Entanglement of polymers

Interpenetration of the bioadhesive polymer chains and entanglement of polymer and muein ehains, and... 

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),... 

It is important to note that there is a critical threshold molecular weight below which there is little if any entanglement of polymer chains. Melt viscosity is a measure of the tendency (speed) of melted materials to flow. 

As polymerization proceeds beyond the theoretical gel point and the resulting prepolymer concentration becomes higher, entanglements of polymer chains are... 

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... 

The water content in the PMAA gel contributes to the segmental motion of the network polymer as described above. On the other hand, the restraint of chain mobility in poly(A-vinylpyrrolidone) gel, caused by the presence of crosslinking and entanglement of polymer chains, was identified [35]. The Ti for the PMAA in the gel was also measured as a function of the degree of crosslinking with constant water content. The Ti values obtained for the main and side chain carbons of the network polymer in the PMAA gel (q = 3.4), as a function of the mole ratio of MBAA to MAA (F) and uncrosslinked PMAA solution (29.4 w%), are plotted in Fig. 20.12(a, b). 

One of the most important bulk property variables of polymers is the glass transition temperature 7g, which must be well below the use temperature to allow the interdiffusion and entanglement of polymer chains when the particles get in contact, once the aqueous phase has been evaporated. Thus, the monomer(s) used have to be selected such that the desired is obtained. Useful tables showing Tg and other physical and chemical properties of homopolymers are available in the literature [66-68]. The well-known Fox equation [69] can be used to estimate the Tg of a copolymer as a function of monomer composition and TgS of the component monomers. It is important to take into account that polar polymers tend to hydroplasticize, reducing the in the film formation process [70]. Several commercial latexes are terpolymers that contain two of the monomers present in major amounts to grossly obtain the basic desired properties, with the third monomer present in a minor amount for fine tuning of a special property [71-73]. 

Fig. 6.4 Illustration of physical entanglement and topological entanglement of polymer chains...

For example, it is possible to prepare hyperbranched polyimides from 3,5-dimethoxyphenol and 4-nitrophthalonitrile in the presence of diphenyl(2,3-dihydro-2-thioxo-3-benzoxazolyl) phosphonate (DBOP) as a condensation agent at room temperature. Hyperbranched polyimide was obtained through thermal or chemical imidization of the precursor (polyamic acid) (Scheme 1.3) [19]. The obtained hyperbranched polyimide had a relatively great molecular mass (A/ ) of about 190000gmor but low inhinsic viscosity of 0.30 dLg . Therefore, it had a compact configuration and the lack of entanglement of polymer chains. The polymer obtained via chemical imidization was soluble in apiotic polar solvents such as tetrahydrofuran (THF), while the polymer from thermal imidization was insoluble in any solvents. 

A mechanism behind the drag reduction and drag increase may be that polymer molecules or possibly entanglements of polymer molecules stretch in the flow field and become elongated. This stretching is quantified by measuring on a relaxation time behaviour for the polymer solution leaving the filter. 

The strength of weld lines in injection-molded articles is generally weaker than that of the bulk. This is due to the incomplete entanglement of polymer chains at the two impinging fountain flow fronts in the mold cavity. When the two flow fronts meet in the cold cavity, the molecular orientation at the interface remains parallel to the weld line as evidenced by the frozen-in molecular orientation found in the molded article under proper injection-molding conditions... 

The binding sites in these materials rely on noncovalent entanglement of polymer chains which exist as long as the membrane is exposed to a nonsolvent. Thus, the memory effects can be erased by solvent exposure and the method hence suffers from a limited robustness. Instead of this one-pot approach, composite membranes are growing in importance. Here the MIP formation is decoupled from the phase inversion process or technique to form a membrane support of choice. This support can then be used for grafting MIPS either in the film format or by attaching preformed MIP particles. " ... 

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