Spontaneous hydrolytic degradability of copolyesters having tetrahydropyran rings in their backbones

Abstract

SYNOPSISHomo-and copolyesters, containing 2,5-linked tetrahydropyran rings in their backbones, were prepared by cationic ring-opening polymerization of bicyclic lactones, 2,g-dioxabicyclo [ 2.2.21 octan-3-one ( 1 ), and its 4-methoxy-carbonyl and 4-benzyloxycarbonyl derivatives ( 3 and 4 ) . Copolyesters, having pendant carboxyl groups, were derived from the copolymers containing 4 as one of the comonomers by the catalytic hydrogenolysis of the pendant benzyloxyxarbonyl groups. Copolyesters, containing both 2,5-linked and 2,6-linked tetrahydropyran rings in the main chains, were obtained by the copolymerization of 1 with 6,8-dioxabicyclo [ 3.2.11 octan-7-one ( 13 ) , which is a structural isomer of 1. Spontaneous hydrolytic degradability of these polyesters was investigated in a phosphate buffer solution (pH 7.5) at 27°C. The degradability of the polyesters markedly depended on the molecular structure: hydrophobic pendant groups retarded the hydrolytic degradation, whereas hydrophilic pendant groups accelerated it. In particular, a small amount of pendant carboxyl groups significantly enhanced the hydrolytic degradability of the copolyesters from 1. Polyesters, containing 2,6-linked tetrahydropyran rings in their backbones, underwent hydrolytic degradation more readily than those entirely consisting of 2,5-linked tetrahydropyran rings. INTRODUCTIONPollution by wasted plastics is one of the major factors that are worsening the ecological environment on the earth. There are two approaches to solving this troublesome problem: one is the material design of readily recyclable polymers; the other is the development of spontaneously degradable polymeric materials. As for the latter approach, one of the most promising materials is a class of photodegradable polymers. A variety of photodegradable polymers have been designed and synthesized, and some of them are commercialized.' Polymers, which are spontaneously hydrolyzable under neutral conditions to yield harmless low molecular weight compounds, would be of practical value if they were * To whom correspondence should be addressed. CCC OOZ1-8995/94/061035-09 readily processable and had the desirable mechanical and thermal properties. Of particular importance are biodegradable polymers, which are hydrolyzed and catabolized by microorganisms in a natural environment.On the other hand, from the viewpoint of biomedical materials, considerable attention has been directed toward spontaneously hydrolyzable, biodegradable, synthetic polymers, especially poly (a-hydroxy acid) s, such as poly (glycolic acid), poly ( lactic acid), and their analogues.2 Since the hydrolysis rates of these polyesters are relatively low, because of their high crystallinity and low hydrophilicity, several biodegradable polyesters with pendant carboxyl groups have been synthesized in order to impart higher hydrophilicity. Lenz et al.3'4 prepared homo-and copolymers of p-malic acid and its alkyl esters by ring-opening polymerization of benzyl malolactonate, followed by hydrogenolytic debenzylation. O...

Recent Trends in Catalytic Polymerizations

“…The development of the ROP of lactones saw a large surge in popularity in the 1990s with the growing public awareness of environmental issues and rising prices of petroleum (Scheme ). The periodic table in Figure highlights any element that bonds or coordinates with an active site for lactone polymerization, and illustrates the massive number of catalysts reported for the ring opening polymerizations of lactones. ,− The most commonly used metals are zinc, aluminum, tin, yttrium, and lanthanides. New metal catalysts providing higher polymerization rates at lower loadings, while maintaining molecular weight and stereocontrol are continuously being reported. ,− Additionally, the development of highly active catalysts has enabled the polymerization of novel monomers, like (un)­substituted butyrolactones, that can be easily depolymerized, opening up new possibilities for fully recyclable polymeric systems. − …”

“…Elements with catalytic activity for the ROP of lactones (colored), including metals (orange) and nonmetals (green). Gray lettering designates synthetically prepared elements. ,− …”

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