Reversible crosslinked polymers, benzylic hydroxl...

Details Reversible crosslinked polymers, benzylic hydroxl... Reversible crosslinked polymers, benzylic hydroxl...

2000-11-24

2003-05-06

Gorr, Rachel (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From reactant having at least one -n=c=x group as well as...

C528S085000

Reexamination Certificate

active

06559263

ABSTRACT:

FIELD OF THE INVENTION
The invention involves crosslinked polyurethanes and other polymers not conventionally known as polyurethanes, with added urethane crosslinks where the crosslinkers are based on compounds having one or more benzylic hydroxyl groups, and methods of making the polymers and crosslinkers. The polymers are useful to make elastomers, fibers, sheets, moldings, coatings and other articles typically produced from polymers.
BACKGROUND OF THE INVENTION
Organic polyisocyanates have been reacted with compounds having active hydrogen groups, such as hydroxyl groups, to produce a wide variety of useful urethane containing materials such as coatings, hot-melt adhesives, moldings and materials used in injection molding applications and composite or laminate fabrications. Urethane bonds are used ubiquitously in polymer chemistry to produce a wide variety of useful compositions. Typical of the art is the patent to Markle et al, U.S. Pat. No. 5,097,010.
The urethane bond is conveniently obtained by the addition reaction of an isocyanate group (either an aliphatic or an aromatic isocyanate) and an aliphatic alcohol or an aromatic (also known as aryl) hydroxyl group (also known as a phenolic group). The urethane bond is formed between the oxygen atom of the hydroxyl group and the carbon atom of the isocyanate group. An alternate term often used is “urethane linkage”. This reaction is reversible at sufficiently high temperatures as indicated by showing the following reaction as an equilibrium process.
In this equation, R is alkyl or aryl and R′ independently is alkyl or aryl. The equilibrium constant K is defined as k
1
/k
2
where k
1
is the rate constant of the forward, or urethane bond forming reaction, where k
2
is the rate constant of the reverse reaction involving reformation of RNCO and R′OH. These rate constants each vary as a function of the temperature, with k
1
and k
2
both increasing as the temperature increases. However, k
1
will dominate (i.e., k
1
>>k
2
) over some temperature range between ambient temperature and some intermediate higher temperature since the forward reaction typically has a lower activation energy than the reverse reaction. As a result of these activation energy differences, k
2
will increase more rapidly than k
1
as the temperature is increased. Thus, at some higher temperature, k
2
may equal k
1
(where the equilibrium constant K=1) and may in certain cases become appreciably greater than k
1
at still higher temperatures. Hence, the equilibrium constant will range from quite high values at ambient temperature but can become relatively smaller at sufficiently high temperatures so that significant and useful concentrations of isocyanate groups will be present.
The forward, or urethane bond forming reaction, can be affected by simply heating an equimolar mixture of isocyanate and hydroxyl groups to the temperature at which k
1
is large enough that urethane bond formation occurs in an acceptable, or practical, period of time (from a few minutes to several hours). Catalysts, such as tertiary amines or certain organotin compounds, can speed both the forward and reverse processes, but are not necessary to bring about the urethane bond forming reaction or the establishment of equilibrium. If both compound types are difunctional, that is, if they are diisocyanates and dialcohols or diphenols, the forward reaction will produce polymeric products (polyurethanes) of very high molecular weights. The achievable molecular weight of fully reacted (i.e., of essentially non-reversed) pairs will be limited by the presence and concentration of monofunctional isocyanates or monofunctional alcohols; by the isocyanate concentration and the dialcohol or the diphenol concentrations not being equal to each other; or, by the intervention of adventitious impurities which deplete the amount of either isocyanate or hydroxyl groups by side reactions. However, as the temperature of the polyurethane is further increased and k
2
increases faster in comparison to the increase in k
1
, significant and measurable reverse reaction to isocyanate and either alcohol or phenol will occur. The approximate reversion onset temperatures of urethanes derived from representative combinations of aliphatic or aryl isocyanates and alkyl or aryl hydroxyl groups (as defined earlier) have been previously reported by Z. W. Wicks, Jr., “Blocked Isocyanates” Progress in Organic Coatings, 3, pp. 73-99 (1975) as shown in Table 1 below:
TABLE 1
Approximate Urethane
Reversion Onset
Isocyanate Type
Alcohol Type
Temperature (° C.)
Aryl (e.g. MDI)
a
Aryl (e.g. Phenol)
120
Alkyl (e.g. HDI)
b
Aryl (e.g. Phenol)
180 (118)
c
Aryl (e.g. MDI)
Alkyl (e.g. n-Butanol)
200
Alkyl (e.g. HDI)
Alkyl (e.g. n-Butanol)
250
a
MDI = 4,4′-diphenylmethane diisocyanate
b
HDI = 1,6-hexamethylene diisocyanate
c
a wide variation of reversion onset temperatures exists in the literature for urethanes prepared from aliphatic isocyanates and phenolic compounds, the lowest being 118° C. (M. Gedan-Smolka, Thermochimica Acta, 351, pp 95-105 (2000).)
These reversion onset temperatures are approximate values which represent the onset of reversal or a temperature where the practical effect of reversal, such as the onset of distillation or evaporation of a phenolic compound or an alcohol from a heated mixture occurs, or where infrared (IR) spectroscopy of heated samples indicates the onset of isocyanate and alcohol or phenol formation from a previously unreversed urethane compound.
Crosslinkihg in polymers is known to improve their physical properties and increase mechanical properties (such as but not limited to tensile and flexural strengths and moduli). Typically, crosslinked polymers do not melt or dissolve in solvents (for the uncrosslinked polymers). Hence they cannot be melt or solution processed. However, if crosslinks are present that contain at least one thermally reversible bond, the polymer should maintain the advantageous properties associated with crosslinking while below the reversion onset temperature of such crosslinks, but should be readily either melt or solution processable at some temperature above the reversion onset temperature.
In the work described herein, it was sought to identify combinations of particular diisocyanates or polyisocyanates and dialcohols or diphenols, or polyalcohols or polyphenols, which would possess reversibility of practical utility (described further below) in terms of some relatively high temperature at which onset of reversion would occur. This would allow the preparation of polymers with both backbone urethane bonds (i.e. urethane bonds as part of the structure of the long molecular strands constituting a polymer chain), and crosslinking urethane bonds (i.e. urethane bonds connecting two of the long molecular strands constituting a polymer chain with bridging bonds, which result in dramatic increases in average molecular weight, such as for example a doubling thereof) which might be expected to have practical utility up to, or very close to, the urethane reversion onset temperature as described above. If sufficient reversible bonds, including crosslinks, are incorporated into such a reversible bond-containing polymer structure, polymers may be formed at some elevated temperature, by first heating the mixture of reactive components to some temperature above the practical reversion onset temperature such that a mixture of molten, or dissolved, partially assembled, urethane bond-containing, polymer fragments is established. Such mixture will be easily stirrable, have a low viscosity, and can be melt processed by methods such as melt spinning of fibers and fabrication of components by injection molding and extrusion processing. It will also be solution processable, provided the mixture is heated in a solvent which dissolves both the starting components and partially assembled, but uncrosslinked components. For example, both dry and wet fiber spinning of fibers are possible. As this mixture is cooled below this reversion onset tempera

Affiliated with

Also associated with

Rating

Reversible crosslinked polymers, benzylic hydroxl... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Reversible crosslinked polymers, benzylic hydroxl..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reversible crosslinked polymers, benzylic hydroxl... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3076637