| Abstract: | Thermal effects accompanying vacuum deposition of poly(chloro-para-xylylene) in the temperature range between ?196 and 0°C have been studied using two separate methods. One is based on the recording of the rate of evaporation of liquid nitrogen and it is used for the deposition at ?196°C, and the second involves the recording of changes in the substrate temperature and is used for the deposition in the range of ?162 to 0°C. These methods enable us to observe two distinct effects: fast (discrete), resulting in the appearance of sharp, exothermic spikes; and slow (continuous), resulting in the shift of the baseline. The shift of the baseline exhibits a well-defined maximum at about ?65°C and this temperature is attributed to the melting point of the monomer. The fast process always occurs below this temperature and is explained as a solid state, chain addition polymerization. The quantification of the heat effect at ?196°C strongly suggests that the quinonoid form of the monomer participates in the propagation step of this chain reaction. The fast (solid state) and the continuous modes of polymerization may occur simultaneously in the range of about ?140 and ?65°C. The frequency of the initiation which is the formation of dimer radical seems to control the occurrence of these two modes of polymerization. |
