Polymerization induced phase separation

The mixing entropy given by Equation (11.9) is only valid when both components of the binary composite are small molecules. When one (or both) of the components is a polymer, the number of distinct states decreased because of the constraint that consecutive monomers in a polymer chain must be in the neighboring lattice sites. Therefore the mixing entropy decreases [8]. 

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Fig. 15. A schematic representation for the polymerization-induced phase separation of DOPE and poly 16 leading to fusion of vesicles due to bilayer contact of the enriched PE domains. See text for description.

Fig. 38 Polymerization-induced phase separation of a supramolecular polymer. Reprinted with permission from [141]...

Figure 4. Schematic diagram of the polymerization induced phase separation process.

Figure 1. Schematic representation of the influence of various factors on the miscibility and phase separation. The shaded areas represent the two-phase regions. The arrows show the paths for phase separation, while the reverse directions would be the paths for miscibility. From left-to-right Temperature-induced phase separation solvent-induced phase separation reaction (i.e. polymerization) -induced phase separation (the two-phase regions are entered with increasing degree of polymerization (DP)) and pressure-induced phase separation. < ) = polymer concentration, S2 and SI solvent and nonsolvent PI andP2 = polymer 1 and polymer 2.

Phase Separation. All experimental work concerning PSLC s suggests, more or less strongly, that phase separation of a polymer-rich phase occurs upon polymerization. Such polymerization-induced phase separation may be expected, since the total mole fraction of monomer and polymer molecules, and therefore also the entropy of mixing, decreases dramatically upon polymerization. There are changes in the enthalpy of mixing, also as a result of reaction, as the acrylate moiety is converted to its saturated counterpart. 

Matsushita, Y., Furukawa, H., Okada, M. Crystal-like pattern formation in polymerization-induced phase separation. Phys Rev E Stat Nonlin Soft Matter Phys 70(4 Pt 1), 040501-1-040501-3 (2004)... 

Fig. 8.24 TEM micrographs of the phase-separated structure of styrene/PMMA/ AIBN(80/20/0.2) blend after polymerization at 80 °C in polymerization-induced phase separation...

Several factors are found responsible for why numerous blend systems are not successful. First, the component polymers are usually not miscible with each other due to thermodynamic constraints, for example, lack of solubility and finite inter-fadal tension. Second, immiscible polymer blend preparation is often affected by kinetic constraints, for example, slower rate of deformation of the dispersed polymer and faster rate of coalescence of the droplets. In turn, these rates are directly influenced by the type of flow field, for example, shear versus extensional, strain history, chemical reactions, for example, grafting reactions at polymer-polymer interfaces or polymerization-induced phase separation, and polymer properties, such as viscosity and interfacial tension. Accordingly, the multidisciplinary efforts to analyze, understand, and design polymer blends with improved properties extend from synthesis and characterization to processing and manufacturing. Such efforts... 

Odian, G., 1991. Principles of Polymerization, John WUey and Sons, New York Oh, J., and Rey, A. D., 2002. Computer simulation of functional polymeric materials formation via polymerization-induced phase separation imder a temperature gradient , in Phase Separation in Polymer Solutions and Blends, R K. Chan (Ed.), Research Signpost, Trivandrum, India. Panayiotou, C., and Vera, J. H., 1982. Polym. J., 14,681-694. 

T. Schneider, F. Nicholson, A. Kahn, and J. W. Doane, Flexible encapsulated cholesteric LCDs by polymerization induced phase separation, SID Inti Symp. Digest Tech. Papers, 36, 1568-1571 (2005). 

In PDLCs with weak anchoring, the drive voltage is usually low. One example is the PDLC made from E7 (from Merck) and NOA65 (Norland Optical Adhesive) by photo-polymerization-induced phase separation [27]. The cell thickness is 12 pm. The square of the drive voltage Vd is approximately linearly proportional to 1/D, as shown in Figure 11.18. 

Szczepanski CR, Pfeifer CS et al (2012) A new approach to network heterogeneity polymerization induced phase separation in photo-initiated, free-radical methacrylic systems. Polymer 53 4694-4701... 

There are three principal methods of fabricating PDLC (to disperse liquid crystals in polymer matrix) phase separation, encapsulation and permeation. In the phase separation method, liquid crystal materials, prepoljnner (monomer or oligomer) and photoinitiator (curing agent) are mixed, and then polymerization is brought about by heating [2] or UV irradiation [3]. During the polymerization, the liquid crystal material phase separates from the solution, and liquid crystal droplets and a polymer matrix are formed. By measurement of the nematic-isotropic transition temperature, the purity of the liquid crystal in the droplets can be checked. In the case that the polymerization-induced phase separation is not complete and unreacted prepolymer is dissolved in the liquid crystal droplets, the... 

In the case of polymerization-induced phase separation, due to the positive feedback arising from the Tromsdorff effects, it was found that the phase separation induced by polymerization also becomes autocatalytic. The phase separation proceeds with a maximum rate in the vicinity of the irradiation time at which the rate of polymerization reaches its maximum. As a consequence, a local strain field is generated and develops as the reaction continues. For small-molecule systems, this reaction-induced strain quickly relaxes and its effects on the subsequent reaction and phase separation are not significant. For polymeric systems, this reaction-induced strain is not negligible and therefore affects the concentration fluctuations as a long-range interaction. 

C. Polymerization-Induced Phase Separation Outlook and the Modular Approach... 

The dynamic flexibility of supramolecular polymers is exploited by Keizer et al. [34]. in polymerization-induced phase separation (PIPS) with hydrogen-bonded supramolecular polymers. In PIPS, a supramolecular polymer is dissolved in a reactive monomer, which is subsequently polymerized to cause phase separation resulting in two polymeric phases with certain morphology. PIPS is currently used to produce multiphase composite materials like high-impact polystyrene, avoiding the use of solvent and consequently resulting in the fast and clean production of polymeric materials. 

Polymerization-induced phase separation (PIPS) (Yuhong 2013). 

Yuhong Liu. Polymerization-induced phase separation and resulting thermomechanical properties of thermosetting/reactive nonlinear polymer hlends. J. Appl. Polym. Sci. 127 no. 5 (2013) 3279-3292. 

The phase-separation method was developed at Kent State University in the late 1980s. It consists of in sitn segregation of liqnid crystalline microdroplets from a homogeneous mixture of liquid crystal and polymer/prepolymer, indnced by a factor that gave the techniqne its name, as follows (a) polymerization-induced phase separation (PIPS) (b) solvent-induced phase separation (SIPS) and (c) thermally induced phase separation (TIPS). 

Polymerization-induced phase separation consists of segregation of the liquid crystal from a homogeneous mixture with a prepolymer as the polymerization proceeds and polymerization medinm hardens, the liquid crystal droplets are forced... 

Liquid crystal and polymer dispersions are fabricated using thermally-induced phase separation (TIPS), solvent-induced phase separation (SIPS), or Polymerization-induced phase separation (PIPSX/I)- For TIPS, a homogeneous mixture of a low-molecular weight liquid crystal and thermoplastic polymer is cooled below the critical phase separation temperature to induce phase separation into liquid crystal rich and polymer rich domains. The morphological properties (domain size, number of domains per unit volume, and the composition of the domains) depend primarily on the choice of liquid crystal and thermoplastic polymer, the initial weight fraction of liquid crystal in die initial mixture, and the rate of cooling. 

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