Nova Patents
EP0335499A2

Method of producing thermoplastic elastomers having alternate crystalline structure for use as binders in high-energy compositions.

Abstract

A method is provided for synthesizing block polymers which are thermoplastic elastomers. The thermoplastic elastomers are useful as binders in high-energy compositions, such as propellants, explosives, gasifiers or the like. The block polymers have both (A) and (B) blocks; the A blocks being crystalline at temperatures below 60°C and the B blocks being amorphous at temperatures above -20°C. Both the A and B blocks are polyethers formed from monomers of oxetanes and/or tetrahydrofuran. To prepare the block polymers, the (A) and (B) blocks are separately prepared and separately end-capped by reacting each block with a diisocyanate in which one of the isocyanate moieties is substantially more reactive with the terminal hydroxyl groups of the blocks than the other. Reaction of the more reactive isocyanate moiety with the terminal hydroxyl groups leaves the other isocyanate group free. The end-capped (A) and (B) blocks are mixed and reacted with a short linking compound which has two isocyanate-reactive groups.

EP0335499A2, drawing sheet 1
Sheet 1 of 7

Term

Term ended

Projected expiry passed 24 February 2009, 17.6 years ago.

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13 claims: 3 independent, 10 dependent

  1. 1
    A method of preparing a thermoplastic elastomer having A blocks and at least one B block, wherein said A blocks are crystalline at temperatures below about 60°C and said B block(s) is amorphous at temperatures above about -20°C, said A blocks each being polyethers derived from monomers of oxetane and its derivatives and/or tetrahydrofuran and its derivatives, the method comprising providing hydroxyl terminated A blocks which are crystalline at temperatures below about 60°C and separately providing hydroxyl terminated B blocks which are amorphous at temperatures above about -20°C, end-capping said A blocks and said B blocks by separately reacting each of said A blocks and B blocks with a diisocyanate in which one isocyanate moiety is at least about five times as reactive with the terminal hydroxyl groups of each of the blocks as the other isocyanate moiety, whereby the more reactive isocyanate moiety tends to react with terminal hydroxyl groups of the blocks, leaving the less reactive isocyanate moiety free and unreacted, mixing said end-capped A blocks and said end-capped B blocks together at approximately the stoichiometric ratios that they are intended to be present in the thermoplastic elastomer, and reacting said mixture with a linking compound having two isocyanate-reactive groups which are sufficiently unhindered to react with the free isocyanate groups of said end-capped polymer.
  2. 12
    A method according to any preceding Claim wherein each of said A blocks and said B blocks are difunctional and said linking compound is provided at about a 0.4 to 0.6 molar ratio relative to total A and B blocks, whereby an (AB)n polymer is produced.
  3. 13
    A method according to any preceding Claim wherein in said end-capping reaction, when either of said blocks has a pair of terminal hydroxyl groups, said diisocyanate is provided at between a 1.75 and a 2.2 molar ratio.
Independent claims3