Research Of Polymerization Reaction Dynamics Of Liquid Silicone Rubber By Mechanical Spectroscopy

Various approaches appeared along with the development of science technology.Aftergoing through the process from macroscopic reaction dynamics to microscopic reactiondynamics, chemical reaction dynamics has been one of the most important branches ofphysical chemistry. The theories and laws of chemical reactions, which are the questions needto be answered by chemical reaction dynamics, have been called one of the four problems ofchemistry in the21century. Although there are more and more research methods, deeperinvestigation of chemical reaction dynamics, as well as new research techniques, are stillnecessary.Nowadays, research of polymeric functional materials is getting deeper. For this reason,researches about polymerization dynamics become very important, as polymers are usuallypolymerized from monomers with low molecular weight. As a result, it can be considered thatpolymerization is one of the most fundamental and general reactions. As far back as thebeginning of the twentieth century, material science was greatly elevated because of theappearance of various polymerization methods. And research of polymerization has maderemarkable progress until today. As we can see from the history of development, it issignificant to explore a new technique to detect and a new method to research, because it willalways offer new information about polymerization process. In this paper, the curing(vulcanization) process of liquid silicone rubber (LSR), which is a typical kind ofpolymerization, was investigated by Reed-vibration Mechanical Spectroscopy for Liquids(RMS-L) that recently invented by Yi-neng Huang and co-workers. By this approach, thecuring process as well as mechanical spectrum was detected in real-time, and some usefulconclusions were achieved by analyzing and discussing the experiment results.First of all, the vulcanization of one-component condensed liquid silicone rubber wasdetected in real-time and analyzed in this paper based on RMS-L method and the recent workof our group about mechanical spectroscopy research of acrylate structure adhesive curingprocess. It revealed that, during the curing process, the dissipation factordropped rapidly atfirst, corresponding to the course of condensation reaction and gradual formation ofcross-linking structure between the molecular chains in the sample. Later, the resonancefrequency showed a linear increase, which has a relationship with the even volatilization oflow molecular weight by-products generated during the reaction. As a result, RMS-L is able toperform sensitive detection of cross-linking generation and volatilization of low molecularweight by products during the reaction.Meanwhile, polymerization of two-component addition-cured type liquid silicone rubberwas detected by RMS-L and analyzed. The results show that the mechanical spectroscopy during the reaction of the two-component addition-cured liquid silicone rubber was similarwith one-component condensation type liquid silicone rubber. The difference was that theresonance frequency didn’t show the character of linear increase. In other words, there was novolatile by-product generated in this reaction, which coincides with the vulcanizationmechanism of the two-component addition-cured type liquid silicone rubber.Besides the above, polymerization process of the two-component liquid silicone gel wasalso investigated based on RMS-L method. Analysis indicates that the molecular chainsaddition reacted with each other and formed cross-linking structures gradually at the verybeginning, which resulted in rapid decrease of internal friction and fast rise of resonancefrequency. But due to the large weight and long chain of basic polymer in the sample, theinternal stress induced by the mixture would relax slowly with the effect of stress fromvibrated substrate. For this sake, the internal friction appeared a step-like decrease, andmaintained a stable value after that, which means finish of the reaction.The results of RMS-L research of three kinds of samples above show that RMS-Lmethod can give a qualitative analysis though, it is still supposed offer more accurateinformation of reaction dynamics if work with other techniques. Because of this, the researchwork in this paper could provide some consultation and basis for deeper research ofpolymerization reaction dynamics.