38  US 8,114,570 B2  37  Illustrative, non-limiting examples of the recurring units of  formula (5) are given below.  c+---?-J  c+---?-J  i  Fo i  Fo  0~  0  0  0  H  H  (++)  i  Fa  0  0  H  H  (++)  i  Fa  0  c+-/-J  J  >=o  ~o  0  c+-/-J  c+-/-J  J  Fa  J  Fa  0  0  0  0  H  H  H  H  (++)  i  Fa  (++)  i  Fo  b-0  ~o  0  c+---?-J  c+---?-J  i  Fo  i  Fo  0  0  0  0  H  H  (++)  i  Fa  c+---?-J  i  Fa  0  0  H  H  H  H  (++)(++)  i  Fa  i  Fa  0  0  0  0  -continued 