Unprecedented Scissor Effect of Macromolecular Cross-linkers on the Glass Transition Temperature of Poly(N-vinylimidazole), Crystallinity Suppression of Poly(tetrahydrofuran) and Molecular Mobility by Solid State NMR in Poly(N-vinylimidazole)-l-poly(tetrahydrofuran) Conetworks

Unexpected correlations have been found between structural parameters and glass transition temperatures (Tg) of poly(N-vinylimidazole) (PVIm) and crystallinity of poly(tetrahydrofuran) (PTHF) in a series of novel, unique PVIm-l-PTHF amphiphilic conetworks synthesized in broad composition ranges via free radical copolymerisation of VIm and semicrystalline, methacrylate-telechelic PTHF macromolecular cross-linkers with varying Mn from 2170 to 10 000 g mol−1. Differential scanning calorimetry (DSC) investigations revealed microphase separation between the covalently bonded PVIm and PTHF components, that is two distinct Tgs corresponding to the respective polymers (PVIm and PTHF) were obtained in these optically clear, transparent materials. Complete microphase separation, i.e. absence of mixed phases, was also confirmed by solid state NMR measurements. The Tg of the PVIm phase significantly decreases with increasing PTHF content, and Fox–Flory type correlation was surprisingly found between the Tg of PVIm and its Mc (average molecular weight between cross-links). This striking finding indicates a unique, unpredicted scissor effect of the macromolecular PTHF cross-linker in these materials, i.e. with respect to glass transition, PVIm behaves as individual chains between cross-links. The molecular mobility in the PVIm chain segments obtained by solid state NMR investigations shows a similar trend as a function of Mc. In the DSC thermograms, the semicrystalline PTHF has a sharp endothermic melting peak (Tm) indicating partial crystallisation of this polymer. It was found that the Tm and the crystalline fraction (Xc) of the PTHF phase are suppressed by even a minimal content of PVIm phase in the conetworks. Even complete diminishing of Xc occurs in conetworks with lower than 40 wt% PTHF of the lowest Mn (2170 g mol−1). Unexpectedly, Tm linearly decreases with Mc in conetworks with constant Mn of PTHF. These data indicate that the decrease of both Tm and Xc of PTHF is not only composition dependent, but the MW of the macromolecular PTHF cross-linker and the Mc of the PVIm component also have effects on these parameters. These results also indicate that chemical bonding of polymer chains in conetworks yields novel materials with unprecedented property variation. This provides unique opportunities for fine tuning of the investigated fundamental material properties, i.e. Tg, Tm and Xc, within certain ranges in the novel PVIm-l-PTHF amphiphilic conetworks by selecting the proper synthesis parameters, that is, composition and MW of the telechelic PTHF macromonomer cross-linker

Understanding the role of MAM molecular weight in the production of PMMA/MAM nanocellular polymers

Nanostructured polymer blends with CO2-philic domains can be used to produce nanocellular materials with controlled nucleation. It is well known that this nanostructuration can be induced by the addition of a block copolymer poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) (MAM) to a poly(methyl methacrylate) (PMMA) matrix. However, the effect of the block copolymer molecular weight on the production of nanocellular materials is still unknown. In this work, this effect is analysed by using three types of MAM triblock copolymers with different molecular weights, and a fixed blend ratio of 90 wt% PMMA and 10 wt% of MAM. Blends were produced by extrusion. As a result of the extrusion process, a non-equilibrium nanostructuration takes place in the blends, and the micelle density increases as MAM molecular weight increases. Micelle formation is proposed to occur as result of two mechanisms: dispersion, controlled by the extrusion parameters and the relative viscosities of the polymers, and self-assembly of MAM molecules in the dispersed domains. On the other hand, in the nanocellular materials produced with these blends, cell size decreases from 200 to 120 nm as MAM molecular weight increases. Cell growth is suggested to be controlled by the intermicelle distance and limited by the cell wall thickness. Furthermore, a theoretical explanation of the mechanisms underlying the limited expansion of PMMA/MAM systems is proposed and discussed

Anisotropy in nanocellular polymers promoted by the addition of needle‐like sepiolites

This work presents a new strategy for obtaining nanocellular materials with high anisotropy ratios by means of the addition of needle‐like nanoparticles. Nanocellular polymers are of great interest due to their outstanding properties, whereas anisotropic structures allow the realization of improved thermal and mechanical properties in certain directions. Nanocomposites based on poly(methyl methacrylate) (PMMA) with nanometric sepiolites are generated by extrusion. From the extruded filaments, cellular materials are produced using a two‐step gas dissolution foaming method. The effect of adding various types and contents of sepiolites is investigated. As a result of the extrusion process, the needle‐like sepiolites are aligned in the machine direction in the solid nanocomposites. Regarding the cellular materials, the addition of sepiolites allows one to obtain anisotropic nanocellular polymers with cell sizes of 150 to 420 nm and cell nucleation densities of 1013–1014 nuclei cm−3 and presenting anisotropy ratios ranging from 1.38 to 2.15, the extrusion direction being the direction of the anisotropy. To explain the appearance of anisotropy, a mechanism based on cell coalescence is proposed and discussed. In addition, it is shown that it is possible to control the anisotropy ratio of the PMMA/sepiolite nanocellular polymers by changing the amount of well‐dispersed sepiolites in the solid nanocomposites

Polymer Release out of a Spherical Vesicle through a Pore

Translocation of a polymer out of curved surface or membrane is studied via mean first passage time approach. Membrane curvature gives rise to a constraint on polymer conformation, which effectively drives the polymer to the outside of membrane where the available volume of polymer conformational fluctuation is larger. Considering a polymer release out of spherical vesicle, polymer translocation time $\tau$ is changed to the scaling behavior $\tau\sim L^2$ for $R<R_G$, from $\tau\sim L^3$ for $R\gg R_G$, where $L$ is the polymer contour length and $R$, $R_G$ are vesicle radius and polymer radius of gyration respectively. Also the polymer capture into a spherical budd is studied and possible apparatus for easy capture is suggested.Comment: 14 pages RevTeX, 6 postscript figures, published in Phys. Rev. E 57, 730 (1998

Quasi-melt Processes For Single Polymer Composites And Products Thereof

Processes and compounds are described herein for single polymer composites based on a process for making the single polymer composites that includes the steps of heating a matrix material to create polymer melt, cooling the polymer melt to below its Tm to create an undercooled polymer melt, or quasi-melt, and combining the melt with an enhancing or reinforcing material to produce a single polymer composite. The process can produce materials that do not have any degradation of the polymer characteristic of the enhancing material due to melting of the polymer in the enhancing material.Georgia Tech Research Corporatio

Polymer Film-producing Methods And Devices Produced Therefrom

Described herein are improved methods of forming polymer films, the polymer films formed thereby, and electronic devices formed form the polymer films. The methods generally include contacting a polymer with a solvent to at least partially solvate the polymer in the solvent, exposing the at least partially solvated polymer and solvent to ultrasonic energy for a duration effective to form a plurality of ordered assemblies of the polymer in the solvent, and forming a solid film of the polymer, wherein the solid film comprises the plurality of ordered assemblies of the polymer.Georgia Tech Research Corporatio

How to derive and parameterize effective potentials in colloid-polymer mixtures

Polymer chains in colloid-polymer mixtures can be coarse-grained by replacing them with single soft particles interacting via effective polymer-polymer and polymer-colloid pair potentials. Here we describe in detail how Ornstein-Zernike inversion techniques, originally developed for atomic and molecular fluids, can be generalized to complex fluids and used to derive effective potentials from computer simulations on a microscopic level. In particular, we consider polymer solutions for which we derive effective potentials between the centers of mass, and also between mid-points or end-points from simulations of self-avoiding walk polymers. In addition, we derive effective potentials for polymers near a hard wall or a hard sphere. We emphasize the importance of including both structural and thermodynamic information (through sum-rules) from the underlying simulations. In addition we develop a simple numerical scheme to optimize the parameterization of the density dependent polymer-polymer, polymer-wall and polymer-sphere potentials for dilute and semi-dilute polymer densities, thus opening up the possibility of performing large-scale simulations of colloid-polymer mixtures. The methods developed here should be applicable to a much wider range effective potentials in complex fluids.Comment: uses revtex4.cls; submitted for archival purpose

Membrane formation by immersion precipitation : the role of a polymeric additive

In this thesis the immersion precipitation process is studied for systems in which two polymers are present.\ud In its basic form, immersion precipitation is carried out by immersing a thin film of a concentrated polymer solution into a bath of nonsolvent. By exchange of solvent from the polymer solution, and nonsolvent from the coagulation bath, the polymer solution becomes instable. Liquid-liquid phase separation results in a polymer lean phase and a polymer rich phase. The polymer lean phase forms pores inside a matrix created by the polymer rich phase, which forms the membrane.\ud The objective of this thesis is to investigate the effects of the addition of a second polymer into the polymer solution. The use of a second polymer (polymeric additive) that is miscible with the nonsolvent can result in more open porous (co-continuous) structures and a better defined porosity

A flexible polymer chain in a critical solvent: Coil or globule?

We study the behavior of a flexible polymer chain in the presence of a low-molecular weight solvent in the vicinity of a liquid-gas critical point within the framework of a self-consistent field theory. The total free energy of the dilute polymer solution is expressed as a function of the radius of gyration of the polymer and the average solvent number density within the gyration volume at the level of the mean-field approximation. Varying the strength of attraction between polymer and solvent we show that two qualitatively different regimes occur at the liquid-gas critical point. In case of weak polymer-solvent interactions the polymer chain is in a globular state. On the contrary, in case of strong polymer-solvent interactions the polymer chain attains an expanded conformation. We discuss the influence of the critical solvent density fluctuations on the polymer conformation. The reported effect could be used to excert control on the polymer conformation by changing the thermodynamic state of the solvent. It could also be helpful to estimate the solvent density within the gyration volume of the polymer for drug delivery and molecular imprinting applications