Study On Carbon Dioxide Ternary Copolymerization

The copolymerization of carbon dioxide and epoxides to generate biodegradable aliphatic polycarbonates was one of the focuses on the field of carbon dioxide research. Most of the researches aim at the binary copolymerization reaction of CO2 and epoxides, while the thermal and mechanical properties of the copolymers are poor. Introducing the third monomer was not only can change the molecular chain structure of the polymers, but also help increase the thermal stability. However, most of the comonomers focus on petroleum and petroleum derivatives that are non-renewable resources. In this paper, the new polycarbonates were successfully synthesized and characterized based on the terpolymerization of CO2, cyclohexene oxide and alpha-pinene oxide or 1,2-limonene oxide using homogeneous SalenCrⅢCl catalyst and bis (triphenylphosphine) ammonium chloride ([PPN]C1) as cocatalyst, respectively. The third monomers alpha-pinene oxide and 1,2-limonene oxide, derived from the pure natural renewable resources occurring epoxidation reaction. In the meantime, we studied the influence of several factors on the copolymerization reaction and analysed the thermal degradation kinetics of copolymers in order to get the possible thermal degradation mechanism. The main contents are as follows:1. The new polycarbonates were successfully synthesized based on the terpolymerization of CO2, cyclohexene oxide and alpha-pinene oxide or 1,2-limonene oxide using homogeneous SalenCrⅢCl catalyst according to the report method, respectively. FT-IR, 1H NMR and 13C NMR are used to characterize and analyse the copolymers. The results show that alpha-pinene oxide and 1,2-limonene oxide have successfully participated in the terpolymerization.2. The factors for the terpolymerization of CO2 and epoxides have been investigated, including the mole ratio of comonomer, reaction time, reaction temperature and reaction pressure. The optimum conditions of the terpolymerization of CO2, cyclohexene oxide and alpha-pinene oxide are:SalenCrⅢCl:[PPN]C1:CHO: alpha-pinene oxide=1:1:1000:300 (mole ratio, m(SalenCrⅢCl)=0.020g, VcHO=3.225mL), T=90℃, t=20h, PCO2=5.0MPa, catalytic activity=153.67gter/gcat, Mw=11.94×103g/mol, Mn=9.87×103g/mol, PDI=1.21; The optimum conditions of the terpolymerization of CO2, cyclohexene oxide and 1,2-limonene oxide are: SalenCrⅢCl:[PPN]C1:CHO:1,2-limonene oxide=1:1:500:200 (mole ratio, m(SalenCrⅢCl)=0.0253g, VCHo=2.05mL), T=90℃, t=24h, PCO2=4.5MPa, catalytic activity=89.09gter/gcat, Mw=9.08×103g/mol, Mn=7.84×103g/mol, PDI=1.16.3. The terpolymers were analyzed by gel permeation chromatography (GPC), thermogravimetry (TG). derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). The results indicated that the yield of copolymers, the molecular weights and the molecular weight distribution of the terpolymers are improved. At the same time, the temperature corresponding to the maximum degradation rate (Tp) and the glass transition temperature (Tg) of the terpolymers were higher than binary copolymer, the thermal stability of the terpolymers is better.4. The thermal degradation and kinetics of the binary copolymer and the terpolymers under different heating rates were studied by using thermogravimetry. The possible thermal degradation mechanisms of the copolymers were calculated according to FWO method, Kissinger method and Coats-Redfern method. The results show that the kinetic mechanism of thermal degradation for binary copolymer based on copolymerization of CO2 and cyclohexene oxide conforms to a power law (P1); the kinetic mechanism of thermal degradation for the terpolymers based on terpolymerization of CO2, cyclohexene oxide and alpha-pinene oxide or 1,2-limonene oxide conform to the secondary Avrami-Erofe’ev (A2).