Toughness enhancement of high‐impact polystyrene based on γ‐radiation vulcanized natural rubber latex by using block copolymer

Polyisoprene‐block‐polystyrene‐block‐polyisoprene (ISI) was synthesized by the iniferter route and its use, as compared to a commercial polystyrene‐block‐polyisoprene‐block‐polystyrene (SIS), in the enhancement of the toughness of high‐impact polystyrene (HIPS), prepared by the γ‐radiation vulcanized natural rubber (RVNR) latex/phase transfer/bulk polymerization technique, was investigated. Addition of 5% SIS was adequate as an interfacial agent, which effectively increased the unnotched Izod impact energy of HIPS, whereas use of 10% of ISI was required. A long polyisoprene block with two polystyrene segments of SIS was favorable for compatibilization of HIPS. Transmission electron micrographs revealed the uniform distribution of the block copolymer at the shell region of the rubber particle. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1307–1316, 2002     

Synthesis and characterization of (star po1ystyrene)-block- (linear polydimethylsi1oxane)-block-(star polystyrene) triblock copolymers

Summary (Star po1ystyrene)-block-(linear polydimethy1siloxane)-block-(Star polystyrene) triblock copolymers were synthesized by making living Star-shaped polystyrenes through a convergent living anionic polymerization procedure, followed by ring-opening polymerization of hexamethylcyclotrisiloxane (D₃) then difunctional coupling. The molecular weights of the resulting polymers were characterized by gel permeation chromatography (GPC), multi angle laser light scattering (MALLS) and ¹H NMR spectroscopy. Triblock copolymers with relatively narrow molecular weight distributions were obtained. Received: 22 April 2002/ Revised version: 15 August 2002/ Accepted: 16 August 2002 Correspondence to Daniel M. Knauss Email: dknauss@mines.edu, Fax: (303) 273 3629     

In situ generated half-lanthanidocene based catalysts for the controlled oligomerisation of styrene: Selectivity, block copolymerisation and chain transfer

The Cp^∗Nd(BH₄)₂(THF)₂/n-butylethylmagnesium combination affords a controlled and syndioselective oligomerisation of styrene. Living oligostyrenes can be used as macromonomers for block copolymerisation, leading to the unprecedented synthesis of a (polystyrene)-block-(1,4-trans polyisoprene) copolymer. Reversible transmetallation between the neodymium and the magnesium atom is further established with a transfer efficiency close to 100%.     

Synthesis of poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene triblock copolymers by two-step atom transfer radical polymerization

The synthesis of ABC triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO-b-PMMA-b-PS) via atom transfer radical polymerization (ATRP) is reported. First, a PEO-Br macroinitiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide, which was subsequently used in the preparation of halo-terminated poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymers under ATRP conditions. Then PEO-b-PMMA-b-PS triblock copolymer was synthesized by ATRP of styrene using PEO-b-PMMA as a macroinitiator. The structures and molecular characteristics of the PEO-b-PMMA-b-PS triblock copolymers were studied by FT-IR, GPC and ¹H NMR.     

Preparation of star polymers based on polystyrene or poly(styrene-b-N-isopropyl acrylamide) and divinylbenzene via reversible addition-fragmentation chain transfer polymerization

Star polymers based on styrene/divinyl benzene (St/DVB) and PSt-b-poly(N-isopropyl acrylamide) (NIPAAM)/DVB have been successively prepared by ‘arm-first’ method via reversible addition-fragmentation chain transfer (RAFT) polymerization. The linear macro RAFT agent PSt-SC(S)Ph was prepared by RAFT polymerization of St using benzyl dithiobenzoate and AIBN as RAFT agent and initiator. Successive RAFT polymerization of NIPAAM with PSt-SC(S)Ph as macro RAFT agent to afford diblock copolymer, PSt-b-PNIPAAM-SC(S)Ph. The coupling reactions of PSt-SC(S)Ph or PSt-b-PNIPAAM-SC(S)Ph in the presence of DVB produced the star copolymers, C(PSt)_n or C(PSt-b-PNIPAAM)_n. The molar ratio of DVB/PSt-SC(S)Ph and polymerization time influenced the yields, molecular weight and distribution of the star-shaped polymers, which was characterized by ¹H NMR and IR spectra, GPC measurements as well as DLS.     

A novel amphiphilic AB2 star copolymer synthesized by the combination of ring-opening metathesis polymerization and atom transfer radical polymerization

A new amphiphilic AB₂ star copolymer was synthesized by the combination of ring-opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP). Two different routes (methods A and B) were employed firstly to prepare the poly(oxanorbornene)-based monotelechelic polymers as the hydrophobic arm bearing dibromo-ended group via ROMP in the presence of two different terminating agents catalyzed by first generation Grubbs catalyst. The values of capping efficiency (CE) of the polymers were determined by NMR, which were 94% and 67% for methods A and B, respectively. Then, the dibromo-ended ROMP polymers were used as the macroinitiators for ATRP of 2-(dimethylamino)ethyl methacrylate (DMAEMA) to produce two hydrophilic arms. The prepared amphiphilic AB₂ star copolymers poly(7-oxanorborn-5-ene-exo,exo-2,3-dicarboxylic acid dimethyl ester)-block-bis[poly(2-(dimethylamino)ethyl methacrylate)] (PONBDM_n-b-(PDMAEMA_m)₂) with a fixed chain length of hydrophobic PONBDM and various hydrophilic PDMAEMA chain lengths can self-assemble spontaneously in water to form polymeric micelles, which were characterized by dynamic light scattering, atom force microscopy, and transmission electron microscopy measurements.     

Singlet oxygen generation and adhesive loss in stimuli‐responsive,fullerene‐polymer blends,containing polystyrene‐block‐polybutadiene‐block‐polystyrene and polystyrene‐block‐polyisoprene‐block‐polystyrene rubber‐based adhesives

The adhesive properties, as measured by bulk tack and peel strength analysis, were found to decrease in polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) and polystyrene‐block‐polyisoprene‐block‐polystyrene (SIS) PSA films containing common singlet oxygen generators, acridine, rose bengal, and C₆₀ fullerene, when irradiated with a tungsten halogen light in air. The addition of the singlet oxygen quencher, β‐carotene, to the C₆₀ fullerene samples was found to significantly deter the rate of adhesive loss in the fullerene‐SBS and ‐SIS PSA nanocomposites. The presence of oxygen was essential to the mechanism of adhesive loss and, in combination with the effects of singlet oxygen generators and a singlet oxygen scavenger, strongly supports a singlet‐oxygen mediated process. FTIR investigations of fullerene‐SBS and ‐SIS systems suggest the initial formation of peroxides which, upon further irradiation, lead to the generation of carbonyl‐containing compounds of a ketonic type after crosslinking. Rates of SBS and SIS C‐H abstraction were comparable and found to decrease when the high‐pressure, mercury xenon irradiation source was filtered to allow only light of λ > 390 nm. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of poly(l-glutamic acid)-block-poly(l-phenylalanine)

Poly(γ-benzyl l-glutamate)-block-poly(l-phenylalanine) was prepared via the ring opening polymerization of γ-benzyl l-glutamate N-carboxyanhydride and l-phenylalanine N-carboxyanhydride using n-butylamine·HCl as an initiator for the living polymerization. Polymerization was confirmed by ¹H-nuclear magnetic resonance spectroscopy and matrix assisted laser desorption ionization time of flight mass spectroscopy. After deprotection, the vesicular nanostructure of poly(l-glutamic acid)-block-poly(l-phenylalanine) particles was examined by transmission electron microscopy and dynamic light scattering. The pH-dependent properties of the nanoparticles were evaluated by means of ζ-potential and transmittance measurements. The results showed that the block copolypeptide could be prepared using simple techniques. Moreover, the easily prepared PGA-PPA block copolypeptide showed pH-dependent properties due to changes in the PGA ionization state as a function of pH; this characteristic could potentially be exploited for drug delivery applications.     

Synthesis of biodegradable poly(trans-4-hydroxy-N-benzyloxycarbonyl-l-proline)-block-poly(ε-caprolactone) copolymers and micellar characterizations

A series of novel types of diblock poly(trans-4-hydroxy-N-benzyloxycarbonyl-l-proline)-block-poly(ε-caprolactone) (PHpr10-b-PCL) copolymers were synthesized by ring-opening polymerization from macroinitiator poly(trans-4-hydroxy-N-benzyloxycarbonyl-l-proline) (PHpr10) and ε-caprolactone (ε-CL) in the presence of organocatalyst dl-lactic acid (dl-LA). The M_n of the copolymers increased from 3370 to 19,040 g mol⁻¹ with the molar ratio (10-100) of ε-CL to PHpr10. These products were characterized by differential scanning calorimetry (DSC), ¹H NMR, and gel permeation chromatography. According to DSC, the glass-transition temperature (T_g) of the diblock copolymers depend on the molar ratio of monomer/initiator that were added. The hydrolytic degradation behavior of PHpr-b-PCLs was evaluated from weight-loss measurements and the change of M_n and M_w/M_n. With higher PCL contents resulted in a slower weight loss, while having a higher molecular weight loss percentage. Their micellar characteristics in an aqueous phase were investigated by fluorescence spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The block copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 1.33-4.22 mg L⁻¹. The micelles exhibited a spindly shape and showed a narrow monodisperse size distribution. The obtained micelles have a relatively high drug-loading of about 26% when the feed weight ratio of amitriptyline hydrochloride (AM) to polymer was 1/1. An increase of molecular weight and hydrophobic components in copolymers produced a higher CMC value and greater loading efficiencies were observed.     

Phase separation of polystyrene-b-(ethylene-co-butylene)-b-styrene (SEBS) deposited on polystyrene thin films

Phase separation of a triblock copolymer, polystyrene-b-(ethylene-co-butylene)-b-styrene (SEBS) on the thin films of a homopolymer, polystyrene (PS), was studied by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The final morphology after phase separation was found to be greatly dependent on the relation between the molecular weight of the PS block and homo-PS. Dispersed spherical and worm-like micelles of SEBS were observed when the molecular weight of homo-PS is smaller than the PS block in SEBS, while large structures with inner micro-phase separation of SEBS was found when the molecular weight of homo-PS was much higher than that of the PS block. The origin of such a change in morphology is attributed to the difference of structure and interfacial tension at the interface between the matrix homo-PS and the PS block in SEBS triblock copolymer assembly.     

苯乙烯/异戊二烯/丁二烯(S/I/B)星型嵌段聚合物的研制方法

介绍了近年来的苯乙烯／异戊二烯／丁二烯（S／I／B）星型嵌段聚合物的发展与研制方法。重点评述了星型嵌段聚合物SIB、IB、IBI、SIS的研制方法，提出应用阴离子聚合方法合成星型聚合物的巨大潜力以及目前的任务。     

Poly[(2-ethylhexyl acrylate)-ran-(tert-butyl acrylate)]-block-poly(2-cinnamoyloxyethyl acrylate) synthesis and properties

Poly[(2-ethylhexyl acrylate)-ran-(tert-butyl acrylate)]-block-poly(2-cinnamoyloxyethyl acrylate) or P(EXA-r-tBA)-PCEA was synthesized by atom transfer radical polymerization. Reactivity ratios of EXA and tBA for copolymerization were determined. The specific refractive index increments of six diblocks were measured as a function of their composition. The diblocks were thermally stable and formed micelles in an automobile engine oil. Such micelles may be useful as an anti-friction additive in lubricating oils.     

Reaction-induced microphase separation in polybenzoxazine thermosets containing poly(N-vinyl pyrrolidone)-block-polystyrene diblock copolymer

Poly(N-vinyl pyrrolidone)-block-polystyrene diblock copolymer (PVPy-b-PS) was synthesized via sequential reversible radical-fragmentation transfer polymerization with S-1-phenylethyl O-ethylxanthate as a chain transfer agent. The block copolymer was incorporated into polybenzoxazine to access the nanostructures in the thermosets. The nanostructures in the thermosets were investigated by means of transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). It was found that disordered and/or ordered PS nanophases were formed in the PBa thermosets. It is judged that the formation of nanophases followed the mechanism of reaction-induced microphase separation in terms of the miscibility of the subchains of the diblock copolymer (viz. PVPy and PS) with polybenzoxazine after and before curing reaction.     

Self-assemblies formed by four-arm star copolymers with amphiphilic diblock arms in aqueous solutions

The self-assembly of two star copolymers, each consisting of four diblock arms of either poly(?-caprolactone)-block-poly(ethylene oxide), PCL-PEO, or polylactide-block-poly(ethylene oxide), PLA-PEO, with PEO blocks in the centers of the stars, have been studied by a combination of light scattering, atomic force microscopy, fluorometry and ¹H NMR spectroscopy. Results of the study show that despite the very similar architecture of both star copolymers, the structures of their self-assembled nanoparticles differ. Unlike the (PLA-PEO)₄ star copolymer which forms core/shell flower-like micelles, the association of the (PCL-PEO)₄ copolymer leads to large micellar aggregates in which individual micelles are interconnected by shared unimers, having joint coronas formed by hydrophilic centers of the stars.     

Toughness and morphology of radiation‐crosslinked natural rubber modified polystyrene

γ‐Radiation vulcanized natural rubber (RVNR)/phase transfer/suspension polymerization technique was used to prepare high‐impact polystyrene (HIPS) in bead form. The high notched Izod impact resistance of HIPS based on RVNR was observed and compared with that of unmodified PS. The impact resistance of HIPS based on RVNR was further enhanced by addition of 10% of polystyrene‐block‐polyisoprene‐block‐polystyrene copolymer. A mesh structure of all crosslinked rubber particles containing polystyrene and long crazes in HIPS were observed under electron microscopy. Copyright © 2003 Society of Chemical Industry     

Temperature dependence of tack and pulse NMR analysis of polystyrene block copolymer/tackifier system

The influence of tackifier structure on the temperature dependence of tack for a polystyrene block copolymer/tackifier system was investigated. A blend of polystyrene-block-polyisoprene-block- polystyrene triblock and polystyrene-block-polyisoprene diblock copolymers was used as the base polymer. Four different tackifiers were used: special rosin ester resin (RE), rosin phenolic resin (RP), hydrogenated cyclo-aliphatic resin (HC), and aliphatic petroleum resin (C5). Tack at 20?°C increased with the tackifier content for both RE and HC tackifier systems. Tack is affected by two factors: the work of adhesion at the adherend interface and the viscoelastic properties of the adhesive. The good balance of these two factors brought high tack. The adhesive with 10 wt.% tackifier exhibited the highest tack at 20?°C, whereas those with 30 and 50 wt.% tackifier were lower than those systems with 10 wt.% of the RP or C5 tackifiers. The adhesive with overly high hardness lowered the work of adhesion and the tack was not improved with more than 30 wt.%. A compatibility test in toluene solution and in solid state showed that tackifier RE has good compatibility with both polyisoprene and polystyrene, whereas tackifier RP has lower compatibility. Tackifiers HC and C5 had good compatibility with polyisoprene, but poor compatibility with polystyrene, and that of C5 was poorer. Pulse nuclear magnetic resonance (NMR) analyses indicated that tackifiers RE and HC effectively restrict the molecular mobility of polyisoprene phase.     

Synthesis and characterisation of hydroxyl end-capped telechelic polymers with poly(methyl methacrylate)-block-poly(n-butyl acrylate) backbones via atom transfer radical polymerisation

Hydroxyl end-capped telechelic polymers with poly(methyl methacrylate)-block-poly(n-butyl acrylate) (PMMA-b-PBA) backbones have been prepared via atom transfer radical polymerisation (ATRP) together with a nucleophilic substitution reaction. A hydroxyl-functionalised PMMA macroinitiator (HO-PMMA-Br) was prepared via ATRP at the optimised reaction temperature (60 °C) using 2-hydroxyethyl 2-bromoisobutyrate as the initiator. The high functionality of the bromo end group in the macroinitiator was confirmed by both ¹H NMR technique and a chain-extension reaction. Electrospray ionisation mass spectrometer proved to be a valuable tool for characterising PMMAs with a bromo end group (PMMA-Br), which provided signals corresponding to the intact polymers although multiply charged polymer chains were observed. The well-defined block copolymers HO-PMMA-b-PBA-Br were obtained by the ATRP of n-butyl acrylate using HO-PMMA-Br as a macroinitiator in a one-pot reaction at 100 °C. The kinetics as well as the dependence of the M_n,SEC and PDIs of the obtained block copolymers on the conversions of n-butyl acrylate in the chain-extension reaction suggested negligible radical termination during the reaction, demonstrating that the well-defined HO-PMMA-b-PBA-Br with a high functionality of bromo end group were obtained. The nucleophilic substitution reaction of a monohydroxyl-functionalised block copolymer HO-PMMA-b-PBA-Br with 5-amino-1-pentanol in dimethyl sulfoxide at room temperature was verified with ¹H and ¹³C NMR techniques, which resulted in a series of telechelic polymers HO-PMMA-b-PBA-OH with a functionality of hydroxyl groups up to 1.7 according to the gradient polymer elution chromatography.     

Precise preparation of four-arm-poly(ethylene glycol)-block-poly(trimethylene carbonate) star block copolymers via activated monomer mechanism and examination of their solution properties

The polymerization of trimethylene carbonate (TMC) in the presence of HCl·Et₂O via activated monomer mechanism was performed to synthesize 4a-PEG-b-PTMC star block copolymers composed of poly(ethylene glycol) (PEG) and poly(trimethylene carbonate) (PTMC) using four-arm (4a) PEG as an initiator. The TMC conversion and molecular weight of PTMC increased linearly with the polymerization time or the feed ratios of the TMC to 4a-PEG in the presence of HCl·Et₂O in CH₂Cl₂ at 25 °C. The obtained PTMC had molecular weights close to the theoretical value calculated from TMC to PEG molar ratio and exhibited monomodal GPC curve. We prepared successfully 4a-PEG-b-PTMC star block copolymers without metal catalyst at room temperature via living ring-opening polymerization (ROP) of TMC from 4a-PEG as an initiator in the presence of HCl·Et₂O as a monomer activator. The CMCs of the 4a-PEG-b-PTMC star block copolymers determined from fluorescence measurements. The CMCs of the 4a-PEG-b-PTMC star block copolymers decreased in the order of the increase in the PTMC segment. The partition equilibrium constant, K_v, which is an indicator of the hydrophobicity of the micelles of the 4a-PEG-b-PTMC star block copolymers in aqueous media, increased with the increase in the PTMC segment. In conclusion, we confirmed that the 4a-PEG-b-PTMC star block copolymers form micelles and hence may be potential hydrophobic-drug delivery vehicles.     

Biodegradable vesicular nanocarriers based on poly(?-caprolactone)-block-poly(ethyl ethylene phosphate) for drug delivery

Biodegradable polymer vesicle for drug delivery is reported. Poly(?-caprolactone)-block-poly(ethyl ethylene phosphate) with well-defined structure (PCL₁₅₀-b-PEEP₃₀) has been prepared by ring-opening polymerization. It forms vesicles in aqueous solution using the thin-film hydration method and further exclusion of the as-formed vesicles results in vesicles at nano-size, demonstrated by confocal laser scanning microscope (CLSM) and transmission electron microscopy observations. Doxorubicin (DOX) has been loaded into the vesicles with a loading content of 4.38% using an acid gradient method. The release of DOX from the vesicles is accelerated in the presence of an enzyme phosphodiesterase I that is known to catalyze the degradation of polyphosphoester, achieving 83.8% release of total loaded DOX in 140 h. The DOX-loaded vesicles can be successfully internalized by A549 cells, and it results in enhanced inhibition to A549 cell proliferation, likely owning to the sustained intracellular release of DOX as observed by CLSM. With these properties, the vesicles based on the block copolymer of PCL and PEEP are attractive as drug carriers for pharmaceutical application.