Search results for "polymerization"
showing 10 items of 1689 documents
Molecular modifications—Mechanical behaviour relationships for gamma irradiated LLDPE/PA6 blends
1994
Abstract The molecular modifications, due to γ radiation under vacuum, of linear low density polyethylene/polyamide 6 blends are presented and related to their mechanical behaviour. Solubility and melt viscosity tests indicate that in blends the polyethylene component undergoes mainly crosslinking phenomena, whereas the main effect on polyamide is chain branching. According to these molecular modifications, the most relevant effect is the increase of the tensile modulus for the polyethylene rich blends and the increase of the impact strength for the polyamide rich blends.
Demixing and polymerization in systems of anisotropic globular particles: A molecular dynamics simulation study
1991
We report a first set of results of Molecular Dynamics simulations of phase separation in a two-dimensional system of identical particles bearing attachment sites at their surface. Morphology of regions of aggregation so obtained appear similar to images of biologically self-assembled structures. Also, they evidence the relevance of the region of thermodynamic instability and of the presence and range of interaction of specific attachment sites. Particles of our system are apt to represent indifferently, though grossly, globular proteins or rigid cells, bearing specific and fixed adhesion sites at their surface. Results illustrate some basic aspects of the origin of the morphology of extend…
Crystal structure and morphology of polymers from solid-state reactions
1975
Some solid-state reactions which give rise to the formation of polymer crystals are discussed and the observation of the nascent polymer morphology is used as a guide-line to learn about the reaction mechanism of solid-state polymerizations. Examples for the following three different mechanisms are treated in detail: (a) crystallization succeeding polymerization, (b) simultaneous polymerization and crystallization, and (c) polymerization in solid solution. The nascent morphology of poly(alkylene)s obtained by Ziegler-Natta catalysis is taken as an example for crystallization succeeding polymerization. Another example is the cationic polymerization of 1,3,5-trioxane from solution. In this ca…
Living and Controlled Anionic Polymerization of Methacrylates and Acrylates in the Presence of Tetraalkylammonium Halide-Alkylaluminum Complexes in T…
1997
The size of both the cation and the anion of added NR4 X influences the rate of living polymerization of acrylates and methacrylates with alkylaluminum compounds. This controlled reaction, which occurs near to room temperature, provides unimodal polymers with narrow molecular-weight distributions. The complex shown to the right is suggested as a possible active species. R=Me, Et, nBu; R'=Me, Et; X=Cl, Br, I.
Telechele des methylpropens durch kationische polymerisation
1986
Amorcage par des hydrocarbures aromatiques et aliphatiques contenant des groupes terminaux chlorure d'isopropyle, associes a du trichlorure de bore. Mecanisme. Recyclage du coamorceur et du solvant
Mechanism of anionic polymerization of (meth)acrylates in the presence of aluminium alkyls
1995
Summary Methyl methacrylate was polymerized with tert-butyl lithium in the presence of triethylaluminum or triisobutylaluminium at -78~ in toluene. As indicated by GPC and MALDI-TOF mass spectrometry, the polymerization is accompanied by side reactions. The lower oligomers were fractionated by distillation and characterised by NMR, FT-IR, UV and electron impact (EI) mass spectrometry. All these data show that part of the polymer chains are carrying exactly one tert-butyl isoprenyl ketone unit. In order to avoid the formation of tert-butyl isoprenyl ketone a molar ratio of A1/Li > 2 is necessary.
γ-radiation-initiated polymerization of vinylidene fluoride in dense carbon dioxide
2002
The γ-ray-initiated batch polymerization of vinylidene fluoride (VF2) has been investigated in dense carbon dioxide under relatively mild operative conditions (T ≤ 40 °C and P < 25 MPa). When the initial VF2 molar concentration was increased from 3.4 to 6.4 mol/L, monomer conversion increased from 20 to 73%; a similar trend was observed for the number-average molecular weight and the molecular complexity of synthesized poly(vinylidene fluoride) (PVDF) as determined from rheological measurements. Under all adopted experimental conditions, a synthesized PVDF polymer was collected in the form of a white powder. Despite the inherent heterogeneous character of the polymerization process, a homog…
Step-growth Polymerization ofBistriazolinediones with1,1-Diphenylethylene
1996
The reactions of 4-ethyl-1,2,4-triazoline-3,5-dione (ETD) (1) and 4-phenyl-1,2,4-triazoline-3,5-dione (PhTD) (2) with 1,1-diphenylethylene (DPE) (3) were investigated at room temperature. The reactions are very fast and are completed in less than 4 min. These reactions lead to the formation of two 2 :1 adducts via double Diels-Alder and Diels-Alder-ene reactions in a ratio of 1.35 : 1. The structure of these adducts where R = Et were determined by X-ray analysis of a single crystal. These compounds were used as models for the polymerization reactions. The reaction of bistriazolinediones (1,6-bis-(3,5-dioxo-1,2,4-triazoline-4-yl)hexane and bis-(p-3,5-dioxo-1,2,4-triazoline-4-ylphenyl)methane…
Cyclodextrins in Polymer Synthesis: Enantiodiscrimination in Free-Radical Polymerization of Cyclodextrin-Complexed Racemic N -Methacryloyl-D,L -pheny…
2003
The enantiodiscriminating polymerization of racemic cyclodextrin-complexed N-methacryloylphenylalanine methyl ester is investigated 1 H NMR spectra of the complexes with methylated β-cyclodextrin in D 2 O manifest splittings due to chiral recognition. The different stabilities of the diastereomeric complexes influence the kinetics of the homopolymerization, particularly at 0°C. An enrichment of the residual N-methacryloyl-L-phenylalanine methyl ester of 14% was achieved after 21 h of polymerization.
NMR and Quantum-Chemical Study on the Structure of Ester Enolate−Aluminum Alkyl Complexes as Models of the Active Center in the Anionic Polymerizatio…
1999
6Li and 13C NMR on ethyl α-lithioisobutyrate (EiBLi) and quantum-chemical (DFT) calculations on methyl α-lithioisobutyrate (MiBLi) were used to elucidate the structure of the active center in the anionic polymerization of methacrylates in the presence of triethylaluminum (AlEt3) in toluene. This study reveals ester enolate/aluminum alkyl complexes with different degrees of association, (MiBLi·AlEt3)n (n = 1, 2, 4), and different stoichiometries, MiBLi·xAlEt3 (x = 1, 2). In the presence of methyl pivalate (MPiv), which is taken as a model compound for the monomer and polymer, complexes such as (MiBLi·MPiv·AlEt3)n (n = 1, 2) are formed. These complexes can dissociate into MiBLi·2AlEt3 and MPi…