Table I.

Factors and treatment levels.

Factor	Symbol	Low (−1)	High (1)
Ester ClSi reaction time	A	24 h	72 h
Grafting reaction time	B	2 4 h	7 2 h
CuBr2	C	1 mg cm−2	2 mg cm−2
Vitamin C	D	39.5 mg cm−2	79 mg cm−2
Covariate	—	Preupgrade	Postupgrade