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e1
QUESTIONS
1. Draw the molecular structure represented by the
shorthand notation D5. What is its chemical name?
2. What functions can fillers serve in silicone elastomers?
a. material extender to reduce bulk cost
3. Describe at least two of the fundamental differences
between the high consistency (HCR) and liquid sili-
cone (LSR) rubber elastomers.
4. Which of the three major types of silicone adhesives
are not generally appropriate for adhering wound
5. Why does silicone make a good coating for paper
release liners used with adhesive labels?
ANSWERS
1. The molecular structure of D5 is,
Si
SiO
O
CH
3
CH
3
CH
3
CH
3
and known as “decamethylcyclopentasiloxane.”
2. The correct answer is (e). While elastomer fillers are
primarily used to reinforce the cross-linked elastomer
network, resulting in increased material properties
implants used in or near hard tissue to make the elas-
tomer more visible on X-ray. (Silicone implants in
soft tissue are typically visible on X-ray without the
need for BaSO4.) As the name implies, fillers, which
are typically less expensive than siloxane polymers,
can be used as a material extender.
HCRs are made with tremendously viscous gum-
like materials with very high molecular weights.
In contrast, LSRs are made with shorter silox-
ane molecules that are less viscous and therefore
pumpable.
molding (LIM). The millable HCRs are limited
to less automated molding technologies, such as
compression and transfer molding.
c. HCRs offer higher tensile elongation and lower
tensile moduli than LSRs of similar hardness.
d. Although not mentioned here, LSRs sometimes
have a lower density than their HCR counter-
parts. Since silicone materials are usually sold by
weight, the lower density material can make more
parts per kilogram.
4. Silicone pressure-sensitive adhesives (PSAs) and gel
adhesives (often called soft-skin adhesives or SSAs)
low alcohol such as methanol or ethanol. These cure
by-products tend to contraindicate use of silicone
bonding adhesive directly on the skin. The correct
I.2.2.B
Silicones
e2
is exceptionally low. PDMS (polydimethylsiloxane)
easily turns its methyl groups to the surface, giving it
many release liners. They also possess a critical sur-
face tension of wetting that is higher than their low
