Poly chemically crosslinked

First step (a) represents the initial system - solution of the poly(acrylic acid) (urea and formaldehyde are not shown). Then, growing macromolecules of urea-formaldehyde polymer recognize matrix molecules and associate with them forming polycomplex. This process leads to physical network formation and gelation of the system (step b). Further process is accompanied by polycomplex formation to the total saturation of the template molecules by the urea-formaldehyde polymer (step c). Chemical crosslinking makes the polycomplex insoluble and non-separable into the components. In the final step (c), fibrilar structure can be formed by further polycondensation of excess of urea and formaldehyde. 

Figure 10.3 Mean molecular mass between chemical crosslinks and trapped chain entanglements Mc+e in a cured mixture of a poly(ethylene glycol) diacrylate (PEGDA) and 2-ethylhexyl acrylate (EHA) as a function of the EHA content [52]. Mc+e values were determined from (1/T2s)max and the plateau modulus (see Figure 10.2). A substantial difference in Mc+e value, as determined by these two methods at low crosslink density, is caused by the effect of network defects which decrease volume average network density determined by DMA (see Section 10.3). The molecular mass of PEGDA (Mn = 700 g/mol) is indicated by an arrow. The molecular mass of network chains in cured PEGDA is about three times smaller than that of the initial monomer. The molecular origin of this difference is discussed in Section 10.3...

Recently, a versatile class of poly(ethylene propylene)/poly(ethylene oxide) block copolymer micelles were introduced they were stable due to a combination of high block incompatibility, kinetically frozen core, and high interfacial tension between core and solvent [53, 58]. Moreover, by using a co-solvent of varying composition, the aggregation number was controlled and soft spheres from star-like to micelle-like could be obtained. Another way is core stabilization via chemical crosslinking, say by UV radiation [59-64]. 

Castro, C., Vesterinen, A., Zuluaga, R., Caro, G., Filpponen, 1., Rojas, 0. J., Kortaberria, G., and Ganan, P. (2014). In situ production of nanocomposites of poly(vinyl alcohol) and cellulose nanofibrils from Gluconacetobacter bacteria Effect of chemical crosslinking. Cellulose, in Press. 

S. Umeda, H. Nakade, T. Kakuchi, Preparation of superabs bent hydrogels from poly (aspartic acid) by chemical crosslinking, Polym. Bull. 67 (2011) 1285-1292. 

Otsuka E, Kudo S, Sugiyama M, Suzuki A (2011) Effects of microcrystallites on swelling behavior in chemically crosslinked poly(vinyl alcohol) gels. J Polym Sci Polym Phys 49 96-102... 

In previous papers(i-.3), we have reported that a specially prepared poly(vinyl alcohol) (PVA) film is very low in protein adsorption and platelet adhesion compared with conventional PVA and other polymers. When PVA is used for practical applications as non aqueous solutions, physical or chemical crosslinking or acetalization is introduced to PVA to make it insoluble in water. Acetalization with formaldehyde and physical crosslinking by heat treatment (annealing) are the most common among the insolubilization methods(. However, for the minimum protein adsorption and platelet adhesion, these physical and chemical modifications have to be avoided because significant interactions with biological components are observed for such PVA, similar to the conventional polymers. 

Shen EW., HA. McKeUop, and R. Salovey. 1996. Irradiation of chemically crosslinked UHMWPE. 7 Poly Sci Poly Phys 34 1063-1077. 

C. Staudt-Bickel, W. J. Koros, Improvement of CO2/CH4 separation characteristics of poly-imides by chemical crosslinking, J. Membr. Sci., 155, 145-154 (1999). 

Poly(Propylene Fumarate) (PPF) is a linear, unsaturated, hydrophobic polyester (Structure 12) containing hydrolyzable ester bonds along its backbone. PPF is highly viscous at room temperature and is soluble in chloroform, methylene chloride, tetrahydrofuran, acetone, alcohol, and ethyl acetate [66]. The double bonds of PPF can form chemical crosslinks with various monomers, such as W-vinyl pyrrolidone, poly(ethylene glycol)-dimethacrylate, PPF-diacrylate (PPF-DA), and diethyl fumarate [67,68]. The choice of monomer and radical initiator directly influence the degradative and mechanical properties of the crosslinked polymer. Once crosslinked, PPF forms a solid material with mechanical properties suitable for a range of bone engineering applications. 

The polyethers generally have a functionality greater than 2 to introduce some chemical crosslinking into the systems to improve the set-up and stiffness at demould. For fast reaction with the isocyanate the polyethers are usually poly(ethylene oxide)-tipped to give a high proportion of primary hydroxyl groups on the poly(propylene oxide)-based backbone. 

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