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Cationic Polymerization of Lactams.

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i.e., pure carbonium ion mechanism. Interpretation is
provided by the relative strengths of the interaction between
cation and halogen on the one hand and between anion and
H o n the other. If the two interactions are comparable in
strength, the E2 mechanism is found to operate; if interaction
between cation and halogen is the stronger, the El mechanism
is observed.
Stereoselectivity decreases with rise in temperature.
temperatures above 190 O C , this compound cyclizes
partially at the terminal NHz group with loss of water.
[VB 116 1El
Lecture at Koln (Germany) on November 24, 1967
German version: Angew. Chem. 80, 242 (1968)
[*] Prof. Dr. M. Rothe
~
[*I Prof. Dr. H. Noller
Physikalisch-Chemisches Institut der Universitat
8 Miinchen 2, Sophienstr. 11 (Germany)
Cationic Polymerization of Lactams
By M. Rothe[*]
Polymerization of lactams by Brernsted acids (protic acids,
ammonium salts, HzO) and by Lewis acids[1,2J can be
assigned similar types of mechanism in which the active end
of the chain is always an ammonium ionL31. Chain growth
can occur after proton exchange with lactams; the lactam
cation that is formed acylates the amino group thus freed.
0
M N H z + CO(CHz),NH2
(1)
0
*NH-CO(CH~),NHS
Differences in the course of polymerization with different
initiators can be ascribed t o the mechanism of the corresponding starting reactions as well as t o side reactions brought
about by the different end groups formed [(a) carboxyl, (b)
N-acyllactam, (c) amidine groups 1411; such end groups can
contribute t o different types of chain growth (a, b) or lead
to chain termination (c). Also of importance are ring size and
substitution of the lactam: 5- and 6-membered lactams give
only short-chain oligomers; N-methylcaprolactam does not
react, but N-methylaminocaproic acid forms the lactam
quantitatively with cationic initiators; 8- and higher-membered lactams, on the contrary, give polymers almost
quantitatively because termination with amidine formation,
which must lead t o rings of medium size, does not occur.
Polymerization with protic acids (halogen hydrides. various
phosphorus and sulfonic acids, picric acid, CF3COOH) occurs
with acylation of the lactam by the corresponding lactam
salt to form the N-(o-aminoacy1)lactam salt.
CO(CH2),NH
+
0
CO(CHz),NHz
(2)
This and the next higher oligomers were detected, as previously with caprolactam 111, during polymerization of the
other Iactams mentioned by IR spectroscopy and by electrophoresis with help of the hydroxamic acid reaction. Model
reactions with oligomers confirm the mechanism assigned.Acy1lactams react with ammonium groups with fission of lactam 151
(chain growth o n the C-terminal end); this is indicated by a
decrease in the acyllactam content of the polymer during
polymerization, as determined titrimetrically and by IR
spectroscopy.
The amidine formation was demonstrated chromatographically in the oligomer region, which is easier t o study, for
H2N(CHz)5CO-[NH(CH2)5C0]2-NHCH2C~H5.HCl;
at
Angew. Chem. internat. Edit.
1 Vol. 7 (1968) 1 No. 3
Lewis acids (BF3, PzO5) and lactams give adducts that acylate
monomers in accord with eq. (2). However, polymerization
occurs only in presence of cocatalysts (HzO), the H[BF30Hl
formed acting as protic acid.
IVB 117 1El
Lecture at Ziirich (Switzerland) on December 14, 1967
German version: Angew. Chem. 80, 245 (1968)
Organisch-Chemisches Institut der Universitat
65 Mainz, Johann-Joachim-Becher-Weg 18-20 (Germany)
[l] M. Rothe, G. Reinisch, W . Jaeger, and I. Sthopov, Makromolekulare Chem. 54,183 (1962); M. Rothe, H. Boenisch, and D . Essig
ibid. 91, 24 (1966).
[2] M. Rothe, D . Essig, G. Gabra, and J. Muzanek, unpublished.
[3] F. Wiloth, Makromolekulare Chem. 27, 37 (1958); D . Heikens,
P . H . Hernians, and G . M . van der Want, J. Polymer Sci. 44, 437
(1960).
[4] P. Schluck, lecture, Berlin 1965.
[5] Cf. S. Doubravszky, and F. Geleji, Makromolekulare Chem.
105, 261 (1967).
Thermokinetic Measurements
By F. Becker[*l
The principle of thermokinetic measurements is t o follow
the progress of a chemical reaction by means of its evolution
of heat. Apart from the fact that it gives heats of reaction
as well as velocity constants, the method has the advantage
that the output dQR,’dt can be recorded as a function of the
heat of the reaction QR as the reaction proceeds; and the rate
laws are thus evaluated directly in their simple differential
form. For a reaction of the first order the function dQR/dt =f(&) is a straight line with the slope k l ; its intercept with the
abscissa represents the heat of reaction for complete conversion. For a reaction of the second order with equal
initial concentrations, recording the function [ d Q ~ / d t’h
] ~=
f(QR) gives a straight line that can be evaluated equally
simply.
Two methods were used for experimental realization of this
measuring principle. The first is isothermal calorimetry with
controlled Peltier cooling, in which the cooling current from
a semiconductor Peltier battery in thermal contact with the
reaction vessel is controlled so as to provide a cooling output
equivalent at each moment t o the heat output of the reaction,
whereby the initial temperature of the calorimeter is unchanged. The measuring signal is then a voltage proportional
t o the cooling current i,, which is recorded by a two-coordinate pen as function of the integral Jik dt provided by an
electronic integrator. The second method is “quasi-isothermal” heat flow calorimetry, in which the temperature
difference 4 T between the calorimeter and the thermostat
liquid, which is proportional to the heat flow dQ/dt, is
used as measuring signal and a function analogous to
dQ/dt = f(Q) is recorded, again by means of an electronic
integrator and, when required, a root function generator.
Sufficient heat flow is provided so that AT remains
< 0.05 deg, whereupon the temperature-dependence of the
rate constants can be neglected. A theoretical study was made
of the conditions under which the relation of heat flow
dQ/dt t o total heat removed Q has the same mathematical
form as the thermokinetic rate law dQR!’dt = f(QR).
Examples of reactions were provided t o show that these
methods enable rate constants t o be determined within 3- 1 ”/,
and reaction enthalpies within :+ 2 % , 25 ml of 0.02-0.04
molar solutions of reactants and reaction times of 5-10 min
sufficing for this purpose.
Lecture at Bonn (Germany) on November 28, 1Q67
[VB 120 IE]
German version: Angew. Chem. 80, 242 (1968)
[*] Prof. Dr. F. Becker
Institut fur physikalische Chemie der Universitat
66 Saarbriicken 15 (Germany)
233
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lactam, polymerization, cationic
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