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Crystal growth is achieved by the further addition of folded polymer chain segments and only occurs for temperatures below the melting temperature T m and above the glass transition temperature T g. Higher temperatures destroy the molecular arrangement and below the glass transition temperature, the movement of molecular chains is frozen. [ 6 ]
Principle of lamellae formation during the crystallization of polymers. Arrow shows the direction of temperature gradient. [1]If a molten linear polymer (such as polyethylene) is cooled down rapidly, then the orientation of its molecules, which are randomly aligned, curved and entangled remain frozen and the solid has disordered structure.
In addition, by changing the alignment of the monomer within the crystal, the tacticity/stereochemistry of the polymer product could be easily controlled. An intuitive example is shown in the figure. In topochemical polymerization of 1,3-diene carboxylic acid derivatives, polymers with four different configurations can be prepared. Their ...
Amorphous polymers (A) do not exhibit other phase transitions, though semicrystalline polymers (B) undergo crystallization and melting (at temperatures T c and T m, respectively). Depending on their chemical structures, polymers may be either semi-crystalline or amorphous.
A common practice is to cool the solutions by flash evaporation: when a liquid at a given T 0 temperature is transferred in a chamber at a pressure P 1 such that the liquid saturation temperature T 1 at P 1 is lower than T 0, the liquid will release heat according to the temperature difference and a quantity of solvent, whose total latent heat ...
Polymers have both a melting temperature T m and a glass transition temperature T g. Above the T m, the polymer chains lose their molecular ordering and exhibit reptation, or mobility. Below the T m, but still above the T g, the polymer chains lose some of their long-range mobility and can form either crystalline or amorphous regions. In this ...
In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening ("curing") a soft solid or viscous liquid prepolymer . [1] Curing is induced by heat or suitable radiation and may be promoted by high pressure or mixing with a catalyst .
Temperature, the stiffness of the polymers, and the molecular weight of the polymers can affect the liquid crystal transformation. Lyotropic side chain LCPs such as alkyl polyoxyethylene surfactants attached to polysiloxane polymers may be used in personal care products like liquid soap.