Abstract
Vinyl pivalate (VPi) was polymerized in bulk by ultraviolet-ray initiation at low temperatures using 2,2'-azobis(2,4-dimethylvaleronitrile) (ADMVN) and 2,2'-azobis(isobutyronitrile) (AIBN) as photoinitiators. High molecular weight (HMW) poly(vinyl pivalate) (PVPi), having a number-average degree of polymerization (P n ) of 13,000-28,000, was obtained at conversions below 30% and converted by saponification to a syndiotacticity-rich HMW poly(vinyl alcohol) (PVA) microfibrillar fiber with P n of 7300-18,300, syndiotactic diad (S-diad) and triad contents of ∼ 64% and ∼39%, respectively, and crystal melting temperature (T m ) of ∼249°C. ADMVN gave higher P n than AIBN. On the other hand, conversion was smaller with the former than with the latter, and it was found that the initiation rate of ADMVN was lower than that of AIBN. P n of PVA was constant while P n of the precursor PVPi increased with increasing conversion. The syndiotacticity, T m and thermal stability of PVA obtained from PVPi were much superior to those of PVA derived from poly(vinyl acetate) prepared under the same polymerization conditions. Polymerization of VPi at lower temperatures gave PVA with higher syndiotacticity.
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