Photostabilizing effectiveness of new HALS produced by isocyanation of hindered piperidine derivatives

PII:

Polymer Degradation and Stability 60 (I 998) 459 464 9 1998 Elsevier Science Limited. All rights reserved Printed in Northern Ireland 0141-3910/98/$19.00

SO141-3910(97)00108-0

ELSEVIER

Photostabilizing effectiveness of new HALS produced by isocyanation of hindered piperidine derivatives Wayne W. Y. Lau* dz Jiang-Qing

Pant

Department of Chemical Engineering, National University of Singapore, Singapore 119260, Republic of Singapore (Received

7 April

1997; accepted

17 May 1997)

Twelve new hindered-amine light stabilisers (HALS) were prepared by isocyanation of the hindered piperidine derivatives 2,2,6,6-tetramethyl-4-piperidinol, 1,2,2,6,6pentamethyl-4-piperidinol and 4-amino_2,2,6,6_tetramethylpiperidine, by using dibutyltin dilaurate as catalyst. Test results show that these new HALS are effective light stabilisers, some of them comparable to a commercial HALS, Tinuvin-770. Reactions of these hindered piperidines with isocyanates proceed at temperatures varying from room temperature to 80°C and take less than 30 min to complete. The reactions are quantitative and no toxic byproducts are produced. 0 1998 Elsevier Science Limited. All rights reserved

1 INTRODUCTION

HALS prepared derivatives.

Polymer materials exposed to sunlight undergo degradation which shortens their service life, mainly as a consequence of photo-oxidation.‘,2 There are several ways to combat photo-oxidation of polymers, and addition of light stabilisers is still the most convenient and effective way as such an addition will not alter the processing conditions to any significant extent and there are many effective stabilisers. Hindered-amine light stabilisers (HALS) are the most effective stabilisers known today: they are two to six times more effective than nickel chelate light stabilisers and four to 10 times more effective than ultraviolet (UV) absorbers3 Extensive research results, patents and reviews have been published.“’ Our experience with and understanding of HALS show that, through reactions of isocyanates with hindered piperidine deriviatives, which are inexpensive and commercially available, effective new HALS can be prepared. In this paper, we report the preparation and photostabilising effectiveness of new

from

isocyanation

of piperidine

2 EXPERIMENTAL 2.1 Materials Octadecyl isocyanate (01) hexamethylene diisocyanate (HMDI) and toluene-2,4-diisocyanate (TDI) were supplied by Tokyo Chemical Industry Japan. 1,2,2,6,6-Pentamethyl-4-piperidinol PtiP) was supplied by Taiyuang Institute of Chemical Industry of China. Methylene diphenylene diisocyanate was supplied by Polysciences, Inc. USA. 2,2,6,6-Tetramethyl-4-piperidinol (TMP), 4amino-2,2,6,6_tetramethylpiperidine (ATMP) and dibutyltin dilaurate (DBTDL) were supplied by Fluka Co. DBTDL was in form of a solution of 80% DBTDL in benzene. 2.2 Synthesis A typical preparation may be described as follows. To a three-necked flask equipped with a condenser, a nitrogen inlet and a magnetic stirrer in an oil bath, 5.32Og TMP was added, followed by

*To whom correspondence should be addressed. tpermanent address: Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China. 459

460

Iv. Iv. Y. Lull J.-Q. Pun

addition of 37ml of benzene at 80°C. Then lO.OOOg 01 was added. Finally, 0.01 ml DBTDL was added. Reaction was maintained at 80°C for 6 h with stirring under nitrogen. The reaction product was in solution in benzene. Upon cooling it turned to an emulsion. Addition of hexane caused precipitation of the crude product. A needle-like crystalline product (A) was obtained with 80% yield by recrystallisation of the crude product from methanol. The preparations of the other new HALS were similar, except that for some of them use of an ice bath was necessary to control the reaction. They are summarised in Table 1.

elsewhere.” Photo-oxidation was monitored with a PerkinElmer 782 IR spectrophotometer at a wavenumber of 17 10 cm ‘. The induction period was determined from a plot of carbonyl absorption versus irradiation time.

AND DISCUSSION

3 RESULTS 3.1 Synthesis

It has been reportedi I6 that isocyanate can react easily with simple primary alcohols in stoichiometric quantities. Our experimental results show that the reactions of isocyanates with hindered piperidines are also stoichiometric. Without catalyst the reaction is slow at 80°C. Faster, exothermic reaction occurs in the presence of DBTDL. The use of a reflux condenser is necessary to keep the reaction temperature at 80°C. After addition of DBTDL, it is necessary to raise the temperature to. and keep it at, 80°C for 6 h for higher yield and to reduce side reactions. DBTDL is a wax-like substance at room temperature; it is, therefore. more convenient to add DBTDL in the form of a solution of 80% DBTDL in benzene. It has also been reported”ml6 that the isocyanate group reacts readily with amino compounds stoichiometrically. Among amino compounds. aliphatic primary amines possess very high reactivity even at 0&25”C. Our experimental results show that the reactions of isocyanates with ATMP are stoichiometric. The reaction is fast and strongly exothermic. Therefore, use of vigorous stirring, a condenser with reflux, and dropwise addition of isocyanate are necessary in this preparation so as to avoid evaporation loss of the isocyanates during

2.3 Analysis Infra-red (IR) spectra were recorded with a Shimadzu FTIR 8000 Fourier transform infra-red spectrophotometer. Analytical elemental analysis for carbon, hydrogen and nitrogen was performed with a Perkin Elmer 2400 CHN Elemental Analyzer. Proton nuclear magnetic resonance (NMR) spectra were obtained with an FX-100 FT-NMR instrument. DCC13 was used as solvent and tetramethylsilane (TMS) as internal standard. Thermogravimetric analysis (TGA) was performed in a Du Pont 9900 Thermal Analyzer at a heating rate of 20°C mini and a nitrogen flow rate of 75cm”min i. 2.4 Photo-oxidation The preparation and photo-oxidation of polypropylene (PP) samples containing these new HALS followed the standard procedure reported

Table 1. Preparations of new HALS Purification

Isocyanate (8)

Hindered amine (g)

DBTDL (ml)

Benzene (solvent) (ml)

(0:)

A

01 (l0.000)

TMP (5.320)

0.01

37

80

B C D E F G H 1 J K L

HMDI (3.000) TDI (3.400) MD1 (2.500) 01 (3.716) HMDI (2.000) TDI (1.700) MDJ (2.500) 01 (12.277) HMDI (3.360) TDI (3.480) MD1 (5.000)

0.01 0.01 0.01 0.01 0.01 0.01 0.01

25 40 40 IO 20 IO IO 20 20 20 20

80 80 80 x0 x0 80 80 Ice bath Ice bath Ice bath Ice bath

Product

TMP TMP TMP PMP PMP PMP PMP ATMP ATMP ATMP ATMP

(5.700) (6.200) (3.140) (2.154) (4.080) (3.043) (3.420) (6.240) (6.240) (6.240) (6.240)

(k) 6 6 6 6 6 6 6 6 0.5 0.5 0.5 0.5

Precipitation recrystallisation Precipitation Extraction Extraction Extraction Extraction Extraction Extraction Extraction Extraction Extraction Extraction

in hexane, from methanol in hexane by hexane by hexane by pentane by pentane by hexane by hexane by pentane by pentane by pentane by pentane

Yield (%) 80.0 90.2

88.1 82.6 77.3 72.9 86.3 94.5 95.2 9x. I 97.7 91.3

New HALS from hindered piperidine HN

the strongly exothermic reaction. The use of an ice bath for the reaction flask and sufficient solvent (benzene) are advisable. In general, reactions in this study can be finished within about 30min. 3.2 Structural analysis of the new HALS Typical IR and NMR spectra of the product (A) from 01 and TMP are shown in Figs 1 and 2. From Fig. 1 it can be seen that the isocyanate group in 01 (2255 cm-‘) disappears after reacting for 6 h with TMP at 80°C and that a new carbamate group (1680, 3300-3400cm-‘) is formed in the product (A). These IR results indicate that the following reaction had taken place: 100 CIBH,,-N=C=O

461

derivatives 0H+O=C=N-C,8H37-HN

0-fi-y-C,,H,, 0

(TMP)

H

(01 + TMP)

(01)

From Fig. 2 it can be seen that a new carbamate group [-C( = O)NH-, 4.60 ppm] had been formed in product A. Moreover, octadecyl groups from 01 (CH3, 0.88 ppm; methylene at 1.25 ppm, 32H; and N-CH2, 3.16 ppm) as well as piperidine ring structures from TMP (2,2,6,6_tetramethyl, at 1.14 and 1.24ppm; 3,5-methylene at 1.48 and 1.96ppm and 4-proton at 5.08ppm) appeared in the product A. These NMR results are consistent with results from IR spectra. The other reaction products summarised in Table 1 show similar results. The major findings from IR, NMR and elemental analyses of the new HALS prepared in this work are summarised in Tables 2 and 3.

b

NH

H,C tCH,+

a

c

60

1 ;_-_Jj ) __,--._.,___* ----, Tj;_

i-,2. 4000

2000

Fig. 1. IR spectra

61000 Ii

1500

Wave number

of product

‘-

400

Reaction

A from 01 + TMP.

Fig. 2. NMR spectrum

01 + TMP

B C D E F G H

HMDI+TMP TDI + TMP MD1 + TMP 01 + PMP HMDI+PMP TDI + PMP MD1 + PMP

I J K L

01 + ATMP HMDI + ATMP TDI + ATMP MD1 + ATMP

“No suitable

solvent

New absorption

-N=C=()

1680, 3300-3400

2255 (disappears) yes yes yes yes yes yes yes yes yes yes yes

1697, 3300 1600, 1725, 3040, 1600, 1720, 3040, 1690, 3300 1690, 3300 1600, 1720, 3040, 1600, 1720, 3040,

3300 3300 3300 3300

1650, 3300 1640, 3300 1600, 1640, 3040, 33040 1600, 1650, 3040, 3300

for NMR.

3

2

I

0

of product

A from 01

+

TMP.

of new HALS

IR change (cm-‘)

A

4

5-

PPM

Table 2. Characterisation New HALS

6

7

(cm-‘)

NMR (ppm) Piperidine

-NCH2-

-NH

1.14, 1.24, 5.08

3.16

4.60

0.88

1.14, 1.02, 1.04, 1.08, 1.06,

1.24, 4.94 1.12, 5.02 1.12, 5.0 1.16, 4.93 1.16, 4.80 U U

3.20

5.06 6.22 6.44 4.60 4.84

2.04, 6.92 3.72, 6.88-7.20 0.88

1.12, 1.19, 1.09, 1.12,

1.26, 1.24, 1.12, 1.24,

3.14 3.20

4.18 4.05 3.10 4.58

3.10 3.12

4.02, 5.08, 6.14, 6.20,

4.24 5.27 6.45 6.27

N-CH-,

2.25 2.39

Other

0.88 2.01, 7.07, 7.36 3.90, 7.13

W. W. Y. Lau, J.-Q. Pun

462

From Tables 2 and 3, it can be deduced following reactions have occurred:

that the

___N=C=O+ H()_R__________________._> _____N__C__O__R tib (carbamate formation) ___N=C=O

+

m-R’

_________-___________>_-__~__

__v__R’

H 8 H (urea formation)

where -N=C = 0 is the isocyanate group in 01, HMDI, TDI and MDI; H-O-R is TMP (in products A, B, C and D) or PMP (in products E, F, G and H); and H-N-R’ is ATMP (in products I, J, K and L). The structures of these new HALS are:

New HALS

A B C D E F G H I J K L

Table 3. Elemetal analysis of new HALS ____~ ~. Calculated Found (%) H C ~~~.~~~ _~~ 73.00 12.82 65.12 1055 65.58 9.15 72.61 8.63 74.19 13.18 65.X4 11.49 65.73 8.48 68.16 7.79 73.82 14.65 59.88 12.44 60.00 10.32 68.44 9.43

CH,

0

H,C-N>O-[-I+-;-i-OG-CH,

o-N--tC,H,+N-C-o

rlr



CH,

0

OH

C,,H,,-N-C-O Ii!





H&-N

0-C-N-eC,H,2+N-C-~ %

N-CH,

N ~~6.54 I I .36 I 1.20 9.20 6.50 II.00 12.96 9.20 8.98 16.00 14.87 14.30

c ~~74.34 64.73 66.39 70.20 74.68 65.88 67.44 70.95 74.50 65.00 66.67 70.46

(%) N

H ~12.39 10.37 9.02 8.51 11.45 IO.59 9.30 8.7X 12.64 10.83 9.47 8.96

6.20

I I .62 I I .48 9.93 6.10 10.98 10.85 9.46 9.31 17.50 17.2x 14.95

New HALS from hindered piperidine 3.3

Properties

463

derivatives

organic solvents can be enhanced. For product A formed from 01 and TMP readily in most of these organic solvents.

The properties of these new HALS are summarised in Tables 4 and 5, from which it can be seen that their thermal stabilities and their solubility in various organic solvents are similar to that of Tinuvin770, which has the following structure:

example, dissolves

3.4 Photostabilising effectiveness The photo-oxidation induction periods of PP films containing these new HALS, obtained from the plot of carbonyl absorption versus irradiation time shown in Fig. 3, are summarised in Table 6. From this table it may be seen that HALS A, B and C possess very high photostabilising effectiveness, comparable to that of Tinuvin-770, mainly as a consequence of their higher compatibility with the

0-C+CH,-)i-C-O II 0

When long alkyl chains, such as octadecyl in 01, are introduced into the HALS, their solubility in

Table 4. The properties of new HALS A-L

Tm (“‘4

A

B

C

D

55 223 n.c.

131-133 252

193-196 228

w.P

w.P

155-156 200 w.P

Heat stability Appearance

(“C)

T, is melting

temperature;

n.c. is needle crystals,

EFG 65 75-78 230 264 w.p w.p

265 233 w.p

H

I

J

K

L

110

152-154 248 w.P

64-65 241 w.P

194-195 224

204-205 233 w.P

22&221 267 w.P

81-85 223 w.P

W.S

w.p. is white powder.

Table 5. Solubility” of new HALS A-L S (cal m1-3)“2 h

Solvent

7.0 1.4 8.2 8.9 9.1 9.1 9.2 9.3 9.9 11.9 12.7 14.5 23.4

Cd12 C6Hl4

Cyclohexane Toluene Ethyl acetate THF Benzene HCC13 Acetone Propanol Ethanol Methanol Water

C

D

E

FGHI

sxxxsxxxxxxx s x x s x h

x

s

x

x

x

es es h

h hs s

x x x

400

B

es

hs s

h es

es

es

es

es

es

s

x

es es

hs es

h es

h es

s s

es

es

es

es

s

es

s

s

s

s

s

s

s

s

s

es

s

s h h

hs es hs s es es

x h x x x x

h h h h x h x x x x

x

x

x

x

x

x

x

x

es--dissolves

K

L

710

x

x

x

x

X

x s s s s s s s s s

x hs x hs hs s x s s s

x x x hs hs

x x x x hs

S

ess

S

es

S

x

x

S

S

li

S

S

hs

S

S

X

x

x

x

x

X

s S

easily.

600 Irradiation

J

X

x h es

es

“Key: s-soluble; x-cannot dissolve, hs-hard to dissolve, “6 is solubility parameter of the organic solvent.

200

A

X00 rime

IO00

I200

1400

(h)

Fig. 3. Photostabilising effectiveness of new HALS for PP film containing 0.3 wt% of HALS: 0, blank (PP film); samples A-L are PP film samples each containing 0.3 wt% of new HALS A to L; sample 770 is a PP film sample containing 0.3 wt% of Tinuvin-770.

464

W. W. Y. Luu, J.-Q

Table 6. Photo-oxidation induction periods (IP) of PP films containing 0.3 wt% of new HALS No. 0

I 2 3 4 5 6 7 8 9 IO II I2 I3

HALS

MW

blank (PP) A B C D E F G H J J K L 710

452 482 488 564 466 510 516 592 451 480 486 562 480

Nitrogen

“Nitrogen (%)- -piperidine nitrogen lated from structural formula.

(%)(I

19 1100 1350 1100 600 496 588 140 260 240 500 340 70 1300

3.10 5.81 5.14 4.96 3.00 5.49 5.43 4.73 3.10 5.83 5.76 4.96 5.81 content

IF’ (h)

in HALS

calcu-

polypropylene substrate. HALS I, J, K and L are less effective than Tinuvin-770, owing to the presence of polar urea groups which lower their compatibility with polypropylene. It should be pointed out that the HALS made from 01 with piperidinol (TMP, PMP) possess higher photostabilising effectiveness even though their effective nitrogen content (N in the piperidine ring) is about half that of the other HALS. This is attributable to the presence of very long alkyl chains ((C1sH3,) that have effectively increased their compatibility with the polypropylene substrate.

4 CONCLUSIONS 1. Twelve new HALS were synthesised by isocyanation of hindered piperidine deriviatives. These new HALS are effective light stabilisers,

Pan

some of them are as effective as the commercial HALS Tinuvin-770. Being in the suitable molecular weight range of 400 to 600, these new HALS can be developed to become new commercial light stabilisers. The compatibility of a HALS with its polymer matrix is very important. Introduction of very long alkyl chains such as octadecyl in 01 into the HALS structure will improve their performance.

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