution-cast poly(methyl methacrylate)/poly(styrene-co-maleic anhydride) (PMMA/SMA) blends was investigated via a combination of dynamic rheological measurement and broadband dielectric spectroscopy. Chain entanglement density increases when the annealing temperature and/or time increases, resulting from the increased efficiency of chain packing and entanglement recovery. The results of the annealing treatment without cooling revealed that the increase of the entanglement density occurred during the annealing process instead of the subsequent cooling procedure. Annealing above Tg exerts a profound effect on segmental motion, including the transition temperature and dynamics. Namely, Tg shifts to higher temperatures and the relaxation time (τmax) increases due to the increased entanglement density and decreased molecular mobility. Either Tg or τmax approaches an equilibrium value gradually, corresponding to the equilibrium entanglement density that might be obtained through the theoretical predictions. However, no obvious distribution broadening is observed due to the unchanged heterogeneous dynamics. Furthermore, side group rotational motion could be freely achieved without overcoming the chain entanglement resistance. Hence, neither the dynamics nor the distribution width of the subglass relaxation (β- and γ-relaxation) processes is affected by chain entanglement resulting from annealing, indicating that the local environment of the segments is unchanged.
Co-reporter:Yu Lin, Yonggang Shangguan, Min Zuo, Eileen Harkin-Jones, Qiang Zheng
Polymer 2012 Volume 53(Issue 6) pp:1418-1427
Publication Date(Web):9 March 2012
DOI:10.1016/j.polymer.2012.01.039
Poly(methyl methacrylate)/poly(styrene-co-maleic anhydride) (PMMA/SMA) blends with various compositions were prepared through solution casting and melt blending. Two preparation routes, solution casting and melt blending, were used to achieve different degrees of molecular entanglement in the samples with solution casting giving rise to a lower degree of entanglement. Therefore, the effect of molecular entanglement on molecular dynamics and phase-separation kinetics of PMMA/SMA blends was investigated by using broadband dielectric spectroscopy and small-angle laser light scattering (SALLS). Molecular entanglement is found to have a pronounced effect on the α-relaxation process. The glass transition temperature (Tg) is related to the degree of entanglement and a higher degree of entanglement can result in a higher Tg which shifts to a higher temperature after annealing. The relaxation time (τ) of the α-relaxation process is lower for lower degrees of entanglement. Neither the dynamics nor the distribution width of the β-relaxation process is affected by degree of entanglement, regardless of the blend composition. The kinetics of phase-separation by spinodal decomposition (SD) in PMMA/SMA blends are however significantly influenced by the degrees of entanglement with decomposition rate being higher at lower degrees of entanglement.
Co-reporter:Chunhui Zhang;Ruifen Chen;Qiang Zheng
Journal of Applied Polymer Science 2011 Volume 119( Issue 3) pp:1560-1566
Publication Date(Web):
DOI:10.1002/app.32827
Abstract
An impact polypropylene copolymer (IPC) was fractionated into three fractions using n-octane as solvent by means of temperature-gradient extraction fractionation. The glass transitions, melting, and crystallization behavior of these three fractions were studied by modulated differential scanning calorimeter (MDSC) and wide-angle X-ray diffraction (WAXD). In addition, successive self-nucleation and annealing (SSA) technique was adopted to further examine the heterogeneity and the structure of its fractions. The results reveal that the 50°C fraction (F50) mainly consists of ethylene-propylene random copolymer and the molecular chains may contain a few of short but crystallizable propylene and/or ethylene unit sequences; moreover, the lamellae thicknesses of the resulting crystals are extremely low. Furthermore, 100°C fraction (F100) mainly consist of some branched polyethylene and various ethylene-propylene block copolymers in which some ethylene and propylene units also randomly arrange in certain segments, and some polypropylene segments can form crystals with various lamellae thickness. An obvious thermal fractionation effect for F100 samples after being treated by SSA process is ascribed to the irregular and nonuniform arrangement of ethylene and propylene segments. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Co-reporter:Jianping Zhou;Qiang Wu;Qiang Zheng
Polymer International 2011 Volume 60( Issue 3) pp:353-361
Publication Date(Web):
DOI:10.1002/pi.2955
Abstract
Hydrophobically modified polyelectrolytes (HMPEs) were synthesized using sodium 2-acrylamido-2-methyl-propanesulfonate and N-n-dodecylacrylamide as monomers with the same feeding ratio via micellar and solution copolymerization. The effects of hydrophobic association and electrostatic interaction on the solution properties of the HMPEs were studied. Compared with HMPE obtained via solution copolymerization (s-PAD), the hydrophobic interaction of HMPE obtained via micellar copolymerization (m-PAD) is more obvious due to the micro-blocky distribution of hydrophobic groups. The viscosity properties of m-PAD in deionized water or brine follow well the scaling theory of polyelectrolytes. However, for s-PAD, the concentration where zero-shear viscosity (η0) and solvent viscosity (ηs) follow η0 ≈ 2ηs is more likely to be critical entanglement concentration (ce) rather than critical overlap concentration (c*). It is suggested that modifying of the transition region from c* to ce is valid and reasonable for s-PAD. It is believed that the different solution properties of s-PAD and m-PAD should be attributed to the distributions of hydrophobic groups in the chains. Copyright © 2010 Society of Chemical Industry
Co-reporter:Ruifen Chen, Yonggang Shangguan, Chunhui Zhang, Feng Chen, Eileen Harkin-Jones, Qiang Zheng
Polymer 2011 Volume 52(Issue 13) pp:2956-2963
Publication Date(Web):8 June 2011
DOI:10.1016/j.polymer.2011.05.005
The phase structure evolution of high impact polypropylene copolymer (IPC) during molten-state annealing and its influence on crystallization behaviour were studied. An entirely different architecture of the IPC melt was observed after being annealed, and this architecture resulted in variations of the crystallization behaviour. In addition, it was found that the core-shell structure of the dispersed phase was completely destroyed and the sizes of the dispersed domains increased sharply after being annealed at 200 °C for 200 min. Through examination of the coarseness of the phase morphology using phase contrast microscopy (PCM), it was found that a co-continuous structure and an abnormal ‘sea-island’ structure generally appeared with an increase in annealing time. The original matrix PP component appeared as a dispersed phase, whereas the copolymer components formed a continuous ‘sea-island’ structure. This change is ascribed to the large tension induced by solidification at the phase interface and the great content difference between the components. When the temperature was reduced the structure reverted to its original form. With increasing annealing time, the spherulite profiles became more defined and the spherulite birefringence changed from vague to clear. Overall crystallization rates and nucleation densities decreased, but the spherulite radial growth rates remained almost constant, indicating that molten-state annealing mainly affects the nucleation ability of IPC, due to a coarsened microstructure and decreased interface area.
Co-reporter:Chun-hui Zhang;Rui-fen Chen;Feng Chen
Chinese Journal of Polymer Science 2011 Volume 29( Issue 4) pp:497-505
Publication Date(Web):2011 July
DOI:10.1007/s10118-011-1059-1
The impact propylene copolymer (IPC) and isotactic polypropylene (iPP) were separately selected to prepare laminates with high density polyethylene (HDPE) by hot press. The peel forces of IPC/HDPE and iPP/HDPE laminates were examined, and it was found that the welded joint strength in IPC/HDPE laminate was dramatically higher than that of iPP/HDPE laminate. According to the special microstructure of IPC, the co-crystallization of the ethylene segments in ethylene-propylene block copolymer (EbP) component of IPC and the PE chain in HDPE was proposed to explain the highstrength welding. The DSC results indicated that there indeed existed some interaction between IPC and HDPE, and the crystallizable PE component in IPC could affect the crystallization of HDPE. The scanning electron microscope (SEM) observations of IPC/HDPE blends demonstrated that HDPE tended to stay with the PE-rich EbP chains to form the dispersed phase, indicating the good miscibility between HDPE and EbP components of IPC. According to the above results, the effect of co-crystallization of the PE components of the IPC and HDPE on the high weld strength of IPC/HDPE laminate was confirmed.
Co-reporter:Chunhui Zhang, Yonggang Shangguan, Ruifen Chen, Yuanzhi Wu, Feng Chen, Qiang Zheng, Guohua Hu
Polymer 2010 Volume 51(Issue 21) pp:4969-4977
Publication Date(Web):1 October 2010
DOI:10.1016/j.polymer.2010.08.021
The morphology of impact polypropylene copolymer (IPC) was studied through scanning electron microscope (SEM) and transmission electron microscope (TEM) observation, and a modified dispersed phase model of IPC with core-shell structure was proposed. Through fractionation of IPC, the glass transitions of the ethylene–propylene random copolymer (EPR) fraction, ethylene–propylene block copolymer (EbP) fraction and propylene homopolymer (iPP) fraction were detected, respectively. Moreover, the glass transitions and crystallization behaviors of EbP/iPP and EPR/EbP fraction blends were systemically investigated and several reasonable chain structures of EbP component were confirmed. The results reveal that the EbP component presents three glass transition peaks, and the glass transition temperature of ethylene–propylene random copolymer in IPC sample is remarkably lower than that of pure EPR fraction due to the existence of special structure of EbP component in IPC. In addition, co-crystallization occurring between the polypropylene chains in EbP fraction and in iPP fraction was found for solution-mixed EbP/iPP blends, and it is believed that there exists a dilute effect of EPR on the crystallization of EbP fraction for the solution-mixed EPR/EbP blends. Accordingly, it can be inferred that EbP fraction has good compatibility with both EPR and iPP fraction, and indeed it confirms that the compatibilization effect of EbP fraction in IPC was good.
Co-reporter:Huixia Hu;Min Zuo;Qiang Zheng
Journal of Polymer Science Part B: Polymer Physics 2008 Volume 46( Issue 18) pp:1923-1931
Publication Date(Web):
DOI:10.1002/polb.21526
Abstract
The liquid–liquid phase-separation (LLPS) behavior of poly(n-methyl methacrylimide)/poly(vinylidene fluoride) (PMMI/PVDF) blend was studied by using small-angle laser light scattering (SALLS) and phase contrast microscopy (PCM). The cloud point (Tc) of PMMI/PVDF blend was obtained using SALLS at the heating rate of 1 °C min−1 and it was found that PMMI/PVDF exhibited a low critical solution temperature (LCST) behavior similar to that of PMMA/PVDF. Moreover, Tc of PMMI/PVDF is higher than its melting temperature (Tm) and a large temperature gap between Tc and Tm exists. At the early phase-separation stage, the apparent diffusion coefficient (Dapp) and the product (2Mk) of the molecules mobility coefficient (M) and the energy gradient coefficient (k) arising from contributions of composition gradient to the energy for PMMI/PVDF (50/50 wt) blend were calculated on the basis of linearized Cahn-Hilliard-Cook theory. The kinetic results showed that LLPS of PMMI/PVDF blends followed the spinodal decomposition (SD) mechanism. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1923–1931, 2008
Co-reporter:Yonggang Shangguan, Feng Chen, Jie Yang, Erwen Jia, Qiang Zheng
Polymer (10 March 2017) Volume 112() pp:
Publication Date(Web):10 March 2017
DOI:10.1016/j.polymer.2017.02.022
•A new strategy for fabricating polypropylene alloy with good low-temperature toughness was proposed.•SEP could effectively shift the brittle-tough transition of PP/EPR blend to lower temperature.•PP/EPR/SEP alloy presents excellent low-temperature toughness and balanced toughness-rigidity.A new strategy for fabricating polypropylene alloy with good low-temperature toughness was reported. Glass transition temperature (Tg) of rubber phase in polypropylene/ethylene-propylene rubber/poly(styrene-b-ethylene/propylene) diblock copolymer (PP/EPR/SEP) blend was continuously reduced through strengthening the interfacial tensile force on rubber phase by using the concept of mismatched thermal expansion coefficient. As a result, the brittle-tough transition (BTT) of PP alloy shifted to lower temperature and subsequently excellent impact strength at low temperature was achieved. Through qualitative analysis of impact force, it was found that the theoretical temperature at which BTT occurred was close to that obtained by experiment, indicating BTT of rubber toughened plastic system is indeed controlled by rubber's Tg at impact instant. Furthermore, the PP alloy with excellent low-temperature toughness shows balanced toughness-rigidity, on the contrary, the blends presents poor rigidity when SEP or EPR is used to toughen PP alone.Download high-res image (331KB)Download full-size image
