Search results for "Addition polymer"

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…

Mechanism of Anionic Polymerization of (Meth)acrylates in the Presence of Aluminum Alkyls, 6. Polymerization of Primary and Tertiary Acrylates

1998

The kinetics of the polymerization of n-butyl acrylate initiated by lithiated ester enolates in the presence of aluminum alkyls was investigated in toluene and in toluene/Lewis base mixed solvents at −78 °C. In pure toluene, curved time−conversion plots, incomplete monomer conversion, and broad molecular weight distributions (Mw/Mn ≈ 2) are observedin the absence of aluminum alkyls the molecular weight distributions are significantly broader (Mw/Mn > 14). High monomer conversions and narrower molecular weight distributions (Mw/Mn ≈ 1.5) are obtained when using Lewis bases (e.g., methyl pivalate) as cosolvents. The polymerization of tert-butyl acrylate rapidly reaches full monomer conversion…

Synthesis and solution properties of star-shaped poly(tert-butyl acrylate)

2000

A series of star polymers consisting of poly(tert-butyl acrylate) arms and an ethyleneglycol dimethacrylate (EGDMA) microgel core were synthesized using anionic polymerization. The effect of various parameters (precursor length, ratio [[EGDMA]/[Initiator], reaction time, and overall concentrations) on the average number of arms was investigated. Molecular weights were determined using GPC coupled with an online viscometer and MALLS. The exponents for the relation between intrinsic viscosity or radius of gyration and molecular weight, respectively, are extremely low, indicating that the dimensions of the star polymers only slightly increase with the number of arms. After a certain number of …

1993

The influence of lithium tert-butoxide (tBuOLi) and of lithium chloride on the oligomerization of tert-butyl acrylate (tBuA) initiated by tert-butyl α-lithioisobutyrate (tBiB-Li) was investigated. These additives affect both the kinetics and the product distribution. Whereas the addition of LiCl leads to a narrower molecular-weight distribution (MWD) the presence of tBuOLi induces broader MWD's, characterized by a very high fraction of the dimer. Both additives decrease the rates of propagation to different degrees. These effects are discussed on the basis of the formation of aggregates and adducts, the lithiated dimer having a higher tendency to form aggregates than the other oligomers. Th…

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

Polymerization with heterogeneous metalorganic catalysts. VI. Differences in polymerization activity of α-olefins and some kinetic results on butene-…

1967

Relative changes in polymerization activity of ethylene, propylene, and butene-1 in Ziegler-Natta polymerization were compared by use of TiCl3 samples contaminated with O2 and H2O to various extents. Catalyst depletion varied for the three monomers which supported the existence of different active centers. In butene-1 polymerizations with the system Al(C2H5)2Cl–TiCl3, the formation of active centers involves an irreversible and a reversible (adsorption) reaction, the former pertaining to the formation of Al(C2H5)Cl2 and dependent upon the purity of the TiCl3. The kinetic treatment of the rate curves suggests a mixed order of catalyst deactivation and again points to the importance of Al(C2H…

Some New Copolymers by Ionic Polymerization

1980

In the first part the cationic polymerization of a homologous series of cyclic ether–acetals with ring sizes of 11, 14, and 17 atoms is described. During the polymerization of triethylene glycol formal (TGF) an equilibrium is reached and besides high polymers cyclic oligomers are formed. The oligomers and the polymers are built up of a regular sequence of one oxymethylene unit and three oxyethylene units –[–(OCH2) (OC2H4)3–]–x. They are therefore be labelled a “sequenced copolymer.” The equilibrium concentrations of the cyclic oligomers with a polymerization degree from 2 to 15 follow the Jacobson–Stockmayer equation. The 14- and 17-membered monomers POC and HOC forms cyclic oligomers and h…

Homogeneous Langmuir-Blodgett Film of Double-Chain Ammonium Amphiphile Complexed with Anionic Polymer

1988

Heterogeneous textures suggesting the coexistence of a fluid and a solid phase were found both in a surface monolayer and in a deposited Langmuir-Blodgett (LB) film of double-chain ammonium amphiphiles by fluorescence microscopy. Although an annealing of the surface monolayer at 40°C allowed crystal growth, the heterogeneous phase separation remained in the LB film. A drastic change of the fluorescence image shows that the recrystallization of the complexed monolayer with anionic polymers conducted the homogeneous monolayer.

Über zwei formen des initiators Na-naphthalin und die bestimmung der „lebenden” kettenenden bei der anionischen polymerisation

1969

Na-Naphthalin in THF kommt in (mindestens) 2 Formen I und I' vor, die sich beim Start der anionischen Polymerisation von Styrol sehr verschieden verhalten. Ohne Zusatg von NaBPh4 wirken beide Formen als Initiatoren. Bei Zusatz von NzBPh4 wird die From I' desktiviert, wobei auf ein Molekul I' zwei Molekule NaBPh4 entfallen. Die hierbei entstehende inaktive Verbindung hat in der Umgebung der Wellenlange 350 nm fast den gleichen Extinktionskoeffizienten wie die “lebenden” Enden. Bei Nichtberucksichtigung dieses Effektes erhalt man daher fur die Konzentration der “lebenden” enden aus Absorptionsmessungen einen zu hohen Wert und fur die Geschwindigkeitskonstante kw(±) der Polymerisaton uber das …

Hyperbranched Polyglycerol-Based Lipids via Oxyanionic Polymerization: Toward Multifunctional Stealth Liposomes

2010

We describe the synthesis of linear-hyperbranched lipids for liposome preparation based on linear poly(ethylene glycol) (PEG) and hyperbranched polyglycerol (PG). Molecular weights were adjusted to values around 3000 g/mol with varying degrees of polymerization of the linear and the branched segments in analogy to PEG-based stealth lipids; polydispersities were generally low and below 1.3. The hydrophobic anchors were introduced into the lipid structures as initiators for the anionic polymerization of ethylene oxide and are either based on cholesterol or on different aliphatic glyceryl ethers. Complete incorporation of the apolar initiators was evidenced by MALDI-ToF analysis at all stages …