Login In
2019 Volume 37 Issue 3
2019, 37(3):
Abstract:
2019, 37(3): 197-207
doi: 10.1007/s10118-019-2199-y
Abstract:
In this contribution, we reported a novel approach to crosslink poly(ε-caprolactone) (PCL) via supramolecular hydrogen bonding interactions. First, a series of octa-armed poly(ε-caprolactone) stars with polyhedral oligomeric silsesquioxane (POSS) cores were synthesized via the ring-opening polymerizations. Thereafter, the arm ends of organic-inorganic star-shaped PCLs were reacted with 2-(6-isocyanatohexylaminocarbonylamino)-6-methyl-4[1H]-pyrimidinone to obtain 2-ureido-4[1H]-pyrimidone (UPy)-terminated PCL stars. Notably, the UPy-terminated PCL stars were physically crosslinked, which was evidenced by means of dynamic mechanical thermal analysis (DMTA) and rheological analysis. Owing to the formation of the physically-crosslinked networks, the organic-inorganic PCL stars displayed significant shape memory properties with about 100% of shape recovery, which was in marked contrast to the PCL stars without UPy termini.
In this contribution, we reported a novel approach to crosslink poly(ε-caprolactone) (PCL) via supramolecular hydrogen bonding interactions. First, a series of octa-armed poly(ε-caprolactone) stars with polyhedral oligomeric silsesquioxane (POSS) cores were synthesized via the ring-opening polymerizations. Thereafter, the arm ends of organic-inorganic star-shaped PCLs were reacted with 2-(6-isocyanatohexylaminocarbonylamino)-6-methyl-4[1H]-pyrimidinone to obtain 2-ureido-4[1H]-pyrimidone (UPy)-terminated PCL stars. Notably, the UPy-terminated PCL stars were physically crosslinked, which was evidenced by means of dynamic mechanical thermal analysis (DMTA) and rheological analysis. Owing to the formation of the physically-crosslinked networks, the organic-inorganic PCL stars displayed significant shape memory properties with about 100% of shape recovery, which was in marked contrast to the PCL stars without UPy termini.
2019, 37(3): 208-215
doi: 10.1007/s10118-019-2196-1
Abstract:
Rare earth catalysts possessing characteristics of cation-anion ion pair show advantages of adjusting electronegativity and steric hindrance of metal active sites, which can control the catalytic performance and stereoselectivity better than those of traditional metallocene and Ziegler-Natta catalysts in diene polymerization. In this work, a series of neodymium organic sulfonate complexes, Nd(CF3SO3)3·xH2O·yL (x, y: the coordination number; L refers to an organic electron donating ligand, such as acetylacetone (acac), iso-octyl alcohol (IAOH), tributyl phosphate (TBP), etc.), have been synthesized to form the cationic active species in the presence of alkylaluminum such as Al(i-Bu)3, AlEt3, and Al(i-Bu)2H, which display high activities and distinguishing cis-1,4 selectivities (up to 99.9%) for the polymerization of butadiene. The microstructures, yield, molecular weight, and molecular weight distribution of the resulting polymer are well controlled by adjusting electronegativity/steric hindrance of the complexes. In addition, the kinetics, active species, and the possible process of polymerization are also discussed in this article.
Rare earth catalysts possessing characteristics of cation-anion ion pair show advantages of adjusting electronegativity and steric hindrance of metal active sites, which can control the catalytic performance and stereoselectivity better than those of traditional metallocene and Ziegler-Natta catalysts in diene polymerization. In this work, a series of neodymium organic sulfonate complexes, Nd(CF3SO3)3·xH2O·yL (x, y: the coordination number; L refers to an organic electron donating ligand, such as acetylacetone (acac), iso-octyl alcohol (IAOH), tributyl phosphate (TBP), etc.), have been synthesized to form the cationic active species in the presence of alkylaluminum such as Al(i-Bu)3, AlEt3, and Al(i-Bu)2H, which display high activities and distinguishing cis-1,4 selectivities (up to 99.9%) for the polymerization of butadiene. The microstructures, yield, molecular weight, and molecular weight distribution of the resulting polymer are well controlled by adjusting electronegativity/steric hindrance of the complexes. In addition, the kinetics, active species, and the possible process of polymerization are also discussed in this article.
2019, 37(3): 216-226
doi: 10.1007/s10118-019-2191-6
Abstract:
The low melt strength and poor crystallization behavior severely limit the processing and application of poly(lactic acid) (PLA) as biodegradable film materials. In this work, three-arm poly(L-lactic acid) (3A-PLLA) grafted silica nanoparticles with two kinds of topology structures were introduced into PLA matrix to improve the biodegradation performance. Different methods were used to characterize the structure of the grafted 3A-PLLA chains, the grafting density, and the thermal decomposition behavior of the nanoparticles. By varying the mass ratios of raw materials and altering the order of dropping solution in the reaction, high grafting density-tangled 3A-PLLA grafted SiO2 was synthesized as " 3A-PLLA grafting to SiO2” (GTS), while low grafting density-stretched 3A-PLLA grafted SiO2 was obtained as " SiO2 grafting to 3A-PLLA” (GTA). Topology of nanoparticles as well as the filler-matrix interaction is critically important to structure bio-nanocomposites with desirable properties. Thus, the GTS and GTA nanoparticles were introduced into PLA matrix to assess the effect. The SEM images showed the uniform dispersion of the modified nanoparticles, while the shear rheology results revealed that GTA nanoparticles made a more significant contribution on the melt-strengthening and relaxation time-extension of PLA. Moreover, it is suggested that GTA nanoparticles were more effective to act as a nucleating agent for PLA, which was proved by differential scanning calorimetry (DSC) and polarized optical microscopy (POM) researches. All of the improvements mentioned above of GTA nanocomposites can be ascribed to stronger entanglements between 3A-PLLA stretched by nano-SiO2 and PLA matrix.
The low melt strength and poor crystallization behavior severely limit the processing and application of poly(lactic acid) (PLA) as biodegradable film materials. In this work, three-arm poly(L-lactic acid) (3A-PLLA) grafted silica nanoparticles with two kinds of topology structures were introduced into PLA matrix to improve the biodegradation performance. Different methods were used to characterize the structure of the grafted 3A-PLLA chains, the grafting density, and the thermal decomposition behavior of the nanoparticles. By varying the mass ratios of raw materials and altering the order of dropping solution in the reaction, high grafting density-tangled 3A-PLLA grafted SiO2 was synthesized as " 3A-PLLA grafting to SiO2” (GTS), while low grafting density-stretched 3A-PLLA grafted SiO2 was obtained as " SiO2 grafting to 3A-PLLA” (GTA). Topology of nanoparticles as well as the filler-matrix interaction is critically important to structure bio-nanocomposites with desirable properties. Thus, the GTS and GTA nanoparticles were introduced into PLA matrix to assess the effect. The SEM images showed the uniform dispersion of the modified nanoparticles, while the shear rheology results revealed that GTA nanoparticles made a more significant contribution on the melt-strengthening and relaxation time-extension of PLA. Moreover, it is suggested that GTA nanoparticles were more effective to act as a nucleating agent for PLA, which was proved by differential scanning calorimetry (DSC) and polarized optical microscopy (POM) researches. All of the improvements mentioned above of GTA nanocomposites can be ascribed to stronger entanglements between 3A-PLLA stretched by nano-SiO2 and PLA matrix.
2019, 37(3): 227-234
doi: 10.1007/s10118-019-2200-9
Abstract:
This work described the preparation of easily colored meta-aramid (PMIA) copolymers from m-phenylenediamine (MPD), isophthaloyl dichloride (IPC), and 3,4′-oxydianiline (3,4′-ODA) via solution polycondensation in N,N-dimethylacetamide (DMAc). The novel co-PMIAs were obtained in relatively high inherent viscosities ranging from 1.32 dL/g to 2.53 dL/g, which could be easily cast into flexible films with high transparence or spun into fibers. All the newly synthesized copolymers possessed excellent thermal stabilities even better than that of commercial PMIA, with 5% weight loss temperatures higher than 430 °C in nitrogen measured by TGA and glass transition temperature of 267–277 °C measured by DSC. The cast films exhibited good mechanical properties with a tensile strength up to 107 MPa and a tensile modulus up to 2.2 GPa. The resultant PMIAs also showed good solubility and better dye ability for cationic dyes.
This work described the preparation of easily colored meta-aramid (PMIA) copolymers from m-phenylenediamine (MPD), isophthaloyl dichloride (IPC), and 3,4′-oxydianiline (3,4′-ODA) via solution polycondensation in N,N-dimethylacetamide (DMAc). The novel co-PMIAs were obtained in relatively high inherent viscosities ranging from 1.32 dL/g to 2.53 dL/g, which could be easily cast into flexible films with high transparence or spun into fibers. All the newly synthesized copolymers possessed excellent thermal stabilities even better than that of commercial PMIA, with 5% weight loss temperatures higher than 430 °C in nitrogen measured by TGA and glass transition temperature of 267–277 °C measured by DSC. The cast films exhibited good mechanical properties with a tensile strength up to 107 MPa and a tensile modulus up to 2.2 GPa. The resultant PMIAs also showed good solubility and better dye ability for cationic dyes.
2019, 37(3): 235-242
doi: 10.1007/s10118-019-2182-7
Abstract:
Microgels with a thermo-sensitive poly(N-isopropylacrylamide) (polyNIPAm) backbone and bis-imidazolium (VIM) ionic cross-links, denoted as poly(NIPAm-co-VIM), were successfully prepared. The as-synthesized ionic microgels were converted to nanoreactors, denoted as Au@PNI MGs, upon generation and immobilization of gold nanoparticles (Au NPs) of 5–8 nm in size into poly(NIPAm-co-VIM). The content of Au NPs in microgels could be regulated by controlling the 1,6-dibromohexane/vinylimidazole molar ratio in the quaternization reaction. The microgel-based nanoreactors were morphologically spherical and uniform in size, and presented reversible thermo-sensitive behavior with volume phase transition temperatures (VPTTs) at 39–40 °C. The Au@PNI MGs were used for the reduction of 4-nitrophenol, of which the catalytic activity could be modulated by temperature.
Microgels with a thermo-sensitive poly(N-isopropylacrylamide) (polyNIPAm) backbone and bis-imidazolium (VIM) ionic cross-links, denoted as poly(NIPAm-co-VIM), were successfully prepared. The as-synthesized ionic microgels were converted to nanoreactors, denoted as Au@PNI MGs, upon generation and immobilization of gold nanoparticles (Au NPs) of 5–8 nm in size into poly(NIPAm-co-VIM). The content of Au NPs in microgels could be regulated by controlling the 1,6-dibromohexane/vinylimidazole molar ratio in the quaternization reaction. The microgel-based nanoreactors were morphologically spherical and uniform in size, and presented reversible thermo-sensitive behavior with volume phase transition temperatures (VPTTs) at 39–40 °C. The Au@PNI MGs were used for the reduction of 4-nitrophenol, of which the catalytic activity could be modulated by temperature.
2019, 37(3): 243-252
doi: 10.1007/s10118-019-2192-5
Abstract:
To investigate the performance of graphene (Gra) modified with ethoxycarbonyl ionic liquid (IL), chain mobility and crystallization kinetics of poly(L-lactic acid) (PLLA), a series of PLLA nanocomposites have been prepared using solution-cast method. IL can improve the dispersion of Gra in PLLA matrix and the samples containing IL have higher growth rate of PLLA spherulite than neat PLLA does. PLLA/IL/Gra and PLLA/2Gra exhibit the same relaxation strength and time of αN relaxation that corresponds to the longest normal mode motion at 110−140 °C. PLLA/IL/Gra shows a faster crystallization rate than PLLA/2Gra does, which might be attributed to the Gra-imidazolium cation interaction in IL modified Gra, the significant dispersion effect of IL at Gra surface, and the increase of nuclei density of PLLA/IL/Gra.
To investigate the performance of graphene (Gra) modified with ethoxycarbonyl ionic liquid (IL), chain mobility and crystallization kinetics of poly(L-lactic acid) (PLLA), a series of PLLA nanocomposites have been prepared using solution-cast method. IL can improve the dispersion of Gra in PLLA matrix and the samples containing IL have higher growth rate of PLLA spherulite than neat PLLA does. PLLA/IL/Gra and PLLA/2Gra exhibit the same relaxation strength and time of αN relaxation that corresponds to the longest normal mode motion at 110−140 °C. PLLA/IL/Gra shows a faster crystallization rate than PLLA/2Gra does, which might be attributed to the Gra-imidazolium cation interaction in IL modified Gra, the significant dispersion effect of IL at Gra surface, and the increase of nuclei density of PLLA/IL/Gra.
2019, 37(3): 253-257
doi: 10.1007/s10118-019-2184-5
Abstract:
The structural transformation of mesophase to crystalline phase of strain-induced poly(L-lactic acid) has been investigated by differential scanning calorimetry (DSC) and in situ temperature dependent polarized Fourier transform infrared (FTIR) spectroscopy. It is found that, as the drawing temperature increases, melting of strain-induced mesophase in the heating process can remarkably interfere the crystallization behavior subsequently. Coupling with in situ polarized FTIR, from 60 °C to 76 °C, the mesophase melts partially rather than completely melting, and changes immediately to three-dimensional ordered structure. Of particular note, through monitoring the subtle spectral change in the critical phase transformation temperature from 60 °C to 64 °C, it is clearly demonstrated that relaxation of oriented amorphous chains initially takes place prior to the melting of mesophase.
The structural transformation of mesophase to crystalline phase of strain-induced poly(L-lactic acid) has been investigated by differential scanning calorimetry (DSC) and in situ temperature dependent polarized Fourier transform infrared (FTIR) spectroscopy. It is found that, as the drawing temperature increases, melting of strain-induced mesophase in the heating process can remarkably interfere the crystallization behavior subsequently. Coupling with in situ polarized FTIR, from 60 °C to 76 °C, the mesophase melts partially rather than completely melting, and changes immediately to three-dimensional ordered structure. Of particular note, through monitoring the subtle spectral change in the critical phase transformation temperature from 60 °C to 64 °C, it is clearly demonstrated that relaxation of oriented amorphous chains initially takes place prior to the melting of mesophase.
2019, 37(3): 258-267
doi: 10.1007/s10118-019-2202-7
Abstract:
The effect of the architecture of poly(ethylene glycol)/poly(L-lactide) (PEG/PLLA) block copolymers on the non-isothermal crystallization behaviors of PLLA blocks was investigated by differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). 1-Arm MPEG-b-PLLA and 4-arm PEG-b-PLLA (4PEG-b-PLLA) were synthesized by the ring-opening polymerization of L-lactide in the presence of poly(ethylene glycol) methyl ether (MPEG) and 4-arm poly(ethylene glycol) (4PEG). 4-Arm PLLA-b-MPEG (4PLLA-b-PEG) was synthesized by coupling 4-arm PLLA and MPEG. The WAXD results indicated that the crystalline structure of PLLA blocks did not alter due to the different chain architectures. The average values of Avrami index ( \begin{document}$\bar n$\end{document} ![]()
![]()
) were all above 4, which indicated that the nucleation mechanism of PLLA blocks was heterogeneous nucleation, regardless of the architectures. The overall crystallization rates were decreased markedly as following: MPEG-b-PLLA > 4PEG- b-PLLA > 4PLLA- b-PEG, ascribed to the different confinement by PEG blocks and to the steric hindrance of chain architectures. Therefore, the crystallization of PLLA blocks became more difficult and the crystallization activation energy of the PLLA blocks increased due to the confinement of chain architectures.
The effect of the architecture of poly(ethylene glycol)/poly(L-lactide) (PEG/PLLA) block copolymers on the non-isothermal crystallization behaviors of PLLA blocks was investigated by differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). 1-Arm MPEG-b-PLLA and 4-arm PEG-b-PLLA (4PEG-b-PLLA) were synthesized by the ring-opening polymerization of L-lactide in the presence of poly(ethylene glycol) methyl ether (MPEG) and 4-arm poly(ethylene glycol) (4PEG). 4-Arm PLLA-b-MPEG (4PLLA-b-PEG) was synthesized by coupling 4-arm PLLA and MPEG. The WAXD results indicated that the crystalline structure of PLLA blocks did not alter due to the different chain architectures. The average values of Avrami index (
2019, 37(3): 268-278
doi: 10.1007/s10118-019-2173-8
Abstract:
The thermal and mechanical properties of the chemically imidized polyimide (CIPI) films and thermally imidized polyimide (TIPI) films were investigated systematically. Experimental results indicated that the CIPI films show dramatically enhanced tensile strength and modulus with obviously reduced coefficient of thermal expansion (CTE) in comparison with TIPI films. These enhancements results from the high in-plane orientation and close packing of the CIPI backbones. Compared with thermal imidization which starts at about 140 °C, the chemical imidization activated by acetic anhydride and isoquinoline initiates the cyclization even at room temperature. The resulting imide rings restrict the mobility of polymer chains and lead to the in-plane orientation with solvent evaporation. Additionally, fewer small molecules remain in the films after treated at 120 °C by chemical imidization than by thermal imidization. The polymer chain plasticization caused by the evaporation of small molecules at high temperature is obviously restricted. Moreover, the partially imidized polymer inhibits the decomposition of mainchains that occurs at subsequent high temperature process, being beneficial to the formation of high molecular weight PI films. Hence, chemical imidization pathway shows apparent advantage to produce PI films with great combined properties, including high modulus, strength and toughness, as well as high thermal dimension stability etc.
The thermal and mechanical properties of the chemically imidized polyimide (CIPI) films and thermally imidized polyimide (TIPI) films were investigated systematically. Experimental results indicated that the CIPI films show dramatically enhanced tensile strength and modulus with obviously reduced coefficient of thermal expansion (CTE) in comparison with TIPI films. These enhancements results from the high in-plane orientation and close packing of the CIPI backbones. Compared with thermal imidization which starts at about 140 °C, the chemical imidization activated by acetic anhydride and isoquinoline initiates the cyclization even at room temperature. The resulting imide rings restrict the mobility of polymer chains and lead to the in-plane orientation with solvent evaporation. Additionally, fewer small molecules remain in the films after treated at 120 °C by chemical imidization than by thermal imidization. The polymer chain plasticization caused by the evaporation of small molecules at high temperature is obviously restricted. Moreover, the partially imidized polymer inhibits the decomposition of mainchains that occurs at subsequent high temperature process, being beneficial to the formation of high molecular weight PI films. Hence, chemical imidization pathway shows apparent advantage to produce PI films with great combined properties, including high modulus, strength and toughness, as well as high thermal dimension stability etc.
2019, 37(3): 279-288
doi: 10.1007/s10118-019-2187-2
Abstract:
Cellular foams are widely applied as protective and energy absorption materials in both civil and military fields. A facile and simple one-step heating method to fabricate polymeric foams is measured by adopting thermally expandable microspheres (TEMs). The ideal foaming parameters for various density foams were determined. Moreover, a mechanical testing machine and split Hopkinson bar (SHPB) were utilized to explore the quasi-static and dynamic compressive properties. Results showed that the cell sizes of the as-prepared TEMs foams were in the micrometer range of 11 μm to 20 μm with a uniform cell size distribution. All the foams exhibited good compressive behavior under both quasi-static and high strain rate conditions, and were related to both foam densities and strain rates. The compressive strength of the TEMs foams at 8400 s−1 was up to 4 times higher than that at 10−4 s−1. The effects exerted by the strain rate and sample density were evaluated by a power law equation. With increasing density, the strain rate effect was more prominent. At quasi-static strain rates below 3000 s−1 regime, initial cell wall buckling and subsequent cellular structure flattening were the main failure mechanisms. However, in the high strain rate (HSR) regime (above 5000 s−1), the foams were split into pieces by the following transverse inertia force.
Cellular foams are widely applied as protective and energy absorption materials in both civil and military fields. A facile and simple one-step heating method to fabricate polymeric foams is measured by adopting thermally expandable microspheres (TEMs). The ideal foaming parameters for various density foams were determined. Moreover, a mechanical testing machine and split Hopkinson bar (SHPB) were utilized to explore the quasi-static and dynamic compressive properties. Results showed that the cell sizes of the as-prepared TEMs foams were in the micrometer range of 11 μm to 20 μm with a uniform cell size distribution. All the foams exhibited good compressive behavior under both quasi-static and high strain rate conditions, and were related to both foam densities and strain rates. The compressive strength of the TEMs foams at 8400 s−1 was up to 4 times higher than that at 10−4 s−1. The effects exerted by the strain rate and sample density were evaluated by a power law equation. With increasing density, the strain rate effect was more prominent. At quasi-static strain rates below 3000 s−1 regime, initial cell wall buckling and subsequent cellular structure flattening were the main failure mechanisms. However, in the high strain rate (HSR) regime (above 5000 s−1), the foams were split into pieces by the following transverse inertia force.
