Thermal initiation resin systems

Thermally Initiated Resin Systems Employing Peroxides... 

Dentures require accurate fit, reasonable chewing efficiency, and lifelike appearance (189). The chewing efficiency of artificial dentures is one-sixth that of natural dentition (190). AcryHc resins are generally used as powder/Hquid formulations for denture base, bone cement, and related appHcations. Polymerization is achieved thermally using initiators photochemicaHy using photoactive chemicals and either uv or visible light irradiation and at ambient temperatures using initiator/activator systems. 

The chemistry involved in LfV-curable resin systems has been extensively investigated and thoroughly surveyed [88-94]. LfV-radiation polymerization, is in principle, completely analogous to the conventional addition polymerization. A photoinitiator is used in UV polymerization. Its function is the same as the free-radical initiator. A conventional initiator possesses a thermally labile bond which is cleaved to form free-radical species, but the photoinitiator has a bond which breaks upon absorption of radiant energy. Benzoin ethers, benzyldialkyl ketals, benzophenone, and acetophenone derivatives are the important LfV-photoinitiators [95-99]. 

The thermal stability of holes burned at low temperatures has been investigated by temperature cycling experiments. As an example, we present (Table 2.13 ) the changes in hole profiles of the TPP/phenoxy resin system during successive increase in excursion temperature and subsequent cooling of the hole burned initially at 4 K.27) The detection of a hole for TPP at an excursion temperature is limited to 50 K in PMMA and most conventional polymers, but it can reach up to 80 K in a phenoxy resin and in poly(vinyl alcohol). In this temperature domain, hydrogen bonding of TPP to these polymer matrices, is believed to help suppress structural relaxations. 

All the AT-resins synthesized by the new procedure showed good thermal stability and several exhibited excellent cured Tgs. The high initial Tgs of the systems remain a problem. Recent investigation of an AT-reactive diluent which can be added to the... 

Polymer resins were first introduced in the early 1940s as an aesthetic alternative to repair defects in anterior teeth. Some of the first resins were unfilled polymers of methyl methacrylate. Presently, these unfilled resins have been replaced by filled composite materials that limit the problems associated with polymerization volume shrinkage, abrasion or wear resistance, mechanical properties, water sorption, solubility, and thermal expansion. Polymeric composite materials generally consist of a monomer resin, a ceramic filler, a polymerization initiator or initiating system, and a coupling agent which binds the polymer... 

The most widely used initiators for curing unsaturated resins are peroxide compounds, which form free radicals on thermal breakdown, or redox systems. Duration of the process, lifetime of ini-... 

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