Dynamics of single-walled carbon nanotube (SWNT)/polyisoprene (PI) nanocomposites in electric and mechanical fields

Relaxation dynamics of single-walled carbon nanotube (SWNT)/polyisoprene (PI) nanocomposites were examined by dielectric relaxation spectroscopy (DRS) and dynamic mechanical spectroscopy (DMS) over a wide range of frequency and temperature. Both functionalized (SWNT-f) and pristine (SWNT-p) nanotubes were used and their effect on dynamics compared. Functionalized (PISF) nanocomposites were characterized by an increase in the time scale of the normal mode process as a consequence of the strong surface interactions between the polymer matrix and the nanotubes. The exact opposite is seen in pristine (PISP) nanocomposites where a decrease in the time scale of the normal mode relaxation is observed and attributed to weaker surface interactions and the effect of confinement on dynamics. The segmental process in PISF or PISP is not affected by the presence of nanotubes. The temperature dependence of the average relaxation time for normal and segmental modes is of the Vogel-Fulcher-Tammann (VFT) type. A good agreement is observed in the time scale of processes measured by DRS and DMS in PISF nanocomposites. In PISP nanocomposites, however, the time scales obtained from DRS and DMS measurements are not in consistently good agreement and an explanation is offered in terms of confinement.     

高性能轮胎用聚异戊二烯橡胶的进展*

聚异戊二烯橡胶的化学组成与天然橡胶相同,通常用于生产轮胎、橡胶工业制品等领域。采用不同的催化体系,可得三种性能截然不同的同分异构体。本文分析了不同结构聚异戊二烯橡胶研究现状,着重介绍了三种聚异戊二烯橡胶的结构、催化体系、性能特点以及它们在轮胎工业中的应用。最后展望了我国聚异戊二烯橡胶的发展。     

Synthesis of well-defined star-branched polymers by stepwise iterative methodology using living anionic polymerization

This article reviews the synthesis of regular and asymmetric star-branched polymers with well-defined structures by methodologies using living anionic polymerization, especially focusing on the synthetic approaches accessible for precisely controlled architectures of star-branched polymers concerning molecular weight, molecular weight distribution, arm number, and composition. The reason for selecting living anionic polymerization from many living/controlled polymerization systems so far developed is that this living polymerization system is still the best to meet the strict requirements for the precise structures of star-branched polymers. Furthermore, we herein mainly introduce a novel and quite versatile stepwise iterative methodology recently developed by our group for the successive synthesis of many-armed and multi-compositional asymmetric star-branched polymers. The methodology basically involves only two sets of the reaction conditions for the entire iterative synthetic sequence. The reaction sequence can be, in principle, limitlessly iterated to introduce a definite number of the same or different polymer segments at each stage of the iteration. As a result, a wide variety of many-armed and multi-compositional asymmetric star-branched polymers can be synthesized.     

Effect of Pre-coated Vs. Added Coupling Agents on the Vulcanization of Silica-filled Polyisoprene

Solid-state ¹³C NMR was utilized in analysis of the crosslink structure in silica-filled polyisoprene. Samples containing either a pre-coated coupling agent, a coupling agent added in the mixing process, or polyethylene glycol (PEG) were vulcanized and the type and density of crosslinking determined. The precoated coupling agent sample gave lower %swelling, lower extraction amounts, and a lower T ₂ relaxation than the mixed coupling agent, indicating increased crosslinking or increased filler –rubber interaction. The precoated also showed less cis –trans isomerization than the mixed, which may be due to its more uniform coating effect on the silica. The PEG sample yielded a ¹³C spectrum similar to an unfilled sample indicating decreased silica adsorption of vulcanization agents. Neither coupling agent significantly decreased the total sulfurization nor the percent monosulfidic crosslinks from that of a silica-filled sample without coupling agent.     

Highly efficient cis-1,4 polymerisation of isoprene using simple homoleptic amido rare earth-based catalysts

Polymerisation of isoprene was performed by means of ternary catalytic systems made of Ln[N(SiMe₃)₂]₃ (Ln = Nd (1), Y (2))/borate/Al(ⁱBu)₃ combinations (borate = [HNMe₂Ph][B(C₆F₅)₄] (HNB), [CPh₃][B(C₆F₅)₄] (TB) or B(C₆F₅)₃ (Barf)). With borate activator B(C₆F₅)₃, highly active (up to 4700 kg mol⁻¹h⁻¹) and selective catalysts are obtained with both neodymium and yttrium metals, leading up to 96% cis-1,4-polyisoprene.     

Thermal and catalytic conversion of used tyre rubber and its polymeric constituents using Py-GC/MS

This paper investigates the effect of various acid catalysts in the conversion of tyre rubber into hydrocarbon products. A used tyre rubber and three pure elastomers (cis-1,4-polyisoprene, polystyrene-co-butadiene and cis-polybutadiene) were characterised for their chemical composition and thermal behaviour in order to determine the main constituent of the waste material. Five acid solids of comparable aluminium contents but varying textural and/or acid characteristics were used as catalysts, including three zeolites (standard ZSM-5, nanocrystalline n-ZSM-5 and beta) and two mesostructured materials (Al-MCM-41 and Al-SBA-15). The presence of catalysts did not affect the degradation temperature of waste tyre rubber, although significant differences were observed in the nature of the resulting hydrocarbons. All zeolitic materials showed a marked selectivity towards the formation of aromatic species, particularly toluene (up to 19.82%), m/p-xylene (up to 16.91%) and benzene (up to 10.28%). This behaviour was slightly more marked in zeolites with stronger acid properties and reduced steric impediments, like nanocrystalline n-ZSM-5. Mesostructured catalysts (Al-MCM-41 and Al-SBA-15) not only exhibited strong aromatisation properties but also a marked benzene alkylation capacity, which resulted in the formation of a wider range of alkylaromatic products. This behaviour was associated with their weaker Lewis type acid character and also to their larger pore sizes, which posed no impediment to the formation of larger molecular size products.     

Effect of Pre-coated Vs. Added Coupling Agents on the Vulcanization of Silica-filled Polyisoprene

Solid-state ¹³C NMR was utilized in analysis of the crosslink structure in silica-filled polyisoprene. Samples containing either a pre-coated coupling agent, a coupling agent added in the mixing process, or polyethylene glycol (PEG) were vulcanized and the type and density of crosslinking determined. The precoated coupling agent sample gave lower %swelling, lower extraction amounts, and a lower T₂ relaxation than the mixed coupling agent, indicating increased crosslinking or increased filler -rubber interaction. The precoated also showed less cis -trans isomerization than the mixed, which may be due to its more uniform coating effect on the silica. The PEG sample yielded a ¹³C spectrum similar to an unfilled sample indicating decreased silica adsorption of vulcanization agents. Neither coupling agent significantly decreased the total sulfurization nor the percent monosulfidic crosslinks from that of a silica-filled sample without coupling agent.     

聚异戊二烯接枝聚苯乙烯改性沥青的性能

通过自由基聚合获得聚异戊二烯接枝聚苯乙烯,将其与沥青通过高速剪切共混制备了IR-g-PS改性沥青。考察了IR-g-PS改性沥青的感温性、耐老化性和高温储存稳定性。结果表明,当IR-g-PS的质量分数为6%时,与基质沥青和SIS相比,改性沥青的感温性、耐老化性和高温储存稳定性明显改善。     

对发展我国异戊橡胶的看法

本文论述了国内外异戊橡胶的发展概况，结合我国实际情况，提出了发展我国异戊橡胶的几点看法。