Single solvent process for preparation of glutarimide containing polymers

A process for preparing glutarimide resins by the amidization and cycloimidization of methacrylate resins in the presence of a solvent characterized in that the solvent consists essentially of cyclohexanol.

The present invention relates to a process for preparing a resin containing 
glutarimide units. More particularly the present invention relates to a 
process for preparing such polymers which employs a single solvent 
In U.S. Pat. No. 4,745,159 there is disclosed a process for preparing 
glutarimide containing polymers (referred to as methacrylimide units) 
which employs a solvent mixture in a process for the amidization and 
cycloimidization of methacrylate based polymers. Suitable solvent systems 
were said to include mixtures of two or more components selected from 
aliphatic alcohols, aromatic hydrocarbons and ketone or ether compounds. 
Such a solvent system was found necessary to maintain the solubility of 
the various reactants and products during the process and to insure that 
the resulting polymer's properties, especially transparence was not 
adversely affected. 
Although the process disclosed in the foregoing U.S. patent does succeed in 
producing glutarimide containing polymers having good physical properties, 
the requirement of a multicomponent solvent system introduces complexity 
and expense into the procedure. Separate storage and supply facilities and 
more complex purification and recovery systems are required in a process 
employing a multicomponent solvent system compared to a process employing 
only one solvent. Thus, it would be desirable if there could be provided a 
single solvent which is suitable for use in the amidization and 
cycloimidization of methacrylate resins without sacrifice of resulting 
physical properties of the glutarimide polymer. 
According to the present invention there is provided a process for 
preparing glutarimide resins by the amidization and cycloimidization of 
methyl methacrylate or methacrylic acid resins in the presence of a 
solvent characterized in that the solvent consists essentially of 
cyclohexanol. 
The present invention provides a composition comprising glutarimide units 
of the following formula: 
##STR1## 
wherein R each occurrence is hydrogen or methyl and R' is a hydrogen atom 
or an aliphatic, alicyclic or aromatic hydrocarbon group having from 1 to 
20 carbon atoms. 
Further, the present invention provides a process for preparing a 
glutarimide resin which comprises reacting a resin comprising methyl 
methacrylate or methacrylic acid units, with an amine of the formula 
R'NH.sub.2 wherein R' is as defined above, under conditions such that said 
resin is dissolved in cyclohexanol under amidization and cycloimidization 
conditions. 
Suitable methyl methacrylate or methacrylic acid resins (referred to 
hereafter as methacrylate resins) to be employed in the present invention 
include methyl methacrylate, or methacrylic acid homopolymers as well as 
copolymers of methyl methacrylate or methacrylic acid with other 
copolymerizable monomers such as acrylic esters, C.sub.2 -C.sub.12 alkyl, 
cycloalkyl or aryl esters of methacrylic acid, acrylic acid, C.sub.1 
-C.sub.12 alkyl or aryl esters of acrylic acid, styrene, .alpha.-methyl 
styrene, etc. Such polymers usually have an intrinsic viscosity of from 
0.01 to 3.0 dl/g (at 25.degree. C. in dimethyl formamide). Other 
copolymerizable monomers are used in an amount of preferably not higher 
than 90 percent by weight based on the monomer mixture. The acrylic esters 
preferably include methyl acrylate, ethyl acrylate, butyl acrylate, 
cyclohexyl acrylate, 2-ethylhexyl acrylate and benzyl acrylate, and the 
C.sub.1 -C.sub.12 alkyl esters of methacrylic acid include ethyl 
methacrylate, butyl methacrylate, cyclohexyl methacrylate and benzyl 
methacrylate. These monomers may be used alone or in a combination of two 
or more different kinds. Preferred polymers contain less than 1,000 ppm, 
more preferably less than 500 ppm of methyl methacrylate dimer. 
Highly preferred methacrylate polymers are polymethyl methacrylate and 
copolymers of styrene and/or C.sub.2-12 alkylesters or C.sub.6-12 
cycloalkylesters of methacrylic acid and methyl methacrylate containing 
from 25 to 90 weight percent methyl methacrylate. 
The production of the glutarimide resin composition of the present 
invention may be divided into two steps, the amidization step and the 
cycloimidization step, as mentioned above. The two steps of the process 
may be conducted individually if desired but are preferably conducted 
sequentially in a single, unified process. In the amidization step the 
methacrylate resin and the amine of the formula R'NH.sub.2 are reacted 
under the specific condition to induce a condensation reaction among the 
polymer side chains of the methacrylate resin. Preferably the amine of the 
formula R'NH.sub.2 is dissolved into a solution of the methacrylate resin 
in cyclohexanol solvent and reacted with the resin. The quantity of amine 
reactant employed depends on the degree of cycloimidization desired in the 
resulting polymer. At a minimum, one mole of amine should be employed for 
each mole of cyclic imide functionality desired in the resulting polymer. 
Preferably a slight excess of amine is employed where maximum 
cycloimidization of methyl methacrylate functionality is desired. In the 
case where a copolymer of a higher alkyl methacrylate and methyl 
methacrylate is desired, it has been found that only the methyl 
methacrylate units are affected by the amidization process, but that 
C.sub.2 -C.sub.12 alkyl, cycloalkyl or aryl esters of methacrylic acid 
adjacent to methacrylamide moieties (resulting from the amidization of 
methyl methacrylate or methacrylic acid) undergo cycloimidization. 
Suitable reaction conditions for the amidization and cycloimidization 
process are temperatures from 100.degree. to 300.degree. C., preferably 
from 50.degree. to 275.degree. C., most preferably from 80.degree. to 
250.degree. C. Elevated pressures are preferably employed depending on the 
temperature utilized. Suitably pressures from 1 to 15 MPa, preferably from 
3 to 10 MPa, most preferably from 5 to 8 MPa are employed. Suitable 
reaction times are from several minutes to many hours particularly from: 1 
hour to 20 hours, more preferably from 3 hours to 10 hours, most 
preferably from 5 hours to 12 hours. The quantity of amine reactant 
expressed as a mole ratio based on moles of methyl methacrylate present in 
the polymer is desirably from 0.1:1 to 2.0:1, preferably from 0.3:1 to 
1:1. 
A sufficient quantity of cyclohexanol solvent is employed in the 
aforementioned amidization process to provide a polymer concentration in 
the range from 10 to 70 percent by weight, preferably from 15 to 40 
percent by weight. Preferred amines represented by the formula R'NH.sub.2 
used in the process of the present invention are those wherein R' is an 
aliphatic hydrocarbon group, especially methylamine, ethylamine and 
propylamine. It is also possible to generate the foregoing amine reactant 
in situ by the use of compounds capable of producing such amines under 
heating, such as urea, 1,3-dimethylurea, 1,3-diethylurea and 
1,3-dipropylurea. 
As amines wherein R' is an aromatic hydrocarbon group, aniline, toluidine 
and trichloroaniline may be mentioned. As an amine wherein R' is an 
alicyclic hydrocarbon group, cyclohexyl amine may be mentioned. 
Any reactor may be employed for the amidization or cycloimidization so long 
as the object of the present invention can be accomplished without 
hindrance. However, it is preferred to employ a plug flow type reactor 
provided with an inlet, an outlet and static mixing devices adapted to 
provide a mixing function throughout the interior of the reactor. The 
product may be isolated by devolatilization, precipitation or similar 
technique. Preferably the product is recovered by the use of a vented 
extruder that allows removal of cyclohexanol solvent and direct 
pelletizing of the product resin. 
In the process of the present invention, it may be preferred to add a small 
amount of an antioxidant to prevent a decrease of the molecular weight due 
to the radical depolymerization of the methacrylate resin starting 
material under a high temperature reaction condition. Suitable 
antioxidants include phosphite type antioxidants such as tricresyl 
phosphite, cresylphenyl phosphite, trioctyl phosphite or tributoxyethyl 
phosphite, hindered phenol type antioxidants such as hydroquinone, 
2,6-ditertiarybutylphenol, 2,6-ditertiarybutyl-4-methylphenol, etc. 
The surprising feature of the present invention is that one solvent can be 
employed which is capable of dissolving the methacrylate resin starting 
material and retaining the resulting reaction products of both the 
amidization and cycloimidization in solution. Previous artisans had 
disclosed that one solvent cannot be employed in order to obtain both 
complete amidization and imidization as is desired. The resulting product 
where such defects occur contains a high yellowness index. 
Additives such as plasticizers, lubricants, ultraviolet absorber, coloring 
agents and pigments, may be incorporated into the resulting glutarimide 
product if desired. The resin may be used as a molding resin in the 
preparation of molded articles for automotive, instrument and appliance 
manufacture.

Having described the invention the following examples are provided as 
further illustrative and are not to be construed as limiting. Unless 
stated to the contrary parts and percentages are based on weight. 
EXAMPLES 1 AND 2 
Partial polymer solutions (30 percent) were prepared for a series of 
copolymer samples containing differing levels of styrene (STY) and 
methylmethacrylate (MMA). Reagent grade cyclohexanol and for the 
comparative polymers a solvent mixture of toluene/methanol (90/10) were 
used to dissolve the various polymer samples. In the case of the 
cyclohexanol solvent, the cyclohexanol and polymer were initially heated 
at approximately 50.degree. C. to dissolve the polymer. Once the samples 
were dissolved, approximately 150 grams of solution was transferred to a 
300 ml pressure reactor. The reactor contents were thoroughly flushed with 
nitrogen, evacuated to approximately 10 mm Hg, and loaded with methylamine 
to give a 1:1 ratio based on MMA content. The reactor was then heated to a 
reaction temperature of 230.degree. C. The reactor pressure typically 
ranged from 2 to 4 MPa depending on the solvent system, quantity of amine, 
etc. The reaction was allowed to proceed for a total of ten hours. Once 
the reactor pressure had subsided, the contents were drained into an 
aluminum foil pan and thoroughly devolatilized for approximately 1-2 hours 
at 220.degree. C./4 Torr. The polymer samples were then compression molded 
for polymer evaluation. The results of this study are shown in Table I. 
In Table I the physical properties of the initial methacrylate polymers 
prior to amination and cycloimidization, the comparative polymers 
(comparative) and polymers according to the invention are reported. 
Molecular weights (Mw) were measured by gel permeation chromatography 
(GPC) utilizing a polystyrene standard. 
TABLE I 
__________________________________________________________________________ 
Composition (mole %) Tg Mw .times. 
Flex Stress 
Flex Modulus 
MFR* 
Example 
S MMA meMAM 
meGI 
(.degree.C.) 
10.sup.3 
Mw/Mn 
psi (MPa) 
psi (MPa) 
(I) 
__________________________________________________________________________ 
Initial 
34 
66 -- -- 108 
96 1.9 12,100 
(83) 
437,000 
(3000) 
15.9 
Compara- 
46 
-- 13 41 153 
94 2.1 13,300 
(92) 
552,000 
(3800) 
0.9 
tive 
1 46 
-- 13 41 159 
86 1.9 9,600 
(66) 
544,000 
(3800) 
1.0 
Initial 
63 
37 -- -- 105 
130 2.0 10,700 
(74) 
432,000 
(2900) 
29.7 
Compara- 
69 
-- 15 16 141 
111 2.2 11,200 
(77) 
500,000 
(3500) 
3.7 
tive 
2 69 
-- 15 16 145 
113 2.3 11,000 
(75) 
522,000 
(3600) 
3.9 
__________________________________________________________________________ 
S = styrene 
MMA = methyl methacrylate 
meMAM = Nmethyl methacrylamide 
meGI = Nmethyl dimethylglutarimide 
*MFR (I) = melt flow rate g/10 min. Condition IASTM D 1238