Effects of temperature on cure kinetics and mechanical properties of vinyl–ester resins

The relationships among cure temperature, chemical kinetics, microstructure, and mechanical performance have been investigated for vinyl–ester resins. Fourier transform infrared spectroscopy was used to follow the reactions of vinyl–ester and styrene during isothermal curing of Dow Derakane 411‐C‐50 at 30 and 90°C. Reactivity ratios of vinyl–ester and styrene vinyl groups were evaluated using the copolymer composition equation. The results indicate that the ratio of vinyl–ester to styrene double bonds incorporated into the network is greater for 30 than for 90°C cure. Mechanical properties were obtained for systems subjected to isothermal cures at 30 and 90°C and postcured above ultimate T_g. The results show that the initial cure temperature significantly affects the mechanical behavior of vinyl–ester resin systems. In particular, values of strength and fracture toughness for postcured samples initially cured isothermally at 30°C are significantly higher than those obtained for samples cured isothermally at 90°C. Examination of fracture surfaces using atomic force microscopy revealed the existence of a nodular microstructure possessing characteristic nodule dimensions that are affected by the temperature of cure. Such features suggest the existence of phase separation during cure. A binary interaction model in conjunction with chemical kinetic data and estimated solubility parameters was used to evaluate enthalpic interactions between the growing polymer network and monomers of the vinyl–ester system. The results indicate that the interaction energy becomes increasingly endothermic as cure progresses and that this energy is affected by the temperature of cure through differences in copolymerization behavior. Hence, in addition to entropic factors, the changes in enthalpic contribution to the Gibbs free energy suggest that the probability of phase separation increases with extent of cure and that its onset is potentially affected by cure temperature. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 725–744, 1999     

Thermo-mechanical characterisation of in-plane properties for CSM E-glass epoxy polymer composite materials – Part 1: Thermal and chemical strain

The in-plane thermo-mechanical properties and residual stresses of a CSM E-glass/Epoxy material are characterised through the use of DSC and TMA. The measured data is used to generate material models which describe the mechanical behaviour as a function of conversion and temperature. The in-plane thermal expansion coefficient (α) of the composite material decreases above the glass transition temperature (T_g), which is compensated by a higher out of plane deformation above T_g. Comparison of α and chemical shrinkage measurements suggests that chemical bonds between the polymer matrix and the glass fibres are formed prior to shrinkage of the epoxy matrix, i.e., at an early processing stage. This suggests that production of composites with low residual stresses requires focus on reactivity between the matrix and the sizing rather than the matrix cure properties. As a consequence, residual stresses in the composite material are mainly a result of restricted cure shrinkage rather than mismatch between thermal expansion coefficients.     

Microphase separation in solutions of crystallizable segmented polyurethane

At present time the level of microphase separation together with polymer nture is considered to be a main factor in determining the physico‐mechanical properties of polyurethane materials. The researches show that realization of a certain polymer structure and properties of polymer are defined by microstructure of polyurethane chain. The purpose of this work was to study physico‐chemical regularities between nucleation and growth of microphase aggregations in crystallizable segmented polyurethane compstions as a function of the phase state of the system during transferring from comon solvent to a selective solvent. Besides we investigated the architecture of macromolecules, associates and phase particles of segmented polyurethane (SPU) formed in different regions of the phase diagram.     

Structure and extinction of counterflow diffusion flames above condensed fuels: Comparison between poly(methyl methacrylate) and its liquid monomer,both burning in nitrogen–air mixtures

Since poly(methyl methacrylate) is known to depolymerize largely to its monomer when heated, the chemical kinetics in the gaseous diffusion flame produced by this polymer in a fire may coincide with that of burning liquid methyl methacrylate. To test this hypothesis, flat diffusion flames were probed and extinguished adjacent to surfaces of each of these fuels. Profiles of temperature and of concentrations of stable chemical species are reported, as are gas velocities of approach flow required to produce extinction for various oxygen/nitrogen ratios of the stream. Results revealed structural differences attributable to differing thermal properties of the fuels. Many fuel species were observed in the gas phase, their profiles being partially rationalized on the basis of a suggested decomposition mechanism for gaseous methyl methacrylate. Overall kinetic parameters for gasphase combustion, obtained by use of extinction results in a previously developed theory, are nearly the same for the polymer and monomer but appear to differ by amounts exceeding experimental uncertainties. It is suggested that this may be traced to small differences in fuel species leaving the condensed phase which, for the polymer, is covered by a thin, two-phase region.     

一些热塑改性热固性树脂体系结构对反应诱导相分离时间/温度依赖性的影响

利用光学显微镜、DSC等手段研究了一些上临界共溶温度(UCST)类型的热塑性改性热固性树脂体系反应诱导相分离时间/温度依赖性随组分化学结构的变化规律.结果表明,分相活化能Ea(ps)受热塑性树脂的主链结构、热固性单体、交联剂结构、化学计量比等因素的影响.利用相互作用能密度解释了实验所研究的UCST体系的相分离活化能Ea(ps)随组分结构的变化规律.     

Nanomechanical and Chemical Mapping of the Structure and Interfacial Properties in Immiscible Ternary Polymer Systems

It is a challenge to identify each phase in a multi-component polymer system and uniquely determine the interfacial properties between the different phases. Using atomic force microscopy nanomechanical mapping(AFM-NM) and AFM-based infrared spectroscopy(AFMIR), we identify each phase, visualize structural developments, and determine the interfacial properties in a blend of three polymers: high-density polyethylene(HDPE), polyamide(PA6) and poly(styrene-b-ethylene-co-butylene-b-styrene)(SEBS). Each phase can be identified from the Young's modulus, along with the structural development within the phases before and after compatibilization. The interfacial widths between HDPE/PA6,HDPE/SEBS and SEBS/PA6 were determined independently in one measurement from a Young's modulus map. The structural, mechanical property development and identity of the phases were determined by AFM-NM, while AFM-IR, providing complementary chemical information,identified interfacial reactions, showed the chemical affinity of a compatibilizer with the component phases, and mapped the distribution of the compatibilizer in the ternary polymer blends. The chemical, structural and interfacial information obtained by these measurements provide information that is essential for producing mechanically robust materials from incompatible mixtures of polymers.     

Evaluation of polymers based on a silicone backbone as pseudostationary phases for electrokinetic chromatography.

The feasibility of polymeric phases based on a silicone polymer backbone as pseudostationary phases for electrokinetic chromatography has been investigated. Silicone phases were studied because of the range of chemistries that could be developed based on these backbones, and because successful development of silicone phases would make it possible to employ much of the stationary phase chemistry developed in the past thirty years. Three silicone polymer structures have been investigated, but only one had sufficient aqueous solubility to permit application in electrokinetic chromatography. This phase was characterized by a variety of methods and was shown to be a mixture of partially hydrolyzed poly(bis-(3-cyanopropyl) siloxanes. When employed as a pseudostationary phase, this material provided selective and efficient separations. The electrophoretic mobility of the silicone polymer is greater than that of sodium dodecyl sulfate (SDS) micelles and poly(sodium 10-undecenylsulfate), providing an extended migration time range. A striking characteristic of the polymer is that the electrophoretic mobility is greater than typical electroosmotic mobilities. The chemical selectivity of the phase is significantly different from that of SDS micelles or poly(sodium 10-undecenylsulfate). The silicone phase is a more cohesive, basic and polar phase than SDS micelles. In buffers modified with a high concentration of organic solvents, the chromatographic properties of the silicone polymer are inferior to those of the poly(sodium 10-undecenylsulfate). The greatest limitation of silicone polymers for this application appears to be limited aqueous solubility, which will make it difficult to realize a family of such polymers with different chemical selectivities.     

The Research of Biomedical Intelligent Polymer Materials

The properties of biomedical intelligent polymer materials can be changed obviously when there is a little physical or chemical change caused by external condition. They are in the forms of solids, solutions and the polymers on the surface of carrier, and include water solution of hydrophilic polymers, cross-linking hydrophilic polymers(i.e. hydrogels) and the polymers on the surface of carrier. The environmental stimulating factors are temperature, pH value, composition of solution, ionic intention, light intention, electric field, stress field and magnetic field etc.. The properties of intelligent polymer are those of phase, photics, mechanics, electric field, surface energy,reaction ratio, penetrating ratio and recognition etc..Stimulation-response of intelligent water-soluble polymerWater-soluble intelligent polymer can be separated out from solution under special external condition. It can be used as the switch of temperature or pH indicator. When water-soluble intelligent polymer is mixed with soluble-enzyme matter or cell suspension, the polymer can bring phase separation and react with soluble-enzyme matter or cell membrane through accepting some external stimulation. Other water-soluble intelligent polymer is that can make the main chemical group of some natural biomolecular recognition sequence section to arrange on skeleton of polymer at random. It is the same ratio as natural biomolecules.Stimulation-response of intelligent polymer of carrier surface Intelligent polymer can be fixed on the surface of solid polymer carrier through chemical grafting or physical adsorption. When the external conditions are changed, the thickness, humidity and electric field of the surface layer will be changed. Intelligent polymer can be preparated the permanence switch by precipitating into the hole of porous surface, and it can control on-off state of the hole. When protein or cell interacts with intelligent polymer surface to be placed in to open or close, they can be selectively absorbed on hydrophobic surface.Stimulation-response of intelligent polymer hydrogelIntelligent polymer hydrogel's construction, physical property, and chemical property can change with the changing of external environmental conditions. When environmental stimulation signal, for example, solution composition, pH value, ionic intention, temperature, light intention, electric field,magnetic field and substance etc. changes, the intelligent polymer will occur to break of volume.This is the intelligence of polymer hydrogel.The intelligence of these polymers will be widely applied in biomedical fields.     

不饱和聚酯／聚氨酯复合体系的研究

以端羟基不饱和聚酯（ＨＵＰ）与聚氨酯（ＰＵ）浇注型复合网络聚合物（ＣＰＮｓ）为基材，考察了化学动力学及相分离对ＣＰＮ聚合物物理机械性能的影响．数据揭示了不饱和聚酯／聚附聚氨酯（ＨＵＰ／ＰＵ－ｅｓ）ＣＰＮ，当ｒ＝ＮＣＯ／ＯＨ＝０．４时，它的物理力学性能优于不饱和聚酯／聚醚聚氨酯（ＨＵＰ／ＰＵ－ｅｔ）ＣＰＮ或ＨＵＰ／ＰＡＰＩＣＰＮ组成物．最佳ＣＰＮ可通过调整聚氨酯中软段和硬段组分及网络组成而设计与制备．     

Coarse-grained Dynamics Simulation in Polymer Systems: from Structures to Material Properties

Polymers are widely used in our daily life and industry because of their intrinsic characteristics, such as multi-functionality, low cost, light mass, ease of processability, and excellent chemical stability. Polymers have multiscale space-time properties, which are mainly reflected in the fact that the properties of polymer systems depend not only on chemical structure and molecular properties, but also to a large extent on the aggregation state of molecules, that is, phase structure and condensed state structure. Thanks to the continuous development of simulation methods and the rapid improvement of scientific computation, computer simulation has played an increasingly important role in investigating the structure and properties of polymer systems. Among them, coarse-grained dynamics simulations provide a powerful tool for studying the self-assembly structure and dynamic behavior of polymers, such as glass transition and entanglement dynamics. This review summarizes the coarse-grained models and methods in the dynamic simulations for polymers and their composite systems based on graphics processing unit(GPU) algorithms, and discusses the characteristics, applications, and advantages of different simulation methods. Based on recent studies in our group, the main progress of coarse-grained simulation methods in studying the structure, properties and physical mechanism of polymer materials is reviewed. It is anticipated to provide a reference for further development of coarse-grained simulation methods and software suitable for polymer research.     

Oligomeric bisphenol A‐based PEEK‐like phthalonitrile‐cure and polymer properties

The cure behavior and properties of oligomeric bisphenol A‐based PEEK‐like phthalonitrile (PN) are thoroughly examined in this article. The resin is easily processed from the melt at a relatively low temperature (150–200 °C) and the monomer cure occurs in a controlled manner as a function of the amine content and processing thermal conditions. Dynamic mechanical measurements and thermogravimetric analysis show that the polymer properties improve as the maximum PN postcure temperature is increased to 415 °C. The effects of the amine and polymer postcure conditions on the flexural and tensile properties of the PN polymer are investigated. The mechanical properties of the polymer are maximized after postcuring to moderate temperatures (330–350 °C). The polymer exhibits an average flexural strength and tensile strength at break of 117 and 71 MPa, respectively. After oxidative aging at 302 °C for 100 h, the polymer retains excellent mechanical properties. The average flexural and tensile strength retention of the polymers are 81 and 75%, respectively. Microscale calorimetric measurements reveal that the flammability parameters of the oligomeric PN are low compared to other thermosets. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3769–3777     

Synthesis of nonspherical colloidal particles with anisotropic properties

We describe a promising and flexible technique for fabricating uniform nonspherical particles with anisotropic phase and surface properties. Our approach is based on the seeded polymerization technique in which monomer-swollen particles are polymerized. The polymerization causes a phase separation to occur, giving rise to two-phase nonspherical particles. We show that the elastic contraction of the swollen polymer particles induced by elevated polymerization temperatures plays an important role in the phase separation. Moreover, chemical anisotropy of nonspherical particles can be obtained by using immiscible polymer pairs and by employing surface treatments. Furthermore, we are able to produce amphiphilic dumbbell particles consisting of two different bulbs: hydrophilic poly (ethylene imine)-coated polystyrene and hydrophobic polystyrene. Controlled geometries of these amphiphilic nonspherical particles will allow a wide range of potential applications, such as engineered colloid surfactants.     

Curing kinetics and morphology of IPNs from a flexible dimethacrylate and a rigid epoxy via sequential photo and thermal polymerization

The curing kinetics and morphology of Interpenetrating polymer networks (IPNs) formed from a rigid epoxy resin thermally cured by an anhydride, and a photocured flexible dimethacrylate resin, have been studied by temperature ramping differential scanning calorimetry (DSC), near-infrared (NIR), and dynamic mechanical thermal analyzer (DMTA). This combination of cross-linkable resins permits the partial or complete cure of each component independent of the other. Also, since the monomers are polar but chemically dissimilar thermosetting resins, their IPNs should offer considerable variation in properties. DSC studies showed that the possible interactions between each component in the IPN could be minimized, but that the curing rate and conversion of the second polymerizing component was affected by vitrification, network topology, or phase separation in the IPN. NIR was also used to confirm that virtually independent cure was achievable by the combination of the thermal and photochemical methods. Dynamical mechanical thermal analysis was used to investigate the effect of curing one or both components and of order of curing on the phase morphology of the IPN. The modulus in the rubbery region also provided information on loop formation and co-continuity of each network component through the polymer matrix. The modulus and tan δ curves showed large differences in the glass transition region of the IPNs with different curing schedules, however phase separation occurred in all fully cured IPNs. These observations conflict with a previously advanced hypothesis that rapid polymerization and gelation of the last-cured component interlocks the two networks into a single phase structure and leads to the inclusion of a caveat that the components require sufficient attraction for interlocking of the networks to occur.     

AFM nanoindentation to determine Young’s modulus for different EPDM elastomers

AFM nanoindentation was investigated as a method for determining the micromechanical properties of polymer materials. It is generally accepted that the shape of the tip of the cantilever undergoes a change in a standard AFM setup. The shape defines the projected contact area, so it is a parameter directly proportional to the elastic modulus; any change in the shape thus affects the accuracy of the results. The method suggested in this paper relies on the introduction of an experimentally determined tip-area function. Values for Young’s modulus were calculated for EPDM samples with different degrees of cure and crystallinity. The degree of crystallinity has a greater impact on the mechanical properties of the material than the degree of cure. Depending on the amplitude of the indentation, the E-moduli determined by AFM are systematically higher. When studying different regions of polymer materials, the values of the E-modulus determined by AFM become identical to those measured by means of DMA on extrapolation of the modulus at zero indentation.     

接枝共聚法制备聚乙二醇(PEG)/聚乙烯醇(PVA)高分子固-固相变材料性能研究

用接枝共聚法将具有相变特征的聚乙二醇(PEG)接枝到具有较高熔点的聚乙烯醇(PVA)主链上,得到了系列性能稳定的PEG/PVA高分子固-固相转变材料,用DSC,WAXD和POM对其相变行为及形态结构进行了研究.结果表明,该材料呈现出可逆的固-固相转变特性;其结晶峰值温度和相变焓比纯PEG低,接枝率对相变温度和归一化相变焓影响不大;接枝率只影响结晶与熔融行为,不影响结晶结构.     

Interdiffusion at the interface between poly(vinylpyrrolidone) and epoxy

Electron microprobe analysis (EMP) was used to study interdiffusion in bilayer films of thermoplastic poly(vinylpyrrolidone) (PVP) and a thermoset epoxy. The bilayer films were prepared by casting a stoichiometric mixture of the uncured diglycidyl ether of bisphenol A epoxy (DGEBA) and 4,4′-diaminodiphenylsulfone (DDS) on the PVP film and then curing the system in a two-step process under a nitrogen atmosphere. For the EMP studies, the sulfur signal was used as a probe for DDS, while the nitrogen signal served as a probe for both DDS and PVP. The addition of brominated DGEBA to the conventional DGEBA in a 1: 1 weight ratio allowed the bromine signal to be used as a probe for the epoxy phase. It was found that the interfacial thickness was much larger for the film prepared from low molecular weight PVP than that from high molecular weight PVP. Interdiffusion was suppressed when the initial cure temperature in the two-step cure cycle was 130°C compared to 170°C, in which the first stage of the cure reaction dominated the interdiffusion process. More importantly, it was demonstrated that the diffusion front of the curing agent was located closer to the thermoplastic polymer phase as compared to that of the thermoset polymer in the interface region. This tendency was more significant in the system with the larger interfacial thickness. These results have important consequences on interphase structures and properties. They suggest that crosslinking of the epoxy in the interphase may be suppressed because of an insufficient amount of curing agent and that the not-fully-reacted curing agent in the PVP phase may act to plasticize this phase. © 1997 John Wiley & Sons, Inc.     

Chemical transformations and phase transitions in polymer rheology and technology

Fundamental rheokinetic effects observed in processes of linear polymerization and three-dimensional oligomer curing are discussed. It was shown that changes in rheological properties during linear polymerization can be described by relationships based on treating a reactive mass as a polymer solution, if a newly formed polymer is soluble in reactive medium. Phase separation limits this approach and leads to some new rheological consequences such as change in the rate of viscosity growth (in some cases viscosity can even decrease in the course of polymerization). Shearing influences temperature of a phase transition and kinetics of chemical reaction if it proceeds in heterogeneous conditions. The same phenomena were also observed for oligomer curing which can occur in heterogeneous manner with microgelation and formation of colloid particles of a new phase before the gelation of a system as a whole.     

Electrochemical control of solid phase micro-extraction: conducting polymer coated film material applicable for preconcentration/analysis of neutral species

Exploitation of the physical, chemical and electrically conductive properties of poly(3-dodecylthiophene) (P3DDT) for the preconcentration and release in solid phase microextraction (SPME) of organometallic arsenobetaine (AsB) from aqueous media was investigated. Hydrophobic interactions between this neutral arsenic species and an undoped polythiophene (no applied potential) with n-substituted alkyl groups (n=12) in the three position were used for the diffusion-controlled preconcentration. After absorption into the polymer matrix, the chemical properties of this conductive polymer were changed by applying an external potential. This potential provides a sufficient driving force for desorption of the analyte from the extraction phase into an aqueous solution for subsequent analysis. The applied positive potential oxidizes the polymer to its charged hydrophilic state, which releases the neutral analyte. The concentration and speciation of the analyte from the sample matrix was analyzed by HPLC coupled to an ICP-MS. The diffusion-controlled uptake was fast (equilibrium attained within minutes) and did not require pretreatment of the analyte. The electrochemically-controlled release of the analyte is also very rapid (within minutes). This conducting polymer film system, therefore, can offer analytical applications for the convenient preconcentration and subsequent analysis of neutral environmental species.     

Thermotropic rigid chain copolymers I. crystallization kinetics and thermodynamic properties

The kinetics of structure formation and the thermal properties of the ordered phase were analyzed calorimetrically for a rigid polymer, characterized by an irregular chemical structure. The transition from the nematic melt to a partially ordered state was found to involve two different processes, a fast and a slow one. The fast one corresponds apparently to a thermally activated nucleation and growth mechanism, whereas the slow one is strongly self delaying. Its transition rate is only weakly dependent on the temperature. The thermal properties of the ordered phase, resulting from this process, vary strongly with the annealing temperature and annealing time. The enthalpy and entropy of fusion, characteristic for the pure ordered phase, are lower by a factor of about 10 in comparison to the corresponding values of flexible chain molecules.     

溶胶凝胶法制备β-环糊精聚合物/二氧化钛有机-无机杂化材料

通过烯丙基环糊精(allyl-β-CD)与丙烯酸(AA)的共聚合反应在环糊精聚合物链中引入了活性基团羧基, 运用溶胶-凝胶法制备了新型的环糊精聚合物P(CD-co-AA)/TiO₂有机-无机杂化材料. 溶剂抽提结果和FT-IR表明杂化材料中有机无机两相间存在着化学键. 通过XRD, SEM, TGA研究表明有机无机两相高度相容, 热稳定性能有大大的提高. 另外还发现, 在所制的材料中TiO₂的含量对材料的结构和性能有很大的影响, 当TiO₂的含量为60% (w)时, 材料表面均匀光滑, 有机无机两相相容性和材料的热稳定性能最好.