Research On The Homo-and Copolymerization Of Cyclic Lactones And Styrene Catalyzed By Tris(pentafluorophenyl)borane

Styrene and cyclic lactones are common monomers in polymer synthetic chemistry,and their polymerization can be catalyzed by various Lewis acids.Tris（pentafluorophenyl）borane [B（C₆F₅）₃] is a nontraditional Lewis acid,and that has been applied in the research of various polymerization reactions.The homopolymerization of styrene,ε-caprolactone,β-butyrolactone and the hybrid copolymerization of styrene with the two lactones were investigated using B（C₆F₅）₃ as a catalyst without extra initiator in this study.The main contents and results of this study are listed as follows:（1）The polymerization of styrene was carried out at 25 ℃ using B（C₆F₅）₃ as a catalyst without extra cationic source.Structure of the obtained polystyrene was characterized by ¹H nuclear magnetic resonance（¹H NMR）,gel permeation chromatography（GPC）as well as matrix-assisted laser desorption-ionization time of flight mass spectrometry（MALDI-TOF MS）methods.The analyses of ¹H NMR and MALDI-TOF MS revealed that indanyl ring was formed between the penultimate monomer unit and the propagating carbocation.GPC results showed that the resultant polymers have relatively broad molecular weight distributions（PDI）and molecular weight control is not very good.The polymerization mechanism was studied using 2,6-di-tert-butylpyridine（DtBP）as a proton trap,which revealed that the true cationic source was adventitious moisture and the polymerization proceeded along with intramolecular ring formation reaction.The influence of polymerization time and solvent were studied,which revealed that all the monomer can be completely consumed within several hours in low polar haloalkane,such as dichloromethane（CH₂Cl₂）.（2）The polymerization of ε-caprolactone and β-butyrolactone were carried out at 80 ℃ and 25 ℃ using B（C₆F₅）₃ as a catalyst without extra initiator respectively.Structure of the resultant polymers was characterized by ¹H NMR,GPC and MALDI-TOF MS.The analyses of ¹H NMR and MALDI-TOF MS revealed that poly（ε-caprolactone）is linear polyester with uniform hydroxyl chain end and there are two structures in the obtained poly（β-butyrolactone）,that is cyclic and linear polymer chain.GPC results showed that both the PDI of poly（ε-caprolactone）and poly（β-butyrolactone）are relatively low,but their molecular weight control are not very good.The mechanism for the polymerization of β-butyrolactone was studied using density functional theory（DFT）.A possible zwitterionic ring opening polymerization mechanism was proposed for the polymerization of β-butyrolactone.The influence of reaction time for the polymerization of ε-caprolactone was studied,which revealed that the monomer conversion increased with reaction time at low conversion rate.（3）The hybrid copolymerization of styrene with ε-caprolactone and β-butyrolactone were carried out using B（C₆F₅）₃ as a catalyst without extra initiator respectively.Experimental results indicated that the copolymerization of styrene and ε-caprolactone cannot be carried out by B（C₆F₅）₃ at 25 ℃ or 80 ℃,but the copolymerization of styrene and β-butyrolactone proceeded successfully at 25 ℃.Structure and properties of the obtained copolymer of styrene and β-butyrolactone were characterized by 1D NMR,2D NMR,GPC and differential scanning calorimetry（DSC）.The analysis of 1D and 2D NMR revealed that the proportion of styrene unit in obtained copolymer is higher than the feed ratio of styrene to β-butyrolactone.GPC results showed that the PDI of obtained copolymer is relatively low and the amount of B（C₆F₅）₃ had little effect on the molecular weight.GPC results showed that all obtained copolymer exhibited a single glass transition temperature（Tg）and that decreased with the decreasing of the proportion of styrene unit in obtained copolymer.Mechanism of the copolymerization of styrene and β-butyrolactone was discussed,the polymerization was initiated by an adduct of B（C₆F₅）₃ and β-butyrolactone and a possible isomerization polymerization mechanism was proposed.