Copolymers transparency

Figure 34. Atomic force microscopy surfaces of a styrene/i -propyl-acrylate copolymer transparent foil (a) before irradiation (b) after 2 h irradiation under vacuum. 

CleapacL PainipponInk Chem.] Styrene-based copolymer transparent high intact thermoptotic for inj. molding and extrusion of business machine parts, pkg. materials for electronics or food. 

Barex Polyacrylonitrile and acrylonitrile copolymers transparent for bottles, films, etc. BP Chemicals, Inti. 

Bisphenol A based poly(arylene ether triphenylphosphine oxide/diphenyl sulfone) copolymers were solution blended with Bisphenol A dimethacrylate vinyl ester/styrene and cured with peroxide [921]. Increasing the triphenyl phosphine oxide content in the copolymer yielded improved solubihty in the vinyl ester/styrene mixture as well as the apparent miscibility of the crosslinked blend. With 100% triphenyl phosphine oxide in the copolymer, transparent blends with the cured vinyl ester were observed. Intermediate levels of the triphenyl phosphine oxide, however, gave the best fracture toughness (controlled phase separation appeared to be desired). 

Properties transparent molding low-shrink copolymer mineral-filled reinforced unfilled... 

Poly(phenylquinoxaline—arnide—imides) are thermally stable up to 430°C and are soluble in polar organic solvents (17). Transparent films of these materials exhibit electrical insulating properties. Quinoxaline—imide copolymer films prepared by polycondensation of 6,6 -meth5lene bis(2-methyl-3,l-benzoxazine-4-one) and 3,3, 4,4 -benzophenone tetracarboxyUc dianhydride and 4,4 -oxydianiline exhibit good chemical etching properties (18). The polymers are soluble, but stable only up to 200—300°C. 

Most Kaminsky catalysts contain only one type of active center. They produce ethylene—a-olefin copolymers with uniform compositional distributions and quite narrow MWDs which, at their limit, can be characterized by M.Jratios of about 2.0 and MFR of about 15. These features of the catalysts determine their first appHcations in the specialty resin area, to be used in the synthesis of either uniformly branched VLDPE resins or completely amorphous PE plastomers. Kaminsky catalysts have been gradually replacing Ziegler catalysts in the manufacture of certain commodity LLDPE products. They also faciUtate the copolymerization of ethylene with cycHc dienes such as cyclopentene and norhornene (33,34). These copolymers are compositionaHy uniform and can be used as LLDPE resins with special properties. Ethylene—norhornene copolymers are resistant to chemicals and heat, have high glass transitions, and very high transparency which makes them suitable for polymer optical fibers (34). 

Small amounts of TAIC together with DAP have been used to cure unsaturated polyesters in glass-reinforced thermo sets (131). It has been used with polyfunctional methacrylate esters in anaerobic adhesives (132). TAIC and vinyl acetate are copolymerized in aqueous suspension, and vinyl alcohol copolymer gels are made from the products (133). Electron cure of poly(ethylene terephthalate) moldings containing TAIC improves heat resistance and transparency (134). 

Copolymers are typically manufactured using weU-mixed continuous-stirred tank reactor (cstr) processes, where the lack of composition drift does not cause loss of transparency. SAN copolymers prepared in batch or continuous plug-flow processes, on the other hand, are typically hazy on account of composition drift. SAN copolymers with as Httle as 4% by wt difference in acrylonitrile composition are immiscible (44). SAN is extremely incompatible with PS as Httle as 50 ppm of PS contamination in SAN causes haze. Copolymers with over 30 wt % acrylonitrile are available and have good barrier properties. If the acrylonitrile content of the copolymer is increased to >40 wt %, the copolymer becomes ductile. These copolymers also constitute the rigid matrix phase of the ABS engineering plastics. 

I ew Rubber-Modified Styrene Copolymers. Rubber modification of styrene copolymers other than HIPS and ABS has been useful for specialty purposes. Transparency has been achieved with the use of methyl methacrylate as a comonomer styrene—methyl methacrylate copolymers have been successfully modified with mbber. Improved weatherability is achieved by modifying SAN copolymers with saturated, aging-resistant elastomers (88). 

Copolymerisation also affects morphology under other crystallisation conditions. Copolymers ia the form of cast or molded sheets are much more transparent because of the small spheruHte size. In extreme cases, crystallinity cannot be detected optically, but its effect on mechanical properties is pronounced. Before crystallisation, films are soft and mbbery, with low modulus and high elongation. After crystallisation, they are leathery and tough, with higher modulus and lower elongation. 

This daia indicates that the random copolymer has greater transparency but inferior low temperature impact strength. 

Transparent toughened polystyrene polymers are produced by blending polystyrene with SBS block copolymers (see Section 11.8). During the 1970s and 1980s most development was with block copolymers with a radial (or star) shape. Two types were developed block copolymers with a central butadiene block, and block copolymers with a central polystyrene block. 

Tough transparent sheet may be produced by blending standard polystyrene with block copolymer in an extruder in the ratios 80 20 to 20 80, depending on the application of the products subsequently thermoformed from the sheet. For example, sheet for thermoforming an egg tray will not require the same level of impact strength as that required for jam jars. 

The important features of rigidity and transparency make the material competitive with polystyrene, cellulose acetate and poly(methyl methacrylate) for a number of applications. In general the copolymer is cheaper than poly(methyl methacrylate) and cellulose acetate, tougher than poly(methyl methacrylate) and polystyrene and superior in chemical and most physical properties to polystyrene and cellulose acetate. It does not have such a high transparency or such food weathering properties as poly(methyl methacrylate). As a result of these considerations the styrene-acrylonitrile copolymers have found applications for dials, knobs and covers for domestic appliances, electrical equipment and car equipment, for picnic ware and housewares, and a number of other industrial and domestic applications with requirements somewhat more stringent than can be met by polystyrene. 

Polymers of a-methylstyrene have been marketed for various purposes but have not become of importance for mouldings and extrusions. On the other hand copolymers containing a-methylstyrene are currently marketed. Styrene-a -methylstyrene polymers are transparent, water-white materials with BS softening points of 104-106°C (c.f. 100°C for normal polystyrenes). These materials have melt viscosities slightly higher than that of heat-resistant polystyrene homopolymer. 

Copolymers of vinylidene chloride with 5-50% acrylonitrile were investigated by IG Farben during World War II and found to be promising for cast films. Early patents by ICC and Dow indicated that the copolymers were rigid, transparent and with a high impact strength. 

Polycarbonates with superior notched impact strength, made by reacting bisphenol A, bis-phenol S and phosgene, were introduced in 1980 (Merlon T). These copolymers have a better impact strength at low temperatures than conventional polycarbonate, with little or no sacrifice in transparency. These co-carbonate polymers are also less notch sensitive and, unlike for the standard bis-phenol A polymer, the notched impact strength is almost independent of specimen thickness. Impact resistance increases with increase in the bis-phenol S component in the polymer feed. Whilst tensile and flexural properties are similar to those of the bis-phenol A polycarbonate, the polyco-carbonates have a slightly lower deflection temperature under load of about 126°C at 1.81 MPa loading. 

Where transparency is required, a range of polymers is available. Polystyrene is the least expensive but polymethylmethacrylate has an outstanding high light transmission combined with excellent weathering properties. Also to be considered are the polycarbonates, glass-clear polyamides, SAN, butadiene-styrene block copolymers, MBS polymers, plasticised PVC, ionomers and cellulose esters such as cellulose acetate. 

A major development in fluoroplastks is the recent small scale production of Teflon AF, a noncrystaUme (amorphous) fluorocarbon polymer with a high glass transition temperature (240 °C) This optically transparent TFE copolymer is soluble m certan fluorocabons and has the same chemical and oxidative stability as crystallme TFE homopolymers [5]... 

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