polymer intro 1 and 2 Flashcards
difference between crystalline and amorphous polymers
crystalline- highly ordered, close packing, regular pattern of interactions, more dense, less space, rigid, motion limited by extensive intermolecular interactions
amorphous- disordered, random molecular arrangement, loosely packed, random intermolecular interactions at points of entanglement, lots of space, easy motion, only limited by points of entanglement
factors that influence crystallinity
speed and temp of solidification- when a melted polymer cools/dries rapidly it is an amorphous, if slowly then its crystalline
molecular structure must be regular, irregular polymers cant form regular arrangements
crystalline state is lowest energy and favoured
how do crystalline polymers form
- nucleation- polymer dries/cools and tiny crystals form at points of molecular contact
- if enough molecular space/time/thermal motion the molecules rearrange and there is crystal growth from nucleation sites, crystalline regions grow outwards
- if moth polymer is involved, material becomes polycrystalline, microstructure turns milk opaque and dense
what is semi crystalline
polymers that possess both ordered and disorganised amorphous domains
what are different ways to calculate polymer MW (eh?)
-polymer with chains of molecules with similar length, the bell curve distribution of mass peaks will be narrow
-polymer with broad MW weight distribution the number average and weight average MW will be very different
-polydispersity index close to 1 means the number and weight average MW are similar
name and draw the graph of 5 regions of viscoelastic behaviour of amorphous polymers
glassy, transition, rubbery, rubbery flow, liquid
viscoelastic behaviour of amorphous polymers depends on what external factors
temperature, plasticiser content, speed of deformation
a decrease in molecular contact/intermolecular interactions/entanglement increases freedom for chains for…
thermal movement-creates internal space
stretching-elastic behaviour
flow-viscous behaviour
how does temperature and plasticiser levels affect polymers
decreases interchain bonding and allows more molecular freedom
what are plasticisers
small molecules that dissolve in polymers and interact
properties of the viscoelastic regions and their pharma uses
glassy= hard and brittle= tablet compression
transition= tough solid to flexible leather, not brittle= durability and strength
rubbery= elastic solid, extends like rubber bands= gel, rubbery solids
rubbery flow= elastic with viscous flow= smearing semisolids
liquid= sticky liquid= adhesives
what is cross linking and its effects
induces covalent bonds between polymer chains making the material more durable
-increases resistance to temperature change/thermal stability
what is the importance of the diagram of amorphous polymer properties
-shows you can adjust polymer type or crystallinity or plasticiser content to give a wide range of useful pharma properties
-explains changes in physical properties when a polymer system melts/cools, hydrates/dries, grows crystalline regions
describe how deformation changes the graph, draw it
higher speed of deformation=graph moves to the left (higher temperature=higher speed of deformation)
what happens if polymer deforms suddenly
molecule cant flow so polymer exhibits solid properties
