Polymerization reactive melt

Reactive Melt Polymerization. The liquid composite molding (LCM) method is established for the fahricarion of thermosets. In contrast, reac-rive thermoplastic LCM processes are developed to only a few engineering polymers. The technique was applied to low-melting PA 6T/6I oligo-... 

First, the infusible nature of many of these polymers precludes the use of conventional bulk polymerization and melt processing techniques. Second, aromatic diamines are significantly less reactive than aliphatic diamines toward polyamidation. This requires the use of more reactive dicarboxylic acid intermediates or some activation mechanism to complete the polycondensation in a reasonable period of time. Some technological breakthroughs were necessary to make progress in the synthesis of aromatic polyamides. These came in the late... 

Because of limited solubility and differing monomer reactivity, melt polymerization may be the process of choice for creating biphenol-based copolymers [159-163], but these copolymers can be prepared by interfacial processes as well [164]. Under appropriate polymerization conditions, transparent resins can be obtained by using up to 50 mol % of biphenol [165]. Copolymers with more than 60 mol % biphenol will exhibit liquid crystalline behavior [166]. 

PTT is melt-polymerized by either the transesterification of PDO with DMT or by the direct esterification of PDO with TPA. The process is similar to the polymerization of PET but with several important differences. Since the reactivity of PDO is much lower than that of ethylene glycol, hot catalysts such as titanium butoxide (12) and dibutyl tin oxide (13), normally too fast for PET, are used to polymerize PTT. Melt polymerization is carried out between 250 and 275°C, about 40° C lower than that used for PET. PTT has different polymerization side reaction products. Instead of cyclic trimers, PTT produces cyclic dimers. It also gives off acrolein and allyl alcohol instead of acetaldehyde gaseous by-products. Acrolein requires special handling and disposal. 

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. 

While the chemistry of radiation curable hot melt adhesives is the same as that used in liquid (syrup) adhesives and coatings discussed elsewhere in this volume, there is a fundamental difference between the objectives of reaction in the two types of systems. Syrups consist largely or entirely of reactive monomeric and/or oligomeric materials. Radiation is used to initiate the polymerization of virtually the entire mass. In contrast, hot melts generally contain polymers initially, and these polymers are capable of reaction via radiation to produce chain extension and... 

Polyurethane adhesives are formed by the reaction of various types of isoeyanates with polyols. The polar urethane group enables adhesion to various surfaees. Depending on the raw materials, glue lines with rubber-like elastic to brittle-hard behavior ean be aehieved. The presence of reactive terminal groups provides a ehemieally hardened adhesive. When polymerized to a high enough molecular weight, the adhesive ean be physically rather than chemically hardened, i.e. a hot melt. 

For very high melting polymers (Tm > 300°C), a solution polymerization is normally employed. If this is started from the reactive acid chloride, the reaction temperature can be low. Polymers from acid chlorides can also be prepared by the interfacial method. Semicrystalline PA can be postcondensed in the solid state to higher molecular weights. To do this, the polymer powder/particles are heated for many hours below their melting temperature in an inert atmosphere. 

PA-6,10 is synthesized from 1,6-hexamethylenediamine and sebacic acid, and PA-6,12 from 1,6-hexamethylenediamine and dodecanedioic acid. The melt synthesis from their salts is very similar to PA-6,6 (see Example 1). These diacids are less susceptible to thermal degradation.55 PA-6,10 can also be synthesized by interfacial methods at room temperature starting with the very reactive sebacyl dichloride.4 35 A demonstration experiment for interfacial polycondensation without stirring can be carried out on PA-6,10. In this nice classroom experiment, a polymer rope can be pulled from the polymerization interface.34... 

Although each of these cyclic siloxane monomers can be polymerized separately to synthesize the respective homopolymers, in practice they are primarily used to modify and further improve some specific properties of polydimethylsiloxanes. The properties that can be changed or modified by the variations in the siloxane backbone include the low temperature flexibility (glass transition temperature, crystallization and melting behavior), thermal, oxidation, and radiation stability, solubility characteristics and chemical reactivity. Table 9 summarizes the effect of various substituents on the physical properties of resulting siloxane homopolymers. The... 

---