Aliphatic Polyisocyanurate Composites


 Number/Link: WO 2017/191216  (German)

Applicant/Assignee:  Covestro

Publication date: 9 November 2017

Gist”: Partially trimerized aliphatic diisocyanates are mixed with glass fiber and reacted using a trimerization catalyst

Why it is interesting: Conventional fiber-reinforced composites based on unsaturated polyesters, epoxies, polyurethane and the like are not weather-stable and need to be coated for outdoor use. Weather stable polyisocyanurate composites are known (WO2007/096216 – Huntsman) but are based on aromatic diisocyanates and show high reactivity and short ‘pot life’. According to this invention, PIR composites with improved reaction profile and weatherability can be prepared from partially trimerized aliphatic diisocyanates with a diisocyanate monomer content of less than 20% (w/w). In the examples commercially available HDI and IPDI trimer is used together with short glass fiber and a potassium acetate/PEG 400 blend as catalyst cured at a temperature of 160 to 180°C.

Isophorone diisocyanate (IPDI)


Triptycene Chain Extenders


 Number/Link: US20150191408

Applicant/Assignee: not yet recorded. Research supported by US Army

Publication date: 9-07-2015

Gist”: A novel primary diol derived from triptycene is useful as chain extender for polyurethanes and polyesters.

Why it is interesting: Polymers with increased mechanical properties and stiffness can be obtained by incorporating rigid structures in the polymer chain.  This however also results in increased glass transition temperature and reduced ductility because of reduced chain flexiblity and entanglements.  According to this invention polyurethanes (and copolyesters) with high modulus and good ductility at low temperatures can obtained by using triptycene-1,4-hydroquinone-bis(2-hydroxyethyl ether) or TD. In and example TD capped with PEG400 is reacted with a 4,4’MDI- PTMEG1000 prepolymer.  The resulting material indeed has a very low softblock Tg of  -65ºC and a much higher Y modulus compared to a PU made with HQEE as chain extender. According to the inventors the PU is highly suitable as a matrix material in KEVLAR or UHMWPE fiber composites.
In my opinion this is a very interesting chain extender as it appears to prevent H-bond formation and increase molar volume thereby substantially decreasing Tg. However lack of availability, and (most probably) price, will prevent this from becoming mainstream anytime soon.

Tryptycene-1,4-hydroquinone-bis(2-hydroxyethyl ether)

Triptycene-1,4-hydroquinone-bis(2-hydroxyethyl ether)


Steam-Treated Polyisocyanurate


 Number/Link: WO2014/160616

Applicant/Assignee: Dow

Publication date: 2-10-2014

Gist”: Treating PUR-PIR with hot water at superatmospheric pressure results in a Tg increase.

Why it is interesting: Fiber-reinforced phenol-formaldehyde composites are used to make pipes among other things.  They are however not completely stable in hot humid conditions so that they are less well suited for off-shore piping systems for example. According to this patent application, polyisocyanurate (PIR) or polyurethane-polyisocyanurate (PUR-PIR) systems are more suitable materials for such applications because properties of these materials remain stable and -surprisingly- glass transition temperature increases when subjected to high pressure water or steam. In the examples PUR-PIR systems based on polymeric MDI submerged in water at 120°C and 3500 kPa for 7 days show indeed an increase in Tg.  In my opinion it would be interesting to repeat the experiment with 4,4′-MDI based PUR/PIR.  Because 4,4′ MDI will show a higher conversion rate to PIR the ‘steam effect’ may well dissapear.

Isocyanurate group

Isocyanurate group

Classic PU Patent of the Month: Upjohn’s “Isoplast®” (1981)

Title: Polyurethane prepared by reaction of an organic polyisocyanate, a chain extender and an isocyanate-reactive material of m.w. 500-20,000 characterized by the use of only 2-25 percent by weight of the latter material

 Number/Link: US4376834

Applicant/Assignee: Upjohn

Publication date: 15-03-1983

Gist”: Very high hardblock TPU from MDI and chain extenders.

Why it is interesting: “Isoplast” is a so-called engineering thermoplastic useful in niche applications where high impact strength and high chemical resistance are required. The material can be clear or reinforced and can also be used in fiber-reinforced composites.  Currently the trademark is owned by Lubrizol who acquired it from Dow who in turn bought it from Upjohn in the 1980s.  Isoplast is made from 4,4′ MDI and a mixture of chain extenders selected from MEG,DEG, neopentyl glycol, 1,4-cyclohexanedimethanol etc. The choice of chain extenders controls the crystallinity/glassiness of the polymer.  A few percent of high mole weight polyol may be added to improve impact resistance. A very interesting material with interesting melt-flow characteristics because of its depolymerization and repolymerization behaviour during processing.

Screw from reinforced Isoplast

Screw from reinforced Isoplast

Prepregs from Glass Fiber and Reactive Polyurethane Powder


 Number/Link: US2014065911

Applicant/Assignee: Evonik

Publication date: 6-03-2014

Gist”: A reactive polyurethane powder is prepared from a mixture of a  solid polyester polyol and a solid dimerised IPDI and subsequently used to make glass fiber prepregs.

Why it is interesting:  A polyurethane powder is made from (pref.) a mixture of  a solid (at room temperature) polyster polyol and a solid, blocked isocyanate.  The isocyanate is preferably an “internally” blocked IPDI.  Internally blocked meaning that the isocyanate contains uretidinedione groups.  The powder is scattered over a fibrous support and heated to over melting temperature but below curing temperature to make the prepreg.  Prepregs made with PU powder instead of the conventional resins have the advantage of being non-sticky, non-toxic and of having a very high storage stability (45 days in the examples).

Prepreg production with reactive PU powder

Prepreg production with reactive PU powder