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Styrene Monomer (styrene + monomer)
Selected AbstractsCover Picture: Structural Modifications to Polystyrene via Self-Assembling Molecules (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 3 2005Mater. Abstract The cover shows tensile failure of a sample of pure polystyrene (left), and a polystyrene sample with greater impact strength containing 1% by weight of dispersed nanoribbons (right), as reported in work by Stupp and co-workers on p.,487. The nanoribbons are formed by self-assembly of molecules known as dendron rodcoils (DRCs) in styrene monomer, resulting in the formation of a gel. This gel can then be polymerized thermally. We have previously reported that small quantities of self-assembling molecules known as dendron rodcoils (DRCs) can be used as supramolecular additives to modify the properties of polystyrene (PS). These molecules spontaneously assemble into supramolecular nanoribbons that can be incorporated into bulk PS in such a way that the orientation of the polymer is significantly enhanced when mechanically drawn above the glass-transition temperature. In the current study, we more closely evaluate the structural role of the DRC nanoribbons in PS by investigating the mechanical properties and deformation microstructures of polymers modified by self-assembly. In comparision to PS homopolymer, PS containing small amounts (,,1.0,wt.-%) of self-assembling DRC molecules exhibit greater Charpy impact strengths in double-notch four-point bending and significantly greater elongations to failure in uniaxial tension at 250,% prestrain. Although the DRC-modified polymer shows significantly smaller elongations to failure at 1000,% prestrain, both low- and high-prestrain specimens maintain tensile strengths that are comparable to those of the homopolymer. The improved toughness and ductility of DRC-modified PS appears to be related to the increased stress whitening and craze density that was observed near fracture surfaces. However, the mechanism by which the self-assembling DRC molecules toughen PS is different from that of conventional additives. These molecules assemble into supramolecular nanoribbons that enhance polymer orientation, which in turn modifies crazing patterns and improves impact strength and ductility. [source] Catalytic synthesis of styryl-capped isotactic polypropylenesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2010Huahua Huang Abstract Bis-styrenic molecules, 1,4-divinylbenzene (DVB) and 1,2-bis(4-vinylphenyl)ethane (BVPE), were successfully combined with hydrogen (H2) to form consecutive chain transfer complexes in propylene polymerization mediated by an isospecific metallocene catalyst (i.e., rac -dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride, I) activated with methylaluminoxane (MAO), rendering a catalytic access to styryl-capped isotactic polypropylenes (i -PP). The chain transfer reaction took place in a unique way where prior to the ultimate chain transfer DVB/H2 or BVPE/H2 caused a copolymerization-like reaction leading to the formation of main chain benzene rings. A preemptive polymer chain reinsertion was deduced after the consecutive actions of DVB/H2 or BVPE/H2, which gave the styryl-terminated polymer chain alongside a metal-hydride active species. It was confirmed that the chain reinsertion occurred in a regio-irregular 1,2-fashion, which contrasted with a normal 2,1-insertion of styrene monomer and ensured subsequent continuous propylene insertions, directing the polymerization to repeated DVB or BVPE incorporations inside polymer chain. Only as a competitive reaction, the insertion of propylene into metal-hydride site broke the chain propagation resumption process while completed the chain transfer process by releasing the styryl-terminated polymer chain. BVPE was found with much higher chain transfer efficiency than DVB, which was attributed to its non-conjugated structure with much divided styrene moieties resulting in higher polymerization reactivity but lower chain reinsertion tendency. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3709,3713, 2010 [source] Process of grafting styrene onto LLDPE by swelling and suspension copolymerizationPOLYMER ENGINEERING & SCIENCE, Issue 9 2010Jing Yan A technology of swelling and suspension copolymerization was conducted to graft styrene onto linear low-density polyethylene (LLDPE). The graft mechanism of styrene with LLDPE had been described by 1H NMR and IR. The mean particle diameter and size distribution of the products with different proportions of LLDPE to styrene monomer were calculated. The morphology and thermal behavior of copolymers were characterized by scanning electron microscopy and differential scanning calorimetry. The glass transition temperature of copolymers increased with the addition of LLDPE, which proved the existence of the polyethylene- g -polystyrene copolymer. The grafting efficiency and granulation rate of suspension copolymerization were investigated. It was found that the grafting efficiency increased and the granulation rate decreased with the addition of LLDPE. POLYM. ENG. SCI., 50:1713,1720, 2010. © 2010 Society of Plastics Engineers [source] New aspects of unsaturated polyester resin synthesis.POLYMER INTERNATIONAL, Issue 5 2003Part 2. Abstract The distribution of unsaturations in the prepolymer of a typical unsaturated polyester (UP) resin (maleic anhydride, phthalic anhydride and 1,2-propylene glycol) has been shown to influence the kinetics of the cure process with styrene monomer. Segments containing double bonds in close proximity appear to lower the reactivity of the resin due to steric hindrance, as indicated by the fact that the rate of cure and the final degree of cure, measured by differential scanning calorimetry (DSC), increase as the average sequence length (SL) of maleic units decreases. This implies that the reactivity of UP resins may be improved by synthesis of prepolymers with certain reactant sequence-length distributions. The copolymer formed by the melt condensation process of maleic anhydride, phthalic anhydride and 1,2-propylene glycol in the absence of a transesterification catalyst has a non-random structure with a tendency towards blockiness. This was established using 1H NMR analysis in tandem with deterministic and Monte Carlo modelling techniques. Copyright © 2003 Society of Chemical Industry [source] Preparation of exfoliated high-impact polystyrene/MMT nanocomposites via in situ polymerization under controlling viscosity of the reaction mediumPOLYMER COMPOSITES, Issue 2 2008Periyayya Uthirakumar Exfoliated high-impact polystyrene (HIPS)/montmorillonite (MMT) nanocomposites were prepared via in situ polymerization of styrene in the presence of polybutadiene, using an intercalated cationic radical initiator-MMT hybrid (organoclay). In the solution polymerization in toluene, the silicate layers of the clay were well exfoliated, due to the low extra-gallery viscosity that can facilitate the diffusion of styrene monomers into the clay layers during the polymerization. The exfoliated HIPS/MMT nanocomposites were also successfully prepared by controlling the viscosity of the reaction medium with prolong swelling of the organoclay in styrene, prior to bulk polymerization. The HIPS/MMT nanocomposites, obtained from bulk polymerization, exhibited a significant improvement in thermal stability, compared to those obtained from solution polymerization as well as the pure polymer counterparts. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers [source] | ||||||||||