Polymethyl-methacrylate

Polymethyl methacrylate (PMMA), also called Plexiglas, Lucite, or Perspex, is a colorless clear transparent plastic with excellent outdoor stability if UV absorbers are added to the polymer— otherwise, it yellows on exposure to sunlight. Like styrene, it also unzips on heating to reform the monomer. It has poor scratch resistance but was the plastic of choice for early contact lenses. 

Polymethyl methacrylate (PMMA) is a typical transparent amorphous polymer. It has been widely used as an important material in optical devices. It has several advantages, including good flexibility, high strength and excellent dimensional stability however, it suffers from shortcomings such as poor heat resistance, a weak mechanical surface and low refractive index [41, 42]. 

PMMA is widely used for biomedical implants, barriers, membranes, microlithography and optical applications. In fact, it was the first implanted biomedical polymer [46-49]. Table 2.8 illnstrates the properties of PMMA. 

It has been found that the Tg of PMMA-silica nanocomposites [152] increased with silica content. Also the thermal properties were enhanced. Thus, the degradation temperature at 10% weight loss was about 30 °C higher than that of pristine PMMA. The results could be due to the trapping effect . 

To protect against discoloration under thermal load caused by contamination, steri-cally hindered phenolic antioxidants are added to the material in very small amounts (e.g., 100 ppm) [86]. 

UV stabilizers such as hydroxybenzotriazole, hydroxybenzophenone, and steri-cally hindered amines are proven successful for PMMA [86]. 

In special applications, such as tanning beds, PMMA is efficiently protected by any type of HALS light stabilizer. Low-molecular additives, such as alcohols, act as even more efficient radical scavengers [558]. 

Because of its excellent weathering resistance, PMMA is used as weathering protection in the form of co-extruded layers or laminates for PVC and ABS products. HALS-type UV-absorbers and light stabilizers in concentrations up to 2% in thin PMMA layers offer not only effective surface protection, but also light protection, e.g., for PVC-window profiles or phenol resin panels in exterior applications. 

Often polymethacrylates are not pure PMMA, but rather copolymers with acrylates in order to increase thermal stability, or they are multi-phase systems with butyl acrylate in order to ensure required impact resistance. Acrylates are considerably more reactive in the photooxidation process because of their molecular structure with a tertiary carbon next to the functional group. Butyl ester side chains provide additional, competing reaction paths during photooxidation, which have a negative impact on stability [559]. 

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After brief discussion of the state-of-the-art of modern Py-GC/MS, some most recent applications for stixictural and compositional chai acterization of polymeric materials are described in detail. These include microstixictural studies on sequence distributions of copolymers, stereoregularity and end group chai acterization for various vinyl-type polymers such as polystyrene and polymethyl methacrylate by use of conventional analytical pyrolysis. 

Figure 3.5. Biaxial orientation of polymethyl methacrylate. Variation of impact strength with percentage stretch. (After Ladbury )...

Polymethyl methacrylate Poly(methyl 2-methyl Poly [ 1 -(methoxycarbonyl)-... 

The main experimental techniques used to study the failure processes at the scale of a chain have involved the use of deuterated polymers, particularly copolymers, at the interface and the measurement of the amounts of the deuterated copolymers at each of the fracture surfaces. The presence and quantity of the deuterated copolymer has typically been measured using forward recoil ion scattering (FRES) or secondary ion mass spectroscopy (SIMS). The technique was originally used in a study of the effects of placing polystyrene-polymethyl methacrylate (PS-PMMA) block copolymers of total molecular weight of 200,000 Da at an interface between polyphenylene ether (PPE or PPO) and PMMA copolymers [1]. The PS block is miscible in the PPE. The use of copolymers where just the PS block was deuterated and copolymers where just the PMMA block was deuterated showed that, when the interface was fractured, the copolymer molecules all broke close to their junction points The basic idea of this technique is shown in Fig, I. 

All of the eommereial alkyl eyanoaerylate monomers are low-viseosity liquids, and for some applications this can be an advantage. However, there are instances where a viseous liquid or a gel adhesive would be preferred, sueh as for application to a vertical surface or on porous substrates. A variety of viscosity control agents, depending upon the desired properties, have been added to increase the viscosity of instant adhesives [21]. The materials, which have been utilized, include polymethyl methacrylate, hydrophobic silica, hydrophobic alumina, treated quartz, polyethyl cyanoacrylate, cellulose esters, polycarbonates, and carbon black. For example, the addition of 5-10% of amorphous, non-crystalline, fumed silica to ethyl cyanoacrylate changes the monomer viscosity from a 2-cps liquid to a gelled material [22]. Because of the sensitivity of cyanoacrylate esters to basic materials, some additives require treatment with an acid to prevent premature gelation of the product. 

Examples of thermoplastics are polyethylene, polyvinyl chloride, polystyrene, nylon, cellulose acetate, acetal, polycarbonate, polymethyl methacrylate and polypropylene. 

Polymethyl Methacrylate (PMMA), This material has exceptional optical clarity and resistance to outdoor exposure. It is resistant to alkalis, detergents, oils and dilute acids but is attacked by most solvents. Its peculiar property of total internal reflection is useful in advertising signs and some medical applications. 

A series of fatigue crack growth tests on a moulding grade of polymethyl methacrylate gave the following results... 

Cellulose Esters Epoxy Resins Lignins Polystyrene Poly (2-vinyl pyridine) Polyvinyl Chloride Polymethyl methacrylate Polyphenylene Oxide Phenolics Polycarbonate Polyvinyl Acetate, etc. Polyvinyl butyral SBR rubber, etc., etc. 

In another study, uniform composite polymethyl-methacrylate/polystyrene (PMMA/PS) composite particles in the size range of 1-10 fim were prepared by the seeded emulsion polymerization of styrene [121]. The PMMA seed particles were initially prepared by the dispersion polymerization of MMA by using AIBN as the initiator. In this polymerization, poly(7V-vinyl pyrolli-done) and methyl tricaprylyl ammonium chloride were used as the stabilizer and the costabilizer, respectively, in the methanol medium. Seed particles were swollen with styrene monomer in a medium comprised of seed particles, styrene, water, poly(7V-vinyl pyrollidone), Polywet KX-3 and aeorosol MA emulsifiers, sodium bicarbonate, hydroquinone inhibitor, and azobis(2-methylbu-... 

Grafting reactions onto a polymer backbone with a polymeric initiator have recently been reported by Hazer [56-60]. Active polystyrene [56], active polymethyl methacrylate [57], or macroazoinitiator [58,59] was mixed with a biopolyester polyhydroxynonanaate [60] (PHN) or polybutadiene to be carried out by thermal grafting reactions. The grafting reactions of PHN with polymer radicals may proceed by H-abstraction from the tertier carbon atom in the same manner as free radical modification reactions of polypropylene or polyhy-droxybutyratevalerate [61,62]. 

Scheme 1 Schematic structure of graft block copolymer [51] TTTm = polymethyl methacrylate segment w AA = po-lydimethylsiloxane segment.

In other instances the reactions appear to occur in sequence down the chain, for example in the depolymerisation reaction of polyformaldehyde (polyacetal) and polymethyl methacrylate which are referred to as zippering or sometimes unzippering reactions. In other cases cyclisation reactions can occur such as on heating polyacrylonitrile ... 

Formation of block polymers is not limited to hydrocarbon monomers only. For example, living polystyrene initiates polymerization of methyl methacrylate and a block polymer of polystyrene and of polymethyl methacrylate results.34 However, methyl methacrylate represents a class of monomers which may be named a suicide monomer. Its polymerization can be initiated by carbanions or by an electron transfer process, the propagation reaction is rapid but eventually termination takes place. Presumably, the reactive carbanion interacts with the methyl group of the ester according to the following reaction... 

Platinum-cobalt alloy, enthalpy of formation, 144 Polarizability, of carbon, 75 of hydrogen molecule, 65, 75 and ionization potential data, 70 Polyamide, 181 Poly butadiene, 170, 181 Polydispersed systems, 183 Polyfunctional polymer, 178 Polymerization, of butadiene, 163 of solid acetaldehyde, 163 of vinyl monomers, 154 Polymers, star-shaped, 183 Polymethyl methacrylate, 180 Polystyrene, 172 Polystyril carbanions, 154 Potential barriers of internal rotation, 368, 374... 

SBR (Styrene Butadiene Rubber) ABS (Acrylonitrile Butadiene Styrene Polymethyl methacrylate PAN (Polyacrylonitrile)... 

Acrylic These polymethyl methacrylate (PMMA) plastics have high optical clarity,... 

PMMA polymethyl methacrylate RAPRA Rubber Plastics Research... 

This molecule is a copolymer with polymethyl methacrylate (PMMA) in acrylic latex paints, where the hydrophobic PMMA is surrounded by hydrophilic polyvinyl acetate molecules. Such a suspension of a hydrophobic polymer wrapped in a hydrophilic polymer is called a latex. 

When the methyl methacrylate molecule polymerizes, it is polymethyl methacrylate—Plexiglas. 

Polymethyl methacrylate (PMMA) octylacrylamide/acrylates/butyl-aminoethyl methacrylate copolymer Plexiglas... 

Sf.I F-Test 8.15B The osmotic pressure of 1.50 g of polymethyl methacrylate dissolved in enough methylbenzene to produce 175 mL of solution was 2.11 kPa at 20°C. Calculate the average molar mass of the sample of polymethyl methacrylate. 

Kinetic studies of the polymerization of mono-functional polymethyl methacrylate led to the determination of the propagation constants, k , of the sodium, potassium, and cesium salts 29- 35 36) of polymethyl methacrylates anions. Surprisingly, they... 

The lack of solvent separated pairs raises the question whether some alternative mode of solvation should be considered. The ester group of the penultimate unit of the polymer, or the one preceeding it, could act as a solvating agent. The idea of intramolecular solvation was proposed by several workers in the field 37) and it is supported by the results of nmr studies of polymethyl methacrylate formed under various experimental conditions 38). Hypothetical structures such as those depicted below were proposed 39 h... 

The proposed intramolecular solvation is not the only feature differentiating between the polystyryl and polymethyl methacrylate salts. The former are classified as the salts of carbanions, whereas the latter are ambident salts having the character of allylic enolates with the cation interacting with the partially negatively charged carbon and oxygen atoms. The degree to which the one or the other interaction is favored is affected by the size of the cation. 

Table 1. Propagation constants of polymethyl methacrylate ion-pairs in THF at —98 °C 43)...

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