偏氟乙烯/三氟氯乙烯交替共聚物在TATB表面吸附的分子动力学模拟

采用COMPASS力场和NVT正则系综的动力学模拟方法, 搭建了聚合度分别为10, 50和100的偏氟乙烯(VDF)/三氟氯乙烯(CTFE)交替共聚物, 对交替共聚物在1,3,5-三氨基-2,4,6-三硝基苯(TATB)的(0,0,1)晶面上的吸附和结构进行了分子动力学(MD)模拟. 结果表明, 在300～320 K温区, 聚合度为100的VDF/CTFE交替共聚物链对TATB晶体有理想的表面活性和吸附能力, 以train型构象平铺于TATB表面. 通过对聚合度为10的交替共聚物的多链体系在TATB表面吸附的MD模拟, 表明了VDF/CTFE交替共聚物具有非凝聚吸附的高表面活性特征. 对搭建的乙酸乙酯溶剂化的聚合度为50的VDF/CTFE交替共聚物在TATB晶体表面吸附的模拟, 实验证明了溶剂小分子能够降低共聚物链的吸附能力, 且链以tail型构象吸附于TATB表面.     

TATB基PBX结合能的分子动力学模拟

用分子动力学（MD）方法, 模拟计算了四种氟聚合物(聚偏二氟乙烯（PVDF）、聚三氟氯乙烯（PCTFE）、氟橡胶（F₂₃₁₁)、氟树脂(F₂₃₁₄))与TATB(1,3,5- 三氨基- 2,4,6- 三硝基苯)晶体的相互作用. 结果发现, 四种氟聚物与TATB的结合能大小排序为PVDF>F₂₃₁₁>F₂₃₁₄>PCTFE, 各氟聚物在TATB不同晶面上的结合能大小排序为(001)>(010)>(100), 结合能主要由分子间氢键决定.     

TATB/氟聚物PBX沿不同晶面力学性能的分子动力学模拟

用分子动力学(MD)方法, 模拟计算了著名钝感炸药TATB(1, 3, 5-三氨基-2, 4, 6-三硝基苯)与四种氟聚合物[聚偏二氟乙烯(PVDF)、聚三氟氯乙烯(PCTFE)、氟橡胶(F₂₃₁₁)、氟树脂(F₂₃₁₄)]构成的高聚物粘结炸药(PBX)的力学性能. 结果表明, 在TATB中添加少量氟聚物能有效改善其力学性能; 沿TATB不同晶面与氟聚物“粘结”, 构成PBX的力学性能有所不同, 改善力学性能的整体效应为(010)≈(100)>(001).     

核壳型含氟丙烯酸酯共聚物的合成及性能

采用饥饿态半连续种子乳液聚合方法, 在十二烷基硫酸钠(SDS)/辛基苯基聚氧乙烯醚(TX-10)复合乳化剂的作用下, 分别选用甲基丙烯酸三氟乙酯(TFEM)、甲基丙烯酸六氟正丁酯(HFBM)和甲基丙烯酸十二氟庚酯(DFHM)为含氟单体, 合成以丙烯酸正丁酯(BA)、甲基丙烯酸甲酯(MMA)和含氟单体为原料的核壳型结构含氟丙烯酸酯共聚物乳液. FTIR, 1H NMR, TEM和DSC分析结果显示, 获得了BA/MMA/含氟单体的共聚物乳液, 且乳液具有明显的核壳结构. DSC, TGA和SEM-EDX的分析显示, 核壳型结构的共聚物具有优异的热力学稳定性能和成膜性能; 长侧链或短侧链含氟单体对共聚物的热稳定性影响不明显, 但侧链较长的含氟单体所获得的聚合物在成膜过程中更易向表面迁移, 更能体现含氟聚合物的优点.     

两亲性树枝状嵌段共聚物刷的合成与构象研究

近期研究发现两亲性嵌段共聚物刷能引发“有序自发乳化”,一步法制备有序多孔光晶微球.上述研究主要基于侧链为线形聚合物的嵌段共聚物刷,而侧链拓扑结构变化对乳液受限自组装的影响尚不明确.本工作中设计合成了亲水和疏水的降冰片烯基楔形单体,并通过顺序开环易位聚合(ROMP)成功合成了一类两亲性树枝状嵌段共聚物刷.通过核磁氢谱(¹H-NMR)清晰表征了产物的化学结构,凝胶渗透色谱(GPC)表明共聚物的分子量呈较窄的单峰分布,聚合反应过程具有较好的可控性.通过改变单体和催化剂的比例获得不同分子量的共聚物刷,利用凝胶渗透色谱联用光散射(GPC-MALS)研究了侧链结构对聚合物溶液构象的影响,结果显示一代树枝状共聚物刷表现为无规线团构象,而二代产物则呈现棒状构象,单个聚合物链的原子力(AFM)表征证实了上述结果.     

含长氟链丙烯酸酯共聚物的合成及应用展望

采用传统自由基共聚合方法合成了新型的含氟大分子单体PFMA-MA,并将其与甲基丙烯酸甲酯(MMA)、丙烯酸异丁酯(IBA)和γ-甲基丙烯酰氧基丙基三甲氧基硅烷(MPTS)进行自由基共聚合成了长氟链丙烯酸酯共聚物(ACLC)。对该聚合物的表面性能以及本体性能进行了研究。结果表明,少量的PFMA-MA便可使得到的共聚物ACLC的憎水性大幅度提高。通过X射线光电子能谱(XPS)研究大幅提高憎水性的机理,结果表明ACLC中的长氟链段具有强烈的迁移特性,氟原子富集于表面,使得材料憎水性得到提高。ACLC具有优异的附着力、硬度和低吸水率。含长氟侧链梳形丙烯酸酯共聚物有望应用在疏水、防水涂层材料等领域。     

孔雀石绿分子印迹聚合物的制备及其吸附

采用本体聚合法制备了孔雀石绿分子印迹聚合物,对功能单体的种类及用量、交联剂用量、模板浓度和聚合时间等参数进行了优化,并通过等温吸附实验,考察聚合物的吸附性能。 结果表明,以α-甲基丙烯酸为功能单体,当孔雀石绿、α-甲基丙烯酸和乙二醇二甲基丙烯酸酯的摩尔比为1∶4∶20时,所合成的聚合物具有最大的吸附容量,印迹因子（α=QMIP/QNIP）可达到3.6,表明合成的印迹聚合物对孔雀石绿有良好的识别和富集能力。     

乙烯基二联苯单体的螺旋选择性自由基聚合

为了深入理解乙烯基二联苯单体自由基聚合过程中的手性传递,进行了手性单体(+)-2-[(S)-异丁氧羰基-5-(4′-己氧基苯基)苯乙烯、非手性单体2-丁氧羰基-5-(4′-己氧基苯基)苯乙烯的均聚反应及它们二者的共聚反应,探讨了聚合温度和溶剂性质对手性单体均聚物旋光活性、手性单体含量对共聚物旋光活性以及聚合反应溶剂的超分子手性对共聚物旋光活性的影响.研究发现,降低聚合温度、采用液晶性反应介质有利于得到旋光度大的聚合物;少量手性单体的引入即可诱导共聚物形成某一方向占优的螺旋构象,比旋光度随手性单体的含量增加呈线性增长;在胆甾相液晶中制备的非手性单体聚合物不具有光学活性.这些结果表明,该类乙烯基二联苯聚合物具有动态螺旋构象,其光学活性主要依赖于主链的立构规整度和侧基不对称原子的手性.     

Fe(acac)_3-Al(i-Bu)_3-α,α′-联吡啶催化丙烯腈与苯乙烯共聚合

研究了Fe(acac)3-A l(i-Bu)3-α,α′-联吡啶(acac=乙酰丙酮)催化体系催化丙烯腈(AN)与苯乙烯共聚合,用元素分析和核磁共振研究了共聚物的结构,在单体比为1∶1时共聚物中丙烯腈/苯乙烯含量分别为49.3%和50.7%.用凝胶渗透色谱研究了聚合物分子量和分子量分布,共聚物分子量分布较窄.动力学研究表明共聚合反应对单体浓度呈一级关系,表观活化能为57.8 kJ/mol.     

接枝改性PVDF基含氟聚合物

聚偏氟乙烯(PVDF基)含氟聚合物由于其独特的性能受到了广泛的关注。将功能化链段引入PVDF基含氟聚合物可以进一步提升其性能并拓展其应用领域。相较于物理共混法和直接共聚改性法,通过接枝改性法将功能化单体引入含氟聚合物的侧链具有更显著的优势,可便捷、高效地得到组成精确,结构可控的接枝共聚物。本文综述了通过活性自由基聚合(包括ATRP、SET-LRP、有机催化原子转移自由基聚合(O-ATRP)、光诱导Cu(Ⅱ)介导RDRP)和高能射线辐射(γ射线,紫外,电子束)等对PVDF基含氟聚合物功能化接枝改性的方法,并对其发展趋势以及改性聚合物的应用前景进行了展望。     

Molecular dynamics simulation of mechanical properties of TATB/fluorine-polymer PBXs along different surfaces

TATB (1,3,5-triamino-2,4,6-trinitrobenzene) is the well-known high insensitive explosive. With TATB as the main body (90% and above) the polymer bonded explosives ( PBXs) contain a small amount of poly-mers (5%―10%). The composite materials with good saf…     

Molecular dynamics simulations of trans-1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin-based polymer-bonded explosives

Molecular dynamics has been applied to investigate the low-sensitivity explosive TNAD (trans-1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin)-based polymer-bonded explosives (PBXs) with four typical fluorine polymers, PVDF (polyvinylidenedifluoride), PCTFE (polychlorotrifluoroethylene), F(2311) (fluorine rubber), and F(2314) (fluorine resin). The elastic constants, mechanical properties (tensile modulus, bulk modulus, shear modulus, and Poission ratio), binding energies, and detonation performances are first reported for the TNAD-based PBXs. The results show that the mechanical properties of TNAD can be effectively improved by the addition of small amounts of fluorine polymers, and the overall effect of fluorine polymers on the mechanical properties of the PBXs along three crystalline surfaces is (001) > (010) > (100). On each crystal surface, improvement in the ductibility made by the fluorine polymers changes approximately in the sequence of PVDF > F(2311) > F(2314) > PCTFE. The binding energies between different TNAD crystalline surfaces and different polymer binders with the same chain segment or mass fraction both decrease in the order of (010) > (100) > (001). The binding properties of the polymers with the same chain segment on each crystal surface of TNAD increase as PVDF < F(2311) < F(2314) < PCTFE, while those of different polymers in the same content decrease in the sequence of PVDF > F(2311) > F(2314) > PCTFE. The detonation performances of the PBXs decrease in comparison with the pure crystal, but they are superior to those of TNT.     

Understanding interactions between poly(styrene-co-sodium styrene sulfonate) and single-walled carbon nanotubes

Understanding formation mechanisms of hybrids of carbon nanotubes (CNTs) wrapped by polymers and their interactions is critical in modifying solubility of CNTs in aqueous solution and developing new nanotube-based polymer materials. In the present work, we investigate the structural details of poly(styrene-co-sodium styrene sulfonate) (PSS) wrapping around the CNT and the interactions between the PSS chain and the CNT using molecular dynamics (MD) simulations. The fraction of sulfonated groups significantly influences the wrapping conformations of the PSS chain. Due to limited time scale in the MD simulations, two different initial conformations of the chains are introduced to explore the effect of the initial state on the wrapping behavior. When the chains initially wrap around the CNT in a perfect helix manner, more compact pseudo-helical conformations are obtained. For initial straight line arrangement of the chain monomers, the chains adopt looser wrapping conformations. The free-energy analysis and binding interaction of the PSS chain on the CNT surface take a glance on the relationship between the conformational transition of the chain and the energy evolution.     

Determination of the polymer tacticity from calculation of infrared spectra based on classical molecular simulations

The infrared absorption spectra of poly(tetrafluoroethylene), PTFE, and poly(chlorotrifluoroethylene), PCTFE, are simulated using a method based on a combination of classical molecular simulations of the amorphous polymer phase with Kramers-Kronig relations. The differences and the analogies between experimental and calculated spectra of the non-stereoregular fluoride polymer, PTFE, are first reported. The isotactic and syndiotactic configurations of PCTFE are then investigated. The comparison between experimental and simulated spectra is established on a vibrational analysis. It reveals the preferred syndiotactic configuration adopted by the PCTFE chain.     

Stoichiometric polyelectrolyte complexes as comb copolymers

The collapse behavior of a single comblike copolymer chain has been studied by Monte Carlo simulations. It has been supposed that the solvent is good for the side chains but the solvent quality for the backbone chain changes. It has been shown that depending on the structural parameters of the comb copolymer (the lengths of the backbone and side chains, grafting density of the side chains) various thermodynamically stable morphologies of the collapsed backbone chain can be realized. In addition to ordinary spherical globule we have observed elongated structures as well as necklace-like conformations. The proposed model can be used to describe conformational behavior of stoichiometric complexes between block copolymers with a polyelectrolyte short block and oppositely charged linear homopolymers.     

Solid-state 19F MAS NMR study on the conformation and molecular mobility of poly(chlorotrifluoroethylene)

The temperature dependence of molecular mobility and conformational changes of poly(chlorotrifluoro- ethylene) (PCTFE) have been investigated by solid-state (19)F magic angle spinning (MAS) NMR spectroscopy. The pulse techniques of dipolar-filter and T(1rho)-filter allow selective observation of the amorphous and crystalline domains, respectively. The temperature dependence of T(1rho) (F) revealed that the segmental motion in the amorphous domain becomes vigorous above ca 80 degrees C, which is well above the glass transition (T(g)) temperature (52 degrees C) and more close to the beta-relaxation temperature (95 degrees C). On the other hand, vigorous molecular motions in the crystalline domain occur above 120 degrees C, which is much below the melting temperature (212 degrees C). This indicates that the polymer chains in the PCTFE crystallites are more mobile than those of typical semicrystalline fluoropolymers like poly(vinylidene fluoride) (PVDF), which can be associated with structural imperfections in the crystallites. In addition, the density functional theory (DFT) calculations of (19)F magnetic shielding suggest that the high-frequency shifts observed for the crystalline signals above 80 degrees C can be ascribed to the conformational change around meso diads toward more twisted and/or helical conformations in the main chain.     

Conformation studies on sol-gel transition in triblock copolymer solutions

The gelation of physically associating triblock copolymers in a good solvent was investigated by means of the Monte Carlo simulation and a gelation process based on the conformation transition of the copolymer that was described in detail. In our simulative system, it has been found that the gelation is closely related with chain conformations, and there exist four types of chains defined as free, dangling, loop, and bridge conformations. The copolymer chains with different conformations contribute to the formation of gel in different ways. We proposed a conformational transition model, by which we evaluated the role of these four types of chains in sol-gel transition. It was concluded that the free chains keeping the conformation transition equilibrium and the dangling conformation being the hinge of conformation transition, while the chain with loop conformation enlarges the size of the congeries and the chain with bridge conformations binds the congeries consisted of the copolymer chains. In addition, the effects of temperature and concentration on the physical gelation, the association of the copolymer congeries, and the copolymer chain conformations' distribution were discussed. Furthermore, we employed the structure factor analysis to study the association of copolymer conformations and long-range order of the simulation system and found our results are in agreement with the previous experimental conclusions.     

TATB/氟聚物PBX力学性能、结合能和爆炸性能的模拟计算

Molecular dynamics （MD） method was used to simulate 1,3,5-triamino-2,4,6-trinitrobenzene （TATB） coated with fluorine containing polymers. The mechanical properties and binding energies of PBXs were obtained. It was found that when the number of chain monomers of fluorine containing polymers was the same, the elasticity of TATB/F2314 was increased more greatly than others and the binding energy of TATB/F2311 was the largest among four PBXs. Detonation heat and velocity of such four PBXs were calculated according to theoretical and empirical formulas. The results show that the order of detonation heat is TATB〉TATB/PVDF〉TATB/F2311〉TATB/ F2314 〉 TATB/PCTFE while the order of detonation velocity is TATB/PVDF 〈 TATB/F2311 〈 TATB/F2314 〈 TATB/PCTFE 〈TATB.