Soft-start polymerization

At the molecular level, the effect of soft-start polymerization is to extend the gelation time of the composite [67], By reducing the rate of early polymerization, the rate of shrinkage is also reduced. This helps to maintain the seal at the margins of the restoration, and may allow relaxation processes to take place, so that stresses do not build up to the same extent as in conventional cure regimes. 

Some authorities advocate soft-start polymerization, but this practice is not supported by the evidence. 

D.C. Watts, A. al Hindi, Intrinsic soft-start polymerization shrinkage-kinetics in an acrylate-based resin-composite. Dent. Mater. 15 (1999) 39-45. 

A. Sahafi, A. Peutzfeldt, E. Asmussen, Soft-start polymerization and marginal gap formation in vitro. Am. J. Dent. 14 (2001) 145-147. 

Y.Z. Bayindir, M. Yildis, F. Bayindir, The effect of soft-start polymerization on surface hardness of two packable composites. Dent. Mater. J. 22 (2003) 610-616. 

D.C.N. Chan, W.D. Browning, K.B. Frazier, M.G. Brackett, Clinical evaluation of the soft-start (pulse-delay) polymerization techniqne in Class I and Class II composite restorations, Oper. Dent. 33 (2008) 265-271. 

Recent demands for polymeric materials request them to be multifunctional and high performance. Therefore, the research and development of composite materials have become more important because single-polymeric materials can never satisfy such requests. Especially, nanocomposite materials where nanoscale fillers are incorporated with polymeric materials draw much more attention, which accelerates the development of evaluation techniques that have nanometer-scale resolution." To date, transmission electron microscopy (TEM) has been widely used for this purpose, while the technique never catches mechanical information of such materials in general. The realization of much-higher-performance materials requires the evaluation technique that enables us to investigate morphological and mechanical properties at the same time. AFM must be an appropriate candidate because it has almost comparable resolution with TEM. Furthermore, mechanical properties can be readily obtained by AFM due to the fact that the sharp probe tip attached to soft cantilever directly touches the surface of materials in question. Therefore, many of polymer researchers have started to use this novel technique." In this section, we introduce the results using the method described in Section 21.3.3 on CB-reinforced NR. 

The starting amino acid for nylon-11 is produced from methyl ricinoleate [141-24-2], which is obtained from castor oil (qv). The methyl ricinoleate is pyrolized to methyl 10-undecylenate [25339-67-7] and heptanal [111-71-7]. The unsaturated ester is hydrolyzed and then converted to the amino acid by hydrobromination, followed by ammoniation and acidification. The CO-amino acid product is a soft paste containing water, which is dried in the first step of the polymerization process. 

Vinyl ethers, CH2=CH —OR, are obtained from ethylene and alcohols by reacting in the presence of oxygen, or by the addition of alcohols into acetylene. Vinyl ethers are cationically polymerized. In the commercial polymerization, a small portion of the monomer is added to dioxane at 5 C, the initiator is added (BF3 2H2O), and, after the start of the polymerization, further monomer is added in such a way that polymerization can take place by reverse flow at 100 C. Poly (vinyl ethers) form soft resins which are very... 

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