Comparative Study on Properties of PBAT/PBSA Film Modified by a Multi-Functional Epoxide Chain Extender or Benzoyl Peroxide

Poly(butylene adipate-co-terephthalate)(PBAT)and poly(butylene succinate-co-adipate)(PBSA)blend films were prepared with different contents of a multifunctional epoxide chain extender Joncryl ADR-4468(ADR)or benzoyl peroxide(BPO).The long-chain-branching(LCB)introduced by ADR and branched/crosslinked entanglement induced by BPO increased melt elasticity,viscosity and compatibility,as indicated by thermal properties,rheological and morphological analyses.It was found that the elongation at break and the tensile strength were significantly improved,due to the enhancement of compatibility and the interfacial adhesion by the incorporation of ADR or BPO.The best mechanical properties were obtained in PBAT/PBSA/ADR(60/40/0.3)(A4T6A_(0.3))and PBAT/PBSA/BPO(60/40/0.9)(A4T6B_(0.9))films,respectively.With the rapid initiation of chain growth by BPO,it has significantly improved the transparency of the film.ADR and BPO can be used interchangeably in improving the comprehensive properties of PBAT/PBSA films,and it would provide more strategies for developing biodegradable materials for various applications.

Chain Extender-induced Hydrogen Bonding Organization Determines the Morphology and Properties of Thermoplastic Polycarbonate Polyurethane

Thermoplastic polycarbonate polyurethanes(PCUs) are multiblock copolymers that have been applied for medical devices for long time. Aliphatic diols are common chain extenders(CE) involved in the composition of the hard segments of PCU. However, limited knowledge was discovered about how the chemical structure of CE affects the hydrogen bonding organization within PCUs and their mechanical properties.To investigate this problem, a group of PCUs were synthesized respectively by extending the polymer chain with 1,4-butanediol(BDO),aminoethanol(MEA), ethanediol(EO) as three kinds of chain extenders. Tiny differences in the CE chemical structure results in remarkable variations in phase separation, condensed morphologies, thermal and mechanical properties, which are characterized by Fourier transform infrared spectrometer, atomic force microscopy, small-angle X-ray scattering, differential scanning calorimetry, and tensile tests. The microstructural evolution during unilateral deformation and the different mechanism induced by the different CEs was probed and unveil by in situ wide-and small-angle X-ray diffraction. Symmetry of CE can improve the organization of the hydrogen bonding. The coherence strength of the urethane/urea group also plays a key role by comparing the two PCUs with ethanediol and aminoethanol.

Effect of Chain Extender on Hydrogen Bond and Microphase Structure of Biodegradable Thermoplastic Polyurethanes

Thermomechanical properties of polyurethanes（PUs） strongly depend on the molecular interactions and microphase structure. In this work, two chain extenders with different ratios, flexile 1,4-butanediol（BDO） and branched trimethylolpropane mono allyl ether（TMPAE）, are used to tune the molecular interactions and microphase structures of a series of biodegradable thermoplastic polyurethanes（TPUs）. In TPUs, the biodegradable polycaprolactone（PCL, M_n of 2000） is used as soft segment while 1,6-diisocyanatohexane（HDI） and chain extenders are used as hard segment. Fourier transform infrared spectroscopy（FTIR）, proton nuclear magnetic resonance spectroscppy（~1 H-NMR）, gel permeation chromatography（GPC）, differential scanning calorimetry（DSC）, dynamic mechanical analysis（DMA） and mechanical tests were performed to characterize the bulk structure and properties of TPUs. Compared with BDO, the steric bulk of TMPAE is larger. The increment of TMPAE can help to increase the hydrogen bond content, microphase separation, and the elastic modulus ratio（R）, which would strongly affect the thermomechanical property of the TPUs. The results of this work verify the importance of the structure of chain extender on the properties of TPUs. It provides valuable information for further understanding the structure-property relationships of these polyurethanes.

Melt Synthesis and Characterization of Poly(L-lactic Acid) Chain Linked by Multifunctional Epoxy Compound

High molecular weight（Mw） poly（L-lactic acid）s（PLLAs） were synthesized using multifunctional epoxy compound（Joncryl-ADR4370） as chain extender. The products were characterized by gel permeation chromatography（GPC） and spectroscopy（1HNMR and FTIR）. The results indicated that the Mw of PLLA increased with the increasing of the ratio of epoxy compound and the extending of reaction time. The highest Mw of PLLA reached 360 000 g/mol when the ratio of epoxy compound was 1.5 wt%. However, the reactants turned to cross-linking when the ratio of epoxy compound was over 1.5 wt%. Differential scanning calorimetry（DSC） measurements demonstrated that the glass transition（Tg） and melting temperatures（Tm） of products increased slightly as the increase of the molecular weight. Analysis of the hydrolytic degradation in vitro showed that the branched PLLA possessed the quicker degradability than that of the linear PLLA.

Testing and Evaluation for Web Usability Based on Extended Markov Chain Model

As the increasing popularity and complexity of Web applications and the emergence of their new characteristics, the testing and maintenance of large, complex Web applications are becoming more complex and difficult. Web applications generally contain lots of pages and are used by enormous users. Statistical testing is an effective way of ensuring their quality. Web usage can be accurately described by Markov chain which has been proved to be an ideal model for software statistical testing. The results of unit testing can be utilized in the latter stages, which is an important strategy for bottom-to-top integration testing, and the other improvement of extended Markov chain model (EMM) is to present the error type vector which is treated as a part of page node. this paper also proposes the algorithm for generating test cases of usage paths. Finally, optional usage reliability evaluation methods and an incremental usability regression testing model for testing and evaluation are presented. Key words statistical testing - evaluation for Web usability - extended Markov chain model (EMM) - Web log mining - reliability evaluation CLC number TP311. 5 Foundation item: Supported by the National Defence Research Project (No. 41315. 9. 2) and National Science and Technology Plan (2001BA102A04-02-03)Biography: MAO Cheng-ying (1978-), male, Ph.D. candidate, research direction: software testing. Research direction: advanced database system, software testing, component technology and data mining.

MORPHOLOGY EVOLUTION IN PTFE AS A FUNCTION OF MELT TIME AND TEMPERATURE——Ⅱ.LOW MOLECULAR WEIGHT FOLDED CHAIN SINGLE CRYSTALS AND BAND STRUCTURES

The effect of sintering dispersed and bulk,low molecular weight(M_n=50,000 Da),nano-emulsionpolytetrafluoroethylene(PTFE)particles near their melting point is described.With the nascent particles consisting of ca.75 nm diameter,hexagonal,single crystals,sintering at,e.g.,350℃,results,initially,in merger of neighboring particles,followed by individual molecular motion on the substrate and the formation of folded chain,lamellar single crystals andspherulites,and on-edge ribbons.It is suggested these structures develop,with time,in the mesomorphic“melt”.Sintering ofthe bulk resin yields extended chain,band structures,as well as folded chain lamellae;end-surface to end-surface merger,possibly by end-to-end polymerization,occurs with increasing time.

Synthesis and characterization of N,N-(pyromellitoyl)-bis-L-phenylalanine diacid ester butynediol

N,N-（pyromellitoyl）-bis-L-phenylalanine diacid ester butynediol（PBDCB）from pyromellitic dianhydride（PMDA）,butynediol（2-butyne-1,4-diol）and DL-phenylalanine（DLP）was synthesized.The PBDCB can be used as chain extender for thermoplastic polyurethane.The starting material of N,N-（pyromellitoyl）-bis-L-phenylalanine diacid（PBD）was synthesized through addition reaction between PMDA and DLP.Then,PBD was esterified using triethylamine as catalyst and attached antacids as well as dimethylacetamide（DMAc）as solvent.The obtained PBDCB was characterized using Fourier transformed infrared spectroscopy（FTIR）,nuclear magnetic resonance（1 H NMR）spectroscopy,mass spectrometry（MS）,thermal gravimetric（TG）,and differential scanning calorimetry（DSC）.The results showed that the PBDCB was highly thermal stable.

A Defective Linear Pentachromium Complex for the Enhanced Catalysis of the Cycloaddition of CO2 with Propylene Oxide

Based on the ligand（2,7-bis（α-pyrimidylamino）-1,8-naphthyridine（H2 bpmany））, a linear pentachromium complex [Cr5（μ5-bpmany）4Cl2]PF6（1, μ5-bpmany = 2,7-bis（a-pyrimidylamino）-1,8-naphthyridine） was synthesized. The crystal structure of compound 1 has been characterized by X-ray crystallography. Interestingly, one metal atom in the center is missing in this linear chain, leading to the defective pentachromium metal string structure which is similar with the reported complex [Cr5（μ5-dpznda）4Cl2]（2, dpznda = N^2,N^7-di（pyrazin-2-yl）-1,8-naphthyridine-2,7-diamine）. The central Cr（Ⅲ） ion of 1 is eight-coordinated and is also rare in the chromium complex. The reaction of carbon dioxide with propylene oxide that generates propylene carbonate（PC） when catalyzed by [Cr5（μ5-bpmany）4Cl2]PF6 was investigated. Different reaction conditions including temperature and pressure were studied to optimize the reaction conditions.

Silicone Elastomer with High Elongation at Break Used in Digital Light Processing 3D Printing

3D printing silicone elastomer has demonstrated great potential in diverse areas such as medical devices,flexible electronics and soft robotics.It is of great value to investigate how to improve the mechanical properties,including tensile strength and elongation at break of printed parts.In this work,a light curing system that can be applied in silicone elastomer 3D printing is explored,which is composed of vinyl terminated polysiloxane as the macromer and thiol containing polysiloxane as the crosslinking agent,and a chain extension reaction is also introduced into this light curing system via the addition of the chain extender dithiol molecules,and a light curing system accompanied with chain extension is designed and realized based on the thiol-ene click reaction mechanism.After reinforced with silica fillers,the obtained light curing system can endow the light curing silicone elastomer with better mechanical properties under the condition of a lower viscosity of the precursor,the tensile strength and elongation at break can reach 525.5 k Pa and 601%,respectively.This light curing system provides a feasible method to solve the contradiction between the viscosity of the precursor and the mechanical properties of the light curing elastomer in the digital light processing(DLP)3D printing field.

HIGH SPEED INJECTION MOLDING OF HIGH DENSITY POLYETHYLENE—EFFECTS OF INJECTION SPEED ON STRUCTURE AND PROPERTIES

Thin wall samples of high density polyethylene （HDPE） were prepared via injection molding with different injection speeds ranging from 100 mm/s to 1200 mm/s. A significant decrease in the tensile strength and Young＇s modulus was observed with increasing injection speed. In order to investigate the mechanism behind this decrease, the orientation, molecular weight, molecular weight distribution, melt flow rate, crystallinity and crystal morphology of HDPE were characterized using two-dimensional wide-angle X-ray diffraction （2D-WAXD）, gel permeation chromatography （GPC）, capillary rheometry and differential scanning calorimetry （DSC）, respectively. It is demonstrated that the orientation, molecular weight, molecular weight distribution, melt flow rate and crystallinity have no obvious change with increasing injection speed. Nevertheless, the content of extended chain crystals or large folded chain crystals was found to decrease with increasing injection speed. Therefore, it is concluded that the decrease in tensile properties is mainly contributed by the reduced content of extended chain crystals or large folded chain crystals. This study provides industry with valuable information for the application of high speed injection molding.

Synthesis and characterization of poly(p-dioxanone)-based degradable copolymers with enhanced thermal and hydrolytic stabilities

Herein, we presented a novel biodegradable copolymer via the chain extending reaction of poly(pdioxanone)-co-poly(2-(2-hydroxyethoxy) benzoate)(PPDO-co-PDHB) prepolymer with hexamethylene diisocyanate(HDI) as a chain extender. The structures and molecular weight of PPDO-co-PDHB prepolymer and PPDO-co-PDHB-PU chain-extended copolymer are characterized via hydrogen nuclear magnetic resonance spectroscopy(1 H NMR) and viscosity test. The relationship between the molecular structures and properties of the chain-extended copolymers is established. The PPDO-co-PDHB-PU copolymers possess a better thermal stability comparing with the PPDO homopolymer. The study of mechanical properties shows that the elongation-at-break of PPDO-co-PDHB-PU is much higher than that of PPDO. The investigation of hydrolytic degradation behaviors indicates the degradation rate of PPDO can be controlled by adjusting the PDHB compositions, and proves that chain-extended copolymers exhibit an excellent hydrolytic stability being better than that of PPDO.