Branched Structure Research Articles

Controlled pyrolysis of epoxy through highly silicone-branched structures to construct a compact porous char layer for ablation resistant coatings

Excellent mechanical and adhesive properties make epoxy an ideal coating, but speedy pyrolysis rate, excessive gas products, and low residual char lead to low ablation efficiency, limiting the application in long-time thermal protection environments. In this paper, through branching structure design including pre-curing and alcohol exchange reactions, highly silicon-branched epoxy resins with different degrees of branching and silicon contents were synthesized. And the synthesis of highly silicone-branched epoxy resins with different branching degrees was verified by FTIR and viscosity curves. Through the analysis of thermal stability and pyrolysis history, the influence of the branched structure and content of silicone on the ablation mechanism of epoxy resin was investigated in detail. With 90 phr addition, the char residue increased to 42.3 %, and the release of pyrolysis products including a variety of flammable products was significantly inhibited. Furthermore, under a torch test of 160 kW/m2, due to the deposition mechanism in the gas and liquid phases of degradation products, a compact porous char was constructed during the ablation. The linear ablative rate of EP-3M@90P was reduced by more than 60 %, and the maximum value of back-surface temperature decreased by 48 °C compared to EP. Besides, the silicone-branched epoxy resin exhibits excellent mechanical properties, and the impact strength of EP-3M@90P nearly doubled compared to EP. Predictably, the design of silicone-branched structures to achieve control of the degradation history of epoxy resins provides a superior method for the preparation of high-strength and high-toughness thermal protective coatings.

Straightforward Synthesis of the Poly(ADP-ribose) Branched Core Structure.

Poly(ADP-ribosyl)ation is a post-translational modification that produces poly(ADP-ribose) with a branched structure every 20–50 units; such branching structure has been previously suggested to be involved in regulating chromatin remodeling. To elucidate its detailed functions, we developed a straightforward method for the synthesis of the poly(ADP-ribose) branched core structure, α-d-ribofuranosyl-(1‴ → 2″)-α-d-ribofuranosyl-(1″ → 2′)-adenosine 5′,5′′,5‴-trisphosphate 1, from 6-chloropurine ribofuranoside 4 in 10 steps and 6.1% overall yield. The structure poses synthetic challenges for constructing iterative α-1,2-cis-glycosidic bonds in the presence of a purine base and the installation of three phosphate groups at primary hydroxyl groups. Iterative glycosidic bonds were formed by α-1,2-cis-selective ribofuranosylation using 2-O-(2-naphthylmethyl)-protected thioglycoside donor 6 and a thiophilic bismuth promoter. After the construction of diribofuranosyl adenosine 5 had been constructed, it was chemo- and regioselectively phosphorylated at a later stage. Subsequent deprotection provided the synthetic target 1.

Adjacent double branches exist in the branching structure of starch

Starch is composed of two giant polymers of glucose-linked amylose and amylopectin but is not considered to have a branched structure with adjacent α-1,6-linkages (adjacent double branches). We previously discovered that the oligosaccharide DP6-1 contains adjacent double branches in sake, a Japanese rice wine. In this study, we analyzed the oligosaccharides generated from rice starch following porcine pancreatic α-amylase and glucoamylase digestion by hydrophilic interaction chromatography coupled with time-of-flight/mass spectrometry. We found that their elution times were identical to those of the oligosaccharides containing adjacent double branches observed in sake. Nuclear magnetic resonance (NMR) analysis confirmed that one of the oligosaccharides was identical to DP6-1. This indicates for the first time that adjacent double branches exist in the branching structure of starch. The adjacent double branches were estimated to be present at a ratio of approximately 1:100 of the total branching points in rice starch, suggesting that the contribution of the adjacent double branch to the entire structure of starch may be limited. Nonetheless, we found adjacent double branches in starch from rice, maize, wheat, and potato, which indicates that this novel branching pattern is universally present in starch.

Detrital zircon and apatite U-Pb geochronology of Ediacaran fossil–bearing strata spanning the late Ediacaran–Cambrian boundary in central Iran

The Neoproterozoic successions exposed in the Koushk and Chahmir areas of central Iran include both volcanic, and shallow to deep marine siliciclastic and carbonate units. We obtained detrital zircon dates from tuffaceous shales bearing Ediacaran fossils, including Corumbella, Persimedusites, ?Kimberella, ?Cloudina, and Namalia-like forms, together with a single metazoan holdfast structure from the Dargazin area of the Koushk region that correlates with the upper part of the Wedge succession dated at 555 ± 14 Ma. Zircon grains of the tuffaceous siltstones containing Corumbella, Persimedusites, ?Kimberella, ?Cloudina, Namalia-like structures, ?Spriggina, ?Pteridinium, holdfasts and algae-like branching structures in the Wedge section of the Koushk area, produced an age of 581 ± 9 Ma, whereas pyroclastic sandstones bearing Corumbella, Persimedusites, a possible holdfast, ?Pteridinium, ?Cloudina, algae-like branched structure, possible trace fossils and marine algal remains in the Chahmir area yielded an age of 541 ± 5 Ma. Zircon dates from the Dargazin and Wedge deposits are of late Ediacaran and Chahmir strata are of a late Ediacaran to early Cambrian age. Ages of the Chahmir sedimentary rocks are close to those from Dargazin. Based on our results, the maximum depositional age of the detrital zircons indicates relatively consistent sedimentation throughout the late Ediacaran and the early Cambrian, ranging from 590 to 530 Ma. Farnoosh Farjandi [ ffarjandi@swin.edu.au ], Faculty of Science, Engineering and Technology, Swinburne University of Technology, Melbourne (Hawthorn), Victoria 3122, Australia and Department of Geochemical Exploration, Geological Survey of Iran, Tehran, Iran; Patricia Vickers Rich [ prich@swin.edu.au ], Faculty of Science, Engineering and Technology, Swinburne University of Technology, Melbourne (Hawthorn), Victoria 3122, Australia and School of Earth, Atmosphere and Environment, Monash University, Melbourne (Clayton), Victoria 3800, Australia; Ulf Linnemann [ ulf.linnemann@senckenberg.de ] and Mandy Hofmann [ mandy.hofmann@senckenberg.de ], Senckenberg Naturhistorische Sammlungen Dresden, Sektion Geochronologie, 01109 Dresden, Germany; Massimo Raveggi [ massimo.raveggi@monash.edu ] and Michael Hall [ mike.hall@monash.edu ], School of Earth, Atmosphere and Environment, Monash University, Melbourne (Clayton), Victoria 3800, Australia; Thomas H. Rich [trich@museum.vic.gov.au ], Museum Victoria, Melbourne, Victoria, 3000, Australia

The hydrolytic stability and structure of the cured melamine-urea-formaldehyde resin

ABSTRACT The hydrolysis of cured melamine-urea-formaldehyde (MUF) resin leads to the increment of formaldehyde emission of the MUF resin-bond wood boards. To learn the influencing factors on the hydrolytic stability of cure MUF resin, a variety of amino resins (UF resin, MF resin, MUF resin) were synthesized in the laboratory. The amount of formaldehyde liberated and mass loss of cured amino resins were attained after acidic hydrolysis. The branched structure of cured MUF resins with different melamine levels added at different addition stages was characterized by the XRD technology. The relationship between the hydrolytic stability and branched structure of cured MUF resin was disclosed. The TG and DSC curves of MUF and UF resins were obtained by the differential scanning calorimetry (DSC) at the normal pressure. Their DTG curves were obtained by taking the first derivative of TG curves. The DTG curve shows the variation of the mass-loss rate of UF resin and MUF resin with temperature. The results indicate that the hydrolytic stability of cured MUF resin is lower than that of cured UF resin. The melamine decreases the hydrolytic stability of cured MUF resin by increasing the branched degree of cured MUF resin. The melamine added at different stages affects the branching structure of cured MUF resins in different ways.

Adsorption behavior and application performance of branched aliphatic alcohol polyoxyethylene ether phosphate

Phosphate ester surfactants has been extensively studied in the recent past. However, the information on detailed studies on branched alcohol ether phosphates is only sparsely reported in the literature. To help cover this gap in the research of branched alcohol ether phosphates, in this article, branched alcohol ether phosphates (A13E5P, A10E5P) as the main research object and linear alcohol ether phosphates (A12E5P) as the control group. By measuring the static surface tension (SST), dynamic surface tension (DST) and dynamic contact angle (DCA) of the samples, the adsorption performance of AEP with different hydrophobic structures was studied. Studies have shown that the branching structure strengthens the hydrophobic effect, which brought lower surface tension, higher surface activity, and more excellent wetting properties. And it is found that the change of ionic strength has a greater effect on the branched AEP. In addition, the branched AEP showed better permeability, while linear AEP showed better foam performance, antistatic performance and softness. This paper shows that the branched structure of AEP is beneficial to improve the adsorption performance of the gas-liquid interface, but not to the adsorption of the solid-liquid interface.

四种不同生活型树种细根寿命及影响因素

PDF HTML阅读 XML下载 导出引用 引用提醒 四种不同生活型树种细根寿命及影响因素 DOI: 10.5846/stxb201904020641 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（30800137，31270489） Fine root lifespan and influencing factors of four tree species with different life forms Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以4种不同生活型树种（常绿阔叶和针叶树种、落叶阔叶和针叶树种）为研究对象，通过微根管法现地观测细根的生长动态，比较不同生活型树种细根寿命在种内和种间的差异，探讨影响细根寿命的主要因子，研究结果对理解和预测森林生态系统碳及养分循环过程具有重要的理论意义。结果表明：（1）细根形态特征（分枝结构和直径）显著影响种内细根寿命，分枝等级越低、直径越小，细根的寿命越短；（2）4个树种的细根寿命表现出明显的土层效应和季节效应，即随土壤深度增加，细根的累积存活率逐渐增加，寿命延长；而不同季节出生的细根其寿命长短模式在树种间不一致，春季或夏季出生的细根寿命要长于秋冬季；（3）常绿树种（柳杉、石栎）的细根寿命要长于落叶树种（池杉、麻栎），同时，针叶树种（池杉、柳杉）的细根寿命要长于阔叶树种（麻栎、石栎）。在同一树种内，细根寿命受细根直径、根系分枝结构、土壤环境因子（土层）等因素显著影响，但在不同树种间，细根寿命可能更依赖于树木生长速率、碳分配模式等树木整体的功能性状差异。 Abstract:In this study, four tree species with different life forms (evergreen broad-leaved, coniferous species, deciduous broad-leaved, and coniferous species) were used as the experimental materials. The growth dynamics of fine roots were observed by minirhizotron method. We compared differences in the root lifespan for tree species with different life forms within and between species, and also explored the main factors affecting the lifespan of fine roots. The study would help us to understand carbon and nutrient cycling processes in forest ecosystems. The results showed that: (1) fine root morphological characteristics (branched structure and root diameter) significantly affected the lifespan of fine roots within the species. The fine root lifespan with the lower branching order and the smaller diameter was shorter than that of the higher-order roots and the coarser roots. (2) The root lifespan showed obvious soil layer effect and the seasonal effect, that is, with the increase of soil depth, the cumulative survival rate of fine roots gradually increased and the root lifespan was prolonged; while the lifespan pattern of fine roots born in different seasons was inconsistent among tree species. The lifespan of the fine roots born in spring or summer was longer than that born in autumn and winter. (3) The fine roots lifespan of evergreen trees (Lithocarpus glaber and Cryptomeria fortunei) was longer than that of deciduous trees (Quercus acutissima and Taxodium ascendens). The fine root lifespan of conifers trees was longer than that of broadleaf species. Generally, within the tree species, the fine root lifespan is significantly affected by factors such as fine root diameter, root branching structure, and soil environmental factors (soil layer). However, between tree species, fine root lifespan may be more dependent on the differences in functional traits of trees as a whole, such as tree growth rate, carbohydrate distribution patterns. 参考文献 相似文献 引证文献

Crosslinked polybenzimidazole containing branching structure with no sacrifice of effective N-H sites: Towards high-performance high-temperature proton exchange membranes for fuel cells

N-H sites are crucial to proton transportation for phosphoric acid (PA)-doped polybenzimidazole (PBI). However, these sites in crosslinked PBI are easily reacted by crosslinker, leading to a decreasing proton conductivity. Herein, a novel crosslinker is synthesized and a series of crosslinked PBIs containing branched structure without sacrifice of effective N-H sites are prepared using the special crosslinker. The branching structure can effectively elevate free volume and PA absorption of these membranes, while N-H sites in the PBIs still remain for efficient proton transport. The prepared membranes exhibit improved proton conductivity (0.073 S cm−1, 160 °C, anhydrous), mechanical performance and superior oxidative stability. In the case of actual usage in a single cell, a peak power density of 690 mW cm−2 is measured, single-cell performance under laboratory conditions at 160 °C with a constant current load (200 mA cm−2) is maintained for 200 h without membrane degradation, and H2 permeability remains almost unaffected during this test. The results indicate that the crosslinked PBIs containing branching structure with no sacrifice of effective N-H sites can potentially be used as high temperature proton exchange membrane.

Radical polymerization in the presence of peroxide and reducing agent monomer for branched polymers

ABSTRACTIn this article, we report the radical polymerization in the presence of peroxide and commercially available or designed reducing agent monomer (RAM) for the preparation of branched poly(methyl methacrylate)s (PMMAs). The reaction behavior of the RAM was studied by NMR. Triple‐detection SEC (TD‐SEC) analysis was used to confirm the branching structure of the prepared PMMAs and to investigate the influence of peroxide concentration and RAM concentration on molecular weight and branched structure. The obtained branched PMMAs exhibited high molecular weights and relatively narrow polydispersities at high conversion of MMA. Interestingly, a significant increase in molecular weight and degree of branching of the obtained polymers are observed in higher BPO concentration, these results are quite different from that reported in the literature. The unique radical polymerization mechanism in the RAM/BPO redox‐initiated radical polymerization system resulted in branched PMMAs with high molecular weights at relatively high RAM and BPO concentrations. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 833–840

The morphological evolution and β-crystal distribution of isotactic polypropylene with the assistance of a long chain branched structure at micro-injection molding condition

Long chain branching polypropylene (LCBPP) has good application prospect but the synergistic effects of the long chain branching (LCB) structure and complex flow field on the crystallization behavior of LCB polymers are still elusive. In the present work, microparts of isotactic polypropylene (iPP)/LCBPP blends were prepared by microinjection molding (MIM). The effect of the LCB structure on the morphology evolution and the β-crystal distribution in microparts were investigated. Interestingly, adding LCBPP facilitates the formation of oriented β-crystals along the shear direction in the core layer of the microparts but unexpectedly, decreases the relative content of β-crystals due to the heterogeneous nucleation effect of LCBPP. Moreover, the introduction of LCBPP can also improve the orientation degree of the molecular chains and shrink the thickness of the core layer thereby inevitably suppressing the “skin–core” structure which might optimize the properties of MIM parts.

Discovery of new spontaneous sources of amylose-free cassava starch and analysis of their structure and techno-functional properties

Waxy cassava starch (WS) from a spontaneous mutation offer enough advantages to encourage the development of commercial varieties. However, breeding work is limited because only one source of WS was available. This article reports the discovery of five new sources of WS which were compared with commercial (CC) and high amylose (HA) cassava starches (19.9 and 30.2% amylose, respectively). Waxy starch gels were considerably clearer and had higher solubility and swelling power than those from CC. Pasting temperature and peak viscosity in WS were higher (68.5 °C and 1149 cP) than in CC (64.2 °C and 993 cP). No retrogradation or syneresis could be detected in refrigerated gels or after freeze/thaw cycles in any WS gel. Average λmax for WS, CC and HA were 540.2, 591.3 nm, and 607.0 nm, respectively. Amylopectins from WS displayed M¯w between 271 × 106 and 551 × 106 g mol−1, R¯G ranged between 229 and 298 nm and νG values ranged between 0.38 and 0.40 (between the sphere and the random coil). The apparent density distributions in all WS suggested close densities and branching structure. The corrected average number of glucosyl units in a linear chain averaged 21.2 in WS and 23.1 in CC. Amylopectins from WS showed a slightly more branched structure (average 4.8%) than in CC (average 4.3%), but lower than in HA (7.0%). WS exhibited larger average granule size (15.9 μm) compared with CC (14.3 μm). New sources of WS will contribute the breeding efforts to develop successful commercial varieties.

Synthesis of 6H-SiC nanowires on bamboo leaves by carbothermal method

6H silicon carbide (SiC) nanowires were fabricated on bamboo leaves infiltrated with tetraethyl orthosilicate (TEOS) by carbothermal method at 1300–1400°C. The bamboo leaves were the carbon source and template for the growth of SiC. The TEOS was the silicon source. The crystalline structure, morphology, and the distribution of the prepared SiC were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy. The SiC had a hexagonal 6H- structure with diameter of 60 to 160nm and length up to tens of microns. The yield of SiC grown on the top surface of the bamboo leaf was higher and had a branched structure. The SiC on the bottom surface showed a bamboo-like structure. The nanowires were mainly 6H phase, however cubic 3C-SiC phase was found on the divisions in the branch structure and the nodes in the bamboo-like structure. The difference in density of SiC nanowires between the two surfaces is proposed to be related to the structural and compositional differences of the two surfaces. TEOS was preferred to attach the hydrophilic top surface, which led to larger amount of SiC. Meanwhile, the Al content inside the bottom surface prohibited the growth of the SiC nanowires. The growth mechanism of the SiC nanowires is also discussed.

Thermoresponsive extraction of cadmium(II) ions by poly(TPEN–NIPA) gels. Effect of chain length and branched spacer structure on gel formation and extraction behavior

N,N,N’,N’-(tetrakis-2-pyridylmethyl)ethylenediamine (TPEN) derivatives bearing a polymerizable double bond in the substituent structure of the pyridine ring were synthesized and subjected to copolymerization with N-isopropylacrylamide in the presence of azobisisobutyronitrile. The obtained poly(TPEN–NIPA) gels show thermoresponsive swelling/shrinking behaviors, and are used for the extraction of cadmium(II) (CdII) ions from an aqueous solution to examine the relationship between gel characteristics and extraction performance. Polymer gels composed of TPEN derivatives bearing C3, C4, C10 and branched C3 spacer chains were synthesized, and the temperature-dependent Cd ion extraction behaviors of the gels were compared. The gels extracted CdII ions efficiently from the aqueous solution in a swelling state at 5 °C, whereas little extraction was observed at 45 °C in the shrinking state. Poly(TPEN–NIPA) gel with branched C3 spacers (C3b) shows excellent thermoresponsive extraction performance. N,N,N’,N’-(tetrakis-2-pyridylmethyl)ethylenediamine–N-isopropylacrylamide (TPEN–NIPA) gels bearing polymerizable double bonds with different spacer length and branch structure are synthesized. The obtained poly(TPEN-NIPA) gels show thermoresponsive swelling/shrinking behaviors and are used for the extraction of cadmium(II) (CdII) ion. The polymer gels showed a temperature-dependent change of extraction performance between swelling and shrinking. Among these, TPEN gel-bearing C3 spacer with branched structure showed the best performance in CdII extraction.

Effects of Branching on the Pressure−Volume−Temperature Behaviors of PP/CO2 Solutions

The pressure−volume−temperature (PVT) properties of polymer/gas solutions are characterized by determining their volume dilation at a known temperature and pressure. This paper presents the results of an experiment that measured the volume swelling of linear and branched polypropylene (PP) with CO2 using a new PVT measurement apparatus. The swellings and specific volumes for linear and branched PP/CO2 are compared. The swelling mechanism that occurred due to CO2 dissolution, and the effects of the branched structure on volume swelling are investigated and discussed. Due to its entangled branch structure, the branched PP underwent a lesser degree of volume swelling than did the linear PP.

Aggregation behavior of block polyethers with branched structure at air/water surface

The block polyethers with various branch structure, such as TEPA[(PO) 36(EO) 100] 7, TEPA[(PO) 36(EO) 100(PO) 36] 7, and TEPA[(PO) 36(EO) 100(PO) 56] 7 were synthesized. Moreover, the aggregation behavior was investigated via the measurements of equilibrium surface tension, dynamic surface tension, and surface dilational viscoelasticity, in order to probe the effect of the block structure on the property of the branched block polyethers. The surface tension results show that the efficiency and effectiveness of the block polyethers to lower surface tension increase with the increase of the PO group numbers. The maximum surface excess concentration ( Γ max) values and the minimum occupied area per molecule at the air/water interface ( A min) values of the branched block polyethers obtained from Gibbs adsorption equations increase and decrease with the increases of the PO group numbers, respectively. The dynamic parameters n and t ∗ representing the diffusion speed of the polyether molecules from bulky solution to the subsurface and from the subsurface to the air/water surface are obtained according to the equation proposed by Rosen. The results show that the n values firstly increase and then decrease and t ∗ values decrease with the increase of the polyether concentrations. The results of surface dilational viscoelasticity show that the dilational modulus of TEPA[(PO) 36(EO) 100(PO) 56] 7 is the largest among the three block copolymers at the low concentration (<1 mg L −1) but that of TEPA[(PO) 36(EO) 100] 7 is the largest at the high concentration (>1 mg L −1).

Gas diffusion in a pulmonary acinus model: experiments with hyperpolarized helium-3

Diffusion of hyperpolarized helium-3 in epoxy phantoms was experimentally studied by pulsed-gradient nuclear magnetic resonance (NMR). One phantom with a dichotomic branching structure densely filling a cubic volume was built using the Kitaoka algorithm to model a healthy human acinus. Two other phantoms, one with a different size and the other one with a partial destruction of the branched structure, were built to simulate changes occurring at the early stages of emphysema. Gas pressure and composition (mixture with nitrogen) were varied, thus exploring different diffusion regimes. Preliminary measurements in a cylindrical glass cell allowed us to calibrate the gradient intensity with 1% accuracy. Measurements of NMR signal attenuation due to gas diffusion were compared to a classical Gaussian model and to Monte Carlo simulations. In the slow diffusion regime, the Gaussian model was in reasonable agreement with experiments for low gradient intensity, but there was a significant systematic deviation at larger gradient intensity. An apparent diffusion coefficient Dapp was deduced, and in agreement with previous findings, a linear decrease of Dapp/D0 with D0(1/2) was observed, where D0 is the free diffusion coefficient. In the regime of intermediate diffusion, experimental data could be described by the Gaussian model for very small gradient intensities only. The corresponding Dapp/D0 values seemed to reach a constant value. Monte Carlo simulations were generally in fair agreement with the measurements in both regimes. Our results suggest that, for diffusion times typical of medical magnetic resonance imaging, an increase in alveolar size has more impact on signal attenuation than a partial destruction of the branched structure at equivalent surface-to-volume ratio.

Structural Characterization of Long Unit-Chains of Amylopectin

Long chains (LC) were fractionated by 1-butanol precipitation from isoamylase-debranched amylopectins of rice, maize, wheat, buckwheat, and sweet potato. The structure of the precipitate (LCppt) was characterized by high-performance size-exclusion chromatography (HPSEC) with pre-column labeling with 2-aminopyridine. HPSEC showed that LCppt corresponded to the LC fraction of unit-chain distribution of amylopectin. LCppt had a number-average degree of polymerization of 330-490 and an average-number of chains of 1.2-1.4, indicating that the structure of LCppt is very similar irrespective of its botanical sources and is distinct from amylose. HPSEC revealed that size distribution of LCppt was also similar among the specimens examined. The distribution was distinct from and much narrower than that of amylose. Still, LCppt consisted of a significant amount (by weight) of chains as long as amylose. LCppt contained 5.1-9.4 mol% of branched molecules, which had ∼5 chains per molecule (except for 10 of indica rice IR36), indicating incomplete debranching of the side chains on LC by isoamylase. The structure of the isoamylase-resistant branches is unknown. In this respect, LCppt and amylose appear to have a common branched structure, which is unusual in starch α-glucans.

Synthesis and properties of star-shaped polylactide attached to poly(amidoamine) dendrimer.

Star-shaped polylactide was synthesized by bulk polymerization of lactide with poly(amidoamine) (PAMAM) dendrimer as initiator, which was marked as PAMAM-g-PLA for simplicity. The nonlinear architecture of PAMAM-g-PLA was confirmed by gel permeation chromatograph, nuclear magnetic resonance, and differential scanning calorimetry analysis. Unlike the linear polylactide (PLA) with similar molecular weight, PAMAM-g-PLA had a higher hydrophilicity and a faster degradation rate because of shortened polymer chains and increased polar terminal endgroups due to its branch structure. The highly branched structure significantly accelerated the release of water-soluble bovine serum albumin from PAMAM-g-PLA microspheres, whereas the linear PLA with similar molecular weight exhibited an initial time lag release. This star polymer may have potential applications for hydrophilic drug delivery in tissue engineering, including growth factor and antibodies to induce tissue regeneration, by adjusting the chain lengths of PLA branches.

Details of Dynamic Mechanical Properties of Dendritic Poly(ether ketone)s in Conjunction with their Highly Branched Structure and Degree of Branching

Full Paper: To investigate the effects of unique hyperbranched structure on viscoelastic properties, three fluoroterminated hyperbranched poly(ether ketone)s (HPEKs) with different degrees of branching (i. e., 0.49; HPEK49, 0.62; HPEK62, and 0.67; HPEK67) and the analogous linear poly(ether ketone) (LPEK), whose chemical structure and molecular weights were similar to those of HPEKs, were synthesized and characterized. From the analysis of plots of the dynamic loss modulus G99(x) versus the storage modulus G9(x) of the individual polymers, it was confirmed that the amount of entanglements between polymer molecules decreased as the degree of branching increased, exhibiting a nearly Newtonian behavior particular for the HPEK with degree of branching of 0.67 (HPEK67). Furthermore, the G99(x) versus G9(x) plots indicated the narrowing of molecular weight distribution and/or shortening of branches with increasing degree of branching, being shown to shift the curves from lower to higher G99(x) values. From the master curves of HPEKs obtained by the time-temperature superposition principle, it was investigated that the rubbery plateau region and the crossover of G9(x) and G99(x) started to disappear at a critical value (A 0.62 ‐ 0.67) of the degree of branching, indicating a nearly Newtonian or little entanglement flow. Moreover, it could be predicted from the tendency of the shift factor aT, obtained from the master curve, that the molecular mobility and temperature dependence of individual HPEKs increased as the degree of branching increased. The shift factors of HPEKs fit with the Williams-LandelFerry (WLF) equation resulted in a more temperature dependent non-Arrhenius behavior than that of LPEK as the degree of branching increased, implying a fragile amorphous polymer. From the nonlinear curve fittings of shift factors by the Vogel-Tamman-Fulcher (VTF) equation, it was further quantified that the HPEKs were more fragile than the LPEK and the fragility increased with increasing degree of branching, which indicated that the branching structure induced the fragility in the materials.

Details of Dynamic Mechanical Properties of Dendritic Poly(ether ketone)s in Conjunction with their Highly Branched Structure and Degree of Branching

Details of Dynamic Mechanical Properties of Dendritic Poly(ether ketone)s in Conjunction with their Highly Branched Structure and Degree of Branching