Deformation of elastomeric polyolefin spherulites

The ethylene‐octene block copolymers in this study consist of long crystallizable sequences with low comonomer content alternating with rubbery amorphous blocks with high comonomer content. The crystallizable blocks form lamellae that organize into space‐filling spherulites even when the fraction of crystallizable block is so low that the crystallinity is only 7%. These unusual spherulites are highly elastic and recover from strains as high as 300%. This new class of thermoplastic elastomers is fundamentally different from conventional elastomeric olefin copolymers that depend on isolated, fringed micellar‐like crystals to provide the junctions for the elastomeric network. The elastomeric block copolymers are shown to be unique in that a hierarchical organization of space‐filling lamellar spherulites provides the junctions for the elastomeric network. The deformation of the elastic spherulites is readily studied with small angle light scattering, wide angle X‐ray diffractograms, and atomic force microscopy. At strains in excess of 300%, the spherulites break up into a fibrillar structure following lamellar deformation processes that are similar to those established for high density ethylenic polymers. The crystalline transformation produces a stiffer elastomer that exhibits complete recovery on subsequent loadings. Similar experiments on elastomeric random ethylene‐octene copolymers where fringed micellar crystals provide the physical crosslinks that connect the rubbery, amorphous chain segments reveal significant differences. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1313–1330, 2009     

New polyolefin elastomers from metallocenes

In this paper, new polyolefin elastomers, obtained from metallocene based catalytic systems, are presented. The potentialities of metallocenes for the preparation of polyolefin elastomers are discussed with reference to the traditional vanadium and titanium based catalysts. The role played by a Ziegler - Natta catalyst, either stereospecific or aspecific, is discussed.     

Thermal properties and influence of orientation on crystalline morphologies in stereoblock polypropylene and related elastomers

Atomic force microscopy (AFM), small angle X‐ray scattering (SAXS), temperature modulated differential scanning calorimetry (TMDSC), variable heating rate DSC, an independent rapid heating rate method for melting points, and cyclic mechanical testing were used to study semicrystalline thermoplastic elastomeric polypropylenes (ELPPs) and related semicrystalline polyolefins including ethylene copolymers. Low crystallinity (ca., 9 and 15%) ELPP samples were studied by AFM in the nonoriented and melt‐oriented states. AFM images taken as a function of time after quenching of a melt‐drawn and highly nucleated film resolved details of secondary crystallization involving lateral growth on the ordered row‐nucleated structures. For nonoriented films, isothermal melt crystallization at high temperatures (110 °C) led to similar features for the two ELPPs. The dominant crystalline morphology studied by AFM consisted of small (several nm in width) granular crystallites organized into immature but large spherulites spanning tens of microns. A striking cross‐hatch morphology was detected in regions of the surface in 110 °C crystallized samples, which is contrasted with melt‐drawn films where row nucleated structures dominated the morphology in the film under no external stress. AFM was also used to monitor the morphological changes that occurred as the films were stretched at 25 °C. Break‐down of lamellae was observed, resulting in oriented narrow fibrils. Cyclic stress‐strain curves showed the expected result where lower crystallinity ELPPs had higher recoverable levels of set after both 100 and 500% elongation. TMDSC was used to resolve the broad melting and recrystallization regions in these low to medium crystallinity ELPP systems, and to contrast the results with ethylene copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Photo-oxidation of elastomers. A fundamental approach based on the study of a series of photo-sensitive elastomeric systems: A review

The photo-oxidation and crosslinking of increasingly complex photo-sensitized elastomers were quantitatively investigated. An ethylene-propenebutadiene terpolymer (EPDM), selected as an elastomeric medium exhibiting reactive unsaturated side chains, was photo-sensitized with various chromophoric groups: grafted phenyl groups (systems I and II), different carbonyl functions (systems III and IV), blended photo-initiators dimethoxyphenylacetophenone (DMPA) (system V) and benzophenone (BP) (system VI). Knowledge of the behaviour of these model systems proves necessary to the understanding of the predominant processes involved in the photo-oxidation of ethylene-propene rubber (EPR or EPM) blended with DMPA (system VII) or BP (system VIII) and of a random styrene-butadiene (SBR) copolymer (system IX).     

The influence of thermoplastic elastomers on structure and crystallisation behaviour of polyolefin blends

The influence of a styrene-ethylene/butylene-styrene triblock copolymer (SEBS) on an isotactic polypropylene / polyethylene blend was investigated. For comparison binary blends with polypropylene and SEBS alone were also prepared. The blends obtained by solution mixing were characterised by small-angle x-ray scattering, light microscopy and dynamic mechanical analysis. The role of SEBS as matrix reinforcer or interfacial agent is composition dependent. Experimental data also reveal a different influence of SEBS on the binary blends than on the ternary blends containing polyethylene.     

PP/LDPE共混体系的辐射效应

研究了在多官能团单体—三烯丙基异氰脲酸酯存在下ＰＰ／ＬＤＰＥ共混体系接受γ－辐射的效果。用溶解度参数和ＴＥＭ技术评估了共混体系的相容性与多官能团单体在共混体系中的分布，并用ＳＥＭ、ＤＳＣ、动态力学等方法对共混体系相容性进行了表征。结果表明，ＰＰ／ＬＤＰＥ是不相容的共混体系，三烯丙基异氰脲酸酯主要分布在共混体系的相界面区域，辐照强化了共混体系的相间结合，增加了界面厚度，改善了共混体系的相容性。     

Sealants based on polysulfide elastomers

Processes of vulcanization and adhesion of polysulfide sealants are reviewed and vulcanizing agents constituting polysulfide sealants are described.     

辐射增强PP／BR共混体系的力学性能

研究了在多官能团单体－三烯丙基异氰酸酯存在下，共混体系聚丙烯／１．４－聚丁二烯橡胶的辐射效应，用ＤＳＣ，动态粘弹谱对其进行表征。结果显示，三烯丙基异氰酸酯主要分布于聚丙烯／１．４－聚丁二烯橡胶共混物的界面自高能射线作用下，被引发参与界面反应，从而改善了共混体系的相容性，增强也界面粘接，提高了共混物的力学性能。     

Dynamic elastomers based on bio-derived crosslinker

Petroleum-derived monomers are the most common building blocks for ester-based thermosets. Bio-derived thermoset elastomers are becoming viable alternatives to conventional thermosets. Herein, we developed a biobased vitrimer-type thermoset elastomers using abundant and sustainable raspberry ketone as feedstock. We utilize raspberry ketone to create building blocks for dynamic oxime chemistry and crosslinked these through free radical polymerization with poly(ethylene glycol) methyl ether methacrylate as a comonomer. In contrast to other dynamic networks based on ester bonds, which need catalysts, this is undesirable since catalyst deactivation or leaching lowers its effect over time and may impair reuse. This network incorporates catalyst-free bond exchange reactions in catalyst-dependent polyester networks by substituting oxime-esters for typical ester linkages. The elastomer exhibits stress relaxation, a low glass transition temperature (T_g) (−55 to −40.2°C) and tensile strength up to 5.2 ± 3.0 kPa. Furthermore, the dynamic oxime transesterification exchange mechanism allows elastomers to be reprocessed using a hot press at 160°C and 8 × 10³ kPa pressure. After reprocessing, the tensile strength of elastomers can be recovered up to 78.1 ± 10.9%. This work integrates the principles of catalyst-free dynamic exchange process and mechanical recycling coupled with biobased components to provide a rational solution towards conventional elastomers. In the future, these elastomers can be exploited for the development of hydrogels, recyclable elastomers, and commodity plastics.     

Biopolymers and biomaterials based on elastomeric proteins

Elastomeric proteins represent a very interesting subject of investigation, not only for their molecular mechanism(s) of elasticity, but also for their great potential as novel biomaterials. This review is intended to give an overview of the properties of the main elastic proteins, with particular focus on elastin and, at the same time, a report on the most recent acquisitions in the field of elastomeric biomaterials.

TEM image of poly(OrnGlyGlyOrnGly) after crosslinking reaction with GTA. The bar represents 100 nm.     

Bulk propylene polymerization in the presence of ansa-metallocenes of C 2 and C 1 symmetries: From a rigid thermoplastic to elastomeric stereoblock polypropylene

Bulk propylene polymerization in the presence of ansa-metallocenes with C ₂ and C ₁ symmetries has been studied. The catalytic activity, polymerization kinetics, and the molecular weight of polypropylene (PP) depend strongly on catalyst formation conditions. Mixtures of rac and meso isomers of metallocenes make it possible to rapidly produce a high-molecular-weight isotactic PP with high stereoregularity and mechanical characteristics and thus skip the stage of the isolation of pure rac isomer in the catalyst synthesis. The ability of triisobutylaluminum to serve as a cocatalyst is studied for ansa-metallocenes of C ₁ symmetry. In this case, the molecular weight of PP is higher, indicating that organoaluminum compounds participate in chain termination reactions. An increase in the reaction temperature results in an increase in the stereoregularity and crystallinity of PP. Polypropylene synthesized using ansa-metallocenes of C ₁ symmetry has good elastomeric properties.     

PP－g－PMMA在PP／PVDF共混体系中的应用

利用聚丙烯等离子体接枝甲基丙烯酸甲酯共聚物（ＰＰ－ｇ－ＰＭＭＡ）作增容剂，研究了其在聚丙烯／聚偏氟乙烯（ＰＶＤＦ）共混体系中的作用。增容是通过ＰＭＭＡ与ＰＶＤＦ的偶极－偶极相互作用实现的。接枝共聚物使共混体系的抗张强度和模量均有提高，由不同等离子体处理时间所得的ＰＰ－ｇ－ＰＭＭＡ，接枝率在７．７％～３００％具有最好的增容效果；而由不同后聚合时间所得的共聚物，接枝率在３０％～８０％具有最好的增容效果。     

Shear‐Induced Morphological Change in PP/LLDPE Blend

The morphology of a PP/LLDPE blend (50 : 50) by phase dissolution at high shear rate combined with dynamic packing injection molding at low shear rate was investigated by atomic force microscopy. Phase dissolution under high shear rate is manifested by a co‐continuous two‐phase structure that could be broken down to an island‐like structure when a low shear rate is applied via dynamic packing injection molding or simply by manual deformation.     

注压成型纳米结构PP/POE共混物表面的液滴低温冲击行为

以制备的阳极氧化不锈钢模板为模具嵌件, 采用注射压缩成型(ICM)工艺快速成型表面具有纳米丝结构的柔性聚丙烯/乙烯-辛烯共聚物(PP/POE, PP与POE质量比为3∶1)共混物复制物和准刚性PP复制物, 研究常温液滴冲击?10 ℃复制物表面的动态行为. 结果表明, 致密的纳米丝使复制物表面呈现超疏水、 极低黏附的润湿状态. 在低冲击速度范围内, 共混物复制物表面上液滴的接触时间比PP复制物上的短, 可归因于液滴铺展阶段柔性纳米丝储存的弹性势能在回缩阶段转换为液滴的动能; 在高冲击速度范围内, 共混物复制物基板和纳米丝储存的弹性势能被转换为液滴的动能, 进一步缩短了液滴的接触时间. 此结果表明, 共混物复制物的柔性和表面超疏水性使其具有优异的防冻黏性能. 共混物复制物表面上水滴(50 μL)的结冰时间得到明显延长、 冰黏附强度明显降低. 研究结果表明, 可采用ICM快速成型具有优异防冻黏和防冰性能的柔性超疏水高分子材料表面.     

Phase behavior of liquid crystalline elastomers based on a tri-vinyl mesogenic cross-linker

A series of cross-linked liquid crystalline polymers are prepared by graft copolymerization, and their liquid crystalline properties are characterized by DSC and POM. The results show that low levels of cross-linking do not obviously affect the phase behavior of the network polymers; in contrast, high levels of cross-linking may have more drastic influences, and liquid crystalline phases may lose, and more marked variation in phase transition will occur in materials with more direct coupling through a shorter or stiffer coupling chain between mesogenic side units and polymer backbone. At the same time, the coupling between the polymer chain and sidegroups results in stress-induced orientation in LCEs.     

Polypropylene modified with elastomeric metallocene‐catalyzed polyolefin blends: Fracture behavior and development of damage mechanisms

The fracture behavior and deformation mechanisms of polypropylene modified by elastomeric metallocene‐catalyzed polyolefin blends were investigated under both static and dynamic loading conditions. The fracture toughness was evaluated with the J integral approach. The development of damage mechanisms was studied by the examination of fracture surfaces with scanning electron microscopy and by the examination of single‐edge, double‐notch, four‐point‐bending or low‐impact‐energy fractured samples with optical microscopy. In addition, tensile dilatometry measurements were carried out to determine the nature of the deformation micromechanisms. The fracture behavior and the size and shape of the damage zones were drastically influenced by the elastomeric particles and the imposed constraint. The role of the elastomeric particles was different, depending on the strain rate. Under impact loading, particle pullout and crazing were responsible for the increased fracture toughness of polypropylene. Under quasistatic loading, stable fracture growth was caused by particle cavitation, which promoted ductile tearing of polypropylene before failure continued in an unstable fashion via crazing. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1075–1089, 2004     

Polyurethane elastomers based on Krasol LBH 3000 oligobutadienediol

Curing of a composition based on Krasol LBH 3000 oligobutadienediol by polymethylenepolyphenylenepolyisocyanate and oligodienediisocyanates in the presence of glycerol is studied. The influence of the ratio between isocyanate and hydroxyl groups and glycerol amount on the mechanical properties of oligourethane is investigated. An increase of the compatibility of the isocyanate component of the composition cured provides an increase of the level of the elastomer strength properties.