Isocyanate Ring Monomer Rare Earth Catalytic Polymerization And Copolymerization Study

The homopolymerization of isocyanates, ε-caprolactone (CL), L-lactide (L-LA) and the copolymerization of isocyanates with CL or propylene oxide (PO) were studied in this dissertation. The influences of the composition and structure of rare earth catalysts, reaction conditions on the polymerization, and the characteristics, kinetics, mechanism of polymerization were investigated. The structure and the properties of polymers obtained were characterized, and the potential applications of the copolymer obtained were also tested.The polymerizations of octyl isocyanate (OIC) catalyzed by binary rare earth catalyst system Ln(P₂₀₄)₃/AL(I-Bu)₃ has been investigated and the polymer obtained was characterized by GPC, FT-IR, NMR, DSC, TGA etc. The catalyst system is fairly high efficient for this monomer at -50℃ to 50℃, and the polyoctylisocyanate(POIC) obtained with high molecular weight and narrow molecular weight distribution(MWD). POIC with yield of 88.3%, intrinsic viscosity ([(?)]) of 15.4dL/g, molecular weight (Mn) of 38.9×10⁴, and polydispersity (PD) of 3.53 was obtained under following conditions: [Nd]=49.6×10^-3 mol/L, [OIC]=4.96mol/L, Al/Nd=10(molar ratio), polymerized in bulk at -10℃ for 12h. The solution polymerization in toluene was also studied, and the kinetics study indicates that the polymerization is of first order with respect to monomer and to catalyst concentration respectively, and the overall activation energy amounts to 58.7 kJ/mol. ¹H-NMR and FT-IR analyses of POIC demonstrate that the polymerization of OIC proceeds through coordination polymerization of carbon-nitrogen bond cleavage.Binary rare earth catalytic systems: Ln(Vers)₃/AliBu₃ were used for the polymerization of alkyl isocyanates and they are good catalytic systems for the polymerizations of alkyl isocyanates at mild polymerization conditions. The features of bulk polymerizations and solution polymerizations of three alkyl isocyanates: n-butyl isocyanates (BIC), n-hexyl isocyanates (HIC) and n-octyl isocyanats (OIC) were investigated. The polymerization results show that OIC has the highest reactivity, and BIC has the lowest reactivity, while the sequence of molecular weight of the polymers obtained is opposite. At the polymerization conditions tested, the polyisocyanates with Mn=18× l0⁴～170×10⁴, MWD=2.4⁵.7 can be prepared at -10°C. The kinetics studies of solution polymerizations of these three alkyl isocyanates indicated that the polymerizations are of first order with respect to monomer concentrations and to catalyst concentrations respectively. The overall activation energy of BIC, HIC, and OIC polymers are 39.7kJ/mol, 36.2kJ/mol, 29.2kJ/mol respectively, which is coincide with the reactivities of these monomers.Three sorts of rare earth Schiff base complexes were synthesized from cheap and easily avalible rare earth chlorides and proved to be good catalysts for the polymerization of alkyl isocyanates.The polymerization of alkyl isocyanates catalyzed by rare earth chloride salen complexes/ alkyl aluminum (LnSalenCl₃/AlR₃) were investigated and La(H₂salen)-2Cl₃· 2C₂H₇OH/AliBu₃ is a fairly high efficient catalyst for the polymerization of alkyl isocyanates preparing high molecular weight polyisocyanates with narrow MWD at 20℃. This is unique rare earth catalyst for the polymerization of alkyl isocyanates. PHIC can be prepared with yield of 74.0% , Mn of 40.20×10⁴ and PD of 1.79 under the following conditions: Al/La=30(molar ratio), [HIC]/[La]=100(molar ratio), [HIC]= 3.43 mol/L polymerization at 20℃ for 12h in toluene. At the same polymerization conditions, the POIC with yield of 67.3%, Mn of 190×10⁴, and PD of 2.34, the PBIC with yield of 45.5%, Mn of 1.10×10⁴, and PD of 2.38 can be prepared. The effects of different rare earth elements, various Schiff base ligands and solvents, and the other polymerization conditions on the polymerizations of these three alkyl isocyanates were discussed. The kinetics of the polymerizations were also investigated.Polymerizition of HIC has been carried out with rare earth chloride schiff base complexes/alkyl aluminium (LnCl(salen)₂/AliBu₃) catalyitic systems at -10 to 20 ℃ and the PHIC with Mn of 10×10⁴～100×10⁴ and PD of 1.3-5.8 was obtained.Several single component catalysts of rare earth schiff base complexes(Ln(Salen)₃) were synthesized and used for the polymerization of alkyl isocyanates and La(paSalen)₃) is the best catalysts among these complexes. The appropriate polymerization conditions for HIC are [HIC]=3.43mol/L, [La]=8.58×10^-3mol/L, -40℃,12h, in toluene and the PHIC obtained is with yield of 75.5%, Mn=6.00×10⁴ and PD of 3.86.Copolymerizations of HIC with CL were performed by rare earth lanthanum (La(OAr)₃) at 10℃ and the copolymers obtained have the HIC units of 5 to 40mol%. The copolymer was characterized by NMR, DSC, GPC, TGA and POM. The degradation experiments for the copolymer of HIC with CL carried out in acidic and basic buffer solutions denoted that the introducing of isocyanate units in copolymer improves the degradability of PCL. The results of histologic section observation of the copolymer buried in rats demonstrated that the copolymer is low toxicity, stable and well histocompatibility.Random copolymerization of phenyl isocyanate (PhIC) with PO has been succesfully conducted with Nd(P₂₀₄)₃/AliBu₃ catalytic system. The optimium condition are Al/Nd=10(molar ratio), aging at 50℃ for 5h, ([PhIC]+[PO]):[Nd]=400(molar ratio), [PhIC]:[PO] =1 :1(molar ratio), polymerization at 20℃for 24h. The molecular weight of the copolymer incresed with the prolonging of polymerization time, and the copolymer yield decreased with the increasing of the PO molar ratio in the comonomers mixture.LaCl₃/PO/DMF catalytic system is cheap and easily available which could initiate the ring opening polymerization of CL. The PCL prepared with yield of 83.3% and Mn of 1.93×10⁴ when [CL]= 9.04mol/L, PO/La=20(molar ratio), DMF/LaCl₃=10 (molar ratio), [CL]/[LaCl₃] = 500(molar ratio), 30℃ for 1h in bulk and PCL with yieldof 78.7% and Mv of 1.55×10⁴ can be obtained under the following conditions: [CL]=4.52mol/L, PO/La=20(molar ratio), DMF/LaCl₃=10(molar ratio), [CL]/[LaCl₃]=500(molar ratio), in toluene, 30℃ for 2h.Sevral rare earth schiff base complexes can be used as single component catalysts for the ring opening polymerization of L-LA, and La(dtbpaSalen)3 is the best amoung these catalysts. The ring opening polymerization of L-LA with La(dtbpaSalen)₃ could prepared PL-LA with yield of 96.5%, Mn of 2.52×10⁴ and PD of 2.52 under following conditions: [L-LA]=2.0 mol/L, [La]=2.0×10^-3mol/L polymerization at 80 ℃ for 40min intoluene.