Temperature-composition phase diagrams of binary blends of block copolymer and homopolymer

The temperature-composition phase diagrams for six pairs of diblock copolymer and homopolymer are presented, putting emphasis on the effects of block copolymer composition and the molecular weight of added homopolymers. For the study, two polystyrene-block-polyisoprene (SI diblock) copolymers having lamellar or spherical microdomains, a polystyrene-block-polybutadiene (SB diblock) copolymer having lamellar microdomains, and a series of polystyrene (PS), polyisoprene (PI), and polybutadiene (PB) were used to prepare SI/PS, SI/PI, SB/PS, and SB/PB binary blends, via solvent casting, over a wide range of compositions. The shape of temperature-composition phase diagram of block copolymer/homopolymer blend is greatly affected by a small change in the ratio of the molecular weight of added homopolymer to the molecular weight of corresponding block (M_H,A/M_C,A or M_H,B/M_C,B) when the block copolymer is highly asymmetric in composition but only moderately even for a large change in M_H,A/M_C,A ratio when the block copolymer is symmetric or nearly symmetric in composition. The boundary between the mesophase (M₁) of block copolymer and the homogeneous phase (H) of block copolymer/homopolymer blend was determined using oscillatory shear rheometry, and the boundary between the homogeneous phase (H) and two-phase liquid mixture (L₁+L₂) with L₁ being disordered block copolymer and L₂ being macrophase-separated homopolymer was determined using cloud point measurement. It is found that the addition of PI to a lamella-forming SI diblock copolymer or the addition of PB to a lamella-forming SB diblock copolymer gives rise to disordered micelles (DM) having no long-range order, while the addition of PS to a lamella-forming SB diblock copolymer retains lamellar microdomain structure until microdomains disappear completely. Thus, the phase diagram of SI/PI or SB/PB blends looks more complicated than that of SI/PS or SB/PS blends.     

Preparation of poly(styrene‐b‐2‐hydroxyethyl acrylate) block copolymer using reverse iodine transfer polymerization

Reverse iodine transfer polymerizations (RITP) of 2‐h‐ydroxyethyl acrylate (HEA) were performed in N,N‐dimethylformamide at 75°C using AIBN as initiator. Poly(2‐hydroxyethyl acrylate) (PHEA) with M_n = 3300 g mol^?1 and M_w/M_n <1.5 were obtained. Homopolymerization of styrene in RITP was also carried out under similar conditions using toluene as solvent. The resulting iodo‐polystyrene (PS‐I) with (M_{n, SEC} = 607 g mol^?1, polydispersity index (PDI) = 1.31) was used as a macroinitiator for the synthesis of amphiphilic block copolymers based on HEA with controlled well‐defined structure. Poly(styrene‐b‐2‐hydroxyethyl acrylate) (PS‐b‐PHEA) with M_n = 13,000 g mol^?1 and polydispersity index (M_w/M_n) = 1.4 was obtained, copolymer composition was characterized using ¹H‐NMR and FTIR, whereas SEC and gradient HPLC were used to confirm the formation of block copolymer and the living character of polymer chains. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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 of an amphiphilic conjugated polymer through block copolymerization of phenylacetylene and (p-trityloxycarbonylphenyl)acetylene and the subsequent hydrolysis

Summary The polymerization of (p-trityloxycarbonylphenyl)acetylene (p-TrOCOPA) with [(nbd)RhCl]₂/Ph₂C=C(Ph)Li/Ph₃P ternary catalyst proceeded in a living fashion to provide polymer with low polydispersity index (M _w/M _n∼1.1) in good yield. Block copolymerizations of p-TrOCOPA with phenylacetylene (PA) selectively formed the corresponding block copolymers regardless of the order of monomer addition. The hydrolysis of the homo- and block copolymers of p-TrOCOPA catalyzed by hydrochloric acid gave carboxyl-containing hydrophilic homopolymer and amphiphilic block copolymers, respectively. The amphiphilic block copolymer formed micelles in solution and monomolecular membrane at the air-water interface. Received: 2 April 2001/Accepted: 17 April 2001     

Evaluation of the potential use of ultrasound during the industrial manufacturing of high impact polystyrene

During the production of high impact polystyrene the rubber particle formation process is very important to control the final physical property balance. Besides the rubber viscosity, the presence of a copolymer to reduce the interfacial tension between the rubber and polystyrene phase is central. Such a copolymer can be added or can be made during the polymerization. In this study, it was attempted to create a block rubber in situ using ultrasound. Polybutadiene dissolved in styrene has been sonicated to create macroradicals. It was anticipated that these macroradicals would initiate the polymerization of styrene thus generating a poly(butadiene‐block‐styrene) acting as emulsifier during the production of high impact polystyrene. No evidence was found for the formation of a block copolymer but the higher reactivity and the resulting rubber particles indicate that besides rubber molecular weight reduction extra functionality was introduced on the rubber. No attempts were made to define the nature of the functionality. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Self‐assembled structures in blends of disordered and lamellar block copolymers: SAXS,SANS and TEM study

BACKGROUND: The phase behaviour of copolymers and their blends is of great interest due to the phase transitions, self‐assembly and formation of ordered structures. Phenomena associated with the microdomain morphology of parent copolymers and phase behaviour in blends of deuterated block copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA), i.e. (dPS‐block‐dPMMA)₁/(dPS‐block‐PMMA)₂, were investigated using small‐angle X‐ray scattering, small‐angle neutron scattering and transmission electron microscopy as a function of molecular weight, concentration of added copolymers and temperature. RESULTS: Binary blends of the diblock copolymers having different molecular weights and different original micromorphology (one copolymer was in a disordered state and the others were of lamellar phase) were prepared by a solution‐cast process. The blends were found to be completely miscible on the molecular level at all compositions, if their molecular weight ratio was smaller than about 5. The domain spacing D of the blends can be scaled with M_n by D ～ M_n^2/3 as predicted by a previously published postulate (originally suggested and proved for blends of lamellar polystyrene‐block‐polyisoprene copolymers). CONCLUSIONS: The criterion for forming a single‐domain morphology (molecularly mixed blend) taking into account the different solubilization of copolymer blocks has been applied to explain the changes in microdomain morphology during the self‐assembling process in two copolymer blends. Evidently the criterion, suggested originally for blends of lamellar polystyrene‐block‐polyisoprene copolymers, can be employed to a much broader range of block copolymer blends. Copyright © 2008 Society of Chemical Industry     

Compatibilization effects of styrenic/rubber block copolymers in polypropylene/polystyrene blends

Compatibilizing effects of styrene/rubber block copolymers poly(styrene‐b‐butadiene‐b‐styrene) (SBS), poly(styrene‐b‐ethylene‐co‐propylene) (SEP), and two types of poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) (SEBS), which differ in their molecular weights on morphology and selected mechanical properties of immiscible polypropylene/polystyrene (PP/PS) 70/30 blend were investigated. Three different concentrations of styrene/rubber block copolymers were used (2.5, 5, and 10 wt %). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the phase morphology of blends. The SEM analysis revealed that the size of the dispersed particles decreases as the content of the compatibilizer increases. Reduction of the dispersed particles sizes of blends compatibilized with SEP, SBS, and low‐molecular weight SEBS agrees well with the theoretical predictions based on interaction energy densities determined by the binary interaction model of Paul and Barlow. The SEM analysis confirmed improved interfacial adhesion between matrix and dispersed phase. The TEM micrographs showed that SBS, SEP, and low‐molecular weight SEBS enveloped and joined pure PS particles into complex dispersed aggregates. Bimodal particle size distribution was observed in the case of SEP and low‐molecular weight SEBS addition. Notched impact strength (a_k), elongation at yield (ε_y), and Young's modulus (E) were measured as a function of weight percent of different types of styrene/rubber block copolymers. The a_k and ε_y were improved whereas E gradually decreased with increasing amount of the compatibilizer. The a_k was improved significantly by the addition of SEP. It was found that the compatibilizing efficiency of block copolymer used is strongly dependent on the chemical structure of rubber block, molecular weight of block copolymer molecule, and its concentration. The SEP diblock copolymer proved to be a superior compatibilizer over SBS and SEBS triblock copolymers. Low‐molecular weight SEBS appeared to be a more efficient compatibilizer in PP/PS blend than high‐molecular weight SEBS. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 291–307, 1999     

Recycling of high impact polystyrene in coextruded sheet: Influence of the number of processing cycles on the microstructure and macroscopic properties

High impact polystyrene(HIPS) was repeatedly coextruded at 220°C, maintaining a constant composition of 70 wt% of virgin HIPS and 30 wt% of recycled HIPS. The gel content (GC), grafting degree (GD), swell index (SI), morphology of the rubber phase, and average molecular weight of the polystyrene (PS) matrix ( _w) were characterized after each processing cycle. The effect of these parameters on the melt flow index (MFI), the shear viscosity (η), the power law index (n), the Izod impact, and the stress at break were evaluated. The results demonstrated that the rheological properties changed with the number of processing cycles, e.g. the MFI decreased in the first cycle from 2.8 to 1.7 g/10 min, while from the second to the sixth cycle increased to 3.4 ± 0.2 g/10 min. The power law index increased from n = 0.29, after the first processing cycle, to n = 0.34 in the sixth cycle. The changes in MFI and n were attributed to changes in the physical structure of the rubber phase and to chain scissions in the PS matrix, caused by the recycling. Finally, the impact strength decreased with the increasing number of processing cycles, while the tensile stress at break remained constant. POLYM. ENG. SCI., 46:1698–1705, 2006. © 2006 Society of Plastics Engineers     

Self‐assembled structures in d8‐polystyrene‐block‐polyisoprene/polystyrene blends in the weak segregation regime: SAXS and TEM study

BACKGROUND: This paper reports an investigation of the microphase‐separated morphology and phase behaviour in blends of d‐polystyrene‐block‐polyisoprene with homopolystyrene in the weak segregation regime, using small‐angle X‐ray scattering and transmission electron microscopy, as a function of composition, weight‐average molecular weight and temperature. The chain length ratio parameter r_M = M_H/M_C (where M_H and M_C are the weight‐average molecular weights of the homopolymer and corresponding block copolymer chain) was selected to encompass all possible types of mutual homopolymer/block copolymer sizes. RESULTS: In the weak segregation regime the polystyrene block chains behave as a ‘wet brush’ for r_M < 1 similarly to the intermediate and strong segregation regimes. For r_M > 1 a macroscopic phase separation occurs. The domain spacing D increases systematically in the range 0 < r_M ≤ 1 with increasing concentration of homopolymer w_P and increasing r_M regardless of the implemented specific morphology, but the slope of the periodicity D versus w_P relation is smaller than in the intermediate and strong segregation regimes. CONCLUSION: The criterion for ‘wet and dry brush’ morphologies has been applied to explain the changes in microdomain morphology during the self‐assembly process. It has been shown that the parameters r_M and χ^3/2N (where χ is the Flory–Huggins parameter and N the number of segments per chain) characterize the slope of the D versus w_P relation in the weak and intermediate segregation regimes. Copyright © 2009 Society of Chemical Industry     

Optical properties of polystyrene and polyarylate block copolymer and their control by morphology generation

Relationship between phase morphology and optical properties of polystyrene and polyarylate (PS‐PAr) block copolymers synthesized from telechelic polystyrene has been investigated. In the PS‐PAr block copolymers, the PAr domains with higher melt viscosity were dispersed in the PS phase matrix with lower melt viscosity over the wide range of their composition from PS/PAr = 25/75 to 75/25 (wt ratio). The PAr domain size was dependent on the reactive ratio of PAr determined analogously by the mole fraction of the fed telechelic polystyrene. By controlling the mole fraction of the telechelic polystyrene more than 0.016 in synthesizing the PS‐PAr block copolymer, the size of PAr domains could be reduced to the microscopic scale (smaller than 100 nm). Then, the PS‐PAr block copolymers exhibited almost the same transparency as PAr in spite of the large difference in the refractive index between the PS and the PAr phase. Birefringence free condition for the PS‐PAr block copolymers was determined by not only the PS/PAr composition but also the balance in the degree of molecular orientation of these chains. The latter factor suggests that PS and PAr chains undergo inhomogeneous stress and relaxation history during the injection process. By controlling Mn (number average molecular weight) and weight fraction of the fed OH‐PS‐OH around 20 000 and 55 wt %, respectively, in the synthesis of the PS‐PAr block copolymer, the PS‐PAr block copolymer exhibited almost zero birefringence without any sacrifice of transparency. Because in the PS‐PAr block copolymer low birefringence and high transparency can coexist by controlling the adequate feeding condition in the synthesis process, the PS‐PAr block copolymer would be a promising material for optical applications, such as a substrate of optical disks or optical lenses. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 953–961, 2000     

Flexible and flame‐retardant S‐SEB‐S triblock copolymer/PPE nano‐alloy

We observed that modified polyphenylene ether (PPE) was solubilized in thermoplastic styrenic elastomer (TPS) and that a two‐phase lacy structure formed on nanometer scales when the TPS composition was 67 wt % and modified PPE and polystyrene‐block‐poly(styrene‐co‐ethylene‐co‐butylene)‐block‐polystyrene (S‐SEB‐S triblock copolymer) were blended. However, the molecular weight of the outer PS block segments M_outPS and the content of the outer PS block segments ?_outPS were <10,000 g/mol and 20 wt %, respectively. The resulting S‐SEB‐S/modified PPE nano‐alloy exhibited both flexibility and flame retardancy, unlike other materials, where a trade‐off exists between these two properties; that is, the flame retardancy was excellent when the phosphorus additive was present. This combination of properties might be attributed to the two‐phase nanometer‐scale structure consisting of flame‐retardant styrene/PPE domains and a continuous soft, lacy SEB matrix. The results for polystyrene‐block‐poly(ethylene‐co‐butylene)‐block‐polystyrene (S‐EB‐S triblock copolymer)/modified PPE blends were presented for comparison. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40446.     

Crystallization behavior of dry‐brush PEO‐PS block copolymer and PEO homopolymer blend

The crystallization behavior of semicrystalline PEO homopolymer/triblock PS‐PEO‐PS copolymer blend system, which exhibited “Dry‐Brush” in the melt. A symmetric polystyrene–poly(ethylene oxide)–polystyrene triblock copolymer was blended with PEO homopolymer (h‐PEO) having the same molecular weight as that of the PEO block in the copolymer. Considering the composition of the blend (W_ps ≥ 0.8), PEO spheres were formed in the blend. Because of the dry‐brush phase behavior of this blend, h‐PEO added was localized in the PEO microdomains, which increases the domain size without changing the microdomain morphology. The crystallization of PEO block was confined within the microdomains and the crystallization temperature was about 60°C lower than normal. Self‐seeding tests were performed to clarify the nucleation mechanism of the blend. Because the droplets size varies greatly, multicrystallization peaks were witnessed in the self‐seeding process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The viscoelastic properties of rubber–resin blends. II. The effect of resin molecular weight

In blends of rubber and low molecular weight resins, the compatibility of the system controls the viscoelastic properties and ultimately the performance of the composition as a pressure sensitive adhesive. The effect of the resin molecular weight on compatibility was examined by studying rubber–resin blends prepared from resins which represent a range of molecular weights. Viscoelastic properties were measured using a mechanical spectrometer on 1:1 blends of rubber and a series of polystyrene resins and poly(vinylcyclohexane) resins. Based on plots of G′ and tan δ vs. temperature, blends of natural rubber and polystyrene resin show incompatibility at resin M_w of about 600 and above. Blends of natural rubber and poly(vinyl cyclohexane) are incompatible at resin M_w of about 1800, but are compatible at M_w of about 650. Blends of styrene–butadiene rubber and polystyrene resins are compatible at resin M_w of about 650 but appear to contain a low volume incompatible phase at M_w of about 900. Therefore, the compatibility of a rubber–resin blend depends upon the molecular weight of the resin. Even systems expected to be compatible will show evidence of incompatibility as the molecular weight of the resin is raised above some limiting value.     

Electroreductive block copolymerization of dichlorosilanes in the presence of disilane additives

The electroreductive polymerization of dichloromethylphenylsilane in the presence of triphenylsilyl group‐containing disilanes such as hexaphenyldisilane followed by the electroreductive termination with chlorotriphenylsilane afforded triphenylsilyl group‐terminated polymethylphenylsilane in 15–32% yield. The isolated polymethylphenylsilane (M_n = 3350 g mol^?1, M_w/M_n = 1.4) was found to react as a macroinitiator to copolymerize with dibutyldichlorosilane under electroreductive conditions producing the corresponding block copolymer (M_n = 4730 g mol^?1, M_w/M_n = 1.2) in 38% yield. The ratio of monomer units (? MeSiPh? to? BuSiBu? ) of the copolymer was determined to be 75:25 using ¹H NMR analysis, which was in good agreement with the calculated ratio (74:26) on the assumption that molecular weight of the macroinitiator was not changed. The block structure of the resulting copolymer, poly(methylphenylsilane)‐block‐poly(dibutylsilane), was also confirmed by comparing its ¹H NMR and UV absorption spectra with those of polymethylphenylsilane, polydibutylsilane and a statistical copolymer prepared by electroreductive polymerization of dichloromethylphenylsilane with dibutyldichlorosilane. This method is applicable to the preparation of other types of macroinitiator such as triphenylsilyl group‐terminated polydibutylsilane, and polydibutylsilane‐block‐polymethylphenylsilane was also obtained using this macroinitiator. Copyright © 2011 Society of Chemical Industry     

Factors influencing the impact strength of high impact polystyrene

The relationship between synthesis factors and the impact resistance of high impact polystyrene (HIPS) is investigated in the light of its morphology and dynamic mechanical properties. A decrease in polymerization temperature results in an increase in T_g, melt viscosity and molecular weight of the continuous polystyrene phase as characterized by gel permeation chromatography. The separated, occluded polystyrene phase however shows an invariant T_g suggesting that the grafting and/or crosslinking effect overweighs the molecular weight effect. The observed high impact strength has been correlated with the homogeneous 1-2 μ rubber particle size distribution, a comparatively sharp rubber T_g transition at lower temperature, and a much lower occluded polystyrene content in the dispersed phase.     

Microhardness of styrene/butadiene block copolymer systems: Influence of molecular architecture

The influence of molecular architecture on the mechanical properties of styrene/butadiene block copolymers was investigated by means of the microhardness technique. It was found that the microhardness of the styrene/butadiene block copolymers is dictated by the nature of microphase separated morphology. In contrast to polymer blends and random copolymers, in which the microhardness generally follows the additivity rule, the behavior of the investigated block copolymers was found to significantly deviate depending on their molecular architecture. The glass‐transition temperature of the polystyrene phase (T_g‐PS), which practically remained constant and that of the polybutadiene phase (T_g‐PB), which varied with the change in the block copolymer architecture, apparently do not influence the microhardness values of the block copolymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1670–1677, 2003     

Synthesis of methyl methacrylate and N‐aryl itaconimide block copolymers via atom‐transfer radical polymerization

The paper describes the synthesis of block copolymers of methyl methacrylate (MMA) and N‐aryl itaconimides using atom‐transfer radical polymerization (ATRP) via a poly(methyl methacrylate)–Cl/CuBr/bipyridine initiating system or a reverse ATRP AIBN/FeCl₃·6H₂O/PPh₃ initiating system. Poly(methyl methacrylate) (PMMA) macroinitiator, ie with a chlorine chain‐end (PMMA‐Cl), having a predetermined molecular weight (M_n = 1.27 × 10⁴ g mol^?1) and narrow polydispersity index (PDI = 1.29) was prepared using AIBN/FeCl₃·6H₂O/PPh₃, which was then used to polymerize N‐aryl itaconimides. Increase in molecular weight with little effect on polydispersity was observed on polymerization of N‐aryl itaconimides using the PMMA‐Cl/CuBr/Bpy initiating system. Only oligomeric blocks of N‐aryl itaconimides could be incorporated in the PMMA backbone. High molecular weight copolymer with a narrow PDI (1.43) could be prepared using tosyl chloride (TsCl) as an initiator and CuBr/bipyridine as catalyst when a mixture of MMA and N‐(p‐chlorophenyl) itaconimide in the molar ratio of 0.83:0.17 was used. Thermal characterization was performed using differential scanning calorimetry (DSC) and dynamic thermogravimetry. DSC traces of the block copolymers showed two shifts in base‐line in some of the block copolymers; the first transition corresponds to the glass transition temperature of PMMA and second transition corresponds to the glass transition temperature of poly(N‐aryl itaconimides). A copolymer obtained by taking a mixture of monomers ie MMA:N‐(p‐chlorophenyl) itaconimide in the molar ratio of 0.83:0.17 showed a single glass transition temperature. Copyright © 2005 Society of Chemical Industry     

Dynamic mechanical and thermal properties of fire-retardant high-impact polystyrene

The interaction of a series of fire-retardant additives with high-impact polystyrene (HIPS) has been inferred from their dynamic mechanical and thermal properties. High-melting additives phase separate and act as inert filler in both the rubber and polystyrene phases, while low-melting additives raise the T_g of the rubber phase and plasticize the polystyrene phase. Antimony oxide antiplasticizes the grafted rubber phase but acts as inert filler in the polystyrene phase. The impact strength of these fire-retardant HIPS's shows good correlation with the integrated loss tangent of the rubber T_g peak indicative of large energy dissipation in the rubbery region during impact causing the matrix to craze or flow. It is also suggested that additives which are compatible with, and localized in, the polystyrene phase help retain the impact strength of HIPS.     

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     

Investigation of the Tu(>Tg) relaxation in homopolymers and block copolymers of styrene by torsional braid analysis

Investigation of the T_u (>T_g) relaxation in amorphous polymers of styrene by the technique of torsional braid analysis is reviewed. For the most part the relaxation behaves like the glass transition (T_g) in its dependence on molecular weight, on average molecular weight in binary polystyrene blends, and on composition in a polystyrene homogeneously plasticized throughout the range of composition. Diblock and triblock copolymers also display a T > T_g relaxation above the T_g, of the polystyrene phase. Two results in particular suggest that the T_u relaxation is molecularly based. (1) The T_u temperature is determined by the number average molecular weight for binary blends of polystyrene when both components have molecular weights below M_c. (the critical molecular weight for chain entanglements). (2) Homopolymers, and diblock and triblock copolymers of styrene, have a T > T_g relaxation at approximately the same temperature when the molecular weight of the styrene block is equal to that of the homopolymer.