Poly depolymerising

Some polymers such as the polyacetals (polyformaldehyde) and poly(methyl methacrylate) depolymerise to monomer on heating. At processing temperatures such monomers are in the gaseous phase and even where there is only a small amount of depolymerisation a large number of bubbles can be formed in the products. 

A number of thermoplastics undergo depolymerisation on heating. These include poly(styrene), poly(methyl methacrylate), and poly(oxymethylene). Such depolymerisation will occur regardless of the prevailing oxygen concentration and under well aerated conditions will provide a ready source of fuel for sustained combustion. 

Journal of Applied Polymer Science 82, No. 1, 3rd October 2001, p.99-107 ALKALINE DEPOLYMERISATION OF POLY(TRIMETHYLENE TEREPHTHALATE)... 

The alkali-catalysed methanolysis of poly(2,2-bis(4-hydroxyphenyljpropane carbonate) (PC) in a mixture of methanol (MeOH) and toluene or dioxane was studied. The treatment of PC in meOH, with a catalytic amount of sodium hydroxide, yielded only 7% bisphenol A. Using a mixed solvent of MeOH and toluene completely depolymerised PC to give 96% free bisphenol A in solid form and dimethyl carbonate in solution. The eharaeteristies of the catalysis are discussed together with the pseudo-first rate kinetics of the depolymerisation. The reaetion eonditions were investigated to facilitate the reeyeling of PC plasties. 17 refs. 

A rare exception to the dominance of enthalpic driving force is provided by the unstrained eight-membered ring (Me2SiO)4, which undergoes ROP to give poly(dimethylsiloxane). For this process, A//rop is approximately zero but the remarkable skeletal flexibility of the polysiloxane backbone makes the TAArop term favourable and entropy provides the driving force for ROP. Exceptional behaviour occurs in the extremely rare cases of monomers where the polymerisation is driven by entropy and A7/rop is unfavourable. In these cases, the formation of polymer is favoured at elevated temperatures. For example, cyclo-Sg will polymerise above 150 °C (where the favourable TAArop term dominates), but slowly depolymerises back to the cyclic Sg monomer at room temperature. ... 

Under most conditions, only the simple polypropylene ketone) is formed in propylene/carbon monoxide alternating copolymerisation. Isomerisation of poly(ketone) to poly(spiroketal) can occur, and it may be assisted by cationic palladium species and protonic acids. It must be emphasised that a low reaction temperature favours the formation of a spiroketal structure [107]. At a temperature above the ceiling temperature, the poly(spiroketal) depolymerises to the more flexible and entropically favoured poly (ketone) [481]. 

It is worth noting that the polycondensation of hydrocarbon monomers is completely reversible [34]. Unsaturated polymers such as 1,4-poly (butadiene) can be converted to diene monomers via depolymerisation with ethylene [35-37] ... 

An understanding of the thermodynamics of ring-chain equilibration reactions is important in Inorganic Chemistry where such reactions abound (sse, for example. Allcock (65), Gee (66), Gimblett (67), and Moedritzer (65)). Two such reactions are found (i) in polyphosphazene chemistry (69) where a polymerisation-depolymerisation equilibrium can be established (70) and (ii) in silicon-sulphur chemistry, where the analogue of the poly(dimethylsiloxane) system has been studied (71) and shown to contain cyclics such as the dimer ( (013)2 SiS)2 the trimer ((CH3)2SiS)3, as well as small amounts of chain molecules of limited chain length. 

Poly(acrylates) and (alkyl acrylates) - The 3-relaxation time of poly(methyl methacrylate) (PMMA) is broadened by UV irradiation, indicating that whilst chain scission is occurring depolymerisation is minimal. The presence of polybutadiene accelerates the photooxidation of PMMA as does poly(vinyl acetate) " when used as blends. 

Weak links, particularly terminal weak links, can be the site of initiation of a chain unzipping reaction. A monomer or other simple molecule may be abstracted from the end of the chain in such a way that the new chain end is also unstable. The reaction repeats itself and the polymer depolymerises or otherwise degrades. This phenomenon occurs to a serious extent with polyacetals, poly(methyl methacrylate) and, it is believed, with PVC. 

As natural rubber is a product of nature, its properties are determined by the biochemical pathway by which the polymer is synthesized in the plant. In the case of natural rubber the polymerization process cannot be tailored like that of synthetic rubbers. The only option to modify natural rubber is after it has been harvested from the tree. The important modified forms of natural rubber include hydrogenated natural rubber, chlorinated natural rubber, hydro-halogenated natural rubber, cyclized natural rubber, depolymerised liquid natural rubber, resin modified natural rubber, poly(methyl methacrylate) grafted natural rubber, poly(styrene) grafted natural rubber, and epoxidized natural rubber [33,34]. Thermoplastic natural rubber prepared by blending natural rubber and PP is considered as a physically modified form of natural rubber. 

Mishra, S., Zope, V., and Goje, A. Kinetic and thermodynamic studies of depolymerisation of poly (ethylene terephthalate) by saponification reaction. Polymer international, 51(12) 1310-1315, 2002. 

Finally, in a significant departure from the more traditional pericychc-based mechanophores, colleagues in the Moore group were able to induce mechanically the heterolytic depolymerisation of cyclic and linear poly(ort/j )-phthalaldehyde)... 

Abstract Hyphenation of electrospray ionization witii ion-trap multistage mass spectrometry (ESI-MS°) provides charactoisation of subtle molecular structure of both syntiietic and natural aliphatic polyesters as well as oligomeric products of their biodegradation. Implementation of multisti e MS technique for structural studies of the novel bio-inspired polymers including poly[(R,S)-3-hydroxybutyrate], a-PHB, telechelics and a-PHB conjugates with oligopeptides has been demonstrated. The novel results concerned with evaluation of the subtle structure of macroinitiators obtained by partial depolymerisation of selected natural poly(3-hydroxyalkanoate)s, PHA, are also presented. 

Copolymere von a-Chloracrylnitril mit Styrol und mit Methyl-methacrylat sind thermisch weniger stabil als Polystyrol und Poly-(methylmethacrylat) (16S). Schon bei 150 C findet bei den genannten Copolymeren eine Depolymerisation statt. 

To depolymerise poly(ethene), carry out the cracking experiment described earlier (page 313), replacing Vaseline and mineral wool with pieces of poly(ethene). 

What equation represents the depolymerisation of poly(ethene) ... 

In the case of poly(4-hydroxybenzoate) [29], thermo-oxidative degradation occurs only at very high temperature and even then only slowly. From the data available, it would appear that oxidation occurs at chain ends, and that reduction in molecular weight is brought about essentially by a depolymerisation process. This conjecture is backed by the fact that, even at 75% weight loss, the chemical composition of the remaining polymer is virtually unchanged. 

They found that thermal degradation of poly(4- -alkyl styrenes) followed mainly a free radical depolymerisation mechanism. The main product is a monomer similar to unsubstituted PS, i.e., 59% to 92% monomer from poly(4-n alkyl styrenes) ranging from 136,500-737,000 and = 37,000-99,000. The amoxmts of this monomer decrease with increasing length of alkyl sidechain from hexyl to decyl. This behaviour is connected with the stability of monomer under isothermal pyrolysis conditions at 600 °C. 

Traces of oxygen-containing materials such as water initiate cross-linking by providing bridging atoms, but poly-dichlorophosphazene (phosphonitrilic chloride polymer) decomposes slowly in contact with atmospheric moisture, and hydrolysis occurs rapidly and completely in water at 100°C. The tetramer polymerises more slowly than the trimer when heated, but eventually gives the same products. When the rubbery products are heated above about 350°C, depolymerisation begins (12.230). 

Primary recycling. This is the depolymerisation of waste plastics into their constituent monomers or monomer precursors so that new synthetic polymers materials can be manufactured to the same exacting standards as the original materials. An example of this would be in the methanolysis of used poly(ethylene terephthalate) (PET) soft drinks containers to produce dimethyl terephthalate which is a precursor in one of the routes in the manufacture of PET [9]. 

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