Controlled synthesis of carboxylic acid end‐capped poly(heptadecafluorodecyl acrylate) and copolymers with 2‐hydroxyethyl acrylate

1H,1H,2H,2H‐Heptadecafluorodecyl acrylate (AC8) was polymerized by reversible addition–fragmentation chain transfer and copolymerized with 2‐hydroxyethyl acrylate with the formation of random and block copolymers, respectively. The kinetics of the (co)polymerization was monitored with ¹H NMR spectroscopy and showed that the homopolymerization and random copolymerization of AC8 were under control. As a result of this control and the use of S‐1‐dodecyl‐S‐(α,α′‐dimethyl‐α″‐acetic acid)trithiocarbonate as a chain‐transfer agent, the copolymer chains were end‐capped by an α‐carboxylic acid group. Moreover, the controlled polymerization of AC8 was confirmed by the successful synthesis of poly(1H,1H,2H,2H‐heptadecafluorodecyl acrylate)‐b‐poly(2‐hydroxyethyl acrylate) diblock copolymers, which were typically amphiphilic compounds. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1499–1506, 2007     

Fractionation of ethylene/1‐pentene copolymers using a combination of SEC‐FTIR and SEC‐HPer DSC

The short chain branching distribution (SCBD) and thermal properties of ethylene/1‐pentene copolymers were studied using SEC‐FTIR and SEC‐HPer DSC. The copolymers, synthesized with Cp₂ZrCl₂/MAO, were fractionated using size exclusion chromatography (SEC). The infrared analysis of the fractions showed that the copolymers had—on average—higher 1‐pentene concentration in the low molecular weight range. Furthermore, the thermal properties of the SEC deposits of these copolymers on a Germanium disc were studied using high performance differential scanning calorimetry (HPer DSC). Single SEC separations were used to accumulate fractions in the microgram range that were directly analyzed with regard to their thermal properties, thus allowing us to study SCBD as well as thermal behavior simultaneously. When these fractions (with masses ranging from 10–80 μg) were analyzed using HPer DSC, good melting and crystallization temperature distributions were obtained, proving that HPer DSC can be used as a complementary method to SEC‐FTIR. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2956–2965, 2007     

Synthesis of water‐dispersible,fluorinated particles with grafting sulfonate chains by the core crosslinking of block copolymer micelles

Fluorinated polymer particles with grafting sulfonate chains, which showed high dispersion stability in aqueous media, were synthesized by the crosslinking of block copolymer micelles. A crosslinkable block copolymer, poly[(2,3,4,5,6‐pentafluorostyrene)‐co‐4‐(1‐methylsilacyclobutyl)styrene]‐b‐poly(neopentyl 4‐styrenesulfonate), composed of a statistical copolymer segment of 2,3,4,5,6‐pentafluorostyrene with 4‐(1‐methylsilacyclobutyl)styrene and a neopentyl 4‐styrenesulfonate segment, was prepared by the nitroxy‐mediated living radical polymerization of a 2,3,4,5,6‐pentafluorostyrene/4‐(1‐methylsilacyclobutyl)styrene mixture and neopentyl 4‐styrenesulfonate. The block copolymer formed micelles with a poly[(2,3,4,5,6‐pentafluorostyrene)‐co‐4‐(1‐methylsilacyclobutyl)styrene] core in acetonitrile, which were crosslinked via the ring‐opening reaction of silacyclobutyl groups in the core by a treatment with a platinum catalyst. The deprotection of sulfonate groups in the micelle corona by exposure to trimethylsilyl iodide and a treatment with aqueous HCl, followed by neutralization with aqueous NaOH, provided a polymer particle with polymer chains of sodium 4‐styrenesulfonate grafted on its surface. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1316–1323, 2007     

Synthesis of stable “gold nanoparticle–polymeric micelle” conjugates: A new class of star “molecular chimera” that self‐assemble into linear arrays of spherical micelles

Stable and aggregation‐free “gold nanoparticle–polymeric micelle” conjugates were prepared using a new and simple protocol enabled by the hydrogen bonding between surface‐capping ligands and polymeric micelles. Individual gold nanoparticles were initially capped using a phosphatidylthio–ethanol lipid and further conjugated with a star poly(styrene‐block‐glutamic acid) copolymer micelle using a one‐pot preparation method. The morphology and stability of these gold–polymer conjugates were characterized using transmission electron microscopy (TEM) and UV–vis spectroscopy. The self‐assembly of this class of polymer‐b‐polypeptide in aqueous an medium to form spherical micelles and further their intermicelle reorganization to form necklace‐like chains was also investigated. TEM and laser light scattering techniques were employed to study the morphology and size of these micelles. Polymeric micelles were formed with diameters in the range of 65–75 nm, and supermicellular patterns were observed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3570–3579, 2007     

Novel synthesis of biodegradable star poly(ethylene glycol)‐block‐poly(lactide) copolymers

Biodegradable star‐shaped poly(ethylene glycol)‐block‐poly(lactide) copolymers were synthesized by ring‐opening polymerization of lactide, using star poly(ethylene glycol) as an initiator and potassium hexamethyldisilazide as a catalyst. Polymerizations were carried out in toluene at room temperature. Two series of three‐ and four‐armed PEG‐PLA copolymers were synthesized and characterized by gel permeation chromatography (GPC) as well as ¹H and ¹³C NMR spectroscopy. The polymerization under the used conditions is very fast, yielding copolymers of controlled molecular weight and tailored molecular architecture. The chemical structure of the copolymers investigated by ¹H and ¹³C NMR indicates the formation of block copolymers. The monomodal profile of molecular weight distribution by GPC provided further evidence of controlled and defined star‐shaped copolymers as well as the absence of cyclic oligomeric species. The effects of copolymer composition and lactide stereochemistry on the physical properties were investigated by GPC and differential scanning calorimetry. For the same PLA chain length, the materials obtained in the case of linear copolymers are more viscous, whereas in the case of star copolymer, solid materials are obtained with reduction in their T_g and T_m temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3966–3974, 2007     

Preparation and characterization of poly(2‐methacryloyloxyethyl phosphorylcholine)‐block‐poly(D,L‐lactide) polymer nanoparticles

A poly(D,L ‐lactide)–bromine macroinitiator was synthesized for use in the preparation of a novel biocompatible polymer. This amphiphilic diblock copolymer consisted of biodegradable poly(D,L ‐lactide) and 2‐methacryloyloxyethyl phosphorylcholine and was formed by atom transfer radical polymerization. Polymeric nanoparticles were prepared by a dialysis process in a select solvent. The shape and structure of the polymeric nanoparticles were determined by ¹H NMR, atomic force microscopy, and ζ‐potential measurements. The results of cytotoxicity tests showed the good cytocompatibility of the lipid‐like diblock copolymer poly(2‐methacryloyloxyethyl phosphorylcholine)‐block‐poly(D,L ‐lactide). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 688–698, 2007     

Nanoindentation of biodegradable cellulose diacetate‐graft‐poly(L‐lactide) copolymers: Effect of molecular composition and thermal aging on mechanical properties

Nanoindentation of cellulose diacetate‐graft‐poly(lactide)s (CDA‐g‐PLLAs) synthesized by ring opening graft copolymerization of L ‐lactide in bulk onto the residual hydroxyl positions on CDA were conducted to investigate the effect of the molecular composition and thermal aging on mechanical properties and creep behavior. Continuous stiffness measurement (CSM) technique was used to obtained hardness and elastic modulus. These material properties were expressed as a mean value from 100 to 300 nm depths and an unloading value at final indentation depth. The hardness and elastic modulus in all CDA‐g‐PLLAs were higher than those in pure CDA, indicating that the introduction of PLLA increases the hardness and elastic modulus. With an increase of crystallinity by thermal aging, the hardness and elastic modulus were increased in both CDA‐g‐PLLA and PLLA. The creep test performed by CSM showed that the creep strain of CDA was decreased by the grafting of PLLA. Thermal aging decreased the creep strain of CDA‐g‐PLLA and PLLA. With an increase of holding time, hardness was decreased, whereas elastic modulus was kept almost constant. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1114–1121, 2007     

Catalyzed chain growth of polyethylene on magnesium for the synthesis of macroalkoxyamines: Application to the production of block copolymers using controlled radical polymerization

A synthetic method for the production of polyethylene (PE) chains carrying alkoxyamine end‐group has been proposed first by successfully reacting the well‐known 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) and N‐(2‐methyl‐2‐propyl)‐N‐(1‐diethylphosphono‐2,2‐dimethylpropyl)‐N‐oxyl (commonly called SG1) stable radicals with dipolyethylenylmagnesium compounds to give PE‐TEMPO and PE‐SG1. Since the homolytic cleavage of these two macroalkoxyamines for the production of block copolymers using controlled radical polymerization would require temperatures higher than 160 °C, two original new nitroxides (4‐[(2,2‐dimethyl‐4‐(N‐tert‐Butyl‐N‐(1‐diethoxyphosphoryl‐2,2‐dimethylpropyl)aminoxy)‐4‐n‐butoxycarbonyl)butanoyloxyl]‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy, DD1) and 4‐[(2,2‐dimethyl‐4‐(N‐tert‐Butyl‐N‐(1‐diethoxyphosphoryl‐2,2‐dimethylpropyl)aminoxy)‐4‐phenyl) butanoyloxyl]‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy, DD2) containing a TEMPO moiety and incorporating an SG1‐based alkoxyamine (cleavage temperature: 60 °C) were then synthesized. NMR analyses showed that the resulting PE‐DD1 and PE‐DD2 were obtained using this functionalization strategy though with low to moderate yields (from 17% to 40%). PE‐DD2 (40% functionalization) was used under controlled radical polymerization conditions of n‐butyl acrylate. SEC analyses together with ¹H NMR analysis showed that a poly(ethylene‐b‐n‐butyl acrylate) block copolymer was produced and that the polymerization proceeded under control. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2705–2718, 2007     

Gas permeability and selectivity of benzophenone aromatic isophthalic copolyamides

The synthesis, thermal, and gas transport properties of poly(benzophenone isophthalamide), DBF/ISO, poly(benzophenone‐5‐tert‐butylisophthalamide), DBF/TERT, homopolymers, and their copolyamides with different DBF/TERT ratios are reported. The results indicate that the glass transition temperatures of the copolyamides increase as the concentration of DBF/TERT in the polyamide increases. The gas permeability coefficients for DBF/ISO are around 10^?2 Barrers for O₂ which situates this polymer as a barrier polymer. It was also found that permeability coefficients in all polyamides and copolyamides are independent of pressure for He or decrease slightly particularly with O₂, CO₂, and N₂. It was seen that DBF/TERT is up to 15 times more permeable than DBF/ISO, depending on the gas being considered. This behavior was assigned to the presence of the bulky lateral substituent, the tert‐butyl group, in DBF/TERT and DBF/TERT‐co‐DBF/ISO copolyamides. This bulky substituent increases fractional free volume and interchain spacing; as a consequence, the gas permeability and diffusion coefficients generally increase. The experimental results for the gas permeability coefficients and permselectivity for the copolyamides was well represented by a semilogarithmic mixing rule of the homopolyamides permeability coefficients as a function of their volume fraction. The selectivity of gas pairs, such as He/O₂ and He/CO₂, decreased slightly with the addition of DBF/TERT. The temperature dependence of permeability for homopolyamides and copolyamides can be described by an Arrhenius type equation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2083–2096, 2007     

A starlike amphiphilic graft copolymer with hydrophilic poly(acrylic acid) backbones and hydrophobic polystyrene side chains

A well‐defined starlike amphiphilic graft copolymer bearing hydrophilic poly(acrylic acid) backbones and hydrophobic polystyrene side chains was synthesized by successive atom transfer radical polymerization followed by the hydrolysis of poly‐(methoxymethyl acrylate) backbone. A grafting‐from strategy was employed for the synthesis of a graft copolymer with narrow molecular weight distribution. Hydrophobic polystyrene side chains were connected to the backbones through stable C? C bonds. The poly(methoxymethyl acrylate) backbones can be easily hydrolyzed with HCl without affecting the hydrophobic polystyrene side chains. This kind of amphiphilic graft copolymer can form stable sphere micelles in water. The sizes of the micelles were dependent on the ionic strength and pH value. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3687–3697, 2007