PMMA, properties

Table 9 compares the most important properties of substrate materials based on BPA-PC, PMMA, and CPO (three different products) (216,217). The future will prove if the current disadvantages of CPO against BPA-PC regarding warp, processibiUty (melt viscosity), and especially cost can be alleviated. CycHc polyolefins (CPO) and, especially cycloolefin copolymers (COC) (218) and blends of cycloolefin copolymers with suitable engineering plastics have the potential to be interesting materials for substrate disks for optical data storage. 

Hard lenses can be defined as plastic lenses that contain no water, have moduli in excess of 5 MPa (500 g/mm ), and have T well above the temperature of the ocular environment. Poly(methyl methacrylate) (PMMA) has excellent optical and mechanical properties and scratch resistance and was the first and only plastic used as a hard lens material before higher oxygen-permeable materials were developed. PMMA lenses also show excellent wetting in the ocular environment even though they are hydrophobic, eg, the contact angle is 66°. 

High impact strength, increased hardness, lower thermal expansion, and high fatigue strength are also important properties required of denture-base materials. To address these deficiencies, alternatives to the traditional PMMA dentures have been sought. These include the use of other base polymers and reinforced designed denture systems. 

Rather more recently Rohm and Haas GmbH have introduced Plexidur plus which is a copolymer of acrylonitrile and methyl methacrylate. It is best considered as a glazing material for use in schools, sports halls and vehicles. The material also has good clarity, rigidity and surface hardness. Some typical properties compared with PMMA are given in Table 15.2. 

Property Test standard DIN Unit ABS ASA High-impact PMMA High-impact PMMA pmma ... 

DR (Rohm and Haas) and Plex 8535-F (Rohm GmbH). Some typical properties of these materials compared with straight PMMA and with the competitive ABS and ASA polymers (discussed in Chapter 16) are given in Table 15.3. 

An example of this improvement in toughness can be demonstrated by the addition of Vamac B-124, an ethylene/methyl acrylate copolymer from DuPont, to ethyl cyanoacrylate [24-26]. Three model instant adhesive formulations, a control without any polymeric additive (A), a formulation with poly(methyl methacrylate) (PMMA) (B), and a formulation with Vamac B-124 (C), are shown in Table 4. The formulation with PMMA, a thermoplastic which is added to modify viscosity, was included to determine if the addition of any polymer, not only rubbers, could improve the toughness properties of an alkyl cyanoacrylate instant adhesive. To demonstrate an improvement in toughness, the three formulations were tested for impact strength, 180° peel strength, and lapshear adhesive strength on steel specimens, before and after thermal exposure at 121°C. 

The data also demonstrate that the addition of the thermoplastic, PMMA, does not have the significant effect on the toughness or adhesion properties as does the addition of the rubber, Vamac B-124. Clearly, the physical properties of the polymeric additive determine the magnitude of the adhesive physical property modifications, which result from their addition to an alkyl cyanoacrylate monomer. 

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. 

It is evident from these results that the interactive properties of the investigated SEC PS/DVB or DVB gels are very different. Because polar electroneutral macromolecules of PMMA were more retained from a nonpolar solvent (toluene) than from polar ones (THF, chloroform), we conclude that the dipol-dipol interactions were operative. Columns No. 1 and No. 2 were very interactive and can be applied successfully to LC techniques that combine exclusion and interaction (adsorption) mechanisms. These emerging techniques are LC at the critical adsorption point (18), the already mentioned LC under limiting conditions of adsorption (15,18), and LC under limiting conditions of desorption (16). In these cases, the adsorptivity of the SEC columns may even be advantageous. In most conventional SEC applications, however, the interactive properties of columns may cause important problems. In any case, interactive properties of SEC columns should be considered when applying the universal calibration, especially for medium polar and polar polymers. It is therefore advisable to check the elution properties of SEC columns before use with the... 

The producer of column No. 6 tried to supplementary remove admixtures from the gel matrix by applying liquid extractions. He revealed that the extraction process was very slow and that the apparently clean material started to bleed again after some time or when the temperature of extraction was raised. This result indicates that the retention properties of SEC columns may change in the course of their use as a result of cleaning their surface. Maybe the recipes for the gel synthesis will have to be modified to suppress the effects of additives. It seems that the producer of column No. 5 is not far from the ideal situation, at least for the PMMA-toluene system. We cannot exclude... 

PMMA-b-PBA shows improved izod impact strength compared to PMMA homopolymer (41). Polyisobutylene (PIB) or its hydrogenated one (PIB-H) also acts as an impact modifier [31]. PSt-b-PIB, PSt-b-PIB-H, and PMMA-b-PIB-H derived from MAI have high- and wide-range molecuiar weight and show high flexibiiity and flow property [42]. The improved flexibiiity of PMMA-b-PEG synthesized as an elastomer, was confirmed by dynamic viscoelastic measurement [43]. 

The usually reported second largest market for plastics is building and construction consuming about 20 wt%. However, the amount of plastics is only about 5% of all materials consumed in building and construction so that a large growth area exists for plastics when the price is right since then-properties provide durability, performances, insulation, cosmetics, etc. (Fig. 4-5). Different plastics are used that include PVCs, PEs, PMMA, PSs, phenolics, TS polyesters, and many more. Examples of products are listed in Table 4-1. 

Most of over six million dentures produced annually in the USA are made of acrylics (PMMAs) that includes full dentures, partial dentures, teeth, denture reliners, fillings and miscellaneous uses. Plastics have been edging into the dental market for over a half century. Even before the introduction of acrylics to the dental profession in 1937, nitrocellulose, phenol-formaldehyde and vinyl plastics were used as denture base materials. Results, however, were not wholly satisfactory because these plastics did not have the proper requisites of dental plastics. Since then, PMMAs have kept their lead as the most useful dental plastics, although many new plastics have appeared and are still being tested. Predominance of PMMAs is not surprising, for they are reasonably strong, have exceptional optical properties, low water absorption and solubility, and excellent dimensional stability. Most denture base materials, therefore, contain PMMA as the main ingredient. 

An outstanding property of EPS is its extremely low density (when compared to other processes), that by alteration of the preforming treatment can be varied according to the end use. Other types of plastics are employed to produce expandable plastic foam (EPF), including PE, PP, PMMA, and ethylene-styrene copolymers. They can use the same equipment, with only slight modifications. These plastics have different properties from those of EPS and open up different markets. They provide improved sound insulation, resistances to additional heat deformation, better recovery of shapes in moldings, and so on. 

Minor (by amount) functionality is introduced into polymers as a consequence of the initiation, termination and chain transfer processes (Chapters 3, 5 and 6 respectively). These groups may either be at the chain ends (as a result of initiation, disproportionation, or chain transfer,) or they may be part of the backbone (as a consequence of termination by combination or the copolymerization of byproducts or impurities). In Section 8.2 wc consider three polymers (PS, PMMA and PVC) and discuss the types of defect structure that may be present, their origin and influence on polymer properties, and the prospects for controlling these properties through appropriate selection of polymerization conditions. 

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