Abstract
Meldrum’s acid (MA) could perform thermolysis reaction, with releasing acetone and CO2 molecules, to generate a highly reactive ketene group, which could perform self-dimerization to generate 4-membered cyclic 1,3-dione group and addition reactions toward other unsaturated groups and nucleophile groups. Consequently, MA is highly potential for involving in thermally induced crosslinking reactions and preparation of corresponding thermosetting resins. The features of MA and its derivatives have been utilized in this work for developments of new types of thermosetting resins and crosslinked polymers. The first part of this work involves design and synthesis of multi-functional MA derivatives to be used as reactive monomers, like other conventional thermosetting resins, for demonstration a new type of MA-based thermosetting resins. Two monomers, MA-SS which is a MA compound possesses two styrenic groups and MA-FS possessing one styrenic and one furan group, have been synthesized and spectrally characterized. Both monomers result in thermosetting resins showing high glass transition temperatures above 210 oC, high thermal stability (>350 oC), and satisfied mechanical strength. It is noteworthy that the MA-based resins exhibit relatively low dielectric constants of about 2.0, which has been attributed to their high free volume fractions generated with the evolved acetone and CO2 molecules in the curing processes. Hence, a new type of MA-based thermosetting resins possessing inherent low dielectric constants has been explored. The second part is preparation of biodegradable polyesters with MA derivatives. A bifunctional aliphatic MA compound is prepared as used as a monomer to reactive various aliphatic diol and triol compounds to result in the corresponding linear and crosslinked aliphatic polyesters. The polyesters have been subjected to biodegradability tests, and the biodegradation behavior has been observed with weight loss and SEM. The polyesters show a high fraction of biodegradation-induced weight loss of 70 wt%. It is concluded here that a novel and convenient approach for preparation of biodegradable polyesters has been demonstrated. The final part of this work is about the developments of polymerization routes directly using MA as a monomer. MA has been reacted with dihalide compounds through dehydrohalide reaction to result in the corresponding polymers possessing MA pendent groups. The prepared polymers hence are reactive polymers which could carry out further polymer modification and crosslinking reaction through the pendent MA groups. The chemical structures and molecular weights of the obtained polymers have been characterized with spectral methods and gel permeation chromatography method, respectively. It is noteworthy that the crosslinked products of the MA-containing polymers still shows low dielectric constants of about 2.0, providing addition supports to that MA based polymers could exhibit inherent low-dielectric constants.