Polymer interpenetration

Polymers interpenetration of polymer chains, phase separation, compatibility between polymers, interdiffusion of latex particles, interface thickness in blends of polymers, light-harvesting polymers, etc. 

Assemblies of macromolecules include polymer blends, semi-interpenetrating polymer networks, network polymers, interpenetrating polymer networks and polymer—polymer complexes. 

Interpenetrating network (IPN) A combination of two polymers into a stable interpenetrating network. In a true IPN each polymer is cross-linked to itself, but not to the other, and the two polymers interpenetrate each other. In a semi-lPN, only one of the polymers is cross-linked the other is linear and by itself would be a thermoplastic. The purpose of producing IPN is to improve strength, stiffness, and chemical resistance of certain polymeric systems. 

Steric stabilisers are usually block copolymer molecules (e.g. poly (ethylene oxide) surfactants), with a lyophobic part (the anchor group) which attaches strongly to the particle surface, and a lyophilic chain which trails freely in the dispersion medium. The conditions for stabilisation are similar to those for polymer solubility outlined in the previous section. If the dispersion medium is a good solvent for the lyophilic moieties of the adsorbed polymer, interpenetration is not favoured and interparticle repulsion results but if, on the other hand, the dispersion medium is a poor solvent, interpenetration of the polymer chains is favoured and attraction results. In the latter case, the polymer chains will interpenetrate to the point where further interpenetration is prevented by elastic repulsion. 

Considerable reluctance has been displayed, even by polymer chemists, in accepting the concept of free polymer interpenetration as proposed by Flory for d-solvents, melts and higher polymer concentrations in good solvents. This reluctance has quite properly spawned attempts to devise experiments that disprove the interpenetration hypothesis using chemical means. As it happened, many of the early innovative studies of Vollmert, well summarized in his 1975 review (Vollmert, 1975), appeared to demonstrate that interpenetration did not occur significantly in more concentrated solutions. 

When the process involves two competitive reactions, some people prrfer to call those modified polymers interpenetrated polymer networks (IPNs) [5]. The formation of a polyether-urethane network in a loosely crosslinked poly(methyl methacrylate) matrix to increase its toughness can serve as one of the examples. From a general point of view, the analysis of the reaction-induced phase separation is the same (perhaps more complex) for IPNs than for rubber-modified epoxies or for high-impact polystyrene. 

G. Milczarek, O. Inganas, Renewable Cathode Materials from Biopolymer/ Conjugated Polymer Interpenetrating Networks. Science 2012,335,1468-1471. 

Random coils of polymers are separated from each other in a dilute solution. With an increase in the concentration of the solution, the mean distance between them is reduced, and they start to overlap. With a further increase in concentration, the polymers interpenetrate each other so deeply that the properties of each individual chain become difficult to observe (Figure 2.19). The concentration at which polymers start to overlap is called the overlap concentration. The overlap concentration can be found by the condition such that the volume fraction na /R of monomers within the region occupied by the random coil of each polymer becomes the same order as that of the concentration (p of the solution... 

Figure 7.23. Stress-strain curves of gradient polymer, interpenetrating networks, and random copolymer of methyl methacrylate and methyl acrylate (ratio 60/40) temperature, 80°C strain rate, 0.03 sec (From Akovali et al.)...

Y. Minoura, Entanglement in crosslinking Polymers Interpenetrating Polymer Networks, Kobunshi 27(3), 189 (1978). Review of IPNs. 

Furthermore, BC/SiO NPs aerogels (4-9 wt%) prepared by freeze drying and showing a polymer interpenetrating network microstructure of BC and silica, (Figure 2.24), presented density, specific surface area and low thermal conductivity values (2 x 10 g.cm 734 m. g 3.1 x 10 W.mfK S respectively) comparable to those of pure silica aerogels, and are simultaneously more flexible due to the presence of micro-cracks left by freeze drying [246]. 

To enhance polymer interpenetration conditions and to form small domain sizes, compatibility with the solvent should be maintained even after water or alcohol is released as a polymerization by-product. 

D. Boyer, and T. S. Chan, on bioadhesion, calcification and on biomaterials for dental restorations. It was found that the only satisfactory adhesion for plastic tooth restorations can be obtained by elastomeric interliners, that for lasting bioadhesion a thin zone of polymer-interpenetration, precipitation and/or reaction has to be created, and that this zone should be lightly calcified. 

If the interpenetration free energy Fint is much smaller than kT, the two polymers interpenetrate almost freely. They are diaphanous to each other and a mean-field theory (Eq. 4) may be used to calculate the mutual virial coefficient Gab ... 

Milczarek G, higanas O (2012) Renewable cathode materials from biopolymer/conjugated polymer interpenetrating networks. Science 335 1468-1471... 

Abbasi et al. bulk- and surface-modified PDMS with poly(acrylic acid) using a sequential method for preparation of polymer interpenetrating networks of PDMS/acrylic acid, as shown in Figure 23.5 [1,26]. This was used as an effective biomaterial for cochlear implants. Cured PDMS was swollen when in contact with the monomer solution of acrylic acid, which contained the initiator as well as the crosslinker. The swollen PDMS was then kept under polymerization conditions to activate the initiator and the crosslinker. The curing after polymerization helped in formation of interpenetrating networks. These led to hydrophilic silicone polymer IPN that improved the material s cell adhesion to its surface. 

HBP-SA, HBP-SA-Ac, HBP-PA and HBP-PA-Ac polymers, interpenetrated electrolyte membrane HBP-SA-co-HBP-Ac, and the crosslmked membranes CL-HBP-SA and CL-HBP-PA showed the VTF-type temperature dependence. These polymers and membranes are thermally stable up to 260 °C, and they had suitable thermal stability as an electrolyte in the polymer electrolyte fuel cell operating under non-humidified conditions. Fuel cell measurement using a single membrane electrode assembly cell with crosslinked membranes CL-HBP-SA and CL-HBP-PA was successfully performed under non-humidified conditions, and polarization curves were observed. The concept of the proton conduction coupled with the polymer chain motion was proposed as one possible approach toward high temperature fuel cells. 

Equation 3 assumes every point of intersection results in immediate and irreversible attachment, chemically equivalent to an infinite condensation rate. Finite condensation rates mitigate the criterion for mutual transparency, i.e. since every point of intersection does not result in immediate and irreversible "condensation", interpenetration may occur for structures characterized by D > 1.5. The value of equation 3 is that it provides a qualitative understanding of the effect of structure on the extent of polymer interpenetration and thus porosity smaller polymer sizes and lower mass fractal dimensions favor denser films, and larger polymer sizes and greater mass fractal dimensions favor more porous films. In all cases increased condensation rates reduce the tendency toward interpenetration, favoring more porous films. 

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