Heat distortion polyester resin

OC-Methylstyrene. This compound is not a styrenic monomer in the strict sense. The methyl substitution on the side chain, rather than the aromatic ring, moderates its reactivity in polymerization. It is used as a specialty monomer in ABS resins, coatings, polyester resins, and hot-melt adhesives. As a copolymer in ABS and polystyrene, it increases the heat-distortion resistance of the product. In coatings and resins, it moderates reaction rates and improves clarity. Physical properties of a-methylstyrene [98-83-9] are shown in Table 12. 

Typically, polyester resins are used for high-end applications that require excellent electrical and thermal resistance. When dimensional stability under load is more critical, glass fibers are incorporated to increase the heat distortion temperature and the stiffness of the part. Examples of glass fiber reinforced parts include electrical housings, electrical adapters, computer components, telephone housings, and light bulb sockets. When impact modified, polybutylene terephthalate can be injection molded to make car bumpers. 

Standard bisphenol-A fumarate resins are derived from the propylene glycol or oxide diether of bisphenol-A and fumaric acid. The aromatic structure provided by the bisphenol-A provides several benefits. Thermal stability is improved, and the heat distortion point of the resin is mainly raised from the more rigid nature of the aromatic structure. The number of interior chain ester groups is reduced so the resistance to hydrolysis and saponification is increased. Bisphenol A fumarate polyesters have the best hydrolysis resistance of any commercial unsaturated polyester. 

Consider unsaturated polyesters as illustrations of some of the earlier discussed principles. They are not outstanding in their thermal stability, but they are extensively used in composite fabrication and have heat distortion temperatures in the range 55-120°C depending on molecular structure. Above this temperature a significant decrease in the modulus is noticed and accelerated creep is observed. Resins cannot be used for load bearing applications within 20-30°C of the Tg, or even 50°C in situations involving substantial solvent or moisture pickup, and standard polyesters are not usually used above about 100°C, even though they do not decompose chemically until around 150°C. 

The constitution of the unsaturated polyester resin used to make a gelcoat is obviously a prime factor in determining its weathering performance. Base polyesters (which are subsequently dissolved in the monomer) are made by reacting together saturated and unsaturated diacids and diols, and variation of these ingredients enables properties such as flexibility, heat distortion... 

The mechanical properties of the resole phenoUcs are comparable with those of orthophthaUc polyesters. Typical values are given in Table 3.4. However the high heat distortion temperature and fire resistance are leading to greater use of these materials. Low shrinkage compared with polyesters is a characteristic of this resin. 

Polyester resins derived from orthophthalic anhydride have good all-round properties, whereas isophthalic acid gives a tougher resin with some improvement in chemical resistance. Resins derived from terephthalic acid have properties similar to their isophthalic counterparts, but with a slightly greater heat distortion temperature (HDT). 

A high quality polyester surface primer that provides outstanding filling and levelling properties, offering a rapid coat build-up for plugs and master mould surfacing. Adheres to epoxy resins and exhibits a heat distortion temperature of 150 C. 

Structural elements of unsaturated polyester resins that affect the properties of the cured products include molecular weight and molecular weight distribution, distribution of various repeating units, type of unsaturation, and ratio of acid to glycol components. An overall concept regarding the structural features of polyester resin and the performance properties of cured product is not available. However, it is known that the structural features determine the values of hardness, impact strength, heat-distortion temperature, water absorption, chemical resistance, and heat resistance. 

The influence of end and center structures on polyester properties have received some study.It appears that fumarate unsaturation near the chain ends in the isophthalate polyesters results in styrene-crosslinked resins with improved water resistance, heat distortion, and better color. 

Resins with similar heat distortion temperatures are shown in Table 4.1. However, higher temperature versions of these resins are also available, for example, iso-polyesters have the highest HDT (c.l30°C), iso-NPG, somewhat lower (c.llO°C) and ortho-polyesters the lowest (c.lOO°C). 

These four thermosetting resins have somewhat different load-carrying capabilities at elevated temperatures. Polyester, epoxy and vinyl ester have similar heat distortion temperatures (130 -150 C) and from these data, one can infer that epoxy is best at intermediate temperatures and vinyl ester at higher temperatures. Overall, however, the phenolic has the best temperature resistance, in line with its much higher HDT (250 C). 

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