THERMAL POLYMERISATION

Hydrogel lenses are obtained by photo or thermal polymerisation of monomers in bulk or in solution. A variety of thermal and photo catalysts have been used in hydrogel formulations. 

The anionic mechanism is similar to that postulated to explain the thermal polymerisation. The apparent general similarity of the polymers produced by the two methods of initiation justifies this. Cross-linking involves additions to the free CN groups, and regular networks with two or more interconnected polymer chains are possible. Thus the structure of the azulmine is highly complex. Termination must occur by reactions of the growing anions with H2CN+ ions formed in the reaction... 

A special arrangement of taps and ducts below a standing burette is shown in Fig. 3.2 and has proved useful for metering freshly distilled styrene into a reactor (KPG). The device allows any excess in the burette to be returned to the reservoir at the end of the metering and is useful when fresh distillation immediately before the reaction is desirable, as is the case for thermally polymerisable monomers. It also prevents residual monomer from polymerising in the ducts. 

The thermal decarboxylation of NCA s involves the 2-carbonyl group of the oxazolidine-2,5-dione ring. This was proved (9) by labelling glycine NCA with C13 and examining the C13 content of the carbon dioxide evolved in thermal polymerisation. 

The support membrane is soaked in the prepolymerisation mixture consisting of functional monomer, crosslinker and template. An MIP layer is formed on or in the porous support by in situ photo or thermal polymerisation of the monomer mixture. This was first demonstrated by Haupt and coworkers on an amino acid specific MIP synthesised in the pores of a polypropylene membrane. Composite membranes... 

M. Manley-Harris and G. N. Richards, A novel fructoglycan from the thermal polymerisation of sucrose, Carbohydr. Res., 240 (1993) 183-196. 

The photophysical properties and photostability of oxazine dye molecules for use in luminescent solar concentrators have been reported. Tests have shown that the optical efficiencies of luminescent solar concentrators prepared using a single dye in a liquid methyl methacrylate polymer are as efficient as those fabricated using the same single dye dissolved in methyl methacrylate, and which is then thermally polymerised. ... 

Evidence indicates that when oils are heated at high temperatures, a Diels-Alder reaction takes place between a conjugated double bond and an isolated or individual double bond of another conjugated double bond and a dimer will be formed (Fig. 3.5). The rate of polymerisation shows a stronger dependence on the degree of unsaturation than in the oxidative polymerisation of thermally polymerised safflower and rapeseed oils. The relationship between the bulk viscosity (v) (polymerised at 320°C) and the average molecular weight for such polymerisations is found, v = 1.39 x 10 Mw . 

Inhibitors (such as 4-ferf-butylcatechol) (306) are usually added to monomers to be stored or transported to prevent premature thermal polymerisation. In precisely-controlled laboratory experiments, it is necessary to remove the inhibitor by distillation. However, industrial processes do not require the removal of inhibitor. Additional amounts of initiator are added to compensate for the presence of inhibitor. 

Figure 17 Examples of bismaleimide (BMI) monomer 38 and maleimide-terminated resin 39 prepared via Michael-type addition of 4,4 -methylenebisbenzeneamine 34 to the carbon-carbon double bond of BMI 38. Thermal polymerisation of ohgoimide 39 generates the cross-linked network 40.

Thermal polymerisation of short chain BMI resins occurs through radical polymerisation of the maleimide double bond producing highly cross-linked and brittle networks. A number of experimental results have been published that allow one to correlate the chemical structure of BMIs with the processability windows Tp - Tin , where Tp is the onset of polymerisation exotherm and is the maximum... 

Mono-, di- and trimeric fatty acids, formed by thermal polymerisation, were resolved on a short packed column, containing 3 % JXR (a methylsilicone) and temperature-programmed to 350°C [1013]. 

For measurements well off the resonance, i.e. with wavelengths larger than 720 nm, p-TS6 crystals were prepared by thermal polymerisation of monomer crystals, grown out of a saturated solution and manually cut using a shaver blade. Thickness of these crystals varies between 40-100 pm. 

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