Dibenzylic Structures on Macro Molecular

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Pergamon

Eur. fo/w. J. Vol. 32, No. 10, 1235-1242, 1996p.

Copyright 0 1996 Ekevier Science Ltd

PII: S00143057(96)000618Printed in Great Britain. All rights reserved

0014-3057/96 $15.00 + 0.00

DIBENZYLIC STRUCTURES ON MACROMOLECULARCHAIN: IX. THE INTERACTION OF

URETHANE-ISOCYANATE GROUPS IN POLYURETHANE

FORMATION

ADRIAN A. CARACULACU*, IOAN AGHERGHINEI, PAUL BARON, GEORGETACARACULACU and SERGIU COSERI*

Romanian Academy, Institute of Macromolecular Chemistry “P. Poni”, Aleea Gr. Ghica Voda No. 41

A, 6600 Jassy, Romania

(Received 3 February 1995; accepted in fina l form 17 Oct ober 1995)

Abstract-The interaction of isocyanate-urethane and isocyanate-amide groups in urethane groupformation is studied. Bibenzil-2,2’-di-yl diisocyanate (27 BBDI) presents specific behaviour due to thesteric specificity of its structure. Rotation of the two aromatic nuclei around ethylenic bridges favoursstrong intramolecular anchimeric assistance in the second step of the 2,2’ BBDI with n-butanol (BuOH)reaction. This assistance also enhances secondary reactions leading to unexpected cyclic allophanatestructure. Mechanisms for these reactions are proposed in concordance with kinetic measurements.Copyright 0 1996 Elsevier Science Ltd

INTRODUCTION studies concerning the introduction of such structureson a macromolecular backbone, a series of polymers

Dibenzyl structures have variable geometry owing to which contain these structures were presented [l-3].the rotation around the ethylenic bridge. In previous As was pointed out in these studies, a special case was

that of polymers which contain dibenzylic structuresderived from monomers, having their functional

~ groups placed in the 2,2’ position.*To whom all correspondence should be addressed. These polymers are characterized by lower

NC0

+Scheme 1

1235



1236 A. A. Caraculacu et al.

molecular weights compared to those derived fromhomologous monomers substituted in the 4,4’ or 2,4’positions [l-3].

In some cases we have also succeeded in pointingout the formation of small cyclic oligomers [I, 21,even when their appearance implies greater energies

of formation such as the cyclic urea II. This is the caseof the reaction between 2,2’ BBDI and water [l]. Aswas shown, the structure of the cyclic urea II hasaromatic nuclei simultaneously distributed in aneclipsed cis conformation, related to the ethylenicbridge, similar to the structure of the orthocy-clophane [l] (Scheme 1).

Further studies proved that these specific featuresof the isomer 2,2’ BBDI are due not only to any sterichindrance that limits the access of the reactionpartner to the functional groups. It also seems that aconsiderable reciprocal anchimeric assistance be-

tween functional groups in the 2 and 2’ positionsmodifies substantially their chemical behaviourduring the reaction.

Table 1. Model compounds

Typ GHIN(R’)COOR’

NO. R’ R: - Reference

I -H -CHI IO

2 -H _(CHz),CH, 11

3 -H -CHzCH, 10

4 -CH, -CHICHI 13

Type R’-OCONH-(o Ph)

-(CHz),(o Phj-NHCOOR:

R’ R: Reference

5 CH>(CH+ CH,(CH+ 4

6 CHr CH,(CH+ 4

7 CHr CHr 4

Other

8

In a previous work, we have studied the specificbehaviour of 2,2’BBDI in the reaction with BuOH141.After the first sten of the reaction the urethanegioup formed, has’ increased considerablyreactivity of the second NC0 group:

COOBU COOBu

where kz >> ,

Thus when the reaction is performed in benzene,the monoreacted product m is not able to be isolatedeven when working with excess 2,2’ BBDI [4].

On the other hand, the kinetic study of the reactionbetween isocyanates and alcohols or glycols [S-7] hasenabled us to point out some new aspects of themechanism of this reaction in which a decisive role isplayed by the hydrogen bond associated with thealcohol-alcohol or alcohol-urethane types, as well asbetween isocyanate-alcohol or isocyanate-urethaneones.

As the isocyanate-urethane interaction is generallyignored or even doubted [8], we consider that the

study of the reaction between 2,2’ BBDI and BuOHcan offer strong evidence with this subject due to itsspecificity.

Before undertaking the study of the complex

behaviour of the 2,2’ BBDI reaction in the first partof this paper we have attempted to define moreaccurately the influence of urethanes and amides inthe simplest case, represented by the reaction betweenphenylisocyanate (PhNCO) and BuOH. The con-clusions obtained have been verified in the case of the2,2’ BBDI reaction with BuOH.

Necessary model substances for the kinetic studyby high performance liquid chromatography (HPLC)were synthesized (see Table 1).



Dibenzylic structures on macromolecular chain 1237

1

4000 3000 2000 1600 1200 800 600 400

-I

Fig. 1. IR spectra for tht:yclic allophanate, Al.

EXPERIMENTAL

AnalaR PhNCO, minimum 99.9% purity, verifiedchromatographically, was used. 2,2’ BBDI was synthesizedaccording to the data available in the literature [9]. TheNC0 content and purity were established by chemicalmethods [5] and HPLC.

Solvents

Tetrahydrofuran (THF) and benzene (Bz) were dried withsodium and distilled before use. P.a. grade N,N-dimethyl-formamide (DMF) was dried for 24 hr with 2% (weight)4,4’-methylenediphenyldiisocyanate (MDI), at 60°C andthen vacuum distilled. P.a. grade BuOH was dried withcalcium hydride and then distilled.

The melting points were established by means of acapillary tube. IR (KBr pellets) measurements were carriedout on a Specord M 80 Carl Zeiss Jena spectrophotometer.

IH-NMR measurements were performed with a 60 MHzJEOL spectrometer.

Model synthesis

Carbanilic acid methyl ester (CME), carbanilic acid

n-butyl ester (CBE) and carbanilic acid ethyl ester (CEE)models (Table 1, nos l-3) were obtained starting from a 3/lalcohol-PhNCO molar ratio mixture. To the correspondingquantity of the alcohol, a solution of 25% PhNCO in Bz wasadded over 1 hr at 60°C. The reaction mixture wasadditionally stirred for 2 hr and maintained overnight at60°C. After removal of Bz and alcohol excess by vacuumdistillation, the crude product was recrystallized.

Ethylformamide (EFA) and N-methyl carbanilic acidethyl ester (MCEE) (Table 1, no. 4) models were synthesizedaccording to literature methods [l2, 131. 1,2-Ethylenebis(o-carbanilic acid) di-n-butyl ester, 1,2-ethylene bis(o-carbanilic acid) methyl, n-butyl ester and 1,2-ethylene

bis(o-carbanilic acid) dimethyl ester models (Table 1, nos57) were synthesized and purified according to previouslypublished methods 14, 141.

The cyclic allophanate (Al) (Table 1, no. 8) was obtainedas a secondary product of the reaction between 2,2’ BBDIand BuOH in a l/l molar ratio, beside no. 5 representingthe main reaction product. The solvent used was a mixtureof Bz/DMF = 3 (vol.). The insoluble Al in the reactionmixture was separated by filtration and purified byrecrystallization from DMF-H20 l/l vol. mixture. Meltingpoint: 32l-325°C; molecular weight for CXIHZNZOS:calculated, M = 338.41, found = 356 (a Knauer vapour

co-o -CHz-CHI-CH~-CH,

I 3 4 5 6

12

i

1

8 7 6 5 4 3 2 I 0

6 @pm)

Fig. 2. NMR spectra for the cyclic allophanate, Al.



1238 A. A. Caraculacu ef al .

Table 2. HPLC conditions

Mobile phaseRetention tune

Water MeOH Flow Wavelength .__- ____

No. Isocvanate (% vol.) Column (mL:min) (nm) SWXS” Model Mtn

PhNCO 40 60 LichrosorbRP IB-10pm

I 237 ?I’ I 4.45Additwe I 5.41Additive 2 7.43

I 7 10.85

2.2’ BBDl ii 67 LlchrosorbRP 8-10 pm

I 254 II 4.48n, h 8.38Al X 19.5h 5 23.07

“No I 11’= unreacted PhNCO (blocked as I): r = reacted PhNCO (model 2); additwe I = CEE; additive 2 = MCEENo.?. K = unreacted dlisocyanate (blocked as 7); m’ = monoreacted diisocyanates (blocked as 6): Al = cychcallophanate (model X): h = blreacted dlisocyanates (model 5).

pressure osmometer. solvent DMF. was used); elementalanalysis: calculated. C, 70.92; H. 6.1 I; N. 7.98: found: C.70.98; H. 6.55; N. 8.28. IR and NMR spectra arc given inFigs I and 2.

Kinetics

A similar technique to that described previously for

diisocyanateebutanol, PhNCO-glycols or alcohols reactions

was used [5, 141.

HPLC ana1wi.t

A Hewlett-Packard 1084 A chromatograph fitted withUV variable wavelength detector 1030 B was used. Thereversed-phase method was preferred using LichrosorbRP-18 and respective RP-8 columns 10 pm (Brownie Labs.USA) of 250 mm length and 4.6 mm internal diameter.

Injection volume 5 mm3, column temperature 40°C. flow

1 cm’ min-I. The chromatography conditions are given inTable 2.

RESULTS AND DISCUSSION

As indicated in previous work [4] and from Table 3.the urethane (CEE) addition in the reaction betweenPhNCO and BuOH produces a significant increaseof the reaction rate constant. This catalytic action

requires the presence of the urethanic hydrogen in theurethane molecule. The substitution of the urethanegroup hydrogen with an alkyl as in MCEEdetermines the disappearance of the catalytic effect

and even the appearance of an inhibiting effect. Thisinhibition takes place as a result of alcohol oxydrilichydrogen blocking by a hydrogen bond with the

N-alkyl urethane group of MCEE, similar to thecases of the reaction in the presence of esters or of

ethers [4] (Table 3, no. 3).Taking into account the amide group being similar

Table 3. Reaction of PhNCO wth I-BuOH at 60 C

Concentration (mol/l) Extent of secondary reaction (%) with:~~__.. ~_~~ _ . .____.

Alcohol + Ratio Alcohol and x-1x IO’ Trace ofNO. additve OH/NC0 additive PhNCO (mol -I min ~I LJ Solvent DMF” moisture Urethane’ EFA’

I-BuOHI-BuOH

+

CEE

I BuOH

M&EI-BuOH

+DMF

ImBuOH

EZAImBuOH

D&FI-BuOH

2:l2:I

2 I

?:I

0.3502 0. I758 32.92 BZ 0 . 2

0.3506 0. I792 78 32 B7_ 0.3

0.70920.3491

0.1761lb

Ih BZ 17

0.702’)0.3496 0. I706 105.36 BZ

0.70340.3501

0.70930.3499

6.4P0.17.50

0. I747

0 1749

0.3493

5x4 BZ

73 1 BziDMFI:1

772 BqDMF

3:1

BZ

8.1X

39 0 5

4.74

2.39 x 10 3.18 0.32 x 10~’

?.I

2.1

I.?

7 4 +DMF

I-BuOH

TAFI-BuOH

Tl iF

x

9

I

3.241

0.3500

0.17500.3501

6.17,

2:I

2:1

0.1747 26.4

0.1792 17.06

3.75 _

8.1 _~z/THFI:1

“The mixture Bz/DMF = l/l (vol.) represents 6.49 mol/L DMF in Bz.“The mixture Bz/DMF = 3/I (vol.) represents 3.24 mol/L DMF in Bz.‘The mixture Bz/THF = l/l (vol.) represents 6.17 mol/L THF in Bz.teading to GHs-N = CH-N(CH,)s.‘Leading to C6HrNHCSNH-CaH~.‘Leading to allophanate formation type: CaHrN(COOB~)-C~NH-CsHI.“Leading to C6HINH-CGN(CzHS~H0.



Dibenzylic structures on macromolecular chain I239

to the urethane one, as regards the hydrogen bondingpossibilities, a special situation is presented by theinfluence of the DMF addition. In line with theconsiderations above, we ought to expect aninhibiting action similar to that of N-alkylatedurethane, MCEE. the DMF being an amide without

amide hydrogen. The results obtained do not confirmthis supposition. The reaction rate has increasedconsiderably (see Table 3, nos 4, 6 and 7).

The situation can be explained by supposing thatin the DMF case, two opposite effects take place. Inthe first, DMF inactivates the alcohol reactivity dueto the appearance of hydrogen bonding between anOH group and DMF (equation (3)). The second effectof DMF is that of activation of the PhNCO by -NC0group polarisation presented by structures a inequation (4). At higher temperatures the interactionbetween -NC0 and DMF can ease even a total

movement of electrons, resulting in the formamidinicgroup appearance (equation (4)). In our kineticconditions the formamidine is not observed; theprecision of our detection could even determine0.32 x IO-’ mol/L formamidine.

The possible perturbatory secondary reaction betweenEFA and PhNCO we found to be below 0.5% in our

reaction conditions:

Ph NC0 + CzH<NHCHO-+PhNHCON(C?H)CHO (5)

After these introductory studies concerning thesimplest reaction between PhNCO and BuOH. wewere able to understand better the behaviour of themore complicated system represented by the reactionbetween 2,2’ BBDI and BuOH and also to explain theeffects of DMF addition.

In concordance with our recent proposed generalurethane reaction mechanism [7], the reaction of2,2’ BBDI with BuOH is not a simple process. For thereaction it is necessary that both -NC0 and -OHgroups be activated. Thus the process starts in thefirst step of reaction by the interaction of one alcohol

molecule (activated by hydrogen bonds) with onefrom the two -NC0 groups of 2.2’ BBDI (activatedalso by other alcohol or urethane molecules). Thisfirst step of the reaction is characterized by a rateconstant, k,. and is also sensitive to the catalytic

R-OH---O=CH-N

\CH3

Inhibition

R-N- &-0”“-7-c”

(CH&N -CH-0

(3)

l-4)

a

Activation

Regarding these two effects, the experimentalresults presented above demonstrate that during thereaction between PhNCO and BuOH, the activatingeffect of DMF (equation (4)) is prevalent.

Taking into account the difference between thecatalytic effect of unsubstituted and substitutedurethanes mentioned above (see Table 3, nos 2and 3), by also considering the mechanism rep-

resented by equations (3) and (4). a monosubstitutedamide (which posses an amidic group hydrogen)ought to show, similarly to unsubstituted urethanes,a more activating effect even than that of DMF.

Indeed. according to the experimental data(see Table 3, no. 5) the addition of ethylformamide

(EFA). instead of DMF, determines a furtherincrease of reactivity, six times higher than in thecase of the addition of an equivalent quantity ofDMF.

EPJ 321&F

action of DMF, as in the case of the reaction betweenPhNCO and BuOH (Table 3).

As we have shown in the Introduction. when thefirst stage of the 2,2’ BBDI reaction is achieved, theappearance of the resulting urethane group createsthe condition of a powerful intramolecular catalyticaction, accelerating considerably the second step ofthe reaction. In this stage the supplementary catalytic

effect of the DMF becomes imperceptible. Moreoverthe inhibition effect of DMF on alcohol reactivity(equation (3)), could even decrease the k2 value.

Indeed, the kinetic measurements (see Table 4no. 2) confirm these suppositions.

Thus, the addition of 3.24 mol dm-’ DMF. resultsin a 30-times increase in the k, value. Simultaneouslythe value of k, decreases to a half of its initialmagnitude. Further, on increasing the DMF concen-tration it is expected to result only in an increase of



I240 A. A. Caraculacu et al

Table 4. Reactmn of 2,2’ BBDl wth I-BuOH m benzene at 60 C (rate constants m mol-’ minm’ L)

Extent of secondaryreaction (%) with:

Concenrrauon mol.L Concentrauon

Ratlo - of additive UrethaneNo. OH/NC0 Alcohol 2.2’ BBDI (DMF), mol:L h, I IO K = kt:k: ky x IO’ k, x IO’ H>O to Al

I I.2 0.1750 0.1751 None ,I 0.0082 280 6.85 0 0.97

2 1.2 0.1750 0.175 I 3.24 64 0.49 140 69 3.6 14.23 I :2 0.1750 0.175 I 6.49 147 1.07 137 43 2.66 7.17

kt = reaction rate constant for monourethane. m. formation: k . = reaction rate constant for biurethane, b, formation; kl = reaction rateconstant for allophanate. Al. formation (equation (8)).’

k,. the kl value remaining practically unchanged dueto the fact that the BuOH is already entirely hydrogenbonded with the DMF. The experimental resultswholly verified these suppositions (see Table 4, no. 3).

A more detailed analysis of the reaction mixturecomposition in the reaction of 2,2’ BBDI with BuOHhas evidenced the formation of an unexpectedproduct for these mild conditions of reaction. that isthe cyclic allophanate (Al) (see Table 1, no. 8).

We have supposed that this product appears as aresult of a secondary reaction of the intramolecularlyactivated state X (Scheme 2) formed after the firststage of the reaction of 2,2’ BBDI and it is caused bythe intramolecular urethane-isocyanate group inter-action.

The DMF addition inhibits the alcohol reactivity.lowering the k 2value. The internal cyclization leadingto allophanate (Al) consequently facilitates andincreases the value of kz (see Table 4, nos 1 and 2).

To verify this hypothesis, two reaction routes wereconsidered for the allophanate appearance. The firststarts from the monourethane m, without theassistance of another alcohol molecule; the secondimplies the internal activation complex X (Scheme 2).which involves the supplementary participation of analcohol molecule.

In the first case, the formation of Al could be

determined by the kinetic equation:

d[Al]/dr = k,[M] (7)

IOOO-

750 -

$

where [Al] = the concentration of allophanate, Al,

and [M] = the concentration of the monoreaction

product, m.

In the second case, the kinetic equation becomes:

d[Al]/dt = k,[M][A]

where [A] = the concentration of the alcohol (a).

The graphic representation of the dependence InF+V~O s regards the 7 value in both cases is given inFigs 3 and 4.

-o-o-

r 1

0 5 IO IS 2 0 25 30

T x 10m3 mol min drnm3

Fig. 3. Dependence of In I& (%), function of [T], for

allophanate Al formation, considering equation (7): 0,kinetic no. I; 0, kinetic no. 2: 0, kinetic no. 3 (from

Table 4).

0 50 100 150 200 250 300 350 400

z mol min dm-’

Fig. 4. Dependence of In iGclP (%), function of [T], for allophanate Al formation, considering equation(8): 0, kinetic no. 1; $, kinetic no. 2: 0, kinetic no. 3 (from Table 4).



Dibenzylic structures on macromolecular chain 1241



I242 A. A. Caraculacu et 01.

The fact that equation (8) demonstrates a betterlinear dependence (Fig. 4) supports the hypothesisthat the Al probably arises from the same activatedstate X which also leads to biurethane product b

6.appearance.

The above shows that the seemingly unexpected 7.

behaviour of the 2,2’ BBDI reaction with BuOHmight not have been understood without con-sidering the urethane reaction mechanism previously 8.

proposed by us [7].9.

10.

REFERENCESII.

1. A. A. Caraculacu and L. Misina. Rerisrcr Ma~eri&

P/mice 32, 38 (1995). II!.

2. A. A. Caraculacu and G. Caraculacu. J. MNU~~W/. .%i. 13.

Chefs. A22, 63 I (1985).

V. Cozan. J. Mnwo~~~ol. Sci. Chenl. A27, 1547

(1990).

A. A. Caraculacu. 1. Agherghinei. P. Baron and

S. Coseri. Rer. Rournnirte de C/h. 41. 539 (1996).

A. A. Caraculacu. 1. Agherghinei. ‘P. Baron ‘and

D. Timpu. Rev. Rowmine de C/h.. in press.

A. A. Caraculacu, I. Agherghinei. G. Caraculacu.

P. Baron and D. Timpu. Rer. Rounmine de C/h..

in press.

A. E. Oberth and R. S. Bruenner. J. fh,vs. C/tern. 72.

845 (1968).

A. A. Caraculacu. 1. Bestinuc, Z. Kellemen. V. Popescu.

Romanian Patent 81570 (May 1983).

R. L. Shriner and F. B. Cox. J. Ain. Clrew. Sot. 53,

1601 (1931).

G. T. Morgan and A. E. J. Pettet. J. C/rear. Sot. I I24

(1931).

F. Gamier. L;ehigs Anncrlen r/w Chemie 4, 241 (1887).

J. van Romburgh. Rewed de.7 Trnwws Chirtlie des

Pqs-Bus 48, 925 (1929).

A. A. Caraculacu. I. Agherghinei, M. Gaspar and Cr.

Prisacarium. J. C/tent. Sot. Perkin Trans. 2, 1343.^^_

3. E. Scortanu. A. A. Caraculacu. G. Caraculacu and14.

I. Agherghinei. Eur. PO/WI. J. 29, 999 (1993).

4. A. A. Caraculacu. I. Agherghinei. Cr. Prisacariu and (IYYO)

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Dibenzylic Structures on Macro Molecular