Micromechanisms of Tack of Soft Adhesives Based on Styrenic Block Copolymers

The tackiness of model soft adhesive layers based on styrene‐isoprene‐styrene block copolymers and a tackifying resin were investigated with a flat‐ended cylindrical steel probe. The contact between the probe and the adhesive was maintained for 1 s at a nominal pressure of 1 MPa before being detached at a constant velocity. The effect of resin content, probe velocity during debonding and temperature were systematically investigated. Failure was initiated by two main mechanisms: an interfacial cavitation at low debonding rates, giving relatively low adhesion energies, and a bulk cavitation process at higher debonding rates, which gave much higher adhesion energies. In both cases failure occurred at the end by interfacial detachment of fibrils. The characteristic probe velocity where the transition between these two mechanisms took place was controlled primarily by the linear viscoelastic properties of the adhesives. However, the important quantitative parameters obtained from a tack test, i.e., the maximum debonding stress and the adhesion energy, could not be predicted by the linear viscoelastic properties of these adhesives alone.     

RAFT聚合制备嵌段共聚物的研究进展

RAFT聚合具有反应条件温和,对单体纯度和环境的要求相对较低等优势,近年来通过RAFT方法制备嵌段共聚物已经受到了高分子化学领域研究者的广泛关注。简要介绍了近10年来通过RAFT方法制备嵌段共聚物所常用的RAFT试剂和单体的研究进展,主要介绍了近10年来线型两嵌段、三嵌段共聚物和星型嵌段共聚物的RAFT聚合及应用。     

新型聚硅氧烷嵌段共聚物制备的研究进展

综述了近年来国内外嵌段聚硅氧烷的研究进展,对几种主要类型的嵌段聚硅氧烷,即纯聚硅氧主链嵌段型、聚氨酯型、聚烯烃型以及聚醚型作了较全面的总结,并对其应用前景进行了展望。     

Conformation of Styrene-Isoprene Block Copolymers in Dilute Solution

Abstract

Viscosity, gel permeation chromatography and light scattering data for two-and three-block copolymers of styrene and isoprene of various compositions and molecular weights have been determined in methylisobutyl ketone at 35°, a near theta solvent for both polystyrene and polyisoprene. The three techniques show that the molecular dimensions of the copolymers are only slightly larger than the sum of the unperturbed dimensions of individual sequences. Such results are interpreted in favour of a nearly segregated conformation with a limited number of heterocontacts.     

水溶性线型-超支化嵌均共聚物的合成及表征

采用三羟甲基丙烷三马来酸单酯(TMPTM)与甲基丙烯酸(MAA)在水中进行自由基共聚,合成线型-超支化嵌均聚合物(LHBPs)。单体竞聚率数值表明TMPTM与MAA之间为典型的嵌均共聚,NMR、lg[η]-lgMw关系规律以及支化因子g'研究结果表明,当单体摩尔比n(MAA)/n(TMPTM)小于48时,产物显示超支化聚合物特征,当n(MAA)/n(TMPTM)≥48后,聚合物呈线型聚合物特征。DSC分析表明,LHBP-3聚合物玻璃化转变温度约为209.98℃;TGA表明,在50~600℃升温过程中,LHBP聚合物有两次分解,分解温度分别为206.38℃(脱羧)和429.57℃(骨架分解)。     

ATRP以及ATRP法制备嵌段共聚物研究进展综述

原子转移自由基聚合(ATRP)是合成嵌段共聚物的有效途径。本文介绍了原子转移自由基聚合(ATRP)的基本原理以及ATRP在反应体系,实验方案的研究进展,并且概述了近年来采用ATRP制备嵌段共聚物的研究进展。     

离子液体在萃取有机物方面的应用

近些年来,世界各国学者对离子液体的研究越来越多,随着对离子液体研究的深入,离子液体的应用逐渐渗透到各个领域中。主要介绍近年来离子液体在萃取有机物方面的应用进展。     

Solid Polymer Electrolyte Complexes of Polyoxyethylene-Containing Star-Shaped Block Copolymers and Copolymers with Uniform Grafts

Ionic conductivities of salt complexes of polyoxyethylene (PEO)-containing star-shaped block copolymers and copolymers with uniform grafts were measured. The results were compared with the thermal characteristics and crystallinity of the complexes obtained from DSC and WAXD analysis. The conductivity increases with PEO content of the copolymers, more noticeably at PEO contents over 50%. For the complexes of the star-shaped block copolymers of styrene (S) and ethylene oxide (EO), conductivity decreases in the following order of salts: KCNS > NH₄CNS > NaCNS. The room temperature conductivity of the KCNS complex with EO/K ratio = 20 can reach a value of 2 × 10^?5 S cm^?1 at 57% PEO content of the copolymer. The complex with FeCl₂ displays a conductivity even higher than that of the NaCNS complex. Addition of γ-butyrolactone reduces the crystallinity and enhances markedly the ionic conductivity. For complexes of the copolymers with uniform PEO grafts the conductivity decreases in the following order of salts: KCNS > LiClO₄ > FeCl₂. Complexes with LiClO₄ exhibit a maximum conductivity at EO/Li = 20. For different kinds of copolymers with uniform PEO grafts, conductivity of the complexes increases in the order: PS-g-PEO < PMMA-g-PEO < polymethyl acrylate-g-PEO.     

PA6-b-PPG嵌段共聚物的合成与表征

以己内酰胺、己二酸、聚丙二醇(PPG)等为原料,采用高压反应釜进行熔融缩聚,合成了一系列热塑性弹性体尼龙6-b-PPG(PA6-b-PPG)嵌段共聚物。通过傅立叶变换红外分析、核磁共振氢谱对其化学结构进行表征,通过差示扫描量热、热失重分析其热性能,通过差示扫描量热分析、广角X射线衍射及偏光显微镜分析其结晶性能,并测试了材料的力学性能。结果表明,聚合产物为PA6硬段与PPG软段的嵌段共聚物;制备的系列PA6-b-PPG嵌段共聚物熔点在209~225℃之间,起始热分解温度在380~397℃之间。随着PPG含量的增加,PA6-b-PPG嵌段共聚物从γ型结晶向α型结晶转变,密度、硬度、拉伸强度、弯曲强度逐渐降低,而断裂伸长率逐渐增加。可以通过调整软硬段的比例得到不同力学性能的PA6-b-PPG嵌段共聚物,以满足不同条件下的需求。     

热塑性弹性体SBC的生产及其在塑料改性方面的应用

介绍了热塑性弹性体SBC的生产技术现状及进展,分析了国内外SBC的生产消费现状及发展前景,提出了发展我国SBC生产的建议。     

Polyester-Polyether Block Copolymers II. Thermal and Mechanical Properties of Poly(hexamethylene terephthalate)/Poly(oxytetramethylene) Block Copolymers

The melting and crystallisation behaviour of crystalline phases in poly (hexamethylene terephthalate)/poly(oxytetramethylene) block copolymers have been investigated in relation to copolymer composition and polyether block molecular weight (m.w.). In contrast to that in corresponding homopolymer blends, the polyester crystallinity in the block polymers is greatly reduced by incorporation of polyether units, though some persists even at low polyester contents. Concomitant changes in the glass transition temperatures show part of the polyester component to form a homogeneous component of the amorphous phase. The mechanical properties change with composition in parallel with the changes in copolymer crystallinity and T_g. Copolymers with 20-60 w % of poly(oxytetramethylene) units of m.w. 2000 are highly extensible elastomers. Those with higher m. w. polyether blocks have higher modulus and strength but suffer a serious loss of properties at 60d?C. The observations are interpreted in terms of a model in which polyester crystallites (and polyether crystallites also, for the higher m. w. polyether blocks) are supported within an amorphous matrix by tie-molecules whose nature changes with the copolymer compositions. The results are compared with those for analogous polyester-polyethers having different structural components.     

Glycidyl Azide‐butadiene Block Copolymers: 2 Synthesis from a Mesylated Precursor

Glycidyl azide‐butadiene block copolymers are potential binders for solid propellants. The azidic part contributes to the overall energy outputs, while the butadiene block improves the mechanical properties. Synthetic strategies proposed in literature are not appropriate for production of large‐scale quantities. The mesylation of one homopolymer, followed by reaction with the OH terminal groups of the second is proposed here. The reaction is simple and does not show the drawbacks of the previously suggested alternatives. The block copolymers can be used as “partially” energetic binders. Moreover, they work well as compatibilizer in mechanical blends of the two homopolymers, that otherwise rapidly segregate in two distinct phases.     

苯乙烯类嵌段共聚物的国内外市场

分析了国内外苯乙烯类嵌段共聚物(SBC)的供需状况，提出了发展我国SBC生产的一些建议。     

Polyester-Polyether Block Copolymers III. Supramolecular Texture in Poly(hexamethylene terephthalate)/Poly(oxytetramethylene) Block Copolymers and Related Homopolymers and Blends

Optical and electron microscopy and small-angle X-ray scattering have been used to investigate the texture of poly(hexamethylene terephthalate)/poly(oxtetramethylene) multi-block copolymers. The findings are consistent with a substantial separation of the combined sub-species into separate phases, and with the aggregation of the alkylene terephthalate ‘hard’ segment blocks into crystalline forms analogous to those of the homopolymer alone and connected by microfibrillar units. The observations are correlated with the mechanical properties of the copolymers in terms of a ‘string of beads’ model, and compared with existing knowledge of phase-separation morphology in other families of block copolymers. Some investigation has also been made into the morphology of poly(hexamethylene terephthalate) and poly(oxytetramethylene) homopolymers and their blends crystallised from the melt. The results are considered in relation to the properties of the corresponding copolymers.     

Microstructure Control in Block and Graft Copolymers,and Polymer Blends

Block and graft copolymers with incompatible sequences exhibit characteristic morphological behavior and interesting properties, owing to microdomain formation in the solid state. The thermodynamic approach to the problem of microdomain formation for block copolymers has been worked out [1–5] by demonstrating that the morphology of the domain structure-such as equilibrium size, shape, and interfacial thickness-can be described in terms of a balance of physical factors. It has been established, especially by electron microscopy, small-angle X-ray scattering, and X-ray diffraction, that segregated microphases can be spheres, cylinders, or lamellae. The type of morphology adopted by the copolymer essentially depends on its composition [6]. The morphological changes on AB block copolymer will be observed also by changing the selectivity of the casting solvent for the A component in solution-cast films or in ordered solutions [7–9], simply because selectivity changes the ratio between the effective radii or gyration of A- and B-block chains. More recently, a new morphology named “tetrapod-network” structures were found in a block copolymer [10], a three-component pentablock copolymer [11], and in star- block polymers [12–14]. Generally, physical properties of these multicomponent polymer systems depend strongly on the morphology of domain structure. According to the foregoing results, thc establishment of a synthesis method for well-defined block and graft copolymers will be important in the design of the desired morphology of the domain structure (domain spacing and shape).     

Application of GPC in the Study of Stereospecific Block Copolymers

Abstract

Three different techniques involved in the preparation of Stereospecific block copolymers were studied using gel permeation chromatography (GPC). These techniques involved the use of a monofunctional organo-lithium catalyst, a difunctional organolithium catalyst, and a combination of a monofunctional organolithium catalyst and a coupling technique. GPC curves were obtained on the block copolymers using two different column sequences and solvents. The ABA block copolymers studied contained styrene, vinyl toluene, or α-methyl styrene as thermoplastic monomers and butadiene as the elastomeric monomer. The results obtained showed that block copolymers prepared using monomers and catalyst systems free of impurities generally exhibited single peaked GPC curves. In systems where impurities were found to be present, small amounts of A block homopolymer and AB block copolymer were formed. In such cases, the GPC curves were observed to have two or three peaks.     

Glycidyl Azide‐Butadiene Block Copolymers: Synthesis from the Homopolymers and a Chain Extender

Glycidyl azide polymer (GAP) is an “energetic” alternative to hydroxyl‐terminated polybutadiene (HTPB), but has poorer mechanical properties. Since HTPB‐GAP mechanical blends are markedly biphasic, the use of block copolymers may be the solution to join the advantages of both. The copolymers were synthesized from the homopolymers by using two chain extenders: hexamethylene diisocyanate (HDI) and adipoyl chloride (AdCl). Both reagents gave homogeneous and stable polymeric mixtures, but with HDI there are risks of gelation during reaction. Therefore, the product obtained with AdCl is the best candidate to be used as binder or as compatibilizer in GAP‐HTPB mechanical blends.     

线形-枝状碳硅两亲嵌段聚合物的合成与表面性能

通过对聚乙二醇端羟基烯丙基化及硅氢化加成反应,将疏水性有机硅基团接枝到亲水的聚乙二醇链段两端,得到有机硅接枝单元数量不同的两种线形-枝状两亲聚合物,用NMR、FTIR对其结构进行了表征,并评价了其表面活性。两种聚合物具有良好的表面活性,其临界聚集浓度(CAC)值分别为5.13×10-4mol/L和4.83×10-5mol/L,γCAC值分别为32.48 m N/m和32.21 m N/m。此外,该聚合物水溶液的表面张力-浓度曲线呈现"两段式"变化,说明聚合物分子在空气/水表面上有构象变换过程,而聚合物PEG链段、含硅枝状结构将显著影响吸附层中聚合物的分子构象。