Polymethylmethacrylate sedimentation

Organic solvents are most commonly used, and encapsulating polymers include ethylcellu-lose, NC, polyvinylidene chloride, polystyrene, polycarbonate, polymethylmethacrylate, polyvinyl acetate and others. Interfacial polymerization produces a polymer such as nylon at the interface between layered solns of two precursor materials such as (in the case of a nylon) a diamine and a diacid (Refs 3 11). If the particle or droplet to be encapsulated is made to pass thru the interface by, say, sedimentation, it will pick up a coating of the polymer as it passes thru... 

One important exception to this rule is vinylketone polymers in which the Norrish type II reaction is responsible for the decrease of the molecular weight of irradiated polymers (see section 4). In contrast to polymethylmethacrylate, polymethylacrylate becomes insoluble on irradiation with 253.7 nm in vacuo [82]. In air, no visible insoluble material is formed and an apparent quantum yield of chain scission of 1.3 x 10-2 has been determined by viscosity measurements [82]. However, a qualitative comparison of sedimentation patterns of initial and irradiated samples indicates that crosslinking also occurs in the presence of air even if gelation is retarded by oxygen. This makes the above-mentioned value meaningless. Photolysis of thin polymethylacrylate films at 253.7 nm in vacuo has also been studied by measuring the insoluble fraction as a function of dose as described in section 2. Quantum yields of 1.9 x 10-3 have been estimated for both the chain scission and the crosslinking processes [83]. 

Nystrom, et al. examine the effect of polymer branching on sedimentation by comparing sedimentation rates of linear polymethylmethacrylate and branched poly-2-triphenylmethoxyethylmethacrylate (PTEMA) samples(14). For each sample, 5(c) is described reasonably accurately by Eq. 2.6. In dilute solutions, sq varies by no more than 50% between these polymers. At larger concentrations, 5(c) for PTEMA is nearly independent of M. Over the concentrations seen in Figure 2.4, 5(c) falls tenfold. At elevated concentration, nondilute linear chains sediment one-third as fast as the branched chains of close to the same molecular weight, while a for the branched chains is a quarter or a third of a for the linear chain. 

Nemoto, et al. report sedimentation and tracer diffusion of dilute polymethylmethacrylate probes in dilute and nondilute polystyrene thiophenol(24,25). Polystyrene and thiophenol are isopycnic, permitting s of PMMA probes in polystyrene thiophenol to be determined unambiguously with ultracentrifugation. 

Figure 2.14 Sedimentation of 343 kDa polymethylmethacrylate through (Q) 44, ( ) 186, (0) 775, and (A) 8420 kDa polystyrene in thiophenol, from measurements...

N. Nemoto, T. Inoue, Y. Makita, Y. Tsunashima, and M. Kurata. Dynamics of polymer-polymer-solvent ternary systems 2. Diffusion and sedimentation of polymethylmethacrylate in semidilute solutions of polystyrene in thiophenol. Macromolecules, 18(1985), 2516-2522. 

Differential Scanning Calorimetry. Heat produced by the inteidiffusion and crystallization of the multilayer reactants was quantified using differential scanning calorimetry. Approximately 1 mg of sample free of the substrate was used. These samples were obtained by first coating a three inch silicon wafer with polymethylmethacrylate (PMMA) using a 3% solution in chlorobenzene deposited by spin coating at 1000 rpm. The desired multilayer structure was then deposited upon the PMMA coated substrate. After the sample was removed from the chamber, it was immersed in acetone, which dissolved the PMMA, causing the multilayer film to float off of the substrate. Typically, the films broke up and rolled into many small pieces, which were collected via sedimentation into an aluminum DSC pan. The sample was dried under reduced pressure to remove residual acetone. Finally the pan was crimped closed. 

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