Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From sulfur-containing reactant
Patent
1990-11-05
1993-01-05
Kight, III, John
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From sulfur-containing reactant
524700, 528373, C08G 7504, C08G 7500, C08J 300
Patent
active
051771829
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the manufacture of polysulphide compositions of the type used, for example, as sealants in glazing and in other applications in the construction industry.
In preparing polysulphide sealants, a mercaptanterminated polymer, generally a liquid polysulphide of relatively low molecular weight, is reacted with a curing agent, preferably an oxidising agent such as calcium peroxide, to cure it to a solid state. The preferred liquid polysulphide polymers are those having a molecular weight of 1000-8000, a viscosity of 10 to 2000 poise and a degree of crosslinking of 2.0 or less. The preferred polymers are those prepared by Morton Thiokol Inc. and known as LP-2, LP-32 etc. The chemistry embodied in this reaction applies to all mercaptan terminated liquid polymers. ##STR1##
Curing agents such as calcium peroxide require the presence of water to activate them. It is therefore possible, instead of using a cumbersome two-part sealant composition, to use a one-part composition of liquid polysulphide and curing agent which is kept free of water until used. Once the sealant is in place it forms a skin and slowly cures to a rubber state through the presence of atmospheric moisture.
One known polysulphide composition comprises 100 parts by weight of liquid polysulphide LP32C (Morton International Inc) and 10 parts by weight of calcium peroxide. Such a composition generally takes several days to cure, having a skin time of 72 hours or more. To cure such a composition in a shorter time requires a temperature of 25.degree. C. or more and a relative humidity of 95%.
There is therefore a need for polysulphide sealant compositions which can be easily prepared, are stable during storage and which cure in a short time once in position.
The inventors have found that when polysulphides are cured with a curing agent, for example with a strong oxidising agent such as a metal peroxide, the cure generally proceeds in three distinct stages.
The stages are: and the system approaches the gel state. viscometer. The final stages of polymer network formation take place.
The precise shape of the viscosity-time curve is dependent on many factors such as catalyst type, catalyst level, temperature etc.
The time required for the induction step (I) can vary considerably but in many cases, for example single part sealants based on polysulphide polymers and cured with calcium peroxide, this first step is very long. This is advantageous with respect to storage stability, but a disadvantage after application with respect to rate of cure. The reaction between polysulphide polymers and metal peroxides are catalysed by water and as such can be retarded to substantially a zero rate by dehydration.
The present invention consists in a method of making a polysulphide composition wherein a prepolymer having free mercaptan groups is mixed with a curing agent of a type activated by water, characterized in that the composition is subjected to a partial cure with water, the reaction then being stopped by dehydration.
The invention thus provides a technique which allows the reaction to proceed along the path of step I, induction, to a point just prior to commencement of Step II and no further.
At the completion of Step I the reaction is stopped by rapid dehydration, preferably by the use of molecular sieve. The subsequent exposure of this system to moist air reinitiates the reaction at the commencement of Step II, i.e. there is no longer an induction period.
Suitable molecular sieve types include types 3A, 4A, 13X and 14X.
The stabilised polysulphide polymer, which has reached the end of the induction step is hereafter referred to as "Prereacted" LP polysulphide polymer.
It is possible by the means described above to make stable prereacted LP polymers using ingredients commonly found in single part polysulphide sealants. These polymers blended with other ingredients form sealants which cure more rapidly than conventional polysulphide sealants.
The liquid polysulphides preferred for the purposes of the invention have the general formula: --S.
REFERENCES:
patent: 3349046 (1967-10-01), Sheard
patent: 3991039 (1976-11-01), Gunter et al.
patent: 3997613 (1976-12-01), Lenke
Lee Timothy C. P.
Lowe George B.
Robinson Raymond
Kight III John
LaMarre Mark F.
Morton International Limited
Mosley T.
White Gerald K.
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