Acrylic polymer radicals structural dependence

The TREPR experiments and simulations described here have provided an enormous amount of structural and dynamic information about a class of free radicals that were not reported in the hterature prior to our first paper on this topic in 2000. Magnetic parameters for many main-chain acrylic radicals have been established, and interesting solvent effects have been observed such as spin relaxation rates and the novel pH dependence of the polyacid radical spectra. It is fair to conclude from these studies that the photodegradation mechanism of acrylic polymers is general, proceeding through Norrish 1 a-cleavage of the ester (or acid) side chain. Recently, model systems have... 

Depending on the mode of termination of the propagating polymer radicals, and the efficiency of the initiation process, the block copolymers that result can have diblock, triblock or multiblock structures. When methacrylate esters are polymerized, diblock (AB) or triblock (ABA, where A = polyM and B = polysiloxane) copolymers are expected because termination occurs by disproportionation. When acrylates or styrenes are polymerized, multiblock (AB) should be obtained. 

Table 1 displays rate data for alkoxyamine-termi-nated polymers and low molecular model compounds and shows some important trends. At about the same temperature, the dissociation rate constants Ad of alkoxyamines (Schemes 12 and 30) with the same leaving radical (polystyryl, 1-phenylethyl) increase in the order 3 (TEMPO) < 6 < 8 (DEPN) < 1 (DBNO) by a factor of about 30. Acrylate radicals dissociate markedly slower than styryl radicals from 1 (DBNO), but there is no appreciable difference for 8 (DEPN). The dependence of Ad on the nitroxide structure has been addressed by Moad et al.104 They found the order five membered ring < six membered ring < open chain nitroxides and pointed out additional steric (compare 3 and 6) and polar effects. 

The IR spectrum of the polymer film prepared under Condition B is shown in Fig. 23. A structure close to polystyrene is revealed as evidenced by peaks at 540, 700, 760, 840, 1070, 1450, 1490 and 1600 cm . Solubility tests with various solvents proved that the polymer was highly cross-linked. The spectrum of the polymer powder is quite different from that of the film. Peaks assignable to acrylic ester and/or epoxy groups (3400, 1720, 1600, 1500, 1200 and 820 cm ) prevail in that spectrum together with that of polystyrene as shown in Fig. 24. Oxidation of the polymer may be the result of reaction with oxygen in the air after the polymer was taken out from the reactor, as pointed out by several authors (8). It suggests that the powder contains many more active sites, e.g. radicals, than the film. The spectrum corresponding to Condition A is shown in Fig. 25, and is seen to have features similar to both of the previous spectra. Thus, it is seen that the structure of the plasma-polymer depends on the polymerization conditions. 

The analysis of the diffusion-eontrolled features might be simplified by identifying the two types of free radieals the active and the trapped ones. Electron spin resonance speetroseopy shows that active (mobile) radicals give a 13-line spectrum and trapped (statie) radicals give a nine-line spectrum. Also, photopolymerization of a number of neat acrylate monomers used in polymer coatings for optical fiber was studied with photo DSC and with a cure monitor using a fluorescent probe. The acrylates had a functionality of one to six. It was found that conversion of monomers ranges from 40% to 100%. This, however, is depended upon functionality and structure of particular monomers. It can also be a function of the type and amount of the photoinitiator used. 

Polymer latex nanoparticles can be prepared in many materials such as polystyrene and acrylate with controllable size, through radical-initiated polymerization in heterogeneous media (Figure 14.2). The sizes of latex nanoparticles are very dependent on the polymerization conditions. To yield nanosized particles, the polymerization is usually carried out in miaoemulsions [34], For some applications, two or more monomers are used. For example, for polystyrene nanoparticles, divinylbenzene (DVB) is used as a cross-linker to improve the structural performance [35] and methacrylic acid (MAA) or methacrylate (MMA) is used as a co-monomer to provide the nanoparticles with desirable surface chemistry [36,37], Furthermore, some fluorochromes or magnetic materials are incorporated into polymer nanoparticles, to render the particles multifunctional [38,39],... 

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