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.
The effect of the sublimation rate of di‐p‐xylylene on the crystallinity and morphology of Parylene N deposited on stainless steel was studied as a function of substrate temperature. For a given rate of dimer sublimation, the deposition rate increases with decreasing substrate temperature. Increasing the sublimation rate of the dimer increases the deposition rate 10‐fold, decreases the crystallinity, and shifts the appearance of the hexagonal β structure towards higher substrate temperature for samples synthesized from room temperature (RT) to −60°C. Solution annealing resulting from solvent extraction, and isothermal annealing, increase the crystallinity of the polymers and result in structures containing both α and β polymorphs. The surface topology, as revealed by scanning electron microscopy (SEM), for polymers synthesized from RT to −40°C shows a globular structure, whereas low temperature samples exhibit a rod‐type morphology. For higher sublimation rates of the dimer, SEM micrographs show that oligomeric species start appearing on the polymer films after a period of 4–5 days. Solvent extraction removes the oligomeric crystals, and GPC analysis of the resulting extract indicates that most of the oligomers range in molecular weight from 100 to 900. The cross‐sectional morphology for fractured low temperature samples, however, reveals different morphologies as polymerization proceeds. It is postulated that in the temperature range −50 to −78°C, both surface condensation and surface adsorption of monomer occurs, leading to different morphologies and lower crystallinity. The polymer synthesized at liquid nitrogen temperature shows the presence of voids along with different morphologies. X‐ray diffractograms of polymers synthesized at liquid nitrogen reveal a considerable amount of amorphous phase in the films. Hence, it is inferred that, although the liquid nitrogen polymerization is a solid state polymerization of the crystalline monomer, it does not lead to 100% crystalline material, and the reasons for this are discussed.
SYNOPSISPolyimidothioethers were synthesized as possible polymers for evaluation as X-ray resists. These polymers were varied in the ratio of the monomers and in their structures. Aliphatic thiols, bismaleimides, and iodonium monomers were used. The composition was varied using ratios of the bisimide to iodonium of 9 : 1,8 : 2, 7 : 3 , 6 : 4, 5 : 5, and 0 : 1. The ratio of the thiols, containing 6 to 10 -CH2--groups, to the monomers was 1 : 1. The synthesis and characterization of the intermediate compounds and polymers are described in detail.
SynopsisPoly(ch1oro-p-xylylene) was synthesized in a manner similar to poly( p-xylylene) using Gorham's method at various cryogenic temperatures. The effect of the sublimation rate of dimer on the kinetics of deposition, crystallinity, and crystalline structure was studied. Increasing the sublimation rate of the dimer increases the deposition rate similar to that of poly( p-xylylene). However, an increase in crystallinity, in contrast to Parylene N, is observed, although, in general, Parylene C has lower crystallinity relative to Parylene N. No polymorphism is observed either by decreasing the deposition temperature or by increasing the sublimation rate of the dimer. Solution annealing and isothermal annealing both bring about crystallization without any structural transformation. Solution annealing removes the oligomers and dimers, but no crystalline oligomers are ever detected under the scanning electron microscope (SEM). The surface topology of films synthesized from ambient temperature to -40°C is very similar to Parylene N. At lower temperatures, in the region -50 to -60°C, a rod-type morphology is observed similar to Parylene N. The surface topology of samples synthesized at -196°C is totally different from that of Parylene N. All low temperature synthesized samples are amorphous.
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