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Effects of Long-Chain Branches on the Degradation Kinetics of Polymers.

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Effects of Long-Chain Branches on the Degradation
Kinetics of Polymers
CH3
R
(4)
The deuteration pattern of the amines obtained indicates
that the reaction proceeds, as previously suggested, via an
immonium formate, which is then reduced by deuteride
transfer to the amine.
c =o
DCOOO
<&a
Procedure
A solution of 3-(p-tert-butylphenyl)-2-methylpropanol
(10.2g, 0.05mol) in toluene (70ml) is treated with cis-2,6dimethylmorpholine (6 g). After azeotropic removal of the
water with toluene (which distills over until an internal flask
temperature of ca. 120°C is reached), 2.5g of (2) in 5ml
toluene is slowly added and the mixture of amines (3) and
( 4 ) finally distilled at 142--145"C/0.3 torr. In the case of
( 6 ) and (7) the {'HJ-noise-decoupled I3C-NMR spectra
show a triplet at 6=64.77, and in the case of (9) a triplet
at 6=31.82; in all cases by coupling with the deuterium nucleus. (3) and ( 4 ) each show two triplets at 6=64.53 and
31.71. The 'H-NMR spectra of ( 6 ) and (7) with signals
at 7.3 (2, d), 7.1 (2, d), 3.7 (2, t), 2.8 (1, m), 2.7 (1, m), 2.35
(1, m), 2.2 (1, m), 2.15 (1, m), 2.0 (1, m), 1.7 (2, m), 1.3 (9,
s), 1.15 (6, d) and 0.85 (3, d) confirm this assignment by
the changing signal splitting; ( 3 ) and ( 4 ) as well as ( 6 )
and (7) are present as 40: 60 mixtures.
Received: January 31, 1979 [Z 184 IE]
German version: Angew. Chem. 91, 341 (1979)
CAS Registry numbers:
( I ), 69668-13-9;(2), 920-42-3;(3), 69668-14-0;(4), 69743-83-5;( 5 ) , 91771-5; ( 6 ) , 69668-15-1 ; (7), 69743-84-6;( S ) , 925-94-0;(9), 69668-16-2;
3-(p-terr-hutylphenyI)-2-methylpropanal,
80-54-6;cis-2,6-dimethylmorpholine, 6485-55-8
[1] P. de Benneuilk, J. Macartney, J. Am. Chem. SOC. 72, 3073 (1950).
[2] 13C-NMR (Bruker WH-270, CDCl3, TMS int.): 6=148.19 (I, s), 137.77
(1, s), 128.90 (2, d), 124.80 (2, d), 71.53 (2, d), 64.99 (1, t). 60.09 (1,
t). 59.98 (1, t), 40.75 (1, t). 34.20 (1, s), 32.04 (1,d), 31.47 (3, q), 19.12
(2,4). 18.04 (1, 4).
[3] N. J . Leonard, R . R . Sauers, J. Am. Chem. SOC. 79, 6210 (1957); J .
J . Panouse er a/., Bull. SOC.Chim. Fr. 1963, 1753.
By Klaus H . Ebert, Hanns J . Ederer, and Arno M a x Basedow"]
Dedicated to Professor Horst Pornrner on the occasion of his
50th birthday
Experimental investigations on the kinetics of the hydrolytic
degradation of dextran in solution[' showed that small molemles are formed more frequently than should be the case
in a random reaction. O n assuming, firstly that the dextran
molecules are unbranched, and secondly that the "individual"
degradation constants ( K J along the polymer chain vary
according to a parabolic function, we could establish the
curvature of this parabola as b =0.4 from experimentally determined molecular-weight distributions via the combined
polydispersity ratio CPR = A?$/@,, .M,) by mathematical
simulation. This means that the polymer bonds at the ends
of the molecule are about three times more reactive than
in the center of the molecule. Freudenberg, Kuhn, et u/.['I
likewise deduced a non-random degradation from the acid
hydrolysis of cellulose and starch.
The assumption that the dextrans are unbranched is especially critical, since the experimentally determined molecularweight distributions of the degradation products can in principle also be explained by long-chain branching and random
degradation (see ['I).
Relatively little is known about branching in dextranL3.'I.
Dextran obtained enzymatically from Leuconostoc Mesenteroides B 512 F has, at most, branching on 5 % of its repeating
units[51.Of these at most 15 % are longer than two glucose
unitsL6],so that the proportion of branching points with sidechains longer than ten monomer units can be assumed to
be about 0.1 %, i.e. for every 1000 structural moieties there
is one long-chain branch. Short-chain branches (side-chain
lengths < five monomer units) do not influence the molecular
weight distribution of the degradation products.
We have investigated the influence of long-chain branching
on the product distribution in a random degradation reaction
by mathematical simulations of various branched model molecules, which were generated by a Monte Carlo method.
The results are expressed in terms of the dependence of KS,l
on 1. Here K s , l is the rate constant for the cleavage of a
molecule having a degree of polymerization s into two fragments with degrees of polymerization 1and s-1. For unbranched
molecules, Ks,l is a measure of the probability of cleavage
at site 1. These diagrams are identical with the molecular
weight distributions obtained, assuming every molecule has
undergone a simple chain rupture.
Our model calculations are based on molecules having
a degree of polymerization of 1000 (Table 1). Model 1 is
for singly branched molecules in which the length and position
of the side-chain are randomly distributed. In models 2 and
3 the number of long-chain branches is increased respectively
to three and seven, while the lengths and positions of the
side chains are again randomly distributed; however, only
one side chain can branch at each position of the main chain.
Figure 1 a shows that the curvature of the curves increases
with increasing number of branches. The effect is very
pronounced even with one side chain; the curve is almost
parabolic with b=0.8. The unbranched molecule gives a
straight line parallel to the abscissa at 1.
[*]Prof. Dr.K. H. Ehert, Dr. H. J .
321
Anqew Chem I n t Ed Engl 18 (1979) N o 4
0 Verlag Chemie, GmbH, 6940 Weinheim, 1979
Ederer. Dr. A. M. Basedow
Institut fur Angewandte Physikalische Chemie und SFB 123 der Universitat
Im Neuenheimer Feld 253, D-6900 Heidelberg 1 (Germany)
0570-0833/79,0404-0321$ 02.50/0
Table I . Parameters of model molecules. s=degree of polymerization = 1000, h=length of the main chain, u,=length of the side chain ( i = 1 ... z ) , z=number of
side chains, p, = position of the branch i on the main chain, rnd. (x ...y ) = random choice within interval (x . . . j )R,E = residue of s not used in the selection process.
-
2
Model 1
4
3
5
6
7
to
10
10
-
h
G;
.
md. (1 . ..s - 1 }
rnd. {3.. .s - 31
md. {X.. ,s -8)
vl=~-h
u I = m d . (1 ...s - 1)
UI
u2 = rnd. { l ... RE - 1 }
=RE
Z
1
p,
rnd. { I
Fig.
1a
. ._h - 1 }
=rnd. (1 ...s -h}
ui = m d .
(1 ...RE-(2-i)}
s / 2 = 500
ui=rnd. /30 ... 80;
G, =rnd. {20...220} u1 = m d . { 1 .. . %(s-h))
RE rnd. distributed RE c o x . like 4
over ui
v 2 - 8 = md. ( 1 ... RE,}
for 1 i i i 7
v,=RE
u1 = m d . { 1 ... s -h}
L
)
v g = RE
~
=
- ~rnd. (1 . _ 2
./3
RE,]
=RE
3
7
9
9
9
9
rnd. { l .. .h - 1 }
each pi selectable
only once
rnd. like 2
md. like 2
i
i
i
la
la
Ib
lb
Ic
Ic
-
of the products in degradation reactions. From the shape
of the distributions, quantitative information can be gained
about the number of branches and lengths of the side
chains, and sometimes also about the main chain. Thus, e. g.,
from our experiments on dextran it can be concluded, assuming
random probability of cleavage, that the number of long-chain
branches lies below 0.2 %.-For a more accurate analysis
of the long chain branching, the shape of the K S , ,curve should
be determined from the experimental molecular weight distributions, and not only from molecular weight averages and
the CPR.
R 1
Idl
h
3!\
Received: February 5, 1979 [Z 185 IE]
German version: Angew. Chem. 91, 341 (1979)
~~
[l] A . M. Basedow, K . H . Ebert, H . J . Ederer, Macromolecules 11, 774
Fig. 1. Dependence of the rate constants Ks,, on the degree of polymerization
1 of the fragment (K*=experimental degradation constant). The curves are
model 3; b)
model
symmetric about s/2. a) A model 1, 0 model 2,
4, model 5; c) model 6, model 7.
Model 4 contains nine long-chain branches and the main
chain is as long as the sum of the side chains; these were
varied randomly between 30 and 80 monomer units. The
branching points on the main chain were likewise randomly
chosen. In model 5 the main chain was shortened to ten
monomer units and the lengths of the side chains distributed
randomly between 20 and 220. Model 4 can be regarded
as a “comb”, model 5 as a “star”. Figure 1 b shows that
shorter side chains lead to higher K,,,-values at small I-values;
in the case of larger /-values (up to 4 2 ) longer side chains
and the main chain are decisive. The models 6 and 7 are
“stars” with a greater distribution in the length of the side
chains. Model 6 permits a random choice of z/3 of the residual
monomer units available in the generating process, in the
case of model 7 the lengths of the side chains are chosen
randomly (Fig. Ic) from the total number of the residual
monomer units (Table 1). Model 6 contains more side chains
with average degrees of polymerization; hence the curve falls
more slowly at low /-values. In the random model 7 the
number of large fragments is greater; hence the larger values
near to the center of the molecule 42.
Our models cover all polymer molecules without compound
branches as well as all molecules in which double branching
is peripheral. More strongly branched or crosslinked molecules
require more complicated models.
Our simultaneous show that long-chain branches have considerable influence on thedistribution of the molecular weights
322
(1 978).
[2] K . Freudmberg, W Kuhn, W Diirr, F. Bolz, G . Steinhrunn, Ber. Dtsch.
Chem. Ges. 63, 1510 (1930).
[3] K . H . Eberr, M. Brosche, Biopolymers 5 , 423 (1967).
[4] K . H . Eberr, G . Schenk, Adv. Enzymol. 30, 179 (1968).
[ 5 ] K . Frombling, F. Patot, Makromol. Chem. 25, 41 (1957).
161 0. Larm, 8.Lmdbery, S. Szensson, Carbohydr. Res. 20, 39 (1971).
tvans-Bis(l-alkynyl)-4B-metalPhthalocyanines[**l
By Michael Hanack, Konrad Mitulla, Georg Pawlowski, and
L. R. Subramanian[*I
Dedicated to Professor Horst Pommer on the occasion of his
60th birthday
Monomeric phthalocyanine derivatives of type ( 3 ) of elements of the 4th main group having two axial metal-carbon
bonds are model substances for new polymer structures, which
according to EHMO calculations ought to show pronounced
electrical conductivity“].
Octahedral silicon phthalocyanines having one axial Si-C
bond have already been reported[’]; and the tin phthalocyanine
( 3 ) , R = C6H5,has been synthesized, but only in 1% yieldc3].
Analogous meso-tetraphenylporphyrins were recently described14!
We obtained trans-bis(1 -alkynyl)-4B-metal phthalocyanines
( 3 ) in yields of about 90 % by reaction of the corresponding
[*] Prof. Dr. M. Hanack, Dip1.-Chem. K. Mitulla, DipLChem. G. Pawlowski,
Dr. L. R. Subramanian
Institut fur Organische Chemie der Universitat
Auf der Morgenstelle 18, D-7400 Tubingen 1 (Germany)
Part 3 of The Synthesis and Properties of Novel One-Dimensional
Conductors.-Parts I and 2: [l].
[**I
Angew. Chem. Int. Ed. Enyl. 18 (1979) No. 4
0 Verlag Chemie, GmbH, 6940 Weinlreim, 1979
0570-0833/79/0404-0322 $ 02.SOjO
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