Controlled ring-opening polymerization : Polymers with designed macromolecular architechture
This thesis summarizes the development of new catalyst systems for ring-opening
polymerization and their use in the production of macromolecules with advanced architecture.
The influences of reaction conditions, i.e. reaction temperature, solvent and reaction time,
on the polymerization kinetics have been evaluated for the ring-opening polymerization (ROP)
of 1,5-dioxepan-2-one (DXO) initiated by a cyclic tin-alkoxide. The purpose has been to
achieve a controlled ring-opening polymerization of lactones and lactides, resulting in polymers
with desirable properties. The mechanism and kinetics of controlled ring-opening
polymerization of L-lactide (L-LA) have been investigated, leading to hydroxy telechelic
polymers to be used in macromer reactions of various natures.
The ROP mechanism of DXO with stannous octoate as catalyst has been investigated
theoretically with hybrid density functional methods. A new mechanism has been proposed
which provides an explanation of the experimental observations. The ROP mechanism has
been shown to involve the formation of a tin-alkoxide complex, which subsequently
coordinates a monomer. It has been demonstrated that the ring-opening of the monomer
proceeds via a concerted four-center transition state.
Elastomeric tri-block copolymers have been obtained from L-LA and DXO with a
difunctional tin-initiator. A two-step process has been developed to achieve a well-defined triblock
copolymer, poly(L-lactide-b-1,5-dioxepan-2-one-b-L-lactide) (poly(L-LA-b-DXO-b-L-
LA)), in good yield. Thermal analysis of the poly(L-LA-b-DXO-b-L-LA) has been used to
examine the morphology of the block copolymer. The crystallinity and melting temperature
have been shown to increase with increasing amount of L-LA in the copolymer, but the glass
transition temperature was only slightly influenced by the polymer composition.
Poly(L-LA-b-DXO-b-L-LA) has been subjected to hydrolytic degradation in phosphate
buffer solution. The influence of molecular weight and chemical composition on the
hydrolysability has been investigated. The molecular weight change, weight loss and
composition changes have been characterized in order to determine the degradation pathway.
The degradation of poly(L-LA-b-DXO-b-L-LA) was characterized by a significant decrease in
molecular weight immediately after immersion in the buffer solution and a progressive increase
the amount of L-LA in the remaining copolymer with increasing degradation time. The primary
degradation products formed during hydrolysis have been detected as lactic acid and 3-(2hydroxyethyl)-propanoic
acid. Results indicate that the composition had no effect on the rate of
degradation. The major factor determining the degradation rate was the original molecular
School:Kungliga Tekniska högskolan
Source Type:Doctoral Dissertation
Date of Publication:01/01/2000