Polymerization of PMMA

As previously mentioned, the results of this approach in the polymerization of PMMA have already been published and tested (e.g. 0). Also, a few workers have r ently begun to ro ognize some of the value of utilizing chromatogram heights (15, 1. ... 

Use of a Reliable Homemade Dilatometer To Study the Kinetics of the Radical Chain Polymerization of PMMA 123... 

A similar experiment is reported in (60) in-situ polymerization of PMMA in presence of MWCNT at analogous experimental conditions (in methanol, using PVP as stabilizer and AIBN as initiator) produced monodisperse PMMA/MWCNT microspheres only with the help of mechanical stirring. The spheres diameters decreased from about 11.6 pm to 6.0 pm as the content of MWCNT increased from 0 to 0.03 wt%. Additional analyses identified carbon nanotubes to be present both in the interior and on the surface of the particles. 

Figure 30.27 Time to reach the maximum temperature during the polymerization of PMMA bone cement as a function of peroxide concentration on the plasma-treated X-ray opaque powder surfaces.

NMR studies indicate that hydroxyl groups on the surface of silica are consumed during polymerization of PMMA. These groups are utilized in a reaction with poly-mer. Polymer adsorbed on the surface of alumina changes conformation. "... 

Surfactants have also been used to overcome the solubility limitation of synthetic polymers in CO2 (most common synthetic polymers would be considered to be C02-phobic). For example, surfactants have been used to aid in the dispersion polymerization of poly(methylmethacrylate) (PMMA) in CO2 (58-60). The surfactants used in the polymerizations of PMMA are more accurately referred to as stabilizers. The C02-phobic region acts as anchor to the growing polymer, either by physical adsorption or by chemical grafting. The C02-philic region sterically stabilizes the growing polymer particles, preventing flocculation and precipitation. When a biopolymer is not soluble in CO2, specific surfactants may be designed to aid in the solubilization of the polymer into CO2. 

PMMA is produced by emulsion polymerization, solution polymerization, and bulk polymerization. Generally, radical initiation is used (including living polymerization methods), bnt anionic polymerization of PMMA can also be performed. PMMA prodnced by radical polymerization (all commercial PMMA) is atactic and completely amorphous. Free-radical polymerization is carried out using benzoyl peroxide as an initiator in the presence of AdV-dimethyl-p-tolnidine (Figure 1.12) [60]. 

MALDI end-group analysis was investigated for the determination of the chain transfer coefficients (Cs) for free-radical polymerization of PMMA with AIBN as inihator and 2-methyl-2-propanethiol as a chain transfer agent in toluene. Flowever, the values of Cs obtained were not consistent with those obtained with standard methods, and the relahve intensities of the peak series relahve to the oligomers with different end-groups were found to be dependent on the selechon of cahon (Li" or Na - ... 

H NMR Monitored Copper-Mediated Radical Polymerization of PMMA using PEG-based Macroinitiators... 

Continuous-flow stirred-tank reactors (CSTRs) can be cooled in three ways. The most elegant method is to allow boiling of the monomer or solvent so that the heat of reaction is removed in an overhead condenser. The pressure in the vessel is set to give the desired temperature. The condensate can be returned to the vessel or recycled back to the feed. This process is commonly used for polystyrene. Chilling the feed is another means for managing the exotherm in a CSTR. Refrigeration to -40°C has been used for the bulk, continuous polymerization of PMMA. Laboratory reactors and small-scale industrial reactors can be cooled using jackets or internal coils, but this method scales up poorly. 

In cemented total joint arthroplasties, acrylic bone cement functions as the piima ry load bearing material used to transfer loads from the implant to the bone. Bone cement Is formed from an exothermic reaction of benzoyl peroxide initiator present In polymethylmethacrylate powder (PMMA) and AI,AI-dimethyl-p-tolui-dene In methylmethacrylate monomer liquid (MMA), resulting in polymerization of PMMA to form a solid cement matrix. The in vivo integrity and performance of bone cement Is necessary for longevity of orthopedic implants, because it is believed that mechanical failure of the bone cement layer can lead to aseptic loosening of the Implant [101]. 

A silicone macromonomer has also been used to stabilize the dispersion polymerization of PMMA (44). The PDMS macromonomer used in this study was a commercially available methacryloxy functional PDMS macromonomer (Fig. 9). The polymerizations were carried out at 340 bar and 65 C for 4 h. When no PDMS macromonomer was added to the polymerization, only low conversions could be achieved and the polymer precipitated. Addition of a small amount of PDMS macromonomer (0.05 wt %) to the polymerizations increased the molecular weight and the yield of the polymer, but at least 3.5 wt % was necessary to obtain monodispersed polymer particles at high yield. PDMS homopolymer, which lacks the reactive MMA functional group, was not effective in stabilizing the polymerization in that a much greater concentration of the... 

Nowadays, commercially available acrylic bone cements are sold in a kit of two components, a solid phase (polymer powder with initiator) and a liquid ampoule containing the methyl methacrylate (MMA) and a tertiaryamine. This is based on the fact that polymerization of PMMA can also be initiated by oxidation-reduction reactions. An advantage of a redox initiator is that the radical production starts at lower temperatures in comparison to the traditional initiators, where a high temperature is necessary to generate the radical initiator. Generally, the most used combination includes benzoyl peroxide and NdV-dimethylaniline. The proposed initiation mechanism is shown in Figure 12.9. 

Microwave irradiation was applied for in situ polymerization of PMMA/clay (ClOA) layered nanocomposites. The polymerizations were carried out using a microwave reactor at 70 °C with 200W of irradiation power. An intercalated/exfo-liated stmcture was observed by both XRD and transmission electron microscopy (TEM) analyses. Thermogravimetry analysis (TGA) of pure PMMA and PMMA/clay nanocomposites... 

It was shown that high molar mass, polydisperse acrylic PnBA/PMMA diblock and triblock copolymers prepared by SGl-mediated polymerization were shown to self-assemble into various nanostmctures despite substantial molecular dis-order. ° Lamellae are observed around 55-65 vol.% PMMA, while perfectly symmetrical copolymers adopt a curved interface concave toward PMMA and form cylinders or cylindrical micelles with poor lattice order. This was assigned to unbalanced polydispersity between the two blocks arising from the lack of control over polymerization of PMMA under the synthesis conditions used. 

IV and V. Chain transfer to BPO also forms structure IV. Termination of the propagating radicals by disproportionation gives end groups VI and VII. Termination by combination forms structure VIII in the middle of the polymer chain. Table 7.3 gives the numbers of end groups per chain for the polymerization of PMMA with BPO in toluene at 100°C. 

Numbers of end groups per chain for the polymerization of PMMA with BPO in toluene at 100°C... 

An early smdy on in situ polymerization was employed for the synthesis of PMMA-MWNT composites by fia and co-workers in 1999. In their reported work, in situ radical polymerization was performed using a radical initiator 2,2 -azobisisobutyronittile (AIBN) to initiate the ix bonds in CNTs to participate in the polymerization of PMMA, consequently forming a strong interface between the MWNTs and the PMMA matrix. Since then, some other groups have also used AIBN as an initiator of in situ radical polymerization to introduce functionalized MWNTs and SWNTs into PMMA matiices. """ """... 

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