Search results for "Methyl methacrylate"

Anionic Polymerization of (Meth)acrylates in the Presence of Cesium Halide−Trialkylaluminum Complexes in Toluene

2001

The polymerization of methyl methacrylate and various acrylates initiated by ester enolates in the presence of cesium halide-trialkylaluminum complexes, Cs[Al n R 2n X] (n = 1, 2; R = Et, Bu'), in toluene has living and controlled character at -20 °C for methacrylates (X = Cl) and at -65 °C for n-butyl acrylate (X = F). Quantitative monomer conversions are usually reached, leading to polymers with narrow molecular weight distributions (M w /M n < 1.1). Kinetic investigations indicate a rather complex polymerization mechanism, and we assume an equilibrium between at least two active species. With this new initiating system, beside acrylate homopolymers, random and graft copolymers can be syn…

Interfacial stabilization by soft Janus nanoparticles

2016

Abstract The stabilization of water/air, water/oil and water/solid interfaces by Janus particles with polystyrene (PS) and poly(methacrylic acid) (PMAA) hemispheres was systematically investigated. The stabilization of these interfaces is of relevance for the formulation of foams, emulsions and dispersions. The Janus particles were prepared from micellar solutions of polystyrene-b-polyisoprene-b-poly(tert-butyl methacrylate) (PS-PI-PtBMA) triblock terpolymers by selective cross-linking of the polyisoprene domain on a multi-gram scale, followed by hydrolysis of the PtBMA block. For the investigation of water/oil-emulsions a series of hydrophobic oils (paraffin oil, xylene, peanut oil, isopro…

Copolymerization of n-Butyl Acrylate with Methyl Methacrylate and PMMA Macromonomers:  Comparison of Reactivity Ratios in Conventional and Atom Trans…

1999

The reactivity ratios of n-butyl acrylate (nBuA) with methyl methacrylate (MMA) and ω-methacryloyl-PMMA macromonomers (MM) in conventional and atom transfer radical copolymerization (ATRP) have been determined. For the copolymerization of nBuA with MMA, good agreement of the ratios is observed between conventional and controlled radical copolymerization, indicating that chemoselectivities in both processes are similar. The relative reactivity of the MM (1/rnBuA) in conventional copolymerization is significantly lower than that of MMA. It depends on the concentration of the comonomers but is not significantly influenced by the length of the MM. At high concentrations the relative reactivity …

Intrastromal corneal ring segment implantation in paracentral keratoconus with coincident topographic and coma axis.

2012

To evaluate the efficacy, predictability, and safety of implantation of Ferrara-type intrastromal corneal ring segments (ICRS) for refractive correction of paracentral keratoconus.Fernández-Vega Ophthalmological Institute, Oviedo, Spain.Cohort study.Snellen uncorrected (UDVA) and corrected (CDVA) distance visual acuities and residual refractive errors were recorded before and 6 months after ICRS implantation for keratoconus. The tunnels for ICRS implantation were created with a femtosecond laser. The power vector and the Alpins method were used to analyze postoperative refractive outcomes.The study evaluated 56 eyes of 49 patients. The mean UDVA was 0.17 ± 0.14 (SD) preoperatively and 0.41 …

Femtosecond laser–assisted intrastromal corneal ring segment implantation for high astigmatism correction after penetrating keratoplasty

2013

PURPOSE: To assess the visual and refractive outcomes of femtosecond laser-assisted implanta- tion of Ferrara-type intrastromal corneal ring segments (ICRS) in post-penetrating keratoplasty (PKP) eyes. SETTING: Instituto OftalmolFernOviedo, Spain. DESIGN: Cohort study. METHODS: Patients with previous PKP had ICRS implantation after femtosecond laser tunnel creation. The uncorrected (UDVA) and corrected (CDVA) distance visual acuities and residual refractive errors were recorded before and 6 months after ICRS implantation. The power vector method was used to analyze refractive errors preoperatively and postoperatively. RESULTS: This study enrolled 32 eyes of 30 patients. The mean UDVA (Snell…

Mechanism of anionic polymerization of (meth)acrylates in the presence of aluminium alkyls, 1. 13C NMR studies of model compounds in toluene

1994

The bimetallic ate complex [(CH 3 ) 2 C=C(OEt)(O - AlR 3 )]Li + is regarded to be the model of the active centre of the polymerization of methyl methacrylate in the presence of aluminium alkyls. This complex is detectable by 13 C NMR up to 273 K. At ambient temperature irreversible decomposition takes place. Apart from the formation of the ate complex, excess aluminium chloride coordinates to the ester carbonyl groups of both the monomer and the polymer chain

1981

The anionic polymerization of tert-butyl methacrylate (TBMA) in tetrahydrofuran, using Na+ and Cs+ as counterions proceeds without side reactions even at room temperature. The resulting molecular weight distributions are nearly monodisperse (Mw/Mn ⩽ 1,01). The rate constants for the propagation of ion pairs were measured in the range from + 15 to −100°C. The Arrhenius plots are linear, but different for the two counterions, resulting in the following numerical values for the frequency exponent A and the activation energy Ea: A = 8,5 and Ea = 7,2 kcal/mol = 30 kJ/mol for Na+; A = 9,5 and Ea = 5,6 kcal/mol = 23 kJ/mol for Cs+. The difference between the counterions, which is in contrast to th…

1986

The terpolymerization of the three monomers (3-vinyl phenylazo)methylmalodinitrile (1), (3-vinyl phenylazo)phenylsulfid (2) or 1-(3-vinylphenylazo)-1,1′-diphenyl methylacetate (3) with methyl methacrylate and butanediol-1,4-dimethyacrylate leads to networks in which the thermolabile azo groups remain intact. Both, the azo monomer and the crosslinking agent are essentially quantitatively incorporated into the network before the conversion of the third monomer is complete. The networks have been characterized in terms of their swelling in benzene, chlorobenzene, and methacrylonitrile. Die Terpolymerisation der drei Monomeren (3-Vinylphenylazo)-methylmalodinitril (1), (3-Vinylphenylazo)phenyls…

Implantation of the modified endocapsular bending ring in pediatric cataract surgery using a viscoadaptive viscoelastic agent.

1999

Cataract surgery and intraocular lens (IOL) implantation in pediatric eyes remain controversial. Using a viscoadaptive viscoelastic agent, we implanted a modified capsular bending ring (CBR) as well as an acrylic IOL with a sharp-optic-edge design in the capsular bag. All operated eyes demonstrated a low postoperative inflammatory reaction and a clinically well-centered IOL. The band-shaped, sharp-edged CBR facilitates the creation of a sharp, discontinuous bend in the equatorial capsule, which prevents anterior and posterior capsule opacification. Combining the viscoadaptive viscoelastic agent and the CBR enhances the safety of primary and secondary posterior chamber IOL implantation in pe…

Nanoscale Chemical Interaction Enhances the Physical Properties of Bioglass Composites

2013

Bioglasses are favorable biomaterials for bone tissue engineering; however, their applications are limited due to their brittleness. In addition, the early failure in the interface is a common problem of composites of bioglass and a polymer with high mechanical strength. This effect is due to the phase separation, nonhomogeneous mixture, nonuniform mechanical strength, and different degradation properties of two compounds. To address these issues, in this study a nanoscale interaction between poly(methyl methacrylate) (PMMA) and bioactive glass was formed via silane coupling agent (3-trimethoxysilyl)propyl methacrylate (MPMA). A monolith was produced at optimum composition from this hybrid …