ABA Type Copolymers of Lactide with Poly(ethylene glycol). Kinetic, Mechanistic, and Model Studies

Abstract

Block copolymers of lactide and poly(ethy1ene glycol) with various mclar ratios were synthesized. Tin(I1) bis(2-ethylhexanoate) has been used as a catalyst. Kinetic measurement and mechanistic studies suggest that the reactivity of the initiator, a hydroxyl group bearing reagent, is an important parameter on the polymerization course. In the case of primary and secondary alcohols, Le., poly(ethy1ene glycol) and methyl lactate, it is found that when the initiator concentration exceeds the catalyst concentration, the number of chains formed exceeds the number of catalyst molecules. The chains are propagated through shifts of catalysts from one chain to another. In the case of tertiary alcohols, it appears that the number of chains formed is about the number of catalyst molecules. Therefore, by choosing an appropriate initiator, reaction course and molecular weight as well as molecular weight distribution can be designed. A model based on the assumptions of fast initiation reaction and random propagation reaction is established. Both initiator and catalyst are found to have an influence on the increase of molecular weight and molecular weight distribution.

Synthesis and characterization of new ABA triblock copolymers with poly[3(S)-isobutylmorpholine-2,5-dione] and poly(ethylene oxide) blocks

“…Sn(Oct) 2 as the catalyst forms an effective initiation system with the a ,xhydroxyl end groups of PEO. A reaction mechanism for block copolymer formation of lactide with PEO was proposed and described in detail in several papers 18,19) . This mechanism can be extended to the block copolymerization of IBMD with PEO 20) , because the ring-opening of IBMD occurs exclusively at the ester group.…”

“…More recently, poly(ethylene oxide)-polyester block copolymers were prepared using a monohydroxy-or an a ,x-dihydroxy-poly(ethylene oxide) (PEO) as the initiator for the polymerization of the lactone monomers [9][10][11][12][13] . The amphiphilic block copolymers exhibit properties, i. e., permeability and degradability, which may lead to new applications.…”

New synthetic absorbable polymers as BMP carriers: Plastic properties of poly-D,L-lactic acid-polyethylene glycol block copolymers

“…6,7,10,[13][14][15][41][42][43] Therefore, the efficacy of the P-1 polymer as a BMP carrier must be confirmed in a nonhuman primate trial. Although there are many reports on the synthesis, characterization, and biocompatibility of PLA-PEG block copolymers, 38,39,[44][45][46][47][48][49][50][51][52][53][54][55][56] further preclinical investigations must be undertaken to confirm the safety of this polymer as an implant material before clinical trials can be undertaken.…”

“…When the hydroxylterminated polymers, PEG and PLA-PEG, were reacted with the isocyanate group of trichloroacetyl isocyanate, ␣-CH 2 protons and CH proton shifted to the respective low fields of 0.5-1 and 1-1.5 ppm. As PEG was found to have chemically shifted to around 4.4 ppm and the area at 4.2-4.3 ppm was reduced to the value of the CH 2 protons neighboring the PLA segment, 39 the presence of PEG and AB type PLA-PEG can be assumed to be negligible.…”

MgH2/PEG initiating system for ring opening polymerization of lactone and lactide

“…Many publications and patents deal with related syntheses in wide range of applications [1][2][3][4][5][6][7].…”