Kinetic of crystallization from the melt and chain folding in polyethylene fractions revisited: theory and experiment

Radical polymerization with reversible addition−fragmentation chain transfer (RAFT polymerization) can be used to synthesize a wide range of polymers of controlled architecture and narrow molecular weight distribution. The polymerizations use addition−fragmentation chain transfer agents (RAFT agents) that possess high transfer coefficients in free radical polymerization and confer living character on the polymerization. This paper explores the effect of the substituents R of dithiobenzoate RAFT agents [SC(Ph)S−R] on the outcome of polymerizations of styrene, methyl methacrylate (MMA) and butyl (BA) or methyl acrylate (MA). In MMA polymerization at 60 °C, effectiveness depends strongly on R decreasing in the order where R is:  −C(Alkyl)2CN ∼ −C(Me)2Ar > −C(Me)2C(O)O(alkyl) > −C(Me)2C(O)NH(alkyl) > −C(Me)2CH2C(Me)3 ≥ −C(Me)HPh > −C(Me)3 ∼ −CH2Ph. Of these, only the compounds with R = −C(Me)2Ph and −C(Me)2CN provided polymers with substantially narrowed polydispersities in batch polymerization and gave molec...

Thiocarbonylthio Compounds [SC(Ph)S−R] in Free Radical Polymerization with Reversible Addition-Fragmentation Chain Transfer (RAFT Polymerization). Role of the Free-Radical Leaving Group (R)

▪ Abstract This review summarizes recent experimental studies of instabilities in free-surface flows driven by thermocapillarity. Two broad classes are considered, depending upon whether the imposed temperature gradient is perpendicular (Marangoni-convection instability) or parallel (thermocapillary-convection instability) to the free surface. Both steady and time-dependent instabilites are reviewed in experiments employing both large- and small-aspect-ratio geometries of various symmetries.

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Experiments on thermocapillary instabilities

A. Temperature Chambers 1735 B. Pressure Cells 1735 C. Stretching Equipment 1736 D. Fiber Spinning Equipment 1737 E. Fiber Drawing Apparatus 1738 F. Shear Apparatus 1739 IV. Combined Techniques 1739 A. Simultaneous SAXS/WAXD 1739 B. Raman Spectroscopy 1740 C. Laser Light Scattering 1741 D. Fourier Transform IR Spectroscopy 1743 V. Applications 1743 A. Materials-Based Studies 1743 1. Block Copolymers 1743 2. Ionomers 1745 3. Liquid Crystalline Polymers 1745 4. Biopolymers 1746 B. Phenomenon-Based Studies 1747 1. Polymer Solutions and Gels 1747 2. Colloidal Suspensions, Micellar Solutions, and Microemulsions 1749

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Small-angle X-ray scattering of polymers.

This paper reviews the degradation behavior of aliphatic polyesters of current interest, including polylactide, polycaprolactone, poly(3-hydroxybutyrate) and their copolymers. Special focus is given to degradation products formed in different abiotic and biotic environments. The influence of processing and processing additives on the properties and degradation behavior is also briefly discussed.

Aliphatic polyesters : Abiotic and biotic degradation and degradation products

This paper presents a study of the convection in acetone due jointly to the thermocapillary (Marangoni) and thermogravitational effects. The liquid (acetone) is submitted to a horizontal temperature difference. Experiments and numerical simulations both show the existence of three different states : monocellular steady states, multicellular steady states and spatio-temporal structures. The results are discussed and compared with the linear stability analysis of Smith & Davis (1983).

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022112092000880

Coupled buoyancy and Marangoni convection in acetone: experiments and comparison with numerical simulations

Performing detailed studies of viscoelastic dewetting of thin polystyrene films on solid substrates, we demonstrate the existence of residual stress due to strongly out of equilibrium chain conformations and a reduced entanglement density resulting from film preparation by spin coating. The ratio of stress over elastic modulus was found to increase strongly with decreasing film thickness and increasing chain length. Full equilibration of chain conformations required long times comparable to bulk reptation times. However, for chains longer than about 3000 monomers, the residual stress relaxed faster, at a rate independent of chain length.

Relaxation of residual stress and reentanglement of polymers in spin-coated films.

Les mesures de tension interfaciale ont ete faites a l'interface eau/alcanol (C 4 a C 12 ) Les resultats indiquent que la tension interfaciale augmente avec la temperature

D. Villers

Papers

Coupled buoyancy and Marangoni convection in acetone: experiments and comparison with numerical simulations

Relaxation of residual stress and reentanglement of polymers in spin-coated films.

Temperature dependence of the interfacial tension between water and long-chain alcohols

Aromatic homopolymers obtained by precipitation polycondensation: 1. Synthesis of naphthalene-containing polyketones

Optimization of an Hough transform algorithm for the search of a center