if you look to the kinetics equation you will recognize the different parameters you should play on to increase the MW. Among which the initiator concentration. Reduce it and you will endup with higher MW. Regards
Please read this paper , which I think would help you to synthesize the PVA
"Synthesis of high-molecular-weight poly(vinyl alcohol) with high yield by novel one-batch suspension polymerization of vinyl acetate and saponification"