5
The free radical polymerizations of cyclic ketene acetals have recently evoked a lot of interest.
The use of enzyme catalysis in organic media for polymer-forming reactions is gaining
increasing attention. The hallmark of enzymes is their ability to achieve high enantio- and
regioselectivity for various chemical transformations.
1
Furthermore, enzymes represent a family
of “environmentally friendly” catalysts. Advantages of using enzymes in organic as opposed to
aqueous media are as follows: (i) increased enzyme thermal stability, (ii) solubility of a wide
range of substrate types in the reaction media, (iii) no requirement for pH adjustment as the
reaction proceeds, and (iv) readily recyclable.
2,3
Whereas aromatic polycarbonates have achieved wide application and great importance as
polymer materials since 1954,
1
aliphatic polycarbonates have been less interesting due to their
poor thermal stability and easy hydrolysis. During the past decade, increasing attention has
been paid to aliphatic polycarbonates for their potential in the medical field and in the
environmental control of plastics.
2-8
Stimulated by the need for bioresorbable medical materials with a wide range of physical
properties and degradation rates, there has been considerable interest in exploring aliphatic
polycarbonate prepared by ring-opening polymerization of cyclic carbonate monomers.
1-7
Efforts
have thus far focused on polymerizations of five- and six-membered ring aliphatic cyclic
carbonates.
二
阐述目前该领域的研究现状﹑存在问题﹑待解决的问题
Ring-opening polymerization of six-membered cyclic carbonates have been studied in detail by
Kricheldorf et al. [4,5] and Sarell et al. [6-8] after the first work on their reactivity by Searles [9].
In recent years there has been renewal of interest in polymerization of six-membered cyclic
carbonate since Endo et al. demonstrated that TMC showed volume expansion during
polymerization [10].
Although the cationic ring-opening polymerization of SOCs has been investigated extensively,
only a low molecular weight (MW) polymer was obtained and the MW cannot be controlled.
Although the utility of these materials as sutures and in a number of drug delivery applications is
well established, some material’s needs cannot be satisfied by their use. For example, all
polyesters release acidic degradation products [6-8], limiting their utility to applications where
acidity at the implant site is not a concern. The above polyesters also tend to be relatively rigid,
inflexible materials [9], This can be a definite disadvantage when mechanical compliance with
soft tissue or blood vessels is required. Finally, none of the above polyesters provides a
chemically reactive pendent chain for the easy attachment of drugs, crosslinkers and biologically
active moieties.
The investigation of poly(ether carbonate)s started in the 1960s. …However, copolymers of
