SalenAl(OiPr) complex

prepared by reaction of SalenH2（N

N′-bis(salicylidene)-1

2－phenylenediamine） and isopropoxide aluminum

has been shown to be an effective catalyst for the coupling of carbon dioxide and cyclohexene oxide to afford poly(cyclohexenylene carbonate) (PCHC) with small quantities of byproduct. The addition of various cocatalysts

including 4-dimethyl(amino) pyridine (DMAP)

N-methyl imidazole (N-MeIm)

1

8-diazabicyclo(5.4.0)undec-7-ene (DBU) and tetra-n-butylammonium chloride (Bu4NCl) can greatly enhance the catalytic efficiency

and more donating DMAP can offer the best copolymerization result.The relative DMAP loading also plays an important role in polymer formation.Experiments indicated that 1 equiv of DMAP was the optimum cocatalyst loading.At higher cocatalyst loading

there is a little increase in polyether linkages as well as a dramatic decrease in the molecular weight of the coplymer. Effects of reaction condition such as catalyst concentration

reaction time

temperature

CO2 pressure on copoymerization were probed in detail.Through varying catalyst concentration

it was found that both lower and higher catalyst concentration led to lower catalytic efficiency and lower Mw

and maximum catalytic efficiency was observed in the presence of catalyst concentration around 2 g/L.The catalyst concentration seemed not to influence the carbonate content in the copolymer significantly.Almost in all cases highly alternative copolymers were obtained.As far as reaction time is concerned

the catalytic efficiency and molecular weight are enhanced with increasing time at the beginning

it reaches a maximum around 32 h

and then drops slowly.Carbonate content as low as 96.5% was observed at the very beginning

afterward the copolymerization quickly tended to proceed alternatively.Both the catalytic efficiency in copolymerization and molecular weight of PCHC raised with increasing reaction temperature from 40℃ to 80°C.At temperatures above 80℃

the polymer yield and molecular weight went down with further increasing temperature due to serious degradation of the obtained polymer.Increasing CO2 pressure

while was less than 4 MPa

enhanced the catalytic efficiency.Higher pressure favored the formation of alternative copolymer as expected

but rather high CO2 pressure was harmful to copolymerization. In conclusion

the best results were obtained from the reaction at 80℃ for 32 h

with 2.0 g/L SalenAl(OiPr) and CO2 pressure of 4 MPa using 1.0 equiv of 4-dimethylaminopyridine (DMAP) as cocatalysts.The highest turnover number (TON) is 495 g of polymer/g of catalyst.The produced copolymer is completely alternated polymer (percent of carbonate 99%)

and had a Mn value of 55900 with a polydispersity index of 1.32 as determined by gel permeation chromatography.On 13C-NMR spectroscopy

chemical shifts observerd at 153.7

153.2

and 153.0 indicate the production of largely atactic polymer.The thermal properties of the copolymer were obtained by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) in N2 and at a heating rate of 10 K/min.DSC showed that the high alternating PCHC copolymer exhibited higher glass transition temperature (136℃) than their corresponding values reported in the literature

and TGA results indicated that the high alternating PCHC copolymer began its decomposition at 280℃ and then decomposed completely upon 350℃.The high alternating PCHC has excellent thermal decompose properties

and can be applied as MEMS sacrificial material.