The preparation and compatibilizing ability of heteroarm star-shaped block copolymers (6 and 8) composed of polystyrene and nylon 6 units diverged from the phosphazene core were investigated. The heteroarm star-shaped copolymers were prepared by a partial coupling reaction of the acid chloride of hexakis(4-carboxyphenoxy)cyclotriphosphazene [4, (4-ClCOC6H4O)6N3P3] with polystyrene having a terminal amino group (PSt−NH2) or poly(styryllithium), followed by the ring-opening polymerization of ε-caprolactam (ε-CL) with the residual carboxyl group in the phosphazene core. The coupling reaction of telechelic PSt−NH2 and poly(styryllthium) with 4 occurs smoothly to give carboxyphenoxycyclotriphosphazenes carrying 2.2−4.7 polystyrene chains, 5 and 7, respectively. The polymerization of ε-CL with hexakis(4-carboxyphenoxy)cyclotriphosphazene [2, (4-HOOCC6H4O)6N3P3] showed that all carboxyl groups participate in the initiation of polymerization to give hexaarmed star-shaped polymers. This implies that the residual carboxyl groups in 5 and 7 could also initiate the polymerization of ε-CL. The molecular weights of copolymers obtained from the polymerization of ε-CL with 5 and 7 are in agreement with those of calculated values, suggesting the formation of heteroarm star-shaped block copolymers with phosphazene core (6 and 8). When these copolymers were used as a compatibilizer of an immiscible blend, poly(2,6-dimethylphenylene oxide) (PPO) and nylon 6, DSC profiles showed a single transition temperature that shifted to lower temperature from the T g of PPO. The SEM photograph indicates that PPO disperses regularly and finely with 0.3 μm size in the nylon domain. Furthermore, the tensile strength and elongation at break of ternary blends increased with increasing the copolymer content. These results indicate that the effective penetration of each block sequence of the heteroarm star-shaped copolymers into the blend components is operative, that is, these copolymers act as an excellent compatibilizer for PPO/nylon 6 blends.

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Partial discharge (PD) resistance of biodegradable poly-L-lactic acid (PLLA) was examined at temperatures between room temperature and 70 • C, namely at around the glass transition temperature of 57 • C. The PD activity becomes more pronounced at temperatures above 60 • C, reflecting that the permittivity increases in the rubber state. Furthermore, we have changed the crystallinity of PLLA by drawing or annealing thermally, and have examined its effect on the PD resistance. Although the depth eroded by a fixed period of PD degradation becomes shallower when the sample was crystallized by the drawing or the heat treatment, its reduction ratio is almost equal to the reduction ratio of PD activities due to the decrease in permittivity. Therefore, it is hard to assume that crystallization of PLLA improves its PD resistance to a unit amount of charge. 

We have changed the crystallinity of biodegradable poly-L-lactide (PLLA) by drawing or by annealing thermally, and have examined its effect on the partial discharge (PD) resistance. Although the depth eroded by a fixed period of PD degradation becomes shallower when the sample was crystallized by the drawing or by the heat treatment, its reduction ratio is almost equal to the reduction ratio of PD activities due to the decrease in permittivity. Therefore, it is hard to assume that crystallization of PLLA improves its PD resistance to a unit amount of charge.