Biodegradable synthetic polymers: Preparation, functionalization and biomedical application

Organocatalysis offers a number of opportunities in polymer synthesis and was among the earliest methods of catalyzing the synthesis of polyesters. In the following Perspective we attempt to highlight the opportunities and challenges in the use of organic molecules as catalysts or initiators for polymerization reactions. The ring-opening polymerization of cyclic monomers is used as a representative polymerization process to illustrate some of the features of organic catalysts and initiators and to compare them to metal-based approaches. The convergence of convenience, functional group tolerance, fast rates, and selectivities will continue to drive innovations in polymerization catalysis, and it is our perspective that organocatalysis will continue to play an important role in these developments.

Organocatalysis: Opportunities and Challenges for Polymer Synthesis

In nature, living organisms are constantly producing different macromolecules for their metabolic needs. These macromolecules, such as polysaccharides, polynucleotides, proteins, or polyesters, are essential to organism survival. Their synthesis generally involves in vivo enzyme-catalyzed chaingrowth polymerization reactions of activated monomers, which are generally formed within the cells by complex metabolic processes. Because of their diversity and renewability, microbial polymers such as polysaccharides, bacterial polyhydroxyalkanoates (1) and polyanions such as poly(γ-glutamic acid) (2) have received increasing attention as candidates for industrial applications. In many cases, microorganisms carry out polymer syntheses that are impractical or impossible to accomplish with conventional chemistry. Thus, microbial catalysts enable the production of materials that might otherwise be unavailable. Microbial polymers are synthesized from renewable low-cost feedstocks, and the polymerizations operate under mild process conditions with minimal environmental impact. In addition, microbial polymers provide products that, when disposed, can degrade to nontoxic products.

https://homepages.rpi.edu/~grossr/_doc/publication/Chem.%20Rev.%202001,%20101,%202097-2124.pdf

Polymer Synthesis by In Vitro Enzyme Catalysis

Polymeric materials, natural and unnatural, are indispensable to the modern society. They are widely used from everyday life usages as commodity materials to industry and technology usages in the fields such as electronics, machinery, communications, transportations, pharmacy, and medicine as highly advanced materials. Today, it is hard to think of the present society without polymeric materials. Developments of various polymeric materials have been owed to epoch-making innovative works as exemplified typically by the discovery of Ziegler-Natta catalyst,1-3 the concept of living polymerization,4 the discovery of conducting polymers,5 and the discovery of metathesis catalyst.6,7 These observations demonstrate that new polymeric materials are often brought about by new production methods including polymerization catalysts. Historically, polymerization catalysts utilized classical catalysts of acids (Brønsted acids, Lewis acids, and various cations), bases (Lewis bases and various anions), and radical generating compounds since the 1920s, the early stage of polymer chemistry. In the following * To whom correspondence should be addressed. Fax/Tel: (+81)-75-7247688. E-mail: kobayash@kit.ac.jp. † Kyoto Institute of Technology and Emeritus Professor of Kyoto University. ‡ Kyoto University. Chem. Rev. 2009, 109, 5288–5353 5288

Enzymatic polymer synthesis: an opportunity for green polymer chemistry.

Recent advances in the synthesis of aliphatic polyesters by ring-opening polymerization.

Water-soluble polycarbonate having pendent carboxyl groups on the main-chain carbons is reported for the first time. This paper describes synthesis and enzyme-catalyzed ring-opening polymerization of a novel carbonate monomer, 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one (1). Various commercially available lipases were screened for their ability to polymerize 1 in bulk at 80 °C. Monomer conversion and molecular weight of the polymer were significantly influenced by the source of the enzyme. For example, of the seven lipases screened, lipase AK (from Pseudomonas fluorescens) gave the highest monomer conversion (97%) and molecular weight (Mn = 6100). In reactions carried out under identical experimental conditions, no polymerization was observed when thermally deactivated lipase AK was used. Debenzylation of 2 by catalytic hydrogenation led to the corresponding linear polycarbonate, 3, with pendent carboxyl groups. Presence of pendent carboxyl groups is expected to enhance the biodegradability of the polyc...

Novel Functional Polycarbonate by Lipase-Catalyzed Ring-Opening Polymerization of 5-Methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one

Highly (S)-enriched substituted poly(e-caprolactone)s were synthesized from 4-methyl-e-caprolactone (4-MeCL) and 4-ethyl-e-caprolactone (4-EtCL) by lipase Novozym-435 (from Candida antarctica) catalyzed ring-opening polymerizations. The polymerizations were performed in bulk, thus eliminating the need for solvents in the polymerization process. Poly(4-EtCL) and poly(4-MeCL) having >95% enantiomeric purity (eep) have been prepared. Number-average molecular weights of the poly(4-EtCL) and poly(4-MeCL) were 4400 and 5400, respectively. The effect of reaction temperature on enzyme enantioselectivity, polymer molecular weight, and monomer conversion was also investigated at 45 and 60 °C. Contrary to many literature reports and conventional wisdom, the enantioselectivity of the lipase was greater at 60 °C, the higher reaction temperature. The solventless polymerization process appeared to be diffusion-controlled in which the monomer conversion and polymer molecular weight increased at higher reaction temperature.

Solventless Enantioelective Ring-Opening Polymerization of Substituted ∊-Caprolactones by Enzymatic Catalysis

Enzyme-catalyzed ring-opening copolymerization of 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one (MBC) with trimethylene carbonate (TMC): synthesis and characterization.

Functionalized polycarbonate derived from tartaric acid: enzymatic ring-opening polymerization of a seven-membered cyclic carbonate.

The ring-opening polymerization of a monomer containing a free carboxylic acid group is reported for the first time. The monomer, 5-methyl-5-carboxyl-1,3-dioxan-2-one (MCC), was copolymerized with trimethylene carbonate (TMC) in an enzymatic ring-opening polymerization conducted in bulk at 80 °C. The low-melting TMC comonomer also solubilized the high-melting MCC monomer, allowing for solvent-free polymerizations. Six commercially available lipases were screened, and Candida antarctica lipase-B (Novozym-435) and Pseudomonas cepacia lipase were selected to catalyze the copolymerization because of their higher monomer conversions. Higher molecular weight polymers (weight-average molecular weight = 7800-9200) were prepared when Novozym-435 was used, with less MCC incorporated into the copolymer than used in the monomer feed. However, Pseudomonas cepacia lipase showed good agreement between the molar feed ratios and the molar composition, but the molecular weights (weight-average molecular weight = 3600-4800) were lower than those obtained when Novozym-435 was used. 13 C NMR spectral data were used for microstructural analysis, which suggested the formation of random, linear, and pendant carboxylic acid groups containing polycarbonates with hydroxyl groups at both chain ends.

Talal F. Al-Azemi

Papers

Novel Functional Polycarbonate by Lipase-Catalyzed Ring-Opening Polymerization of 5-Methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one

Solventless Enantioelective Ring-Opening Polymerization of Substituted ∊-Caprolactones by Enzymatic Catalysis

Enzyme-catalyzed ring-opening copolymerization of 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one (MBC) with trimethylene carbonate (TMC): synthesis and characterization.

Functionalized polycarbonate derived from tartaric acid: enzymatic ring-opening polymerization of a seven-membered cyclic carbonate.

One‐step synthesis of polycarbonates bearing pendant carboxyl groups by lipase‐catalyzed ring‐opening polymerization