ULTRA LOW DENSITY BIODEGRADABLE SHAPE MEMORY POLYMER FOAMS WITH TUNABLE PHYSICAL PROPERTIES
Compositions and/or structures of degradable shape memory polymers (SMPs) ranging in form from neat/unfoamed to ultra low density materials of down to 0.005 g/cc density. These materials show controllable degradation rate, actuation temperature and breadth of transitions along with high modulus and excellent shape memory behavior. A method of making extremely low density foams (up to 0.005 g/cc) via use of combined chemical and physical blowing agents, where the physical blowing agents may be a single compound or mixtures of two or more compounds, and other related methods, including of using multiple co-blowing agents of successively higher boiling points in order to achieve a large range of densities for a fixed net chemical composition. Methods of optimization of the physical properties of the foams such as porosity, cell size and distribution, cell openness etc. of these materials, to further expand their uses and improve their performance.
1 . A shape memory polymer composition comprising a polymer composition resulting from the reaction of a branched monomer having three or more branches in its structure with hydroxyl end groups with:
a difunctional monomer an acid group on one end and a hydroxyl group on the other end,
a difunctional monomer having hydroxyl end groups or
a branched polyol with di-carboxylic acid, resulting in an polycarboxylic acid monomer containing ester linkages.
2 . The composition of claim 1 wherein a branched monomer having three or more branches in its structure with hydroxyl end groups is reacted with a difunctional monomer with an acid group on one end and a hydroxyl group on the other end and a difunctional monomer having hydroxyl end groups in succession.
3 . The composition of claim 1 wherein the a branched monomer having three or more branches in its structure with hydroxyl end groups is selected from the group consisting of Triethanol amine (TEA), Hydroxy propyl ethylene diamine (HPED), Glycerol, Pentaerythritol or Trimethylolpropane, Bis-tris methane, Bis-tris propane, 1,2,4 Butane triol, Miglitol, Trimethylolethane and Tris(hydroxymethyl)aminomethane.
4 . The composition of claim 1 wherein the difunctional monomer an acid group on one end and a hydroxyl group on the other end is selected from the group consisting of L-Threonic acid, Tricine, Shikimic acid, 3-Hydroxybutyrate, ε-Caprolactone, Lactic acid, and Glycolic acid.
5 . The composition of claim 1 wherein the difunctional monomer having hydroxyl end groups is selected from the group consisting of Polyethylene glycol, 1,3-Propanediol, 1,4-Butanediol, 1,5-Pentanediol, 1,2-Propanediol, 1,2-Butanediol, 2,3-Butanediol, 1,3-Butanediol, 1,2-Pentanediol, Etohexadiol and 2-Methyl-2,4-pentanediol.
6 . The composition of claim 1 wherein the branched polyol with di-carboxylic acid are selected from the group consisting of 1,4-benzoquinonetetracarboxylic acid, Ethylenediamine-N,N′-disuccinic acid, furantetracarboxylic acid, hydroxycitric acid, citric acid, Nitrilotriacetic acid, Aconitic acid, isocitric acid and Propane-1,2,3-tricarboxylic acid.
7 . The composition of claim 1 wherein Triethanol amine is end capped with 3-Hydroxybutyrate (HB).
8 . The composition of claim 1 wherein a tetrafunctional hydroxyl monomer prepared by end capping Citric acid (CA) with 1,3 Propane diol is one of the reactants.
9 . The composition of claim 1 wherein Polycaprolactone triol (PCT) obtained from grafting ε-Caprolactone on Trimethylolpropane is one of the reactants.
10 . The composition of claim 1 wherein stoichiometric amounts of hydroxyl monomer and diisocyanate are vigorously mixed together until a clear one phase solution is formed, the resulting composition degassed and cast into molds.
11 . A method for controlling cell structure of polymer foams made from the compositions of claim 1 comprising control of the viscosity of the composition solution, a prepolymer, to be foamed by control of the amount hydroxyl monomer in the prepolymer wherein cell size is inversely proportional to the viscosity.
12 . The method of claim 11 wherein viscosity of the viscosity is reduced by addition of inert liquid phase solvent.
13 . The method of claim 11 wherein the viscosity is controlled by the duration and speed of mixing the composition to be foamed, wherein higher duration or speed of mixing of gives finer cell size with denser foams.
14 . A method of producing low density foams from the compositions of claim 1 comprising increasing the concentration of gas in the composition solution to be foamed at regular intervals.
15 . The method of claim 14 comprising using successively higher boiling point blowing agents as foaming progresses.
16 . The method of claim 14 comprising simultaneous increase in the surfactant levels as the concentration of gas in increased.
17 . The method of claim 14 comprising addition of particulate nucleating agents to the compositions to be foamed.
18 . The method of claim 17 comprising leachable porogens as nucleating agents.
19 . The method of claim 14 comprising conducting the foaming under vacuum.
20 . The method of claim 14 comprising using higher functionality carboxylic acids as a blowing agent.
21 . A method of producing improved cell opening in foams produced from the compositions of claim 1 comprising the addition of high z metal nano- or micro-particles.
22 . The method of claim 21 wherein the z metal particles are selected from the group consisting of tungsten, tantalum, platinum and, palladium.
23 . The method of claim 21 comprising surface modification of the metal particles with a low surface energy coating.