Main-chain poly(phosphoester)s: History, syntheses, degradation, bio-and flame-retardant applications

Abstract Nature on planet earth is dominated by poly(phosphoester)s (PPEs). They structure and determine life in the form of deoxy- and ribonucleic acid (DNA & RNA), and, as pyrophosphates, they store chemical energy in organisms. Polymer chemistry, however, is dominated by the non-degradable polyolefins and degradable polycarboxylic esters (PCEs) produced on a large scale today. Recent work has illustrated the potential of PPEs for future applications beyond flame-retardancy, the main application of PPEs today, and provided a coherent vision to implement this classic biopolymer in modern applications that demand biocompatibility and degradability as well as the possibility to adjust the properties to individual needs. This comprehensive review summarizes synthetic protocols to PPEs, their applications in biomedicine, e.g., as biodegradable drug carrier or in tissue engineering, and their flame retardant properties. We highlight recent developments that may make phosphorus-based polymers attractive materials for various future applications.

Poly(phosphoester)s: History, syntheses, degradation, bio-and flame-retardant applications

Novel organophosphorus flame retardants and their synergistic application in novolac epoxy resin

The synthesis of aromatic polyphosphonates based on the step polymerization of various bisphenols and dichlorophenyl phosphine oxide was investigated. The effect of catalyst, type, concentration, and polymerization time were systematically varied to obtain high molecular weight polymers. Very high molecular weight tough, ductile materials with a high degree of optical clarity were synthesized. In contrast with the aromatic polycarbonates, the refractive index was increased from 1.58 to 1.60 (for the bisphenol A-based system) and 1.64 for a biphenol-based system. The latter was still an amorphous soluble polymer as a result of the non-coplanar nature of the phenyl phosphine oxide bond, unlike the analogous polycarbonate. Hydrolytically stable melt-processable cumyl phenol end-capped polyphosphonates were successfully achieved for the first time. Rheological studies show that these end-capped systems are melt-stable at 200 °C, whereas the systems of initially higher molecular weight but without any well-defined end capping clearly degraded quickly probably as a result of an acid-catalyzed hydrolysis process. Extensive high char yields were produced upon pyrolysis in either nitrogen or air, suggesting good fire resistance. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2904–2910, 2001

Synthesis of high refractive-index melt-stable aromatic polyphosphonates

Two phosphorus-containing acrylate monomers were synthesized from the reaction of ethyl α-chloromethyl acrylate and t-butyl α-bromomethyl acrylate with triethyl phosphite. The selective hydrolysis of the ethyl ester monomer with trimethylsilyl bromide (TMSBr) gave a phosphonic acid monomer. The attempted bulk polymerizations of the monomers at 57–60 °C with 2,2′-azobisisobutyronitrile (AIBN) were unsuccessful; however, the monomers were copolymerized with methyl methacrylate (MMA) in bulk at 60 °C with AIBN. The resulting copolymers produced chars on burning, showing potential as flame-retardant materials. Additionally, α-(chloromethyl)acryloyl chloride (CMAC) was reacted with diethyl (hydroxymethyl)phosphonate to obtain a new monomer with identical ester and ether moieties. This monomer was hydrolyzed with TMSBr, homopolymerized, and copolymerized with MMA. The thermal stabilities of the copolymers increased with increasing amounts of the phosphonate monomer in the copolymers. A new route to highly reactive phosphorus-containing acrylate monomers was developed. A new derivative of CMAC with mixed ester and ether groups was synthesized by substitution, first with diethyl (hydroxymethyl)phosphonate and then with sodium acetate. This monomer showed the highest reactivity and gave a crosslinked polymer. The incorporation of an ester group increased the rate of polymerization. The relative reactivities of the synthesized monomers in photopolymerizations were determined and compared with those of the other phosphorous-containing acrylate monomers. Changing the monomer structure allowed control of the polymerization reactivity so that new phosphorus-containing polymers with desirable properties could be obtained. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2207–2217, 2003

Synthesis and copolymerization of new phosphorus‐containing acrylates

The polyaddition of 4,4′-bis[(3-ethyl-3-oxetanyl)methoxy]biphenyl (4,4′-BEOBP) and phenylphosphonic dichloride (PPDC) with quaternary onium salts as catalysts proceeded under mild reaction conditions to afford a polymer containing phosphorous atoms in its main chain. A polyphosphonate with a high number-average molecular weight (10,300) was obtained by the reaction of 4,4′-BEOBP and PPDC in the presence of tetraphenylphosphonium chloride (TPPC) in o-dichlorobenzene at 130 °C for 24 h. The structure of the resulting polymer was confirmed with IR, 1H NMR, and 31P NMR spectroscopy. Furthermore, it was proved that the polyaddition of certain bis(oxetane)s with phosphonic dichlorides proceeded smoothly to give corresponding polyphosphonates with TPPC as the catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3835–3846, 2002

Synthesis of polyphosphonates containing pendant chloromethyl groups by the polyaddition of bis(oxetane)s with phosphonic dichlorides

The polyaddition of bisphenol A diglycidyl ether (BPGE) with bis(4-chlorophenyl) phenylphosphonate was carried out using quaternary onium salts or crown ether complexes as catalysts. When the polyaddition was performed using tetrabutylammonium chloride, tetrabutylphosphonium chloride, or 18-crown-6/KCl in N- methyl-2-pyrrolidone at 110°C for 48 h, the corresponding polyphosphonate with moderated molecular weights was obtained in 88–96% yields. The structure of the resulting polyphosphonate was confirmed by IR and 1H-NMR spectra. The polyaddition of BPGE with various diaryl phosphonates also proceeded very smoothly to produce the corresponding polyphosphonates with moderate molecular weights. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 959–965, 1999

Novel synthesis of polyphosphonates by the polyaddition of bis(epoxide) with diaryl phosphonates

The polyaddition of bis(3-ethyl-3-oxetanylmethyl) terephthalate (BEOT) with dichlorodiphenylsilane (CPS) using tetrabutylammonium bromide (TBAB) as a catalyst proceeded under mild reaction conditions to afford a polymer containing silicon atoms in the polymer main chain. A poly(silyl ether) (P-1) with a high molecular weight (Mn = 53,200) was obtained by the reaction of BEOT with CPS in the presence of 5 mol % of TBAB in toluene at 0 °C for 1 h and then at 50 °C for 24 h. The structure of the resulting polymer was confirmed by IR and 1H NMR spectra. Furthermore, it was proved that the polyaddition of certain bis(oxetane)s with dichlorosilanes proceeds smoothly to give corresponding poly(silyl ether)s with TBAB as the catalyst. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2254–2259, 2000

Synthesis of poly(silyl ether)s containing pendant chloromethyl groups by the polyaddition of bis(oxetane)s with dichlorosilanes

Polysulfonates with reactive pendant chloromethyl groups were synthesized by polyadditions of bisepoxides with disulfonyl chlorides. The polyaddition of bisphenol A diglycidyl ether (BPGE) with m-benzene disulfonyl chloride (m-BDSC) occurred in anisole without any catalyst at 130°C for 24 h. However, polymer with high molecular weight was not obtained. On the other hand, the polyadditions of BPGE with m-BDSC proceeded very smoothly with high yield (81-91%) to give polymers with relatively high molecular weights in anisole at 130°C for 24 h when quaternary phosphonium salts were used as catalysts. The polyaddition was also enhanced by the addition of certain crown ether complexes. However, the catalytic activity of these compounds was less than those of quaternary phosphonium salts. Furthermore, polyadditions of certain bisepoxides with disulfonyl chlorides were also carried out to produce the corresponding polymers under the same reaction conditions.

Synthesis of polysulfonates containing reactive pendant chloromethyl groups by the polyaddition of bisepoxides with disulfonyl chlorides

Phosphorus-containing vinyl ether monomers and 1-propenyl ether monomers were prepared by the regioselective addition reaction of glycidyl vinyl ether (GVE) or 1-propenyl glycidyl ether with diaryl phosphonates with quaternary onium salts as catalysts. The reaction of GVE with bis(4-chlorophenyl) phenylphosphonate gave bis[1-(4-chlorophenoxy methyl)-2-(vinyloxy)ethyl]phenylphosphonate in a 68% yield. The structures of the resulting phosphorus-containing vinyl ether monomers and 1-propenyl ether monomers were confirmed by IR and 1H NMR spectra and elemental analysis. Photoinitiated cationic polymerizations of the resulting phosphorus-containing vinyl ether monomers and 1-propenyl ether monomers were investigated with photoacid generators. The polymerization of vinyl ether groups and 1-propenyl ether groups of the obtained monomers proceeded very smoothly with a sulfonium-type cationic photoinitiator, bis[4-(diphenylsulfonio)phenyl]sulfide-bis(hexafluorophosphate), upon UV irradiation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3105–3115, 2005

Novel photocurable monomers: The synthesis of difunctional vinyl ethers with a phosphonate group and difunctional 1-propenyl ethers with a phosphonate group and their photoinitiated cationic polymerization

Shouji Minegishi

Papers

Synthesis of polyphosphonates containing pendant chloromethyl groups by the polyaddition of bis(oxetane)s with phosphonic dichlorides

Novel synthesis of polyphosphonates by the polyaddition of bis(epoxide) with diaryl phosphonates

Synthesis of poly(silyl ether)s containing pendant chloromethyl groups by the polyaddition of bis(oxetane)s with dichlorosilanes

Synthesis of polysulfonates containing reactive pendant chloromethyl groups by the polyaddition of bisepoxides with disulfonyl chlorides

Novel photocurable monomers: The synthesis of difunctional vinyl ethers with a phosphonate group and difunctional 1-propenyl ethers with a phosphonate group and their photoinitiated cationic polymerization