Synthesis of block copolymers by sequential carbenium ion polymerization

The sequential carbenium ion block copolymerization of ethyl vinyl ether (EVE) and isobutyl vinyl ether (IBVE) with N-vinylcarbazole (NVC) is described. Requisite conditions for the successful application of the sequential synthesis technique to these systems were established: (1) the use of stable carbocation initiator salts (e.g., Ph₃CSbCl₆) which lead to essentially terminationless polymerizations; (2) low solvent-to-monomer ratios in order to suppress any possible chain transfer to methylene dichloride molecules; (3) high ratios of initiator to monomer which create a pseudo-“living” system. The block products (PEVE-b-PNVC and PIBVE-b-PNVC) were isolated by precipitation and extraction. The intrinsic viscosities of these products displayed minima at 30°C.     

Synthesis and kinetic studies of PMMA nanoparticles by non-conventionally initiated emulsion polymerization

The aqueous emulsifier-free emulsion polymerization of methyl methacrylate (MMA) was studied under the catalytic effect of in situ developed bivalent transition metal-EDTA complex with ammonium persulfate (APS, (NH₄)₂S₂O₈) as initiator. Out of these, Cu(II)-EDTA system was selected for detailed kinetic and spectrometric study of polymerization. The apparent activation energy E_a, 34.5 kJ/mol, activation energy of initiator decomposition E_d, 26.9 kJ/mol, energy of propagation E_p, 29 kJ/mol and energy of termination E_t, 16 kJ/mol were reported. The emulsion polymer (PMMA) latex was characterized through the determination of the size and morphology by scanning electron microscopy, the average molecular weight by GPC and viscosity methods and the sound velocity by ultrasonic interferometer. From the kinetic results, the rate of polymerization, R_p at 50 °C was expressed by

     

Synthesis of semifluorinated block copolymers by atom transfer radical polymerization

Two sets of styrene‐based semifluorinated block copolymers, one with a perfluoroether pendant group and another with a perfluoroalkyl group, were synthesized by atom transfer radical polymerization. Microphase separation of the block copolymers was established by small‐angle X‐ray scattering and differential scanning calorimetry (DSC). DSC measurements also showed that the perfluoroether‐based polymer had a low glass‐transition temperature (?44 °C). Contact‐angle measurements indicated that the semifluorinated block copolymers had low surface energies (ca. 13 mJ/m²). These materials hold promise as low‐surface‐energy additives or surfactants for supercritical CO₂ applications. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 853–861, 2004     

Synthesis of zwitterionic block copolymers via RAFT polymerization

A series of poly [2-(dimethylamino)ethyl methacrylate (DMA)-sodium acrylate (SA)] diblock copolymers were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. The polymerization exhibits controlled characters: well-controlled molecular weight, narrow molecular weight distribution, molecular weight increasing with polymerization time. The zwitterionic diblock copolymers show rich solution behaviors. Dynamic light scattering (DLS) indicated the formation of micelles and reverse micelles of copolymers is affected by net charge density of copolymers. Microcalorimetry studies showed that the lower critical solution temperature (LCST) increases with incorporation of hydrophilic segments in buffer.     

Pigment encapsulation by emulsion polymerization using macro-RAFT copolymers

A new method is described, based on living amphipathic random macro-RAFT copolymers, which enables the efficient polymeric encapsulation of both inorganic and organic particulate materials via free-radical polymerization. The mechanism for this new approach is examined in the context of the polymer coating of zirconia- and alumina-coated titanium dioxide particles and its breadth of application demonstrated by the coating of organic phthalocyanine blue pigment particles. The particulate materials were first dispersed in water using a macro-RAFT copolymer as a stabilizer. Monomer and water-soluble initiator were then added to the system, and the monomer polymerized to form the coating. If nucleation of new polymer particles in the aqueous phase was to be avoided, it was found necessary to use a macro-RAFT copolymer that did not form micelles; within this constraint, a broad range of RAFT agents could be used. The macro-RAFT agents used in this work were found not to transfer competitively in the aqueous phase and therefore did not support growth of aqueous-phase polymer. Successful encapsulation of particles was demonstrated by TEM. The process described enables 100% of the particles to be encapsulated with greater than 95% of the polymer finishing up in the polymeric shells around the particles. Moreover, the coating reaction can be carried out at greater than 50% solids in many cases and avoids the agglomeration of particles during the coating step.     

Synthesis and characterization of sulfonated block copolymers by atom transfer radical polymerization

Well‐defined sulfonated polystyrene and block copolymers with n‐butyl acrylate (nBA) were synthesized by CuBr catalyzed living radical polymerization. Neopentyl p‐styrene sulfonate (NSS) was polymerized with ethyl‐2‐bromopropionate initiator and CuBr catalyst with N,N,N′,N′‐pentamethylethyleneamine to give poly(NSS) (PNSS) with a narrow molecular weight distribution (MWD < 1.12). PNSS was then acidified by thermolysis resulting in a polystyrene backbone with 100% sulfonic acid groups. Random copolymers of NSS and styrene with various composition ratios were also synthesized by copolymerization of NSS and styrene with different feed ratios (MWD < 1.11). Well defined block copolymers with nBA were synthesized by sequential polymerization of NSS from a poly(n‐butyl acrylate) (PnBA) precursor using CuBr catalyzed living radical polymerization (MWD < 1.29). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5991–5998, 2008     

Ultrasonically initiated emulsion polymerization of methyl methacrylate

The ultrasonically initiated emulsion polymerization of methyl methacrylate (MMA) was investigated. Experimental results show that sodium dodecyl sulfonate (SDS) surfactant plays a very important role in obtaining a high polymer yield, because in the absence of SDS, monomer conversion is near zero. Thus, the surfactant serves as an initiator and as interfacial modifier in this system (MMA/H₂O), and the monomer conversion increases significantly with increasing SDS concentration. An increase in the reactor temperature also leads to an increase in the monomer conversion. An appropriate increase in the N₂ purging rate also leads to higher conversion. The conversion of MMA decreases with increasing monomer concentration because of the higher viscosity of the system. With the experimental results, optimized reaction conditions were obtained. Accordingly, a high monomer conversion of about 67% and a high molecular weight of several millions can be obtained in a period of about 30 min. Furthermore, transmission electron micrographs show that the latex particles prepared are nanosized, indicating a promising technique for preparing nanoscale latex particles with a small amount of surfactant. In conclusion, a promising technique for ultrasonically initiated emulsion polymerization has been successfully performed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3356–3364, 2001     

Synthesis of block copolymers by the transformation of cationic polymerization into reversible atom transfer radical polymerization

Azo-containing polytetrahydrofuran (PTHF) obtained by cationic polymerization was used as a macroinitiator in the reverse atom transfer radical polymerization (RATRP) of styrene and methyl acrylate in conjunction with CuCl₂/2,2′-bipyridine as a catalyst. Diblock PTHF–polystyrene and PTHF–poly(methyl acrylate) were obtained after a two-step process. In the first step of the reaction, stable chlorine-end-capped PTHF was formed with the thermolysis of azo-linked PTHF at 65–70 °C in the presence of the catalyst. Heating the system at temperatures of 100–110 °C started the polymerization of the second monomer, which resulted in the formation of block copolymers. The decomposition behavior of the azo-linked PTHF and the structure of the block copolymers were determined by ¹H NMR and gel permeation chromatography (GPC). Kinetic studies and GPC analyses further confirmed the controlled/living nature of the RATRP initiated by the polymeric radicals. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2199–2208, 2002     

Kinetics and mechanism of emulsion polymerization initiated by oil-soluble initiators. II. Kinetic behavior of styrene emulsion polymerization initiated by 2,2′-azoisobutyronitrile

In order to clarify the general kinetic behavior of emulsion polymerization initiated by oilsoluble initiators, the emulsion polymerization of styrene initiated by 2,2′-azoisobutyronitrile was as a typical example, investigated thoroughly. The variations of the polymerization rate and the number of polymer particles produced with changes in emulsifier (sodium lauryl sulfate), initiator, and monomer concentrations initially charged and the reaction temperature were determined. It is shown from these experimental results that the kinetic behavior of this emulsion polymerization system is quite similar to that of styrene emulsion polymerization initiated by the water-soluble initiator, potassium persulfate despite the difference in the principal loci of radical production in both systems.     

Synthesis of hybrid block copolymers via integrated ring-opening metathesis polymerization and polymerization of NCA

Linear hybrid block copolymers with well controlled molecular weights and narrow polydispersities were synthesized via ring-opening metathesis polymerization (ROMP) followed by ring-opening polymerization of amino acid N-carboxyanhydrides.     

Synthesis and properties of polydimethylsiloxane-containing block copolymers via living radical polymerization

Polydimethylsiloxane (PDMS) block copolymers were synthesized by using PDMS macroinitiators with copper-mediated living radical polymerization. Diamino PDMS led to initiators that gave ABA block copolymers, but there was low initiator efficiency and molecular weights are somewhat uncontrolled. The use of mono- and difunctional carbinol–hydroxyl functional initiators led to AB and ABA block copolymers with narrow polydispersity indices (PDIs) and controlled number-average molecular weights (M_n's). Polymerization with methyl methacrylate (MMA) and 2-dimethylaminoethyl methacrylate (DMAEMA) was discovered with a range of molecular weights produced. Polymerizations proceeded with excellent first-order kinetics indicative of living polymerization. ABA block copolymers with MMA were prepared with between 28 and 84 wt % poly(methyl methacrylate) with M_n's between 7.6 and 35 K (PDI <1.30), which show thermal transitions characteristic of block copolymers. ABA block copolymers with DMAEMA led to amphiphilic block copolymers with M_n's between 9.5 and 45.7 K (PDIs of 1.25–1.70), which formed aggregates in solution with a critical micelle concentration of 0.1 g dm⁻³ as determined by pyrene fluorimetry experiments. Monocarbinol functional PDMS gave AB block copolymers with both MMA and DMAEMA. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1833–1842, 2001     

Synthesis of SAN‐containing block copolymers using RAFT polymerization

Copolymerization of styrene and acrylonitrile was carried out via reversible addition‐fragmentation chain transfer process (RAFT) in the presence of cumyl dithiobenzoate with AIBN as initiator. Copolymerization proceeded in a controlled/“living” fashion, and the copolymer composition depended on the feed ratio of monomer pairs. Block copolymers comprising styrene and acrylonitrile (SAN) segments and various functional blocks were synthesized through chain extension using the first blocks as macromolecular chain transfer agents (macroCTAs). Since the polymerization of both blocks proceeded through the RAFT process, the resulting block copolymers exhibited relatively narrow molecular weight distribution, with polydispersity indices in the range of 1.29–1.46. Gel permeation chromatography (GPC), and ¹H NMR and FTIR measurements confirmed the successful synthesis of the functionalized block copolymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2260–2269, 2006     

Synthesis of amphiphilic polyelectrolyte block copolymers using “living” radical polymerization. Application as stabilizers in emulsion polymerization

This paper describes the synthesis of amphiphilic block copolymers composed of an ionic poly(styrenesulfonate) first segment and a hydrophobic polystyrene second one, using TEMPO-mediated “living” radical polymerization. These copolymers proved to be efficient stabilizers in the emulsion polymerization of styrene.     

Synthesis of degradable copolymers by ring-opening polymerization

Hydrolysable copolymers made from different cyclic monomers have been studied. The monomers involved are 1,5-dioxepan-2-one (DXO), L-dilactide, 1,3-dioxan-2-one (TMC), oxepan-2,7-dione (AA) and oxepan-2-one (ϵ-CL). The hydrolysis of the DXO/L-dilactide copolymer showed great differences in degradation rate depending on composition. A statistical copolymer made from TMC and ϵ-CL was amorphous with a glass transition temperature of −48°C. TMC and AA could form a blockcopolymer with n-BuLi as initiator in toluene, 0°C.     

MMA/DVB emulsion surface graft polymerization initiated by UV light

Methyl methacrylate/1,2-divinylbenzene (MMA/DVB) in an opaque emulsion were successfully grafted onto the surface of polymeric substrate under the irradiation of UV light with benzophenone (BP) as a photoinitiator that was previously coated on the substrate surface. Monomer conversion, grafting efficiency, and grafting yields were determined by the gravimetric method. ATR-IR, AFM, and TEM were used to characterize the surface composition, to observe the topography of the grafted substrates, and to view inter-film colloid particles formed by cross-linking. The results reveal that, with the opaque MMA/DVB emulsion system and CPP film as substrate, the monomer conversion is in the range of 15-55%, the grafting efficiency is about 80%, the grafting yield reaches 5%, and the thickness of the graft layer can be controlled in the range 0.09-1.5 microm. Images of AFM show that the graft layer is piled up by nanoparticles (about 30-50 nm in diameter), which are linked together and tied to the substrate surface with covalent bonds. A possible model of surface graft polymerization including surface initiating, nucleation, and shish kebab growing is put forward to interpreting the above results.     

Block copolymers via macromercaptan initiated ring opening polymerization

Poly(styrene) macromercaptanes (M_n = 1900, 3600, and 6100 g mol^?1, PDI ≈ 1.2) derived from thiocarbonyl thio capped polymers prepared via reversible addition fragmentation chain transfer polymerization were employed to initiate the ring opening polymerization (ROP) of D ,L ‐lactide under conditions of organo‐catalyis employing 4,4‐dimethylaminopyridine. Poly(styrene)‐block‐poly(lactide) polymers of number average molecular weights up to 25,000 g mol^?1 (PDI ≈ 1.2 to 1.6) were obtained and characterized via multiple detection size exclusion chromatography (SEC) using refractive index as well as UV detection. In addition, diffusion ordered nuclear magnetic resonance and liquid chromatography at critical conditions (of both polystyrene as well as poly(lactide) were employed to assess the copolymers' structure. Furthermore, it was demonstrated that polyethylenes capped with a thiol moiety can also be readily chain extended in a ROP employing D ,L ‐lactide, evidenced via NMR and high temperature SEC. This study indicates that the direct use of macromercaptantes is indeed a methodology to switch from a radical to a ROP process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of fluorinated gradient copolymers by RAFT emulsifier-free emulsion polymerization and their compatibilization in copolymer blends

The gradient copolymers of styrene and fluorinated acrylate were synthesized by reversible addition-fragmentation transfer (RAFT) emulsifier-free emulsion polymerization under the control of amphiphilic RAFT agent. The polymerization conditions were studied in detail. Molecular weights were traced by gel permeation chromatography (GPC) during the polymerization process. The copolymer structures were characterized by ¹H NMR, Fourier transform infrared spectroscopy (FT-IR), and differential scanning calorimetry (DSC). These results proved that the copolymer had a gradient chain structure. The gradient copolymer was used as a compatibilizer to improve the compatibility of the polystyrene/fluoropolymer blend. The effects of molecular weight and adding content of the gradient copolymer on the compatibilization were studied.     

Synthesis of amphiphilic block copolymers via ring opening polymerization and reversible addition-fragmentation chain transfer polymerization

Amphiphilic block copolymers were synthesized via a dual initiator chain transfer agent (inifer) that successfully initiated the ring opening polymerization (ROP) of l -lactide (LLA) and subsequently mediated the reversible addition-fragmentation chain transfer (RAFT) polymerization of poly(ethylene glycol) ethyl ether methacrylate (PEGEEMA). The formation of each polymer block was confirmed using ¹H nuclear magnetic resonance spectroscopy, as well as gel permeation chromatography, and comprehensive kinetics studies provide valuable insights into the factors influencing the synthesis of well-defined block copolymers. The effect of monomer concentration, reaction time, and molar ratios of inifer to catalyst on the ROP of LLA are discussed, as well as the ability to produce poly(lactide) blocks of different molecular weights. The synthesis of hydrophilic PPEGEEMA blocks was also monitored via kinetics to provide a better understanding of the role the chain transfer agent plays in facilitating the complex and sterically demanding RAFT polymerization of PEGEEMA.