12 Thermal Properties 13 Temperature Effects Tg Tm semicrystalline log(Modulus) crosslinked T linear amorphous Temperature 14 Viscoelasticity
The response of polymeric materials to an imposed stress may under certain conditions resemble the behavior of a solid or a liquid.
Stress Strain 15 Mechanical Properties 16 Diffusion in Polymers
Polymers can also act as solvents for low molecular weight compounds. The diffusion of small molecular weight components in polymers is important in a number of fields
purification of gases by membrane separation
prevention of moisture loss in food and drugs (packaging)
controlled drug delivery (transdermal patches Ocusert)
17 Diffusion in Polymers
Flux is dependent on
solubility of component in polymer
diffusivity of component in polymer
These in turn depend on
nature of polymer
nature of component
interaction of component with polymer
18 Solubility Estimation
From Hildebrand the interaction parameter c is defined as
The solubility parameter d reflects the cohesive energy density of a material or the energy of vapourization per unit volume.
While a precise prediction of solubility requires an exact knowledge of the Gibbs energy of mixing solubility parameters are frequently used as a rough estimator.
In general a polymer will dissolve a given solute if the absolute value of the difference in d between the materials is less than 1 (cal/cm3)1/2.
effect of T vs Tg
effect of permeant size
21 Diffusivity Effect of Crystallinity
do not penetrate crystals readily
take path of least resistance
through amorphous regions
increased path length
D1c diffusivity in semi-crystalline polymer D1a diffusivity in amorphous polymer fc volume fraction of crystals x shape factor (2 for spheres) (Mathematics of Diffusion) 22 Example of Undesirable Absorption
poppet-style heart valve
poppet is composed of PDMS
in small of patients the poppet jammed or escaped
recovered poppets were yellow smelled and had strut grooves
23 Leaching - Undesirable
polymers often contain contaminants as a result of their synthesis/manufacturing procedure/equipment
may also contain plasticizers antioxidants and so on
these contaminants are a frequent cause of a polymers observed incompatibility
24 Drug Delivery Ocusert TD - Scopolamine 25 In Vivo Degradation of Polymers
no polymer is impervious to chemical and physical actions of the body
usually involves the abstraction of an H to yield an ion or a radical
direct oxidation by host and/or device
release of superoxide anion and hydrogen peroxide by neutrophils and macrophages
catalyzed by presence of metal ions from corrosion
32 Poly(Carbonates) PEC in vivo M. Acemoglu In. J. Pharm. 277 (2004) 133-139 33 Enzymatic Degradation
Natural polymers degrade primarily via enzyme action
collagen by collagenases lysozyme
glycosaminoglycans by hyaluronidase lysozyme
There is also evidence that degradation of synthetic polymers is due to or enhanced by enzymes.
Z Gan et al. Polymer 40 (1999) 2859 C.G. Pitt et al. J. Control. Rel. 1(1984) 3-14
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