Lecture 1 Flashcards
What is a polymer
A polymer is a substance composed of molecules which have long sequences of one or more species of atoms or groups of atoms linked to each other by primary, usually covalent bonds.
What are dendrimers and hyperbranched polymers?
Dendrimers are highly branched polymers of well-defined structure and molar mass. Hyperbarcnched polymers are polymers which similar to dendrimers but have a much less well-defined strucutre and molar mass.
Applicatins:
Becauses of their high level of branching, they are extremely crowded but as aconsequence have voids and channels within the molecule and have a lare number of end groups around thier periphery that can be functionalized, leading to therapeutic application such as in targeted drug delivery.
What is the definition of Copolymers?
The formal definition of a copolymer is a polymer derived from more than one species of monomer. However, in accordance with the use of the word homopolymer, it is common practice to use a structure-based definition. Thus the word copolymer more commonly is used to describe polymers whose molecules contain two or more different types of REPEAT UNIT.
What are Statistical copolymers?
Statistical copolymers are copolymers in which the sequential distribution of the repeat units obeys known statistical laws (e.g. Markovian).
Important note
by preparing copolymers, it is possible to combine the desirable properties of the homopolymers into a single material. This is not normally
possible by blending because most homopolymers are immiscible with each other
What is special about graft and block copolymers?
block and graft copolymers usually show properties characteristic of each of the constituent homopolymers. They also have some unique properties that arise because the chemical linkage(s) between the homopolymer sequences prevent them from acting entirely independently of each other.
What are thermoplastics?
Thermoplastics, often referred to just as plastics, are linear or branched polymers which become liquid upon the application of heat.
They can be moulded (and remoulded) into virtually any
shape using processing techniques such as injection moulding and extrusion, and now constitute by far the largest proportion of the polymers in commercial production. Generally, thermoplastics do not crystallize easily upon cooling to the solid state because this requires considerable ordering of the highly coiled and entangled macromolecules present in the liquid state. Those which do crystallize invariably do not form perfectly crystalline materials but instead are semi-crystalline with both crystalline and amorphous regions.
Important note
Both Tm and Tg increase with increasing chain stiffness and increasing forces of intermolecular attraction.
It is a common misnomer that completely amorphous polymers ‘melt’; they do not (because they have no ordered phases, there is nothing to melt!) and may simply be considered as reducing steadily in viscosity as temperature increases above Tg until the viscosity becomes low enough for so-called melt processing
What are Elastomers?
Elastomers are crosslinked rubbery polymers (i.e. rubbery networks) that can be stretched easily to high extensions (e.g. 3× to 10× their original dimensions) and which rapidly recover their original dimensions when the applied stress is released. This extremely important and useful property is a reflection of their molecular structure in which the network is of low crosslink density. The rubbery
polymer chains become extended upon deformation but are prevented from permanent flow by the crosslinks, and driven by entropy, spring back to their original positions on removal of the stress.
elastomers are intractable once formed and degrade rather than become fluid upon the application of heat. Hence, their processing into artefacts is often done using processes, such as compression moulding, that require minimum amounts of flow.
What are thermosets?
Thermosets normally are rigid materials and are network polymers in which chain motion is greatly restricted by a high degree of crosslinking
