Melting point polymers

Random insertion of ethylene as comonomer and, in some cases, butene as termonomer, enhances clarity and depresses the polymer melting point and stiffness. Propylene—butene copolymers are also available (47). Consequendy, these polymers are used in apphcations where clarity is essential and as a sealant layer in polypropylene films. The impact resistance of these polymers is sligbdy superior to propylene homopolymers, especially at refrigeration temperatures, but still vastiy inferior to that of heterophasic copolymers. Properties of these polymers are shown in Table 4. 

The properties of the final polymer (melting point, solubiUty, optical properties, etc) depend on the nature of the side chain incorporated into the structure, so that judicious choice of substituent can lead to material tailorabiUty. 

In the suspension process, which was the first method to be commercially developed, propylene is charged into the polymerisation vessel under pressure whilst the catalyst solution and the reaction diluent (usually naphtha) are metered in separately. In batch processes reaction is carried out at temperatures of about 60°C for approximately 1-4 hours. In a typical process an 80-85% conversion to polymer is obtained. Since the reaction is carried out well below the polymer melting point the process involves a form of suspension rather than solution polymerisation. The polymer molecular weight can be controlled in a variety of... 

Polymer Melting point range °C Density g/cm Degree of crystallinity % Stiffness modules psi X 10 ... 

A lattice model that takes such attractions between parallel bonds into account provides a reasonable prediction of polymer melting points [13] and of their interplay with liquid-liquid demixing in polymer solutions [14]. The same factors that favor freezing do affect to a greater or lesser extent the formation of mesophases hence, there is a close relation between polymer crystallization and the formation of mesophases, which are frequently observed before polymer crystallization (see other papers in this issue). 

Table 1. Monomer structures and polymer melting point and glass transition temperatures of the most common aliphatic polyesters obtained by ROP [2,7]...

Typical) Polymer Melting Point (°C) Spinning Temperatui... 

Polymer Melting point (°C) Glass transition (°C) Vicat A (°C) Young s modulus (GPa) Tensile strength (MPa) Strain (%) Impact strength (Izod) (J/m) Density (g/cm)... 

Solution polymerization of these compounds can be brought about by nucleophilic initiators including n-butyllithium, triethylamine, and sodium cyanide. In the absence of such initiators, solution polymerization proceeds very slowly. As an example, l-(p-chlorothiobenzoyl)aziridine at a concentration of 0.5 mole percent in tetrahydrofuran polymerizes at room temperature when initiated with n-butyllithium to give a 94% yield of polymer. Melting point of the polymer is 90-100° C and its reduced viscosity in N-methylpyrrolidone (1% concentration at 30° C)i is 0.15. 

A peculiarity of the anionic activated polymerization process for e-caprolactam is that it proceeds at temperatures below the polymer melting point. This leads to superposition of the polymerization process and crystallization of the newly synthesized polymer. 

Polymer Melting point (°C) Glass-transition temperature (°C) Modulus (Gpaf Degradation time (mo)b... 

Weight of crude copolymer (gram) Weight of extracted polymer (gram) Theoretical % butyla Percent chlorine in polymer Calculated % butyl6 Polymer melting point, °C. 

CBAs are available which decompose at temperatures from 100°C (230°F) to as high as 280 C (537°F). A CBA is available to match any polymer melting point or processing temperature desired. 

The polymer melting point corresponds to the cusp in the retention diagram. 

---