Reactive mixing of PET and PET/PP blends with glycidyl methacrylate–modified styrene‐b‐(ethylene‐co‐olefin) block copolymers

Styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene (SEBS) and styrene‐b‐(ethylene‐co‐propylene) (SEP, SEPSEP) block copolymers with different styrene contents and different numbers of blocks in the copolymer chain were functionalized by melt radical grafting with glycidyl methacrylate (GMA) and employed as compatibilizers for PET‐based blends. Binary blends of PET with both functionalized (SEBS‐g‐GMA, SEP‐g‐GMA, SEPSEP‐g‐GMA) and neat (SEBS, SEP, SEPSEP) copolymers (75 : 25 w/w) and ternary blends of PET and PP (75 : 25 w/w) with various amounts (2.5–10 phr) of both modified and unmodified copolymers were prepared in an internal mixer, and their properties were evaluated by SEM, DSC, melt viscosimetry, and tensile and impact tests. The roles of the chemical structure, grafting degree, and concentration of the various copolymers on blend compatibilization was investigated. The blends with the grafted copolymers showed a neat improvement of phase dispersion and interfacial adhesion compared to the blends with nonfunctionalized copolymers. The addition of grafted copolymers resulted in a marked increase in melt viscosity, which was accounted for by the occurrence of chemical reactions between the epoxide groups of GMA and the carboxyl/hydroxyl end groups of PET during melt mixing. Blends with SEPSEP‐g‐GMA and SEBS‐g‐GMA, at concentrations of 5–10 phr, showed a higher compatibilizing effect with enhanced elongation at break and impact resistance. The effectiveness of GMA‐functionalized SEBS was then compared to that of maleic anhydride–grafted SEBS. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2201–2211, 2005     

Polymer blends of poly(ethylene‐2,6‐naphthalate) with polystyrene compatibilized by styrene‐glycidyl methacrylate copolymers. I. Rheology,morphology, and mechanical properties

The compatibilization of blends of poly(ethylene‐2,6‐naphthalate) (PEN) with polystyrene (PS), through the styrene‐glycidyl methacrylate copolymers (SG) containing various glycidyl methacrylate (GMA) contents, was investigated in this study. SG copolymers are able to react with PEN terminal groups during melt blending, resulting in the formation of desirable SG‐g‐PEN copolymers in the blend. These in situ formed copolymers tend to reside along the interface preferentially as the result of interfacial reaction and thus function as effective compatibilizers in PEN/PS blends. The compatibilized blends exhibit higher viscosity, finer phase domain, and improved mechanical properties. It is found that the degree of grafting of the in situ formed SG‐g‐PEN copolymer has to be considered as well. In blends compatibilized with the SG copolymer containing higher GMA content, heavily grafted copolymers would be produced. The length of the styrene segment in these heavily grafted copolymers would be too short to penetrate deep enough into the PS phase to form effective entanglements, resulting in the lower compatibilization efficiency in PEN/PS blends. Consequently, the in situ formation of SG‐g‐PEN copolymers with an optimal degree of grafting is the key to achieving the best performance for the eventually produced PEN/PS blends through SG copolymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 967–975, 2003     

In situ compatibilization of HDPE/PET blends

The reactive compatibilization of immiscible polymers such as high‐density polyethylene (HDPE) and poly(ethylene terephthalate) (PET) by interfacial grafting of maleic anhydride (MA) without initiator in the molten state was investigated in this study. Grafting reaction of MA onto HDPE was carried out in a Rheocord HAAKE mixer varying reaction parameters such as the temperature, the shear rate, and the time of reaction. Then, the purified copolymers were characterized by infrared spectrometry and the MA content of HDPE‐g‐MA copolymers was determined by volumetric titration. It has been shown that thermomechanical initiation is sufficient to reach grafting yield of 0.3 to 2.5 wt % of MA. We studied then the compatibilization of HDPE/PET blends by interfacial grafting of MA. The in situ interfacial reaction leads to the formation of HDPE‐g‐MA copolymer which acts as a compatibilizer in the blends. The foremost interest of this work is that it provides a simple way of compatibilization of immiscible blends of polyolefin and polyester in one transformation step without using free‐radical initiators. The mechanical properties of the blends are strongly improved by the addition of small quantities of MA. The SEM observations of the compatibilized blends show a deep modification of the structure (i.e., enhanced regularity in the nodule dispersion and better interfacial adhesion). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 874–880, 2001     

Reactive compatibilization of polypropylene/polyethylene terephthalate blends

The reactive compatibilization of polypropylene/polyethylene terephthalate (PP/PET) blends by addition of glycidyl methacrylate grafted PP (PP-g-GMA) was studied. Two PP-g-GMA copolymers, containing either 0.2 or 1.2 wt% of GMA, were used as interface modifiers. These were incorporated into PP blends (with either 70 or 90 wt% PET), replacing 1/5 of PP in the system. The use of these modifiers changed the blends' tensile mechanical behavior from fragile to ductile. Blend tensile strength was improved by 10% and elongation at break showed 10 to 20-fold increases while stiffness remained constant. Scanning electron micrographs showed the PP average domain size in injection molded specimens to decrease to the micron/sub-micron size upon addition of the GMA modified resins, while the unmodified blends exhibited heterogeneous morphology comprising large lamellae 10–20 μm wide. The low-GMA graft content PP seemed slightly more efficient than the high GMA content PP in emulsifiying PP/PET blends. The GMA grafting level on PP had very limited effects on the blends' mechanical behavior in the range of GMA graft density provided by the two modified resins investigated.     

Synthesis and application of MDPE‐g‐GMA as reactive compatibilizer in blends of MDPE/PET and MDPE/PA6

In the present study, glycidyl methacrylate (GMA) grafted medium density polyethylene (MDPE‐g‐GMA) was synthesized in the molten state and applied as a reactive compatibilizer in MDPE/polyamid6 (PA6) and in MDPE/poly(ethylene terephtalate) (PET) blends. Graft copolymerization of GMA onto MDPE was performed in presence and absence of styrene, with different concentrations of dicumyl peroxide (DCP) as a radical initiator. In the presence of styrene, the MDPE‐g‐GMA with 6% GMA was obtained by addition of only 0.1 phr of DCP. Furthermore, the maximum grafting was reached when 0.6 and 0.7 phr concentration of DCP for styrene containing and styrene free samples were used, respectively. Torque‐time measurement showed faster grafting reaction rate in the presence of styrene. Four MDPE‐g‐GMA samples were selected as compatibilizers in the blends. Furthermore, the effects of melt flow index and grafting content of compatibilizers on mechanical properties and morphology of the blends were investigated through tensile tests and SEM analysis. Tensile test results indicated that the presence of compatibilizers in the blends led to 250 and 133% increase in elongation at break for PA6 and PET blends, respectively. Moreover, the best tensile results for blends were obtained using MDPE‐g‐GMA with high flow ability. The average particle size of the dispersed phase decreased by 350% for PA6 and 300% for PET blends compared with nonreactive blends. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Comparison of olefin copolymers as compatibilizers for polypropylene and high‐density polyethylene

Some polyolefin elastomers were compared as compatibilizers for blends of polypropylene (PP) with 30 wt % high‐density polyethylene (HDPE). The compatibilizers included a multiblock ethylene–octene copolymer (OBC), two statistical ethylene–octene copolymers (EO), two propylene–ethylene copolymers (P/E), and a styrenic block copolymer (SBC). Examination of the blend morphology by AFM showed that the compatibilizer was preferentially located at the interface between the PP matrix and the dispersed HDPE particles. The brittle‐to‐ductile (BD) transition was determined from the temperature dependence of the blend toughness, which was taken as the area under the stress–strain curve. All the compatibilized blends had lower BD temperature than PP. However, the blend compatibilized with OBC had the best combination of low BD temperature and high toughness. Examination of the deformed blends by scanning electron microscopy revealed that in the best blends, the compatibilizer provided sufficient interfacial adhesion so that the HDPE domains were able to yield and draw along with the PP matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Compatibilization of polyethylene/poly(propylene)/polystyrene blends

The compatibilization of mixtures of polyolefins or of polyolefins with polystyrene using either liquid polybutadiene (l-PB)/organic peroxide or styrene-butadiene-styrene (SBS) block copolymers was investigated. Tensile impact strength was chosen as a measure of compatibility. Binary blends LDPE/high-impact polystyrene (HIPS) and LDPE/poly(propylene) (PP) as well as LDPE/HDPE/PP/HIPS blends were prepared by blending in the chamber of a Brabender Plasticorder. Composition of the blends corresponds to real commingled plastic waste. It was found that l-PB-based compatibilizer enhanced the impact strength of LDPE/HIPS blends with LDPE contents higher than 60 wt.-% only. Also SBS copolymer enhanced the impact strength of LDPE/PP blends with LDPE contents higher than 40 wt.-%. Both the compatibilizers substantially increased the toughness of LDPE/HDPE/PP/HIPS blends with composition similar to the municipal plastic waste.     

Improved compatibility of high‐density polyethylene/poly(ethylene terephthalate) blend by the use of blocked isocyanate group

The blocked isocyanate group (BHI) was synthesized to improve the storage stability of HI (2‐hydroxyethyl methacrylate combined with isophorone diisocyanate) and characterized by Fourier transform infrared spectroscopy (FTIR). High‐density polyethylene grafted with the blocked isocyanate group (HDPE‐g‐BHI) was used as a reactive compatibilizer for an immiscible high‐density polyethylene/poly(ethylene terephthalate) (HDPE/PET) blend. A possible reactive compatibilization mechanism is that regenerated isocyanate groups of HDPE functionalized by BHI react with the hydroxyl and carboxyl groups of PET during melt blending. The HDPE‐g‐BHI/PET blend showed the smaller size of a dispersed phase compared to the HDPE/PET blend, indicating improved compatibility between HDPE and PET. This increased compatibility was due to the formation of an in situ graft copolymer, which was confirmed by dynamic mechanical analysis. Differential scanning calorimetry (DSC) analysis represented that there were few changes in the crystallinity for the continuous PET phase of the HDPE‐g‐BHI/PET blends, compared with those of the HDPE/PET blends at the same composition. Tensile strengths and elongations at the break of the HDPE‐g‐BHI/PET blends were greater than those of the HDPE/PET blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1017–1024, 2000     

Effect of ethylene-propylene copolymer with residual PE crystallinity on mechanical properties and morphology of PP/HDPE blends

Morphology and mechanical properties of polypropylene (PP)/high density polyethylene (HDPE) blends modified by ethylene-propylene copolymers (EPC) with residual PE crystallinity were investigated. The EPC showed different interfacial behavior in PP/HDPE blends of different compositions. A 25/75 blend of PP/HDPE (weight ratio) showed improved tensile strength and elongation at break at low EPC content (5 wt %). For the PP/HDPE = 50/50 blend, the presence of the EPC component tended to make the PP dispresed phase structure transform into a cocontinuous one, probably caused by improved viscosity matching of the two components. Both tensile strength and elongation at break were improved at EPC content of 5 wt %. For PP/HDPE 75/25 blends, the much smaller dispersed HDPE phase and significantly improved elongation at break resulted from compatibilization by EPC copolymers. © 1995 John Wiley & Sons, Inc.     

Functionalization of high‐density polyethylene in the molten state by glycidyl methacrylate grafting

:This study concerns the melt‐free radical grafting of glycidyl methacrylate (GMA) onto high‐density polyethylene (HDPE). We studied the effect of two initiators (tert‐butyl cumyl peroxide and di‐tert‐butyl peroxide) onto HDPE. Crosslinking of polymer was observed in the presence of 0.3 wt % tert‐butyl cumyl peroxide but not with 0.3 wt % di‐tert‐butyl peroxide. The grafting was carried out in a Brabender batch mixer at 190 °C. The grafting yield of GMA onto HDPE (determined by infrared spectrometry) is weak (<1 wt % for an initial concentration in monomer of 6 wt %). Moreover, it was noted that the degree of grafting did not vary with the concentration and the nature of peroxide used. To increase the grafting yield of GMA, we added to the HDPE/peroxide/GMA system an electron‐donating monomer, such as styrene. Adding this comonomer multiplied the rate of grafted GMA 3‐ or 4‐fold, resulting in a ratio [styrene]_i/[GMA]_i = 1 mol/mol with [GMA]_i = 6 wt %. So, the copolymerization is favored compared with the homopolymerization. This kind of copolymer presenting reactive functions is very attractive in the field of compatibilizing immiscible polymers. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 581–590, 2001     

Compatibilization of polypropylene/ poly(3‐hydroxybutyrate) blends

Blending polypropylene (PP) with biodegradable poly(3‐hydroxybutyrate) (PHB) can be a nice alternative to minimize the disposal problem of PP and the intrinsic brittleness that restricts PHB applications. However, to achieve acceptable engineering properties, the blend needs to be compatibilized because of the immiscibility between PP and PHB. In this work, PP/PHB blends were prepared with different types of copolymers as possible compatibilizers: poly(propylene‐g‐maleic anhydride) (PP–MAH), poly (ethylene‐co‐methyl acrylate) [P(E–MA)], poly(ethylene‐co‐glycidyl methacrylate) [P(E–GMA)], and poly(ethylene‐co‐methyl acrylate‐co‐glycidyl methacrylate) [P(E–MA–GMA)]. The effect of each copolymer on the morphology and mechanical properties of the blends was investigated. The results show that the compatibilizers efficiency decreased in this order: P(E–MA–GMA) > P(E–MA) > P(E–GMA) > PP–MAH; we explained this by taking into consideration the affinity degree of the compatibilizers with the PP matrix, the compatibilizers properties, and their ability to provide physical and/or reactive compatibilization with PHB. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Toughened polyoxymethylene by polyolefin elastomer and glycidyl methacrylate grafted high‐density polyethylene

Ternary blends of polyoxymethylene (POM), polyolefin elastomer (POE), and glycidyl methacrylate grafted high density polyethylene (GMA‐g‐HDPE) with various component ratios were studied for their mechanical and thermal properties. The size of POE dispersed phase increased with increasing the elastomer content due to the observed agglomeration. The notched impact strength demonstrated a parabolic tendency with increasing the elastomer content and reached the peak value of 10.81 kJ/m² when the elastomer addition was 7.5 wt%. The disappearance of epoxy functional groups in the POM/POE/GMA‐g‐HDPE blends indicated that GMA‐g‐HDPE reacted with the terminal hydroxyl groups of POM and formed a new graft copolymer. Higher thermal stability was observed in the modified POM. Both storage modulus and loss modulus decreased from dynamic mechanical analysis tests while the loss factor increased with increasing the elastomer content. GMA‐g‐HDPE showed good compatibility between the POM matrix and the POE dispersed phase due to the reactive compatibilization of the epoxy groups of GMA and the terminal hydroxyl groups of POM. A POM/POE blend without compatibilizer was researched for comparison, it was found that the properties of P‐7.5(POM/POE 92.5 wt%/7.5 wt%) were worse than those of the blend with the GMA‐g‐HDPE compatibilizer. POLYM. ENG. SCI., 57:1119–1126, 2017. © 2017 Society of Plastics Engineers     

Polylactide toughening with epoxy‐functionalized grafted acrylonitrile–butadiene–styrene particles

Glycidyl methacrylate functionalized acrylonitrile–butadiene–styrene (ABS‐g‐GMA) particles were prepared and used to toughen polylactide (PLA). The characteristic absorption at 1728 cm^?1 of the Fourier transform infrared spectra indicated that glycidyl methacrylate (GMA) was grafted onto the polybutadiene phase of acrylonitrile–butadiene–styrene (ABS). Chemical reactions analysis indicated that compatibilization and crosslinking reactions took place simultaneously between the epoxy groups of ABS‐g‐GMA and the end carboxyl or hydroxyl groups of PLA and that the increase of GMA content improved the reaction degree. Scanning electron microscopy results showed that 1 wt % GMA was sufficient to satisfy the compatibilization and that ABS‐g‐GMA particles with 1 wt % GMA dispersed in PLA uniformly. A further increase of GMA content induced the agglomeration of ABS‐g‐GMA particles because of crosslinking reactions. Dynamic mechanical analysis testing showed that the miscibility between PLA and ABS improved with the introduction of GMA onto ABS particles because of compatibilization reactions. The storage modulus decreased for the PLA blends with increasing GMA content. The decrease in the storage modulus was due to the chemical reactions in the PLA/ABS‐g‐GMA blends, which improved the viscosity and decreased the crystallization of PLA. A notched impact strength of 540 J/m was achieved for the PLA/ABS‐g‐GMA blend with 1 wt % GMA, which was 27 times than the impact strength of pure PLA, and a further increase in the GMA content in the ABS‐g‐GMA particles was not beneficial to the toughness improvement. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Compatibilization of nylon 6/liquid crystalline polymer blends with three types of compatibilizers

Polyblends of nylon 6 and liquid crystalline polymer (LCP) (Vectra A 950) are immiscible and highly incompatible, with resultant poor interfacial adhesion, large phase domains, and poor mechanical properties. In the present work, compatibilizing strategies are put forward for blends containing nylon and LCP. Effects of three types of compatibilizers, including ionomer Zn–sulfonated polystyrene (SPS), reactive copolymer styrene–maleic anhydride (SMA), functional grafted copolymers—polypropylene grafted glycidyl methacrylate (PP‐g‐GMA) and polypropylene grafted maleic anhydride (PP‐g‐MAH)—are studied in the aspects of morphology and dynamic mechanical behavior. The addition of compatibilizers decreases the domain size of the dispersed phase and results in improved interfacial adhesion between LCP and matrix. The compatibilization mechanism is discussed by way of diffuse reflectance Fourier transform spectroscopy (DRIFT), showing the reaction between compatibilizers and matrix nylon 6. Mechanical properties are improved by good interfacial adhesion. The contribution of SMA to mechanical properties is more obvious than that of Zn‐SPS and grafted PPs used. The blending procedure is correlated with the improvement of mechanical properties by the addition of compatibilizer. Two‐step blending is demonstrated as an optimum method to obtain composites with better mechanical properties as a result of a greater chance for LCP to contact the compatibilizer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1452–1461, 2003     

Phase structure and viscoelastic properties of compatibilized blends of PET and HDPE recyclates

Immiscible blends of recycled poly(ethylene terephthalate) (R‐PET), containing some amount of polymeric impurities, and high‐density polyethylene (R‐PE), containing admixture of other polyolefins, in weight compositions of 75 : 25 and 25 : 75 were compatibilized with selected compatibilizers: maleated styrene–ethylene/butylene–styrene block copolymer (SEBS‐g‐MA) and ethylene–glycidyl methacrylate copolymer (EGMA). The efficiency of compatibilization was investigated as a function of the compatibilizer content. The rheological properties, phase structure, thermal, and viscoelastic behavior for compatibilized and binary blends were studied. The results are discussed in terms of phase morphology and interfacial adhesion among components. It was shown that the addition of the compatibilizer to R‐PET‐rich blends and R‐PE‐rich blends increases the melt viscosity of these systems above the level characteristic for the respective binary blends. The dispersion of the minor phase improved with increasing compatibilizer content, and the largest effects were observed for blends compatibilized with EGMA. Calorimetric studies indicated that the presence of a compatibilizer had a slight affect on the crystallization behavior of the blends. The dynamic mechanical analysis provided evidence that the occurrence of interactions of the compatibilizer with blend components occurs through temperature shift and intensity change of a β‐relaxation process of the PET component. An analysis of the loss spectra behavior suggests that the optimal concentration of the compatibilizers in the considered blends is close to 5 wt %. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1423–1436, 2001     

Compatibilization of polyethylene terephthalate/polypropylene blends with styrene–ethylene/butylene–styrene (SEBS) block copolymers

Blends of polyethylene terephthalate (PET) and polypropylene (PP) at compositions 20/80 and 80/20 were modified with three different styrene–ethylene/butyl–ene-styrene (SEBS) triblock copolymers with the aim of improving the compatibility and in particular the toughness of the blends. The compatibilizers involved an unfunctionalized SEBS and two functionalized grades containing either maleic anhydride (SEBS-g-MAH) or glycidyl methacrylate (SEBS-g-GMA) grafted to the midblock. The effects of the compatibilizers were evaluated by studies on morphology and mechanical, thermal and rheological properties of the blends. The additon of 5 wt % of a SEBS copolymer was found to stabilize the blend morphology and to improve the impact strength. The effect was, however, far more pronounced with the functionalized copolymers. Particularly high toughness combined with rather high stiffness was achieved with SEBS-g-GMA for the PET-rich composition. Addition of the functionalized SEBS copolymers resulted in a finer dispersion of the minor phase and clearly improved interfacial adhesion. Shifts in the glass transition temperature of the PET phase and increase in the melt viscosity of the compatibilized blends indicated enhanced interactions between the discrete PET and PP phases induced by the functionalized compatibilizer, in particular SEBS-g-GMA. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:241–249, 1997     

Improved compatibility of PET/HDPE blend by using GMA grafted thermoplastic elastomer

ABSTRACT

Herein, graft-modified ethylene-1-octene copolymer (POE-g-GMA) and styrene-butadiene-styrene triblock copolymer (SBS-g-GMA) were found to be excellent reactive compatibilizers for immiscible poly(ethylene terephthalate) (PET)/high-density polyethylene (HDPE) blends via in-situ reaction compatibilization. With increase in compatibilizer amount, uniform phase morphology was observed in all the blends. Thus, exhibiting enhanced mechanical properties, especially, the notched Izod impact strength. In comparison with SBS-g-GMA, compatibilizer POE-g-GMA demonstrated greater impact on the compatibility. The addition of 15% POE-g-GMA produced blends with best mechanical properties. Besides, both POE-g-GMA and SBS-g-GMA enhanced the melt viscosity of PET/HDPE blends.     

高密度聚乙烯／尼龙1010共混体系的研究

采用接枝共聚方法,合成了高密度聚乙烯与马来酸酐,甲基丙烯酸和丙烯酸丁酯的接枝共聚物增容剂,研究了增容剂中接枝单体的种类及含量和增容剂用量等因素对高密度聚乙烯／尼龙1010共混体系力学性能的影响,结果表明在不同类型的接枝共聚物中以聚乙烯马来酸酐接枝共聚物对HDPE／PA1010共混体系的增容效果最好,在接枝单体含量和增容剂用量分别为4％－6％和5％左右时,共混体系的力学性能最好。     

Effect of monomethyl itaconate‐grafted HDPE and EPR on the compatibility and properties of HDPE–EPR blends

To improve the compatibility and properties of blends based on high‐density polyethylene (HDPE) and the ethylene–propylene copolymer (EPR), the functionalization of both through grafting with an itaconic acid derivative, monomethyl itaconate (MMI), was investigated. The grafting reaction was performed at 180°C in a Brabender Plasticorder using an initial monomer concentration of 3 phr in the case of HDPE and 5 phr in the case of EPR. 2,5‐Dimethyl‐2,5‐bis(tert‐butylperoxy)hexane was used as a radical initiator for the functionalization of HDPE and dicumyl peroxide was used as a radical initiator for the modification of EPR. The degree of grafting was 1.56% by weight for HDPE and 0.8% by weight for EPR. The effect of grafting on the processability, morphology, and thermal and mechanical properties of the blends are of particular interest. The results show that the grafting reaction increases the toughness and elongation at break of all tested blends and they retained their strength and stiffness. Moreover, the grafted polymers behaved as nucleating agents, accelerating the HDPE crystallization. These results are particularly relevant when both polymeric phases are modified. Morphological studies are in concordance with the mechanical characterization, showing a reduction of the rubber particle size and a better interfacial adhesion when both polymers are functionalized with MMI. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2239–2248, 2003     

Compatibilization efficacy of poly(isoprene–butyl acrylate) block copolymers in natural/acrylic rubber blends

Poly(isoprene–butyl acrylate) block copolymers with a variety of molecular weights and compositions were prepared via a controlled free‐radical polymerization with an iniferter. Subsequently, the block copolymers were used as compatibilizers in natural/acrylic rubber blends. Scanning electron micrographs revealed a cocontinuous morphology in the case of the normal blends with a low natural rubber content (20 wt %), whereas the blends that contained more natural rubber showed a dispersed‐particle morphology. When the rubbers were blended with 5 wt % block copolymer, the particle size decreased, and the tensile strength of the resulted blends increased, regardless of the block copolymer characteristics. For the blend that exhibited a cocontinuous morphology, the most effective compatibilizer was the block copolymer with an average molecular weight of 22,000 g/mol, containing mainly (87%) polyisoprene block. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 921–927, 2003