John R. Ebdon

Flame retardance of poly(methyl methacrylate) modified with phosphorus-containing compounds

Abstract MMA has been copolymerised with pentavalent phosphorus-containing monomers and the flame retardance of the resulting copolymers has been assessed by limiting oxygen indicies (LOI) and cone calorimetry experiments. The thermal stability of the copolymers has also been assessed by conventional thermogravimetric analysis (TGA). Poly(methyl methacrylate) (PMMA) modified with phosphorus-containing additives have also been synthesised and the flame retardance assessed. All of the modified PMMA samples contain 3.5 wt.%, allowing a comparison of the relative merits of an additive and a reactive approach to flame retardance. The chemical environment of the phosphorus in terms of flame retardance achieved is also considered in this paper. The incorporation of 3.5 wt.% phosphorus in both reactive and additive approaches increases the limiting oxygen index of PMMA from 17.8 to over 21. However, cone calorimetry shows that the phosphorus-containing copolymers are inherently more flame retardant than PMMA and the PMMA modified with phosphorus-containing additives. The methyl methacrylate (MMA) copolymers have significantly reduced peak rates of heat release and leave substantial char residue during combustion, as compared to PMMA. Cone calorimetry has also shown that the phosphates are more effective flame-retardants for PMMA than are the phosphonates in both additive and reactive approaches. TGA of the polymers indicates that the copolymers are more thermally stable than PMMA whilst PMMA containing the additives are less thermally stable. A condensed phase mechanism in which diethyl(methacryloyloxymethyl)phosphonate reduces the flammability of PMMA has been identified.

Flame retarding poly (methyl methacrylate) with phosphorus containing compounds: comparison of an additive with a reactive approach

Abstract The flame retardance and thermal stability of a methyl methacrylate (MMA) copolymer reactively modified by copolymerisation of the MMA with diethyl (methacryloyloxymethyl) phosphonate (DEMMP) have been compared with those of poly(methyl methacrylate) (PMMA) containing equivalent amounts of the additive diethyl ethyl phosphonate (DEEP). DEEP can be regarded as having a structure similar to that of a DEMMP comonomer unit and therefore the two compounds might be expected to confer about the same levels of flame retardance to PMMA when used at similar concentrations. The incorporation of 3.5 wt.% phosphorus in both cases raises the limiting oxygen index of PMMA from 17.2 to over 22. However, cone calorimetry shows that the MMA/DEMMP copolymer is inherently more flame retardant than PMMA containing DEEP: the former has a significantly lower peak rate of heat release than the latter (449 and 583 kW m −2 , respectively) and gives rise to a greater amount of char. Thermogravimetric analysis (TGA) of the polymers indicates also that the MMA/DEMMP copolymer is more thermally stable than PMMA whilst PMMA containing DEEP is less thermally stable. Dynamic mechanical thermal analysis (DMTA) shows that the MMA/DEMMP copolymer has physical and mechanical properties similar to those of PMMA, whilst the low molecular weight DEEP plasticises PMMA, resulting in a significantly reduced glass transition temperature, T g . A condensed phase mechanism of flame retardance in MMA/DEMMP has been identified.

Thermal degradation and flammability characteristics of some polystyrenes and poly(methyl methacrylate)s chemically modified with silicon-containing groups

Several Si-containing methacrylates and acrylates have been free radically copolymerised with methyl methacrylate and with styrene. The copolymers have been examined by DSC to determine glass transition temperatures (Tg), by TGA to determine thermal stabilities, and by measurements of limiting oxygen index (LOI) to determine ignitability/flame retardance. The copolymers are found to have Tgs similar to those of the parent homopolymers suggesting that the mechanical properties are little affected by the incorporation of the Si-containing groups and to have slightly improved flame retardance. LOI and char yields suggest that the mechanism of flame retardance, i.e. whether vapour phase or condensed phase, depends upon the nature of the Si-containing substituent.

Improved synthesis of phosphorus-containing styrenic monomers

Several dialkyl-p-vinylbenzyl phosphonates, for use in making fire-retardant styrenic and acrylic polymers, have been synthesised by reaction of p-vinylbenzyl chloride with various dialkyl phosphonates using the Michaelis-Becker reaction. This reaction is shown to have several benefits over the conventional Arbuzov methodology. Principal amongst these are that the Michaelis-Becker reaction proceeds rapidly at room temperature, or below, to give high yields of products requiring little or no purification, thus avoiding the heating necessary in the Arbuzov procedure, which can lead to premature thermal polymerization of the vinyl reactants and products. The Michaelis-Becker procedure is also shown to give ready access to higher dialkyl-p-vinylbenzyl phosphonates that would be difficult to obtain by the Arbuzov procedure.

Fire and mechanical properties of a novel free-radically cured phenolic resin based on a methacrylate-functional novolac and of its blends with an unsaturated polyester resin

A novel phenolic novolac resin bearing methacrylate functional groups has been synthesized by reaction of the novolac with methacryloyl chloride. This resin has been mixed with styrene and cured (crosslinked) free-radically under the relatively low temperature conditions used to cure unsaturated polyester/styrene mixtures, i.e. there is no need to employ the high temperatures and pressures that are required to cure conventional phenolic resins. Homogeneous cured blends of the methacrylated novolac with unsaturated polyester and styrene have been prepared also. The cured methacrylated novolac, and its blends with unsaturated polyester, are rigid materials with good mechanical strength, and have glass transition temperatures, thermal stabilities and flame retardancies superior to those of cured unsaturated polyester alone.

Blends of unsaturated polyester and phenolic resins for application as fire-resistant matrices in fibre-reinforced composites. Part 1: identifying compatible, co-curable resin mixtures

An unsaturated polyester resin, cured with styrene of commercial origin, has been blended and cured with several commercial phenolic resoles with a view to obtain a homogeneous polymer blend having better fire resistance than unsaturated polyester alone. It is shown that blends of the unsaturated polyester with an allylically modified resole are not only physically compatible (miscible), but also chemically compatible in which they co-cure to an extent to give, probably, a co-continuous interpenetrating polymer network.

Complete ozonolysis of alkyl substituted ethenes at −60 °C: distributions of ozonide and oligomeric products

The distribution of ozonide and oligomeric structures formed on complete ozonolysis of alkenes in a non-participating solvent at −60 °C is governed by the alkyl substitution around the carbon–carbon double bond. The ozonolysis of a 1,1-alkyl substituted ethene generally favours the formation of an ozonide (a 1,2,4-trioxolane). Whereas the ozonolysis of a 1,1,2-alkyl substituted ethene also produces ozonide, a considerable amount of the ozonised products are oligomeric in nature.For example, the ozonolysis of 3-methylpent-2-ene in solution to high conversion in pentane yields oligomers with structural units derived from the fragmentation products of the primary ozonide (a 1,2,3-trioxolane) which are namely butanone carbonyl oxide and acetaldehyde; these can be characterised by electrospray ionisation mass spectroscopy (ESI-MS) under soft ionisation conditions. The predominant oligomers formed are rich in carbonyl oxide units (80 + mol%) and are cyclic in nature. A small proportion of the oligomers formed are open chain compounds with end groups that suggest that chain termination is brought about either by water or by hydrogen peroxide. Residual water in the solvent will react with the carbonyl oxides to produce 2-methoxybut-2-yl hydroperoxide, which we propose readily decomposes generating hydrogen peroxide. A significant yield of oligomers also is obtained from the ozonolysis of a 1,2-alkyl substituted ethene. The ozonolysis of trans-hex-2-ene in pentane yields oligomers containing up to four structural units and are predicted to be mainly cyclic.

Initiation of radical polymerization with radicals produced from thermolyzed alkene ozonates

Alkenes react with ozone to produce a distribution of peroxidic compounds that upon thermolysis can produce radicals and these radicals have been used to polymerize vinyl monomers such as MMA, styrene, vinyl acetate and N-vinyl pyrrolidinone. The process can also be carried out in aqueous emulsion. Ozonolysis of the sulfate surfactant, used in emulsion polymerization, also produces species that can be used as a radical initiator. The alkene can also be part of a polymer chain. Ozonolysis/thermolysis produces a macroradical, which can be used to prepare block copolymers. For example, thermolysis following ozonolysis of alkene functional polyisobutene (PIB) produced PIB macroradicals. Styrene was successfully polymerized with these PIB-ozonates and has been shown to be incorporated as an isobutene/styrene block copolymer. However, although MMA could also be polymerized by the PIB-ozonate, the resulting PMMA was found not to be attached to the PIB.

Emulsion polymerization of methyl methacrylate initiated by alkene ozonates

Ozonolysis of tetramethyl ethene, trans-4-octene or 1-octene in water leads to species, which after thermolysis at 60°C, generate radicals that initiate radical emulsion polymerization of methyl methacrylate (MMA). The course of the reaction is dependent on the structure of the alkene used. Tetramethyl ethene ozonates give the highest final yield of polymer, although the rates of polymerization observed from 0 to approximately 60% conversion are found to be essentially equivalent, regardless of the structure of the alkene employed. The difference in final conversion is attributed to changes in the half life of the generated peroxy species as a function of alkene structure. From these differences it is inferred that the initiating species are organo peroxides, probably hydroxy hydroperoxides, rather than hydrogen peroxide. Two latex systems, one stabilized by a cationic surfactant and the other by an anionic surfactant, were successfully prepared. Ozonolysis of water followed by heating in the presence of MMA does not produce polymer. However, ozonolysis of an aqueous sulphonate surfactant solution does produce a species that forms radicals on thermolysis and these radicals initiate radical polymerization of MMA, which proceeds to high conversion in emulsion.

Building on tradition

Sheffield University has a long and distinguished tradition of research on polymeric materials and in polymer engineering. However, the Universitys profile in polymer research was greatly strengthened first by the appointments in 1998 of Tony Ryan and Richard Jones and by the transfer last year of seven polymer chemists, together with their research students, research associates and equipment, from Lancaster University.