Poly-addition siloncones and Condensation silicones compared
Silicone polymers consist of the repetition of hundreds or thousands of the same or chemically similar molecular units that are called monomers.
A large number of the materials that we encounter in our everyday lives do not exist in nature but, by means of chemical synthesis processes, they are created by the polymerisation of organic compounds. Silicone polymers are usually classified according to the type of reaction that forms them and in this specific instance the Specialist Podiatrist has a choice of two types of silicone that can be used in orthoplastics:
– silicones created by polymerisation by condensation;
– silicones created by polymerisation by poly-addition.
Characteristics of Condensation silicones
Belonging to the 1st generation of silicones, polymers obtained through polymerisation by condensation have elasticity, hardness and safety properties that are not ideal.
The reaction caused by condensation polymerisation is a random chemical process during which synthesis intermediates or secondary products are released (water, alcohol, gas) responsible for:
- Potential points at which the orthosis could fracture;
- Greater or lesser non-uniform hardness of the final product caused by the difficulty in mixing precisely the two stages (base paste and liquid catalyst) in quantities able to guarantee the uniformity and hardness required.
- Increasing the time needed to catalyse (from the moment the base paste is mixed with the liquid catalyst), compromising the work of the Specialist Podiatrist;
- Variations in the size of the final polymer (caused by contraction) due to slow and continuous hardening, the release of mineral oils added to soften the silicone and the loss of alcohol as a by-product of the reaction.
Last but not least in importance is the level of toxicity involved in polymerisation by condensation. This process in fact uses a type of liquid catalyst containing dibutyl-tin dilaurate (an irritant and allergenic to the skin), which can bring medium and long-term professional risks such as irritation/inflammation of the skin and, in the event of accidental contact with the ocular mucosa, the formation of blisters.
Characteristics of Poly-addition silicones
Belonging to the 2nd generation of silicones, polymers obtained through polymerisation by poly-addition have strong biomechanical properties (elasticity and hardness), maintaining a high level of safety.
The reaction of polymerisation by poly-addition is a controlled chemical process that does not release any synthesis intermediates. As a result there is no risk of creating points of fracture in the orthosis, which will possess good dimensional stability thanks to little or no contraction of the monomeric units.
One further feature of poly-addition polymers is a very quick catalyzation time (3-5 minutes), because the polymerisation reaction is quick and precise. In practical terms, speeding up the silicone polymerisation reaction brings significant benefits for both the Specialist Podiatrist and for the patient.
Poly-addition polymers are obtained by mixing together a base paste (containing vinylsilane) with a catalyst paste (containing organic platinum salts). The correct mixing ration between the two stages (1:1) will produce a final polymer that has an ordered molecular lattice structure. This guarantees the orthosis high quality in terms of hardness, elasticity and inalterability.
As Poly-addition polymers are formulated with a Platinum-based catalyst, unlike condensation polymers, they maintain a high safety profile that will not compromise the health of the skin of either the Podiatrist (who mixes and moulds the materials) or the Patient (who wears the orthosis).
