Synthesis and analysis of ethylene-neohexene copolymers with other non ketene-imine group free radicals for solid and hybrid grain propellant saturated hydrocarbon binder progra

Ashcraft, A. C., Jr.

Potts, J. E.

Sullivan, E. M.

Wise, E. W.

English

NASA Technical Reports Server

I '  
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I 
SATURATED HYDROCARBON POLYMERIC BINDER FOR 
ADVANCED SOLID PROPELLANT AND HYBRID SOLID GRAINS 
QUARTERLY REPORT NO. 2 
PERIOD COVERED: February 1, 1966- 
April 30, 1966 
This work was performed under Contract #951210 with the 
Jet Propulsion Laboratory, California Institute of Techno- 
logy, Pasadena, California, sponsored by the National Aero- 
nautics and Space Administration under Contract NAS7-100. 
1 JPL Technically Managed By: F. J. Hendel H. E. Marsh, Jr. 
Report Edited By: 
Contributors : 
James E. Potts 
A. C. Ashcraft, Jr. 
James E. Potts 
E. M. Sullivan 
E. W. Wise  
UNION CARBIDE CORPORATION 
PLASTICS DIVISION 
Polymer Research and Development Department 
. Bound Brook, New Jersey 
https://ntrs.nasa.gov/search.jsp?R=19660022638 2020-03-16T21:13:37+00:00Z
I. OBJECTIVE 
11. SUMMARY 
III. SCOPE OF PROJECT 
W .  INTRODUCTION 
V . TECHNICAL DISCUSSION 
Page 
1 
1 
1 
2 
3 
A .  Preparation of Ethylene-Neohexene Copolymers 3 
Using Organic Peroxide Initiators 
B. Preparation of Diethyl 4 ,d 'asobis -  isobutyrate 9 
(DEAB) and Measurement of Rate of Thermal 
Decomposition . 
VI. 
1. Preparation of DEAB 9 
2. Rate of Decomposition of DEAB 11 
C . Ethylene-Neohexene Copolymers Prepared with 13 
DEAB 
PLANS FOR FUTURE WORK 15 
Union Carbide Corporation, Plastics Division, has agreed 
to provide, on a level of effort basis, between 49 and 55 direct man 
months of effort to assist the Jet Propulsion Laboratory in the develop- 
ment of a new o r  improved polymeric binder for advanced solid propellant 
and hybrid solid grains. 
Quarterly Report No. 1. 
The detailed objectives were  described in 
II. SUMMARY f f 7 g  3f / @  
Ethylene-neohexene prepolymers were  prepared using the 
organic peroxides succinic acid peroxide and glutaric acid peroxide. 
These initiators result in acid terminated prepolyrners which a re  quite 
high in viscosity considering their molecular weights. Esterification 
of the acid end groups resul ts  in a drastic decrease in viscosity, which 
is attributed to elimination of hydrogen bonding association. Function- 
alities approaching two carboxyl groups per molecular have been obtained 
based on molecular weight determinations in benzene. 
determinations in polar solvents such as tetrahydrofuran yield function- 
alities closer to one. 
Molecular weight 
Diethyl o(,&-azobis-isobutyrate has been prepared and its 
kinetics of thermal decomposition measured at 100'C. 
been used to make three copolymerizations which proceeded very smoothly. 
The products a re  being hydrolyzed and characterized. 
This initiator has 
111. SCOPE OF PROJECT 
The scope of this work has not changed from the program 
outlined in the work statement. The major emphasis has been placed on 
selecting a suitable initiator for preparation of the required prepolymer. 
- I -  
_#  
I' 
. 
IV . INTRODUC T€ON 
The first quarterly report described the preparation of 
saturated, amorphous ethylene-neohexene copolymers containing ter- 
minal carboxylic acid groups by the free radical high pressure copoly- 
merization of ethylene and neohexene using azobis-isobutyronitrile a s  
initiator followed by hydrolysis of terminal CN groups to COOH groups. 
These products were  liquids a t  mom temperature which cured with a 
formulation suggested by JPL to yield soft gels. Further examination 
of these products showed that, contrary to expectation, two types of 
end groups re su l t  from the use  of AIBN as initiator and terminator. 
About 5070 of the end groups a re  CN while the other half a re  ketene- 
imine groups. The latter a r e  removed from the polymer by alkaline 
o r  acid hydrolysis. 
of a mixture of: 
The resulting prepolymer is, therefore, made up 
The present report is concerned with the synthesis and 
analysis of ethylene-neohexene copolymers made with other free radi- 
cal initiators which are known not to resu l t  in ketene-imine groups 
being placed in the polymers. 
initiators and azo initiators. 
These fall into two classes, peroxide 
The following sections describe and interpret our experi- 
mental resul ts  for the period February1 - April 30, 1966 and outline 
our plans for future work. 
- 2 -  
V .  TECHNICAL DISCUSSION 
A. Preparation of Ethylene-Neohexene Prepolymers Using Organic 
Peroxide Initiators 
These experiments were carried out using succinic acid per- 
oxide and glutaric acid peroxide. The former was  obtained from the 
Lucidol Division of Wallace and Tiernan, Inc. while the latter was synthe- 
sized within the Corporation. Their s t ruc tures  are: 
0 8 2  q 2  9 0 8 2  H2 P 
HO-k-C-C-C-O-O- \ i=  -C-&-C-OH 
Succinic Acid Peroxide (SAP) 
0, H2 H 2  H 2  ,p 0 I 8 2  7 2  8 2  ,? 
HO - c - -e- C- C- 0- o - c - c -C - c -C -OH 
Glutaric Acid Peroxide (GAP) 
These peroxides decompose at the peroxide linkage, eliminate 
C02 and form primary radicals, which initiate polymerization. 
Table I lists data for the preparation of GAP initiated pre- 
polymers with tetrahydrofuran as solvent, and for two SAP runs made 
using dimethyl formamide and acetone as solvents. 
not dissolve in benzene. 
dibutyric acid) as a chain terminating agent. 
These initiators will  
Run 43 w a s  made with GAP and DTDBA (dithio 
The functionality of products 31, 34 and 38 w e r e  all low, 
regardless of whether the acid number o r  the oxygen analysis was used 
to compute the molecular weight equivalent to one carboxylic acid group. 
The product from run 35 contained nitrogen, indicating that this solvent is 
an active transfer agent. Run 36 gave only one gram of product. 
- 3 -  
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TABLE 11 
Ethylene-Neohexene Copolyniers - Succinic Acid Peroxide Runs 
RunNo. 22EMS 
Initial Chame 
Solvent 
Neohexene , gms. 
Initiator 
Ethylene , gms. 
wt. p s  
wt. gms. 
Fed During Reaction 
Solvent, gms. 
Initiator , gms. 
DTDBAj &mS. 
Reaction Conditions 
Temperature, 'C 
Pressure , psig 
Initial 
Final 
Reaction Time 
Productivity 
Yield, -8 
Conversion , 96 
Rate , %/hr. 
In Benzene-Tertiary Butanol Mixed Solvent 
62 64 66 70 
- 50/50 Benzene/t'-BuOH 
410 402 
315 3 15 
SAP SAP 
21.6 30.2 
116 116 
222 222 
22 22 
- -  -- 
95 95 
10 0 800 
a g e  7700 
Plugged 
3.5 1.5 
7 . 0  22 
1.6 5.1 
0 .5  1.02 
- 5 -  
99 
494 
SAP 
5 
1000 psi 
at RT 
480 
51 
-- 
100 
2225 
15 , 000 
4.25 
104 
15.4. 
4.4 
99 
4 84 
SAP 
5 -- 
16 1 
495 
45.5 -- 
110 
850 
16 , 000 
2.0 
a4 
13 
6.5 
The low functionality in these runs was  attributed to solvent 
chain transfer effects primarily. rrlthough the possibility t h ~ t  these catalysts 
might possess transfer activity was not ignored. It was decided to search 
for a solvent which would dissolve both the acid catalyst and the polymer and 
not be an active transfer agent. A 50/50 mixture of benzene and tertiary 
butanol was found to dissolve DTDBA whereas benzene would not. However, 
no good solvent for SAP which was low in transfer activity was found. 
Table I1 lists those runs made with SAP initiator where the 
mixed benzene/ € -BuOH eolvent wa8 used. Run 62 wae made with all SAP 
charged initially and a solution of DTDBA charged during the reaction. A 
low yield indicated that the DTDBA acted as a retarder; 68% of the DTDM 
was recovered unchanged. Run 64 was a repeat of 62 using one third more 
catalyst. This tripled the yield compared to Run 62. 
Run 66 utilized a slurry technique for feeding SAP. A 50/50  
mixture of benzenelt -BuOH was used to slurry the SAP which was kept in 
suspension by cycling past the suction check of a high pressure injection 
pump using a Viking gear pump. The rupture disk on the pump blew which 
terminated the run. This w a s  caused by a plugged feed line. However, 
this run gave 100 grams of product, which reflected the absence of DTDBA 
and the continual replenishment of initiator during the run. 
Run 70 was a SAP slurry run similar to 66 except that the 
temperature was increased 10" to 110" and the catalyst feed rate w a s  doubled 
which halved the reaction time. The yield was 84 grams. In order to scale 
up this run safely it would be necessary to place the recycling slurry behind 
an explosion proof barricade and install  remote control equipment. Scale 
up to a 2 gallon autoclave would necessitate recycling 2/3 of a pound of per- 
oxide in slurry. The danger arises in injecting the peroxide slurry with a 
high pressure piston pump. Crystals of peroxide might be detonated by 
friction if caught between the piston and cylinder walls. 
Run 64 gave a gross product of molecular weight (benzene) 
The acid 769 and Brookfield viscosity 27,000 cps at room temperature. 
number was  170.4. This results in an apparent functionality of 2.34 
acid groups per molecule. 
one S atom per COOH group) the functionality was 3.05 COOH groups per 
molecule. This product later separated into two phases and was  not fur-  
ther investigated. 
From a sulfur content of 12.69% (assuming 
- 6 -  
I' 
The following characterization data were  obtained for the product 
fron; R m  66. 
Brookfie Id Viscosity 238,000 cps 
Molecular Weight in Chloroform 1432 
Molecular Weight in THF 1465 
Molecular Weight in Benzene 2198 
Neutralization Equivalent 1630 
The functionality calculated from these data are: 
- -  F (Benzene) - 2198 - 1.34 COGH groups/molecde 
16 30 
F (CHC13) - 1432 = 0.88 COOH groups/molecule 
1630 
- F (THF) - 1465 = 0.90 COOH groups/molecule 
1630 
This product was reacted with thionyl chloride to convert the 
COOH groups to COCl groups. This lowered the viscosity from 238,000 
to 90,000 cps as a result of elimination of hydrogen bonding. 
chloride was  converted into the ester which reduced the viscosity to 
12,000 cps. 
on viscosity of eliminating hydrogen bonding. 
The acid 
The drop from 238,000 cps to 12,000 cps illustrates the effect 
The following characterization data were obtained for the 
product from Run 70. 
Molecular Weight in Benzene 1453 
Brookfield Viscosity 87,500 cps 
Oxygen Concentration 6.6570 
Acid Number 76.8 
Neutralization Equivalent 7 31 
Functionality = - 1453 = 1 a 98 COOH/molecule 7 31 
- 7 -  
I '  
This product was further purified and resubmitted for molecular 
weight and acid number with the following results: 
Molecular Weight in Benzene 
Molecular W e i g h t  in THF 
Ne ut ralization Equivalent 793 
11 34 
7 91 
= 1.43 1134 7 93 Functionality (Benzene) = - 
= 0.999 791 7 93 
= -  Functionality (THF') 
The Brookfield Viscosity of this product was  87 , 500 cps , which 
is quite high for a material with a number average molecular weight of 791. 
To test the possibility that this anomaly is due to hydrogen bonding associa- 
tion the acid terminated product w a s  esterified. Conventional Fischer 
esterification, with ethanol and p-toluene sulfonic acid did not proceed to 
conpletion; however, the partially esterified product had a viscosity of 
8,000 cps. By thionyl chloride treatment followed by reacting the acid 
chloride with ethanol in the presence of pyridine the residual COOH groups 
w e r e  converted to COOC2H5. 
only 230 cps, which confirms the hypothesis that COOH association caused 
the high viscosity of the acid product. The number average molecular 
weight of the esterified product was 880, showing that no degradation of the 
product occurred. 
The viscosity of the esterified product was 
The low functionality of the SAP initiated product made in 
mixed benzene/ t -butanol suggests that SAP itself is a chain transfer agent. 
A desirable alternate catalyst is tetramethyl succinic acid peroxide. 
This catalyst contains no hydrogen atoms alpha to a carboxyl 
group and is not likely to undergo chain transfer reactions. The precursor 
of this catalyst, tetramethyl succinic acid is available. 
I '  
B. Preparation of Diethybd,,o(!Azobis- isobutyrate Initiator and 
Measurement of Rate of Decomposition I -  
1. Preparation 
Diethyl- c+f,#dzobis-isobutyrate (I) DEAB can be prepared 
by two routes at present. 8 
The first s tar ts  with the condensation of acetone with hydra- 
zine in the presence of HCN to give o(,e(ihydrazobi&sobutyronitrile, 11. 
I 
CH3 P 3  
2 [ Z O  + NHZNHZ+ ZICN+NiC-  -T+-C-mN 
H3 $H3H k bH3 
I1 
I 
I 
I 
I 
I 
8 
I 
I. 
This material can be hydrolyzed to the dicarboxylic acid I11 
and then esterified with ethanol to  give the diethyl- d,o('-hydrazobis- 
isobutyrate, IV. 
H I11 
- 9 -  
The hydrazoester IV can be oxidized to I by a variety of 
methods: 
An alternate procedure is to oxidize I1 to gived ,d;'-azobia- 
isobutymnitrile (AIBN) and then react AIBN with HC1 in anhydrous etMno1 
to give the iminoether hydrochloride V. 
V 
Mild hydrolysis of V gives I directly. 
I 
The procedure adopted was the latter, using commercially 
available AIBN. This provided I in two steps which are easily carried out 
in the laboratory. The former route is more economical for production 
purposes. 
- 10 - 
2. Rate of Decomposition of DEAB 
Diethyl- 48 4’azobis -isobutyrate@EAB) decomposes smoothly 
when heated to yield nitrogen gas 
I 
CH3 
and free radicals: 
I 
The carbethoxy group in the radical derived from s t ruc ture  I 
stabilizes the radical in much the same way a s  the CN group stabilizes the 
cyanoisopropyl radical derived from AIBN . 
The kinetics of decomposition of I in xylene solution at 100°C 
was  studied. The evolved nitrogen w a s  collected in a gas burette and the 
volume, Vt, measured as a function of time. After the reaction had gone 
to completion the total volume of evolved nitrogen, V- , was  measured. 
At any time, t, the quantity Vao- Vt represents the amount of nitrogen yet 
to be evolved and hence is proportional to the amount of I remaining in the 
reaction mixture. Vd is proportional to the original amount of I, therefore 
the ratio, [Ve -Vt] Va, represents the fraction of I remaining in the 
reaction mixture at time t. According to the u s u a l  kinetic procedure for 
first order reactions, a graph of the logarithm of the fraction of I remaining 
in the reaction mixture plotted versus time gives a straight line passing 
through the origin, with a slope of -K/2.303, where K is the first order rate 
constant. 
Since -log Bv---Vt) + vS] = +log [v-+(vd - vt)] , 
we plotted the latter quantity versus time a s  shown in Figure I. At  100°C 
the rate constant was 0.0645 reciprocal minutes and the half life was 
10.7 minutes (compared with 7 minutes for AIBN). 
- 11 - 
I’ 
I * _  
8 -  
FIGURE I 
8 
I: I a 2  
I 
8 t a 0  
R .2 
8 0 
8 
IO  20 30 40 so 
TIME ( TI MINUTES 1 
KINETICS OF DECOMPOSITION OF 
II DIETHYL- a ,a', AZOBIS-ISOBUTYRATE (DEAB) 
IN XYLENE AT IOWC 8 
- 12 - 
C . Ethylene-Neshexene Copolymers Prepared with DEAB 
Table III lists the reaction conditions used in preparing the first 
series of copolymers with the new catalyst. 
benzene at 9O"C, a solvent in which al l  the components in the reaction a re  
soluble, including DEAB. In order to traverse the molecular weight range 
of interest in this work, the catalyst concentration was varied as was  the 
pressure . 
These w e r e  carried out in 
A s  expected, the samples varied in viscosity and molecular 
weight from 200 cps to 2300 cps. In appearance they were pale yellow 
liquids. The end groups a re  esters which are being hydrolyzed to the acid. 
The molecular weight of sample 99 was determined in two 
polar and one non-polar solvent with remarkable agreement. Hydrogen 
bonding is not a problem in the ester terminated products, which accounts 
for the agreement between molecular weight data in benzene and THF and also 
the observed low viscosities. 
It will be recalled that DEAB was thought to be preferable to 
AIBN because of the latter 's tendency to place ketene-imine groups on the 
end of polymer chains. No evidence for the presence of ketene-acetal 
formation in the DEAB polymer has been found, which. is a very encouraging 
fact. 
These products a r e  being characterized as to functionality and 
w i l l  be reported on more fully in subsequent reports. 
- 13 - 
II 
I 
8 
8 
I 
R 
I 
8 
1 
I 
I 
t 
I 
I 
8 
8 
8 
8 
TABLE I11 
Ethylene-Neohexene Copolymers Prepared With DEAB 
Run No. 
Initial Charge 
Benzene, wt. -6. 
Neohexene. pme. 
Ethylene I @ne e 
DEA-B, w e .  
Fed During Reaction 
Benzene, gms. 
DEAB, m e .  
Reaction Conditions 
Temperature, "C 
Initial Presswe, psig 
Final Pressure, peig 
Reaction Time, hrs. 
Productivity 
Yield, gms. 
70 Conversion 
Rate, 70 per hr. 
Physical Properties 
Brookfield Viscosity, 25" , cps. 
No. Avg. Mol. Wt. in 
Benzene 
CHC13 
THF 
98 
30 
472 
10 
l? 8 
270 
90 
90 
990 
2400 
4.5 
176 
27.2 
6.1 
203 
482 
478 
4 84 
10% 
65 
527 
7.2 
195 
105 
65 
90 
1400 
2675 
4.5 
180 
22.7 
5.1 
898 
7 10 
109 
12 
5 91 
4.0 
21% 
145.6 
36.4 
90 
2800 
3625 
4.5 
164 
20.3 
4.5 
2323 
830 
'I + 
8 
I 
VI. P W - S  FOR FUTURE WORK 
During the next quarter it is planned to examine more completely 
the prepolymers which have been made with the initiator DEAB. Additional 
product will  be made using the most promising reaction conditions. 
Dimethyrp(,o('dzobis-isobutyrate DWB, and dineopentyW,o('- 
azobis-isobutyrate, DNAB, wil l  be synthesized using the synthetic route 
described for .DEAB. 
which will be compared to the DEAB initiated products. 
These initiators wil l  be used to prepare prepolymers 
The molecular still wil l  be used to fractionate selected pre- 
The molecular weight distribution and weight 
The W a t e r s  Gel 
polymer samples to determine functionality distribution as a function of 
polymer molecular weight. 
to number average molecular weight ratio wil l  be determined for the gross 
sample and fractions obtained by molecular distillation. 
Phase Chromatography apparatus will  be used in these studies. 
- 15 - 


Saturated hydrocarbon polymeric binder for advanced solid propellant and hybrid solid grains Quarterly report no. 2, 1 Feb. - 30 Apr. 1966

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