**5. Effect of main chain structure on depolymerization of poly(olefin sulfone)s**

**Figure 11.** Decomposition ratio of polymer 10 heated at 150**°**C for 15 min after UV irradiation as a function of irradiation

**Figure 12.** GPC curves of polymer 10 (a) before UV irradiation, (b) after UV irradiation at 600 mJ/cm<sup>2</sup>

heating at 150**°**C for 15 min, and (c) the corresponding olefin monomer.

, followed by

energy.

130 Alkenes

Photoinduced depolymerization of the polymers shown in **Figure 3** mixed with a low‐ molecular‐weight photo‐base generator (ANC2) was investigated [18]. **Figure 14(a)** shows the change in the IR spectrum of PMPS film coated on a KBr plate without light irradiation, and **Figure 14(b)** shows the corresponding spectrum after light irradiation during heating (post‐exposure heat treatment). The absorption spectrum of the nonirradiated film was independent of the heating time, whereas the sulfonyl stretching bands (1311 and 1130 cm−1) decreased with the heating time after film irradiation, which indicates decomposition of the polymer main chain. The extent of decomposition increased with the irradiation energy density (**Figure 14(c)**), and the extent of PMPS decomposition was estimated to be 95%. Conversion of the polymer to the olefin monomer (extent of depolymerization) was estimated by 1 H NMR as 92%. Therefore, the polymer was converted to monomers with very high efficiency. **Figure 15(a)** shows the residual ratio of the PBS sulfonyl group as a function of heating time after photoirradiation. The change in residual ratio (decomposition of the main‐chain) was slow compared to that for PMPS. In contrast, the change in the residual ratio of PMBS was as fast as that for PMPS (**Figure 15(b)**). The only structural difference between PBS and PMBS is the number of substituents on the main chain. Thus, the decomposition characteristics must be dependent on the structure of the main chain. **Figure 16** shows the residual ratios for all polymers as a function of heating time after photoirradiation. The results show that the decomposition characteristics of the polymers can be divided into two groups: poly(olefin sulfone)s that possess only one type of proton on the main chain (branched 1‐olefins such as PMBS, PMPS, PMHS, and PMNS), and poly(olefin sulfone)s that possess two types of protons

**Figure 14.** Changes in the IR absorption spectra of the sulfonyl group in PMPS coated on a KBr plate (a) without irradiation and (b) after light irradiation at 254‐nm and 180 mJ/cm<sup>2</sup> . The thickness of the film was 2 μm. The post‐ exposure heat treatment time was varied from 0‐15 min at 150**°**C. (c) Residual ratio of the PMPS main‐chain as a function of heating time after irradiation, as estimated by IR absorption. The concentration of the L‐ANC2 (photo‐base generator) was 30 wt%. The heating temperature was 120**°**C and the irradiation energy was 3.15 J/cm<sup>2</sup> .

on the main chain (straight chain 1‐olefins and cycloolefins such as PBS, PPS, PHS, PcycloPS, and PcycloHS). The poly(olefin sulfone)s possessing only one type of proton on the main chain can undergo extensive decomposition, whereas the poly(olefin sulfone)s possessing **Figure 15.** Residual ratios of the main‐chain of poly(olefin sulfone)s in films estimated by IR absorption as a function of heating time after irradiation. (a) PBS film without irradiation (●) and after irradiation (■). (b) PMBS film without irradiation (●) and after irradiation (■). The concentration of the PBG was 30 wt%. The heating temperature was 120**°**C

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.

and the irradiation energy was 3.15 J/cm<sup>2</sup>

**Figure 15.** Residual ratios of the main‐chain of poly(olefin sulfone)s in films estimated by IR absorption as a function of heating time after irradiation. (a) PBS film without irradiation (●) and after irradiation (■). (b) PMBS film without irradiation (●) and after irradiation (■). The concentration of the PBG was 30 wt%. The heating temperature was 120**°**C and the irradiation energy was 3.15 J/cm<sup>2</sup> .

on the main chain (straight chain 1‐olefins and cycloolefins such as PBS, PPS, PHS, PcycloPS, and PcycloHS). The poly(olefin sulfone)s possessing only one type of proton on the main chain can undergo extensive decomposition, whereas the poly(olefin sulfone)s possessing

**Figure 14.** Changes in the IR absorption spectra of the sulfonyl group in PMPS coated on a KBr plate (a) without

exposure heat treatment time was varied from 0‐15 min at 150**°**C. (c) Residual ratio of the PMPS main‐chain as a function of heating time after irradiation, as estimated by IR absorption. The concentration of the L‐ANC2 (photo‐base generator)

. The thickness of the film was 2 μm. The post‐

.

irradiation and (b) after light irradiation at 254‐nm and 180 mJ/cm<sup>2</sup>

132 Alkenes

was 30 wt%. The heating temperature was 120**°**C and the irradiation energy was 3.15 J/cm<sup>2</sup>

**Figure 18** shows the decomposition ratio of P4 and P5 plotted as a function of irradiation energy density. The decomposition ratio of copolymer P4 was greater than that of P5. For P4, a decom-

base‐amplifying group in the side‐chain enhanced the amount of base generated in the P4 film.

. Thus, the presence of a

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position ratio of 98% was obtained at an energy density of 900 mJ/cm<sup>2</sup>

**Figure 17.** Base amplification mechanism and structures of copolymer BA1 and polymer 10.

**Figure 16.** Residual ratios of the main‐chains of poly(olefin sulfone)s in films as a function of heating time after irradiation. The concentration of the PBG was 30 wt%. The heating temperature was 120**°**C and the irradiation energy was 3.15 J/cm<sup>2</sup> .

two types of protons on the main chain undergo only a low extent of decomposition. The number of protons that can be abstracted appears to affect the extent of depolymerization. When many protons existing on a single main chain are abstracted, the yield of monomers was reduced, as shown in the reaction mechanism in **Figure 4**.
