The base catalyzed hydrolysis reaction of poly(propylene carbonate) (PPC)

a highly alternative copolymer synthesized from carbon dioxide and propylene oxide

was investigated systematically in this report.The influences of reaction time

concentration of PPC solution

concentration of base (sodium hydroxide) solution

and residual zinc oxide on the degradation reaction were discussed.1H-NMR spectra were used to analyze the carbonate unit content in the degraded polymer

it was found that the carbonate unit in the final degraded polymer maintained above 80% for all the studied conditions.The number average molecular weight of the final polymer dropped very quickly in the first several hours

a 50% decrease was observed in the first 2～6 h

depending on the concentration of PPC.The higher concentration of PPC was

the slower the decrease in molecular weight

when the concentration of PPC was 0.1 g/L

the number average molecular weight of the final polymer was 18500 after 8 h at 50℃

whereas it was 33700 when the PPC concentration was 0.5 g/L.Degradation time and base concentration were the two important factors for the yield as well as carbonate unit content in the degraded polymer

when the base concentration was 0.25 mol/L

the polymer yield maintained above 90% with carbonate unit over 80% at 48 h

the polymer yield dropped to ca.60% when the base concentration increased to 2.0 mol/L.Generally

prolonged degradation time caused yield loss in the final polymer

and the degradation reaction was enhanced with increasing base concentration.Compared with the purified PPC sample

the existence of zinc oxide in the as-polymerized PPC led to more severe degradation reaction.The GC-MS spectra were used to analyze the liquid compounds of the degraded products

where 1

2-isopropane-diol and propylene carbonate were detected

therefore

it was concluded that the random degradation reaction dominated in the base catalyzed degradation reaction at first stage

however

the unzipping degradation reaction became dominant with the degradation reaction proceeding

a preliminary mechanism for base catalyzed PPC degradation was proposed.Since the base catalyzed degradation can stably produce low molecular weight PPC under controlled conditions

this reaction was therefore considered as a new method to prepare low molecular weight PPC

with number average molecular weight adjustable from 4000 to 10000