Strontium-based initiator system for ring-opening polymerization of cyclic esters

An amino isopropoxyl strontium (Sr-PO) initiator, which was prepared by the reaction of propylene oxide with liquid strontium ammoniate solution, was used to carry out the ring-opening polymerization (ROP) of cyclic esters to obtain aliphatic polyesters, such as poly(epsilon-caprolactone) (PCL) and poly(L-lactide) (PLLA). The Sr-PO initiator demonstrated an effective initiating activity for the ROP of epsilon-caprolactone (epsilon-CL) and L-lactide (LLA) under mild conditions and adjusted the molecular weight by the ratio of monomer to Sr-PO initiator. Block copolymer PCL-b-PLLA was prepared by sequential polymerization of epsilon-CL and LLA, which was demonstrated by H-1 NMR, C-13 NMR, and gel permeation chromatography. The chemical structure of Sr-PO initiator was confirmed by elemental analysis of Sr and N, H-1 NMR analysis of the end groups in epsilon-CL oligomer, and Fourier transform infrared (FTIR) spectroscopy. The end groups of PCL were hydroxyl and isopropoxycarbonyl, and FTIR spectroscopy showed the coordination between Sr-PO initiator and model monomer gamma-butyrolactone. These experimental facts indicated that the ROP of cyclic esters followed a coordination-insertion mechanism, and cyclic esters exclusively inserted into the Sr-O bond.

Multiple melting behavior of isotactic polypropylene and poly(propylene-co-ethylene) after stepwise isothermal crystallization

The multiple melting behavior of several commercial resins of isotactic polypropylene (iPP) and random copolymer, poly(propylene-co-ethylene) (PPE), after stepwise isothermal crystallization (SIC) were studied by differential scanning calorimeter and wide-angle X-ray diffraction (WAXD). For iPP samples, three typical melting endotherms appeared after SIC process when heating rate was lower than 10 degreesC/min. The WAXD experiments proved that only alpha-form crystal was formed during SIC process and no transition from alpha1- to alpha2-form occurred during heating process. Heating rate dependence for each endotherm was discussed and it was concluded that there were only,two major crystals with different thermal stability. For the PPE sample, more melting endotherms appeared after stepwise isothermal crystallization. The introduction of ethylene comonomer in isotactic propylene backbone further decreased the regularity of molecular chain, and the short isotactic propylene sequences could crystallize into gamma-form crystal having a low melting temperature whereas the long sequences crystallized into alpha-form crystal having high melting temperature.

Reverse atom transfer radical polymerization of (-)-menthyl methacrylate

The reverse atom transfer radical polymerization(RATRP) of (-)-menthyl methacrylate ((-)-MnMA) with AIBN(AIBN/CuCl2/bipyridine(bipy) or (-)sparteine((-)Sp) =1/2/4) initiating system in THF has been studied. The dependence of the specific rotation on molecular weight was investigated.

Polymerization of acrylonitrile with (diisopropylamido) bis (indenyl) lanthanides

The polymerization of acrylonitrile was studied using ( diisopropylamido) his ( indenyl) lanthanides, Ind(2)LnN(i-Pr)(2)(Ln = Y, Yb) as a single-component catalyst. The effects of the amount of catalyst, monomer concentration and polymerization temperature on catalytic activity and molecular weight of polyacrylonitrile (PAN) were studied. The results show that the catalytic activity is raised obviously with rising polymerization temperature. The monomer conversion reaches 64% under polymerization temperature, monomer concentration and catalyst concentration are 50 degreesC, 5.1 mol . L (-1) and 0. 3 % (molar ratio) sequentially. The conversion and molecular weight of the polymer increase appreciably with adding additive, PhONa. When the molar ratio of PhONa to the catalyst is three I the conversion and the molecular weight is 76% and 1.32 x 10(4), respectively. The initiation mechanism for the polymerization of acrylonitrile was proposed.