Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2001-07-24
2003-01-28
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S015000, C528S025000, C528S031000, C528S044000, C528S056000, C528S058000, C528S501000
Reexamination Certificate
active
06512086
ABSTRACT:
This invention relates to a process for the preparation of fluid organosilicon compositions which can be used in adhesive, coating and sealant formulations. This process, which involves two consecutive steps conducted in the same reactors, as described below, provides prepolymers able to cross-link under normal moisture and room temperature conditions, forming elastomers as a result of hydrolysis of the silicon-alkoxy groups at the chain ends and subsequent condensation of the silanols generated by the hydrolysis process. The organosilicon compositions obtained with this process have low viscosity and are particularly suitable for the formulation of single-component moisture-curing adhesives and sealants.
STATE OF THE ART
Polyethers able to cross-link through silicon-alkoxy groups at the chain ends are described in U.S. Pat. No. 3,971,751 and DE 2.427.661; the products claimed in those patents are obtained by adding chlorosilanes to prepolymers containing allyl ether groups at the chain end; in the organosilicons thus obtained, the silicon-chlorine bond is transformed into a silicon-alkoxy bond by reaction with methyl alcohol in the presence of a hydrochloric acid acceptor such as a cyclic ether.
The critical point of this synthesis process is the synthesis of the unsaturated prepolymer suitable for addition of chlorosilane; for this purpose, a polyether glycol in the form of sodium or potassium alcoholate is chain-extended by coupling with methylene chloride and functionalised at the chain end by reaction with allyl chloride. The synthesis is somewhat delicate as regards the chain extension, and involves the drawback that it produces alkaline chlorides, from which the prepolymer must be freed by complex processes, as taught, for example, by JP 7932597; in addition, the reaction that leads to the chain extension is non-selective, with consequent broadening of the molecular weight distribution to the detriment of the rheological characteristics of the prepolymers.
In U.S. Pat. No. 5,298,572, polyethers able to cross-link by means of silicon-alkoxy groups at the chain ends are obtained from polyether prepolymers with isocyanate and allyl alcohol endings; the resulting unsaturated polyurethane structure prepolymers are converted to prepolymers with silicon-alkoxy functionality by addition of alkoxysilanes.
The addition of alkoxysilanes to unsaturated polyurethane prepolymers instead of chlorosilanes, which would be preferred for reasons of cost, is necessitated by the fact that the latter attacks the amide bond; another drawback is due to the synthesis of prepolymers with isocyanate endings effected by coupling glycol polyethers with diisocyanates, as that reaction is non-selective and involves broadening of the molecular weight distribution which, together with the presence of a multiplicity of carbamate groups in the polymer structures, contributes to worsening the rheological characteristics of the organosilicon prepolymer.
The synthesis process described in JP 08143660 partly alleviates some of the drawbacks associated with the previous synthesis; according to this patent, glycol polyethers are initially converted to terminally unsaturated polyethers by reaction with allyl isocyanate, and then converted to organosilicons by addition of alkoxysilanes.
With this synthesis, the viscosity of the organosilicon prepolymers is improved by eliminating the chain extension and reducing the concentration of carbamate groups in the prepolymers, but requires alkoxysilanes as silylation reagents of the unsaturated polyurethane prepolymers.
A synthesis route proposed in a large number of patents which does not involve the use of chlorosilanes or alkoxysilanes, and which apparently simplifies the preparation of organosilicons, is based on the addition of an organosilicon coupling agent to a polyether-polyurethane prepolymer with isocyanate groups at the chain ends; this coupling agent is a chemical reagent which presents an organic group containing at least one active hydrogen atom according to Zerewitinoff at one end and a silicon-alkoxy reactive group at the other end of its molecule.
This synthesis route, indicated by way of example in patents U.S. Pat. Nos. 3,952,795 and 3,408,321, EP 732348 and 0459304, and DE 4029504, uses a coupling agent in which the group with active hydrogen according to Zerewitinoff is constituted by an alcoholic hydroxyl, a thiol or preferably a primary amine group, which allows easy quantitative addition to the isocyanate group, giving rise to a ureic group.
Despite the simplicity of synthesis, the organosilicons thus obtained present high viscosity due to the large number of polyurethane groups introduced into the polymer structures and the presence of strongly polar urea groups when alkylene aminoalkoxysilanes are used as coupling agents; it should also be borne in mind that organosilicon coupling agents are in turn obtained by addition of chlorosilanes or alkoxysilanes to olefins, with the result that they still represent an additional cost which must be taken into account.
A synthesis route which leads to organosilicon prepolymers containing urethane groups in their structure without using isocyanates is described in EP 714925 and 714953.
According to this synthesis, a diol polyether is functionalised at the chain end with the acyloyl chloride function by reacting the diol polyether with a dicarboxylic acid dichloride; the reaction with an aminoalkyl alkoxysilane of the polyether thus functionalised allows two silicon-alkoxy groups to be attached to the chain end of the prepolymer via amide bridges.
This process presents problems due to the fact that in the reaction between polyether glycol and diacyloyl chloride, hydrochloric acid is produced which needs to be removed; an increase in the polydispersity of the prepolymer cannot be ruled out since the polyether/diacyloyl chloride coupling reaction is non-selective; and finally, more or less high proportions of hydrolytically unstable ester structures are introduced into the polymer structure.
Some of the drawbacks involved in the use of aminoalkyl alkoxysilane coupling agents can be alleviated by using aminoalkyl alkoxysilanes with a secondary amine group, as described in U.S. Pat. No. 5,539,045 and EP 0676403 or in DE 0596360 and U.S. Pat. No. 6,001,946; an N-phenyl-&ggr;-aminopropyl triethoxysilane is used as coupling agent in the first two patents, and organosilicon coupling agents containing aspartate groups in the others.
These solutions present some advantages compared with those offered by the previous aminoalkyl alkoxysilanes, because they reduce the ureic NH groups and make the organosilicon polymers more flexible after cross-linking; however, they do not eliminate the chain extension of the polyether during its functionalisation with the isocyanate group or the drawback of using more sophisticated, expensive coupling agents than the previous ones; in the particular case in which the use of a coupling agent with an aspartate structure is required, hydrolytically unstable ester groups are introduced into the polymer structures in a position adjacent to the silicon-alkoxy group, which may adversely affect adhesion in the case of calcareous or cementitious substrates.
A particular case of a coupling agent is represented by &ggr;-isocyanate propyl trialkoxysilane which is claimed, for example, in WO 9305089 and JP 08143660; organosilicon prepolymers with only two urethane groups per polymer chain and a narrow molecular weight distribution can be prepared with this coupling agent directly from polyether glycols; however, the coupling agent is not easily accessible, requiring silylation of the allyl isocyanate with alkoxysilanes; in addition, the use of this coupling agent does not eliminate the drawback, common to all the others, of introducing urethane polar groups in the immediate vicinity of the reactive silicon-alkoxy group of the organosilicon prepolymer, which makes the wettability of the fillers in the formulations more problematic than that of prepolymers with a different structure such as those
Ausilio Antonio
Greco Alberto
Pozzi Enrico
Dawson Robert
Griffin & Szipl, P.C.
Mapei S.p.A.
Zimmer Marc S.
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