Diblock and triblock functional copolymers by controlled radical polymerization

Controlled polystyrenes with different molar mass values were synthesized starting from benzoyl peroxide and TEMPO (2,2,6,6‐tetramethylpiperidinyl‐1‐oxy). The polystyrene homopolymers served as initiators for the block copolymerization of phthalimide methylstyrene (PIMS) to synthesize polystyrene‐b‐poly(PIMS) diblock copolymers. Diblock copolymers with well defined structures as well as controlled and narrow molar mass distribution were obtained from the lower‐mass polystyrene homopolymers. The lower‐mass copolymers were found to be active as initiators in the synthesis of the polystyrene‐b‐poly(PIMS)‐b‐polystyrene triblock copolymers. In each reaction step, the effects of conversion and reaction time on the molar mass characteristics of the prepared block copolymers were investigated. The diblock and triblock copolymers were modified using hydrazine as the reagent in order to obtain the corresponding functional amino block copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1237–1244, 1999     

Synthesis and Characterization of New Block Copolymers with Poly(ethylene oxide) and Poly[3(S)‐sec‐butylmorpholine‐2,5‐dione] Sequences

Four different types of polydepsipeptide‐polyether block copolymers were synthesized via ring‐opening polymerization of 3(S)‐sec‐butylmorpholine‐2,5‐dione (BMD) in the presence of hydroxytelechelic poly(ethylene oxide) (PEO) with stannous octoate as a catalyst.The polymers were an AB block copolymer, an ABA block copolymer, an (A)₂B star shaped copolymer and an (A)₂B(A)₂ copolymer, where A is a poly[3(S)‐sec‐butylmorpholine‐2,5‐dione] (PBMD) and B a poly(ethylene oxide) block. The molar ratio of BMD to PEO was varied to obtain copolymers with different weight fractions of PBMD blocks ranging from 59.8 to 96.7 wt.‐%. The crystallinity of the PEO phase in the copolymers decreases in the following order: AB > (A)₂B > ABA > (A)₂B(A)₂ . The static contact angle θ decreases with increasing PEO content in the block copolymers.     

Compatibilization efficiency of styrene–butadiene multiblock copolymers in PS/PP blends

The compatibilizing effect of di‐, tri‐, penta‐, and heptablock (two types) copolymers with styrene and butadiene blocks was studied in polystyrene/polypropylene (PS/PP) 4/1 blends. The structure of PS/PP blends with the addition of 5 or 10 wt % of a block copolymer (BC) was determined on several scale levels by means of transmission electron microscopy (TEM) and small‐angle X‐ray scattering (SAXS). The results of the structure analysis were correlated with measured stress‐transfer properties: elongation at break, impact, and tensile strength. Despite the fact that the molar mass of the PS blocks in all the BCs used was about 10,000, that is, below the critical value M^* (～18,000) necessary for the formation of entanglements of PS chains, all the BCs used were found to be good compatibilizers. According to TEM, a certain amount of a BC is localized at the interface in all the analyzed samples, and this results in a finer dispersion of the PP particles in the PS matrix, the effect being more pronounced with S‐B‐S triblock and S‐B‐S‐B‐S pentablock copolymers. The addition of these two BCs to the PS/PP blend also has the most pronounced effect on the improvement of mechanical properties of these blends. Hence, these two BCs can be assumed to be better compatibilizers for the PS/PP (4/1) blend than the S‐B diblock as well as both S‐B‐S‐B‐S‐B‐S and B‐S‐B‐S‐B‐S‐B heptablock copolymers. In both types of PS/PP/BC blends (5 or 10 wt % BC), the BC added was distributed between both the PS/PP interface and the PS phase, and, according to SAXS, it maintained a more or less ordered supermolecular structure of neat BCs. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 931–942, 2001     

Chromatographic characterization of amphiphilic di‐ and tri‐block copolymers of poly(ethylene oxide) and poly(ε‐caprolactone)

Amphiphilic di‐ and tri‐block copolymers based on poly(ethylene oxide) as a hydrophilic segment and poly(ε‐caprolactone) as a hydrophobic part are synthesized by the ring‐opening polymerization of ε‐caprolactone while using poly(ethylene glycol)s and methoxy poly(ethylene glycol)s of varying molar masses as macro‐initiators. The synthesized block copolymers are characterized with respect to their total relative molar mass and its distribution by size exclusion chromatography. Liquid chromatography at critical conditions of both blocks is established for the analysis of individual block lengths and tracking presence of unwanted homopolymers of both types in the block copolymer samples. New critical conditions of polycaprolactone on reversed phase column are reported using organic mobile phase. The established critical conditions of polycaprolactone extended the applicable molar mass range significantly compared to already reported critical conditions of polycaprolactone in aqueous mobile phase. Block copolymers are also analyzed at critical conditions of poly(ethylene glycol). Complete analysis of the di‐ and tri‐block copolymers at corresponding critical conditions provided a fair estimate of molar mass of non‐critical block besides information regarding presence of homopolymers of both types in the samples.     

Thermoresponsive hydrogels from symmetrical triblock copolymers poly(styrene-block-(methoxy diethylene glycol acrylate)-block-styrene)

A series of symmetrical, thermo-responsive triblock copolymers was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization, and studied in aqueous solution with respect to their ability to form hydrogels. Triblock copolymers were composed of two identical, permanently hydrophobic outer blocks, made of low molar mass polystyrene, and of a hydrophilic inner block of variable length, consisting of poly(methoxy diethylene glycol acrylate) PMDEGA. The polymers exhibited a LCST-type phase transition in the range of 20-40 °C, which markedly depended on molar mass and concentration. Accordingly, the triblock copolymers behaved as amphiphiles at low temperatures, but became water-insoluble at high temperatures. The temperature dependent self-assembly of the amphiphilic block copolymers in aqueous solution was studied by turbidimetry and rheology at concentrations up to 30 wt %, to elucidate the impact of the inner thermoresponsive block on the gel properties. Additionally, small-angle X-ray scattering (SAXS) was performed to access the structural changes in the gel with temperature. For all polymers a gel phase was obtained at low temperatures, which underwent a gel-sol transition at intermediate temperatures, well below the cloud point where phase separation occurred. With increasing length of the PMDEGA inner block, the gel-sol transition shifts to markedly lower concentrations, as well as to higher transition temperatures. For the longest PMDEGA block studied (DP(n) about 450), gels had already formed at 3.5 wt % at low temperatures. The gel-sol transition of the hydrogels and the LCST-type phase transition of the hydrophilic inner block were found to be independent of each other.     

Radical‐cured block copolymer‐modified thermosets

Poly(ethylene‐alt‐propylene)‐b‐poly(ethylene oxide) (PEP‐PEO) diblock copolymers were synthesized and added at 4 wt % to 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloxypropoxy)phenyl]propane (BisGMA), a monomer that cures using free radical chemistry. In separate experiments, poly(ethylene glycol) dimethacrylate (PEGDMA) was combined as a secondary monomer with BisGMA and the monomers were loaded with 4 wt % PEP‐PEO. The diblock copolymers self‐assembled into well‐dispersed spherical micelles with PEP cores and PEO coronas. No appreciable change in the final extent of cure of the thermosets was caused by the addition of diblock copolymer, except in the case of BisGMA, where the addition of the block copolymer increased extent of cure by 12%. Furthermore, the extent of cure was increased by 29% and 37% with the addition of 25 and 50 wt % PEGDMA, respectively. Elastic modulus and fracture resistance were also determined, and the values indicate that the addition of block copolymers does not significantly toughen the thermoset materials. This finding is surprising when compared with the large increase in fracture resistance seen in block copolymer‐modified epoxies, and an explanation is proposed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Synthesis and electroluminescent studies of blue‐emitting copolymers containing phenylene vinylene and oxadiazole moieties in the main chain

Two statistical copolymers III and IV combining features of the two reference polymers I and II were synthesized by a Wittig reaction with the objective of raising the electron‐transport properties and fluorescence quantum yields relative to the alternating block copolymers I and II . The electroluminescent properties of single‐layer LEDs using these copolymers were studied. External quantum efficiencies of 0.035 and 0.11% were obtained from single‐layer devices on the basis of III and IV , respectively, which are higher than those of similar devices using I and II . Two single‐layer LEDs using a blend of I and II (4:1 and 1:1 wt/wt) corresponding to the compositions of copolymers III and IV , respectively, were also fabricated for comparison. Results indicated that the covalent incorporation of oxadiazole is effective in improving the efficiency of LEDs and that the molar content of oxadiazole plays an important role in the performance of the devices. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 235–241, 2002     

Synthesis and characterization of amphiphilic triblock copolymers by iron‐mediated atom transfer radical polymerization

The atom transfer radical polymerization of methyl methacrylate (MMA) and n‐butyl methacrylate (n‐BMA) was initiated by a poly(ethylene oxide) chloro telechelic macroinitiator synthesized by esterification of poly(ethylene oxide) (PEO) with 2‐chloro propionyl chloride. The polymerization, carried out in bulk at 90 °C and catalyzed by iron(II) chloride tetrahydrate in the presence of triphenylphosphine ligand (FeCl₂ · 4H₂O/PPh₃), led to A–B–A amphiphilic triblock copolymers with MMA or n‐BMA as the A block and PEO as the B block. A kinetic study showed that the polymerization was first‐order with respect to the monomer concentration. Moreover, the experimental molecular weights of the block copolymers increased linearly with the monomer conversion, and the molecular weight distribution was acceptably narrow at the end of the reaction. These block copolymers turned out to be water‐soluble through the adjustment of the content of PEO blocks (PEO content >90% by mass). When the PEO content was small [monomer/macroinitiator molar ratio (M/I) = 300], the block copolymers were water‐insoluble and showed only one glass‐transition temperature. With an increase in the concentration of PEO (M/I = 100 or 50) in the copolymer, two glass transitions were detected, indicating phase separation. The macroinitiator and the corresponding triblock copolymers were characterized with Fourier transform infrared, proton nuclear magnetic resonance, size exclusion chromatography analysis, dynamic mechanical analysis, and differential scanning calorimetry. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5049–5061, 2005     

New fluorinated thermoplastic elastomers. III. Novel method of synthesis and characterization of alternating fluorinated polyimide/fluorinated polyhybridsiloxane block copolymers via polycondensation

The synthesis of fluorinated polyimide/fluorinated polyhybridsiloxane (FPI–FPHSX) block copolymers was achieved through the polycondensation of α,ω‐dichlorosilane fluorinated polyimides and α,ω‐disilanol fluorinated polyhybridsiloxanes. Three FPI–FPHSX block copolymers with 41, 50, and 76 wt % polyimide were synthesized and characterized by the tuning of the number‐average molecular weight of the soft polyhybridsiloxane segments. The influence of the soft‐segment length on the behavior of the thermoplastic elastomer material was studied, including the surface tension and thermal properties. The thermomechanical properties of the FPI–FPHSX block copolymers were also examined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2237–2247, 2005     

Block length determination of the block copolymer mPEG‐b‐PS using MALDI‐TOF MS/MS

The molar mass determination of block copolymers, in particular amphiphilic block copolymers, has been challenging with chromatographic techniques. Therefore, methoxy poly(ethylene glycol)‐b‐poly(styrene) (mPEG‐b‐PS) was synthesized by atom transfer radical polymerization (ATRP) and characterized in detail not only by conventional chromatographic techniques, such as size exclusion chromatography (SEC), but also by matrix‐assisted laser/desorption ionization tandem mass spectrometry (MALDI‐TOF MS/MS). As expected, different molar mass values were obtained in the SEC measurements depending on the calibration standards (either PEG or PS). In contrast, MALDI‐TOF MS/MS analysis allowed the molar mass determination of each block, by the scission of the weakest point between the PEG and PS block. Thus, fragments of the individual blocks could be obtained. The PEG block showed a depolymerization reaction, while for the PS block fragments were obtained in the monomeric, dimeric, and trimeric regions as a result of multiple chain scissions. The block length of PEG and PS could be calculated from the fragments recorded in the MALDI‐TOF MS/MS spectrum. Furthermore, the assignment of the substructures of the individual blocks acquired by MALDI‐TOF MS/MS was accomplished with the help of the fragments that were obtained from the corresponding homopolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis and MALDI‐TOF analysis of dendritic‐linear block copolymers of lactides: Influence of architecture on stereocomplexation

Formation of a stereocomplex from polylactide copolymers can be tuned by changing the size and the chain topology of the second block in the copolymer. In particular, the use of a dendritic instead of linear architecture is expected to destabilize the cocrystallisation of polylactide blocks. With this idea in mind, dendritic‐linear block copolymers were synthesized by ring‐opening polymerization (ROP) of lactides using benzyl alcohol dendrons of generation 1–3 as macroinitiators and stannous octoate as catalyst. Polymers with controlled and narrow molar mass distribution were obtained. The MALDI‐TOF mass spectra of these dendritic‐linear block copolymers show well‐resolved signals. Remarkably, 10% or less of odd‐membered polymers are present, indicating that ester‐exchange reactions which occur classically parallel to the polymerization process, were in these conditions, very limited. Thermal analysis of polyenantiomers of generation 1–3 and the corresponding blends were examined. The blend of a pair of enantiomeric dendritic‐linear block copolymers exhibit a higher melting temperature than each copolymer, characteristic for the formation of a stereocomplex. Melting temperatures are strongly dependent on the dendron generation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6782–6789, 2006     

Analysis of polystyrene-b-polyisoprene copolymers by coupling of liquid chromatography at critical conditions to NMR at critical conditions of polystyrene and polyisoprene

For the investigation of the molecular heterogeneity of polystyrene-b-polyisoprene block copolymers, a chromatographic separation method, namely liquid chromatography at critical conditions was developed. This method was coupled on-line with (1)H-NMR(where NMR stands for nuclear magnetic resonance) for the comprehensive analysis of the polystyrene-b-polyisoprene copolymers. The copolymers were synthesized by two different methods: sequential living anionic polymerization and coupling of living precursor blocks. While (1)H-NMR allows just for the analysis of the bulk chemical composition of the block copolymers, the coupling with liquid chromatography at critical conditions provides selective molar mass information on the polystyrene and polyisoprene blocks within the copolymers. The polyisoprene block molar mass is determined by operating at chromatographic conditions corresponding to the critical point of adsorption of polystyrene and size exclusion chromatography mode for polyisoprene. The molar mass of the polystyrene block is determined by operating at the critical conditions of polyisoprene. In addition to the molar mass of each block of the copolymers, the chemical composition distribution of the block copolymers was determined. By using the coupling of liquid chromatography at critical conditions to (1)H-NMR, one can also detect the homopolymers formed during synthesis. Finally the microstructure of the polyisoprene block in the copolymers was evaluated as a function of molar mass.     

Azobenzene‐Containing Block Copolymers as Light‐Induced Reworkable Adhesives: Effects of Molecular Weight,Composition, and Block Copolymer Architectures on the Adhesive Properties

We previously reported that ABA‐type triblock copolymers with azobenzene‐containing terminal blocks can be utilized as a light‐induced reworkable adhesive that enables repeatable bonding and debonding on demand. The reworkability was based on the photoisomerization of the azobenzene moiety and concomitant softening and hardening of the azo blocks. Our aim in this study is to investigate the effect of the composition, molecular weight, and block copolymer architectures on the reworkable adhesive properties. For this purpose, we prepared AB diblock, ABA triblock, and 4‐arm (AB)₄ star‐block copolymers consisting of polymethacrylates bearing an azobenzene moiety (A block) and 2‐ethylhexyl (B block) side chains and performed adhesion tests by using these block copolymers. As a result, among the ABA block copolymers with varied compositions and molecular weights, the ABA triblock copolymers with an azo block content of about 50 wt % and relatively low molecular weight could achieve an appropriate balance between high adhesion strength and low residual adhesion strength upon UV irradiation. Furthermore, the 4‐arm star‐block structure not only enhances the adhesion strength, but also maintains low residual adhesion strength when exposed to UV irradiation. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 806–813     

Synthesis of a novel liquid crystal rod–coil star block copolymer consisting of poly(methyl methacrylate) and poly{2,5‐bis[(4‐methoxy‐phenyl)oxycarbonyl] styrene} via atom transfer radical polymerization

A bromine capped star‐shaped poly(methyl methacrylate) (S‐PMMA‐Br) was synthesized with CuBr/sparteine/PT‐Br as a catalyst and initiator to polymerize methyl methacrylate (MMA) according to atom transfer radical polymerization (ATRP). Then, with S‐PMMA‐Br as a macroinitiator, a series of new liquid crystal rod–coil star block copolymers with different molecular weights and low polydispersity were obtained by this method. The block architecture {coil‐conformation of the MMA segment and rigid‐rod conformation of 2,5‐bis[(4‐methoxyphenyl)oxycarbonyl] styrene segment} of the four‐armed rod–coil star block copolymers were characterized by ¹H NMR. The liquid‐crystalline behavior of these copolymers was studied by differential scanning calorimetry and polarized optical microscopy. We found that the liquid‐crystalline behavior depends on the molecular weight of the rigid segment; only the four‐armed rod–coil star block copolymers with each arm's M_n,_GPC of the rigid block beyond 0.91 × 10⁴ g/mol could form liquid‐crystalline phases above the glass‐transition temperature of the rigid block. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 733–741, 2005     

Thermoresponsive gels based on ABA triblock copolymers: Does the asymmetry matter?

The aim of this study was to investigate the effect of the asymmetry of the triblock copolymers on their thermoresponsive self‐assembly behavior. To this end, nine ABA‐type triblock copolymers with n‐butyl methacrylate and 2‐(dimethylamino)ethyl methacrylate (DMAEMA) consisting of the A and the B blocks, respectively, were synthesized. Polymers of three different DMAEMA contents (50, 60, and 70 wt %) were synthesized while varying the length ratio of the two hydrophobic A blocks. Specifically, one symmetric ABA triblock copolymer and two asymmetric ABA′ triblock copolymers with the length of the second A block to be twice or four times bigger than the length of the first A block (AB2A and AB4A triblock copolymer) were synthesized for each DMAEMA composition. Three statistical copolymers were also synthesized for comparison. The thermoresponsive behavior of the copolymers was studied and it was found that the cloud point and rheological properties of the polymers were strongly affected by the architecture (statistical vs. block) and less strongly by the DMAEMA composition and the asymmetry of the polymers. Nevertheless, interestingly the asymmetry of the ABA triblock copolymers did influence the thermoresponsive behavior with the more symmetric polymers presenting a sol–gel transition at lower temperatures. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2850–2859.     

New fluorinated thermoplastic elastomers. II. Synthesis and characterization of perfectly alternating fluorinated polyimide–fluorinated polyhybridsiloxane block copolymers via polyhydrosilylation

The synthesis of perfectly alternating fluorinated polyimide–fluorinated polyhybridsiloxane block copolymers (FPI‐FPHSX) was achieved through polyhydrosilylation of α,ω‐diallylfluorinated polyimides (AT‐FPI) and α,ω‐dihydrosilane fluorinated–polyhybridsiloxanes (HT‐FPHSX). A series of three FPI‐FPHSX containing 15, 38, and 56 wt % of polyimide was synthesized and characterized by tuning the number‐average molecular weight either of the hard polyimide segments or of the soft polyhybridsiloxane segments. The influence of the soft and hard segment lengths on the behavior of the thermoplastic elastomer material was studied (hardness, surface tension, thermal stability). The FPI‐FPHSX block copolymers thermomechanical properties are also reported. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 200–207, 2004     

High molar mass ethene/1‐olefin copolymers synthesized with acenaphthyl substituted metallocene catalysts

The influence of ligand structure on copolymerization properties of metallocene catalysts was elucidated with three C₁‐symmetric methylalumoxane (MAO) activated zirconocene dichlorides, ethylene(1‐(7, 9)‐diphenylcyclopenta‐[a]‐acenaphthadienyl‐2‐phenyl‐2‐cyclopentadienyl)ZrCl₂ ( 1 ), ethylene(1‐(7, 9)‐diphenylcyclopenta‐[a]‐acenaphthadienyl‐2‐phenyl‐2‐fluorenyl)ZrCl₂ ( 2 ), and ethylene(1‐(9)‐fluorenyl‐(R)1‐phenyl‐2‐(1‐indenyl)ZrCl2 ( 3 ). Polyethenes produced with 1 /MAO had considerable, ca. 10% amount of trans‐vinylene end groups, resulting from the chain end isomerization prior to the chain termination. When ethene was copolymerized with 1‐hexene or 1‐hexadecene using 1 /MAO, molar mass of the copolymers varied from high to moderate (531–116 kg/mol) depending on the comonomer feed. At 50% comonomer feed, ethene/1‐olefin copolymers with high hexene or hexadecene content (around 10%) were achievable. In the series of catalysts, polyethenes with highest molar mass, up to 985 kg/mol, were obtained with sterically most crowded 2 /MAO, but the catalyst was only moderately active to copolymerize higher olefins. Catalyst 3 /MAO produced polyethenes with extremely small amounts of trans‐vinylene end groups and relatively low molar mass 1‐hexene copolymers (from 157 to 38 kg/mol) with similar comonomer content as 1 . These results indicate that the catalyst structure, which favors chain end isomerization, is also capable to produce high molar mass 1‐olefin copolymers with high comonomer content. In addition, an exceptionally strong synergetic effect of the comonomer on the polymerization activity was observed with catalyst 3 /MAO. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 373–382, 2008     

Synthesis and thermal,mechanical, and optical properties of A–B–A or A–B block copolymers containing poly(norbornene‐co‐1‐octene)

A–B–A block copolymers which consist of poly(norbornene‐co‐1‐octene) and atactic polypropylene (PP) segments were synthesized by using ansa‐fluorenylamidotitanium complex as a catalyst varying the ratio of norbornene, 1‐octene, and propylene. The copolymer was obtained quantitatively with high molecular weight (>100,000) and narrow molecular weight distribution (polydispersity index, <1.5). A–B block copolymers of poly(norbornene‐co‐1‐octene) and poly(methyl methacrylate) (PMMA) was also obtained by the same procedure. Mechanical and optical properties of these copolymer films, which were obtained by solution casting process, were also investigated. Introduction of PP soft segment greatly improved mechanical properties, keeping their high transparency. Introduction of PMMA block also increased the tensile strength. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 267–271     

Contact Active Antimicrobial Coatings Prepared by Polymer Blending

Herein, contact active antimicrobial films are prepared by simply blending cationic amphiphilic block copolymers with commercial polystyrene (PS). The copolymers are prepared by combining atom transfer radical polymerization and “click chemistry.” A variety of copolymers are synthesized, and composed of a PS segment and an antimicrobial block bearing flexible side chain with thiazole and triazole groups, 4‐(1‐(2‐(4‐methylthiazol‐5‐yl)ethyl)‐1H‐1,2,3‐triazol‐4‐yl) butyl methacrylate (TTBM). The length of the TTBM block is varied as well as the alkylating agent. Different films are prepared from N,N‐dimethylformamide solution, containing variable PS‐b‐PTTBM/PS ratio: from 0 to 100 wt%. Remarkably, the blend films, especially those with 30 and 50 wt% of copolymers, exhibit excellent antimicrobial activities against Gram‐positive, Gram‐negative bacteria and fungi, even higher than films prepared exclusively from the cationic copolymers. Blends composed of 50 wt% of the copolymers present a more than 99.999% killing efficiency against the studied microorganisms. The better activity found in blends can be due to the higher roughness, which increases the surface area and consequently the contact with the microorganisms. These results demonstrate that the use of blends implies a reduction of the content of antimicrobial agent and also enhances the antimicrobial activity, providing new insights for the better designing of antimicrobial coatings.     

Synthesis and morphology of polyethylene‐block‐poly(methyl methacrylate) through the combination of metallocene catalysis with living radical polymerization

Polyethylene‐block‐poly(methyl methacrylate) (PE‐b‐PMMA) was successfully synthesized through the combination of metallocene catalysis with living radical polymerization. Terminally hydroxylated polyethylene, prepared by ethylene/allyl alcohol copolymerization with a specific zirconium metallocene/methylaluminoxane/triethylaluminum catalyst system, was treated with 2‐bromoisobutyryl bromide to produce terminally esterified polyethylene (PE‐Br). With the resulting PE‐Br as an initiator for transition‐metal‐mediated living radical polymerization, methyl methacrylate polymerization was subsequently performed with CuBr or RuCl₂(PPh₃)₃ as a catalyst. Then, PE‐b‐PMMA block copolymers of different poly(methyl methacrylate) (PMMA) contents were prepared. Transmission electron microscopy of the obtained block copolymers revealed unique morphological features that depended on the content of the PMMA segment. The block copolymer possessing 75 wt % PMMA contained 50–100‐nm spherical polyethylene lamellae uniformly dispersed in the PMMA matrix. Moreover, the PE‐b‐PMMA block copolymers effectively compatibilized homopolyethylene and homo‐PMMA at a nanometer level. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3965–3973, 2003