IL11048A - Improvements in or relating to the treatment of polystyrenes - Google Patents

Description

achieved or the apparatus he used with each a small amount of at one that the yield per hour tends to he very In accordance with the present invention there is provided a process reducing the molecular weight of a polystyrene which comprises subjecting the polystyrene to mechanical in the as a depolymerization controlling of a chain transfer agent a radicalic polymerisation agent or a rubber By this process it is found that a rapid and controllable thermal degradation can be achieved and there is substantially no tendency to produce branched or products and thus reduce the of the Moreover the process is readily The mechanism of the process probably involves the from the depolymeriaation controlling of free radicals which tend to themselves with the polystyrene free radicals produced on scission of the high molecular weight thus transforming them into a state and preventing their Examples of rubber antioxidants which may be employed ares ether oxidants and general all antioxidants exerting a action against th effects of on elastomers and other synthetic are effective to fix the amounts of oxygen which are found associated with the molecules of the polystyrene and which might hinder the producibility of the results chain transfer agents which may be employed as an alternative to the rubber are also believed to function by furnishing free radicals for inactivating the free valencies produced on scission of the polymer among which may be mentioned aromatic peroxides and and will also function as ini tors in processes Kolthoff 1955 chapter When carrying out the process by subjecting the polystyrene to thermal the presence of the depolymerization controlling it is advantageous to hea it to a higher than at about Especially at this temperaturet a substantial degree of polymerization can be obtained in a readily reproducible cess using very small proportions of the depolymerizatlon controlling from to based on the weight of The process can be carried out continuously or batchwise using reactors with or without agitating Among the types of apparatus which may be there may be menioned and The choice of the particular controlling agent to be the amount and the working depend upon For any particular ease the necessary conditions may ascertained by simple Results similar to those by thermal degrada tion can be obtained b mechanical degradation in the presence of the controlling The of the depolymerissatlon controlling agent during such mechanical degradation is remarkable but even so it must be noted that the process is much slower than when thermal degradation is She process of the present invention may be particularly interesting to ieotaetie nes produced using stereospecifie for example as described in the Specifications Applications 9078 and 9163 wherein we are Polymerisation produced ith such catalysts tend to have very high molecular weights the order of to have very low crystallization reducing their molecular weights by the process of the present there is tainable a wide range of polymers with lower molecular weights and substantially the same degree of crystalllnity as the starting Solid polymers having low molecular weights but nevertheless a degree of associated with the previously known isotactie polymers can thus be obtain ed a simple economic following in which all references to proportions are be taken as references to proportions by are given in order to illustrate the Specimens of a substantially isotactie mixed homogeneously with one of the substances listed in fable by impregnating the powder with an acetone solution the substances in question and then drying at room samples of the mixtures were into glass tubes which were then evacuated and The tubes were then introduced into an oven at 250 and kept there for 45 The obtained results are shown in Table Thermal degradation of an polystyrene having a molecular weight of Substances added Molecular 45 45 peroxide 45 peroxide 45 The weights were calculated from the intrinsic viscosity in tetrahydronaphthalene at 100oG on the basis of the intrinsic viscosity in 100 a molecular weight Example Ζ Samples of polystyrene such as that of Example 1 were each mixed with of substances listed in the following liable according to the procedure of Example mixture was sintered for 4 minutes under a press at The product in the form of pieces was then introduced into an apparatus for flow rates of thermoplastics and determining the The melt index was determined after degradation inside the apparatus at for This index depends on the molecular the lower the molecular the higher is this The results obtained are shown in Sable degradation at of an isotactic polystyrene having a molecular of Substances added at about 39 lauryl 24 mercaptan 1 Example 3 polymer of Example 1 was mixed with 1 and after sintering as in was introduced into the apparatus for determining variation of the celt index at depending on time of residence inside the apparatus was determined and the results are shown in Table 3 Thermal degradatio at of an isotaetie polystyrene having a molecular weight of in the pr of minutes index at 0 0 15 45 75 105 135 On varying the percentage of the antioxidant and carrying out the degradation for the following results Table 4 Thermal degradation minutes at of ieotaotio yrene having a molecular of in the presence of various percentages of melt index 0 5 31 1 39 index was determined tinder conditions of D at Samples of powdered substantially polystyrene were mixed with in a powder the thus treated fed to a of mm diameter and 333 kept at an average temperature of The residence time of inside the extruder varied from 5 to 10 The molecular weigh of extruded polymer was determined and the results are given in Table degradation of isotaotic polystyrene in an extruder at Initial molecular Final molecular weight weight 1 20 1 20 30 Samples of the same powdered in each mixed one of the listed in the following according to the procedure of and then ground in a porcelain ball mill at room temperature for 24 results obtained are given in fable TABLE 6 Mechanical degradation of ieotactie polystyrene in a ball Substances added molecular weight mm onitrile 2 Benzoyl peroxide 2 2 ter henol 2 insufficientOCRQuality

Claims (1)

particularly described and ascertained nature of our said invention and in what manner the same to he re declare that what we claim let A process for reducing the molecular weight of polystyrene which comprises the polystyrene to thermal mechanical controlled depolymerizatio in the as a controlling of a trans a radicalic polymerisation agent or a rubber A process according to Claim 1 in which the styrene is subjected to mechanical at room A process according to Claim 1 in which the styrene is subjected to thermal depolymerization or and mechanical at a temperature higher then A process according to any of Claims 1 to which the depolymerization controlling agent is employed in an amount of to based on the weight of the A process according to any one of Claims 1 to which the depolymerization controlling agent is A process a ccording to any one of Claims 1 to in which the controlling agent process according t any one of Claims1 to in A process according to any one of Claims 1 in which the controlling agent an aroaatie peroxide or or a process according to any one of to ia which the depolymerleation controlling agent is benzoyl A process according to any one of

1. Claim 1 to in which the controlling agent ie butyl Bated the 23rd Agents for the insufficientOCRQuality