Grafted polymers poly

Under the conditions used for studying the interactions of graft polymers, poly A and poly U predominantly form the 1 2 complex. The reason may be the low polarity of EG. At pH 4.8, however, the overall stoichiometry of the complex is 2 1 (A U). The temperature dependence of the absorbance of this complex shows two melting steps in the first heating and one in the second. This abnormal profile can be explained by Scheme 16. 

Wang [3] prepared the amphiphilic biocompatible cyclodextrin graft polymer, poly(ethylene glycol-g-cyclodextrin), (III), containing modified cyclodextrin which was used as a bioactive drug delivery agent. 

The grafted polymer poly[(ethylene-co-vinyl acetate-co-carbon monoxide)-graft-vinyl chloride] (PVC/EVACO) known in medical applications as plasticized poly(vinyl chloride) was apphed as a carrier polymer for the covalent immobilization of fibronectin. The surface modifications were carried out on foils both with closed surface structure and with microporous surfaces produced by a phase-inversion technique. The vinyl acetate groups of the carrier polymer were saponified and then reacted with hexamethylene diisocyanate (HDI) as a spacer. Fibronectin is immobilized upon reaction of the free isocyanate group with an amino group of the protein (Fig. 33). The saponification of the carrier polymer was verified by IR-ATR and XPS [149]. The presence of hydroxyhc groups after hydrophihzation is demonstrated by a contact angle of 61° while that of the basic polymer is 110°. 

Vapor phase polymerization from SI-NMP of various vinylic monomers resulted in polymer bmshes with greater thicknesses than those formed by the solution phase process [21]. To explain this result, the authors supposed a more efficient reaction on the surface as a result of prolongation of the mean path of vaporized monomers in a vacuum, higher thermal energy of the monomer, and the possibility of adjusting the reaction parameters independently. Thin films of PS grafted polymer, poly (acrylic acid) (PAA), poly(2-hydroxypropyl methacrylamide) (PHPMA), and poly(lV-isopropylacrylamide) (PNIPAM) were prepared with thicknesses of a few nanometers to submicrometers. This process was also used for the preparation of block copolymers (e.g., PS-b-PAA and PAA-b-PS-PHPMA). It is important to mention that solution phase polymerization of AA, HPMA, and NIPAM is impossible with TEMPO-based alkoxyamines. 

At one time butadiene-acrylonitrile copolymers (nitrile rubbers) were the most important impact modifiers. Today they have been largely replaced by acrylonitrile-butadiene-styrene (ABS) graft terpolymers, methacrylate-buta-diene-styrene (MBS) terpolymers, chlorinated polyethylene, EVA-PVC graft polymers and some poly acrylates. 

It has been found that, for a fixed mineral filler content, the viscosity of PMF-based composites increases when the coat is made of polyethylene [164, 209, 293], poly(vinyl chloride) [316] and polypropylene [326, 327], The picture was different, however, for composites based on the ethylene/vinyl acetate copolymer to which kaolin with grafted poly (vinyl acetate) was added [336]. Addition of PMF with a minimum quantity of grafted polymer results in a sharp drop of flowability (rise of viscosity), in comparison to addition of unmodified filler but with a further increase of the quantity of grafted polymer the flow gradually increases and, depending on the kaolin content and quantity of grafted polymer, may even become higher than in specimens with unmodified filler, for equal concentrations. 

Several attempts have been made to superimpose creep and stress-relaxation data obtained at different temperatures on styrcne-butadiene-styrene block polymers. Shen and Kaelble (258) found that Williams-Landel-Ferry (WLF) (27) shift factors held around each of the glass transition temperatures of the polystyrene and the poly butadiene, but at intermediate temperatures a different type of shift factor had to be used to make a master curve. However, on very similar block polymers, Lim et ai. (25 )) found that a WLF shift factor held only below 15°C in the region between the glass transitions, and at higher temperatures an Arrhenius type of shift factor held. The reason for this difference in the shift factors is not known. Master curves have been made from creep and stress-relaxation data on partially miscible graft polymers of poly(ethyl acrylate) and poly(mcthyl methacrylate) (260). WLF shift factors held approximately, but the master curves covered 20 to 25 decades of time rather than the 10 to 15 decades for normal one-phase polymers. 

Radiation Induced Reactions. Graft polymers have been prepared from poly(vinyl alcohol) by the irradiation of the polymer-monomer system and some other methods. The grafted side chains reported include acrylamide, acrylic acid, acrylonitrile, ethyl acrylate, ethylene, ethyl methacrylate, methyl methacrylate, styrene, vinyl acetate, vinyl chloride, vinyl pyridine and vinyl pyrrolidone (13). Poly(vinyl alcohols) with grafted methyl methacrylate and sometimes methyl acrylate have been studied as membranes for hemodialysis (14). Graft polymers consisting of 50% poly(vinyl alcohol), 25% poly(vinyl acetate) and 25% grafted ethylene oxide units can be used to prepare capsule cases for drugs which do not require any additional plasticizers (15). 

Fig. 5. Structures of Cy5.5-labelled poly(ethylene glycol) poly-(L-lysine) graft polymers 10 and 11. Arrows indicate the enzyme cleavage sites. Published with permission from Weissleder et al. [68,69]...

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