Interpenetrating polymer network Gradient

A series of castor oil polyurethane/poly(methyl methacrylate) interpenetrating polymer networks (IPNs) and gradient IPNs, cured at room temperature, were prepared by a simultaneous IPN method, and nanocomposites with BaTiOs superfine fibre were reported for the systems. A dose-dependent improvement in thermoelectric and mechanical properties was observed in the nanocomposites compared to the pristine systems. 

Hybrid composite materials (HCM) represent the newest group of various composites where more than one type of fibre is used to increase cost-performance effectiveness, i.e., in a composite system reinforced with carbon fibres the cost can be minimised by reducing its content while maximising the performance by optimal partial replacement with an another fibre or by changing the orientations. HCM include nanocomposites [31], functionally gradient materials [32], Hymats (hybrid materials) [33], interpenetrating polymer networks (IPN) [34], and liquid crystal polymers [35]. 

G. C. Berry and M. Dror, Modification of Polyurethanes by Interpenetrating Polymer Network Formation with Hydrogels, Am. Chem. Soc. Div. Org. Coat. Plast. Chem. Pap. 38(1), 465 (1978). Polyether-urethane-urea block copolymers with crosslinked HEMA, NVP, or acrylamide. IPNs and gradient IPNs for biomedical purposes. Strength, water swellability, and good blood compatibility. 

The diffusion theory states that interpenetration and entanglement of polymer chains are additionally responsible for bioadhesion. The intimate contact of the two substrates is essential for diffusion to occur, that is, the driving force for the interdiffusion is the concentration gradient across the interface. The penetration of polymer chains into the mucus network, and vice versa, is dependent on concentration gradients and diffusion coefficients. It is believed that for an effective adhesion bond the interpenetration of the polymer chain should be in the range of 0.2-0.5 pm. It is possible to estimate the penetration depth (/) by Eq. (5),... 

Figure 2. Concentration profiles of poly(2-chloroethyl acrylate) in poly-(methyl methacrylate) along the thickness (L0) dimension of the samples. (GRAD) Gradient polymer, (IPN) interpenetrating networks.

Figure 3. Stress-strain curves of three gradient polymers and one interpenetrating network of poly(methyl methacrylate) with 2-chloroethyl acrylate at comparable strain rates of 2-3% /sec and same temperature of 80° C. The numerals in parentheses indicate concentrations (mole percent) of chloroethyl acrylate in poly(methyl methacrylate).

An interpenetrating network of PEDOT and poly(ethylene oxide) formed a material capable of a reversible angular deflection owing to the built-in gradients of polymer and conductivities [158]. A further network of PEDOT and polybutadiene/poly(ethylene... 

The interpenetration between the polymer chains and the mucin chains in the mucosa is believed to be the main physical mechanism for mucoadhesion, and together with the adsorption theory is the most accepted in the literature. This mechanism was first proposed in the polymer-polymer interface" " but was later applied to mucoadhesion due to the polymeric nature of mucin. Basically, during interpenetration the molecules of the mucoadhesive and the mucin molecules in the mucosa are brought into contact, and due to the concentration gradient the polymer chains penetrate into the mucin network with specific diffusion coefficients (Figure 52.4). 

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.)...

Budovskaya L.D., Tikhonova L.Yu., and Ivanova V.N., Synthesis of Gradient Interpenetrating Networks Based on Oligoetheracrylates, Polymer Optical Materials, Collection of Articles, Chemogolovka, 1989, pp. 101 - 103. (Rus)... 

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